Research Article Hydrothermal Synthesis and Hydrogen

Research ArticleHydrothermal Synthesis and Hydrogen Sensing Properties ofNanostructured SnO2 with Different Morphologies

Weigen Chen1 Hongli Gan1 Wei Zhang2 and Zeyu Mao1

1 State Key Laboratory of Power Transmission Equipment amp System Security and New Technology Chongqing UniversityChongqing 400030 China

2 Key Laboratory of Multi-Scale Manufacturing Technology Chongqing Institute of Green and Intelligent TechnologyChinese Academy of Sciences Chongqing 400714 China

Correspondence should be addressed to Hongli Gan hongliganfoxmailcom and Wei Zhang zhangweicigitaccn

Received 20 February 2014 Revised 1 May 2014 Accepted 15 May 2014 Published 15 June 2014

Academic Editor Wen Zeng

Copyright copy 2014 Weigen Chen et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

In this work nanoscale SnO2with various geometrical morphologies including pine needle-like sphere-like sheet-like grape-

like nanostructures was prepared via a facile hydrothermal process Microstructures and morphologies of all the as-synthesizedproducts were characterized by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) Meanwhilethe specific surface areas of the as-prepared SnO

2nanostructures were determined by Brunauer-Emmett-Teller (BET) analysis Gas

sensors were fabricated and their gas sensing properties towards hydrogenwere systematically investigatedThe results indicate pineneedle-like SnO

2structure exhibits exclusive better gas sensing performances to hydrogen than the other morphologies which can

be attributed to its novel shape with a large specific surface area Such an unexpected morphology is a promising candidate for theuse of SnO

2as a gas sensing material in future hydrogen sensor applications

1 Introduction

As important fundamental materials metal oxides such asZnO [1 2] CuO [3] WO

3[4 5] and SnO

2[6ndash8] have

attracted a remarkable interest due to their unique physico-chemical properties Among them the n-type large gap semi-conductor SnO

2has been extensively applied in the field of

catalysts [9] Li-ion batteries [10] solar cells [11] and gas sen-sors [12ndash14] It is well known that factors such asmorphologycrystal structure and grain size as well as synthesis methodcan dramatically affect the gas sensing properties of SnO

2-

based sensor [15ndash19] Among these factors the fabrication ofwell-defined morphology is of great interest and significanceto enhance the sensing characteristics of SnO

2gas sensors

for the past few years Various SnO2nanoarchitectures with

special morphologies including nanorods [20] nanoflowers[21] nanosheets [22] nanocubes [23] and nanowires [24]have been successfully synthesized via different methodsIndeed these structures have showed good sensitivity andselectivity to inflammable or toxic gases such as C

2H5OH

CO H2S or NO

2 However up to now little attention has

been paid to the effect of different SnO2morphologies on the

H2gas sensing performances To date a variety of methods

have been employed to prepare nanocrystalline SnO2 for

instance sol-gel process [25] chemical vapor deposition [26]coaxial electrospinning [27] and hydrothermal reaction [28]Compared to other techniques hydrothermal approach isoften adopted for its obvious advantages of simplicity mildfabrication condition high purity of product and low cost[28ndash30]

In this work several types of SnO2nanomaterials with

different morphologies were successfully prepared throughan environmentally friendly hydrothermal route Further-more sensing properties of the sensors based on the samplessuch as sensitivity optimumoperating temperature responseand recovery times as well as the long-term stability weresystematically tested and compared with each otherThe pineneedle-like SnO

2displays better sensitivity lower working

temperature and more rapid response-recovery time to H2

than that of the other samples which implies that the gassensing properties of SnO

2sensors can be highly enhanced

by preparing SnO2with desired morphology

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2014 Article ID 291273 7 pageshttpdxdoiorg1011552014291273

2 Journal of Nanomaterials

2 Experimental

21 Materials Synthesis All the reagents purchased fromChongqing Chuandong Chemical Reagent Co Ltd were ofanalytical grade and used as received without any furtherpurification

Pine needle-like sphere-like sheet-like and grape-likeSnO2were realized by the hydrothermal synthesis route [28ndash

30](a) Pine needle-like SnO

2structures were prepared as

follows in a typical experiment 005 g Na2SnO3sdot3H2O and

002 g NaOHwere dissolved into 40mL deionized water withvigorous stirring for 10min and then 003 gHMTwas addedAfter the complete dissolution the precursor was transferredto aTeflon-lined stainless steel autoclave of 50mLvolume andkept at 180∘C for 24 h

