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Sensors and Actuators B 177 (2013) 1180– 1188

Contents lists available at SciVerse ScienceDirect

Sensors and Actuators B: Chemical

journa l h o me pa ge: www.elsev ier .com/ locate /snb

ynthesis, characterization and alcohol-sensing properties of rare earth dopedn2O3 hollow spheres

ing Zhang, Fubo Gu, Dongmei Han, Zhihua Wang ∗, Guangsheng Guo ∗

tate Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing, 100029, China

r t i c l e i n f o

rticle history:eceived 13 August 2012eceived in revised form 16 October 2012ccepted 3 December 2012

a b s t r a c t

In2O3:RE (RE = La, Er, Yb) hollow spheres were successfully prepared by using carbon sphere as template,and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelec-tron spectroscopy (XPS) and Raman spectroscopy. The experimental results showed that the synthesizedhollow spheres had a diameter of ca. 300 nm and the thickness of the shells was ca. 40 nm. The doping of

vailable online 13 December 2012

ey words:n2O3

ollow sphereare earth

rare earth improved the responses of In2O3 sensors to alcohol at the optimal operating temperatures, buthad no obvious effect on the response/recovery times. Moreover, the In2O3:RE sensors exhibited goodselectivity and stability. The possible reasons for the effect of rare earth doping on the alcohol-sensingproperties were studied. The enhancements of the response may be attributed to high surface activity ofthe In2O3:RE, which resulted from the lattice defect and chemisorbed oxygen.

ensor

. Introduction

Indium oxide (In2O3) is an important wide band gap (3.5–3.7 eV)ransparent semiconductor, making it a promising candidate in thepplication of alcohol sensors [1]. Recently, many works have beenocused on improving the sensitivities of gas sensors [2–4]. In par-icular, hollow structures have promising potentials due to theirow density, large surface areas and much more capacious inter-paces [5–7].

Doping is another effective and simple way to improve theas-sensing properties of In2O3 by increasing the response andelectivity, stability, reducing the operating temperature andecreasing the response/recovering times [8,9]. For example, Patelt al. have fabricated indium tin oxide (ITO) thin film sensors by theirect evaporation method [10]. Patil et al. have prepared a highensitive and selective Co-doped In2O3 acetone sensor by sprayyrolysis technique [11]. Recently, rare earth doped compoundsave been studied because of their particular characteristics ofood thermal stability and high chemical reactivity. Kapse et al.ave prepared La-doped nanocrystalline In2O3 gas sensors by aimple hydrothermal decomposition route and the doping of La3+

bviously improving the response to H2S [12]. Niu et al. have

eported the H2S sensing properties based on In2O3 sensors dopedith 5 wt.% Eu2O3, Gd2O3, Ho2O3, and the results indicated that

∗ Corresponding authors.E-mail addresses: zhwang@mail.buct.edu.cn (Z. Wang), guogs@mail.buct.edu.cn

G. Guo).

925-4005/$ – see front matter © 2012 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.snb.2012.12.024

© 2012 Elsevier B.V. All rights reserved.

Ho-In2O3 sensor exhibited the highest response value because ofits smaller grain size and larger lattice distortion [13].

Hence, according to the excellent gas-sensing performances ofrare earth doped semiconductor sensors, a series of rare earthdoped In2O3 hollow spheres were prepared by a carbon spheretemplate route in this paper. Then the gas-sensing properties of thesynthesized hollow spheres for alcohol vapors were investigated,and the reasons for the differences of the sensitivity to alcoholvapors of the In2O3:RE sensors were explored.

2. Experimental

2.1. Synthesis

All reagents used in this work were analytical grade. Carbonspheres were synthesized in glucose solutions by a microwave-hydrothermal route [14], and the used carbon spheres had anaverage diameter of ca. 800 nm. In2O3:RE hollow spheres wereobtained by electrostatic absorption of RE3+ and In3+ on the carbonspheres and subsequently removed the templates by calcinations.Firstly, 1 mmol InCl3·4H2O and 0.05 mmol RE(NO3)3·xH2O (RE = La,Er, Yb) were dissolved in 50 ml of deionized water. Then theprepared carbon spheres (0.2 g) were dispersed in the solution.After sonicated for 15 min, the mixture was transferred into aTeflon-lined stainless-steel autoclave (100 ml) and maintained at

180 ◦C for 6 h. Then the precipitate was separated by centrifuga-tion, washed with deionized water and ethanol, and dried at 60 ◦C.Finally, the obtained sample was calcined at 500 ◦C for 3 h in oxygenatmosphere.

