Research ArticleModification of One-Dimensional TiO2 Nanotubes withCaO Dopants for High CO2 Adsorption
Chin Wei Lai
Nanotechnology amp Catalysis Research Centre (NANOCAT) Institute of Postgraduate Studies (IPS) Universiti Malaya 3rd FloorBlock A 50603 Kuala Lumpur Malaysia
Correspondence should be addressed to Chin Wei Lai cwlaiumedumy
Received 30 January 2014 Revised 21 February 2014 Accepted 21 February 2014 Published 26 March 2014
Academic Editor Tian-Yi Ma
Copyright copy 2014 Chin Wei LaiThis is an open access article distributed under the Creative Commons Attribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited
One-dimensional calcium oxide (CaO-) based titanium dioxide (TiO2) nanotubes were successfully synthesized through a rapid
electrochemical anodization and chemicalwet impregnation techniques In this study calciumnitrate solutionwas used as a calciumsource precursorThe reaction time and concentration of calcium source on the formation ofCaO-TiO
2nanotubeswere investigated
using field emission microscopy energy dispersion X-ray spectroscopy and X-ray diffractionThe adsorption capacity of CO2was
determined by thermal gravimetric analyzer A maximum of 445mmolg was achieved from the CaO-TiO2nanotubes (664 at
of Ca) The finding was attributed to the higher active surface area for CaO to adsorb more CO2gas and then formed CaCO
3
compound during cyclic carbonation-calcination reaction
1 Introduction
Recently solid CO2adsorbents are used as an alternative
and potentially less-energy-intensive separation technol-ogy These CO
2adsorbents can be utilized from ambient
temperature up to 973K by yielding less waste duringcycle In addition their waste can be disposed of withoutundue environmental precautions as compared to liquidadsorbent [1] A variety of solid physical adsorbents havebeen considered for CO
2capture including microporous
and mesoporous materials (carbon-based sorbents such asactivated carbon and carbon molecular sieves zeolites andchemically modified mesoporous materials) metal oxidesand hydrotalcite-like compounds [2 3] These listed adsor-bents usually can be classified into three types based ontheir sorptiondesorption temperatures (1) low temperatureadsorbent lt473K (carbon zeolites MOFsZIFs alkali metalcarbonates and amine-based materials) (2) intermediatetemperature adsorbent 473ndash673K (hydrotalcite-like com-pounds HTLcslayered double hydroxides LDHs) and (3)high-temperature adsorbents gt673K (calcium based andalkali ceramic) The summary of those adsorbents with theirefficiency and operating parameters are shown in Table 1
According toTable 1 CaO and alkali ceramics are promis-ing candidates for CO
2adsorption Therefore CaO-based
adsorbent has gained great attention due to its great capability(116mmolg) as compared to other adsorbents in capturingCO2gases through cyclic carbonation-calcination reaction
In addition CaO-based adsorbent has high reactivity withCO2gases high capacity and low material cost [4] The car-
bonation temperature for CaO-based adsorbents is between873 and 973K and their regeneration temperature is normallyabove 1223K The reversible reaction between CaO and CO
2
isCaO (s) + CO
2(g) 999445999468 CaCO
3(s)
Δ119867∘
87315K = minus1712 kJ molminus1 (for carbonation)(1)
In this manner nanocrystalline of CaO has been provento be useful in the noncatalytic removal of CO
2inH2produc-
tion [5] The nanocrystalline of CaO with vacanciesdefectswhich often related to the presence of basic and acidicsites within their lattice The structural defects normally areinvolved in the basic-acidic catalytic reactions It is a well-known fact that CaO has highly reactive and strong basicsites because of the isolated O2minus centers as well as weak
Hindawi Publishing CorporationInternational Journal of PhotoenergyVolume 2014 Article ID 471713 9 pageshttpdxdoiorg1011552014471713
2 International Journal of Photoenergy
Table 1 The different types of solid CO2 adsorbents based on their sorptiondesorption temperatures
Adsorbent Total capacity(mmolg)
Temperature(K)
Pressure(atm) Reference
Low temperature adsorbentsAmine based
Amine-modified mesoporous silica 45 348 1 (Liu et al 2010) [12]Amine-modified ordered mesoporous silica (OMS) 15 mdash mdash (Zelenak et al 2008) [13]Amine-modified OMSs 02ndash14 348 1 (Liu et al 2010) [12]Amine tetraethylenepentamine (TEPA)OMSs 46 348 1 (Liu et al 2010) [12]
MOFsZIFsMOF-2 32 mdash 41 (Millward and Yaghi 2005) [14]
Carbonactivated carbon basedCoal-based activated carbon 03 323 0001 (Deng et al 2011) [15]Porous carbon nitride (CN) 290 298 mdash (Li et al 2010) [16]N-doped carbons template from zeolite 69 273 1 (Xia et al 2011) [17]Activated carbonN2 375
293 1 (Zhang et al 2010) [18]Activated carbonH2 349Activated carbonNH3 322Activated carbon 15 303 40 (Drage et al 2009) [19]Activated carbon 35 275 1 (Wang et al 2008) [20]Carbon nanotubes (CNTs)3-aminopropyltriethoxysilane(APTS) 245 323 mdash (Su et al 2011) [21]
Alumina based120574-Al2O3 031 295 mdash (Rege and Yang 2001) [22]
Zeolite basedY-type zeolitetetraethyl-enepentamine (TEPA) 427 303ndash333 (Su et al 2010) [23]Natural zeolite 205
298 01 (Ertan and Cakicioglu-Ozkan2005) [24]
Treated zeoliteH3PO4 195Synthetic zeolite-5X 549Synthetic zeolite-13A 682LilSX 017
mdash 1 (Brandani and Ruthven 2004) [25]NaLX 023CaX 02413X (NaX) 294 295 mdash (Rege and Yang 2001) [22]
Magnesium basedMgOAl2O3 136 333 1 (Li et al 2010) [26]
Intermediate temperature adsorbentsLDH
Mg-Al-CO3 LDHs 049 473 005 (Ram Reddy et al 2006) [27]High temperature adsorbents
Lithium orthosilicatesLi4SiO4 614 773 1 (Kato et al 2002) [28]
Lithium zirconatesLi2ZrO3 455 773 1 (Ida and Lin 2003) [29]
Li2ZrO3 450 823 1 (Ochoa-Fernandez et al 2005)[30]
Li2ZrO3 (nanocrystalline) 614 848 1 (Ochoa-Fernandez et al 2006)[31]
International Journal of Photoenergy 3
Table 1 Continued
Adsorbent Total capacity(mmolg)
Temperature(K)
Pressure(atm) Reference
Calcium oxide basedCaO 23 923 mdash (Satrio et al 2005) [32]CaOAl2O3 116 923 mdash (Li et al 2006) [33]CsCaO 49
723 04 (Reddy and Smirniotis 2004)[34]
RbCaO 45KCaO 38NaCaO 31CaCO3 15 573 1 (Kuramoto et al 2003) [35]CaOAl2O3 602 923 1 (Wu et al 2007) [36]Nano CaOAl2O3 602 650 mdash (Wu et al 2008) [37]
200nm
(a)
200nm
(b)
200nm
(c)
Figure 1 FESEM top view image of nanotubes subjected to wet impregnation of 06M calcium nitrate solution for (a) 24 hours (b) 48 hoursand (c) 72 hours and subsequent annealing at 673K in Ar gas for 4 hours
residual OH groups which appear when mixed with the rareearths [6] However these CO
2adsorbents suffer severely
from textural degradation during the sorptiondesorptionoperations These CO
2adsorbents can only run several tens
of cycles before any obvious degradation and are still farfrom practical applications [3] Instantly the conversion ofCaO decreased sharply from 70 in the first cycle to 20
in the eleventh cycle when tested in fluidized bed [7] Thedeactivation primarily results from the formation of thicklayer structured from CaCO
3surrounding the CaO which
severely hinders the diffusion of CO2gas to react with
the inner core Besides it has also been reported that theadsorption capacity for CaO-based sorbents decays as afunction of the sintering of CaO grain at high temperature
4 International Journal of Photoenergy
214
171
128
85
42
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(a)
247
198
148
99
49
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(b)
117
94
70
47
23
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(c)
Figure 2 EDX spectra of nanotubes subjected to wet impregnation of 06M calcium nitrate solution for (a) 24 hours (b) 48 hours and(c) 72 hours (all EDX spectrums are noneditable format based on our FESEM-EDX system)
and a certain loss in the porosity When pores smaller than acritical value (eg 200 nm) are filled the reaction gets muchslower [8] Therefore great efforts have to be made in orderto further improve the cyclic stability of CaO-based sorbents
One of the most promising solutions to improve thecyclic stability of CaO is controlling their architecture intoone-dimensional nanomaterials The main reason might beattributed to the fast reaction (chemical reaction) and theslow reaction (diffusion controlled) could be achieved duringCO2adsorption In this case the diffusion of CO
2into
the particle interior to react with Ca dopants could beprevented and the whole CO
2adsorption process could then
be diffusion-controlled [2 3] Theoretically the small parti-cles size of sorbent (eg 30ndash50 nm) would perform bettercarbonation-calcination reaction which allowed carbonationto take place at the rapid reaction-controlled regime Anotherpromising solution to improve cyclic stability is to incorpo-rate high stability metal oxide (titanium dioxide) into CaOparticlesTheprevention ofCaOoxidation during calcinationstage could be expected Therefore detail investigation onone-dimensional CaO-TiO
2nanotubes for effective CO
2
adsorption will be discussed
2 Experimental Procedure
One-dimensional TiO2nanotube arrays were synthesized
using a rapid-anodic oxidation electrochemical anodizationtechnique A high purity of Ti foil (996 Strem Chemical
USA) with a thickness of 127 120583m was selected as substrateto grow TiO
2nanotubes This process was conducted in a
bath with electrolytes composed of ethylene glycol (C2H6O2
gt995 Merck USA) 5 wt ammonium fluoride (NH4F
98 Merck USA) and 5wt hydrogen peroxide (H2O2
30 H2O2and 70 H
2O J T Baker USA) for 60 minutes
at 60V This experimental condition was selected because itfavors the formation of well-aligned TiO
2nanotube arrays
[9 10] After the anodization process as-anodized sampleswere cleaned using distilled water and dried under a nitrogenstream CaO-TiO
2nanotubes were then prepared through
wet impregnation technique using calcium nitrate tetrahy-drate (Ca(NO
3)2sdot4H2O Merck USA) as the precursor This
was an ex situ approach that was used to incorporate Ca2+ions into TiO
2nanotubes Two different concentrations
of calcium nitrate tetrahydrate solution (06 12M) wereprepared at different reaction times (24 48 72 hours) in awater bath of 80∘C Subsequently the samples were thermal-annealed at 673K in an argon atmosphere for 4 h in order toproduce crystalline TiO
2nanotubes
The surface morphologies of the synthesized sampleswere observed through field emission scanning electronmicroscopy (FESEM) using a Zeiss SUPRA 35VP whichis operated at a working distance of 1mm and 5 kV Theenergy dispersive X-ray spectroscopy (EDX) was appliedto elemental analysis of the CaO-TiO
2nanotubes sorbents
which is equipped in the FESEM The structural variationsand phase determination for CaO-TiO
2nanotubes sorbents
International Journal of Photoenergy 5
200nm
(a)
200nm
(b)
200nm
(c)
Figure 3 FESEM top view image of nanotubes subjected to wet impregnation of 12M calcium nitrate solution for (a) 24 hours (b) 48 hoursand (c) 72 hours and subsequent annealing at 673K in Ar gas for 4 hours
were determined using a Philips PW 1729 X-ray diffraction(XRD) which operated at 45 kV and 40mV patterns Thethermogravimetric analysis (TGA) was used to investigatethe CO
2adsorption for CaO-TiO
2nanotubes sorbents (STA
6000 Perkin Elmer USA)The steps included are N2gas flow
at a rate of 10∘Cmin from room temperature to 673K andthen holding for 30min in CO
2and finally cooling down to
573K byN2gas In the present study carbonation-calcination
reaction is set to be 673K because nanotubular structure canbe collapsed at high temperature (above 773K) [11]
3 Results and Discussion
The surface morphologies of CaO-TiO2nanotubes synthe-
sized in 06Mcalciumnitrate solution for 24 48 and 72 hourswere subsequently observed via FESEM as presented in Fig-ures 1(a) to 1(c) respectively As shown in the FESEM imagesthe opening of the nanotubular structure showed aggregationof CaO species on wall surface of TiO
2nanotubes The
wall thickness of the nanotubes dramatically increased to
75 nm which resulted in a narrow pore entrance for 24 hoursreaction time (Figure 1(a)) Meanwhile as the reaction timeincreased to 48 hours the wall thickness of the nanotubesincreased from about 75 nm to 100 nm (Figure 1(b)) Withfurther increase of the reaction time to 72 hours it wasfound that the nanotubes were covered with excess CaOspecies and clogged the pore entrance (Figure 1(c)) A roughirregular and corrugated surface was formed Based on theFESEM images it could be concluded that the appearanceof TiO
2nanotubes was dependent on the reaction time in
calcium nitrate solution A narrow or blocked pore entranceof nanotubes was formed as increasing soaking period in thesolution Next the average atomic percentage (at) of theelements within CaO-TiO
2nanotubes was determined using
EDX analysis The numerical EDX analyses of the samplesare listed in Table 2 As determined through EDX analysisthe average Ca contents of the nanotubes for 24 48 and 72hours were 101 at 367 at and 459 at respectively Theintensity of the Ca peak (369 keV) increased with increasingreaction time in calcium nitrate solution as presented in
6 International Journal of Photoenergy
274
219
164
109
54
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(a)
252
202
151
101
50
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(b)
295
236
177
118
59
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(c)
Figure 4 EDX spectra of nanotubes subjected to wet impregnation of 12M calcium nitrate solution for (a) 24 hours (b) 48 hours and(c) 72 hours (all EDX spectrums are noneditable format based on our FESEM-EDX system)
Figures 2(a) to 2(c) Another set of experiments was con-ducted to form CaO-TiO
2nanotubes in 12M calcium nitrate
solution for 24 48 and 72 hours All morphologies of thesamples showed similar appearance of CaO-TiO
2nanotubes
synthesized in 06M calcium nitrate solution The irregularCaO layer covered all of the TiO
2nanotubular structure
and nanoporous structure arranged in a nonordered mannerwhich could be observed in Figures 3(a) to 3(c)The chemicalstoichiometry of the resultant samples was determined viaEDX analysis as shown in Figures 4(a) to 4(c) A high Cacontent of 978 atwas determined from those synthesized in12M calciumnitrate solution for 72 hours indicating that theincorporation of the CaO became prominent with increasingthe concentration of calcium nitrate solution Based on theFESEM images and EDX analysis the small Ca2+ ions couldbe diffused into TiO
2nanotubes in the presence of lattice
defects especially nearby to the wall of nanotubes In thiscase the diffusion rate of Ca2+ ions increased significantlywhen increasing the reaction time and concentration of pre-cursor However the content of small Ca2+ ions that diffusedinto the TiO
2lattice could reach a saturation condition and
start to accumulate on the surface of nanotubes The numberof nucleation sites for Ca2+ ions loaded on the wall surface ofthe nanotubes increasedwith longer reaction time and higherconcentration of precursor which produced nanotubes withthicker walls The diffusion of the Ca2+ ions formed CandashObonding withOndashTindashO bonding thus charge neutrality couldbe achieved
Table 2 EDX result of CaO-TiO2 with different soaking time in06M and 12M calcium nitrate solution
Concentration ofcalcium nitratesolution (M)
Element (at)reactiontime (h) Ti O Ca
0624 4607 5292 010148 3888 5745 036772 4230 5311 0459
1224 3644 6066 029048 3264 6064 066472 2883 6110 0978
In the present study XRD analysis was used to determinethe crystallographic structure and the changes in the phasestructure of the CaO-TiO
2nanotubes synthesized in different
reaction times and concentrations of precursor are presentedin Figures 5 and 6 Numerous studies reported that heattreatment at about 400∘C could transform the amorphousstructure of TiO
2into the crystalline anatase phase The
obvious diffraction peaks from the XRD pattern attributedto the anatase phase (JCPDS no 21-1272) were detected fromthe XRD patterns (Figure 5(a)) The diffraction peaks areallocated at 2532∘ 3784∘ 3842∘ 4802∘ 5387∘ 5509∘ 6293∘7065∘ and 7623∘ which correspond to 101 004 112 200105 211 204 220 and 301 crystal planes for the anatase
International Journal of Photoenergy 7
10 20 30 40 50 60 70 80 90
Inte
nsity
(au
)
(d)
(c)
(b)
(a)TA T
T A AT
A T
T
T
2120579 (deg)
Figure 5 XRD pattern of TiO2nanotubes incorporated with Ca in
06M Ca(NO3)2solution at different soaking period (a) pure TiO
2
(b) 24 hours (c) 48 hours and (d) 72 hours (A = anatase phase T =titanium phase)
10 20 30 40 50 60 70 80 90
Inte
nsity
(au
)
AT A
TT
AT
TA
TT (a)
(b)
(c)
(d)
2120579 (deg)
Figure 6 XRD pattern of TiO2nanotubes incorporated with Ca in
12M Ca(NO3)2solution at different soaking period (a) pure TiO
2
(b) 24 hours (c) 48 hours and (d) 72 hours (A = anatase phase T =titanium phase)
phase respectively Apparently the incorporation of Ca2+ions into the lattice of TiO
2hindered the crystallization
of TiO2 resulting in the peak intensity of the 101 peak at
2532∘ decrease The decrease in anatase phase is maybe dueto the interruption of Ca atom which diffused into TiO
2
nanotubes and inhibited the formation of the anatase TheXRD pattern of the sample soaked in 12M for 72 hoursexhibits additional peaks 220 and 400 crystal planes at 54∘and 80∘ corresponding to CaO phase This indicates thatcrystalline CaO are formed once the concentration of Cain TiO
2reaches a higher level Next the resultant anodized
CaO-TiO2nanotubes were used in the characterization of
CO2adsorption using TGA analysis The processing steps
involved in TGA analysis are N2gas flow at a rate of 10∘Cmin
from room temperature to 673K and then holding for 30minin CO
2and finally cooling down to 573K byN
2gasThe TGA
curves for 06M of Ca and 12M of Ca are shown in Figures7 and 8 respectively while the CO
2adsorption capacity is
summarized in Table 3 Based on the TGA analysis it couldbe observed that all CaO-TiO
2samples showed their CO
2
adsorption capacity in the range of 33mmolg to 45mmolgA maximum CO
2adsorption capacity of up to 445mmolg
was observed from the CaO-TiO2nanotubes synthesized in
050100150200250300350400450
996998100
1002100410061008
101101210141016
0 20 40 60 80
Wei
ght (
)
Time (min)
24 hours48 hours
72 hoursTemperature
Tem
pera
ture
(∘C)
Figure 7 TGA curve of soaking in 06M of Ca for different periodsof time
050100150200250300350400450
995
100
1005
101
1015
102
1025
0 20 40 60 80
Wei
ght (
)
Time (min)
Tem
pera
ture
(∘C)
24 hours48 hours
72 hoursTemperature
Figure 8 TGA curve of soaking in 12M of Ca for different periodsof time
Table 3 CO2 adsorption capacity of the CaO-TiO2 samples
Concentration of calciumnitrate solution (M)
Soaking period(hours)