(b) Synthesis of SnO2

nanospheres 40mmolSnCl2sdot2H2O and 10mmol Na

3C6H5O7sdot2H2O were mixed

together in 20mL distilled water and stirred for 5min002mmol NaOH was then added to the above solution withcontinuous stirring to form a homogeneous solution whichwas finally transferred to a 25mL Teflon-lined stainless steelautoclave and heated at 180∘C for 12 h

(c) SnO2

nanosheets were synthesized as thefollowing process in which 009 g SnCl

2sdot2H2O 015 g

Na3C6H5O7sdot2H2O and 005 g NaOH were added into 40mL

basic mixture of ethanol and water (1 1 vv) with intensemagnetic stirring over 30min The reaction mixture wastransferred into a 50mL Teflon-lined stainless steel autoclaveat 180∘C in 12 h

(d) The fabrication of grape-like SnO2structures is as

follows In a typical procedure 04 g SnCl4sdot5H2O was added

into NaOH solution (05 g 20mL) After stirring for 5min30mmolHMTwas added into above solution under vigorousstirringThen 20mL of absolute ethanol was dropwise addedto obtain awhite translucent suspended solution Transfer thewell-mixed solution into a 50mL stainless steel autoclave at180∘C for 24 h

All the above heating autoclaves were cooled to roomtemperature naturally The obtained precipitates wereretrieved by centrifugation and then washed several timeswith distilled water and anhydrous ethanol to remove anypossible residues Finally all the samples were dried in air at60∘C for about 12 h for further characterizations

22 Fabrication of Gas Sensor The detailed fabrication of aside-heated gas sensor was as follows first each of the aboveas-synthesized samples was mixed with diethanolamine andethanol to form a homogeneous paste and then coated ontoan alumina tube on which a pair of Au electrodes waspreviously printed later a Ni-Cr heating wire was insertedinto the tube for adjusting the operating temperature of thesensor Finally all the as-prepared sensors were aged at 300∘Cfor 120 h to enhance their stability and repeatability Theschematic diagram of the gas sensor is shown in Figure 1

23 Characterization andMeasurement of Gas Sensing Proper-ties The crystalline structures of the prepared samples were

Alumina tube

Pt wire

Au electrode

Ni-Cr heater

Sensitive materials

Figure 1 The schematic diagram of the gas sensor

identified by X-ray diffraction (XRD) with a Rigaku DMax-1200X diffractometer employing Cu K120572 radiation (40 kV200mA and 120582 = 15418 A) The general morphologies andmicrostructures were characterized by a Nova 400 Nanofield emission scanning electron microscopy (FESEM FEIHillsboroORUSA) operated at 5 kVMeanwhile the specificsurface areas of the products were estimated using the singlepoint Brunauer-Emmett-Teller (BET) method by the 3H-2000 nitrogen adsorption apparatus

Gas sensing properties were measured by the chemicalgas sensor-8 temperature pressure (CGS-8TP) intelligent gassensing analysis system (Beijing Elite Tech Co Ltd) It isconvenient to gain parameters for sensor resistance sensitiv-ity environmental temperature and operating temperatureas well as relative humidity from the analysis system Allthe sensors needed to be preheated at different operatingtemperatures for about 30min When the sensor resistancevalue kept steady a certain concentration of target gas wasthen injected into the test chamber through a microinjectorThe tested gas and air were mixed together using two fansof the analysis system After the resistance of the sensorattained a new stable value the test chamber was openedto recover the sensor The whole experiment process wascarried out at constant environment temperature and relativehumidity Repeat all the measurements a few times to ensurethe reproducibility of the gas sensing response

The gas response in this paper was defined as the ratioof sensor resistance in dry air to that in tested gases [31] Theresponse and recovery times were expressed as the time takenby the sensor to achieve 90 of the total resistance change inthe case of adsorption and desorption respectively [32 33]

3 Results and Discussion

31 Structural and Morphological Characteristics Figure 2presents the XRD patterns from the final SnO

2products All

diffraction peaks are well in accordance with the tetragonalrutile SnO

2structure (JCPDS file number 41-1445) no other

crystal phases and any characteristic peaks from the impuri-ties are observed confirming that all the samples are of high

Journal of Nanomaterials 3

20 30 40 50 60 70

Grape-like

Sheet-like

(211)

(101)

Inte

nsity

(au

)

(110)

Pine needle-like

Sphere-like

2120579 (deg)

Figure 2 XRD patterns of all the SnO2samples

purity and crystallinity In addition pine needle-like SnO2

has broader peaks in comparison with other samples whichdemonstrates that the pine needle-like sample has smallercrystal size BET analysis results indicate that the surface areaof pine needle-like sphere-like sheet-like and grape-like wasabout 304m2 gminus1 213m2 gminus1 208m2 gminus1 and 182m2 gminus1respectively Clearly pine needle-like SnO

