SYNTHESIS, CHARACTERIZATION AND SORPTION PROPERTIES OF
MICROPOROUS TITANOSILICATE ETS-10 FROM RICE HUSK ASH
JEI CHING YIH
UNIVERSITI TEKNOLOGI MALAYSIA
iii
To my love one
Wong Hon Loong
To my beloved parents
Jei Mok Choon and Wong Mai Yin
To my beloved brother and sister
Jei Jenn Ning and Jei Chien Fong
For their love that made me firm and resolute
iv
ACKNOWLEDGEMENTS
I am eternally grateful to many individuals for the education, knowledge and
experience that I gained over the past two years. First of all, I would like to express
my sincere appreciation to my project supervisor, Associate Professor Dr. Mustaffa
Shamsuddin for giving me the opportunity to carry out research in the fascinating
area of microporous molecular sieves and zeolites. Besides, I also would like to
thank my project co-supervisor, Associate Professor Dr. Azli Sulaiman for his
professional advice and emotional support. I thank for their helpful suggestion,
direction, advice and sympathetic guidance during the entire course of this research.
I would like to thank all the staffs from the Department of Chemistry and
Ibnu Sina Institute for Fundamental Science Studies, UTM for their prompt and
timely help during my study and research. Grateful acknowledge to the Ministry of
Science, Technology and Innovation (MOSTI) Malaysia for its financial support
through research grant, IRPA funding 09-02-06-0057-SR005/09-05 (Vot 74509). I
also would like to thank Universiti Teknologi Malaysia for offering a UTM-PTP
research scholarship.
I am also deeply grateful to everyone who has encouraged me and assisted
me in completing this research. Next, I would also thank my labmates and
housemates. They are so kind and always willing to share their experience and
knowledge with me.
Last but not least, I would like to send my deepest appreciation to my family
and my love one. They are always there to help us when I am facing problems and
give me supporting at all times.
v
PREFACE
This thesis is the result of my work carried out in the Department of Chemistry;
Universiti Teknologi Malaysia between July 2005 to December 2006 under
supervision of Assoc. Prof. Dr. Mustaffa Shamsuddin. Part of my work described in
this thesis has been reported in the following publications or presentations:
1. Jei, C. Y., Sulaiman, A. and Shamsuddin, M. Synthesis and Characterization
of Microporous Titanosilicate, ETS-10 from Agricultural Waste. Proceeding
of 1st Penang International Conference of Young Chemists. Universiti Sains
Malaysia. 2006.
2. Jei, C. Y., Sulaiman, A. and Shamsuddin, M. Physicochemistry Analysis of
ETS-10 Derived from Rice Husk Ash. Poster presentation at the 19th
Simposium Kimia Analisis Malaysia (SKAM-18). Universiti Teknologi
Malaysia, 2006.
vi
ABSTRACT
A new class of nano-sized microporous titanosilicate ETS-10 has been
prepared through hydrothermal synthesis route in the absence of ETS-4 and organic
template agent. Local agriculture waste – rice husk ash (RHA) has been used as the
silica source and commercial titanium oxide namely P25 as titanium source. For
comparison, the colloidal silica source, LUDOX-30 was also used as a silica source
to synthesize the ETS-10. The influence of some synthesis parameters such as
synthesis time and heating temperature on the crystallization of ETS-10 and the gel
oxides composition have also been investigated. The physico-chemical
characterization of these synthesized materials have been carried out by X-ray
Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), UV-Vis
spectroscopy (UV-VIS), Field Emission Scanning Electron Microscopy (FESEM),
Solid State Nuclear Magnetic Resonance (NMR), nitrogen adsorption-desorption
analysis and Raman spectroscopy. The best ETS-10 sample was successfully
obtained under heating at 220°C for 52 hours using the following molar ratio TiO2 :
3.75SiO2 : 1.5NaOH : 0.54KF : 21.25H2O. The ability of the synthesized ETS-10 as
adsorbents for heavy metal ion such as Pb2+, Cd2+ and Cu2+ was investigated. The
study of equilibrium and adsorption isotherm at 298 K was conducted using batch
mode. The uptake rates for these heavy metal ions were extremely fast and fitted well
with the pseudo-second order model and Langmuir equation with an affinity order of
Pb2+ > Cd2+ > Cu2+, with values of 1.86, 1.51 and 1.45 mmol/g respectively, which
are the highest adsorptive capacities of the heavy metal ions on zeolite materials
reported so far. This indicates that ETS-10 is a very promising adsorbent for divalent
heavy metals.