T. Zhang et al. / Sensors and Actuators B 177 (2013) 1180– 1188 1181

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40 nm. The EDS spectra (not shown here) show the presence of In,O with an approximate stoichiometry of In2O3 and the presenceof rare earth in the samples, which indicates that the rare earth isdoped into In2O3. Furthermore, a practical content of rare earth in

Fig. 1. TEM images of In2O3:RE hollow sp

.2. Characterization

The samples were characterized by X-ray diffraction (XRD),ith a scanning speed of 10◦/min, on a Rigaku D/Max2500VB2+/PCiffractometer using graphite monochromatized Cu K� radiation� = 1.54056 A). The mean grain size was estimated using theebye-Scherrer equation, D = K�/(ˇ cos �), where D is the averagerystal diameter, K is a constant related to the shape of the crys-allites (K = 0.89), � is the wavelength of the X-rays employed, ishe corrected peak width (full width at half-maximum), and � ishe diffraction angle. The morphologies of the samples were char-cterized by transmission electron microscopy (TEM, Hitachi-800).PS measurements were performed in a VG Scientific ESCALAB 250pectrometer. The Raman spectra were recorded from 200 nm to00 nm by a 514 nm excitation (Invia Raman Spectrometer man-factured by U.K. Renishaw Corporation). Elemental analyses of

ndium and rare earth of samples were carried out by inductivelyoupled plasma atomic emission spectroscopy (ICP-4700).

.3. Gas-sensing test

The WS-30A (Weisheng Instruments Co., Zhengzhou) gas-ensing system was used to test the sensing properties of theensors. The obtained samples were mixed with ethanol in an agate

ortar to form a homogeneous paste. The paste was coated on a

eramic tube with a pair of Pt wires covered on Au electrodes, andged at 300 ◦C for 24 h in air. Then the ceramic tube was welded on aubstrate and a Ni–Cr wire coil throughout the tube was employed

, In2O3:La (a), In2O3:Er (b), In2O3:Yb (c).

as a heater to control the working temperature by tuning the heat-ing voltage (Scheme 1).

The sensor response is defined as Rair/Rgas, which is calculatedautomatically by the computer of the gas-sensing test system,where Rair and Rgas are the electrical resistances of the sensors inair and in test gas, respectively.

3. Results and discussion

3.1. Morphologies and compositions of the products

Fig. 1 shows the TEM images of the In2O3:RE hollow sphereswith a diameter of ca. 300 nm, and the thickness of the shells is ca.

Scheme 1. Structure illustration of the sensor.

1182 T. Zhang et al. / Sensors and Actuators B 177 (2013) 1180– 1188

tric

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Table 1Mean grain sizes, lattice constants and ICP results of the samples.

Samples Grain size (nm) Lattice constant a = b = c (Å) RE/In (mol %)

In2O3:La 39.1 10.1532 5.3

elements. The peaks at 168.9 eV, 837.8 eV, 185.4 eV attribute to

Fig. 2. XRD patterns of In2O3 and In2O3:RE hollow spheres.

he samples was obtained by ICP, as shown in Table 1. The testingesults indicate that the practical ratio of rare earth and indiumn different samples is almost the same and has a little increaseompared with the theoretical contents (5 mol%).

The typical XRD patterns of the samples are shown in Fig. 2.he as-prepared In2O3 and the In2O3:RE hollow spheres are well-rystallized, and the diffraction peaks can be indexed to be cubic

n2O3 (JCPDS card no. 06-0416). No additional diffraction peaksf rare earth oxides are detected. Furthermore, the peaks of then2O3:RE shift a little compared with the pure In2O3, which may

Fig. 3. XPS spectra of In2O3 and In2O3:RE hollow spheres

In2O3:Er 34.0 10.1579 5.8In2O3:Yb 33.1 10.1544 5.7In2O3 39.5 10.1421 –

be due to the dope of rare earth elements into the In2O3 crystallattices.

The lattice constants were calculated from the XRD peaks andthe mean grain sizes of the samples were estimated using theDebye-Scherrer equation. The calculated values were listed inTable 1. The mean grain sizes of the prepared samples were ca.30∼40 nm, and the lattice constants of the In2O3:RE were changedcompared with the pure In2O3 when the indium atom in the latticesis replaced by the rare earth atoms [15].