2possesses much

higher specific surface area as compared to other samplesGenerally larger surface area means more active sites anddiffusion pathways for gas exchange which may lead to alarger response

To gain insight into the detailed morphology of SnO2

products typical FESEM images of all the samples can beobserved in Figure 3 From Figure 3(a) numerous SnO

2

nanoparticles with smooth surface are clearly observedThey are uniformly distributed and have a nearly sphericalmorphology with average diameter of 350 nm As seen inFigure 3(b) the sample contains a large scale of pine needle-like leaves which are well arranged and rather uniform inshape and size These thin leaves are about 400ndash500 nm inlength and 50ndash80 nm in width No other morphologies couldbe detected suggesting a high yield of these nanostructuresTo the best of our knowledge such unique shape has notbeen reported so far and it may have an obvious influenceon promoting gas sensing performances of SnO

2 Figure 3(c)

exhibits SnO2with grape-like structures assembled from

dozen of rugged spheres Figure 3(d) presents a panoramicimage of the SnO

2sample that consisted of randomly

arranged nanosheets and some unshaped nanosheets whichare growing

32 H2Sensing Properties Operating temperature is an

important fundamental characteristic of gas sensors for itssignificant impact on sensor response Figure 4 describesthe response curves of these sensors to 200 ppm of H

2as a

function of temperature from 220 to 480∘C with an intervalof 20∘C Apparently the responses of the sensors increasewith a raise of temperature and reach the maximum andthen decrease with further increase of working temperature

Usually operating temperature of the oxide semiconductorsensor depends on two parameters electron density of thesensor and reaction rate coefficient between H

2molecules

and adsorbed oxygen species [34] On one hand they bothincrease as the temperature rises On the other hand gasresponse is proportional to reaction rate coefficient butinversely proportional to electron density Therefore thereshould be an optimal temperature to balance the two parame-ters for achieving the maximum sensor response In contrastSnO2sensors using samples of pine needle-like sphere-

like and sheet-like are more sensitive to H2than that of

grape-like at the same temperature The highest gas responsefor pine needle-like sphere-like sheet-like and grape-likeSnO2was about 205 18 17 and 14 at temperature of 360∘C

380∘C 380∘C and 400∘C respectively Herein the optimaloperating temperatures were determined to further examinethe characteristics of the sensors Furthermore the higherresponse of pine needle-like SnO

2probably results from its

very fine grain size and large specific surface areaFigure 5 shows the correlation between the response of

SnO2sensors and H

2gas concentrations where the sensors

worked at their own optimum operating temperature asmentioned above From the curves it is evident that theresponse of the sensors increases nonlinearly with no signof saturation when H

2concentration ranges from 100 to

1000 ppmThis usually is explained through the gas-diffusiontheory by which the oxide based sensor response can bewritten as 119878 = 119886119862119887 + 1 [34 35] In the formula 119886 is acontrollable constant 119887 is a charge parameter which reflectsoxygen ion species on the surface of SnO

2sensors and

119862 is the concentration of the tested gas Normally 119887 hasvalue of 1 for Ominus and 05 for O2minus Besides it is necessaryto know that the growth trends are gradually slowed downwith a further rise of gas concentrations The correspondingdata is not presented This phenomenon might be owingto both the change of stoichiometry about the elementaryreactions and the competitions of gas molecules for reactionsites as gas concentrations increase progressively [36 37]Specifically the SnO

2sensor with pine needle-like structure

shows relatively higher sensitivity to H2than that of other

sensorsThe response and recovery characteristics were studied

with the sensors being orderly exposed to 200 ppm of H2gas

at their own optimum operating temperature and the curvesare depicted in Figure 6The response and recovery times forthe pine needle-like sphere-like sheet-like and grape-likeSnO2were estimated to be 19ndash22 s 22ndash26 s 24ndash27 s and 25ndash

29 s respectively Interestingly it seems that voltages of all thesamples increase dramatically when H

2is in but go back to

their original states when the gas is out Comparing with theother three SnO

2nanostructures it could be noted that the

pine needle-like SnO2has the shortest response and recovery

times reflecting its excellent sensing performance once againFigure 7 displays the long-term stability of the sensors to

200 ppm of H2at their own optimum operating temperature

with relative humidity of 35 It could be known that gasresponse changed slightly after a month suggesting that allthe sensors have good stability and repeatability


500nm

(a)

500nm

(b)

500nm

(c)

500nm

(d)

Figure 3 FESEM images of (a) sphere-like (b) pine needle-like (c) grape-like and (d) sheet-like SnO2

On the basis of above discussions one can draw aconclusion that pine needle-like SnO