vii
ABSTRAK
Titanosilikat ETS-10 mikroliang bersaiz nano telah disintesis melalui tindak
balas hidroterma tanpa ETS-4 sebagai benih dan agen organik. Abu sekam padi yang
merupakan sisa buangan pertanian tempatan telah digunakan sebagai sumber silika
dan titanium oksida komersil (P25) digunakan sebagai sumber titanium. Untuk
tujuan perbandingan, silika koloid (LUDOX-30) juga digunakan sebagai sumber
silika dalam sintesis ETS-10. Parameter yang mempengaruhi proses sintesis ETS-10
dan komposisi oksida gelnya seperti masa dan suhu tindak balas juga dikaji. Hasil
daripada sintesis telah dicirikan menggunakan pembelauan sinar-X (XRD),
spektroskopi infra-merah transformasi Fourier (FT-IR), spektrokopi ultra
lembayung-nampak (UV-VIS), mikroskopi elektron imbasan pancaran medan
(FESEM), spekstroskopi resonans magnet nuklear keadaan pepejal (RMN), analisis
penjerapan dan penyahjerapan nitrogen and spektroskopi Raman. Sampel ETS-10
yang paling tulen didapatkan dengan menggunakan nisbah molar TiO2 : 3.75SiO2 :
1.5NaOH : 0.54KF : 21.25H2O pada suhu 220°C selama 52 jam. Sampel ETS-10
tulen ini kemudiannya digunakan dalam proses penjerapan untuk tujuan
penyingkiran ion logam berat, terutamanya Pb2+, Cd2+ dan Cu2+. Dalam kajian ini,
keseimbangan dan penjerapan isoterma pada suhu 25°C telah dijalankan melalui
kaedah berkelompok. Kadar penjerapan untuk logam berat tersebut sangat pantas dan
mematuhi dengan baik model pseudo tertib kedua dan model isoterma Langmuir
dengan urutan Pb2+ > Cd2+ > Cu2+ dengan nilai keupayaan penjerapan 1.86, 1.51 and
1.45 mmol/g masing-masing yang merupakan muatan penjerapan paling tinggi
berbanding dengan zeolit lain yang dilaporkan setakat ini. Ini membuktikan bahawa
ETS-10 adalah penjerap yang paling berpotensi terutamanya untuk penjerapan logam
berat dwivalen.
viii
TABLE OF CONTENTS
CHAPTER TITLE PAGE
TITLE PAGE
DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENTS iv
PREFACE v
ABSTRACT vi
ABSTRAK vii
TABLE OF CONTENTS viii
LIST OF TABLES xii
LIST OF FIGURES xv
LIST OF SYMBOLS xxi
LIST OF ABBREVIATIONS xxii
LIST OF APPENDICIES xxiii
1 INTRODUCTION
1.1 Research Background 1
1.2 Scope of Study 4
1.3 Objective of Study 5
2 LITERATURE REVIEW
2.1 Techniques for Heavy Metals Uptake from
Contaminated Water
6
2.1.1 Chemical Precipitation Method 7
2.1.2 Coagulation Method 7
ix
2.1.3 Electrodialysis Method 7
2.1.4 Ultrafiltration Method 8
2.1.5 Reverse Osmosis Method 8
2.1.6 Adsorption Method 8
2.1.7 Ion Exchange Method 9
2.2 Microporous Titanosilicate 10
2.3 Microporous Titanosilicate – ETS-10
2.3.1 Synthesis of ETS-10 13
2.3.2 Properties of ETS-10 16
2.3.2.1 Catalysis 16
2.3.2.2 Optical Properties 18
2.3.2.3 Adsorption and Ion-exchange Capability
19
3 EXPERIMENTAL
3.1 Synthesis of Microporous Titanosilicate, ETS-10 22
3.2 Modification of ETS-10
3.2.1 Desilication 23
3.2.2 Ion Exchange with Sodium, Potassium or Proton Ions
24
3.3 Synthesis of Zeolite 25
3.3.1 Synthesis of Zeolite A, X and Y 25
