Research Article Y-Doped ZnO Nanorods by Hydrothermal ...downloads.hindawi.com/journals/jnm/2013/751826.pdf · Y-Doped ZnO Nanorods by Hydrothermal Method and Their Acetone Gas Sensitivity

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2013 Article ID 751826 6 pageshttpdxdoiorg1011552013751826

Research ArticleY-Doped ZnO Nanorods by Hydrothermal Method andTheir Acetone Gas Sensitivity

Peng Yu1 Jing Wang1 Hai-ying Du12 Peng-jun Yao13 Yuwen Hao1 and Xiao-gan Li1

1 School of Electronic Science and Technology Dalian University of Technology Dalian Liaoning 116023 China2Department of Electromechanical Engineering and Information Dalian Nationalities UniversityDalian Liaoning 116600 China

3 School of Educational Technology Shenyang Normal University Shenyang Liaoning 110000 China

Correspondence should be addressed to Jing Wang wangjingdluteducn

Received 21 October 2013 Accepted 9 December 2013

Academic Editor Xiangyu Zhao

Copyright copy 2013 Peng Yu et al This is an open access article distributed under the Creative Commons Attribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Pure and yttrium- (Y-) doped (1 at 3 at and 7 at) ZnO nanorods were synthesized using a hydrothermal process Thecrystallography and microstructure of the synthesized samples were characterized by X-ray diffraction (XRD) scanning electronmicroscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) Comparingwith pure ZnOnanorods Y-dopedZnOexhibitedimproved acetone sensing properties The response of 1 at Y-doped ZnO nanorods to 100 ppm acetone is larger than that of pureZnO nanorods The response and recovery times of 1 at Y-doped ZnO nanorods to 100 ppm acetone are about 30 s and 90 srespectivelyThe gas sensor based on Y-doped ZnO nanorods showed good selectivity to acetone in the interfere gases of ammoniabenzene formaldehyde toluene and methanol The formation mechanism of the ZnO nanorods was briefly analyzed

1 Introduction

As an important IIndashVI semiconducting material with a widedirect band gap (119864119892 = 337 eV at 300K) and large excitonbinding energy (sim60meV) ZnOhas drawnmuch attention inthe last few decades owing to its specific electrical catalyticphotochemical optoelectronic properties and the sensitivityto various gases all of which make ZnO highly promising ina broad range of real-world applications [1 2] Recently ZnOhas shown great potentials for sensing toxic and combustiblegases such as CO H2 NH3 ethanol and acetone [3ndash5]

One way to enhance gas sensing property is by dopingwith other elements For example Niu et al [6] used FeCo and Cr as dopants to improve the gas sensing propertyof pure ZnO and the results showed that ZnFe2O4 hadhigh response and good selectivity to Cl2 Au-doped ZnOenhanced acetone sensing performance [7] Co-doped ZnOnanofibers improved selective acetone sensing properties [8]Pd [9] is also used as dopant to improve CO gas sensingproperty of ZnOThere are some reports about the lanthanideelements of Y-doped ZnO andYdoping has significant effectson the luminescence chemical and surface modification of

ZnO [10 11] However the lanthanide elements of Y as adopant to improve gas sensing property of ZnO are newchallenges Furthermore many synthesis methods have beenused to prepare zinc-oxide nanoparticles (NPs) includingchemical vapor deposition [12] sol-gel method [13] spraypyrolysis method [14] solid state reaction method [15] andhydrothermal method [16] Hydrothermal method is fairlysimple and suitable for industrial production which will pavethe way for the development of a low-cost practical gas sensorfor detection of probable chemical agents

In this paper we report the synthesis and gas sens-ing properties of pure and Y-doped ZnO rods using afacile hydrothermal method One at Y-doped ZnO sensorexhibits improved acetone sensing properties A possibleexplanation of sensingmechanism and the effects of Y dopingon acetone sensing properties has been analyzed

