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Sensors and Actuators B 130 (2008) 222–230

Effect of the chemical composition on the sensing properties ofIn2O3–SnO2 nanoparticles synthesized by a non-aqueous method

Giovanni Neri a,∗, Anna Bonavita a, Giuseppe Micali a, Giuseppe Rizzo a,Nicola Pinna b, Markus Niederberger c, Jianhua Ba c

a Department of Industrial Chemistry and Materials Engineering, University of Messina, Italyb Department of Chemistry, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal

c Max-Plank-Institute of Colloids and Interfaces, Research Campus Golm, 14424 Potsdam, Germany

Available online 9 August 2007

bstract

In2O3–SnO2 nanocrystals have been synthesized by a non-aqueous sol–gel technique with the aim to test them as sensing element in resistiveas sensors. The whole range of compositions between pure indium oxide and 100% tin oxide, was investigated. XRD, FT-IR, TEM and HRTEMnalyses of the synthesized nanopowders give evidence for remarkable structural and sizing variations depending on the tin concentration. Inarticular, with increasing tin content the mean crystallite size decreases, from 25 nm down to 1–2 nm and, at content higher than 75 wt%, it causesmodification of the lattice structure from cubic to tetragonal.

Electrical and sensing tests in dry air have been performed on planar sensor devices in thick film configuration depositing In2O3–SnO2 nanocrystals

y screen-printing. CO and C2H5OH have been tested as gas target. The results obtained are discussed in relation to the chemical and microstructuralroperties of the synthesized In2O3–SnO2 nanocrystals.

2007 Elsevier B.V. All rights reserved.

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eywords: Indium oxide; Tin oxide; Indium–tin oxide; Sol–gel routes; Gas sen

. Introduction

Metal oxides cover almost all aspects of materials sciencend solid state physics. Depending on their composition, thetructural and morphological characteristics, metal oxides offerany properties that are interesting for potential applications:agnetic, catalytic, optical, electrical (such as semiconductiv-

ty or superconductivity), etc. Moreover, the intrinsic propertiesf many metal oxides may be opportunely tailored by doping,ixing, sizing, shaping or texturing [1].Nanoscaling is another way to improve the properties of these

aterials or to achieve new properties [2]. The attempt to reducehe particle size for the sensing layer to the nanometer range,

s the new challenge of the research on gas sensors. In fact, aromoting effect on gas response characteristics was evidencedonsequently to nanosizing [3]. This effect is primarily linked to

∗ Corresponding author at: Contrada di Dio, Vill. S. Agata, 98166 Messina,taly. Tel.: +39 090 3977297; fax: +39 090 3977464.

E-mail address: neri@ingegneria.unime.it (G. Neri).

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925-4005/$ – see front matter © 2007 Elsevier B.V. All rights reserved.oi:10.1016/j.snb.2007.07.141

wider use of the sensing material in the receptor-transductionunctions. In fact, as a consequence of grain size reduction, theurface available for the gas target-sensing layer interaction isaximized. Moreover, when the particle size is small (<4–5 nm)

he gas interacting zone extends over the whole nanocrystali.e. the particle is fully depleted). Finally, nanoscaling playsfundamental role on structural (particle shape factor and planexposure), electronic and adsorption–desorption parameters, allactors influencing the sensing characteristics [4].

In previous papers we have reported data on resistive gas sen-ors based on pure In2O3 and SnO2 nanocrystals, confirmingheir superior sensing performances with respect to correspond-ng bulk materials [5–7]. The nanocrystals were synthesized bynon-aqueous sol–gel route [8]. Conventional aqueous sol–gel

outes allow to obtain metal oxides starting from low costolecular precursors (generally inorganic salts or metal organic

ompounds) via inorganic polymerization reactions such as

ydrolysis and condensation. These routes are simple, versa-ile and inexpensive but the control of the morphological andtructural characteristics of the final product is difficult. Theain drawbacks of sol–gel procedure carried out in aqueous

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olutions are in fact: (i) the fast hydrolysis rate of metal alkox-des which makes the control of the reaction difficult; (ii) theon-crystalline nature of the as-synthesized precipitates whichakes further thermal treatments at high temperature necessary.In comparison to reaction in aqueous media, the synthesis

f metal oxides nanoparticles in organic solvent provides betterontrol over particles size, crystallinity and surface properties8]. The absence of water, in fact, drastically reduces the reactionates allowing a more controlled crystallization.