2exhibits the most

superior sensing properties to H2among the four samples

33 Gas SensingMechanism It is believed that the gas sensingmechanismof SnO

2sensors follows the surface chargemodel

When sensors contact with different gases the resistancewould have a change Both the species and amount of oxygenions play crucial roles in the variation of resistanceWhen thesensors are exposed to air oxygenmolecules adsorbed on thesurface of SnO

2nanostructures would be ionized to O2minus Ominus

or O2

minus by capturing free electrons from the conduction bandof SnO

2 which causes a depletion layer and consequently

increases the resistance of the sensors As a reducing gassuch as H

2is introduced chemical reactions between the H

2

molecules and the ionized oxygen are active This processreleases the trapped electrons back to the SnO

2surface and

thus leads to an increase in the carrier concentration andcarrier mobility of SnO

2 The gas sensing reaction process on

the SnO2surface is seen in Figure 8

The possible reactions involved in the above process areexpressed as follows [38 39]

O2(gas) 997888rarr O

2(ads)

O2(ads) + eminus 997888rarr O

2

minus(ads)

O2(ads) + 2eminus 997888rarr 2Ominus (ads)

O2(ads) + 4eminus 997888rarr 2O2minus (ads)

H2(gas) 997888rarr H

2(ads)

H2(ads) +Ominus (ads) 997888rarr H

2O (ads) + eminus

H2(ads) +O2minus (ads) 997888rarr H

2O (ads) + 2eminus

(1)

In this experiment the different sensing properties ofthe four SnO

2samples toward H

2can be ascribed to the

different morphologies and nanostructures Moreover thehigher sensitivity of pine needle-like SnO

2is mainly based

on its special structure with a large surface area which can


200 240 280 320 360 400 440 480

0

5

10

15

20

Resp

onse

Grape-likeSheet-like

Sphere-likePine needle-like

Temperature (∘C)

Figure 4 Response of the sensors to 200 ppm of H2with different

operating temperature (room temperature at 25∘C and relativehumidity as 35)

0 100 200 300 400 500 600 700 800 900 1000

0

10

20

30

40

50

Resp

onse

Concentration (ppm)



Figure 5 Response of the sensors as a function of H2gas concen-

trations (room temperature at 25∘C and relative humidity as 35)

provide more active sites and quick passages for gas exchangeand thus enhance the interaction between SnO

2surface and

H2molecules

4 Conclusions

In summary SnO2nanostructures with various morpholo-

gies including pine needle-like sphere-like sheet-like andgrape-like were realized by hydrothermal preparation Addi-tionally both their microstructures and gas sensing prop-erties to H

2were tested As compared to other three sen-

sors pine needle-like SnO2sensor exhibits more excellent

performances in terms of higher response faster response-recovery time and lower working temperature The goodsensing propertiesmay be attributed to the novel pine needle-like structure which has a large specific surface area withmassive gas-diffusion channels The obtained results indicate

0 10 20 30 40 50 60 70 80 90 100

10

15

20

25

30

Gas in

Volta

ge (V

)

Time (s)

Gas out



Figure 6 Response-recovery curves of the sensors to 200 ppm ofH2(room temperature at 25∘C and relative humidity as 35)

0 5 10 15 20 25 30

10

15

20

25Re

spon

se

Time (days)



Figure 7 The long-term response value of the sensors to 200 ppmof H2(room temperature at 25∘C and relative humidity as 35)

OO

OO O

O

OOO

O

OO

H2 H2O

OO

OO

Figure 8 Schematic of the H2sensing reaction process


that the gas sensing properties of SnO2sensing materials

can be significantly improved by tailoring their surface struc-tures and shapes These findings offer new opportunities fordesigning and developing high-performance H

2gas sensors

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors appreciate the financial support of the NationalNatural Science Foundation of China (nos 51277185 and51202302) and National Special Fund for Major ResearchInstrumentation Development (no 2012YQ16000705)

References

[1] P Rai Y-S Kim H-M Song M-K Song and Y-T Yu ldquoTherole of gold catalyst on the sensing behavior of ZnO nanorodsfor CO and NO

2gasesrdquo Sensors and Actuators B Chemical vol

165 no 1 pp 133ndash142 2012[2] L Zhang J Zhao J Zheng L Li and Z Zhu ldquoHydrother-

mal synthesis of hierarchical nanoparticle-decorated ZnOmicrodisks and the structure-enhanced acetylene sensing prop-erties at high temperaturesrdquo Sensors and Actuators B Chemicalvol 158 no 1 pp 144ndash150 2011

[3] D Gopalakrishna K Vijayalakshmi and C Ravidhas ldquoEffect ofannealing on the properties of nanostructured CuO thin filmsfor enhanced ethanol sensitivityrdquo Ceramics International vol39 no 7 pp 7685ndash7691 2013