2 Experiments

21 Synthesis and Characterization of ZnO Nanorods Allthe starting materials were analytical grade and were

2 Journal of Nanomaterials

used without further purification Zinc nitrate hexahy-drate (Zn(NO3)2sdot6H2O) and yttrium nitrate hexahydrate(Y(NO3)3sdot6H2O)were used as Zn andY sources respectivelyThe precipitate reagent was hexamethylene tetramine ZnOseed layer was needed before the pure and Y-doped ZnOsamples synthesis In a typical procedure of seed layerpreparation 219mg zinc acetate (Zn(CH3COO)2sdot2H2O)wasdissolved in 50mL deionized water to form a solution withconcentration of 2mM And then the solution was ultrason-ically agitated for 05 h to obtain a uniform and transparentzinc acetate solution This solution was coated onto cleanedglass substrates by a spin coater at a rate of 2200 rpm for30 s The coated substrates were dried in room temperatureand then annealed at 200∘C for 1 h in air to yield a layer ofZnO seed on the substrate And then the spin coat and annealprocess were repeated two times

In this process 630mg of Zn(NO3)2sdot6H2O and certainamount of Y(NO3)3sdot6H2O (0 1 at 3 at and 7 at) weredissolved in 30mL deionized water Subsequently 297mg ofhexamethylenetetramine (HMTA C6H12N4) was dissolvedinto 30mL deionized water in another beaker under vigorousstirring for 05 h The pH of growth solution was sim6 Afterthat two solutions were mixed together under stirring andthen the seeded glass substrates were immersed into thesolution Then the beaker was put into the oven and keptin it for 8 h at 95∘C After the beaker was cooled to roomtemperature naturally the substrate was removed from thesolution and washed with deionized water and absoluteethanol respectively four times The ZnO rod powders wereobtained after the samples were dried in air at 60∘C

X-ray diffraction (XRD) patterns of the powders wereexamined in 2120579 region of 20∘ndash80∘ with Cu 119870120572 (0154 nm)radiation on Rigaku Model DM AX 2400 Japan Scanningelectron microscopy (SEM) images were examined on a FEIQUANTA 200F (USA) microscope equipped with energydispersive X-ray (EDX) spectroscopy

22 Sensor Fabrication and Gas Sensing Performance TestA proper amount of ZnO materials was mixed with severaldrops of deionized water to form a paste The paste wascoated on a ceramic tube on which a pair of gold electrodeswas previously printed and then a Ni-Cr heating wire wasinserted in the tube to form a gas sensor The thickness ofthe sensing films was about 300 120583m The alumina tube wasthen welded onto a pedestal to form a final sensor unitThe sensors were aged at 300∘C for ten days to achieve thestabilization The gas sensing tests were operated in a staticstate gas sensing test system [17] When the resistance of allthe sensors was stable target gas was injected into the testchamber by a microinjector through a rubber plug Aftermeasurement the sensor was exposed to air by openingthe chamber to the atmosphere The output voltages of thesensors were measured under a bias voltage of 10V DC Thesensor response value (119878) was defined as 119878 = 119877119886119877119892 where 119877119886and 119877119892 were the resistance of the sensor in air and in targetgas respectivelyThe time taken by the sensor to achieve 90of the total resistance changewas defined as the response timein the case of response (target gas adsorption) or the recovery

20 40 60 80

3 YZnO

1 YZnO

ZnO

101

Inte

nsity

(au

)

7 YZnO

100

002

102 11

0

103

200 11

220

100

4

202

2120579 (deg)

Figure 1 XRD patterns of pure 1 at 3 at and 7 at Y-dopedZnO nanorods

time in the case of recovery (target gas desorption)Thewholesystem was controlled by a computer automatically All thetests were operated under about 30 relative humidity

3 Results and Discussion

31 Characterization Results and Growth Process Analysis ofZnO Nanorods Figure 1 shows the XRD patterns of pure 1at 3 at and 7 at Y-doped ZnO nanorods The samplesare polycrystalline in nature and no further heat treatmentis required All the diffraction peaks can be indexed ashexagonal ZnO with lattice constants 119886 = 0325 nm and119888 = 0521 nm which are consistent with the values inthe standard card (Joint Committee for Powder DiffractionStudies (JCPDS) card 36-1451)