As a continuation of the previous works, we preparedn2O3–SnO2 nanocrystals by the non-aqueous sol–gel route,nvestigating the whole range of compositions between purendium oxide and 100% tin oxide. The In2O3–SnO2 systemas so far less investigated for sensing applications: the targetases were both reducing gases and vapours (H2, CO, alco-ols) and oxidizing ones, particularly NOx [9–13]. Here, toave a preliminary screening of the sensing behaviour regard-ng the materials under study, CO and ethanol were testeds gas target. Then, a microstructural characterization wasarried out with the purpose to better understand the elec-rical and sensing behaviour of In2O3–SnO2 nanocrystals inhe configuration of thick film devices fabricated by screen-rinting.

. Experimental

.1. Samples preparation and characterization

The In2O3–SnO2 nanopowders were prepared by theon-aqueous sol–gel technique as follows. The starting pre-ursors, indium(III) acetylacetonate, indium(III) isopropoxide,nd tin(IV) tert-butoxide, were stirred with anhydrous benzyllcohol and then transferred in autoclave and maintained at00–220 ◦C for 48 h. The obtained powders were washed withhloroform and dried in air at 60 ◦C. The whole range of relativeatios between pure indium oxide and tin oxide was investigated.amples were codified as ITO-xx, where xx is a numeric valueorresponding to the SnO2 wt.% loading. Complete informationbout the synthesis procedures can be found in Ref. [5] for theure In2O3 and SnO2 samples, in Ref. [6] for the ITO-90 andef. [16] for the other compositions.

XRD analysis was carried out on a Italstructure diffrac-ometer mod. APD 2000 in the 2θ range from 10 to 90◦. The

ean particles diameter was calculated from line broadeningnalysis of the diffraction peaks. The average crystallite size,D〉, was estimated using the Scherrer equation as follows:D〉 = 0.9λ/B cos θ where λ, B, and θ are the X-ray wavelengthf the radiation used (Cu K�1 = 1.54056 A), the full width atalf maximum (FWHM) of the diffraction peak, and the Braggiffraction angle, respectively.

FT-IR spectra were recorded with a Nicolet Nexus 5770 FT-R spectrophotometer having a resolution of 4 cm−1 equipped

ith a diffuse reflectance cell by Thermo mod. Collector II. To

cquire the spectra, the powdered samples, mixed with KBr,ere mounted on the top of the IR diffuse reflectance cellolder.

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tors B 130 (2008) 222–230 223

TEM and HRTEM analyses were carried out on JEOL micro-copes (mod. JEM2010 and JEM2100F), both equipped withxford Instrument INCA-200-TEM systems that allowed ele-ental analysis using energy-dispersive X-ray spectroscopy

EDXS) and on a Philips CM200 FEG equipped with a filedmission gun.

.2. Electrical and sensing test

In order to fabricate the sensor devices, the nanopowders wereixed with water to obtain a paste and then screen printed on

lumina substrates (3 mm × 6 mm) supplied with interdigitatedt electrodes and heating elements. Electrical measurementsere carried out in the working temperature range from 200

o 350 ◦C, with steps of 50 ◦C. The concentrations of targetases were varied from 100 to 1000 ppm for CO and from 50o 400 ppm for ethanol. Measurements were performed underdry air total stream of 200 sccm, collecting the sensors resis-

ance data in the four point mode. A multimeter data acquisitionnit Agilent 34970A was used for this purpose, while a dual-hannel power supplier instrument Agilent E3632A allowed toive the input to the sensors and to perform measurements atuper-ambient temperatures. The full automated and PC assistedeasurement apparatus is equipped with three main systems

llowing to: (i) produce and supply a constant and controlledtream of gas into the test chamber; (ii) regulate and con-rol the sensor working temperature and (iii) read the outputignal.