3.4 Characterization of ETS-10 Samples 26
3.4.1 X-ray Powder Diffraction (XRD) 26
3.4.2 Fourier Transform Infrared Spectroscopy (FTIR)
27
3.4.3 Raman Spectroscopy 27
3.4.4 Diffuse Reflectance Ultraviolet-visible Spectroscopy ( DR UV-vis)
27
3.4.5 Field Emission Scanning Electron Microscopy (FE-SEM)
28
3.4.6 EDAX Elemental Analysis 28
3.4.7 Solid State Nuclear Magnetic Resonance (NMR)
28
3.4.8 BET Surface Area Analysis 29
x
3.4.9 Measurement of Cation Exchange Capacity (CEC)
29
3.4.10 Flame Atomic Absorption Spectroscopy (FAAS)
30
3.5 Batch-Type Sorption Method 31
3.5.1 Sorption Study on Single Metal Ion Systems 31
3.5.1.1 Kinetic Studies 32
3.5.1.2 Effect of Initial pH 32
3.5.1.3 Adsorption Isotherm Studies 33
3.5.2 Sorption Study on Binary and Ternary Metal Ion System
34
3.5.2.1 Kinetic Studies 34
3.5.2.2 Adsorption Isotherm Studies 35
4 RESULTS AND DISCUSSION
4.1 Synthesis of ETS-10
4.1.1 The Effect of Different Ti Sources 36
4.1.2 The Effect of Different Silica Source 39
4.1.3 Influence of the Crystallization Time 40
4.1.4 The Effect of Different Molar Ratio 42
4.2 Characterization of Synthesized ETS-10
4.2.1 Fourier Transform Infrared Spectroscopy (FTIR)
45
4.2.2 Raman Spectroscopy 46
4.2.3 Diffuse Reflectance Ultraviolet-visible Spectroscopy (UV-vis)
48
4.2.4 Field Emission Scanning Electron Microscopy (FESEM)
49
4.2.5 Solid State Nuclear Magnetic Resonance (NMR)
51
4.2.6 BET Surface Area Analysis 54
4.3 Characterization of RHA Synthesized Zeolite A, X, Y 55
4.4 Modification of ETS-10
4.4.1 Desilication 56
4.4.2 Ion Exchange with Sodium, Potassium or Proton Ions
62
xi
4.5 Determination of Cation Exchange Capacity 67
4.6 Sorption Study on Single Metal Ion Systems
4.6.1 Kinetic Study 69
4.6.2 Effect of Initial pH 72
4.6.3 Adsorption Isotherm Studies 73
4.7 Sorption Study on Binary and Ternary Metal Ion System
81
4.7.1 Kinetic Studies 81
4.7.2 Adsorption Isotherm Studies 85
5 CONCLUSIONS AND SUGGESTIONS
5.1 Conclusion 89
5.2 Suggestions 91
REFERENCES 92
Appendices A - C 106
xii
LIST OF TABLES
TABLE NO. TITLE PAGE
3.1 The different reactants molar ratio used for ETS-10 synthesis 23
3.2 The molar ratio, heating temperature and crystallization
period which used for zeolite A, X and Y synthesis 25
3.3 Operating parameters of FAAS in the measurement of the
desired elements 30
3.4 Metal solution used for the sorption kinetic studies 34
4.1 The phases of the final products synthesized using different
Ti sources 38
4.2 The effects of different crystallization time and silica
sources at 220°C towards the ETS-10 synthesis and its
comparative relative crystallinity 41
4.3 The final products synthesized from different molar ratio at
220°C and its comparative relative crystallinity 44
4.4 FTIR spectral data of ETS-10 and the type of vibrations
generating the peaks 46
4.5 The Raman adsorption spectral data of ETS-10 and the type
of vibrations generating the peaks 47
xiii
4.6 The EDAX elementals analytical data for the ETS-10 51