Figure 2 shows the SEM images of the as-preparednanorods with different Y doping rates (a) pure (b) 1 at(c) 3 at and (d) 7 at Y-doped ZnO nanorodsThe averagediameters of pure 1 at 3 at and 7 at Y-doped ZnOnanorods are sim300 nm 300 nmsim15120583m 2sim3 120583m and 2sim3 120583m respectively It can be seen that the average diametersof the products are increased as the Y content increased fromzero to 3 at

Figure 3 demonstrates the EDX analysis for the 1 at Y-doped ZnO nanorods We can see that the energy dispersiveX-ray spectroscopic analysis confirmed the presence of Znand Y elements in the investigated area from the Y-dopedZnO nanorods by a hydrothermal process

The growth process of ZnO crystallites is generallyaccepted via the following mechanism [18ndash20] HMTA(C6H12N4) is extensively used in the synthesis of ZnO nanos-tructures and it provides the ammonia molecules (NH3)and the hydroxide ions (OHminus) to the solution (1) and (2)And Zn(NO3)2sdot6H2O is apparently used to provide the zincions (3) In this experiment OHminus is abundant in the mixedaqueous solution fresh formed Zn(OH)2 precipitation (4)can be dissolved immediately by reacting with superfluousOHminus ions and then a transparent Zn(OH)4

2minus solution isobtained (5) In the hydrothermal process the Zn(OH)4

2minus

Journal of Nanomaterials 3

(a) (b)

(c) (d)

Figure 2 SEM images of (a) pure (b) 1 at (c) 3 at and (d) 7 at Y-doped ZnO nanorods

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Energy (keV)

O

Zn

Y

Zn

Zn

Inte

nsity

(au

)

Figure 3 The EDX analysis of the 1 at Y-doped ZnO nanorods

combines with each other and dehydrates into ZnO nucleisimultaneously And then these ZnO nuclei self-assembleto form the rod-like nanostructures along a preferred axisorientation (6)

C6H12N4 + 6H2Olarrrarr 6HCHO + 4NH3 (1)

NH3 +H2Olarrrarr NH4++OHminus (2)

Zn(NO3)2 997888rarr Zn2+ + 2NO3minus (3)

Zn2+ + 2OHminus 997888rarr Zn(OH)2 darr (4)

Zn(OH)2 + 2OHminus997888rarr Zn(OH)4

2minus (5)

Zn(OH)42minus997888rarr ZnO +H2O + 2OH

minus (6)

32 Gas Sensing Properties Gas sensing properties wereperformed at different temperatures to find out the optimumoperating condition for acetone detection Figure 4 showsthe responses of pure 1 at 3 at and 7 at Y-doped ZnOnanorods gas sensors to 100 ppm acetone vapor at differentoperating temperatures The responses of all samples arefound to increase with increasing the operating temperaturewhich attain the maximum at 400∘C and then decrease witha further rise of the operating temperatureThis behavior canbe explained from the kinetics and mechanics of gas adsorp-tion and desorption on the surface of ZnO [21ndash24] Whenthe operating temperature is low the chemical activation ofnanorods is small leading to a very small response Whenthe temperature is too high some adsorbed gas moleculesmay escape before their reaction with the sensing materialdue to their enhanced activation thus the response willdecrease correspondingly At the optimal temperature of


200 300 400 500

0

10

20

30

40

Resp

onse

Pure ZnO

Operating temperature (∘C)

1 at Y-doped ZnO3 at Y-doped ZnO7 at Y-doped ZnO

Figure 4 Responses of pure 1 at 3 at and 7 at Y-doped ZnOnanorods to 100 ppm acetone at different temperatures

0 1000 2000 3000 4000 50000

20

40

60

80

100

120

140

Resp

onse

Acetone concentration (ppm)

0 100 2000

10

20

30

40

Figure 5 Responses of 1 at Y-doped ZnO nanorods to differentconcentrations of acetone at 400∘C the insert shows the calibrationcurve in low concentration range

400∘C (corresponding to the maximum response) 1 at Y-doped ZnO nanorods exhibit the highest response valuesThus 1 atY-doped ZnOnanorods were applied in the entireinvestigations hereafter