CO2 adsorptioncapacity (mmolg)
0624 38948 33272 400
1224 35948 44572 380
12M of calcium nitrate solution for 48 hours Basically theCO2adsorption capacity based CaO-TiO
2sorbents used the
following reaction CaO + CO2rarr CaCO
3 In this case
the sorbent weight is increased significantly when CO2gas is
applied to the TGA system where all the weight added is CO2
adsorbed This reason clearly explains that CO2adsorption
capacity is increased after carbonation process
8 International Journal of Photoenergy
4 Conclusion
The present study demonstrated that one-dimensional CaO-TiO2nanotubes sorbent was successfully formed using oxi-
dation electrochemical anodization and wet impregnationtechniques All of the resultant CaO-TiO
2nanotubes sorbent
exhibited promising CO2adsorption capacity in the range of
33mmolg to 45mmolg It is shown that high active surfacearea of CaO-TiO
2nanotubes sorbent showed good stability
during extended cyclic carbonation-calcination reaction
Conflict of Interests
The author declares that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
This research is supported by High Impact Research Chan-cellory Grant UMC6251HIR228 (J55001-73873) from theUniversity of Malaya In addition authors would like tothank University of Malaya for sponsoring this work underUniversity of Malaya Research Grant (UMRG no RP022-2012D)
References
[1] Q Wang J Luo Z Zhong and A Borgna ldquoCO2capture by
solid adsorbents and their applications current status and newtrendsrdquo Energy amp Environmental Science vol 4 no 1 pp 42ndash552011
[2] D M DrsquoAlessandro B Smit and J R Long ldquoCarbon dioxidecapture prospects for new materialsrdquo Angewandte ChemieInternational Edition vol 49 no 35 pp 6058ndash6082 2010
[3] SWang S Yan XMa and JGong ldquoRecent advances in captureof carbon dioxide using alkali-metal-based oxidesrdquo Energy ampEnvironmental Science vol 4 no 10 pp 3805ndash3819 2011
[4] N H Florin and A T Harris ldquoReactivity of CaO derived fromnano-sized CaCO
3particles through multiple CO
2capture-
and-release cyclesrdquo Chemical Engineering Science vol 64 no2 pp 187ndash191 2009
[5] J Garcıa T Lopez M Alvarez D H Aguilar and P QuintanaldquoSpectroscopic structural and textural properties of CaO andCaO-SiO
2materials synthesized by sol-gel with different acid
catalystsrdquo Journal of Non-Crystalline Solids vol 354 no 2-9 pp729ndash732 2008
[6] V R Choudhary S A R Mulla and B S Uphade ldquoOxidativecoupling of methane over alkaline earth oxides deposited oncommercial support precoated with rare earth oxidesrdquo Fuel vol78 no 4 pp 427ndash437 1999
[7] D Alvarez and J C Abanades ldquoPore-size and shape effects onthe recarbonation performance of calcium oxide submitted torepeated calcinationrecarbonation cyclesrdquo Energy and Fuelsvol 19 no 1 pp 270ndash278 2005
[8] J-R Li Y Ma M C McCarthy et al ldquoCarbon dioxidecapture-related gas adsorption and separation in metal-organicframeworksrdquo Coordination Chemistry Reviews vol 255 no 15-16 pp 1791ndash1823 2011
[9] S Sreekantan L C Wei and Z Lockman ldquoExtremely fastgrowth rate of TiO
2nanotube arrays in electrochemical bath
containing H2O2rdquo Journal of the Electrochemical Society vol
158 no 12 pp C397ndashC402 2011[10] CW Lai and S Sreekantan ldquoDimensional control of TiO
2nan-
otube arrays with H2O2content for high photoelectrochemical
water splitting performancerdquoMicro ampNano Letters vol 7 no 5pp 443ndash447 2012
[11] Y K Lai J Y Huang H F Zhang et al ldquoNitrogen-doped TiO2
nanotube array films with enhanced photocatalytic activityunder various light sourcesrdquo Journal of Hazardous Materialsvol 184 no 1ndash3 pp 855ndash863 2010
[12] S-H Liu C-H Wu H-K Lee and S-B Liu ldquoHighly stableamine-modified mesoporous silica materials for efficient CO
2
capturerdquo Topics in Catalysis vol 53 no 3-4 pp 210ndash217 2010[13] V Zelenak M Badanicova D Halamova et al ldquoAmine-
modified ordered mesoporous silica effect of pore size oncarbon dioxide capturerdquoChemical Engineering Journal vol 144no 2 pp 336ndash342 2008
[14] A R Millward and O M Yaghi ldquoMetal-organic frameworkswith exceptionally high capacity for storage of carbon dioxideat room temperaturerdquo Journal of the American Chemical Societyvol 127 no 51 pp 17998ndash17999 2005
[15] H Deng H Yi X Tang P Ning andQ Yu ldquoAdsorption of CO2
and N2on coal-based activated carbonrdquo Advanced Materials
Research vol 204-210 pp 1250ndash1253 2011[16] Q Li J Yang D Feng et al ldquoFacile synthesis of porous
carbon nitride spheres with hierarchical three-dimensionalmesostructures for CO
2capturerdquo Nano Research vol 3 no 9
pp 632ndash642 2010[17] Y Xia R Mokaya G S Walker and Y Zhu ldquoSuperior CO
2
adsorption capacity on N-doped high-surface-area microp-orous carbons templated from zeoliterdquo Advanced Energy Mate-rials vol 1 pp 678ndash683 2011
[18] Z Zhang M Xu H Wang and Z Li ldquoEnhancement of CO2
adsorption on high surface area activated carbon modified byN2 H2and ammoniardquo Chemical Engineering Journal vol 160
no 2 pp 571ndash577 2010[19] T C Drage J M Blackman C Pevida and C E Snape
ldquoEvaluation of activated carbon adsorbents for CO2capture in
gasificationrdquo Energy and Fuels vol 23 no 5 pp 2790ndash27962009
[20] Y Wang Y Zhou C Liu and L Zhou ldquoComparative studiesof CO
2and CH
2sorption on activated carbon in presence of
waterrdquoColloids and Surfaces A Physicochemical and EngineeringAspects vol 322 no 1ndash3 pp 14ndash18 2008
[21] F Su C Lu and H-S Chen ldquoAdsorption desorption andthermodynamic studies of CO
2with high-amine-loaded mul-
tiwalled carbon nanotubesrdquo Langmuir vol 27 no 13 pp 8090ndash8098 2011
[22] S U Rege and R T Yang ldquoA novel FTIR method for studyingmixed gas adsorption at low concentrations H
2O and CO
2on
NaX zeolite and 120574-aluminardquo Chemical Engineering Science vol56 no 12 pp 3781ndash3796 2001
[23] F Su C Lu S-C Kuo and W Zeng ldquoAdsorption of CO2on
amine-functionalized y-type zeolitesrdquo Energy and Fuels vol 24no 2 pp 1441ndash1448 2010
[24] A Ertan and F Cakicioglu-Ozkan ldquoCO2and N
2adsorption
on the acid (HCl HNO3 H2SO4and H
3PO4) treated zeolitesrdquo
Adsorption vol 11 no 1 pp 151ndash156 2005[25] F Brandani and D M Ruthven ldquoThe effect of water on the
adsorption of CO2and C
3H8on type X zeolitesrdquo Industrial amp
Engineering Chemistry Research vol 43 no 26 pp 8339ndash83442004
International Journal of Photoenergy 9
[26] L Li X Wen X Fu et al ldquoMgOAl2O3sorbent for CO
2
capturerdquo Energy and Fuels vol 24 no 10 pp 5773ndash5780 2010[27] M K RamReddy Z P Xu GQ Lu and J C DDaCosta ldquoLay-
ered double hydroxides for CO2capture structure evolution
and regenerationrdquo Industrial amp Engineering Chemistry Researchvol 45 no 22 pp 7504ndash7509 2006
[28] M Kato S Yoshikawa and K Nakagawa ldquoCarbon dioxideabsorption by lithium orthosilicate in a wide range of temper-ature and carbon dioxide concentrationsrdquo Journal of MaterialsScience Letters vol 21 no 6 pp 485ndash487 2002
[29] J-I Ida and Y S Lin ldquoMechanism of high-temperature CO2
sorption on lithium zirconaterdquo Environmental Science andTechnology vol 37 no 9 pp 1999ndash2004 2003
[30] E Ochoa-Fernandez H K Rusten H A Jakobsen MRoslashnning A Holmen and D Chen ldquoSorption enhanced hydro-gen production by steam methane reforming using Li
2ZrO3
as sorbent sorption kinetics and reactor simulationrdquo CatalysisToday vol 106 no 1-4 pp 41ndash46 2005
[31] E Ochoa-Fernandez M Roslashnning T Grande and D ChenldquoSynthesis and CO
2capture properties of nanocrystalline
lithium zirconaterdquo Chemistry of Materials vol 18 no 25 pp6037ndash6046 2006
[32] J A Satrio B H Shanks and T D Wheelock ldquoDevelopmentof a novel combined catalyst and sorbent for hydrocarbonreformingrdquo Industrial amp Engineering Chemistry Research vol44 no 11 pp 3901ndash3911 2005
[33] Z-S Li N-S Cai and Y-Y Huang ldquoEffect of preparationtemperature on cyclic CO
2capture and multiple carbonation-
calcination cycles for a new Ca-based CO2sorbentrdquo Industrial
amp Engineering Chemistry Research vol 45 no 6 pp 1911ndash19172006
[34] E P Reddy and P G Smirniotis ldquoHigh-temperature sorbentsfor CO
2made of alkali metals doped on CaO supportsrdquo The
Journal of Physical Chemistry B vol 108 no 23 pp 7794ndash78002004
[35] K Kuramoto S Fujimoto A Morita et al ldquoRepetitivecarbonation-calcination reactions of Ca-based sorbents forefficient CO
2sorption at elevated temperatures and pressuresrdquo
Industrial amp Engineering Chemistry Research vol 42 no 5 pp975ndash981 2003
[36] S F Wu T H Beum J I Yang and J N Kim ldquoProperties ofCa-base CO
2sorbent using Ca(OH)
2as precursorrdquo Industrial amp
Engineering Chemistry Research vol 46 no 24 pp 7896ndash78992007
[37] S F Wu Q H Li J N Kim and K B Yi ldquoProperties of a nanoCaOAl
2O3CO2sorbentrdquo Industrial amp Engineering Chemistry
Research vol 47 no 1 pp 180ndash184 2008
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
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Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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CatalystsJournal of
2 International Journal of Photoenergy
Table 1 The different types of solid CO2 adsorbents based on their sorptiondesorption temperatures
Adsorbent Total capacity(mmolg)
Temperature(K)
Pressure(atm) Reference
Low temperature adsorbentsAmine based
Amine-modified mesoporous silica 45 348 1 (Liu et al 2010) [12]Amine-modified ordered mesoporous silica (OMS) 15 mdash mdash (Zelenak et al 2008) [13]Amine-modified OMSs 02ndash14 348 1 (Liu et al 2010) [12]Amine tetraethylenepentamine (TEPA)OMSs 46 348 1 (Liu et al 2010) [12]
MOFsZIFsMOF-2 32 mdash 41 (Millward and Yaghi 2005) [14]
Carbonactivated carbon basedCoal-based activated carbon 03 323 0001 (Deng et al 2011) [15]Porous carbon nitride (CN) 290 298 mdash (Li et al 2010) [16]N-doped carbons template from zeolite 69 273 1 (Xia et al 2011) [17]Activated carbonN2 375
293 1 (Zhang et al 2010) [18]Activated carbonH2 349Activated carbonNH3 322Activated carbon 15 303 40 (Drage et al 2009) [19]Activated carbon 35 275 1 (Wang et al 2008) [20]Carbon nanotubes (CNTs)3-aminopropyltriethoxysilane(APTS) 245 323 mdash (Su et al 2011) [21]
Alumina based120574-Al2O3 031 295 mdash (Rege and Yang 2001) [22]
Zeolite basedY-type zeolitetetraethyl-enepentamine (TEPA) 427 303ndash333 (Su et al 2010) [23]Natural zeolite 205
298 01 (Ertan and Cakicioglu-Ozkan2005) [24]
Treated zeoliteH3PO4 195Synthetic zeolite-5X 549Synthetic zeolite-13A 682LilSX 017
mdash 1 (Brandani and Ruthven 2004) [25]NaLX 023CaX 02413X (NaX) 294 295 mdash (Rege and Yang 2001) [22]
Magnesium basedMgOAl2O3 136 333 1 (Li et al 2010) [26]
Intermediate temperature adsorbentsLDH
Mg-Al-CO3 LDHs 049 473 005 (Ram Reddy et al 2006) [27]High temperature adsorbents
Lithium orthosilicatesLi4SiO4 614 773 1 (Kato et al 2002) [28]
Lithium zirconatesLi2ZrO3 455 773 1 (Ida and Lin 2003) [29]
Li2ZrO3 450 823 1 (Ochoa-Fernandez et al 2005)[30]
Li2ZrO3 (nanocrystalline) 614 848 1 (Ochoa-Fernandez et al 2006)[31]
International Journal of Photoenergy 3
Table 1 Continued
Adsorbent Total capacity(mmolg)
Temperature(K)
Pressure(atm) Reference
Calcium oxide basedCaO 23 923 mdash (Satrio et al 2005) [32]CaOAl2O3 116 923 mdash (Li et al 2006) [33]CsCaO 49
723 04 (Reddy and Smirniotis 2004)[34]
RbCaO 45KCaO 38NaCaO 31CaCO3 15 573 1 (Kuramoto et al 2003) [35]CaOAl2O3 602 923 1 (Wu et al 2007) [36]Nano CaOAl2O3 602 650 mdash (Wu et al 2008) [37]
200nm
(a)
200nm
(b)
200nm
(c)
Figure 1 FESEM top view image of nanotubes subjected to wet impregnation of 06M calcium nitrate solution for (a) 24 hours (b) 48 hoursand (c) 72 hours and subsequent annealing at 673K in Ar gas for 4 hours
residual OH groups which appear when mixed with the rareearths [6] However these CO
2adsorbents suffer severely
from textural degradation during the sorptiondesorptionoperations These CO
2adsorbents can only run several tens
of cycles before any obvious degradation and are still farfrom practical applications [3] Instantly the conversion ofCaO decreased sharply from 70 in the first cycle to 20
in the eleventh cycle when tested in fluidized bed [7] Thedeactivation primarily results from the formation of thicklayer structured from CaCO
3surrounding the CaO which
severely hinders the diffusion of CO2gas to react with
the inner core Besides it has also been reported that theadsorption capacity for CaO-based sorbents decays as afunction of the sintering of CaO grain at high temperature
4 International Journal of Photoenergy
214
171
128
85
42
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(a)
247
198
148
99
49
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(b)
117
94
70
47
23
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(c)
Figure 2 EDX spectra of nanotubes subjected to wet impregnation of 06M calcium nitrate solution for (a) 24 hours (b) 48 hours and(c) 72 hours (all EDX spectrums are noneditable format based on our FESEM-EDX system)
and a certain loss in the porosity When pores smaller than acritical value (eg 200 nm) are filled the reaction gets muchslower [8] Therefore great efforts have to be made in orderto further improve the cyclic stability of CaO-based sorbents
One of the most promising solutions to improve thecyclic stability of CaO is controlling their architecture intoone-dimensional nanomaterials The main reason might beattributed to the fast reaction (chemical reaction) and theslow reaction (diffusion controlled) could be achieved duringCO2adsorption In this case the diffusion of CO
2into
the particle interior to react with Ca dopants could beprevented and the whole CO
2adsorption process could then
be diffusion-controlled [2 3] Theoretically the small parti-cles size of sorbent (eg 30ndash50 nm) would perform bettercarbonation-calcination reaction which allowed carbonationto take place at the rapid reaction-controlled regime Anotherpromising solution to improve cyclic stability is to incorpo-rate high stability metal oxide (titanium dioxide) into CaOparticlesTheprevention ofCaOoxidation during calcinationstage could be expected Therefore detail investigation onone-dimensional CaO-TiO
2nanotubes for effective CO
2
adsorption will be discussed
2 Experimental Procedure
One-dimensional TiO2nanotube arrays were synthesized
using a rapid-anodic oxidation electrochemical anodizationtechnique A high purity of Ti foil (996 Strem Chemical
USA) with a thickness of 127 120583m was selected as substrateto grow TiO
2nanotubes This process was conducted in a
bath with electrolytes composed of ethylene glycol (C2H6O2
gt995 Merck USA) 5 wt ammonium fluoride (NH4F
98 Merck USA) and 5wt hydrogen peroxide (H2O2
30 H2O2and 70 H
2O J T Baker USA) for 60 minutes
at 60V This experimental condition was selected because itfavors the formation of well-aligned TiO
2nanotube arrays
[9 10] After the anodization process as-anodized sampleswere cleaned using distilled water and dried under a nitrogenstream CaO-TiO
2nanotubes were then prepared through
wet impregnation technique using calcium nitrate tetrahy-drate (Ca(NO
3)2sdot4H2O Merck USA) as the precursor This
was an ex situ approach that was used to incorporate Ca2+ions into TiO
2nanotubes Two different concentrations
of calcium nitrate tetrahydrate solution (06 12M) wereprepared at different reaction times (24 48 72 hours) in awater bath of 80∘C Subsequently the samples were thermal-annealed at 673K in an argon atmosphere for 4 h in order toproduce crystalline TiO
2nanotubes
The surface morphologies of the synthesized sampleswere observed through field emission scanning electronmicroscopy (FESEM) using a Zeiss SUPRA 35VP whichis operated at a working distance of 1mm and 5 kV Theenergy dispersive X-ray spectroscopy (EDX) was appliedto elemental analysis of the CaO-TiO
2nanotubes sorbents
which is equipped in the FESEM The structural variationsand phase determination for CaO-TiO
2nanotubes sorbents
International Journal of Photoenergy 5
200nm
(a)
200nm
(b)
200nm
(c)
Figure 3 FESEM top view image of nanotubes subjected to wet impregnation of 12M calcium nitrate solution for (a) 24 hours (b) 48 hoursand (c) 72 hours and subsequent annealing at 673K in Ar gas for 4 hours
were determined using a Philips PW 1729 X-ray diffraction(XRD) which operated at 45 kV and 40mV patterns Thethermogravimetric analysis (TGA) was used to investigatethe CO
2adsorption for CaO-TiO
2nanotubes sorbents (STA
6000 Perkin Elmer USA)The steps included are N2gas flow
at a rate of 10∘Cmin from room temperature to 673K andthen holding for 30min in CO
2and finally cooling down to
573K byN2gas In the present study carbonation-calcination
reaction is set to be 673K because nanotubular structure canbe collapsed at high temperature (above 773K) [11]
3 Results and Discussion
The surface morphologies of CaO-TiO2nanotubes synthe-
sized in 06Mcalciumnitrate solution for 24 48 and 72 hourswere subsequently observed via FESEM as presented in Fig-ures 1(a) to 1(c) respectively As shown in the FESEM imagesthe opening of the nanotubular structure showed aggregationof CaO species on wall surface of TiO
2nanotubes The
wall thickness of the nanotubes dramatically increased to
75 nm which resulted in a narrow pore entrance for 24 hoursreaction time (Figure 1(a)) Meanwhile as the reaction timeincreased to 48 hours the wall thickness of the nanotubesincreased from about 75 nm to 100 nm (Figure 1(b)) Withfurther increase of the reaction time to 72 hours it wasfound that the nanotubes were covered with excess CaOspecies and clogged the pore entrance (Figure 1(c)) A roughirregular and corrugated surface was formed Based on theFESEM images it could be concluded that the appearanceof TiO
2nanotubes was dependent on the reaction time in
calcium nitrate solution A narrow or blocked pore entranceof nanotubes was formed as increasing soaking period in thesolution Next the average atomic percentage (at) of theelements within CaO-TiO
2nanotubes was determined using
EDX analysis The numerical EDX analyses of the samplesare listed in Table 2 As determined through EDX analysisthe average Ca contents of the nanotubes for 24 48 and 72hours were 101 at 367 at and 459 at respectively Theintensity of the Ca peak (369 keV) increased with increasingreaction time in calcium nitrate solution as presented in
6 International Journal of Photoenergy
274
219
164
109
54
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(a)
252
202
151
101
50
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(b)
295
236
177
118
59
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(c)