The gas response, S, is defined as the ratio Rair/Rg whereair is the electrical resistance of the sensor in dry air andg its electrical resistance at different reducing gas concen-

rations. The response time, τres, is defined here as the timeequired for 90% reduction in resistance when a reducing gass introduced into an environment of air. The recovery time,rec, is the time required for 90% increment in resistance whenhe reducing gas is turned off and air is reintroduced into thehamber.

. Result and discussion

.1. Powders characterization

The In2O3–SnO2 nanopowders synthesized by the non-queous sol–gel method were characterized by TEM, HRTEM,RD and FT-IR. TEM observations have clearly shown homoge-eous samples, with narrow grains size distribution and uniformarticle morphologies. Moreover, the addition of tin to purendium oxide leads to tin-indium mixed oxides with smallerrains size (Fig. 1). In the case of ITO-00, cube-like In2O3 grainsith an average size of about 25 nm have been observed. Increas-

ng the tin loading, the grains become progressively smaller,own to 1–2 nm on samples with 50 wt% SnO2 or higher, assum-ng a spherical morphology.

High resolution images (Fig. 2a and b) indicate that all sam-les are crystalline with well-developed lattice fringes even inhe case of the smaller grain size [8]. Power spectra (Fig. 2cnd d) have been used to elucidate the crystal structure of the

224 G. Neri et al. / Sensors and Actua

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Fig. 1. TEM micrographs of some ITO-XX samples.

ndividual grains. They show that In2O3–SnO2 nanopowdersith SnO2 content <75 wt% have a cubic structure, while the

etragonal structure is characteristic of samples with higher tin

oncentrations.

In Fig. 3 the XRD powder patterns of the In2O3–SnO2 sam-les are displayed. Up to a SnO2 loading of 75 wt%, the samplesave the same cubic, bixbyite structure, of In2O3, (JCPDS 6-

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tors B 130 (2008) 222–230

416). Samples with a loading of SnO2 higher than 75% shownstead the characteristic reflections of the tetragonal cassiteritetructure, SnO2 (JCPDS 41-1445).

It can be further observed that, increasing the tin content, theiffraction peaks in the XRD patterns become larger, indicatingsizing effect. Fig. 4 reports data regarding to the mean crys-

allite size of the ITO powders, as determined by the Scherrerquation from the line broadening of the (1 1 0) reflection forhe tin oxide-like structured samples and the (2 2 2) reflectionor the indium oxide-like structured ones. In agreement withEM observations, a progressive reduction of grains size haseen found. This effect is more evident at the lower tin loading,hereas from ITO-50 to ITO-100 the crystallite size remainuite constant.

Fig. 5 shows FT-IR spectra, in the region between 400 and000 cm−1, of indium–tin oxide nanopowders with differentnO2 loading. The sample ITO-00 shows main bands centred at15, 570, 542 and 510 cm−1, characteristics of crystalline In2O314]. With increasing addition of tin, these bands decrease inntensity and new peaks can be observed at 1416 and 1598 cm−1,ikely associated with the presence of tin in the indium oxide

atrix. Peaks related to isolated SnO2, for example the νSn-Oand at 638 cm−1 [15], are present only on samples with highin loading (>75%). On these latter samples the presence of aide shoulder, at lower wavenumber, on the peak at 638 cm−1

ives indication of the substitution of Sn with In ions.It is interesting to note that the FTIR patterns of the

ndium–tin oxide powders follows strictly the structural changeromoted by the addition of Sn to In2O3. Indeed, a signifi-ant modification of the FTIR pattern has been observed whenhe powders microstructure change, at higher tin loading, fromubic to tetragonal, in full agreement with XRD and HRTEMesults.