Figure 5 shows the sensor response versus acetone con-centration at operating temperature 400∘C and the insertshows the calibration curve in low concentration range Wecan see that the sensitivity (the slop of the curve) of the sensoris higher in low acetone concentration range than in highconcentration rangeThe lowest concentration of the acetonethat the sensor can detect is 10 ppm with the response valueof 43

The transient properties of 1 at Y-doped ZnO nanorodssensor to different concentrations of acetone are shown inFigure 6 For acetone vapor at concentration levels of 100

0 200 400 600 800 1000 12000

20

40

60

Resp

onse

Time (s)

100ppm

200ppm

500ppm

Figure 6 The transient property of 1 at Y-doped ZnO nanorodssensor to 100 200 and 500 ppm acetone consecutively

200 and 500 ppm the responses are about 332 401 and55 respectively The response times are about 30 s 34 s and42 s for 100 ppm 200 ppm and 500 ppm acetone respec-tivily Correspondingly the recovery times are about 90 s100 s and 115 s respectively As the concentration increasesthe response time and the recovery time are both slightlyincreased The sensor selectivity was tested by exposing itto 100 ppm different gases at operating temperature 400∘Cas shown in Figure 7 We can see from Figure 7 that thesensor response to acetone (CH3COCH3) is higher than toammonia (NH3) benzene (C6H6) formaldehyde (HCHO)toluene (C6H5CH3) and methanol (CH3OH)

33 Gas SensingMechanism Formost semiconducting oxidegas sensor the change in resistance is primarily causedby the adsorption and desorption of gas molecules on thesurface of the sensing films [25 26] As a typical 119899-typeMOS sensor the ZnO based sensor belongs to the surface-controlled type [27] namely the sensor response is attributedto the chemisorptions of oxygen on the oxide surface and thesubsequent reaction between adsorbed oxygen and tested gaswhich brings the resistance of the sensing material changeIn ambient air ZnO nanorods adsorb the oxygen moleculeon the surface The adsorbed oxygen is changed to variouschemical adsorptive states (O2

minus O2minus and Ominus) by capturingelectrons from the conductance band

O2(g) lArrrArr O2(ads) (7)

O2(ads) + eminus997888rarr O2(ads)

minus (8)

O2(ads)minus+ eminus 997888rarr 2Ominus

(ads) (9)

Ominus(ads) + e

minus997888rarr O2minus

(ads) (10)

Consequently ZnO will show high resistance Accordingto the report by Takata et al [28] the stable oxygen ions areO2minus below 100∘C Ominus between 100 and 300∘C and O2minus above

300∘CThe operating temperature of the 1 at Y-doped ZnO


0

5

10

15

20

25

30

35

Pure ZnO

Resp

onse

Acetone

FormaldehydeMethanol Toluene

Ammonia Benzene


Figure 7 Responses of pure 1 at 3 at and 7 at Y-doped ZnOnanorods sensors to 100 ppm different gases

nanorods sensor is 400∘C so O2minus is believed to be dominantstate for adsorbed oxygen

When ZnO is exposed to reductive gas acetone(CH3COCH3) the acetone molecules will react withadsorbed O2minus species on the ZnO surface to form CO2 andH2O which leads to the increase of carrier concentrationand the decrease of the electrical resistance

CH3COCH3(g) +O2minus

ads 997888rarr CO2(g) +H2O(g) + 2eminus (11)

As a catalyst Y not only enhances the activity of the semi-conductor surface but also promotes the electrons transferfrom the reducing gas (acetone vapor) to ZnO [8 29] Onthe other hand impurity energy levels introduced by dopingreduced the barrier height of ZnO [30] When Y-doped ZnOnanorods are exposed to acetone vapor its barrier height willbecome lower and depletion layer will be thinner resultingin big changes of the resistance of the sensitive materialTherefore the response of the Y-doped ZnO nanorods toacetone vapor increases However the samples with excessY doping such as 7 at deteriorate with worse response toacetone vapor (as shown in Figure 7) The mechanism of thegas response of ZnO doped with different concentration of Yalso needs further investigation