Figure 4 EDX spectra of nanotubes subjected to wet impregnation of 12M calcium nitrate solution for (a) 24 hours (b) 48 hours and(c) 72 hours (all EDX spectrums are noneditable format based on our FESEM-EDX system)
Figures 2(a) to 2(c) Another set of experiments was con-ducted to form CaO-TiO
2nanotubes in 12M calcium nitrate
solution for 24 48 and 72 hours All morphologies of thesamples showed similar appearance of CaO-TiO
2nanotubes
synthesized in 06M calcium nitrate solution The irregularCaO layer covered all of the TiO
2nanotubular structure
and nanoporous structure arranged in a nonordered mannerwhich could be observed in Figures 3(a) to 3(c)The chemicalstoichiometry of the resultant samples was determined viaEDX analysis as shown in Figures 4(a) to 4(c) A high Cacontent of 978 atwas determined from those synthesized in12M calciumnitrate solution for 72 hours indicating that theincorporation of the CaO became prominent with increasingthe concentration of calcium nitrate solution Based on theFESEM images and EDX analysis the small Ca2+ ions couldbe diffused into TiO
2nanotubes in the presence of lattice
defects especially nearby to the wall of nanotubes In thiscase the diffusion rate of Ca2+ ions increased significantlywhen increasing the reaction time and concentration of pre-cursor However the content of small Ca2+ ions that diffusedinto the TiO
2lattice could reach a saturation condition and
start to accumulate on the surface of nanotubes The numberof nucleation sites for Ca2+ ions loaded on the wall surface ofthe nanotubes increasedwith longer reaction time and higherconcentration of precursor which produced nanotubes withthicker walls The diffusion of the Ca2+ ions formed CandashObonding withOndashTindashO bonding thus charge neutrality couldbe achieved
Table 2 EDX result of CaO-TiO2 with different soaking time in06M and 12M calcium nitrate solution
Concentration ofcalcium nitratesolution (M)
Element (at)reactiontime (h) Ti O Ca
0624 4607 5292 010148 3888 5745 036772 4230 5311 0459
1224 3644 6066 029048 3264 6064 066472 2883 6110 0978
In the present study XRD analysis was used to determinethe crystallographic structure and the changes in the phasestructure of the CaO-TiO
2nanotubes synthesized in different
reaction times and concentrations of precursor are presentedin Figures 5 and 6 Numerous studies reported that heattreatment at about 400∘C could transform the amorphousstructure of TiO
2into the crystalline anatase phase The
obvious diffraction peaks from the XRD pattern attributedto the anatase phase (JCPDS no 21-1272) were detected fromthe XRD patterns (Figure 5(a)) The diffraction peaks areallocated at 2532∘ 3784∘ 3842∘ 4802∘ 5387∘ 5509∘ 6293∘7065∘ and 7623∘ which correspond to 101 004 112 200105 211 204 220 and 301 crystal planes for the anatase
International Journal of Photoenergy 7
10 20 30 40 50 60 70 80 90
Inte
nsity
(au
)
(d)
(c)
(b)
(a)TA T
T A AT
A T
T
T
2120579 (deg)
Figure 5 XRD pattern of TiO2nanotubes incorporated with Ca in
06M Ca(NO3)2solution at different soaking period (a) pure TiO
2
(b) 24 hours (c) 48 hours and (d) 72 hours (A = anatase phase T =titanium phase)
10 20 30 40 50 60 70 80 90
Inte
nsity
(au
)
AT A
TT
AT
TA
TT (a)
(b)
(c)
(d)
2120579 (deg)
Figure 6 XRD pattern of TiO2nanotubes incorporated with Ca in
12M Ca(NO3)2solution at different soaking period (a) pure TiO
2
(b) 24 hours (c) 48 hours and (d) 72 hours (A = anatase phase T =titanium phase)
phase respectively Apparently the incorporation of Ca2+ions into the lattice of TiO
2hindered the crystallization
of TiO2 resulting in the peak intensity of the 101 peak at
2532∘ decrease The decrease in anatase phase is maybe dueto the interruption of Ca atom which diffused into TiO
2
nanotubes and inhibited the formation of the anatase TheXRD pattern of the sample soaked in 12M for 72 hoursexhibits additional peaks 220 and 400 crystal planes at 54∘and 80∘ corresponding to CaO phase This indicates thatcrystalline CaO are formed once the concentration of Cain TiO
2reaches a higher level Next the resultant anodized
CaO-TiO2nanotubes were used in the characterization of
CO2adsorption using TGA analysis The processing steps
involved in TGA analysis are N2gas flow at a rate of 10∘Cmin
from room temperature to 673K and then holding for 30minin CO
2and finally cooling down to 573K byN
2gasThe TGA
curves for 06M of Ca and 12M of Ca are shown in Figures7 and 8 respectively while the CO
2adsorption capacity is
summarized in Table 3 Based on the TGA analysis it couldbe observed that all CaO-TiO
2samples showed their CO
2
adsorption capacity in the range of 33mmolg to 45mmolgA maximum CO
2adsorption capacity of up to 445mmolg
was observed from the CaO-TiO2nanotubes synthesized in
050100150200250300350400450
996998100
1002100410061008
101101210141016
0 20 40 60 80
Wei
ght (
)
Time (min)
24 hours48 hours
72 hoursTemperature
Tem
pera
ture
(∘C)
Figure 7 TGA curve of soaking in 06M of Ca for different periodsof time
050100150200250300350400450
995
100
1005
101
1015
102
1025
0 20 40 60 80
Wei
ght (
)
Time (min)
Tem
pera
ture
(∘C)
24 hours48 hours
72 hoursTemperature
Figure 8 TGA curve of soaking in 12M of Ca for different periodsof time
Table 3 CO2 adsorption capacity of the CaO-TiO2 samples
Concentration of calciumnitrate solution (M)
Soaking period(hours)
CO2 adsorptioncapacity (mmolg)
0624 38948 33272 400
1224 35948 44572 380
12M of calcium nitrate solution for 48 hours Basically theCO2adsorption capacity based CaO-TiO
2sorbents used the
following reaction CaO + CO2rarr CaCO
3 In this case
the sorbent weight is increased significantly when CO2gas is
applied to the TGA system where all the weight added is CO2
adsorbed This reason clearly explains that CO2adsorption
capacity is increased after carbonation process
8 International Journal of Photoenergy
4 Conclusion
The present study demonstrated that one-dimensional CaO-TiO2nanotubes sorbent was successfully formed using oxi-
dation electrochemical anodization and wet impregnationtechniques All of the resultant CaO-TiO
2nanotubes sorbent
exhibited promising CO2adsorption capacity in the range of
33mmolg to 45mmolg It is shown that high active surfacearea of CaO-TiO
2nanotubes sorbent showed good stability
during extended cyclic carbonation-calcination reaction
Conflict of Interests
The author declares that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
This research is supported by High Impact Research Chan-cellory Grant UMC6251HIR228 (J55001-73873) from theUniversity of Malaya In addition authors would like tothank University of Malaya for sponsoring this work underUniversity of Malaya Research Grant (UMRG no RP022-2012D)
References
[1] Q Wang J Luo Z Zhong and A Borgna ldquoCO2capture by
solid adsorbents and their applications current status and newtrendsrdquo Energy amp Environmental Science vol 4 no 1 pp 42ndash552011
[2] D M DrsquoAlessandro B Smit and J R Long ldquoCarbon dioxidecapture prospects for new materialsrdquo Angewandte ChemieInternational Edition vol 49 no 35 pp 6058ndash6082 2010
[3] SWang S Yan XMa and JGong ldquoRecent advances in captureof carbon dioxide using alkali-metal-based oxidesrdquo Energy ampEnvironmental Science vol 4 no 10 pp 3805ndash3819 2011
[4] N H Florin and A T Harris ldquoReactivity of CaO derived fromnano-sized CaCO
3particles through multiple CO
2capture-
and-release cyclesrdquo Chemical Engineering Science vol 64 no2 pp 187ndash191 2009
[5] J Garcıa T Lopez M Alvarez D H Aguilar and P QuintanaldquoSpectroscopic structural and textural properties of CaO andCaO-SiO
2materials synthesized by sol-gel with different acid
catalystsrdquo Journal of Non-Crystalline Solids vol 354 no 2-9 pp729ndash732 2008
[6] V R Choudhary S A R Mulla and B S Uphade ldquoOxidativecoupling of methane over alkaline earth oxides deposited oncommercial support precoated with rare earth oxidesrdquo Fuel vol78 no 4 pp 427ndash437 1999
[7] D Alvarez and J C Abanades ldquoPore-size and shape effects onthe recarbonation performance of calcium oxide submitted torepeated calcinationrecarbonation cyclesrdquo Energy and Fuelsvol 19 no 1 pp 270ndash278 2005
[8] J-R Li Y Ma M C McCarthy et al ldquoCarbon dioxidecapture-related gas adsorption and separation in metal-organicframeworksrdquo Coordination Chemistry Reviews vol 255 no 15-16 pp 1791ndash1823 2011
[9] S Sreekantan L C Wei and Z Lockman ldquoExtremely fastgrowth rate of TiO
2nanotube arrays in electrochemical bath
containing H2O2rdquo Journal of the Electrochemical Society vol
158 no 12 pp C397ndashC402 2011[10] CW Lai and S Sreekantan ldquoDimensional control of TiO
2nan-
otube arrays with H2O2content for high photoelectrochemical
water splitting performancerdquoMicro ampNano Letters vol 7 no 5pp 443ndash447 2012
[11] Y K Lai J Y Huang H F Zhang et al ldquoNitrogen-doped TiO2
nanotube array films with enhanced photocatalytic activityunder various light sourcesrdquo Journal of Hazardous Materialsvol 184 no 1ndash3 pp 855ndash863 2010
[12] S-H Liu C-H Wu H-K Lee and S-B Liu ldquoHighly stableamine-modified mesoporous silica materials for efficient CO
2
capturerdquo Topics in Catalysis vol 53 no 3-4 pp 210ndash217 2010[13] V Zelenak M Badanicova D Halamova et al ldquoAmine-
modified ordered mesoporous silica effect of pore size oncarbon dioxide capturerdquoChemical Engineering Journal vol 144no 2 pp 336ndash342 2008
[14] A R Millward and O M Yaghi ldquoMetal-organic frameworkswith exceptionally high capacity for storage of carbon dioxideat room temperaturerdquo Journal of the American Chemical Societyvol 127 no 51 pp 17998ndash17999 2005
[15] H Deng H Yi X Tang P Ning andQ Yu ldquoAdsorption of CO2
and N2on coal-based activated carbonrdquo Advanced Materials
Research vol 204-210 pp 1250ndash1253 2011[16] Q Li J Yang D Feng et al ldquoFacile synthesis of porous
carbon nitride spheres with hierarchical three-dimensionalmesostructures for CO
2capturerdquo Nano Research vol 3 no 9
pp 632ndash642 2010[17] Y Xia R Mokaya G S Walker and Y Zhu ldquoSuperior CO
2
adsorption capacity on N-doped high-surface-area microp-orous carbons templated from zeoliterdquo Advanced Energy Mate-rials vol 1 pp 678ndash683 2011
[18] Z Zhang M Xu H Wang and Z Li ldquoEnhancement of CO2
adsorption on high surface area activated carbon modified byN2 H2and ammoniardquo Chemical Engineering Journal vol 160
no 2 pp 571ndash577 2010[19] T C Drage J M Blackman C Pevida and C E Snape
ldquoEvaluation of activated carbon adsorbents for CO2capture in
gasificationrdquo Energy and Fuels vol 23 no 5 pp 2790ndash27962009
[20] Y Wang Y Zhou C Liu and L Zhou ldquoComparative studiesof CO
2and CH
2sorption on activated carbon in presence of
waterrdquoColloids and Surfaces A Physicochemical and EngineeringAspects vol 322 no 1ndash3 pp 14ndash18 2008
[21] F Su C Lu and H-S Chen ldquoAdsorption desorption andthermodynamic studies of CO
2with high-amine-loaded mul-
tiwalled carbon nanotubesrdquo Langmuir vol 27 no 13 pp 8090ndash8098 2011
[22] S U Rege and R T Yang ldquoA novel FTIR method for studyingmixed gas adsorption at low concentrations H
2O and CO
2on
NaX zeolite and 120574-aluminardquo Chemical Engineering Science vol56 no 12 pp 3781ndash3796 2001
[23] F Su C Lu S-C Kuo and W Zeng ldquoAdsorption of CO2on
amine-functionalized y-type zeolitesrdquo Energy and Fuels vol 24no 2 pp 1441ndash1448 2010
[24] A Ertan and F Cakicioglu-Ozkan ldquoCO2and N
2adsorption
on the acid (HCl HNO3 H2SO4and H
3PO4) treated zeolitesrdquo
Adsorption vol 11 no 1 pp 151ndash156 2005[25] F Brandani and D M Ruthven ldquoThe effect of water on the
adsorption of CO2and C
3H8on type X zeolitesrdquo Industrial amp
Engineering Chemistry Research vol 43 no 26 pp 8339ndash83442004
International Journal of Photoenergy 9
[26] L Li X Wen X Fu et al ldquoMgOAl2O3sorbent for CO
2
capturerdquo Energy and Fuels vol 24 no 10 pp 5773ndash5780 2010[27] M K RamReddy Z P Xu GQ Lu and J C DDaCosta ldquoLay-
ered double hydroxides for CO2capture structure evolution
and regenerationrdquo Industrial amp Engineering Chemistry Researchvol 45 no 22 pp 7504ndash7509 2006
[28] M Kato S Yoshikawa and K Nakagawa ldquoCarbon dioxideabsorption by lithium orthosilicate in a wide range of temper-ature and carbon dioxide concentrationsrdquo Journal of MaterialsScience Letters vol 21 no 6 pp 485ndash487 2002
[29] J-I Ida and Y S Lin ldquoMechanism of high-temperature CO2
sorption on lithium zirconaterdquo Environmental Science andTechnology vol 37 no 9 pp 1999ndash2004 2003
[30] E Ochoa-Fernandez H K Rusten H A Jakobsen MRoslashnning A Holmen and D Chen ldquoSorption enhanced hydro-gen production by steam methane reforming using Li
2ZrO3
as sorbent sorption kinetics and reactor simulationrdquo CatalysisToday vol 106 no 1-4 pp 41ndash46 2005
[31] E Ochoa-Fernandez M Roslashnning T Grande and D ChenldquoSynthesis and CO
2capture properties of nanocrystalline
lithium zirconaterdquo Chemistry of Materials vol 18 no 25 pp6037ndash6046 2006
[32] J A Satrio B H Shanks and T D Wheelock ldquoDevelopmentof a novel combined catalyst and sorbent for hydrocarbonreformingrdquo Industrial amp Engineering Chemistry Research vol44 no 11 pp 3901ndash3911 2005
[33] Z-S Li N-S Cai and Y-Y Huang ldquoEffect of preparationtemperature on cyclic CO
2capture and multiple carbonation-
calcination cycles for a new Ca-based CO2sorbentrdquo Industrial
amp Engineering Chemistry Research vol 45 no 6 pp 1911ndash19172006
[34] E P Reddy and P G Smirniotis ldquoHigh-temperature sorbentsfor CO
2made of alkali metals doped on CaO supportsrdquo The
Journal of Physical Chemistry B vol 108 no 23 pp 7794ndash78002004
[35] K Kuramoto S Fujimoto A Morita et al ldquoRepetitivecarbonation-calcination reactions of Ca-based sorbents forefficient CO
2sorption at elevated temperatures and pressuresrdquo
Industrial amp Engineering Chemistry Research vol 42 no 5 pp975ndash981 2003
[36] S F Wu T H Beum J I Yang and J N Kim ldquoProperties ofCa-base CO
2sorbent using Ca(OH)
2as precursorrdquo Industrial amp
Engineering Chemistry Research vol 46 no 24 pp 7896ndash78992007
[37] S F Wu Q H Li J N Kim and K B Yi ldquoProperties of a nanoCaOAl
2O3CO2sorbentrdquo Industrial amp Engineering Chemistry
Research vol 47 no 1 pp 180ndash184 2008
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
International Journal of Photoenergy 3
Table 1 Continued
Adsorbent Total capacity(mmolg)
Temperature(K)
Pressure(atm) Reference
Calcium oxide basedCaO 23 923 mdash (Satrio et al 2005) [32]CaOAl2O3 116 923 mdash (Li et al 2006) [33]CsCaO 49
723 04 (Reddy and Smirniotis 2004)[34]
RbCaO 45KCaO 38NaCaO 31CaCO3 15 573 1 (Kuramoto et al 2003) [35]CaOAl2O3 602 923 1 (Wu et al 2007) [36]Nano CaOAl2O3 602 650 mdash (Wu et al 2008) [37]
200nm
(a)
200nm
(b)
200nm
(c)
Figure 1 FESEM top view image of nanotubes subjected to wet impregnation of 06M calcium nitrate solution for (a) 24 hours (b) 48 hoursand (c) 72 hours and subsequent annealing at 673K in Ar gas for 4 hours
residual OH groups which appear when mixed with the rareearths [6] However these CO
2adsorbents suffer severely
from textural degradation during the sorptiondesorptionoperations These CO
2adsorbents can only run several tens
of cycles before any obvious degradation and are still farfrom practical applications [3] Instantly the conversion ofCaO decreased sharply from 70 in the first cycle to 20
in the eleventh cycle when tested in fluidized bed [7] Thedeactivation primarily results from the formation of thicklayer structured from CaCO
3surrounding the CaO which
severely hinders the diffusion of CO2gas to react with
the inner core Besides it has also been reported that theadsorption capacity for CaO-based sorbents decays as afunction of the sintering of CaO grain at high temperature
4 International Journal of Photoenergy
214
171
128
85
42
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(a)
247
198
148
99
49
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(b)
117
94
70
47
23
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(c)
Figure 2 EDX spectra of nanotubes subjected to wet impregnation of 06M calcium nitrate solution for (a) 24 hours (b) 48 hours and(c) 72 hours (all EDX spectrums are noneditable format based on our FESEM-EDX system)
and a certain loss in the porosity When pores smaller than acritical value (eg 200 nm) are filled the reaction gets muchslower [8] Therefore great efforts have to be made in orderto further improve the cyclic stability of CaO-based sorbents
One of the most promising solutions to improve thecyclic stability of CaO is controlling their architecture intoone-dimensional nanomaterials The main reason might beattributed to the fast reaction (chemical reaction) and theslow reaction (diffusion controlled) could be achieved duringCO2adsorption In this case the diffusion of CO
2into
the particle interior to react with Ca dopants could beprevented and the whole CO
2adsorption process could then
be diffusion-controlled [2 3] Theoretically the small parti-cles size of sorbent (eg 30ndash50 nm) would perform bettercarbonation-calcination reaction which allowed carbonationto take place at the rapid reaction-controlled regime Anotherpromising solution to improve cyclic stability is to incorpo-rate high stability metal oxide (titanium dioxide) into CaOparticlesTheprevention ofCaOoxidation during calcinationstage could be expected Therefore detail investigation onone-dimensional CaO-TiO
2nanotubes for effective CO
2
adsorption will be discussed
2 Experimental Procedure
One-dimensional TiO2nanotube arrays were synthesized
using a rapid-anodic oxidation electrochemical anodizationtechnique A high purity of Ti foil (996 Strem Chemical
USA) with a thickness of 127 120583m was selected as substrateto grow TiO
2nanotubes This process was conducted in a
bath with electrolytes composed of ethylene glycol (C2H6O2
gt995 Merck USA) 5 wt ammonium fluoride (NH4F
98 Merck USA) and 5wt hydrogen peroxide (H2O2
30 H2O2and 70 H
2O J T Baker USA) for 60 minutes
at 60V This experimental condition was selected because itfavors the formation of well-aligned TiO
2nanotube arrays
[9 10] After the anodization process as-anodized sampleswere cleaned using distilled water and dried under a nitrogenstream CaO-TiO
2nanotubes were then prepared through
wet impregnation technique using calcium nitrate tetrahy-drate (Ca(NO
3)2sdot4H2O Merck USA) as the precursor This
was an ex situ approach that was used to incorporate Ca2+ions into TiO
2nanotubes Two different concentrations
of calcium nitrate tetrahydrate solution (06 12M) wereprepared at different reaction times (24 48 72 hours) in awater bath of 80∘C Subsequently the samples were thermal-annealed at 673K in an argon atmosphere for 4 h in order toproduce crystalline TiO