.2. Electrical tests

In order to collect data on the electrical behaviour of then2O3–SnO2 nanopowders, measurements were carried out byeating slowly (6 ◦C/min) the samples, deposited as thick filmsn alumina substrates provided with interdigitated electricalontacts, from room temperature up to 350 ◦C in dry air. Fig. 6eports the variation of the electrical resistance with the temper-ture of some samples. At room temperature samples with Snoading higher than 50 wt% show very high resistance (higherhan 107 �). In2O3-rich samples have instead a lower resis-ance (up to 5 order of magnitude with respect to SnO2-richamples). The decrease of resistance occurring on all samplesncreasing the temperature up to 150 ◦C is due to the ther-

al activation of charge carriers and/or water (which acts as aonor molecule) desorption caused by heating and favoured byry air flushing. Above this temperature, the increase/decreasef resistance during heating treatment in air can be causedy adsorption/desorption of electron attractive species (mainly

H , O2 , O ) activated while temperature progressively rises.he above processes are generally limited to the surface of theensing layer, but in our case, their effects likely extend to thehole grain bulk because of the nanometric size. In this tem-

G. Neri et al. / Sensors and Actuators B 130 (2008) 222–230 225

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(ii) ITO samples containing up to 25 wt% of SnO2, show astrong decrease of the intensity of the above maximum,

Fig. 2. HRTEM images of ITO-00 (a) and ITO-100 (b

erature interval (150–350 ◦C) different behaviours among theamples investigated have been noted:

(i) the ITO-00 sample shows a progressive resistance increaseup to 280 ◦C. This can be attributed to oxygen adsoption anddissociation according to the following surface reactions:

O2 + e− → 2O2−

O2− + e− → 2O−

Fig. 3. XRD patterns of In2O3–SnO2 nanopowders.Fv

ples and respective (c) and (d) power spectrum (PS).

causing a decrease in the number of charge carriers (elec-trons). Above this temperature the resistance tends todecrease, because the desorption of oxygen species becomeprevailing.

with a shift at lower temperature (between 200 and 250 ◦C).

ig. 4. Mean grains size by XRD measurements of In2O3–SnO2 nanopowderss. SnO2 loading.

226 G. Neri et al. / Sensors and Actuators B 130 (2008) 222–230

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Fig. 5. FT-IR spectra of In2O3–SnO2 nanopowders.

iii) For samples with higher tin content, two maxima havebeen observed at significantly lower temperature (125 and200 ◦C).

Fig. 7 reports the resistance in dry air as a function of SnO2ontent at different temperatures. Pure In2O3 is a semiconduct-ng oxide with an high intrinsic concentration of carriers and thisxplain the low resistance value measured on the sample ITO-0. Addition of tin causes, initially, a strong resistance decreaseup to 2 order of magnitude). The minimum of resistance

maximum conductance) was observed on the sample ITO-15.hen, the resistance value rises with further increase of the tinontent.

ig. 6. Variation of resistance in dry air vs. temperature of the ITO-based devices.

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ig. 7. Resistances in dry air of ITO-based devices at different working temper-ture vs. SnO2 loading.

In a recent paper some of us investigated in detail ITO sam-les having in their composition 0–30 wt% of SnO2 [16]. Dataeported are in good agreement with the present results. It hashown that on samples from ITO-00 to ITO-15 the specific con-uctivity increase by increasing the Sn content. This effect haseen attributed to the formation of more conductive ITO (indiumin oxide) solid solution, in which Sn4+ ions hosted in the In2O3tructure with variable loading up to 12–15%. It is in fact widelyeported that the substitution of In3+ with Sn4+ ions in the In2O3-type semiconductors causes an increase of charge carriers [17].t higher loading, the conductivity drops and this effect can be

ttributed to oxygen blocking by Sn4+ which causes a lowervailability of charge carriers in the ITO semiconductor and/orecondary phase formation. However, considering the reductionf grain size with tin loading as discussed before, an effect ofhis parameter on the decrease of conductivity noted on sam-les with SnO2 loading higher than 15 wt%, cannot be excludedither. Indeed, as grains size decreases, the electrical resistances drastically enhanced, particularly when nanocrystallites sizes smaller than twice of the space-charge layer thickness [18].