4.7 The chemical shift for LUDOX and RHA synthesized ETS-10 52
4.8 The BET surface area for LUDOX and RHA synthesized
ETS-10 55
4.9 The Raman adsorption spectral data of desilication ETS-10
and the type of vibrations generating the peaks 59
4.10 The CEC and percent of comparative relative crystallinity
for desilicated ETS-10 at different temperature 61
4.11 The CEC and percent of comparative relative crystallinity
for desilicated ETS-10 at different stirring period 61
4.12 The CEC and percent of comparative relative crystallinity
for desilicated ETS-10 at different concentration of sodium
carbonate 62
4.13 The BET surface area for ion exchanged ETS-10 63
4.14 The CEC for Ludox and RHA synthesized ETS-10 at
different time, ion-exchanged ETS-10 and zeolite A, X and
Y 68
4.15 The pseudo-second-order rate constant (k2), correlation
coefficient (r2) and uptake equilibrium (qe) values for the
RHA synthesized ETS-10 in the removal of Pb2+, Cd2+ and
Cu2+ 71
4.16 Some physical parameters of heavy metal ions in solution
[109] 75
xiv
4.17 The Langmuir and Freundlich isotherm parameters of Pb2+,
Cd2+ and Cu2+ on Ludox synthesized ETS-10 (LETS-10)
and RHA synthesized ETS-10 (RETS-10) at pH 5 and 25°C 76
4.18 The Langmuir and Freundlich isotherm parameters of Pb2+,
Cd2+ and Cu2+ on RHA synthesized ETS-10 (RETS-10) and
zeolite A, X and Y at pH 5 and 25°C 80
4.19 The pseudo-second-order rate constant (k2), uptake
equilibrium (qe) values and correlation coefficient (r2) for
the RETS-10 in Pb2+−Cd2+, Pb2+−Cu2+, Cd2+−Cu2+ and
Pb2+−Cu2+−Cd2+ systems 84
4.20 The Langmuir isotherm parameters of Pb2+ and Cd2+ for the
RETS-10 in Pb2+−Cd2+, Pb2+−Cu2+, Cd2+−Cu2+ and
Pb2+−Cu2+−Cd2+ systems 85
xv
LIST OF FIGURES
FIGURE NO. TITLE PAGE
2.1 The structure of (a) ETS-4 [36] and (b) ETS-10 [37] 11
2.2 The ETS-10 structure arrangement where the red colour
represents the SiO4 and the blue colour represents the TiO6 12
2.3 The framework structure of ETS-10 showing chains of
corner-sharing TiO6 octahedra which run along two
perpendicular directions, and which are isolated by corner-
sharing SiO4 tetrahedra: (a) single element of the chain;
(b) single TiO6 chain; (c) three dimensional view. For
clarity, extra framework (charge-balancing) cations were
omitted 19
4.1 XRD pattern of the ETS-10 sample synthesized from
commercial anatase TiO2 at 200°C (a) commercial anatase
TiO2, (b) crystallization at 48 hours, (c) crystallization at 52
hours and (d) crystallization at 72 hours. A indicates
unreacted anatase and Q represents quartz 37
4.2 XRD pattern of the ETS-10 sample synthesized from P25 at
200°C (a) P25, (b) crystallization at 48 hours,
(c) crystallization at 52 hours and (d) crystallization at 72
hours. A indicates unreacted P25 37
xvi
4.3 XRD pattern of the ETS-10 sample synthesized from P25
at 220°C (a) P25 and (b) crystallization at 52 hours 38
4.4 XRD pattern of the ETS-10 samples synthesized from
Ludox-30 at 220°C (a) crystallization at 48 hours, (b)