2nanotubes
The surface morphologies of the synthesized sampleswere observed through field emission scanning electronmicroscopy (FESEM) using a Zeiss SUPRA 35VP whichis operated at a working distance of 1mm and 5 kV Theenergy dispersive X-ray spectroscopy (EDX) was appliedto elemental analysis of the CaO-TiO
2nanotubes sorbents
which is equipped in the FESEM The structural variationsand phase determination for CaO-TiO
2nanotubes sorbents
International Journal of Photoenergy 5
200nm
(a)
200nm
(b)
200nm
(c)
Figure 3 FESEM top view image of nanotubes subjected to wet impregnation of 12M calcium nitrate solution for (a) 24 hours (b) 48 hoursand (c) 72 hours and subsequent annealing at 673K in Ar gas for 4 hours
were determined using a Philips PW 1729 X-ray diffraction(XRD) which operated at 45 kV and 40mV patterns Thethermogravimetric analysis (TGA) was used to investigatethe CO
2adsorption for CaO-TiO
2nanotubes sorbents (STA
6000 Perkin Elmer USA)The steps included are N2gas flow
at a rate of 10∘Cmin from room temperature to 673K andthen holding for 30min in CO
2and finally cooling down to
573K byN2gas In the present study carbonation-calcination
reaction is set to be 673K because nanotubular structure canbe collapsed at high temperature (above 773K) [11]
3 Results and Discussion
The surface morphologies of CaO-TiO2nanotubes synthe-
sized in 06Mcalciumnitrate solution for 24 48 and 72 hourswere subsequently observed via FESEM as presented in Fig-ures 1(a) to 1(c) respectively As shown in the FESEM imagesthe opening of the nanotubular structure showed aggregationof CaO species on wall surface of TiO
2nanotubes The
wall thickness of the nanotubes dramatically increased to
75 nm which resulted in a narrow pore entrance for 24 hoursreaction time (Figure 1(a)) Meanwhile as the reaction timeincreased to 48 hours the wall thickness of the nanotubesincreased from about 75 nm to 100 nm (Figure 1(b)) Withfurther increase of the reaction time to 72 hours it wasfound that the nanotubes were covered with excess CaOspecies and clogged the pore entrance (Figure 1(c)) A roughirregular and corrugated surface was formed Based on theFESEM images it could be concluded that the appearanceof TiO
2nanotubes was dependent on the reaction time in
calcium nitrate solution A narrow or blocked pore entranceof nanotubes was formed as increasing soaking period in thesolution Next the average atomic percentage (at) of theelements within CaO-TiO
2nanotubes was determined using
EDX analysis The numerical EDX analyses of the samplesare listed in Table 2 As determined through EDX analysisthe average Ca contents of the nanotubes for 24 48 and 72hours were 101 at 367 at and 459 at respectively Theintensity of the Ca peak (369 keV) increased with increasingreaction time in calcium nitrate solution as presented in
6 International Journal of Photoenergy
274
219
164
109
54
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(a)
252
202
151
101
50
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(b)
295
236
177
118
59
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(c)
Figure 4 EDX spectra of nanotubes subjected to wet impregnation of 12M calcium nitrate solution for (a) 24 hours (b) 48 hours and(c) 72 hours (all EDX spectrums are noneditable format based on our FESEM-EDX system)
Figures 2(a) to 2(c) Another set of experiments was con-ducted to form CaO-TiO
2nanotubes in 12M calcium nitrate
solution for 24 48 and 72 hours All morphologies of thesamples showed similar appearance of CaO-TiO
2nanotubes
synthesized in 06M calcium nitrate solution The irregularCaO layer covered all of the TiO
2nanotubular structure
and nanoporous structure arranged in a nonordered mannerwhich could be observed in Figures 3(a) to 3(c)The chemicalstoichiometry of the resultant samples was determined viaEDX analysis as shown in Figures 4(a) to 4(c) A high Cacontent of 978 atwas determined from those synthesized in12M calciumnitrate solution for 72 hours indicating that theincorporation of the CaO became prominent with increasingthe concentration of calcium nitrate solution Based on theFESEM images and EDX analysis the small Ca2+ ions couldbe diffused into TiO
2nanotubes in the presence of lattice
defects especially nearby to the wall of nanotubes In thiscase the diffusion rate of Ca2+ ions increased significantlywhen increasing the reaction time and concentration of pre-cursor However the content of small Ca2+ ions that diffusedinto the TiO
2lattice could reach a saturation condition and
start to accumulate on the surface of nanotubes The numberof nucleation sites for Ca2+ ions loaded on the wall surface ofthe nanotubes increasedwith longer reaction time and higherconcentration of precursor which produced nanotubes withthicker walls The diffusion of the Ca2+ ions formed CandashObonding withOndashTindashO bonding thus charge neutrality couldbe achieved
Table 2 EDX result of CaO-TiO2 with different soaking time in06M and 12M calcium nitrate solution
Concentration ofcalcium nitratesolution (M)
Element (at)reactiontime (h) Ti O Ca
0624 4607 5292 010148 3888 5745 036772 4230 5311 0459
1224 3644 6066 029048 3264 6064 066472 2883 6110 0978
In the present study XRD analysis was used to determinethe crystallographic structure and the changes in the phasestructure of the CaO-TiO
2nanotubes synthesized in different
reaction times and concentrations of precursor are presentedin Figures 5 and 6 Numerous studies reported that heattreatment at about 400∘C could transform the amorphousstructure of TiO
2into the crystalline anatase phase The
obvious diffraction peaks from the XRD pattern attributedto the anatase phase (JCPDS no 21-1272) were detected fromthe XRD patterns (Figure 5(a)) The diffraction peaks areallocated at 2532∘ 3784∘ 3842∘ 4802∘ 5387∘ 5509∘ 6293∘7065∘ and 7623∘ which correspond to 101 004 112 200105 211 204 220 and 301 crystal planes for the anatase
International Journal of Photoenergy 7
10 20 30 40 50 60 70 80 90
Inte
nsity
(au
)
(d)
(c)
(b)
(a)TA T
T A AT
A T
T
T
2120579 (deg)
Figure 5 XRD pattern of TiO2nanotubes incorporated with Ca in
06M Ca(NO3)2solution at different soaking period (a) pure TiO
2
(b) 24 hours (c) 48 hours and (d) 72 hours (A = anatase phase T =titanium phase)
10 20 30 40 50 60 70 80 90
Inte
nsity
(au
)
AT A
TT
AT
TA
TT (a)
(b)
(c)
(d)
2120579 (deg)
Figure 6 XRD pattern of TiO2nanotubes incorporated with Ca in
12M Ca(NO3)2solution at different soaking period (a) pure TiO
2
(b) 24 hours (c) 48 hours and (d) 72 hours (A = anatase phase T =titanium phase)
phase respectively Apparently the incorporation of Ca2+ions into the lattice of TiO
2hindered the crystallization
of TiO2 resulting in the peak intensity of the 101 peak at
2532∘ decrease The decrease in anatase phase is maybe dueto the interruption of Ca atom which diffused into TiO
2
nanotubes and inhibited the formation of the anatase TheXRD pattern of the sample soaked in 12M for 72 hoursexhibits additional peaks 220 and 400 crystal planes at 54∘and 80∘ corresponding to CaO phase This indicates thatcrystalline CaO are formed once the concentration of Cain TiO
2reaches a higher level Next the resultant anodized
CaO-TiO2nanotubes were used in the characterization of
CO2adsorption using TGA analysis The processing steps
involved in TGA analysis are N2gas flow at a rate of 10∘Cmin
from room temperature to 673K and then holding for 30minin CO
2and finally cooling down to 573K byN
2gasThe TGA
curves for 06M of Ca and 12M of Ca are shown in Figures7 and 8 respectively while the CO
2adsorption capacity is
summarized in Table 3 Based on the TGA analysis it couldbe observed that all CaO-TiO
2samples showed their CO
2
adsorption capacity in the range of 33mmolg to 45mmolgA maximum CO
2adsorption capacity of up to 445mmolg
was observed from the CaO-TiO2nanotubes synthesized in
050100150200250300350400450
996998100
1002100410061008
101101210141016
0 20 40 60 80
Wei
ght (
)
Time (min)
24 hours48 hours
72 hoursTemperature
Tem
pera
ture
(∘C)
Figure 7 TGA curve of soaking in 06M of Ca for different periodsof time
050100150200250300350400450
995
100
1005
101
1015
102
1025
0 20 40 60 80
Wei
ght (
)
Time (min)
Tem
pera
ture
(∘C)
24 hours48 hours
72 hoursTemperature
Figure 8 TGA curve of soaking in 12M of Ca for different periodsof time
Table 3 CO2 adsorption capacity of the CaO-TiO2 samples
Concentration of calciumnitrate solution (M)
Soaking period(hours)
CO2 adsorptioncapacity (mmolg)
0624 38948 33272 400
1224 35948 44572 380
12M of calcium nitrate solution for 48 hours Basically theCO2adsorption capacity based CaO-TiO
2sorbents used the
following reaction CaO + CO2rarr CaCO
3 In this case
the sorbent weight is increased significantly when CO2gas is
applied to the TGA system where all the weight added is CO2
adsorbed This reason clearly explains that CO2adsorption
capacity is increased after carbonation process
8 International Journal of Photoenergy
4 Conclusion
The present study demonstrated that one-dimensional CaO-TiO2nanotubes sorbent was successfully formed using oxi-
dation electrochemical anodization and wet impregnationtechniques All of the resultant CaO-TiO
2nanotubes sorbent
exhibited promising CO2adsorption capacity in the range of
33mmolg to 45mmolg It is shown that high active surfacearea of CaO-TiO
2nanotubes sorbent showed good stability
during extended cyclic carbonation-calcination reaction
Conflict of Interests
The author declares that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
This research is supported by High Impact Research Chan-cellory Grant UMC6251HIR228 (J55001-73873) from theUniversity of Malaya In addition authors would like tothank University of Malaya for sponsoring this work underUniversity of Malaya Research Grant (UMRG no RP022-2012D)
References
[1] Q Wang J Luo Z Zhong and A Borgna ldquoCO2capture by
solid adsorbents and their applications current status and newtrendsrdquo Energy amp Environmental Science vol 4 no 1 pp 42ndash552011
[2] D M DrsquoAlessandro B Smit and J R Long ldquoCarbon dioxidecapture prospects for new materialsrdquo Angewandte ChemieInternational Edition vol 49 no 35 pp 6058ndash6082 2010
[3] SWang S Yan XMa and JGong ldquoRecent advances in captureof carbon dioxide using alkali-metal-based oxidesrdquo Energy ampEnvironmental Science vol 4 no 10 pp 3805ndash3819 2011
[4] N H Florin and A T Harris ldquoReactivity of CaO derived fromnano-sized CaCO
3particles through multiple CO
2capture-
and-release cyclesrdquo Chemical Engineering Science vol 64 no2 pp 187ndash191 2009
[5] J Garcıa T Lopez M Alvarez D H Aguilar and P QuintanaldquoSpectroscopic structural and textural properties of CaO andCaO-SiO
2materials synthesized by sol-gel with different acid
catalystsrdquo Journal of Non-Crystalline Solids vol 354 no 2-9 pp729ndash732 2008
[6] V R Choudhary S A R Mulla and B S Uphade ldquoOxidativecoupling of methane over alkaline earth oxides deposited oncommercial support precoated with rare earth oxidesrdquo Fuel vol78 no 4 pp 427ndash437 1999
[7] D Alvarez and J C Abanades ldquoPore-size and shape effects onthe recarbonation performance of calcium oxide submitted torepeated calcinationrecarbonation cyclesrdquo Energy and Fuelsvol 19 no 1 pp 270ndash278 2005
[8] J-R Li Y Ma M C McCarthy et al ldquoCarbon dioxidecapture-related gas adsorption and separation in metal-organicframeworksrdquo Coordination Chemistry Reviews vol 255 no 15-16 pp 1791ndash1823 2011
[9] S Sreekantan L C Wei and Z Lockman ldquoExtremely fastgrowth rate of TiO
2nanotube arrays in electrochemical bath
containing H2O2rdquo Journal of the Electrochemical Society vol
158 no 12 pp C397ndashC402 2011[10] CW Lai and S Sreekantan ldquoDimensional control of TiO
2nan-
otube arrays with H2O2content for high photoelectrochemical
water splitting performancerdquoMicro ampNano Letters vol 7 no 5pp 443ndash447 2012
[11] Y K Lai J Y Huang H F Zhang et al ldquoNitrogen-doped TiO2
nanotube array films with enhanced photocatalytic activityunder various light sourcesrdquo Journal of Hazardous Materialsvol 184 no 1ndash3 pp 855ndash863 2010
[12] S-H Liu C-H Wu H-K Lee and S-B Liu ldquoHighly stableamine-modified mesoporous silica materials for efficient CO
2
capturerdquo Topics in Catalysis vol 53 no 3-4 pp 210ndash217 2010[13] V Zelenak M Badanicova D Halamova et al ldquoAmine-
modified ordered mesoporous silica effect of pore size oncarbon dioxide capturerdquoChemical Engineering Journal vol 144no 2 pp 336ndash342 2008
[14] A R Millward and O M Yaghi ldquoMetal-organic frameworkswith exceptionally high capacity for storage of carbon dioxideat room temperaturerdquo Journal of the American Chemical Societyvol 127 no 51 pp 17998ndash17999 2005
[15] H Deng H Yi X Tang P Ning andQ Yu ldquoAdsorption of CO2
and N2on coal-based activated carbonrdquo Advanced Materials
Research vol 204-210 pp 1250ndash1253 2011[16] Q Li J Yang D Feng et al ldquoFacile synthesis of porous
carbon nitride spheres with hierarchical three-dimensionalmesostructures for CO
2capturerdquo Nano Research vol 3 no 9
pp 632ndash642 2010[17] Y Xia R Mokaya G S Walker and Y Zhu ldquoSuperior CO
2
adsorption capacity on N-doped high-surface-area microp-orous carbons templated from zeoliterdquo Advanced Energy Mate-rials vol 1 pp 678ndash683 2011
[18] Z Zhang M Xu H Wang and Z Li ldquoEnhancement of CO2
adsorption on high surface area activated carbon modified byN2 H2and ammoniardquo Chemical Engineering Journal vol 160
no 2 pp 571ndash577 2010[19] T C Drage J M Blackman C Pevida and C E Snape
ldquoEvaluation of activated carbon adsorbents for CO2capture in
gasificationrdquo Energy and Fuels vol 23 no 5 pp 2790ndash27962009
[20] Y Wang Y Zhou C Liu and L Zhou ldquoComparative studiesof CO
2and CH
2sorption on activated carbon in presence of
waterrdquoColloids and Surfaces A Physicochemical and EngineeringAspects vol 322 no 1ndash3 pp 14ndash18 2008
[21] F Su C Lu and H-S Chen ldquoAdsorption desorption andthermodynamic studies of CO
2with high-amine-loaded mul-
tiwalled carbon nanotubesrdquo Langmuir vol 27 no 13 pp 8090ndash8098 2011
[22] S U Rege and R T Yang ldquoA novel FTIR method for studyingmixed gas adsorption at low concentrations H
2O and CO
2on
NaX zeolite and 120574-aluminardquo Chemical Engineering Science vol56 no 12 pp 3781ndash3796 2001
[23] F Su C Lu S-C Kuo and W Zeng ldquoAdsorption of CO2on
amine-functionalized y-type zeolitesrdquo Energy and Fuels vol 24no 2 pp 1441ndash1448 2010
[24] A Ertan and F Cakicioglu-Ozkan ldquoCO2and N
2adsorption
on the acid (HCl HNO3 H2SO4and H
3PO4) treated zeolitesrdquo
Adsorption vol 11 no 1 pp 151ndash156 2005[25] F Brandani and D M Ruthven ldquoThe effect of water on the
adsorption of CO2and C
3H8on type X zeolitesrdquo Industrial amp
Engineering Chemistry Research vol 43 no 26 pp 8339ndash83442004
International Journal of Photoenergy 9
[26] L Li X Wen X Fu et al ldquoMgOAl2O3sorbent for CO
2
capturerdquo Energy and Fuels vol 24 no 10 pp 5773ndash5780 2010[27] M K RamReddy Z P Xu GQ Lu and J C DDaCosta ldquoLay-
ered double hydroxides for CO2capture structure evolution
and regenerationrdquo Industrial amp Engineering Chemistry Researchvol 45 no 22 pp 7504ndash7509 2006
[28] M Kato S Yoshikawa and K Nakagawa ldquoCarbon dioxideabsorption by lithium orthosilicate in a wide range of temper-ature and carbon dioxide concentrationsrdquo Journal of MaterialsScience Letters vol 21 no 6 pp 485ndash487 2002
[29] J-I Ida and Y S Lin ldquoMechanism of high-temperature CO2
sorption on lithium zirconaterdquo Environmental Science andTechnology vol 37 no 9 pp 1999ndash2004 2003
[30] E Ochoa-Fernandez H K Rusten H A Jakobsen MRoslashnning A Holmen and D Chen ldquoSorption enhanced hydro-gen production by steam methane reforming using Li
2ZrO3
as sorbent sorption kinetics and reactor simulationrdquo CatalysisToday vol 106 no 1-4 pp 41ndash46 2005
[31] E Ochoa-Fernandez M Roslashnning T Grande and D ChenldquoSynthesis and CO
2capture properties of nanocrystalline
lithium zirconaterdquo Chemistry of Materials vol 18 no 25 pp6037ndash6046 2006
[32] J A Satrio B H Shanks and T D Wheelock ldquoDevelopmentof a novel combined catalyst and sorbent for hydrocarbonreformingrdquo Industrial amp Engineering Chemistry Research vol44 no 11 pp 3901ndash3911 2005
[33] Z-S Li N-S Cai and Y-Y Huang ldquoEffect of preparationtemperature on cyclic CO
2capture and multiple carbonation-
calcination cycles for a new Ca-based CO2sorbentrdquo Industrial
amp Engineering Chemistry Research vol 45 no 6 pp 1911ndash19172006
[34] E P Reddy and P G Smirniotis ldquoHigh-temperature sorbentsfor CO
2made of alkali metals doped on CaO supportsrdquo The
Journal of Physical Chemistry B vol 108 no 23 pp 7794ndash78002004
[35] K Kuramoto S Fujimoto A Morita et al ldquoRepetitivecarbonation-calcination reactions of Ca-based sorbents forefficient CO
2sorption at elevated temperatures and pressuresrdquo
Industrial amp Engineering Chemistry Research vol 42 no 5 pp975ndash981 2003
[36] S F Wu T H Beum J I Yang and J N Kim ldquoProperties ofCa-base CO
2sorbent using Ca(OH)
2as precursorrdquo Industrial amp
Engineering Chemistry Research vol 46 no 24 pp 7896ndash78992007
[37] S F Wu Q H Li J N Kim and K B Yi ldquoProperties of a nanoCaOAl
2O3CO2sorbentrdquo Industrial amp Engineering Chemistry
Research vol 47 no 1 pp 180ndash184 2008
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
4 International Journal of Photoenergy
214
171
128
85
42
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(a)
247
198
148
99
49
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(b)
117
94
70
47
23
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(c)
Figure 2 EDX spectra of nanotubes subjected to wet impregnation of 06M calcium nitrate solution for (a) 24 hours (b) 48 hours and(c) 72 hours (all EDX spectrums are noneditable format based on our FESEM-EDX system)
and a certain loss in the porosity When pores smaller than acritical value (eg 200 nm) are filled the reaction gets muchslower [8] Therefore great efforts have to be made in orderto further improve the cyclic stability of CaO-based sorbents
One of the most promising solutions to improve thecyclic stability of CaO is controlling their architecture intoone-dimensional nanomaterials The main reason might beattributed to the fast reaction (chemical reaction) and theslow reaction (diffusion controlled) could be achieved duringCO2adsorption In this case the diffusion of CO
2into
the particle interior to react with Ca dopants could beprevented and the whole CO
2adsorption process could then
