Filter paper-templated preparation of ZnO thin films and examination of their gas-sensing properties Filter paper-templated preparation of ZnO thin films and examination of their gas-sensing properties

Filter paper-templated preparation of ZnO thin films and examination of their gas-sensing properties

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  • 论文作者:Bao Wang,Ning Han,Dong Meng,Re
  • 作者单位:School of Chemistry and Environmental Engineering,Institute of Process Engineering,Graduate University of Chinese Academ
  • 更新时间:2020-09-15
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Particuology 9(2011)253-259Contents lists available at Science DirectParticuologyELSEVIERjournalhomepagewww.elsevier.com/locate/particFilter paper-templated preparation of Zno thin films and examination of theirgas-sensing propertiesBao Wang Ning Han, Dong Meng, Renliang Yue b, c, Jinghui Yan Yunfa Chen b,hool of Chemistry and Environmental Engineering, Changchun University of Science and Technology, Changchun 130022, ChinaInstitute of Process Engineering, Chinese Academy of sciences, Beijing 100190, chinaGraduate University of Chinese Academy of Sciences, Beijing 100049, ChinaARTICLE IN FOABSTRACTArticle history:Zno thin films prepared by using quantitative filterReceived 16 November 2009recursor solution were characterized by scannng e/ er as a template and Zn(CH3 CO2):2H20 ethanolectron microscopy(SEM)and X-ray diffractionReceived in revised form 17 March 2010XRD). The effects of sample calcination temperature, precursor concentration and filter paper types wereAccepted 21 February 2011studied and the growth process was investigated by infra-red (Ir) spectroscopy and thermogravimeric analysis/differential thermal analysis(TGA/ DTA). The results show that samples soaked in a 1.5 mol/LKeywords:Zn(CH3 CO2)2-2H2O ethanol solution and calcined at 600'Cyield ZnO films of uniform particle size, approx-mately 30, 40 and 50 nm, for fast-, medium-and slow-speed filter papers, respectively. The formaldehydegas sensing properties of the Zno nanoparticles were tested showing that the material prepared frfast-speed filter paper has a higher response to 120-205 ppm formaldehyde at 400 C than that preparedom medium-or slow-speed paper, which depends on the particle size.o 2011 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy ofSciences. Published by Elsevier B.V. All rights reserved1. Introductiontion method(Xu, Pan, Shun, Tian, 2000). In addition, hierarchicalporous Zno prepared by lauan and fir wood biotemplates exhibitedDue to the good piezoelectric, transparent conductive, photo- a high response to H2S and a low response to formaldehyde (liu,voltaic and gas-sensing properties of ZnO and its ease of integration Fan, Zhang, Gong. Xu, 2009).with a wide variety of semiconductor materials, it has found its One shortcoming of the template method consists of the comway into many fields, such as electronics(Mofor et al., 2008: Sahal, plex processes of preparing a suitable template inserting theHartiti, Ridah, Mollar, Marf, 2008), optical coatings( Caglar, llican, precursors into the template and the final de- templating proce-Caglar, 2009: Sahal et al., 2008)and solar cells(Krunks, Katerski, dure, as indicated in the literature referenced above thereforeDedova, Oja Acik, Mere, 2008). As one of the first materials recog- simplifying these processes is a major focus of the research in thenized for its change in electrical resistance in different atmospheres template synthesis of gas sensing materials. In this context, we used(Moseley Tofield, 1987; Seiyama, Kato, Fuj ishi, Nagatani, 1962 ), quantitative filter paper, which is a commercial product, as the tem-Zno is now becoming widely adopted for the qualitative and or plate. It can quickly absorb Zn(CH3 C02) 2H20 precursor and canquantitative detection of harmful and inflammable gasesbe removed easily by a simple firing process. The results indicateMany preparation methods have been developed to synthe- that Zno thin films prepared by the filter paper template methodsize Zno gas sensing material, such as reactive sputtering( Min, have a high formaldehyde gas response.Tuller, Palzer, wallenstein, Bottner, 2003), sol-gel ( Bae Choi1999), and chemical vapor deposition( Chien et al., 2010). The template method is a versatile means of preparing high-response gas 2. Experimentalnsing materials( Khatko et aL, 2006; Wang, Chu, Wu, 2007).For example, Zno particles prepared by a microemulsion template 2. 1. Synthesis of Zno thin filmsexhibited a higher response than those prepared by a precipita-2H20(A R, Beijing Chemi-cal plar中国煤化二Chemical Plant)was usedas theYHSCNMHGitative filter paper used forCorresponding author. Tel: +86 10 62554676: fax: +86 10 62525716.templaashlessE-mail address: yichen@home ipe ac cn(Y Chen).quantitative filter paper burning ash <0.005%)are listed in Table 11674-2001/s-see front matter o 2011 Chinese Society of Particuology and Institute of Process Engineering Chinese Academy of Sciences. Published by Elsevier B V. All rights reserveddoi:10.1016 j- partic2011.02001B. Wang et aL/ Particuology 9(2011)253-259Characteristics of quantitative filter paper templates used in the experiment.Filter paper typeGrade 589/24-12Slow-speedThe filter paper was first immersed in a precursor solution with aDTAcertain Zn* concentration. After the paper was saturated(about1 min), it was squeezed between two glass sheets to remove bub-bles and excess