crystallization at 52 hours and (c) crystallization at 72
hours. A indicates unreacted P25 and asterisk indicates the
ETS-4 impurities 39
4.5 XRD pattern of the ETS-10 samples synthesized from RHA
at 220°C (a) crystallization at 48 hours, (b) crystallization at
52 hours and (c) crystallization at 72 hours 40
4.6 XRD pattern of the ETS-10 (1) samples synthesized using
batch 1 molar ratio (TiO2 : 5SiO2 : 3NaOH : 0.75KF :
94.5H2O) at 220°C (a) crystallization at 48 hours, (b)
crystallization at 52 hours and (c) crystallization at 72 hours 42
4.7 XRD pattern of the ETS-10 (2) samples synthesized using
batch 2 molar ratio (TiO2 : 3.75SiO2 : 1.5NaOH : 0.54KF :
21.25H2O) at 220°C (a) crystallization at 48 hours, (b)
crystallization at 52 hours and (c) crystallization at 72 hours 43
4.8 XRD pattern of the ETS-10 (3) samples synthesized using
batch 3 molar ratio (TiO2 : 5.5SiO2 : 3.4Na2O : 1.5K2O :
180H2O) at 220°C (a) crystallization at 48 hours,
(b) crystallization at 52 hours and (c) crystallization at 72
hours 43
4.9 FTIR spectra (a) ETS-10 synthesis from RHA and
(b) ETS-10 synthesis from Ludox 45
4.10 Raman spectra (a) ETS-10 synthesis from RHA and
(b) ETS-10 synthesis from Ludox 47
xvii
4.11 Diffuse reflectance UV-Vis spectra for ETS-10 48
4.12 FESEM for ETS-10 that are synthesized using Ludox at
220°C (a) 48 hours, (b) 52 hours and (c) 72 hours 50
4.13 FESEM for ETS-10 that are synthesized using RHA at
220°C (a) 48 hours, (b) 52 hours and (c) 72 hours 50
4.14 The EDAX spectrum for the ETS-10 synthesized using
RHA at 52 hours crystallization time at 220°C 51
4.15 The MAS 29Si NMR spectra for the LUDOX synthesized
ETS-10 at 220°C for (a) 48 hours, (b) 52 hours and (c) 72
hours. Asterisks indicate the AM-3 impurities 53
4.16 The MAS 29Si NMR spectra for the RHA synthesized ETS-
10 at 220°C for (a) 48 hours, (b) 52 hours and (c) 72 hours.
Asterisk indicates the AM-3 impurity 54
4.17 XRD patterns for the RHA synthesized zeolites
(a) Zeolite A, (b) Zeolite X and (c) Zeolite Y 56
4.18 XRD pattern of the desilicated ETS-10 samples at different
temperature (a) 27°C, (b) 40°C, (c) 50°C, (d) 60°C, (e)
70°C, (f) 80°C, (g) 90°C and (h) 100°C 57
4.19 XRD pattern of the desilicated ETS-10 samples at different
temperature (a)1 hour, (b) 2 hours, (c) 3 hours, (d) 4 hours,
(e) 5 hours and (f) 6 hours 58
4.20 XRD pattern of the desilicated ETS-10 samples at different
temperature (a)0.05 M, (b) 0.1 M, (c) 0.2 M, (d) 0.4 M, (e)
0.6 M, (f) 0.8 M and (g) 1 M 58
xviii
4.21 Raman spectra for desilicated ETS-10 59
4.22 The FESEM micrograph of desilicated ETS-10 60
4.23 The MAS 29Si NMR spectrum of the desilicated ETS-10 60
4.24 The XRD patterns for (a) Na-exchanged ETS-10,
(b) K-exchanged ETS-10 and (c) protonated ETS-10 63
4.25 The FESEM micrographs for (a) Na-exchanged ETS-10,
(b) K-exchanged ETS-10 and (c) protonated ETS-10 64
4.26 The MAS 29Si NMR spectra for (a) Na-exchanged ETS-10,
(b) K-exchanged ETS-10 and (c) protonated ETS-10.