be diffusion-controlled [2 3] Theoretically the small parti-cles size of sorbent (eg 30ndash50 nm) would perform bettercarbonation-calcination reaction which allowed carbonationto take place at the rapid reaction-controlled regime Anotherpromising solution to improve cyclic stability is to incorpo-rate high stability metal oxide (titanium dioxide) into CaOparticlesTheprevention ofCaOoxidation during calcinationstage could be expected Therefore detail investigation onone-dimensional CaO-TiO
2nanotubes for effective CO
2
adsorption will be discussed
2 Experimental Procedure
One-dimensional TiO2nanotube arrays were synthesized
using a rapid-anodic oxidation electrochemical anodizationtechnique A high purity of Ti foil (996 Strem Chemical
USA) with a thickness of 127 120583m was selected as substrateto grow TiO
2nanotubes This process was conducted in a
bath with electrolytes composed of ethylene glycol (C2H6O2
gt995 Merck USA) 5 wt ammonium fluoride (NH4F
98 Merck USA) and 5wt hydrogen peroxide (H2O2
30 H2O2and 70 H
2O J T Baker USA) for 60 minutes
at 60V This experimental condition was selected because itfavors the formation of well-aligned TiO
2nanotube arrays
[9 10] After the anodization process as-anodized sampleswere cleaned using distilled water and dried under a nitrogenstream CaO-TiO
2nanotubes were then prepared through
wet impregnation technique using calcium nitrate tetrahy-drate (Ca(NO
3)2sdot4H2O Merck USA) as the precursor This
was an ex situ approach that was used to incorporate Ca2+ions into TiO
2nanotubes Two different concentrations
of calcium nitrate tetrahydrate solution (06 12M) wereprepared at different reaction times (24 48 72 hours) in awater bath of 80∘C Subsequently the samples were thermal-annealed at 673K in an argon atmosphere for 4 h in order toproduce crystalline TiO
2nanotubes
The surface morphologies of the synthesized sampleswere observed through field emission scanning electronmicroscopy (FESEM) using a Zeiss SUPRA 35VP whichis operated at a working distance of 1mm and 5 kV Theenergy dispersive X-ray spectroscopy (EDX) was appliedto elemental analysis of the CaO-TiO
2nanotubes sorbents
which is equipped in the FESEM The structural variationsand phase determination for CaO-TiO
2nanotubes sorbents
International Journal of Photoenergy 5
200nm
(a)
200nm
(b)
200nm
(c)
Figure 3 FESEM top view image of nanotubes subjected to wet impregnation of 12M calcium nitrate solution for (a) 24 hours (b) 48 hoursand (c) 72 hours and subsequent annealing at 673K in Ar gas for 4 hours
were determined using a Philips PW 1729 X-ray diffraction(XRD) which operated at 45 kV and 40mV patterns Thethermogravimetric analysis (TGA) was used to investigatethe CO
2adsorption for CaO-TiO
2nanotubes sorbents (STA
6000 Perkin Elmer USA)The steps included are N2gas flow
at a rate of 10∘Cmin from room temperature to 673K andthen holding for 30min in CO
2and finally cooling down to
573K byN2gas In the present study carbonation-calcination
reaction is set to be 673K because nanotubular structure canbe collapsed at high temperature (above 773K) [11]
3 Results and Discussion
The surface morphologies of CaO-TiO2nanotubes synthe-
sized in 06Mcalciumnitrate solution for 24 48 and 72 hourswere subsequently observed via FESEM as presented in Fig-ures 1(a) to 1(c) respectively As shown in the FESEM imagesthe opening of the nanotubular structure showed aggregationof CaO species on wall surface of TiO
2nanotubes The
wall thickness of the nanotubes dramatically increased to
75 nm which resulted in a narrow pore entrance for 24 hoursreaction time (Figure 1(a)) Meanwhile as the reaction timeincreased to 48 hours the wall thickness of the nanotubesincreased from about 75 nm to 100 nm (Figure 1(b)) Withfurther increase of the reaction time to 72 hours it wasfound that the nanotubes were covered with excess CaOspecies and clogged the pore entrance (Figure 1(c)) A roughirregular and corrugated surface was formed Based on theFESEM images it could be concluded that the appearanceof TiO
2nanotubes was dependent on the reaction time in
calcium nitrate solution A narrow or blocked pore entranceof nanotubes was formed as increasing soaking period in thesolution Next the average atomic percentage (at) of theelements within CaO-TiO
2nanotubes was determined using
EDX analysis The numerical EDX analyses of the samplesare listed in Table 2 As determined through EDX analysisthe average Ca contents of the nanotubes for 24 48 and 72hours were 101 at 367 at and 459 at respectively Theintensity of the Ca peak (369 keV) increased with increasingreaction time in calcium nitrate solution as presented in
6 International Journal of Photoenergy
274
219
164
109
54
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(a)
252
202
151
101
50
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(b)
295
236
177
118
59
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(c)
Figure 4 EDX spectra of nanotubes subjected to wet impregnation of 12M calcium nitrate solution for (a) 24 hours (b) 48 hours and(c) 72 hours (all EDX spectrums are noneditable format based on our FESEM-EDX system)
Figures 2(a) to 2(c) Another set of experiments was con-ducted to form CaO-TiO
2nanotubes in 12M calcium nitrate
solution for 24 48 and 72 hours All morphologies of thesamples showed similar appearance of CaO-TiO
2nanotubes
synthesized in 06M calcium nitrate solution The irregularCaO layer covered all of the TiO
2nanotubular structure
and nanoporous structure arranged in a nonordered mannerwhich could be observed in Figures 3(a) to 3(c)The chemicalstoichiometry of the resultant samples was determined viaEDX analysis as shown in Figures 4(a) to 4(c) A high Cacontent of 978 atwas determined from those synthesized in12M calciumnitrate solution for 72 hours indicating that theincorporation of the CaO became prominent with increasingthe concentration of calcium nitrate solution Based on theFESEM images and EDX analysis the small Ca2+ ions couldbe diffused into TiO
2nanotubes in the presence of lattice
defects especially nearby to the wall of nanotubes In thiscase the diffusion rate of Ca2+ ions increased significantlywhen increasing the reaction time and concentration of pre-cursor However the content of small Ca2+ ions that diffusedinto the TiO
2lattice could reach a saturation condition and
start to accumulate on the surface of nanotubes The numberof nucleation sites for Ca2+ ions loaded on the wall surface ofthe nanotubes increasedwith longer reaction time and higherconcentration of precursor which produced nanotubes withthicker walls The diffusion of the Ca2+ ions formed CandashObonding withOndashTindashO bonding thus charge neutrality couldbe achieved
Table 2 EDX result of CaO-TiO2 with different soaking time in06M and 12M calcium nitrate solution
Concentration ofcalcium nitratesolution (M)
Element (at)reactiontime (h) Ti O Ca
0624 4607 5292 010148 3888 5745 036772 4230 5311 0459
1224 3644 6066 029048 3264 6064 066472 2883 6110 0978
In the present study XRD analysis was used to determinethe crystallographic structure and the changes in the phasestructure of the CaO-TiO
2nanotubes synthesized in different
reaction times and concentrations of precursor are presentedin Figures 5 and 6 Numerous studies reported that heattreatment at about 400∘C could transform the amorphousstructure of TiO
2into the crystalline anatase phase The
obvious diffraction peaks from the XRD pattern attributedto the anatase phase (JCPDS no 21-1272) were detected fromthe XRD patterns (Figure 5(a)) The diffraction peaks areallocated at 2532∘ 3784∘ 3842∘ 4802∘ 5387∘ 5509∘ 6293∘7065∘ and 7623∘ which correspond to 101 004 112 200105 211 204 220 and 301 crystal planes for the anatase
International Journal of Photoenergy 7
10 20 30 40 50 60 70 80 90
Inte
nsity
(au
)
(d)
(c)
(b)
(a)TA T
T A AT
A T
T
T
2120579 (deg)
Figure 5 XRD pattern of TiO2nanotubes incorporated with Ca in
06M Ca(NO3)2solution at different soaking period (a) pure TiO
2
(b) 24 hours (c) 48 hours and (d) 72 hours (A = anatase phase T =titanium phase)
10 20 30 40 50 60 70 80 90
Inte
nsity
(au
)
AT A
TT
AT
TA
TT (a)
(b)
(c)
(d)
2120579 (deg)
Figure 6 XRD pattern of TiO2nanotubes incorporated with Ca in
12M Ca(NO3)2solution at different soaking period (a) pure TiO
2
(b) 24 hours (c) 48 hours and (d) 72 hours (A = anatase phase T =titanium phase)
phase respectively Apparently the incorporation of Ca2+ions into the lattice of TiO
2hindered the crystallization
of TiO2 resulting in the peak intensity of the 101 peak at
2532∘ decrease The decrease in anatase phase is maybe dueto the interruption of Ca atom which diffused into TiO
2
nanotubes and inhibited the formation of the anatase TheXRD pattern of the sample soaked in 12M for 72 hoursexhibits additional peaks 220 and 400 crystal planes at 54∘and 80∘ corresponding to CaO phase This indicates thatcrystalline CaO are formed once the concentration of Cain TiO
2reaches a higher level Next the resultant anodized
CaO-TiO2nanotubes were used in the characterization of
CO2adsorption using TGA analysis The processing steps
involved in TGA analysis are N2gas flow at a rate of 10∘Cmin
from room temperature to 673K and then holding for 30minin CO
2and finally cooling down to 573K byN
2gasThe TGA
curves for 06M of Ca and 12M of Ca are shown in Figures7 and 8 respectively while the CO
2adsorption capacity is
summarized in Table 3 Based on the TGA analysis it couldbe observed that all CaO-TiO
2samples showed their CO
2
adsorption capacity in the range of 33mmolg to 45mmolgA maximum CO
2adsorption capacity of up to 445mmolg
was observed from the CaO-TiO2nanotubes synthesized in
050100150200250300350400450
996998100
1002100410061008
101101210141016
0 20 40 60 80
Wei
ght (
)
Time (min)
24 hours48 hours
72 hoursTemperature
Tem
pera
ture
(∘C)
Figure 7 TGA curve of soaking in 06M of Ca for different periodsof time
050100150200250300350400450
995
100
1005
101
1015
102
1025
0 20 40 60 80
Wei
ght (
)
Time (min)
Tem
pera
ture
(∘C)
24 hours48 hours
72 hoursTemperature
Figure 8 TGA curve of soaking in 12M of Ca for different periodsof time
Table 3 CO2 adsorption capacity of the CaO-TiO2 samples
Concentration of calciumnitrate solution (M)
Soaking period(hours)
CO2 adsorptioncapacity (mmolg)
0624 38948 33272 400
1224 35948 44572 380
12M of calcium nitrate solution for 48 hours Basically theCO2adsorption capacity based CaO-TiO
2sorbents used the
following reaction CaO + CO2rarr CaCO
3 In this case
the sorbent weight is increased significantly when CO2gas is
applied to the TGA system where all the weight added is CO2
adsorbed This reason clearly explains that CO2adsorption
capacity is increased after carbonation process
8 International Journal of Photoenergy
4 Conclusion
The present study demonstrated that one-dimensional CaO-TiO2nanotubes sorbent was successfully formed using oxi-
dation electrochemical anodization and wet impregnationtechniques All of the resultant CaO-TiO
2nanotubes sorbent
exhibited promising CO2adsorption capacity in the range of
33mmolg to 45mmolg It is shown that high active surfacearea of CaO-TiO
2nanotubes sorbent showed good stability
during extended cyclic carbonation-calcination reaction
Conflict of Interests
The author declares that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
This research is supported by High Impact Research Chan-cellory Grant UMC6251HIR228 (J55001-73873) from theUniversity of Malaya In addition authors would like tothank University of Malaya for sponsoring this work underUniversity of Malaya Research Grant (UMRG no RP022-2012D)
References
[1] Q Wang J Luo Z Zhong and A Borgna ldquoCO2capture by
solid adsorbents and their applications current status and newtrendsrdquo Energy amp Environmental Science vol 4 no 1 pp 42ndash552011
[2] D M DrsquoAlessandro B Smit and J R Long ldquoCarbon dioxidecapture prospects for new materialsrdquo Angewandte ChemieInternational Edition vol 49 no 35 pp 6058ndash6082 2010
[3] SWang S Yan XMa and JGong ldquoRecent advances in captureof carbon dioxide using alkali-metal-based oxidesrdquo Energy ampEnvironmental Science vol 4 no 10 pp 3805ndash3819 2011
[4] N H Florin and A T Harris ldquoReactivity of CaO derived fromnano-sized CaCO
3particles through multiple CO
2capture-
and-release cyclesrdquo Chemical Engineering Science vol 64 no2 pp 187ndash191 2009
[5] J Garcıa T Lopez M Alvarez D H Aguilar and P QuintanaldquoSpectroscopic structural and textural properties of CaO andCaO-SiO
2materials synthesized by sol-gel with different acid
catalystsrdquo Journal of Non-Crystalline Solids vol 354 no 2-9 pp729ndash732 2008
[6] V R Choudhary S A R Mulla and B S Uphade ldquoOxidativecoupling of methane over alkaline earth oxides deposited oncommercial support precoated with rare earth oxidesrdquo Fuel vol78 no 4 pp 427ndash437 1999
[7] D Alvarez and J C Abanades ldquoPore-size and shape effects onthe recarbonation performance of calcium oxide submitted torepeated calcinationrecarbonation cyclesrdquo Energy and Fuelsvol 19 no 1 pp 270ndash278 2005
[8] J-R Li Y Ma M C McCarthy et al ldquoCarbon dioxidecapture-related gas adsorption and separation in metal-organicframeworksrdquo Coordination Chemistry Reviews vol 255 no 15-16 pp 1791ndash1823 2011
[9] S Sreekantan L C Wei and Z Lockman ldquoExtremely fastgrowth rate of TiO
2nanotube arrays in electrochemical bath
containing H2O2rdquo Journal of the Electrochemical Society vol
158 no 12 pp C397ndashC402 2011[10] CW Lai and S Sreekantan ldquoDimensional control of TiO
2nan-
otube arrays with H2O2content for high photoelectrochemical
water splitting performancerdquoMicro ampNano Letters vol 7 no 5pp 443ndash447 2012
[11] Y K Lai J Y Huang H F Zhang et al ldquoNitrogen-doped TiO2
nanotube array films with enhanced photocatalytic activityunder various light sourcesrdquo Journal of Hazardous Materialsvol 184 no 1ndash3 pp 855ndash863 2010
[12] S-H Liu C-H Wu H-K Lee and S-B Liu ldquoHighly stableamine-modified mesoporous silica materials for efficient CO
2
capturerdquo Topics in Catalysis vol 53 no 3-4 pp 210ndash217 2010[13] V Zelenak M Badanicova D Halamova et al ldquoAmine-
modified ordered mesoporous silica effect of pore size oncarbon dioxide capturerdquoChemical Engineering Journal vol 144no 2 pp 336ndash342 2008
[14] A R Millward and O M Yaghi ldquoMetal-organic frameworkswith exceptionally high capacity for storage of carbon dioxideat room temperaturerdquo Journal of the American Chemical Societyvol 127 no 51 pp 17998ndash17999 2005
[15] H Deng H Yi X Tang P Ning andQ Yu ldquoAdsorption of CO2
and N2on coal-based activated carbonrdquo Advanced Materials
Research vol 204-210 pp 1250ndash1253 2011[16] Q Li J Yang D Feng et al ldquoFacile synthesis of porous
carbon nitride spheres with hierarchical three-dimensionalmesostructures for CO
2capturerdquo Nano Research vol 3 no 9
pp 632ndash642 2010[17] Y Xia R Mokaya G S Walker and Y Zhu ldquoSuperior CO
2
adsorption capacity on N-doped high-surface-area microp-orous carbons templated from zeoliterdquo Advanced Energy Mate-rials vol 1 pp 678ndash683 2011
[18] Z Zhang M Xu H Wang and Z Li ldquoEnhancement of CO2
adsorption on high surface area activated carbon modified byN2 H2and ammoniardquo Chemical Engineering Journal vol 160
no 2 pp 571ndash577 2010[19] T C Drage J M Blackman C Pevida and C E Snape
ldquoEvaluation of activated carbon adsorbents for CO2capture in
gasificationrdquo Energy and Fuels vol 23 no 5 pp 2790ndash27962009
[20] Y Wang Y Zhou C Liu and L Zhou ldquoComparative studiesof CO
2and CH
2sorption on activated carbon in presence of
waterrdquoColloids and Surfaces A Physicochemical and EngineeringAspects vol 322 no 1ndash3 pp 14ndash18 2008
[21] F Su C Lu and H-S Chen ldquoAdsorption desorption andthermodynamic studies of CO
2with high-amine-loaded mul-
tiwalled carbon nanotubesrdquo Langmuir vol 27 no 13 pp 8090ndash8098 2011
[22] S U Rege and R T Yang ldquoA novel FTIR method for studyingmixed gas adsorption at low concentrations H
2O and CO
2on
NaX zeolite and 120574-aluminardquo Chemical Engineering Science vol56 no 12 pp 3781ndash3796 2001
[23] F Su C Lu S-C Kuo and W Zeng ldquoAdsorption of CO2on
amine-functionalized y-type zeolitesrdquo Energy and Fuels vol 24no 2 pp 1441ndash1448 2010
[24] A Ertan and F Cakicioglu-Ozkan ldquoCO2and N
2adsorption
on the acid (HCl HNO3 H2SO4and H
3PO4) treated zeolitesrdquo
Adsorption vol 11 no 1 pp 151ndash156 2005[25] F Brandani and D M Ruthven ldquoThe effect of water on the
adsorption of CO2and C
3H8on type X zeolitesrdquo Industrial amp
Engineering Chemistry Research vol 43 no 26 pp 8339ndash83442004
International Journal of Photoenergy 9
[26] L Li X Wen X Fu et al ldquoMgOAl2O3sorbent for CO
2
capturerdquo Energy and Fuels vol 24 no 10 pp 5773ndash5780 2010[27] M K RamReddy Z P Xu GQ Lu and J C DDaCosta ldquoLay-
ered double hydroxides for CO2capture structure evolution
and regenerationrdquo Industrial amp Engineering Chemistry Researchvol 45 no 22 pp 7504ndash7509 2006
[28] M Kato S Yoshikawa and K Nakagawa ldquoCarbon dioxideabsorption by lithium orthosilicate in a wide range of temper-ature and carbon dioxide concentrationsrdquo Journal of MaterialsScience Letters vol 21 no 6 pp 485ndash487 2002
[29] J-I Ida and Y S Lin ldquoMechanism of high-temperature CO2
sorption on lithium zirconaterdquo Environmental Science andTechnology vol 37 no 9 pp 1999ndash2004 2003
[30] E Ochoa-Fernandez H K Rusten H A Jakobsen MRoslashnning A Holmen and D Chen ldquoSorption enhanced hydro-gen production by steam methane reforming using Li
2ZrO3
as sorbent sorption kinetics and reactor simulationrdquo CatalysisToday vol 106 no 1-4 pp 41ndash46 2005
[31] E Ochoa-Fernandez M Roslashnning T Grande and D ChenldquoSynthesis and CO
2capture properties of nanocrystalline
lithium zirconaterdquo Chemistry of Materials vol 18 no 25 pp6037ndash6046 2006
[32] J A Satrio B H Shanks and T D Wheelock ldquoDevelopmentof a novel combined catalyst and sorbent for hydrocarbonreformingrdquo Industrial amp Engineering Chemistry Research vol44 no 11 pp 3901ndash3911 2005
[33] Z-S Li N-S Cai and Y-Y Huang ldquoEffect of preparationtemperature on cyclic CO
2capture and multiple carbonation-
calcination cycles for a new Ca-based CO2sorbentrdquo Industrial
amp Engineering Chemistry Research vol 45 no 6 pp 1911ndash19172006
[34] E P Reddy and P G Smirniotis ldquoHigh-temperature sorbentsfor CO
2made of alkali metals doped on CaO supportsrdquo The
Journal of Physical Chemistry B vol 108 no 23 pp 7794ndash78002004
[35] K Kuramoto S Fujimoto A Morita et al ldquoRepetitivecarbonation-calcination reactions of Ca-based sorbents forefficient CO
2sorption at elevated temperatures and pressuresrdquo