Regarding the resistance variation with tin loading at differ-nt temperatures, differences were noted between the In2O3-likeexcept ITO-00 and up to ITO-75) and the SnO2-like struc-ured (ITO-90 and ITO-100) samples. While the temperaturehanges hardly affect the resistance on the first series, for thethers samples the resistance decreases strongly by increasinghe temperature. This behaviour is in agreement with the trendf resistance vs. temperature shown in Fig. 6.

.3. Sensing tests

Sensing tests, aimed to find the optimal conditions of opera-ion of sensors for CO and ethanol, are reported in Figs. 8–10. Foroth gases the operating temperature in the range of 200–300 ◦C

epresents the better compromise between high sensitivity andast response/recovery time. The responses are reversible on allamples and display a linear trend, when plotted in a log–logcale, as a function of the gas target concentration.

G. Neri et al. / Sensors and Actuators B 130 (2008) 222–230 227

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ig. 8. Transient response, response vs. temperature and calibration curve plotsor ethanol detection on ITO-08.

The responses observed on all samples investigated arendicative of a typical n-type semiconductor response behaviour,hich involves adsorbed atmospheric oxygen in the sensingechanism. Oxygen molecule chemisorbs on the surface of the

xide semiconductor as O2− or O−, removing an electron from

he conduction band of the n-type semiconductor and develop-

ng a depletion region on the grain surface, depending on theature and stoichiometry of the oxide semiconductor and parti-le size. The decrease in the resistance is due to the oxidationf the reducing gases upon coming in contact with the oxide

[t

ig. 9. Transient response, response vs. temperature and calibration curve plotsor CO detection on ITO-50.

emiconductor surface, which liberates free electrons in theulk.

CO reacts with the chemisorbed oxygen through the surfaceeaction (1), in which [O] represents the surface oxygen ions:

The oxidation of ethanol takes place instead via two routes19], one the dehydrogenation to acetaldehyde as shown in reac-ion (2) and the other, the dehydration to ethylene, as given by

228 G. Neri et al. / Sensors and Actuators B 130 (2008) 222–230

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(ifeswptirlinked to the different amount of adsorbed oxygen on the surface(high resistance means more surface oxygen available to reactwith reducing gases), which initially decreases with Sn load-

ig. 10. Transient response and calibration curve plots for CO detection atifferent temperatures.

eaction (3):

2H5OH + [O] → CH3CHO + [O] → CO2 + H2O (2)

nd

2H5OH + [O] → C2H4 + [O] → CO2 + H2O (3)Fe

Fig. 11. Relative response to CO, ethanol and NO2 vs. SnO2 loading.

he oxidative hydrogenation reaction is mainly catalyzed byhe basic sites and dehydration is favored by the acidic sites20]. It is known that the first one has more sensitivityhan the latter [21]. The intermediate products, acetaldehydend ethylene are subsequently reduced to carbon dioxide andater.Data related to response towards CO (1000 ppm) and ethanol

100 ppm) are summarized in Fig. 11, relatively to the best work-ng temperature for each gas tested. A similar trend was observedor both gases. Pure In2O3 (ITO-00) has a high sensitivity tothanol and CO. The response decrease strongly adding tin,howing a minimum value around 15% of SnO2. This coincideith the higher conductance value for all In2O3–SnO2 com-ositions. Then, a further increase of tin causes an increase ofhe response showing a maximum around 90% of SnO2. It isnteresting to observe that the response follows fairly well theesistance trend (compare Fig. 7 and Fig. 11). This could be

ig. 12. Response and recovery time of In2O3–SnO2 sensors to 100 ppm ofthanol as a function of SnO2 loading.