4 Conclusion

In summary pure and Y-doped ZnO nanorods are synthe-sized via hydrothermal method Gas sensing measurementreveals that Y doping can enhance the acetone sensingproperties of ZnO nanorods and the optimal doping con-centration was 1 atThe acetone vapor concentration rangesfrom 10 ppm to 5000 ppm The response and recovery timesof 1 atY-doped ZnOnanorods to 100 ppm acetone are about30 s and 90 s respectively The sensor got good selectivity ofacetone to ammonia benzene formaldehyde toluene andmethanol Doping yttrium into ZnO enhances the activity ofthe semiconductor surface and introduces impurity energylevels that reduce the barrier height of ZnO

Acknowledgment

This paper was supported by the National Natural ScienceFoundation of China (61176068 61131004 and 61001054)

References

[1] M H Huang S Mao H Feick et al ldquoRoom-temperatureultraviolet nanowire nanolasersrdquo Science vol 292 no 5523 pp1897ndash1899 2001

[2] S-H Choi G Ankonina D-Y Youn et al ldquoHollow ZnOnanofibers fabricated using electrospun polymer templates andtheir electronic transport propertiesrdquo ACS Nano vol 3 no 9pp 2623ndash2631 2009

[3] Z Yuan X Jiaqiang X Qun L Hui P Qingyi and XPengcheng ldquoBrush-like hierarchical zno nanostructures syn-thesis photoluminescence and gas sensor propertiesrdquo Journalof Physical Chemistry C vol 113 no 9 pp 3430ndash3435 2009

[4] A K Bai A Singh and R K Bedi ldquoCharacterization andammonia sensing properties of pure and modified ZnO filmsrdquoApplied Physics A vol 103 no 2 pp 497ndash503 2011

[5] S K Youn N Ramgir C Wang K Subannajui V Cimalla andM Zacharias ldquoCatalyst-free growth of ZnO nanowires basedon topographical confinement and preferential chemisorptionand their use for room temperature CO detectionrdquo Journal ofPhysical Chemistry C vol 114 no 22 pp 10092ndash10100 2010

[6] X Niu W Du and W Du ldquoPreparation and gas sensingproperties of ZnM2O4 (M = Fe Co Cr)rdquo Sensors and ActuatorsB vol 99 no 2-3 pp 405ndash409 2004

[7] X-J WangWWang and Y-L Liu ldquoEnhanced acetone sensingperformance of Au nanoparticles functionalized flower-likeZnOrdquo Sensors and Actuators B vol 168 pp 39ndash45 2012

[8] L Liu S Li J Zhuang et al ldquoImproved selective acetone sensingproperties of Co-doped ZnO nanofibers by electrospinningrdquoSensors and Actuators B vol 155 no 2 pp 782ndash788 2011

[9] S Wei Y Yu and M Zhou ldquoCO gas sensing of Pd-doped ZnOnanofibers synthesized by electrospinning methodrdquo MaterialsLetters vol 64 no 21 pp 2284ndash2286 2010

[10] T Jia W Wang F Long Z Fu H Wang and Q ZhangldquoSynthesis characterization and luminescence properties of Y-doped and Tb-doped ZnO nanocrystalsrdquoMaterials Science andEngineering B vol 162 no 3 pp 179ndash184 2009

[11] R Kaur A V Singh K Sehrawat N C Mehra and R MMehra ldquoSol-gel derived yttrium doped ZnO nanostructuresrdquoJournal of Non-Crystalline Solids vol 352 pp 2565ndash2568 2006

[12] Y Natsume H Sakata T Hirayama and H Yanagida ldquoLow-temperature conductivity of ZnO films prepared by chemicalvapor depositionrdquo Journal of Applied Physics vol 72 no 9 pp4203ndash4207 1992

[13] J P Xu S B Shi X S Zhang Y W Wang M X Zhu and LLi ldquoStructural and optical properties of (Al K)-co-doped ZnOthin films deposited by a sol-gel techniquerdquoMaterials Science inSemiconductor Processing vol 16 no 3 pp 732ndash737 2013