Industrial amp Engineering Chemistry Research vol 42 no 5 pp975ndash981 2003
[36] S F Wu T H Beum J I Yang and J N Kim ldquoProperties ofCa-base CO
2sorbent using Ca(OH)
2as precursorrdquo Industrial amp
Engineering Chemistry Research vol 46 no 24 pp 7896ndash78992007
[37] S F Wu Q H Li J N Kim and K B Yi ldquoProperties of a nanoCaOAl
2O3CO2sorbentrdquo Industrial amp Engineering Chemistry
Research vol 47 no 1 pp 180ndash184 2008
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
International Journal of Photoenergy 5
200nm
(a)
200nm
(b)
200nm
(c)
Figure 3 FESEM top view image of nanotubes subjected to wet impregnation of 12M calcium nitrate solution for (a) 24 hours (b) 48 hoursand (c) 72 hours and subsequent annealing at 673K in Ar gas for 4 hours
were determined using a Philips PW 1729 X-ray diffraction(XRD) which operated at 45 kV and 40mV patterns Thethermogravimetric analysis (TGA) was used to investigatethe CO
2adsorption for CaO-TiO
2nanotubes sorbents (STA
6000 Perkin Elmer USA)The steps included are N2gas flow
at a rate of 10∘Cmin from room temperature to 673K andthen holding for 30min in CO
2and finally cooling down to
573K byN2gas In the present study carbonation-calcination
reaction is set to be 673K because nanotubular structure canbe collapsed at high temperature (above 773K) [11]
3 Results and Discussion
The surface morphologies of CaO-TiO2nanotubes synthe-
sized in 06Mcalciumnitrate solution for 24 48 and 72 hourswere subsequently observed via FESEM as presented in Fig-ures 1(a) to 1(c) respectively As shown in the FESEM imagesthe opening of the nanotubular structure showed aggregationof CaO species on wall surface of TiO
2nanotubes The
wall thickness of the nanotubes dramatically increased to
75 nm which resulted in a narrow pore entrance for 24 hoursreaction time (Figure 1(a)) Meanwhile as the reaction timeincreased to 48 hours the wall thickness of the nanotubesincreased from about 75 nm to 100 nm (Figure 1(b)) Withfurther increase of the reaction time to 72 hours it wasfound that the nanotubes were covered with excess CaOspecies and clogged the pore entrance (Figure 1(c)) A roughirregular and corrugated surface was formed Based on theFESEM images it could be concluded that the appearanceof TiO
2nanotubes was dependent on the reaction time in
calcium nitrate solution A narrow or blocked pore entranceof nanotubes was formed as increasing soaking period in thesolution Next the average atomic percentage (at) of theelements within CaO-TiO
2nanotubes was determined using
EDX analysis The numerical EDX analyses of the samplesare listed in Table 2 As determined through EDX analysisthe average Ca contents of the nanotubes for 24 48 and 72hours were 101 at 367 at and 459 at respectively Theintensity of the Ca peak (369 keV) increased with increasingreaction time in calcium nitrate solution as presented in
6 International Journal of Photoenergy
274
219
164
109
54
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(a)
252
202
151
101
50
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(b)
295
236
177
118
59
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(c)
Figure 4 EDX spectra of nanotubes subjected to wet impregnation of 12M calcium nitrate solution for (a) 24 hours (b) 48 hours and(c) 72 hours (all EDX spectrums are noneditable format based on our FESEM-EDX system)
Figures 2(a) to 2(c) Another set of experiments was con-ducted to form CaO-TiO
2nanotubes in 12M calcium nitrate
solution for 24 48 and 72 hours All morphologies of thesamples showed similar appearance of CaO-TiO
2nanotubes
synthesized in 06M calcium nitrate solution The irregularCaO layer covered all of the TiO
2nanotubular structure
and nanoporous structure arranged in a nonordered mannerwhich could be observed in Figures 3(a) to 3(c)The chemicalstoichiometry of the resultant samples was determined viaEDX analysis as shown in Figures 4(a) to 4(c) A high Cacontent of 978 atwas determined from those synthesized in12M calciumnitrate solution for 72 hours indicating that theincorporation of the CaO became prominent with increasingthe concentration of calcium nitrate solution Based on theFESEM images and EDX analysis the small Ca2+ ions couldbe diffused into TiO
2nanotubes in the presence of lattice
defects especially nearby to the wall of nanotubes In thiscase the diffusion rate of Ca2+ ions increased significantlywhen increasing the reaction time and concentration of pre-cursor However the content of small Ca2+ ions that diffusedinto the TiO
2lattice could reach a saturation condition and
start to accumulate on the surface of nanotubes The numberof nucleation sites for Ca2+ ions loaded on the wall surface ofthe nanotubes increasedwith longer reaction time and higherconcentration of precursor which produced nanotubes withthicker walls The diffusion of the Ca2+ ions formed CandashObonding withOndashTindashO bonding thus charge neutrality couldbe achieved
Table 2 EDX result of CaO-TiO2 with different soaking time in06M and 12M calcium nitrate solution
Concentration ofcalcium nitratesolution (M)
Element (at)reactiontime (h) Ti O Ca
0624 4607 5292 010148 3888 5745 036772 4230 5311 0459
1224 3644 6066 029048 3264 6064 066472 2883 6110 0978
In the present study XRD analysis was used to determinethe crystallographic structure and the changes in the phasestructure of the CaO-TiO
2nanotubes synthesized in different
reaction times and concentrations of precursor are presentedin Figures 5 and 6 Numerous studies reported that heattreatment at about 400∘C could transform the amorphousstructure of TiO
2into the crystalline anatase phase The
obvious diffraction peaks from the XRD pattern attributedto the anatase phase (JCPDS no 21-1272) were detected fromthe XRD patterns (Figure 5(a)) The diffraction peaks areallocated at 2532∘ 3784∘ 3842∘ 4802∘ 5387∘ 5509∘ 6293∘7065∘ and 7623∘ which correspond to 101 004 112 200105 211 204 220 and 301 crystal planes for the anatase
International Journal of Photoenergy 7
10 20 30 40 50 60 70 80 90
Inte
nsity
(au
)
(d)
(c)
(b)
(a)TA T
T A AT
A T
T
T
2120579 (deg)
Figure 5 XRD pattern of TiO2nanotubes incorporated with Ca in
06M Ca(NO3)2solution at different soaking period (a) pure TiO
2
(b) 24 hours (c) 48 hours and (d) 72 hours (A = anatase phase T =titanium phase)
10 20 30 40 50 60 70 80 90
Inte
nsity
(au
)
AT A
TT
AT
TA
TT (a)
(b)
(c)
(d)
2120579 (deg)
Figure 6 XRD pattern of TiO2nanotubes incorporated with Ca in
12M Ca(NO3)2solution at different soaking period (a) pure TiO
2
(b) 24 hours (c) 48 hours and (d) 72 hours (A = anatase phase T =titanium phase)
phase respectively Apparently the incorporation of Ca2+ions into the lattice of TiO
2hindered the crystallization
of TiO2 resulting in the peak intensity of the 101 peak at
2532∘ decrease The decrease in anatase phase is maybe dueto the interruption of Ca atom which diffused into TiO
2
nanotubes and inhibited the formation of the anatase TheXRD pattern of the sample soaked in 12M for 72 hoursexhibits additional peaks 220 and 400 crystal planes at 54∘and 80∘ corresponding to CaO phase This indicates thatcrystalline CaO are formed once the concentration of Cain TiO
2reaches a higher level Next the resultant anodized
CaO-TiO2nanotubes were used in the characterization of
CO2adsorption using TGA analysis The processing steps
involved in TGA analysis are N2gas flow at a rate of 10∘Cmin
from room temperature to 673K and then holding for 30minin CO
2and finally cooling down to 573K byN
2gasThe TGA
curves for 06M of Ca and 12M of Ca are shown in Figures7 and 8 respectively while the CO
2adsorption capacity is
summarized in Table 3 Based on the TGA analysis it couldbe observed that all CaO-TiO
2samples showed their CO
2
adsorption capacity in the range of 33mmolg to 45mmolgA maximum CO
2adsorption capacity of up to 445mmolg
was observed from the CaO-TiO2nanotubes synthesized in
050100150200250300350400450
996998100
1002100410061008
101101210141016
0 20 40 60 80
Wei
ght (
)
Time (min)
24 hours48 hours
72 hoursTemperature
Tem
pera
ture
(∘C)
Figure 7 TGA curve of soaking in 06M of Ca for different periodsof time
050100150200250300350400450
995
100
1005
101
1015
102
1025
0 20 40 60 80
Wei
ght (
)
Time (min)
Tem
pera
ture
(∘C)
24 hours48 hours
72 hoursTemperature
Figure 8 TGA curve of soaking in 12M of Ca for different periodsof time
Table 3 CO2 adsorption capacity of the CaO-TiO2 samples
Concentration of calciumnitrate solution (M)
Soaking period(hours)
CO2 adsorptioncapacity (mmolg)
0624 38948 33272 400
1224 35948 44572 380
12M of calcium nitrate solution for 48 hours Basically theCO2adsorption capacity based CaO-TiO
2sorbents used the
following reaction CaO + CO2rarr CaCO
3 In this case
the sorbent weight is increased significantly when CO2gas is
applied to the TGA system where all the weight added is CO2
adsorbed This reason clearly explains that CO2adsorption
capacity is increased after carbonation process
8 International Journal of Photoenergy
4 Conclusion
The present study demonstrated that one-dimensional CaO-TiO2nanotubes sorbent was successfully formed using oxi-
dation electrochemical anodization and wet impregnationtechniques All of the resultant CaO-TiO
2nanotubes sorbent
exhibited promising CO2adsorption capacity in the range of
33mmolg to 45mmolg It is shown that high active surfacearea of CaO-TiO
2nanotubes sorbent showed good stability
during extended cyclic carbonation-calcination reaction
Conflict of Interests
The author declares that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
This research is supported by High Impact Research Chan-cellory Grant UMC6251HIR228 (J55001-73873) from theUniversity of Malaya In addition authors would like tothank University of Malaya for sponsoring this work underUniversity of Malaya Research Grant (UMRG no RP022-2012D)
References
[1] Q Wang J Luo Z Zhong and A Borgna ldquoCO2capture by
solid adsorbents and their applications current status and newtrendsrdquo Energy amp Environmental Science vol 4 no 1 pp 42ndash552011
[2] D M DrsquoAlessandro B Smit and J R Long ldquoCarbon dioxidecapture prospects for new materialsrdquo Angewandte ChemieInternational Edition vol 49 no 35 pp 6058ndash6082 2010
[3] SWang S Yan XMa and JGong ldquoRecent advances in captureof carbon dioxide using alkali-metal-based oxidesrdquo Energy ampEnvironmental Science vol 4 no 10 pp 3805ndash3819 2011
[4] N H Florin and A T Harris ldquoReactivity of CaO derived fromnano-sized CaCO
3particles through multiple CO
2capture-
and-release cyclesrdquo Chemical Engineering Science vol 64 no2 pp 187ndash191 2009
[5] J Garcıa T Lopez M Alvarez D H Aguilar and P QuintanaldquoSpectroscopic structural and textural properties of CaO andCaO-SiO
2materials synthesized by sol-gel with different acid
catalystsrdquo Journal of Non-Crystalline Solids vol 354 no 2-9 pp729ndash732 2008
[6] V R Choudhary S A R Mulla and B S Uphade ldquoOxidativecoupling of methane over alkaline earth oxides deposited oncommercial support precoated with rare earth oxidesrdquo Fuel vol78 no 4 pp 427ndash437 1999
[7] D Alvarez and J C Abanades ldquoPore-size and shape effects onthe recarbonation performance of calcium oxide submitted torepeated calcinationrecarbonation cyclesrdquo Energy and Fuelsvol 19 no 1 pp 270ndash278 2005
[8] J-R Li Y Ma M C McCarthy et al ldquoCarbon dioxidecapture-related gas adsorption and separation in metal-organicframeworksrdquo Coordination Chemistry Reviews vol 255 no 15-16 pp 1791ndash1823 2011
[9] S Sreekantan L C Wei and Z Lockman ldquoExtremely fastgrowth rate of TiO
2nanotube arrays in electrochemical bath
containing H2O2rdquo Journal of the Electrochemical Society vol
158 no 12 pp C397ndashC402 2011[10] CW Lai and S Sreekantan ldquoDimensional control of TiO
2nan-
otube arrays with H2O2content for high photoelectrochemical
water splitting performancerdquoMicro ampNano Letters vol 7 no 5pp 443ndash447 2012
[11] Y K Lai J Y Huang H F Zhang et al ldquoNitrogen-doped TiO2
nanotube array films with enhanced photocatalytic activityunder various light sourcesrdquo Journal of Hazardous Materialsvol 184 no 1ndash3 pp 855ndash863 2010
[12] S-H Liu C-H Wu H-K Lee and S-B Liu ldquoHighly stableamine-modified mesoporous silica materials for efficient CO
2
capturerdquo Topics in Catalysis vol 53 no 3-4 pp 210ndash217 2010[13] V Zelenak M Badanicova D Halamova et al ldquoAmine-
modified ordered mesoporous silica effect of pore size oncarbon dioxide capturerdquoChemical Engineering Journal vol 144no 2 pp 336ndash342 2008
[14] A R Millward and O M Yaghi ldquoMetal-organic frameworkswith exceptionally high capacity for storage of carbon dioxideat room temperaturerdquo Journal of the American Chemical Societyvol 127 no 51 pp 17998ndash17999 2005
[15] H Deng H Yi X Tang P Ning andQ Yu ldquoAdsorption of CO2
and N2on coal-based activated carbonrdquo Advanced Materials
Research vol 204-210 pp 1250ndash1253 2011[16] Q Li J Yang D Feng et al ldquoFacile synthesis of porous
carbon nitride spheres with hierarchical three-dimensionalmesostructures for CO
2capturerdquo Nano Research vol 3 no 9
pp 632ndash642 2010[17] Y Xia R Mokaya G S Walker and Y Zhu ldquoSuperior CO
2
adsorption capacity on N-doped high-surface-area microp-orous carbons templated from zeoliterdquo Advanced Energy Mate-rials vol 1 pp 678ndash683 2011
[18] Z Zhang M Xu H Wang and Z Li ldquoEnhancement of CO2
adsorption on high surface area activated carbon modified byN2 H2and ammoniardquo Chemical Engineering Journal vol 160
no 2 pp 571ndash577 2010[19] T C Drage J M Blackman C Pevida and C E Snape
ldquoEvaluation of activated carbon adsorbents for CO2capture in
gasificationrdquo Energy and Fuels vol 23 no 5 pp 2790ndash27962009
[20] Y Wang Y Zhou C Liu and L Zhou ldquoComparative studiesof CO
2and CH
2sorption on activated carbon in presence of
waterrdquoColloids and Surfaces A Physicochemical and EngineeringAspects vol 322 no 1ndash3 pp 14ndash18 2008
[21] F Su C Lu and H-S Chen ldquoAdsorption desorption andthermodynamic studies of CO
2with high-amine-loaded mul-
tiwalled carbon nanotubesrdquo Langmuir vol 27 no 13 pp 8090ndash8098 2011
[22] S U Rege and R T Yang ldquoA novel FTIR method for studyingmixed gas adsorption at low concentrations H
2O and CO
2on
NaX zeolite and 120574-aluminardquo Chemical Engineering Science vol56 no 12 pp 3781ndash3796 2001
[23] F Su C Lu S-C Kuo and W Zeng ldquoAdsorption of CO2on
amine-functionalized y-type zeolitesrdquo Energy and Fuels vol 24no 2 pp 1441ndash1448 2010
[24] A Ertan and F Cakicioglu-Ozkan ldquoCO2and N
2adsorption
on the acid (HCl HNO3 H2SO4and H
3PO4) treated zeolitesrdquo
Adsorption vol 11 no 1 pp 151ndash156 2005[25] F Brandani and D M Ruthven ldquoThe effect of water on the
adsorption of CO2and C
3H8on type X zeolitesrdquo Industrial amp
Engineering Chemistry Research vol 43 no 26 pp 8339ndash83442004
International Journal of Photoenergy 9
[26] L Li X Wen X Fu et al ldquoMgOAl2O3sorbent for CO
2
capturerdquo Energy and Fuels vol 24 no 10 pp 5773ndash5780 2010[27] M K RamReddy Z P Xu GQ Lu and J C DDaCosta ldquoLay-
ered double hydroxides for CO2capture structure evolution
and regenerationrdquo Industrial amp Engineering Chemistry Researchvol 45 no 22 pp 7504ndash7509 2006
[28] M Kato S Yoshikawa and K Nakagawa ldquoCarbon dioxideabsorption by lithium orthosilicate in a wide range of temper-ature and carbon dioxide concentrationsrdquo Journal of MaterialsScience Letters vol 21 no 6 pp 485ndash487 2002
[29] J-I Ida and Y S Lin ldquoMechanism of high-temperature CO2
sorption on lithium zirconaterdquo Environmental Science andTechnology vol 37 no 9 pp 1999ndash2004 2003
[30] E Ochoa-Fernandez H K Rusten H A Jakobsen MRoslashnning A Holmen and D Chen ldquoSorption enhanced hydro-gen production by steam methane reforming using Li
2ZrO3
as sorbent sorption kinetics and reactor simulationrdquo CatalysisToday vol 106 no 1-4 pp 41ndash46 2005
[31] E Ochoa-Fernandez M Roslashnning T Grande and D ChenldquoSynthesis and CO
2capture properties of nanocrystalline
lithium zirconaterdquo Chemistry of Materials vol 18 no 25 pp6037ndash6046 2006
[32] J A Satrio B H Shanks and T D Wheelock ldquoDevelopmentof a novel combined catalyst and sorbent for hydrocarbonreformingrdquo Industrial amp Engineering Chemistry Research vol44 no 11 pp 3901ndash3911 2005
[33] Z-S Li N-S Cai and Y-Y Huang ldquoEffect of preparationtemperature on cyclic CO
2capture and multiple carbonation-
calcination cycles for a new Ca-based CO2sorbentrdquo Industrial
amp Engineering Chemistry Research vol 45 no 6 pp 1911ndash19172006
[34] E P Reddy and P G Smirniotis ldquoHigh-temperature sorbentsfor CO
2made of alkali metals doped on CaO supportsrdquo The
Journal of Physical Chemistry B vol 108 no 23 pp 7794ndash78002004
[35] K Kuramoto S Fujimoto A Morita et al ldquoRepetitivecarbonation-calcination reactions of Ca-based sorbents forefficient CO
2sorption at elevated temperatures and pressuresrdquo
Industrial amp Engineering Chemistry Research vol 42 no 5 pp975ndash981 2003
[36] S F Wu T H Beum J I Yang and J N Kim ldquoProperties ofCa-base CO
2sorbent using Ca(OH)
2as precursorrdquo Industrial amp
Engineering Chemistry Research vol 46 no 24 pp 7896ndash78992007
[37] S F Wu Q H Li J N Kim and K B Yi ldquoProperties of a nanoCaOAl
2O3CO2sorbentrdquo Industrial amp Engineering Chemistry
Research vol 47 no 1 pp 180ndash184 2008
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
6 International Journal of Photoenergy
274
219
164
109
54
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(a)
252
202
151
101
50
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(b)
295
236
177
118
59
0
100 200 300 400 500 600 700 800 900 100
Ti
Ti
Ca
O
(c)
Figure 4 EDX spectra of nanotubes subjected to wet impregnation of 12M calcium nitrate solution for (a) 24 hours (b) 48 hours and(c) 72 hours (all EDX spectrums are noneditable format based on our FESEM-EDX system)
Figures 2(a) to 2(c) Another set of experiments was con-ducted to form CaO-TiO
2nanotubes in 12M calcium nitrate
solution for 24 48 and 72 hours All morphologies of thesamples showed similar appearance of CaO-TiO
2nanotubes
synthesized in 06M calcium nitrate solution The irregularCaO layer covered all of the TiO
2nanotubular structure
and nanoporous structure arranged in a nonordered mannerwhich could be observed in Figures 3(a) to 3(c)The chemicalstoichiometry of the resultant samples was determined viaEDX analysis as shown in Figures 4(a) to 4(c) A high Cacontent of 978 atwas determined from those synthesized in12M calciumnitrate solution for 72 hours indicating that theincorporation of the CaO became prominent with increasingthe concentration of calcium nitrate solution Based on theFESEM images and EDX analysis the small Ca2+ ions couldbe diffused into TiO