[4] J-Y Leng X-J Xu N Lv H-T Fan and T Zhang ldquoSynthesisand gas-sensing characteristics of WO

3nanofibers via electro-

spinningrdquo Journal of Colloid and Interface Science vol 356 no1 pp 54ndash57 2011

[5] X Liu J Zhang T Yang X Guo SWu and SWang ldquoSynthesisof Pt nanoparticles functionalizedWO

3nanorods and their gas

sensing propertiesrdquo Sensors and Actuators B Chemical vol 156no 2 pp 918ndash923 2011

[6] Y J Chen X Y Xue Y G Wang and T H Wang ldquoSynthesisand ethanol sensing characteristics of single crystalline SnO

2

nanorodsrdquo Applied Physics Letters vol 87 Article ID 2335032005

[7] M Wu W Zeng Q He and J Zhang ldquoHydrothermal syn-thesis of SnO

2nanocorals nanofragments and nanograss and

their formaldehyde gas-sensing propertiesrdquoMaterials Science inSemiconductor Processing vol 16 no 6 pp 1495ndash1501 2013

[8] J Liu X-C Tang Y-H Xiao H Jia M-L Gong and F-QHuang ldquoPorous sheet-like and sphere-like nano-architecturesof SnO

2nanoparticles via a solvent-thermal approach and their

gas-sensing performancesrdquo Materials Science and EngineeringB Solid-State Materials for Advanced Technology vol 178 no18 pp 1165ndash1168 2013

[9] I T Weber A Valentini L F D Probst E Longo and E RLeite ldquoCatalytic activity of nanometric pure and rare earth-doped SnO

2samplesrdquo Materials Letters vol 62 no 10-11 pp

1677ndash1680 2008[10] X W Lou Y Wang C Yuan J Y Lee and L A Archer

ldquoTemplate-free synthesis of SnO2hollow nanostructures with

high lithium storage capacityrdquo Advanced Materials vol 18 no17 pp 2325ndash2329 2006

[11] Y Fukai Y Kondo SMori and E Suzuki ldquoHighly efficient dye-sensitized SnO

2solar cells having sufficient electron diffusion

lengthrdquo Electrochemistry Communications vol 9 no 7 pp1439ndash1443 2007

[12] W G Chen Q Z Li H L Gan et al ldquoStudy of CuO-SnO2

heterojunction nanostructures for enhanced CO gas sensingpropertiesrdquo Advances in Applied Ceramics vol 113 no 3 pp139ndash146 2014

[13] M A Andio P N Browning P A Morris and S AAkbar ldquoComparison of gas sensor performance of SnO

2nano-

structures on microhotplate platformsrdquo Sensors and ActuatorsB Chemical vol 165 no 1 pp 13ndash18 2012

[14] Q Yu K Wang C Luan Y Geng G Lian and D Cui ldquoA dual-functional highly responsive gas sensor fabricated from SnO

2

porous nanosolidrdquo Sensors and Actuators B Chemical vol 159no 1 pp 271ndash276 2011

[15] G Zhang and M Liu ldquoEffect of particle size and dopant onproperties of SnO

2-based gas sensorsrdquo Sensors and Actuators B

Chemical vol 69 no 1 pp 144ndash152 2000[16] R K Mishra and P P Sahay ldquoSynthesis characterization and

alcohol sensing property of Zn-doped SnO2nanoparticlesrdquo

Ceramics International vol 38 no 3 pp 2295ndash2304 2012[17] S Dai and Z Yao ldquoSynthesis of flower-like SnO

2single crystals

and its enhanced photocatalytic activityrdquo Applied Surface Sci-ence vol 258 no 15 pp 5703ndash5706 2012

[18] N Talebian and F Jafarinezhad ldquoMorphology-controlled syn-thesis of SnO

2nanostructures using hydrothermal method and

their photocatalytic applicationsrdquo Ceramics International vol39 no 7 pp 8311ndash8317 2013

[19] L Fei Y Xu Z Chen et al ldquoPreparation of porous SnO2helical

nanotubes and SnO2sheetsrdquo Materials Chemistry and Physics

vol 140 no 1 pp 249ndash254 2013[20] S Supothina R Rattanakam S Vichaphund and PThavorniti

ldquoEffect of synthesis condition on morphology and yield ofhydrothermally grown SnO

2nanorod clustersrdquo Journal of the

European Ceramic Society vol 31 no 14 pp 2453ndash2458 2011[21] J Huang K Yu C Gu et al ldquoPreparation of porous flower-

shaped SnO2nanostructures and their gas-sensing propertyrdquo

Sensors and Actuators B Chemical vol 147 no 2 pp 467ndash4742010

[22] P Sun Y Cao J Liu Y Sun J Ma and G Lu ldquoDispersive SnO2

nanosheets hydrothermal synthesis and gas-sensing proper-tiesrdquo Sensors and Actuators B Chemical vol 156 no 2 pp 779ndash783 2011