[14] J Aranovich A Ortiz and R H Bube ldquoOptical and electricalproperties of ZnOfilms prepared by spray pyrolysis for solar cellapplicationsrdquo Journal of Vacuum Science amp Technology vol 16no 4 pp 994ndash1003 1979

[15] X R Ye D Z Jia J Q Yu X Q Xin and Z L Xue ldquoFabricationand characterization of carbon nanotubepoly(vinyl alcohol)compositesrdquo Advanced Materials vol 11 no 11 pp 937ndash9411999


[16] S K Mishra R K Srivastava S G Prakash R S Yadav and AC Pandey ldquoDirect acceleration of an electron in infinite vacuumby a pulsed radially-polarized laser beamrdquo Opto-ElectronicsReview vol 18 no 4 pp 467ndash473 2010

[17] P J Yao J Wang W L Chu and Y W Hao ldquoPreparation andcharacterization of La

1minus119909Sr119909FeO3materials and their formalde-

hyde gas-sensing propertiesrdquo Journal of Materials Science vol48 no 1 pp 441ndash450 2013

[18] J Huang YWu C Gu et al ldquoLarge-scale synthesis of flowerlikeZnO nanostructure by a simple chemical solution route and itsgas-sensing propertyrdquo Sensors and Actuators B vol 146 no 1pp 206ndash212 2010

[19] L L Yang Q X Zhao and M Willander ldquoSize-controlledgrowth of well-aligned ZnO nanorod arrays with two-stepchemical bath deposition methodrdquo Journal of Alloys and Com-pounds vol 469 no 1-2 pp 623ndash629 2009

[20] L Yang D Qiu F Yu S Chen and Y Yin ldquo3D flowerlike ZnOmicro-nanostructures via site-specific second nucleation in thezincethylenediaminehexamethylenetetramine tertiary systemrdquoMaterials Science in Semiconductor Processing vol 14 no 3-4pp 193ndash198 2011

[21] N Yamazoe J Fuchigami M Kishikawa and T SeiyamaldquoInteractions of tin oxide surfacewithO

2 H2OAndH

2rdquo Surface

Science vol 86 pp 335ndash344 1979[22] J Herran O Fernandez-Gonzalez I Castro-Hurtado T

Romero G G Mandayo and E Castano ldquoPhotoactivatedsolid-state gas sensor for carbon dioxide detection at roomtemperaturerdquo Sensors and Actuators B vol 149 no 2 pp 368ndash372 2010

[23] M Ghasdi and H Alamdari ldquoCO sensitive nanocrystallineLaCoO

3perovskite sensor prepared by high energy ball

millingrdquo Sensors and Actuators B vol 148 no 2 pp 478ndash4852010

[24] G Sakai NMatsunaga K Shimanoe andN Yamazoe ldquoTheoryof gas-diffusion controlled sensitivity for thin film semiconduc-tor gas sensorrdquo Sensors and Actuators B vol 80 no 2 pp 125ndash131 2001

[25] 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

[26] Y Shimizu S Kai Y Takao T Hyodo and M EgashiraldquoCorrelation between methylmercaptan gas-sensing propertiesand its surface chemistry of SnO

2-based sensor materialsrdquo

Sensors and Actuators B vol 65 no 1 pp 349ndash357 2000[27] C Peng andY L Liu ldquoEnhanced acetone sensing characteristics

by decorating nanoparticles on ZnO flower-like structuresrdquoApplied Physics A vol 111 no 4 pp 1151ndash1157 2013

[28] M Takata D Tsubone and H Yanagida ldquoDependence ofelectrical conductivity of ZnO on degree of sinteringrdquo Journalof the American Ceramic Society vol 59 no 1-2 pp 4ndash8 1976

[29] M E Franke T J Koplin andU Simon ldquoMetal andmetal oxidenanoparticles in chemiresistors does the nanoscale matterrdquoSmall vol 2 pp 36ndash50 2006