2nanotubes in the presence of lattice
defects especially nearby to the wall of nanotubes In thiscase the diffusion rate of Ca2+ ions increased significantlywhen increasing the reaction time and concentration of pre-cursor However the content of small Ca2+ ions that diffusedinto the TiO
2lattice could reach a saturation condition and
start to accumulate on the surface of nanotubes The numberof nucleation sites for Ca2+ ions loaded on the wall surface ofthe nanotubes increasedwith longer reaction time and higherconcentration of precursor which produced nanotubes withthicker walls The diffusion of the Ca2+ ions formed CandashObonding withOndashTindashO bonding thus charge neutrality couldbe achieved
Table 2 EDX result of CaO-TiO2 with different soaking time in06M and 12M calcium nitrate solution
Concentration ofcalcium nitratesolution (M)
Element (at)reactiontime (h) Ti O Ca
0624 4607 5292 010148 3888 5745 036772 4230 5311 0459
1224 3644 6066 029048 3264 6064 066472 2883 6110 0978
In the present study XRD analysis was used to determinethe crystallographic structure and the changes in the phasestructure of the CaO-TiO
2nanotubes synthesized in different
reaction times and concentrations of precursor are presentedin Figures 5 and 6 Numerous studies reported that heattreatment at about 400∘C could transform the amorphousstructure of TiO
2into the crystalline anatase phase The
obvious diffraction peaks from the XRD pattern attributedto the anatase phase (JCPDS no 21-1272) were detected fromthe XRD patterns (Figure 5(a)) The diffraction peaks areallocated at 2532∘ 3784∘ 3842∘ 4802∘ 5387∘ 5509∘ 6293∘7065∘ and 7623∘ which correspond to 101 004 112 200105 211 204 220 and 301 crystal planes for the anatase
International Journal of Photoenergy 7
10 20 30 40 50 60 70 80 90
Inte
nsity
(au
)
(d)
(c)
(b)
(a)TA T
T A AT
A T
T
T
2120579 (deg)
Figure 5 XRD pattern of TiO2nanotubes incorporated with Ca in
06M Ca(NO3)2solution at different soaking period (a) pure TiO
2
(b) 24 hours (c) 48 hours and (d) 72 hours (A = anatase phase T =titanium phase)
10 20 30 40 50 60 70 80 90
Inte
nsity
(au
)
AT A
TT
AT
TA
TT (a)
(b)
(c)
(d)
2120579 (deg)
Figure 6 XRD pattern of TiO2nanotubes incorporated with Ca in
12M Ca(NO3)2solution at different soaking period (a) pure TiO
2
(b) 24 hours (c) 48 hours and (d) 72 hours (A = anatase phase T =titanium phase)
phase respectively Apparently the incorporation of Ca2+ions into the lattice of TiO
2hindered the crystallization
of TiO2 resulting in the peak intensity of the 101 peak at
2532∘ decrease The decrease in anatase phase is maybe dueto the interruption of Ca atom which diffused into TiO
2
nanotubes and inhibited the formation of the anatase TheXRD pattern of the sample soaked in 12M for 72 hoursexhibits additional peaks 220 and 400 crystal planes at 54∘and 80∘ corresponding to CaO phase This indicates thatcrystalline CaO are formed once the concentration of Cain TiO
2reaches a higher level Next the resultant anodized
CaO-TiO2nanotubes were used in the characterization of
CO2adsorption using TGA analysis The processing steps
involved in TGA analysis are N2gas flow at a rate of 10∘Cmin
from room temperature to 673K and then holding for 30minin CO
2and finally cooling down to 573K byN
2gasThe TGA
curves for 06M of Ca and 12M of Ca are shown in Figures7 and 8 respectively while the CO
2adsorption capacity is
summarized in Table 3 Based on the TGA analysis it couldbe observed that all CaO-TiO
2samples showed their CO
2
adsorption capacity in the range of 33mmolg to 45mmolgA maximum CO
2adsorption capacity of up to 445mmolg
was observed from the CaO-TiO2nanotubes synthesized in
050100150200250300350400450
996998100
1002100410061008
101101210141016
0 20 40 60 80
Wei
ght (
)
Time (min)
24 hours48 hours
72 hoursTemperature
Tem
pera
ture
(∘C)
Figure 7 TGA curve of soaking in 06M of Ca for different periodsof time
050100150200250300350400450
995
100
1005
101
1015
102
1025
0 20 40 60 80
Wei
ght (
)
Time (min)
Tem
pera
ture
(∘C)
24 hours48 hours
72 hoursTemperature
Figure 8 TGA curve of soaking in 12M of Ca for different periodsof time
Table 3 CO2 adsorption capacity of the CaO-TiO2 samples
Concentration of calciumnitrate solution (M)
Soaking period(hours)
CO2 adsorptioncapacity (mmolg)
0624 38948 33272 400
1224 35948 44572 380
12M of calcium nitrate solution for 48 hours Basically theCO2adsorption capacity based CaO-TiO
2sorbents used the
following reaction CaO + CO2rarr CaCO
3 In this case
the sorbent weight is increased significantly when CO2gas is
applied to the TGA system where all the weight added is CO2
adsorbed This reason clearly explains that CO2adsorption
capacity is increased after carbonation process
8 International Journal of Photoenergy
4 Conclusion
The present study demonstrated that one-dimensional CaO-TiO2nanotubes sorbent was successfully formed using oxi-
dation electrochemical anodization and wet impregnationtechniques All of the resultant CaO-TiO
2nanotubes sorbent
exhibited promising CO2adsorption capacity in the range of
33mmolg to 45mmolg It is shown that high active surfacearea of CaO-TiO
2nanotubes sorbent showed good stability
during extended cyclic carbonation-calcination reaction
Conflict of Interests
The author declares that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
This research is supported by High Impact Research Chan-cellory Grant UMC6251HIR228 (J55001-73873) from theUniversity of Malaya In addition authors would like tothank University of Malaya for sponsoring this work underUniversity of Malaya Research Grant (UMRG no RP022-2012D)
References
[1] Q Wang J Luo Z Zhong and A Borgna ldquoCO2capture by
solid adsorbents and their applications current status and newtrendsrdquo Energy amp Environmental Science vol 4 no 1 pp 42ndash552011
[2] D M DrsquoAlessandro B Smit and J R Long ldquoCarbon dioxidecapture prospects for new materialsrdquo Angewandte ChemieInternational Edition vol 49 no 35 pp 6058ndash6082 2010
[3] SWang S Yan XMa and JGong ldquoRecent advances in captureof carbon dioxide using alkali-metal-based oxidesrdquo Energy ampEnvironmental Science vol 4 no 10 pp 3805ndash3819 2011
[4] N H Florin and A T Harris ldquoReactivity of CaO derived fromnano-sized CaCO
3particles through multiple CO
2capture-
and-release cyclesrdquo Chemical Engineering Science vol 64 no2 pp 187ndash191 2009
[5] J Garcıa T Lopez M Alvarez D H Aguilar and P QuintanaldquoSpectroscopic structural and textural properties of CaO andCaO-SiO
2materials synthesized by sol-gel with different acid
catalystsrdquo Journal of Non-Crystalline Solids vol 354 no 2-9 pp729ndash732 2008
[6] V R Choudhary S A R Mulla and B S Uphade ldquoOxidativecoupling of methane over alkaline earth oxides deposited oncommercial support precoated with rare earth oxidesrdquo Fuel vol78 no 4 pp 427ndash437 1999
[7] D Alvarez and J C Abanades ldquoPore-size and shape effects onthe recarbonation performance of calcium oxide submitted torepeated calcinationrecarbonation cyclesrdquo Energy and Fuelsvol 19 no 1 pp 270ndash278 2005
[8] J-R Li Y Ma M C McCarthy et al ldquoCarbon dioxidecapture-related gas adsorption and separation in metal-organicframeworksrdquo Coordination Chemistry Reviews vol 255 no 15-16 pp 1791ndash1823 2011
[9] S Sreekantan L C Wei and Z Lockman ldquoExtremely fastgrowth rate of TiO
2nanotube arrays in electrochemical bath
containing H2O2rdquo Journal of the Electrochemical Society vol
158 no 12 pp C397ndashC402 2011[10] CW Lai and S Sreekantan ldquoDimensional control of TiO
2nan-
otube arrays with H2O2content for high photoelectrochemical
water splitting performancerdquoMicro ampNano Letters vol 7 no 5pp 443ndash447 2012
[11] Y K Lai J Y Huang H F Zhang et al ldquoNitrogen-doped TiO2
nanotube array films with enhanced photocatalytic activityunder various light sourcesrdquo Journal of Hazardous Materialsvol 184 no 1ndash3 pp 855ndash863 2010
[12] S-H Liu C-H Wu H-K Lee and S-B Liu ldquoHighly stableamine-modified mesoporous silica materials for efficient CO
2
capturerdquo Topics in Catalysis vol 53 no 3-4 pp 210ndash217 2010[13] V Zelenak M Badanicova D Halamova et al ldquoAmine-
modified ordered mesoporous silica effect of pore size oncarbon dioxide capturerdquoChemical Engineering Journal vol 144no 2 pp 336ndash342 2008
[14] A R Millward and O M Yaghi ldquoMetal-organic frameworkswith exceptionally high capacity for storage of carbon dioxideat room temperaturerdquo Journal of the American Chemical Societyvol 127 no 51 pp 17998ndash17999 2005
[15] H Deng H Yi X Tang P Ning andQ Yu ldquoAdsorption of CO2
and N2on coal-based activated carbonrdquo Advanced Materials
Research vol 204-210 pp 1250ndash1253 2011[16] Q Li J Yang D Feng et al ldquoFacile synthesis of porous
carbon nitride spheres with hierarchical three-dimensionalmesostructures for CO
2capturerdquo Nano Research vol 3 no 9
pp 632ndash642 2010[17] Y Xia R Mokaya G S Walker and Y Zhu ldquoSuperior CO
2
adsorption capacity on N-doped high-surface-area microp-orous carbons templated from zeoliterdquo Advanced Energy Mate-rials vol 1 pp 678ndash683 2011
[18] Z Zhang M Xu H Wang and Z Li ldquoEnhancement of CO2
adsorption on high surface area activated carbon modified byN2 H2and ammoniardquo Chemical Engineering Journal vol 160
no 2 pp 571ndash577 2010[19] T C Drage J M Blackman C Pevida and C E Snape
ldquoEvaluation of activated carbon adsorbents for CO2capture in
gasificationrdquo Energy and Fuels vol 23 no 5 pp 2790ndash27962009
[20] Y Wang Y Zhou C Liu and L Zhou ldquoComparative studiesof CO
2and CH
2sorption on activated carbon in presence of
waterrdquoColloids and Surfaces A Physicochemical and EngineeringAspects vol 322 no 1ndash3 pp 14ndash18 2008
[21] F Su C Lu and H-S Chen ldquoAdsorption desorption andthermodynamic studies of CO
2with high-amine-loaded mul-
tiwalled carbon nanotubesrdquo Langmuir vol 27 no 13 pp 8090ndash8098 2011
[22] S U Rege and R T Yang ldquoA novel FTIR method for studyingmixed gas adsorption at low concentrations H
2O and CO
2on
NaX zeolite and 120574-aluminardquo Chemical Engineering Science vol56 no 12 pp 3781ndash3796 2001
[23] F Su C Lu S-C Kuo and W Zeng ldquoAdsorption of CO2on
amine-functionalized y-type zeolitesrdquo Energy and Fuels vol 24no 2 pp 1441ndash1448 2010
[24] A Ertan and F Cakicioglu-Ozkan ldquoCO2and N
2adsorption
on the acid (HCl HNO3 H2SO4and H
3PO4) treated zeolitesrdquo
Adsorption vol 11 no 1 pp 151ndash156 2005[25] F Brandani and D M Ruthven ldquoThe effect of water on the
adsorption of CO2and C
3H8on type X zeolitesrdquo Industrial amp
Engineering Chemistry Research vol 43 no 26 pp 8339ndash83442004
International Journal of Photoenergy 9
[26] L Li X Wen X Fu et al ldquoMgOAl2O3sorbent for CO
2
capturerdquo Energy and Fuels vol 24 no 10 pp 5773ndash5780 2010[27] M K RamReddy Z P Xu GQ Lu and J C DDaCosta ldquoLay-
ered double hydroxides for CO2capture structure evolution
and regenerationrdquo Industrial amp Engineering Chemistry Researchvol 45 no 22 pp 7504ndash7509 2006
[28] M Kato S Yoshikawa and K Nakagawa ldquoCarbon dioxideabsorption by lithium orthosilicate in a wide range of temper-ature and carbon dioxide concentrationsrdquo Journal of MaterialsScience Letters vol 21 no 6 pp 485ndash487 2002
[29] J-I Ida and Y S Lin ldquoMechanism of high-temperature CO2
sorption on lithium zirconaterdquo Environmental Science andTechnology vol 37 no 9 pp 1999ndash2004 2003
[30] E Ochoa-Fernandez H K Rusten H A Jakobsen MRoslashnning A Holmen and D Chen ldquoSorption enhanced hydro-gen production by steam methane reforming using Li
2ZrO3
as sorbent sorption kinetics and reactor simulationrdquo CatalysisToday vol 106 no 1-4 pp 41ndash46 2005
[31] E Ochoa-Fernandez M Roslashnning T Grande and D ChenldquoSynthesis and CO
2capture properties of nanocrystalline
lithium zirconaterdquo Chemistry of Materials vol 18 no 25 pp6037ndash6046 2006
[32] J A Satrio B H Shanks and T D Wheelock ldquoDevelopmentof a novel combined catalyst and sorbent for hydrocarbonreformingrdquo Industrial amp Engineering Chemistry Research vol44 no 11 pp 3901ndash3911 2005
[33] Z-S Li N-S Cai and Y-Y Huang ldquoEffect of preparationtemperature on cyclic CO
2capture and multiple carbonation-
calcination cycles for a new Ca-based CO2sorbentrdquo Industrial
amp Engineering Chemistry Research vol 45 no 6 pp 1911ndash19172006
[34] E P Reddy and P G Smirniotis ldquoHigh-temperature sorbentsfor CO
2made of alkali metals doped on CaO supportsrdquo The
Journal of Physical Chemistry B vol 108 no 23 pp 7794ndash78002004
[35] K Kuramoto S Fujimoto A Morita et al ldquoRepetitivecarbonation-calcination reactions of Ca-based sorbents forefficient CO
2sorption at elevated temperatures and pressuresrdquo
Industrial amp Engineering Chemistry Research vol 42 no 5 pp975ndash981 2003
[36] S F Wu T H Beum J I Yang and J N Kim ldquoProperties ofCa-base CO
2sorbent using Ca(OH)
2as precursorrdquo Industrial amp
Engineering Chemistry Research vol 46 no 24 pp 7896ndash78992007
[37] S F Wu Q H Li J N Kim and K B Yi ldquoProperties of a nanoCaOAl
2O3CO2sorbentrdquo Industrial amp Engineering Chemistry
Research vol 47 no 1 pp 180ndash184 2008
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
International Journal of Photoenergy 7
10 20 30 40 50 60 70 80 90
Inte
nsity
(au
)
(d)
(c)
(b)
(a)TA T
T A AT
A T
T
T
2120579 (deg)
Figure 5 XRD pattern of TiO2nanotubes incorporated with Ca in
06M Ca(NO3)2solution at different soaking period (a) pure TiO
2
(b) 24 hours (c) 48 hours and (d) 72 hours (A = anatase phase T =titanium phase)
10 20 30 40 50 60 70 80 90
Inte
nsity
(au
)
AT A
TT
AT
TA
TT (a)
(b)
(c)
(d)
2120579 (deg)
Figure 6 XRD pattern of TiO2nanotubes incorporated with Ca in
12M Ca(NO3)2solution at different soaking period (a) pure TiO
2
(b) 24 hours (c) 48 hours and (d) 72 hours (A = anatase phase T =titanium phase)
phase respectively Apparently the incorporation of Ca2+ions into the lattice of TiO
2hindered the crystallization
of TiO2 resulting in the peak intensity of the 101 peak at
2532∘ decrease The decrease in anatase phase is maybe dueto the interruption of Ca atom which diffused into TiO
2
nanotubes and inhibited the formation of the anatase TheXRD pattern of the sample soaked in 12M for 72 hoursexhibits additional peaks 220 and 400 crystal planes at 54∘and 80∘ corresponding to CaO phase This indicates thatcrystalline CaO are formed once the concentration of Cain TiO
2reaches a higher level Next the resultant anodized
CaO-TiO2nanotubes were used in the characterization of
CO2adsorption using TGA analysis The processing steps
involved in TGA analysis are N2gas flow at a rate of 10∘Cmin
from room temperature to 673K and then holding for 30minin CO
2and finally cooling down to 573K byN
2gasThe TGA
curves for 06M of Ca and 12M of Ca are shown in Figures7 and 8 respectively while the CO
2adsorption capacity is
summarized in Table 3 Based on the TGA analysis it couldbe observed that all CaO-TiO
2samples showed their CO
2
adsorption capacity in the range of 33mmolg to 45mmolgA maximum CO
2adsorption capacity of up to 445mmolg
was observed from the CaO-TiO2nanotubes synthesized in
050100150200250300350400450
996998100
1002100410061008
101101210141016
0 20 40 60 80
Wei
ght (
)
Time (min)
24 hours48 hours
72 hoursTemperature
Tem
pera
ture
(∘C)
Figure 7 TGA curve of soaking in 06M of Ca for different periodsof time
050100150200250300350400450
995
100
1005
101
1015
102
1025
0 20 40 60 80
Wei
ght (
)
Time (min)
Tem
pera
ture
(∘C)
24 hours48 hours
72 hoursTemperature
Figure 8 TGA curve of soaking in 12M of Ca for different periodsof time
Table 3 CO2 adsorption capacity of the CaO-TiO2 samples
Concentration of calciumnitrate solution (M)
Soaking period(hours)
CO2 adsorptioncapacity (mmolg)
0624 38948 33272 400
1224 35948 44572 380
12M of calcium nitrate solution for 48 hours Basically theCO2adsorption capacity based CaO-TiO
2sorbents used the
following reaction CaO + CO2rarr CaCO
3 In this case
the sorbent weight is increased significantly when CO2gas is
applied to the TGA system where all the weight added is CO2
adsorbed This reason clearly explains that CO2adsorption
capacity is increased after carbonation process
8 International Journal of Photoenergy
4 Conclusion
The present study demonstrated that one-dimensional CaO-TiO2nanotubes sorbent was successfully formed using oxi-
dation electrochemical anodization and wet impregnationtechniques All of the resultant CaO-TiO
2nanotubes sorbent
exhibited promising CO2adsorption capacity in the range of
33mmolg to 45mmolg It is shown that high active surfacearea of CaO-TiO
2nanotubes sorbent showed good stability
during extended cyclic carbonation-calcination reaction
Conflict of Interests
The author declares that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
This research is supported by High Impact Research Chan-cellory Grant UMC6251HIR228 (J55001-73873) from theUniversity of Malaya In addition authors would like tothank University of Malaya for sponsoring this work underUniversity of Malaya Research Grant (UMRG no RP022-2012D)
References
[1] Q Wang J Luo Z Zhong and A Borgna ldquoCO2capture by
solid adsorbents and their applications current status and newtrendsrdquo Energy amp Environmental Science vol 4 no 1 pp 42ndash552011
[2] D M DrsquoAlessandro B Smit and J R Long ldquoCarbon dioxidecapture prospects for new materialsrdquo Angewandte ChemieInternational Edition vol 49 no 35 pp 6058ndash6082 2010
[3] SWang S Yan XMa and JGong ldquoRecent advances in captureof carbon dioxide using alkali-metal-based oxidesrdquo Energy ampEnvironmental Science vol 4 no 10 pp 3805ndash3819 2011
[4] N H Florin and A T Harris ldquoReactivity of CaO derived fromnano-sized CaCO
3particles through multiple CO
2capture-
and-release cyclesrdquo Chemical Engineering Science vol 64 no2 pp 187ndash191 2009
[5] J Garcıa T Lopez M Alvarez D H Aguilar and P QuintanaldquoSpectroscopic structural and textural properties of CaO andCaO-SiO
2materials synthesized by sol-gel with different acid
catalystsrdquo Journal of Non-Crystalline Solids vol 354 no 2-9 pp729ndash732 2008
[6] V R Choudhary S A R Mulla and B S Uphade ldquoOxidativecoupling of methane over alkaline earth oxides deposited oncommercial support precoated with rare earth oxidesrdquo Fuel vol78 no 4 pp 427ndash437 1999
[7] D Alvarez and J C Abanades ldquoPore-size and shape effects onthe recarbonation performance of calcium oxide submitted torepeated calcinationrecarbonation cyclesrdquo Energy and Fuelsvol 19 no 1 pp 270ndash278 2005