[23] L Yu M Zhang Y J Chen et al ldquoAssembling SnO2nanocubes

to nanospheres for high-sensitivity sensorsrdquo Solid State Sciencesvol 14 no 4 pp 522ndash527 2012

[24] G D Zhang and N Liu ldquoA novel method for massive synthesisof SnO

2nanowiresrdquo Bulletin of Materials Science vol 36 no 6

pp 953ndash960 2013[25] M A Dal Santos A C Antunes C Ribeiro et al ldquoElectric and

morphologic properties of SnO2films prepared bymodified sol-

gel processrdquo Materials Letters vol 57 no 28 pp 4378ndash43812003

[26] J B Zhang X N Li S L Bai R X Luo A F Chen and YLin ldquoHigh-yield synthesis of SnO

2nanobelts by water-assisted

chemical vapor deposition for sensor applicationsrdquo MaterialsResearch Bulletin vol 47 no 11 pp 3277ndash3282 2012


[27] Y Zhang J Li G An and X He ldquoHighly porous SnO2fibers

by electrospinning and oxygen plasma etching and its ethanol-sensing propertiesrdquo Sensors and Actuators B Chemical vol 144no 1 pp 43ndash48 2010

[28] W G Chen Q Zhou and S D Peng ldquoHydrothermal synthesisof Pt- Fe- and Zn-doped SnO

2nanospheres and carbon

monoxide sensing propertiesrdquo Advances in Materials Scienceand Engineering vol 2013 Article ID 578460 8 pages 2013

[29] Y L Wang M Guo M Zhang and X D Wang ldquoFacilesynthesis of SnO

2nanograss array films by hydrothermal

methodrdquoThin Solid Films vol 518 no 18 pp 5098ndash5103 2010[30] B Mehrabi Matin Y Mortazavi A A Khodadadi A Abbasi

and A Anaraki Firooz ldquoAlkaline- and template-free hydrother-mal synthesis of stable SnO

2nanoparticles andnanorods forCO

and ethanol gas sensingrdquo Sensors andActuators B Chemical vol151 no 1 pp 140ndash145 2010

[31] W G Chen Q Zhou L N Xu et al ldquoImproved methanesensing properties of Co-doped SnO

2electrospun nanofibersrdquo

Journal of Nanomaterials vol 2013 Article ID 173232 9 pages2013

[32] Y Gui F Dong Y Zhang and J Tian ldquoPreparation andgas sensitivity of WO

3hollow microspheres and SnO

2doped

heterojunction sensorsrdquo Materials Science in SemiconductorProcessing vol 16 no 6 pp 1531ndash1537 2013

[33] Q ZhouW Chen L Xu and S Peng ldquoHydrothermal synthesisof various hierarchical ZnO nanostructures and their methanesensing propertiesrdquo Sensors vol 13 no 5 pp 6171ndash6182 2013

[34] N Hongsith E Wongrat T Kerdcharoen and S ChoopunldquoSensor response formula for sensor based on ZnO nanostruc-turesrdquo Sensors and Actuators B Chemical vol 144 no 1 pp 67ndash72 2010

[35] Q Wan Q H Li Y J Chen et al ldquoFabrication and ethanolsensing characteristics of ZnO nanowire gas sensorsrdquo AppliedPhysics Letters vol 84 no 18 pp 3654ndash3656 2004

[36] M Chen Z Wang D Han F Gu and G Guo ldquoHigh-sensitivity NO

2gas sensors based on flower-like and tube-like

ZnO nanomaterialsrdquo Sensors and Actuators B Chemical vol157 no 2 pp 565ndash574 2011

[37] M-W Ahn K-S Park J-H Heo D-W Kim K J Choi and J-G Park ldquoOn-chip fabrication of ZnO-nanowire gas sensor withhigh gas sensitivityrdquo Sensors and Actuators B Chemical vol 138no 1 pp 168ndash173 2009

[38] SMishra C Ghanshyam R AMNathai S Singh R P Bajpaiand R K Bedi ldquoAlcohol sensing of tin oxide thin film preparedby sol-gel processrdquo Bulletin of Materials Science vol 25 no 3pp 231ndash234 2002

[39] MHubner R G Pavelko N Barsan andUWeimar ldquoInfluenceof oxygen backgrounds on hydrogen sensing with SnO

2nano-

materialsrdquo Sensors and Actuators B Chemical vol 154 no 2 pp264ndash269 2011

Submit your manuscripts athttpwwwhindawicom

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CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