Asterisk indicates the AM-3 impurity while Q3 and Q4
indicate the Q3 and Q4 silicon signals 65
4.27 The uptake kinetic of Pb2+, Cd2+ and Cu2+ on ETS-10 at
25°C using the initial concentration of 8 mmol/L and batch
factor of 200 mL/g 69
4.28 Pseudo-second-order sorption kinetics of Pb2+, Cd2+ and
Cu2+ onto ETS-10 71
4.29 The effect of pH on the uptake capacity of Pb2+, Cd2+ and
Cu2+ on ETS-10 at 25°C using the initial concentration of
8 mmol/L and batch factor of 200 mL/g 72
4.30 The uptake isotherms of Pb2+, Cd2+ and Cu2+ on RHA
synthesized ETS-10 at pH 5 and 25°C 73
4.31 The uptake isotherms of Pb2+, Cd2+ and Cu2+ on Ludox
synthesized ETS-10 at pH 5 and 25°C 74
xix
4.32 The adsorption isotherms of Pb2+ on RHA synthesized
ETS-10 and zeolite A, X and Y at pH 5 and 25°C 77
4.33 The adsorption isotherms of Cd2+ ions on RHA synthesized
ETS-10 and zeolite A, X and Y at pH 5 and 25°C 78
4.34 The adsorption isotherms of Cu2+ on RHA synthesized
ETS-10 and zeolite A, X and Y at pH 5 and 25°C 78
4.35 The competitive adsorption kinetics in Pb2+−Cd2+ system
on RETS-10 at 25°C using the initial concentration of 10
mmol/L and batch factor of 200 mL/g 82
4.36 The competitive adsorption kinetics in Pb2+−Cu2+ system
on RETS-10 at 25°C using the initial concentration of 10
mmol/L and batch factor of 200 mL/g 82
4.37 The competitive adsorption kinetics in Cd2+−Cu2+ system
on RETS-10 at 25°C using the initial concentration of
10 mmol/L and batch factor of 200 mL/g 83
4.38 The competitive adsorption kinetics in Pb2+−Cd2+−Cu2+
system on RETS-10 at 25°C using the initial concentration
of 10 mmol/L and batch factor of 200 mL/g 83
4.39 The competitive adsorption isotherm in Pb2+−Cd2+ system
on RETS-10 at 25°C using the initial concentration of 10
mmol/L and batch factor of 200 mL/g 86
4.40 The competitive adsorption isotherm in Pb2+−Cu2+ system
on RETS-10 at 25°C using the initial concentration of 10
mmol/L and batch factor of 200 mL/g 86
xx
4.41 The competitive adsorption isotherm in Cd2+−Cu2+ system
on RETS-10 at 25°C using the initial concentration of 10
mmol/L and batch factor of 200 mL/g 87
4.42 The competitive adsorption isotherm in Pb2+−Cd2+−Cu2+
system on RETS-10 at 25°C using the initial concentration
of 10 mmol/L and batch factor of 200 mL/g 87
xxi
LIST OF SYMBOLS
°C - Degree Celsius
Co - Initial concentration
Ce - Equilibrium concentration
cm - Centi meter
g - Gram
kg - Kilo gram
kV - Kilo Volt
L - Liter
m - Meter
M - Molar
meq - Mili equivalent
mg - Mili gram
MHz - Mega Hertz
mL - Mili Liter
mm - Mili meter
mmol - Mili mol
mW - Mili Watt
N - Normal
nm - Nano meter
ppm - Part per million
Å - Angstrom
µL - Micro Liter
µm - Micro meter
λ - Lambda
δ - Delta
θ - Theta
xxii
LIST OF ABBREVIATIONS
ETS-4 - Engelhard titanosilicate-4
ETS-10 - Engelhard titanosilicate-10
AAS - Atomic Absorption Spectroscopy
BET - Brunauer, Emmet, and Teller
CEC - Cation Exchange Capacity
FAAS - Flame Atomic Absorption Spectroscopy
FAU - Faujasite
FESEM - Field Emission Scanning Electron Microscopy
FTIR - Fourier Transform Infrared
h - Hour
ICP-MS - Inductively Coupled Plasma Mass Spectrometry
FTIR - Fourier Transform Infrared
NMR - Nuclear Magnetic Resonance
RHA - Rice Husk Ash
rpm - Revolution per minute
TEACl - Tetraethylammonium chloride
TMACl - Tetramethylammonium chloride
UV-Vis - Ultra Violet-Visible
XPS - X-ray photoelectron spectroscopy
XRD - X-Ray Diffraction
XRF - X-Ray Flourescence
V - Volume
xxiii
LIST OF APPENDICES
APPENDIX TITLE PAGE
A FAAS Standard Calibration Curve for Lead
(Pb)
106
B FAAS Standard Calibration Curve for
Cadmium (Cd)
107
C FAAS Standard Calibration Curve for Copper
(Cu)
108
1
CHAPTER 1
INTRODUCTION
1.1 Research background
Due to the modern life nowadays, a lot of new technologies bring us to the
easier life but at the same time it also brings the worst effects to the environment.