[30] X C Wang M G Zhao F Liu J F Jia X J Li and L LGao ldquoC

2H2gas sensor based on Ni-doped ZnO electrospun

nanofibersrdquo Ceramics International vol 39 no 3 pp 2883ndash2887 2013

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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


used without further purification Zinc nitrate hexahy-drate (Zn(NO3)2sdot6H2O) and yttrium nitrate hexahydrate(Y(NO3)3sdot6H2O)were used as Zn andY sources respectivelyThe precipitate reagent was hexamethylene tetramine ZnOseed layer was needed before the pure and Y-doped ZnOsamples synthesis In a typical procedure of seed layerpreparation 219mg zinc acetate (Zn(CH3COO)2sdot2H2O)wasdissolved in 50mL deionized water to form a solution withconcentration of 2mM And then the solution was ultrason-ically agitated for 05 h to obtain a uniform and transparentzinc acetate solution This solution was coated onto cleanedglass substrates by a spin coater at a rate of 2200 rpm for30 s The coated substrates were dried in room temperatureand then annealed at 200∘C for 1 h in air to yield a layer ofZnO seed on the substrate And then the spin coat and annealprocess were repeated two times

In this process 630mg of Zn(NO3)2sdot6H2O and certainamount of Y(NO3)3sdot6H2O (0 1 at 3 at and 7 at) weredissolved in 30mL deionized water Subsequently 297mg ofhexamethylenetetramine (HMTA C6H12N4) was dissolvedinto 30mL deionized water in another beaker under vigorousstirring for 05 h The pH of growth solution was sim6 Afterthat two solutions were mixed together under stirring andthen the seeded glass substrates were immersed into thesolution Then the beaker was put into the oven and keptin it for 8 h at 95∘C After the beaker was cooled to roomtemperature naturally the substrate was removed from thesolution and washed with deionized water and absoluteethanol respectively four times The ZnO rod powders wereobtained after the samples were dried in air at 60∘C

X-ray diffraction (XRD) patterns of the powders wereexamined in 2120579 region of 20∘ndash80∘ with Cu 119870120572 (0154 nm)radiation on Rigaku Model DM AX 2400 Japan Scanningelectron microscopy (SEM) images were examined on a FEIQUANTA 200F (USA) microscope equipped with energydispersive X-ray (EDX) spectroscopy

22 Sensor Fabrication and Gas Sensing Performance TestA proper amount of ZnO materials was mixed with severaldrops of deionized water to form a paste The paste wascoated on a ceramic tube on which a pair of gold electrodeswas previously printed and then a Ni-Cr heating wire wasinserted in the tube to form a gas sensor The thickness ofthe sensing films was about 300 120583m The alumina tube wasthen welded onto a pedestal to form a final sensor unitThe sensors were aged at 300∘C for ten days to achieve thestabilization The gas sensing tests were operated in a staticstate gas sensing test system [17] When the resistance of allthe sensors was stable target gas was injected into the testchamber by a microinjector through a rubber plug Aftermeasurement the sensor was exposed to air by openingthe chamber to the atmosphere The output voltages of thesensors were measured under a bias voltage of 10V DC Thesensor response value (119878) was defined as 119878 = 119877119886119877119892 where 119877119886and 119877119892 were the resistance of the sensor in air and in targetgas respectivelyThe time taken by the sensor to achieve 90of the total resistance changewas defined as the response timein the case of response (target gas adsorption) or the recovery

20 40 60 80

3 YZnO

1 YZnO

ZnO

101

Inte

nsity

(au

)

7 YZnO

100

002

102 11

0

103

200 11

220

100

4

202

2120579 (deg)

Figure 1 XRD patterns of pure 1 at 3 at and 7 at Y-dopedZnO nanorods

time in the case of recovery (target gas desorption)Thewholesystem was controlled by a computer automatically All thetests were operated under about 30 relative humidity

3 Results and Discussion

31 Characterization Results and Growth Process Analysis ofZnO Nanorods Figure 1 shows the XRD patterns of pure 1at 3 at and 7 at Y-doped ZnO nanorods The samplesare polycrystalline in nature and no further heat treatmentis required All the diffraction peaks can be indexed ashexagonal ZnO with lattice constants 119886 = 0325 nm and119888 = 0521 nm which are consistent with the values inthe standard card (Joint Committee for Powder DiffractionStudies (JCPDS) card 36-1451)