2 Experimental

21 Materials Synthesis All the reagents purchased fromChongqing Chuandong Chemical Reagent Co Ltd were ofanalytical grade and used as received without any furtherpurification

Pine needle-like sphere-like sheet-like and grape-likeSnO2were realized by the hydrothermal synthesis route [28ndash

30](a) Pine needle-like SnO

2structures were prepared as

follows in a typical experiment 005 g Na2SnO3sdot3H2O and

002 g NaOHwere dissolved into 40mL deionized water withvigorous stirring for 10min and then 003 gHMTwas addedAfter the complete dissolution the precursor was transferredto aTeflon-lined stainless steel autoclave of 50mLvolume andkept at 180∘C for 24 h

(b) Synthesis of SnO2

nanospheres 40mmolSnCl2sdot2H2O and 10mmol Na

3C6H5O7sdot2H2O were mixed

together in 20mL distilled water and stirred for 5min002mmol NaOH was then added to the above solution withcontinuous stirring to form a homogeneous solution whichwas finally transferred to a 25mL Teflon-lined stainless steelautoclave and heated at 180∘C for 12 h

(c) SnO2

nanosheets were synthesized as thefollowing process in which 009 g SnCl

2sdot2H2O 015 g

Na3C6H5O7sdot2H2O and 005 g NaOH were added into 40mL

basic mixture of ethanol and water (1 1 vv) with intensemagnetic stirring over 30min The reaction mixture wastransferred into a 50mL Teflon-lined stainless steel autoclaveat 180∘C in 12 h

(d) The fabrication of grape-like SnO2structures is as

follows In a typical procedure 04 g SnCl4sdot5H2O was added

into NaOH solution (05 g 20mL) After stirring for 5min30mmolHMTwas added into above solution under vigorousstirringThen 20mL of absolute ethanol was dropwise addedto obtain awhite translucent suspended solution Transfer thewell-mixed solution into a 50mL stainless steel autoclave at180∘C for 24 h

All the above heating autoclaves were cooled to roomtemperature naturally The obtained precipitates wereretrieved by centrifugation and then washed several timeswith distilled water and anhydrous ethanol to remove anypossible residues Finally all the samples were dried in air at60∘C for about 12 h for further characterizations

22 Fabrication of Gas Sensor The detailed fabrication of aside-heated gas sensor was as follows first each of the aboveas-synthesized samples was mixed with diethanolamine andethanol to form a homogeneous paste and then coated ontoan alumina tube on which a pair of Au electrodes waspreviously printed later a Ni-Cr heating wire was insertedinto the tube for adjusting the operating temperature of thesensor Finally all the as-prepared sensors were aged at 300∘Cfor 120 h to enhance their stability and repeatability Theschematic diagram of the gas sensor is shown in Figure 1

23 Characterization andMeasurement of Gas Sensing Proper-ties The crystalline structures of the prepared samples were

Alumina tube

Pt wire

Au electrode

Ni-Cr heater

Sensitive materials

Figure 1 The schematic diagram of the gas sensor

identified by X-ray diffraction (XRD) with a Rigaku DMax-1200X diffractometer employing Cu K120572 radiation (40 kV200mA and 120582 = 15418 A) The general morphologies andmicrostructures were characterized by a Nova 400 Nanofield emission scanning electron microscopy (FESEM FEIHillsboroORUSA) operated at 5 kVMeanwhile the specificsurface areas of the products were estimated using the singlepoint Brunauer-Emmett-Teller (BET) method by the 3H-2000 nitrogen adsorption apparatus

Gas sensing properties were measured by the chemicalgas sensor-8 temperature pressure (CGS-8TP) intelligent gassensing analysis system (Beijing Elite Tech Co Ltd) It isconvenient to gain parameters for sensor resistance sensitiv-ity environmental temperature and operating temperatureas well as relative humidity from the analysis system Allthe sensors needed to be preheated at different operatingtemperatures for about 30min When the sensor resistancevalue kept steady a certain concentration of target gas wasthen injected into the test chamber through a microinjectorThe tested gas and air were mixed together using two fansof the analysis system After the resistance of the sensorattained a new stable value the test chamber was openedto recover the sensor The whole experiment process wascarried out at constant environment temperature and relativehumidity Repeat all the measurements a few times to ensurethe reproducibility of the gas sensing response

The gas response in this paper was defined as the ratioof sensor resistance in dry air to that in tested gases [31] Theresponse and recovery times were expressed as the time takenby the sensor to achieve 90 of the total resistance change inthe case of adsorption and desorption respectively [32 33]