The surface element compositions of In2O3:Er, In2O3:La,In2O3:Yb and pure In2O3 were also studied by XPS analysis asshown in Fig. 3. The XPS spectra of the samples show that the hol-low spheres are all composed of indium and oxygen. However, theatomic ratio of oxygen and indium are larger than the stoichiometryof In2O3, indicating more absorbed oxygen on the material surfaces,which may be due to the calcinations in the oxygen atmospheresand the active In2O3 surfaces absorb more oxygen.

The insets of Fig. 3 are the high resolution spectra of rare earth

Er4d, La3d5, Yb4d5, respectively. Compared with the peaks at167.3 eV, 836.0 eV, 182.1 eV of the pure Er2O3, La2O3, Yb2O3, allof the peaks of rare earth atoms shift to the high binding energies

, In2O3:Er (a), In2O3:La (b), In2O3:Yb (c), In2O3 (d).

T. Zhang et al. / Sensors and Actuators B 177 (2013) 1180– 1188 1183

Table 2XPS analysis results of In2O3:Er, In2O3:La, In2O3:Yb and In2O3.

Samples O/In Peak (RE) Peak (In3d5/2) Peak (O1s) RE/In (%)

In2O3: Er 4.24: 2 168.96 443.79 529.35 2.56443.87 530.13 2.65444.27 529.86 3.87444.09 529.61 –

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In2O3: La 4.06: 2 837.85

In2O3: Yb 4.76: 2 185.44

In2O3 5.16: 2 –

hich indicate that Er, La, Yb doped into In2O3[16]. The inset ofig. 3(d) is the characteristic spin-orbit split for In3d5/2 and In3d3/2f trivalent indium, the peaks of In3d5/2 of the In2O3:RE shift tohe low binding energies compared with the pure In2O3 shownn Table 2. This can be explained by the charge density differenceetween metal ions. The ion radius of In3+, Er3+, La3+, Yb3+ are 80,00, 118 and 99 pm, respectively. The higher charge density ionsf RE3+ can withdraw the electrons from indium, so the screeningffect of electrons would decrease for indium, but increase for rarearth. The corresponding binding energies of In3d5/2 orbit decreasend the RE3+ increase [17,18]. This also implied that rare earth ionsoped into the In2O3 lattice, indicating an electronic interactionetween In2O3 and Er3+, La3+, Yb3+.

Raman spectroscopy is a powerful technique to study dopingffects as the incorporation of dopant leads to the shifts of theeaks’ position [19]. Fig. 4 shows the Raman spectra of the pure

n2O3 and the In2O3:RE hollow spheres, the observed Raman bandst 307 cm−1, 366 cm−1, 497 cm−1, and 628 cm−1 are assigned to beubic In2O3 [20]. The peak at 307 cm−1 is assigned to the bend-ng vibration of ı(InO6) octahedrons; the other two peaks 497nd 628 cm−1are assigned to the stretching vibrations of the same(InO6) octahedrons; the 366 cm−1 is assigned to the stretchingibrations of the In-O-In. However, the corresponding data forn2O3:RE are 307, 495, 628, and 363 cm−1 (Er); 307, 495, 628,nd 363 cm−1 (La); and 306, 494, 628, and 367 cm−1 (Yb), respec-ively. The Raman shift indicates that the doping of Er3+, La3+, Yb3+

ay lead to a structural disorder and oxygen deficiencies of In2O321,22].

.2. Gas-sensing test

Operating temperature and response The responses of gas sen-

ors are greatly affected by the operating temperatures and theoncentrations of testing gases. Fig. 5 illustrates the response of theure and the In2O3:RE hollow spheres sensors to 100 ppm alcoholapors at different operating temperatures. It is observed that the

Fig. 4. Raman spectra of In2O3 and In2O3:RE hollow spheres.

Fig. 5. Response curves of In2O3 and In2O3:RE hollow sphere sensors at differentoperating temperatures.

responses of all the samples improve with an increase of the oper-ating temperatures, In2O3:Er and In2O3:La exhibits the maximumresponses to 100 ppm alcohol at 215 ◦C, however, the maximumresponses to In2O3 and In2O3:Yb appear at 235 ◦C. When the oper-ating temperature further increase, the responses will decrease.This can be explained as follows: at low temperature the adsorbedalcohol molecules are not activated enough to overcome the acti-vation energy barrier to react with the adsorbed oxygen species,while at high temperatures the gas adsorption is too difficult to beadequately compensated for the increased surface reactivity [17].It can be found that the doping of Er and La decrease the optimumoperating temperature.