Heavy metals such as lead (Pb), copper (Cu) and cadmium (Cd) which are released
into aquatic environments largely from various anthropogenic activities are serious
concern for human health and the environment. Therefore, removal of the heavy
metal pollutants from aqueous systems has received a considerable amount of
attention in order to control wastewater into an acceptable level according to the
environmental regulations worldwide.
There are many water treatment processes such as chemical precipitation [1],
adsorption [2], reverse osmosis [3], electro-dialysis [4], ultra-filtration [5,6] and ion-
exchange [7,8] that are currently available for removal of heavy metals. Among them,
the sorption process including ion-exchange and adsorption are the attractive ones,
due to their relatively simple and safe process. Ion exchange for cation removal is
often competitive with the classical chemical methods as it exhibits good
performances, reasonable costs and sometimes metal recovery ability [9]. Hence, the
good performances adsorbent has been investigated widely for this purpose.
Since its first introduction for heavy metal removal, it is undoubted that
activated carbon has been the most and widely used adsorbent in wastewater
2
treatment applications throughout the world. In spite of its prolific use, activated
carbon remains an expensive material since higher the quality of the activated carbon,
the higher it cost. Therefore, this situation makes it no longer attractive to be widely
used in the small-scale industries due to cost inefficiency. Until currently, there are
still many researchers working on inexpensive materials in search of the low-cost
adsorbents for heavy metal removal. As a result, the low-cost adsorbents which have
high adsorption capacity and locally available are desired. It is evident from the
literature survey of about 100 papers that low-cost adsorbents have demonstrated
outstanding removal capabilities for certain metal ions as compared to activated
carbon [10].
In the past few decades, both natural and synthetic zeolites have been studied
for heavy metal removal [11]. With increasingly stringent environmental regulations
for heavy metal presence in drinking water and wastewater, novel zeolite ion
exchangers with fast ion exchange rates and high uptake capacities are desired.
Natural zeolites gained a significant interest among scientists due to their ion-
exchange capability to preferentially remove unwanted heavy metals such as
strontium and cesium [10]. This unique property makes zeolites favourable for
wastewater treatment. However, the abundance of natural zeolites, an unavoidable
problem of the utilization is the coexistence of the considerable impurities within the
zeolitic tuffs, which interferes the exchange behavior of natural zeolites with heavy
metals. As a result, synthetic zeolites which usually posses higher exchange capacity,
easily controlled and known physico-chemical properties relative to that natural
zeolites, have been preferred [12].
Currently many researches are being carried out on the synthesis of zeolite or
microporous and mesoporous materials for the better heavy metal removal. In 1989,
a new class of microporous titanosilicate molecular sieves zeolite with octahedral
coordinated titanium framework known as (Engelhard Titanosilicate-4), ETS-4 with
pore size 0.3 – 0.4 nm and ETS-10 with pore size 0.49 – 0.76 nm were discovered by
Kuznicki [13-15]. This new family of microporous titanosilicates have been shown
to possess zeolite-like properties such as catalysis, separation, absorption and ion
exchange [16].
3
The ETS-10 comprises of corner-sharing [SiO4]4- tetrahedra and [TiO6]8-
octahedra linked through oxygen atoms, forming a three-dimensional 12-membered
ring network with pore-opening size of about 0.8 nm [17]. In ETS-10 the titanium
(IV) is found in the centre of the corner-sharing octahedral and the silicon in the
centre of corner sharing tetrahedral. This produces an anionic framework whereby,
whenever titanium is present in the structure, there is an associated two minus charge
which is compensated by extra-framework cations (Na+ and K+ in as-synthesised
ETS-10) [18]. Such a unique framework property has been demonstrated to display
unusual adsorption properties towards heavy metal ions in aqueous solution [19].
Unlike conventional aluminosilicate zeolites which are chemically constituted from
SiO4 and AlO4 tetrahedrals giving rise to one negative charge for each AlO4
tetrahedron balanced by an ion-exchangeable cation like Na+. Therefore the
associated two minus charge in ETS-10 structure make it a very interesting and
suitable material for extremely fast ion exchange especially for divalent heavy metal
cations removal compared with the zeolites which only has one minus charge in the
structure.