[8] J-R Li Y Ma M C McCarthy et al ldquoCarbon dioxidecapture-related gas adsorption and separation in metal-organicframeworksrdquo Coordination Chemistry Reviews vol 255 no 15-16 pp 1791ndash1823 2011
[9] S Sreekantan L C Wei and Z Lockman ldquoExtremely fastgrowth rate of TiO
2nanotube arrays in electrochemical bath
containing H2O2rdquo Journal of the Electrochemical Society vol
158 no 12 pp C397ndashC402 2011[10] CW Lai and S Sreekantan ldquoDimensional control of TiO
2nan-
otube arrays with H2O2content for high photoelectrochemical
water splitting performancerdquoMicro ampNano Letters vol 7 no 5pp 443ndash447 2012
[11] Y K Lai J Y Huang H F Zhang et al ldquoNitrogen-doped TiO2
nanotube array films with enhanced photocatalytic activityunder various light sourcesrdquo Journal of Hazardous Materialsvol 184 no 1ndash3 pp 855ndash863 2010
[12] S-H Liu C-H Wu H-K Lee and S-B Liu ldquoHighly stableamine-modified mesoporous silica materials for efficient CO
2
capturerdquo Topics in Catalysis vol 53 no 3-4 pp 210ndash217 2010[13] V Zelenak M Badanicova D Halamova et al ldquoAmine-
modified ordered mesoporous silica effect of pore size oncarbon dioxide capturerdquoChemical Engineering Journal vol 144no 2 pp 336ndash342 2008
[14] A R Millward and O M Yaghi ldquoMetal-organic frameworkswith exceptionally high capacity for storage of carbon dioxideat room temperaturerdquo Journal of the American Chemical Societyvol 127 no 51 pp 17998ndash17999 2005
[15] H Deng H Yi X Tang P Ning andQ Yu ldquoAdsorption of CO2
and N2on coal-based activated carbonrdquo Advanced Materials
Research vol 204-210 pp 1250ndash1253 2011[16] Q Li J Yang D Feng et al ldquoFacile synthesis of porous
carbon nitride spheres with hierarchical three-dimensionalmesostructures for CO
2capturerdquo Nano Research vol 3 no 9
pp 632ndash642 2010[17] Y Xia R Mokaya G S Walker and Y Zhu ldquoSuperior CO
2
adsorption capacity on N-doped high-surface-area microp-orous carbons templated from zeoliterdquo Advanced Energy Mate-rials vol 1 pp 678ndash683 2011
[18] Z Zhang M Xu H Wang and Z Li ldquoEnhancement of CO2
adsorption on high surface area activated carbon modified byN2 H2and ammoniardquo Chemical Engineering Journal vol 160
no 2 pp 571ndash577 2010[19] T C Drage J M Blackman C Pevida and C E Snape
ldquoEvaluation of activated carbon adsorbents for CO2capture in
gasificationrdquo Energy and Fuels vol 23 no 5 pp 2790ndash27962009
[20] Y Wang Y Zhou C Liu and L Zhou ldquoComparative studiesof CO
2and CH
2sorption on activated carbon in presence of
waterrdquoColloids and Surfaces A Physicochemical and EngineeringAspects vol 322 no 1ndash3 pp 14ndash18 2008
[21] F Su C Lu and H-S Chen ldquoAdsorption desorption andthermodynamic studies of CO
2with high-amine-loaded mul-
tiwalled carbon nanotubesrdquo Langmuir vol 27 no 13 pp 8090ndash8098 2011
[22] S U Rege and R T Yang ldquoA novel FTIR method for studyingmixed gas adsorption at low concentrations H
2O and CO
2on
NaX zeolite and 120574-aluminardquo Chemical Engineering Science vol56 no 12 pp 3781ndash3796 2001
[23] F Su C Lu S-C Kuo and W Zeng ldquoAdsorption of CO2on
amine-functionalized y-type zeolitesrdquo Energy and Fuels vol 24no 2 pp 1441ndash1448 2010
[24] A Ertan and F Cakicioglu-Ozkan ldquoCO2and N
2adsorption
on the acid (HCl HNO3 H2SO4and H
3PO4) treated zeolitesrdquo
Adsorption vol 11 no 1 pp 151ndash156 2005[25] F Brandani and D M Ruthven ldquoThe effect of water on the
adsorption of CO2and C
3H8on type X zeolitesrdquo Industrial amp
Engineering Chemistry Research vol 43 no 26 pp 8339ndash83442004
International Journal of Photoenergy 9
[26] L Li X Wen X Fu et al ldquoMgOAl2O3sorbent for CO
2
capturerdquo Energy and Fuels vol 24 no 10 pp 5773ndash5780 2010[27] M K RamReddy Z P Xu GQ Lu and J C DDaCosta ldquoLay-
ered double hydroxides for CO2capture structure evolution
and regenerationrdquo Industrial amp Engineering Chemistry Researchvol 45 no 22 pp 7504ndash7509 2006
[28] M Kato S Yoshikawa and K Nakagawa ldquoCarbon dioxideabsorption by lithium orthosilicate in a wide range of temper-ature and carbon dioxide concentrationsrdquo Journal of MaterialsScience Letters vol 21 no 6 pp 485ndash487 2002
[29] J-I Ida and Y S Lin ldquoMechanism of high-temperature CO2
sorption on lithium zirconaterdquo Environmental Science andTechnology vol 37 no 9 pp 1999ndash2004 2003
[30] E Ochoa-Fernandez H K Rusten H A Jakobsen MRoslashnning A Holmen and D Chen ldquoSorption enhanced hydro-gen production by steam methane reforming using Li
2ZrO3
as sorbent sorption kinetics and reactor simulationrdquo CatalysisToday vol 106 no 1-4 pp 41ndash46 2005
[31] E Ochoa-Fernandez M Roslashnning T Grande and D ChenldquoSynthesis and CO
2capture properties of nanocrystalline
lithium zirconaterdquo Chemistry of Materials vol 18 no 25 pp6037ndash6046 2006
[32] J A Satrio B H Shanks and T D Wheelock ldquoDevelopmentof a novel combined catalyst and sorbent for hydrocarbonreformingrdquo Industrial amp Engineering Chemistry Research vol44 no 11 pp 3901ndash3911 2005
[33] Z-S Li N-S Cai and Y-Y Huang ldquoEffect of preparationtemperature on cyclic CO
2capture and multiple carbonation-
calcination cycles for a new Ca-based CO2sorbentrdquo Industrial
amp Engineering Chemistry Research vol 45 no 6 pp 1911ndash19172006
[34] E P Reddy and P G Smirniotis ldquoHigh-temperature sorbentsfor CO
2made of alkali metals doped on CaO supportsrdquo The
Journal of Physical Chemistry B vol 108 no 23 pp 7794ndash78002004
[35] K Kuramoto S Fujimoto A Morita et al ldquoRepetitivecarbonation-calcination reactions of Ca-based sorbents forefficient CO
2sorption at elevated temperatures and pressuresrdquo
Industrial amp Engineering Chemistry Research vol 42 no 5 pp975ndash981 2003
[36] S F Wu T H Beum J I Yang and J N Kim ldquoProperties ofCa-base CO
2sorbent using Ca(OH)
2as precursorrdquo Industrial amp
Engineering Chemistry Research vol 46 no 24 pp 7896ndash78992007
[37] S F Wu Q H Li J N Kim and K B Yi ldquoProperties of a nanoCaOAl
2O3CO2sorbentrdquo Industrial amp Engineering Chemistry
Research vol 47 no 1 pp 180ndash184 2008
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
8 International Journal of Photoenergy
4 Conclusion
The present study demonstrated that one-dimensional CaO-TiO2nanotubes sorbent was successfully formed using oxi-
dation electrochemical anodization and wet impregnationtechniques All of the resultant CaO-TiO
2nanotubes sorbent
exhibited promising CO2adsorption capacity in the range of
33mmolg to 45mmolg It is shown that high active surfacearea of CaO-TiO
2nanotubes sorbent showed good stability
during extended cyclic carbonation-calcination reaction
Conflict of Interests
The author declares that there is no conflict of interestsregarding the publication of this paper
Acknowledgments
This research is supported by High Impact Research Chan-cellory Grant UMC6251HIR228 (J55001-73873) from theUniversity of Malaya In addition authors would like tothank University of Malaya for sponsoring this work underUniversity of Malaya Research Grant (UMRG no RP022-2012D)
References
[1] Q Wang J Luo Z Zhong and A Borgna ldquoCO2capture by
solid adsorbents and their applications current status and newtrendsrdquo Energy amp Environmental Science vol 4 no 1 pp 42ndash552011
[2] D M DrsquoAlessandro B Smit and J R Long ldquoCarbon dioxidecapture prospects for new materialsrdquo Angewandte ChemieInternational Edition vol 49 no 35 pp 6058ndash6082 2010
[3] SWang S Yan XMa and JGong ldquoRecent advances in captureof carbon dioxide using alkali-metal-based oxidesrdquo Energy ampEnvironmental Science vol 4 no 10 pp 3805ndash3819 2011
[4] N H Florin and A T Harris ldquoReactivity of CaO derived fromnano-sized CaCO
3particles through multiple CO
2capture-
and-release cyclesrdquo Chemical Engineering Science vol 64 no2 pp 187ndash191 2009
[5] J Garcıa T Lopez M Alvarez D H Aguilar and P QuintanaldquoSpectroscopic structural and textural properties of CaO andCaO-SiO
2materials synthesized by sol-gel with different acid
catalystsrdquo Journal of Non-Crystalline Solids vol 354 no 2-9 pp729ndash732 2008
[6] V R Choudhary S A R Mulla and B S Uphade ldquoOxidativecoupling of methane over alkaline earth oxides deposited oncommercial support precoated with rare earth oxidesrdquo Fuel vol78 no 4 pp 427ndash437 1999
[7] D Alvarez and J C Abanades ldquoPore-size and shape effects onthe recarbonation performance of calcium oxide submitted torepeated calcinationrecarbonation cyclesrdquo Energy and Fuelsvol 19 no 1 pp 270ndash278 2005
[8] J-R Li Y Ma M C McCarthy et al ldquoCarbon dioxidecapture-related gas adsorption and separation in metal-organicframeworksrdquo Coordination Chemistry Reviews vol 255 no 15-16 pp 1791ndash1823 2011
[9] S Sreekantan L C Wei and Z Lockman ldquoExtremely fastgrowth rate of TiO
2nanotube arrays in electrochemical bath
containing H2O2rdquo Journal of the Electrochemical Society vol
158 no 12 pp C397ndashC402 2011[10] CW Lai and S Sreekantan ldquoDimensional control of TiO
2nan-
otube arrays with H2O2content for high photoelectrochemical
water splitting performancerdquoMicro ampNano Letters vol 7 no 5pp 443ndash447 2012
[11] Y K Lai J Y Huang H F Zhang et al ldquoNitrogen-doped TiO2
nanotube array films with enhanced photocatalytic activityunder various light sourcesrdquo Journal of Hazardous Materialsvol 184 no 1ndash3 pp 855ndash863 2010
[12] S-H Liu C-H Wu H-K Lee and S-B Liu ldquoHighly stableamine-modified mesoporous silica materials for efficient CO
2
capturerdquo Topics in Catalysis vol 53 no 3-4 pp 210ndash217 2010[13] V Zelenak M Badanicova D Halamova et al ldquoAmine-
modified ordered mesoporous silica effect of pore size oncarbon dioxide capturerdquoChemical Engineering Journal vol 144no 2 pp 336ndash342 2008
[14] A R Millward and O M Yaghi ldquoMetal-organic frameworkswith exceptionally high capacity for storage of carbon dioxideat room temperaturerdquo Journal of the American Chemical Societyvol 127 no 51 pp 17998ndash17999 2005
[15] H Deng H Yi X Tang P Ning andQ Yu ldquoAdsorption of CO2
and N2on coal-based activated carbonrdquo Advanced Materials
Research vol 204-210 pp 1250ndash1253 2011[16] Q Li J Yang D Feng et al ldquoFacile synthesis of porous
carbon nitride spheres with hierarchical three-dimensionalmesostructures for CO
2capturerdquo Nano Research vol 3 no 9
pp 632ndash642 2010[17] Y Xia R Mokaya G S Walker and Y Zhu ldquoSuperior CO
2
adsorption capacity on N-doped high-surface-area microp-orous carbons templated from zeoliterdquo Advanced Energy Mate-rials vol 1 pp 678ndash683 2011
[18] Z Zhang M Xu H Wang and Z Li ldquoEnhancement of CO2
adsorption on high surface area activated carbon modified byN2 H2and ammoniardquo Chemical Engineering Journal vol 160
no 2 pp 571ndash577 2010[19] T C Drage J M Blackman C Pevida and C E Snape
ldquoEvaluation of activated carbon adsorbents for CO2capture in
gasificationrdquo Energy and Fuels vol 23 no 5 pp 2790ndash27962009
[20] Y Wang Y Zhou C Liu and L Zhou ldquoComparative studiesof CO
2and CH
2sorption on activated carbon in presence of
waterrdquoColloids and Surfaces A Physicochemical and EngineeringAspects vol 322 no 1ndash3 pp 14ndash18 2008
[21] F Su C Lu and H-S Chen ldquoAdsorption desorption andthermodynamic studies of CO
2with high-amine-loaded mul-
tiwalled carbon nanotubesrdquo Langmuir vol 27 no 13 pp 8090ndash8098 2011
[22] S U Rege and R T Yang ldquoA novel FTIR method for studyingmixed gas adsorption at low concentrations H
2O and CO
2on
NaX zeolite and 120574-aluminardquo Chemical Engineering Science vol56 no 12 pp 3781ndash3796 2001
[23] F Su C Lu S-C Kuo and W Zeng ldquoAdsorption of CO2on
amine-functionalized y-type zeolitesrdquo Energy and Fuels vol 24no 2 pp 1441ndash1448 2010
[24] A Ertan and F Cakicioglu-Ozkan ldquoCO2and N
2adsorption
on the acid (HCl HNO3 H2SO4and H
3PO4) treated zeolitesrdquo
Adsorption vol 11 no 1 pp 151ndash156 2005[25] F Brandani and D M Ruthven ldquoThe effect of water on the
adsorption of CO2and C
3H8on type X zeolitesrdquo Industrial amp
Engineering Chemistry Research vol 43 no 26 pp 8339ndash83442004
International Journal of Photoenergy 9
[26] L Li X Wen X Fu et al ldquoMgOAl2O3sorbent for CO
2
capturerdquo Energy and Fuels vol 24 no 10 pp 5773ndash5780 2010[27] M K RamReddy Z P Xu GQ Lu and J C DDaCosta ldquoLay-
ered double hydroxides for CO2capture structure evolution
and regenerationrdquo Industrial amp Engineering Chemistry Researchvol 45 no 22 pp 7504ndash7509 2006
[28] M Kato S Yoshikawa and K Nakagawa ldquoCarbon dioxideabsorption by lithium orthosilicate in a wide range of temper-ature and carbon dioxide concentrationsrdquo Journal of MaterialsScience Letters vol 21 no 6 pp 485ndash487 2002
[29] J-I Ida and Y S Lin ldquoMechanism of high-temperature CO2
sorption on lithium zirconaterdquo Environmental Science andTechnology vol 37 no 9 pp 1999ndash2004 2003
[30] E Ochoa-Fernandez H K Rusten H A Jakobsen MRoslashnning A Holmen and D Chen ldquoSorption enhanced hydro-gen production by steam methane reforming using Li
2ZrO3
as sorbent sorption kinetics and reactor simulationrdquo CatalysisToday vol 106 no 1-4 pp 41ndash46 2005
[31] E Ochoa-Fernandez M Roslashnning T Grande and D ChenldquoSynthesis and CO
2capture properties of nanocrystalline
lithium zirconaterdquo Chemistry of Materials vol 18 no 25 pp6037ndash6046 2006
[32] J A Satrio B H Shanks and T D Wheelock ldquoDevelopmentof a novel combined catalyst and sorbent for hydrocarbonreformingrdquo Industrial amp Engineering Chemistry Research vol44 no 11 pp 3901ndash3911 2005
[33] Z-S Li N-S Cai and Y-Y Huang ldquoEffect of preparationtemperature on cyclic CO
2capture and multiple carbonation-
calcination cycles for a new Ca-based CO2sorbentrdquo Industrial
amp Engineering Chemistry Research vol 45 no 6 pp 1911ndash19172006
[34] E P Reddy and P G Smirniotis ldquoHigh-temperature sorbentsfor CO
2made of alkali metals doped on CaO supportsrdquo The
Journal of Physical Chemistry B vol 108 no 23 pp 7794ndash78002004
[35] K Kuramoto S Fujimoto A Morita et al ldquoRepetitivecarbonation-calcination reactions of Ca-based sorbents forefficient CO
2sorption at elevated temperatures and pressuresrdquo
Industrial amp Engineering Chemistry Research vol 42 no 5 pp975ndash981 2003
[36] S F Wu T H Beum J I Yang and J N Kim ldquoProperties ofCa-base CO
2sorbent using Ca(OH)
2as precursorrdquo Industrial amp
Engineering Chemistry Research vol 46 no 24 pp 7896ndash78992007
[37] S F Wu Q H Li J N Kim and K B Yi ldquoProperties of a nanoCaOAl
2O3CO2sorbentrdquo Industrial amp Engineering Chemistry
Research vol 47 no 1 pp 180ndash184 2008
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
International Journal of Photoenergy 9
[26] L Li X Wen X Fu et al ldquoMgOAl2O3sorbent for CO
2
capturerdquo Energy and Fuels vol 24 no 10 pp 5773ndash5780 2010[27] M K RamReddy Z P Xu GQ Lu and J C DDaCosta ldquoLay-
ered double hydroxides for CO2capture structure evolution
and regenerationrdquo Industrial amp Engineering Chemistry Researchvol 45 no 22 pp 7504ndash7509 2006
[28] M Kato S Yoshikawa and K Nakagawa ldquoCarbon dioxideabsorption by lithium orthosilicate in a wide range of temper-ature and carbon dioxide concentrationsrdquo Journal of MaterialsScience Letters vol 21 no 6 pp 485ndash487 2002
[29] J-I Ida and Y S Lin ldquoMechanism of high-temperature CO2
sorption on lithium zirconaterdquo Environmental Science andTechnology vol 37 no 9 pp 1999ndash2004 2003
[30] E Ochoa-Fernandez H K Rusten H A Jakobsen MRoslashnning A Holmen and D Chen ldquoSorption enhanced hydro-gen production by steam methane reforming using Li
2ZrO3
as sorbent sorption kinetics and reactor simulationrdquo CatalysisToday vol 106 no 1-4 pp 41ndash46 2005
[31] E Ochoa-Fernandez M Roslashnning T Grande and D ChenldquoSynthesis and CO
2capture properties of nanocrystalline
lithium zirconaterdquo Chemistry of Materials vol 18 no 25 pp6037ndash6046 2006
[32] J A Satrio B H Shanks and T D Wheelock ldquoDevelopmentof a novel combined catalyst and sorbent for hydrocarbonreformingrdquo Industrial amp Engineering Chemistry Research vol44 no 11 pp 3901ndash3911 2005
[33] Z-S Li N-S Cai and Y-Y Huang ldquoEffect of preparationtemperature on cyclic CO
2capture and multiple carbonation-
calcination cycles for a new Ca-based CO2sorbentrdquo Industrial
amp Engineering Chemistry Research vol 45 no 6 pp 1911ndash19172006
[34] E P Reddy and P G Smirniotis ldquoHigh-temperature sorbentsfor CO
2made of alkali metals doped on CaO supportsrdquo The
Journal of Physical Chemistry B vol 108 no 23 pp 7794ndash78002004
[35] K Kuramoto S Fujimoto A Morita et al ldquoRepetitivecarbonation-calcination reactions of Ca-based sorbents forefficient CO
2sorption at elevated temperatures and pressuresrdquo
Industrial amp Engineering Chemistry Research vol 42 no 5 pp975ndash981 2003
[36] S F Wu T H Beum J I Yang and J N Kim ldquoProperties ofCa-base CO
2sorbent using Ca(OH)
2as precursorrdquo Industrial amp
Engineering Chemistry Research vol 46 no 24 pp 7896ndash78992007
[37] S F Wu Q H Li J N Kim and K B Yi ldquoProperties of a nanoCaOAl
2O3CO2sorbentrdquo Industrial amp Engineering Chemistry
Research vol 47 no 1 pp 180ndash184 2008
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
Submit your manuscripts athttpwwwhindawicom
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Inorganic ChemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
International Journal ofPhotoenergy
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Carbohydrate Chemistry
International Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Advances in
Physical Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom
Analytical Methods in Chemistry
Journal of
Volume 2014
Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014
SpectroscopyInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014
Medicinal ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Chromatography Research International
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Applied ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Theoretical ChemistryJournal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Spectroscopy
Analytical ChemistryInternational Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Journal of
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Quantum Chemistry
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
Organic Chemistry International
ElectrochemistryInternational Journal of
Hindawi Publishing Corporation httpwwwhindawicom Volume 2014
Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014
CatalystsJournal of
Top Related