From the response curves in Fig. 5, the In2O3:Er, In2O3:La andIn2O3:Yb sensors possess much higher responses than pure In2O3 atthe optimal operating temperature (215 ◦C). The higher responsesare probably attributed to their higher surface activities, whichresult in stronger interactions between alcohol molecules and thesurface active sites [23]. Fig. 6 shows the dynamic responses of theprepared sensors to different concentrations (7∼161 ppm) of alco-hol vapors at 215 ◦C. It is clear that all the sensors exhibit excellentrepeatability and stability.

The variation of the responses of the In2O3 and the In2O3:REhollow spheres sensors with the concentrations of alcohol vaporsis shown in Fig. 7. When the alcohol concentration is in the range of2∼215 ppm, the logarithm of response shows good linearity withthe logarithm of alcohol concentration. The linear relationship canbe expressed as the following equations, in which Eqs. (1)–(4) standfor In2O3:Er, In2O3:La, In2O3:Yb, In2O3, respectively.

Y = 0.95x − 0.46 (1)

Y = 0.91x − 0.47 (2)

Y = 0.68x − 0.02 (3)

Y = 0.55x − 0.08 (4)

1184 T. Zhang et al. / Sensors and Actuator

Fd

ab

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ig. 6. Dynamic response curves of In2O3 and In2O3:RE hollow sphere sensors toifferent concentrations of alcohol.

The linear trend can be related to the conductance model,ccording to the model, the response of the samples is explainedy using the following equation [24,25]:

og�

�0= Ag + log pg (5)

here �0 denotes the conductance in the absence of the target gas,

g is the gas partial pressure, Ag is a prefactor, and is the responserder, this is usually 1 or 1/2, depending on the charge state of theurface species, the stoichiometry of the elementary surface reac-ions, and the microstructure of the materials [24]. The values of pg

ig. 7. Variation curves of the responses of In2O3 and In2O3:RE hollow spheres sensors wid).

s B 177 (2013) 1180– 1188

and �/�0 were replaced by the concentrations of alcohol and theresponses of gas sensors, respectively. Hence, the slopes of straightlines would be the values of gas sensors. From Eqs. (1) to (4), the

values of In2O3, In2O3:Er, In2O3:La and In2O3:Yb are 0.55, 0.95,0.91 and 0.68, respectively. It can be found that the doping of Er,La, Yb increased the values, which can be explained that the elec-tronic interaction between In3+ and Er3+, La3+, Yb3+, resulting thevariation of the microstructure of the materials and the increase of

values.Response and recovery time. The sensor responses and the

response/recovery times of the pure In2O3 and the In2O3:RE hol-low spheres are shown in panels a and b of Fig. 8, respectively.The response times of gas sensors at 215 ◦C are all very fast to be8∼10 s, and the recovery times are all 20∼24 s, indicating that thedoping of rare earth ions just increase the response values to alco-hol and have no obvious effect on the response/recovery times ofgas sensors. The long recovery times may relate to their hollow andporous structures. When the sensor was exposed to gases, alcoholmolecules could diffuse into the inner surfaces of hollow spheresthrough the pores to react with oxygen species. When the gasesremoved from the surfaces of gas sensors, it is difficult for the inneralcohol molecules to escape from the pores of hollow spheres andresulting in the increase of recovery times [26].

Selectivity and stability. The responses of pure In2O3 and theIn2O3:RE sensors to 100 ppm hexamethylene, acetone, dimethyl-

benzene, methanol, formaldehyde, NO2, alcohol at 215 ◦C areshown in Fig. 9(a). Obviously, the responses of the prepared sensorsto alcohol vapors are much higher than to other gases, indicat-ing that the In2O3 sensors exhibit good selectivity to alcohol. The

th the concentration of alcohol vapors, In2O3:Er (a), In2O3:La (b), In2O3:Yb (c), In2O3

T. Zhang et al. / Sensors and Actuator

Fig. 8. Response s (a) and response/recovery times (b) of In2O3 and In2O3:RE hollowspheres sensors to 100 ppm alcohol.

Fig. 9. Selectivity of pure and In2O3:RE hollow spheres sensors to 100 ppm differentgases (a), and long-term stability to 100 ppm alcohol (b).

s B 177 (2013) 1180– 1188 1185

responses of the sensors to 100 ppm alcohol were measured at 1st,8th, 17th, 21st, 30th, 60th days after the first measurement, andthe corresponding long-term stability of sensors to 100 ppm alco-hol are shown in Fig. 9(b). It can be seen that all the sensors havethe nearly constant responses to100 ppm alcohol, indicating goodstability of the sensors.