Since the first report of ETS-10, many titanium sources have been used to
synthesize ETS-10. TiCl3 was used as the Ti source in the initial report of synthesis
of ETS-10 by Kuznicki [13]. Due to the relatively expensive of TiCl3, the search for
alternative Ti source had been carried out. Thus, organotitanium compounds, TiCl4
and TiF4 had been used as Ti precursor to prepare ETS-10. However, the commercial
pure anatase TiO2 and commercial nano-sized TiO2 (commercially known as P25) is
of particular interest for the synthesis of ETS-10 because they are commercially
readily available and do not bring any unwanted guest anions like Cl- and F-.
Silica is one of the basic raw materials in synthesizing ETS-10. Many
researchers have used Ludox to synthesize the ETS-10. At present, there is still no
report of the rice husk ash being used as silica source to synthesize the ETS-10.
Since the rice husk is an agricultural waste material and locally available with high
percentage of silica, it becomes very suitable for low cost ETS-10 production. These
advantages make it an important material for water purification process, especially in
drinking water and waste water treatment. This will lead to an improved water
quality for healthier life and green environment in Malaysia.
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1.2 Scope of Study
In the research, the synthesis of ETS-10 was carried out using locally
produced rice husk ash as the silica source and titanium dioxide (namely P25) as the
titanium source in different molar oxide gel ratio. During the synthesis of ETS-10,
optimisation of the experimental conditions such as pressure, heating temperature,
pH, duration of stirring and reaction time were investigated. The structure and of the
synthesized ETS-10 from rice husk ash will be compared with the ETS-10
synthesized from colloidal silica source, LUDOX-30.
Modification of the ETS-10, will also be carried out where a novel method
called desilication will be applied to the synthesized ETS-10. In this method, some
silicon will be selectively removed from the ETS-10 framework in order to create an
extra ion exchange capacity. The desilication process toward ETS-10 will be
optimized systematically by altering the temperature, time and concentration of the
modifier. The original ETS-10 and desilicated ETS-10 will then be modified with
NaNO3, KNO3 and NH4NO3 to produce the sodium, potassium loaded ETS-10 and
protonated ETS-10 in order to use it as an ion-exchanger.
All the synthesized ETS-10, desilicated ETS-10 and modified ETS-10 were
characterized by Fourier transform infrared spectroscopy (FTIR), Raman
spectroscopy, UV-Vis spectroscopy (UV-Vis), X-ray diffraction (XRD), solid state
nuclear magnetic resonance (NMR), field emission scanning electron microscopy
(FESEM), thermogravimetric analysis and simultaneous differential thermal analysis
(TG-SDTA), nitrogen adsorption-desorption study for surface area analysis and
cation exchange capacity for the ion-exchange capacity analysis (CEC).
The sorption properties of the RHA synthesized ETS-10 were tested using
water samples containing toxic heavy metals such as Pb2+, Cd2+ and Cu2+ under
single, binary or ternary systems. The selectivity, kinetics and equilibrium, efficiency
and ion exchange capacity of the ETS-10 were determined by Flame Atomic
Absorption Spectroscopy (FAAS).
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For comparison purpose, the LUDOX synthesized ETS-10 and RHA
synthesized zeolite such as Zeolite A, Zeolite X and Zeolite Y samples were tested
using water samples containing toxic heavy metals such as Pb2+, Cd2+ and Cu2+ under
single metal ion system. The selectivity, kinetics and equilibrium, efficiency and ion
exchange capacity of this LUDOX synthesized ETS-10 and zeolite will be
determined by Flame Atomic Absorption Spectroscopy (FAAS).
1.3 Objective of Study
(i) To synthesize the microporous titanosilicate 10 (ETS-10) using rice husk ash
as a silica source.
(ii) To modify the synthesized ETS-10 by desilication and ion-exchange methods.
(iii) To characterize the physico-chemical properties of the synthesized and
modified ETS-10.
(iv) To study the sorption properties of the synthesized and modified ETS-10 as
an ion exchanger for Pb2+, Cd2+ or Cu2+ in aqueous samples.
(v) To compare the sorption properties of ETS-10 and zeolite under single metal
ion system toward the removal of Pb2+, Cd2+ or Cu2+ in the aqueous samples.
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