3 Results and Discussion

31 Structural and Morphological Characteristics Figure 2presents the XRD patterns from the final SnO

2products All

diffraction peaks are well in accordance with the tetragonalrutile SnO

2structure (JCPDS file number 41-1445) no other

crystal phases and any characteristic peaks from the impuri-ties are observed confirming that all the samples are of high


20 30 40 50 60 70

Grape-like

Sheet-like

(211)

(101)

Inte

nsity

(au

)

(110)

Pine needle-like

Sphere-like

2120579 (deg)




2possesses much




2


2 Figure 3(c)







2as a



2molecules







SnO2sensors and H





2sensors and
















500nm

(a)

500nm

(b)

500nm

(c)

500nm

(d)



2exhibits the most






or O2





2


2surface and






2(ads)


2

minus(ads)




2(ads)


2O (ads) + eminus


2O (ads) + 2eminus

(1)


2samples toward H



2is mainly based



200 240 280 320 360 400 440 480

0

5

10

15

20

Resp

onse



Temperature (∘C)



0 100 200 300 400 500 600 700 800 900 1000

0

10

20

30

40

50

Resp

onse

Concentration (ppm)






2surface and

H2molecules

4 Conclusions






0 10 20 30 40 50 60 70 80 90 100

10

15

20

25

30

Gas in

Volta

ge (V

)

Time (s)

Gas out




0 5 10 15 20 25 30

10

15

20

25Re

spon

se

Time (days)




OO

OO O

O

OOO

O

OO

H2 H2O

OO

OO





2gas sensors



Acknowledgments


References













2



















2nano-



2







2single crystals










































2doped











2nano-









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




20 30 40 50 60 70

Grape-like

Sheet-like

(211)

(101)

Inte

nsity

(au

)

(110)

Pine needle-like

Sphere-like

2120579 (deg)




2possesses much




2


2 Figure 3(c)







2as a



2molecules







SnO2sensors and H





2sensors and
















500nm

(a)

500nm

(b)

500nm

(c)

500nm

(d)



2exhibits the most






or O2





2


2surface and






2(ads)


2

minus(ads)




2(ads)


2O (ads) + eminus


2O (ads) + 2eminus

(1)


2samples toward H



2is mainly based



200 240 280 320 360 400 440 480

0

5

10

15

20

Resp

onse



Temperature (∘C)



0 100 200 300 400 500 600 700 800 900 1000

0

10

20

30

40

50

Resp

onse

Concentration (ppm)






2surface and

H2molecules

4 Conclusions






0 10 20 30 40 50 60 70 80 90 100

10

15

20

25

30

Gas in

Volta

ge (V

)

Time (s)

Gas out




0 5 10 15 20 25 30

10

15

20

25Re

spon

se

Time (days)




OO

OO O

O

OOO

O

OO

H2 H2O

OO

OO





2gas sensors



Acknowledgments


References













2



















2nano-



2







2single crystals










































2doped











2nano-









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




500nm

(a)

500nm

(b)

500nm

(c)

500nm

(d)



2exhibits the most






or O2





2


2surface and






2(ads)


2

minus(ads)




2(ads)


2O (ads) + eminus


2O (ads) + 2eminus

(1)


2samples toward H



2is mainly based



200 240 280 320 360 400 440 480

0

5

10

15

20

Resp

onse



Temperature (∘C)



0 100 200 300 400 500 600 700 800 900 1000

0

10

20

30

40

50

Resp

onse

Concentration (ppm)






2surface and

H2molecules

4 Conclusions






0 10 20 30 40 50 60 70 80 90 100

10

15

20

25

30

Gas in

Volta

ge (V

)

Time (s)

Gas out




0 5 10 15 20 25 30

10

15

20

25Re

spon

se

Time (days)




OO

OO O

O

OOO

O

OO

H2 H2O

OO

OO





2gas sensors



Acknowledgments


References













2



















2nano-



2







2single crystals










































2doped











2nano-









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




200 240 280 320 360 400 440 480

0

5

10

15

20

Resp

onse



Temperature (∘C)



0 100 200 300 400 500 600 700 800 900 1000

0

10

20

30

40

50

Resp

onse

Concentration (ppm)






2surface and

H2molecules

4 Conclusions






0 10 20 30 40 50 60 70 80 90 100

10

15

20

25

30

Gas in

Volta

ge (V

)

Time (s)

Gas out




0 5 10 15 20 25 30

10

15

20

25Re

spon

se

Time (days)




OO

OO O

O

OOO

O

OO

H2 H2O

OO

OO





2gas sensors



Acknowledgments


References













2



















2nano-



2







2single crystals










































2doped











2nano-









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






2gas sensors



Acknowledgments


References













2



















2nano-



2







2single crystals










































2doped











2nano-









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




















2doped











2nano-









CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



Documents

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