The sensing properties to C2H5OH of the In2O3 based sensoras reported in the literature were summarized in Table 3 [27–34].Table 3 indicates that morphologies and RE dopants have greatimpacts on the gas-sensing properties of In2O3 hollow spheres. Ingeneral, the rare earth doped In2O3 hollow spheres have highersensing response at relative low optimum temperatures, whichprobably attributed to their higher surface activity. However,compared with other morphological In2O3 based materials, rareearth doped In2O3 hollow spheres have longer response andrecover times. The hollow structure may result in the sluggishremoval of adsorbed molecules and/or slow transfer of electrons.

3.3. Gas-sensing mechanism

The gas-sensing mechanism of In2O3 sensors belongs to thesurface-controlled type [9]. The mechanisms in In2O3 and In2O3:REhollow spheres should be unchanged, because of their simi-lar structures and size distributions. In terms of energy bandsrepresentation, the virtual energy bands are flat in the absence ofair (as shown in Fig. 10a).

When the In2O3:RE sensors are exposed to air, O2 adsorb onthe surface and create chemisorbed oxygen species (such as O2

2−)by capturing electrons from the conductance band through Eq. (1),resulting in a high resistance state of the doped In2O3.

O2 + 2e− → O22−(ads) (1)

This electron transfer results in the formation of a space-chargelayer. In the electronic structure representation this situation isdescribed as an upward band bending (Fig. 10b). When the sensorsare exposed to the alcohol, the gases react with the chemisorbedoxygen species and release electrons to the conductance band(Fig. 10c), and meanwhile, the resistance of the doped In2O3decreases. The alcohol decomposed through Eq. (2):

CH3CH2OH + 3O22−(ads) → 2CO2 + 3H2O + 6e− (2)

When exposed to air again, the In2O3:RE sensors recover to theinitial electronic structure (Fig. 10d).

In summary, the reducing gas of alcohol mainly reacts withchemisorbed oxygen species, and electrons are released whichresults in the decrease of the resistance of the In2O3:RE sensors.Our experimental results indicate that the sensing properties aredependent on the chemical composition of the sensor, and differ-ent rare earth elements with their own characteristics differentlyimprove the sensing response to various extents. From the point ofthe catalytic theory, the chemisorbed oxygen of the In2O3:RE couldbe advantageously utilized to favor the alcohol decomposition reac-tion on the sensor surface. Obviously, the change of resistance ofsensors greatly depends on the surface states of the materials, andthe response of the In2O3:RE sensors are related to chemisorbedoxygen on the surface of the sensors.

The Gaussian–Lorentz fitting curves of O1s XPS spectrums ofIn2O3:Er, In2O3:La, In2O3:Yb and pure In2O3 are shown in Fig. 11,and the corresponding data are listed in Table 4. From Fig. 11,three oxygen species can be deconvoluted with peaks at ca. 529 eV,531 eV, 533 eV, which assigned as the lattice oxygen (OI), thechemisorbed oxygen (OII) and the hydroxyl oxygen (OIII), respec-

tively [35]. As shown in Table 4, the In2O3:Er, In2O3:La, In2O3:Ybcontains much more chemisorbed oxygen than the pure In2O3,which means that the In2O3:RE can absorb more oxygen on thesurface, and the In2O3:Er sensors have much more chemisorbed

1186 T. Zhang et al. / Sensors and Actuators B 177 (2013) 1180– 1188

Table 3Sensing properties to C2H5OH of the different materials in the present study and those reported in the literature.

Sensing materials [C2H5OH] (ppm) Optimum temp. (◦C) Response time (s) Recover time (s) Sensor response Reference

In2O3:Er hollow spheres 100 215 10 23 40.3 Present studyIn2O3:La hollow spheres 100 215 9 24 33.0 Present studyIn2O3:Yb hollow spheres 100 215 8 20 30.6 Present studyIn2O3 hollow spheres 100 215 9 22 18.2 Present studyIn2O3 hollow spheres 50 250 7.5 5.3 4.5 [27]In2O3 hollow spheres 100 400 2 830 137.2 [28]In2O3 nanofibers 100 300 1 2 ∼14 [29]In2O3 porous nanoparticles 100 200 6 15 ∼4 [30]Co-doped In2O3 nanowires 100 300 2 3 ∼17 [31]SnO2/In2O3 nanofibers 50 375 – – ∼9 [32]SnO2/In2O3 nanoparticles 100 200 – – ∼4 [33]Pd-doped In2O3 nanofibers 100 200 1 10 ∼28 [34]