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ng, turning to increase on the tin-rich samples with the smallerarticle size.

In Fig. 12 the trend of response and recovery time is reporteds a function of tin loading. At all temperatures tested, a fastesponse was noted in despite of a really slow recovery time.

oreover, particularly for the response time, very large differ-nce has been registered on samples of different composition.his confirms that the sensing mechanism depend strongly on

he surface adsorption–desorption equilibria.To find correlations between the electrical/gas sensing prop-

rties and the morphological and microstructural characteristicsf the samples is more difficult. Indeed, it should be consideredhat the mechanism of gas sensing is fairly complex and theas sensing properties depend on a numbers of parameters suchs chemical (catalytic and acid–base properties of the surface),icrostructural (particle size, crystal structure) and electronic

haracteristics (electronic structure, Fermi level position, trans-ort properties). The rationalization of data obtained on all ouramples is then not straightforward because parameters con-ributing to the sensitivity, may change contemporary.

Here, we limit our discussion only to chemical andicrostructural characteristics. The catalytic properties assumegreat importance on sensing mechanism, particularly if nobleetals are present as dopant [22]. In any case, at elevated tem-

eratures undoped metal oxides can promote oxidation of gasarget and/or intermediates involved in the processes (1)–(3).tudies over catalytic properties of In2O3 are scarce [23] andcomparison with SnO2 has been not so far reported. Also

he surface acidity can play a key role, particularly for ethanoletection. In previous papers we reported that the addition ofsecond oxide phase (CeO2) can modify the acid-base charac-

eristics of the semiconducting metal oxide (Fe2O3) influencinghe response to alcohols [24,25]. In particular it has been shownhat the sensor response is in relation to the number of basicites on the surface. A similar acid–base interaction is likelynvolved in the adsorption and reaction of ethanol on the sur-ace of our In2O3–SnO2-mixed oxides. Regarding this aspect,n absence of any direct measurements of surface acidity, ithould also be taken into account that indium cations in In2O3re less electronegative than tin cations in SnO2, i.e. In2O3as a more basic character than SnO2. Hence, at the In2O3urface dehydrogenation is a more favourable process than dehy-ration leading to a high sensitivity to ethanol. On the otherand, on SnO2 surface, this pathway is limited by the lessasic character of the material. For In2O3–SnO2 samples ofntermediate composition, the prediction of surface acidity isot simple. Therefore, a measurement of the catalytic prop-rties (oxidation activity towards CO, EtOH, and VOC) andurface acidity of these samples by means FT-IR spectroscopyf adsorbed basic probe molecules (i.e. pyridine), has beenlanned.

Finally, the microstructure of the mixed In2O3–SnO2 of dif-erent composition should be taken into account. The decrease

f particle size with tin addition is the first parameter to takento account. However, considering the decrease of both elec-rical resistance and sensitivity observed on samples with lowin loading (<25 wt%) besides the reduction of the grains size,

tors B 130 (2008) 222–230 229

t can be concluded that in this composition range other param-ters are more important. The effect of particle size reductionnstead seems to play a main role at tin loading higher than5%.

Characterization data reported in the previous section havehown that Sn4+ and In3+ ions can enter within the lattice struc-ure of the In2O3 and SnO2, respectively, leading to the formationf solid solutions. This, coupled with the small grain size, causeshe development of a great number of defects and imparts a largereterogeneity on the surface of the sensitive layer. In additione would consider also the different crystal structure of samples

cubic vs. tetragonal). The effect of different crystal structuresn the sensing properties of ITO sensors has been studied by Huhnd coworkers [26]. They found that rhombohedral ITO-basedensors have high sensitivity compared to the cubic ITO-basedensors.