Figure 2 shows the SEM images of the as-preparednanorods with different Y doping rates (a) pure (b) 1 at(c) 3 at and (d) 7 at Y-doped ZnO nanorodsThe averagediameters of pure 1 at 3 at and 7 at Y-doped ZnOnanorods are sim300 nm 300 nmsim15120583m 2sim3 120583m and 2sim3 120583m respectively It can be seen that the average diametersof the products are increased as the Y content increased fromzero to 3 at

Figure 3 demonstrates the EDX analysis for the 1 at Y-doped ZnO nanorods We can see that the energy dispersiveX-ray spectroscopic analysis confirmed the presence of Znand Y elements in the investigated area from the Y-dopedZnO nanorods by a hydrothermal process

The growth process of ZnO crystallites is generallyaccepted via the following mechanism [18ndash20] HMTA(C6H12N4) is extensively used in the synthesis of ZnO nanos-tructures and it provides the ammonia molecules (NH3)and the hydroxide ions (OHminus) to the solution (1) and (2)And Zn(NO3)2sdot6H2O is apparently used to provide the zincions (3) In this experiment OHminus is abundant in the mixedaqueous solution fresh formed Zn(OH)2 precipitation (4)can be dissolved immediately by reacting with superfluousOHminus ions and then a transparent Zn(OH)4

2minus solution isobtained (5) In the hydrothermal process the Zn(OH)4

2minus


(a) (b)

(c) (d)


0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Energy (keV)

O

Zn

Y

Zn

Zn

Inte

nsity

(au

)








2minus (5)


minus (6)



200 300 400 500

0

10

20

30

40

Resp

onse

Pure ZnO




0 1000 2000 3000 4000 50000

20

40

60

80

100

120

140

Resp

onse


0 100 2000

10

20

30

40





0 200 400 600 800 1000 12000

20

40

60

Resp

onse

Time (s)

100ppm

200ppm

500ppm







minus (8)


(ads) (9)

Ominus(ads) + e


(ads) (10)




0

5

10

15

20

25

30

35

Pure ZnO

Resp

onse

Acetone


Ammonia Benzene








4 Conclusion


Acknowledgment


References

























2 H2OAndH

2rdquo Surface
























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)

(c) (d)


0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Energy (keV)

O

Zn

Y

Zn

Zn

Inte

nsity

(au

)








2minus (5)


minus (6)



200 300 400 500

0

10

20

30

40

Resp

onse

Pure ZnO




0 1000 2000 3000 4000 50000

20

40

60

80

100

120

140

Resp

onse


0 100 2000

10

20

30

40





0 200 400 600 800 1000 12000

20

40

60

Resp

onse

Time (s)

100ppm

200ppm

500ppm







minus (8)


(ads) (9)

Ominus(ads) + e


(ads) (10)




0

5

10

15

20

25

30

35

Pure ZnO

Resp

onse

Acetone


Ammonia Benzene








4 Conclusion


Acknowledgment


References

























2 H2OAndH

2rdquo Surface
























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




200 300 400 500

0

10

20

30

40

Resp

onse

Pure ZnO




0 1000 2000 3000 4000 50000

20

40

60

80

100

120

140

Resp

onse


0 100 2000

10

20

30

40





0 200 400 600 800 1000 12000

20

40

60

Resp

onse

Time (s)

100ppm

200ppm

500ppm







minus (8)


(ads) (9)

Ominus(ads) + e


(ads) (10)




0

5

10

15

20

25

30

35

Pure ZnO

Resp

onse

Acetone


Ammonia Benzene








4 Conclusion


Acknowledgment


References

























2 H2OAndH

2rdquo Surface
























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0

5

10

15

20

25

30

35

Pure ZnO

Resp

onse

Acetone


Ammonia Benzene








4 Conclusion


Acknowledgment


References

























2 H2OAndH

2rdquo Surface
























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials












2 H2OAndH

2rdquo Surface
























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

Research Article Y-Doped ZnO Nanorods by Hydrothermal ...downloads.hindawi.com/journals/jnm/2013/751826.pdf · Y-Doped ZnO Nanorods by Hydrothermal Method and Their Acetone Gas Sensitivity