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ig. 10. Diagram of the electronic structure of In2O3:RE in contact with alcohol; ED

xygen than the other In2O3:La and In2O3:Yb sensors. As proposedhat the sensing response is expected to occur mainly via elec-ron transfer and/or variation of chemisorbed oxygen species onhe sensor surface, the sensor performances can be improved with

he increase of chemisorbed oxygen. Hence, the In2O3:Er sensorontains more chemisorbed oxygen to react with the alcohol toossess the highest response to alcohol, which agrees with the

able 4PS analysis results of O1s peak of In2O3:Er, In2O3:La, In2O3:Yb and In2O3.

Samples Peak (OI) Peak (OII) Pea

In2O3:Er 529.31 531.62 533In2O3:La 529.35 532.03 533In2O3:Yb 529.76 531.66 533In2O3 529.59 531.45 532

or energy, EV – valence band edge; EC – conduction band edge; EF – Fermi energy.

testing results of the alcohol sensing properties. It is well knownthat intrinsic defects or the nonstoichiometry mainly determinethe properties of the semiconductor oxides. XRD and Raman resultsindicate that the doping of Er3+, La3+, Yb3+ lead to a structural disor-

der of In2O3. Therefore, the enhancement of chemisorbed oxygenmay due to the doping of rare earth ions which results in morelattice defects.

k (OIII) OI (%) OII (%) OIII (%)

.12 42.28 32.73 24.98

.58 38.57 32.03 29.40

.24 51.16 25.44 23.39

.78 33.65 22.40 43.94

T. Zhang et al. / Sensors and Actuators B 177 (2013) 1180– 1188 1187

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Fig. 11. XPS spectra of O1s of In2O3:Er

. Conclusions

In summary, In2O3:RE hollow spheres have been successfullyynthesized by the carbon sphere template route. The doping ofr3+, La3+, Yb3+ increased the responses of In2O3 sensors to alcohol,hich probably attributed to high surface activity resulted from the

attice defects and chemisorbed oxygen. Furthermore, the preparedare earth-doped sensors exhibited high selectivity and stabilitieso alcohol vapors, suggesting a promising application in detectinglcohol.

cknowledgements

This work was supported by the China National Natural Scienceunds (Nos. 20935002, 20901008) and the Excellent Ph.D. Thesisund of Beijing (YB20091001002).

ppendix A. Supplementary data

Supplementary data associated with this article can be found, inhe online version, at http://dx.doi.org/10.1016/j.snb.2012.12.024.

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Biographies

Ting Zhang majored in applied chemistry and received her Bachelor degree of Engi-neering in 2009 at Haikou University in China. She is currently studying for a master’sdegree at Beijing University of Chemical Technology. Her research subject is indiumoxide nanomaterials for gas-sensing applications.

Fubo Gu received the PhD degree at Beijing University of Chemical Technology in2008. During his studies for doctor degree he worked as a visiting student at OxfordUniversity in 2007. Afterward, he began his career as a college teacher. In 2011,he worked as a visiting scholar at Tufts University. His present interests are thesynthesis and assembling of nanomaterials, and their application in the fields of gassensor and catalysis.

Dongmei Han received her BS degree from Dalian Institute of Light Industry in 1994,and received her MS degree at Beijing University of Chemical Technology. Then sheengaged in teaching college chemistry at the College of Science. She received herPhD degree from Beijing University of Chemical Technology in 2009. Her presentinterests include the application of organic silicon in the protection of cultural relicsand the synthesis of fluorescent quantum dot nanomaterials.

Zhihua Wang is a professor at College of Science in Beijing University of ChemicalTechnology. She received her BS and MS degrees in chemistry from Shandong Uni-versity in 1984 and 1989, respectively, and the PhD degree from Beijing University ofChemical Technology. She worked as a visiting scholar at University of California-SanDiego in USA in 2004. Her present interest is environmental chemistry.

Guangsheng Guo began his college education at Shangdong University in 1979, andthen was successively granted the degrees of BS, MS and PhD (Eng.). In 1995, he stud-

he is serving as a professor at the State Key Laboratory of Chemical Resource Engi-neering of Beijing University of Chemical Technology. His main research interestsinclude laser chemistry and the preparation and application of functional nanoma-terials.