. Conclusions

The effect of different SnO2 loading on the microstructural,lectrical and gas sensing properties of In2O3 samples syn-hesized by a non-aqueous sol–gel technique was evaluated.n2O3–SnO2 nanocrystals have an uniform grain morphologynd narrow particle size distribution. A detailed characteriza-ion proved considerable structural and sizing modifications withhe increase of concentration of tin in the mixed oxide formu-ation. The crystallite size was found to decrease from 25 nmown to 1–2 nm and, at content higher than 75 wt%, tin causesmodification of the lattice structure from cubic to tetragonal.O and C2H5OH sensing tests in dry air have been performedn planar sensor devices in thick film configuration depositingn2O3–SnO2 nanocrystals by screen-printing. The results haveeen discussed in relation to the chemical and microstructuralroperties of the synthesized In2O3–SnO2 nanocrystals. It wasound that different parameters (particle size, acid–base proper-ies, formation of solid solutions, surface heterogeneity, crystaltructure) can contribute to the complex sensing behaviour reg-stered on these samples.

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ihIss

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iographies

iovanni Neri received his degree in chemistry from the University of Messinan 1980. He is full professor of chemistry and Director of the Department ofndustrial Chemistry and Materials Engineering of the University of Messina.is research activity, covers many aspects of the synthesis, characterization

nd chemical–physics of solids with particular emphasis to catalytic and sens-ng properties. In the latter research area his work has been focused on thereparation of metal oxide thick and thin films and their application in gasensors.

nna Bonavita received her degree in materials engineering from the Univer-ity of Messina in 1997. At present time she is at the Department of Industrialhemistry and Materials Engineering of the University of Messina. Her researchctivity concerns with the preparation, characterization and development ofemiconductor films for gas sensing applications.

iuseppe Micali received his degree in electronic engineering from the Uni-ersity of Messina in 2003. At present time he is at the Department of Industrialhemistry and Materials Engineering of the University of Messina. His researchctivity concerns with the implementation of software procedures for automatednstrumentation control and with the electrical characterization of gas sensingevices.

iuseppe Rizzo received his degree in chemistry from the University of Messinan 1999. Actually he works at the Department of Industrial Chemistry and Mate-ials Engineering of the University of Messina. His research activity is focusedn the synthesis and characterization of materials by sol–gel method both foratalytic and optical applications.

icola Pinna, chemist, senior researcher, received his degree in chemistry in998 and his PhD in 2001 from the University Pierre et Marie Curie (Paris,rance). In 2002, he went to the Fritz Haber Institute of the Max Planck SocietyBerlin, Germany). In 2003, he joined the Max Planck Institute of Colloids andnterfaces (Potsdam, Germany). In 2005, he joined the Martin Luther Univer-ity, Halle-Wittenberg (Halle, Germany), as an associate professor of inorganichemistry. In 2006 he joined the associated laboratory CICECO at the Universityf Aveiro in Portugal as senior researcher. His research activity is focused on theynthesis of nanomaterials by non-aqueous sol gel routes, their characterizationnd the study of their physical properties.

arkus Niederberger studied chemistry at the Swiss Federal Institute of Tech-ology (ETH) Zurich, where he also received his PhD degree in the year 2000.fter a postdoctoral stay at the University of California at Santa Barbara (USA),e became group leader at the Max Planck Institute of Colloids and Interfaces atotsdam (Germany). His main research interests lie in the field of non-aqueousol–gel chemistry and synthesis and assembly of metal oxide nanoparticles.

ianhua Ba received his Bachelor degree in polymer materials and engineer-ng in 2001 at Beijing Institute of Technology (China) and his Master degree

n polymer science in 2004 at Free University Berlin (Germany). In 2004,e became a doctoral candidate at the Max Planck Institute of Colloids andnterfaces (Potsdam, Germany) and is currently working on the non-aqueousynthesis of metal oxide nanocrystals and their assembly into mesoporoustructures.