liquid and then extracted slowly. The paper was putTGinto a muffle furnace(Germany Nabo Furnace Industry EquipmentCo, Ltd LH 15/13)pre-heated at 300-1100 C, where it was burnedout(less than 5 min), yielding Zno thin films102.2. CharacterizationTemperature(C)he morphology of the Zno nanoparticles comprising the filmwas observed using scanning electron microscopy ( SEM, JEOLJSM-6700F, Japan, 5 kV, 10 HA). The crystal phase was identified usingX-ray diffraction(XRD. Panalytical X'Pert Pro, the Netherlands,A cuKal=0.15406 nm, tube voltage 40 kV, current 30 mA, scan step0.02, scan speed 0.12 s/step). Infrared(IR) spectroscopy wasperformed ( Vertex 70 Fourier transform infrared spectrometer.3Bruker, Germany)using a KBr tablet with a mass ratio of 1: 100The thermal analysis test was carried out using an HCT-2 TGA/DTA .4system in air with a heating-rate of 10 C/minC DTA o sThe formaldehyde gas sensing apparatus has been detailed inour previous reports(Han, Tian, Wei, Wang, Chen, 2009: Han,Tian, Wu, Chen, 2009). In brief, a Zno thin film is ultrasonically dispersed in ethanol and drop-coated onto a quartz sheet200000(2 cm x 1 cm) with Ag paste on both ends. The as-prepared film isplaced in a tube furnace and formaldehyde( Beijing Yili Inc, China)Temperature(C)introduced by bubbling its aqueous solutions(0, 1.0, 5.0, and Fig. 1. Thermal analysis curves of (a)Zn(CH, CO,) 2H2 0 and(b) plain quantitative10.0 wt%)with dry air at 0.6L/min The formaldehyde concentra- filter papertions were determined to be o ppm (i.., relative humidity of 70%)32 ppm, 85 ppm and 205 ppm, respectively, according to the chi-ese standard(GB/T 15516-1995) A 5 V DC voltage is applied, andthe current is measured twice by a Keithley 2601(Keithley Instrument InC. USA). The response is defined as Ra/Rg, where Ra and Rg are two strong exothermic peaks corresponding to a higher levelare the resistances in air and in formaldehydeof weight loss in the tGa curves, which is caused by an exothermic reaction of the filter paper fiber The dta curve has a broarong exothermic peak fr600 C, indicating that the fil-ter paper fiber continues to undergo an exothermic reaction and1. Determination of de-templating temperaturegradually decomposes.From the thermal analysis results, it can be seen that at 600C,To determine the de-templating temperature, which is a the filter paper fiber will decompose simultaneously while Znoeey factor in the process, TGA/DTA of the filter paper and particles are formed. Various Zno particles were prepared withn (CH3 CO2h 2H20 were performed, as shown in Fig. 1(a)and(b). a precursor concentration of 1.5 mol/L and with a calcinationAs can be seen in Fig. 1(a), a strong endothermic peak at 130c temperature from 300 to 1100 C, with IR spectroscopy charaappears in the dta curve, corresponding with a weight loss step in terization as shown in Figs. 2 and 3. All filter papers used werethe tga curve, in which Zn(CH3 CO h22H20 loses two molecules fast-speedof crystal water. At 242 C the anhydrous Zn( H3 CO2h2 melts, cor- The main component of filter paper is cellulose. from the IRresponding with the second, endothermic peak in the DtA curve, spectrum of filter paper, shown in Fig. 2, the characteristics of a typ-and at 237 C, the weight loss plateaus in the tGa curve, which ical polysaccharide are seen, with a number of complex functionalis consistent with Zn(CH3 CO2h2 melting At higher temperatures, groups marked in the absorption peak position. The IR spectrummolten Zn(CH3 CO2) undergoes thermal decomposition to form of the material prepared at 300C is similar to the IR spectrum ofZnO, which corresponds with the third, endothermic peak at 300c plainh numher of nther functional groups present.and the fourth, exothermic peak at 380 in the dta curve.中国煤化工) group with overlappingFig 1(b)is the thermal analysis of the quantitative filter paper. absorpThere is a slight endothermic weight loss between room tempera- decorCNMHGindicates the incompleteture and 300 C due to a small amount of water loss from the paper also starts to appear at 438 cm-l. but the intensity is very weakThe loss of cellulose from the filter paper mainly occurs between indicating a low Zno content. These results agree with those of the300C and 600C At 320 C and 380C in the DTA curve, there thermal analysesB Wang et al / Particuology 9(2011)253-259bond absorption peak at 438 cm-I becomes more obvious, but itsfilter paperstrength is relatively weaker than that obtained at calcination tem-peratures above 600C, in accordance with the TGA/ DTA resultsThe absorption peaks at 3437 and 1631 cm-I are due to the absorp-tion of water or-OH in the samplesFig 4 shows the SEM images of Zno nanoparticles comprising the films prepared at calcination temperatures between 400and 1100 C From 400 to 500C, the particle size is small, and the300°Csize distribution is relatively uniform, in the range of 20-30nmFig. 4(a)shows that the Zno particles aggregate at 400 C becausea large amount of residual ash exists at this temperature, as confirmed by TGA and IR spectroscopy. At 500 C, the Zno particlesare arranged irregularly, as shown in Fig 4(b). Fig. 4(c)shows themost ideal, homogeneous Zno nanoparticles with a particle size ofabout 30 nm as prepared at the calcination temperature of 600oC.As the calcination temperature increases from 700 to 1100C, the5001000150020002500300035004000Zno particles become continuously bigger and more irregularlyWavenumber(cmshaped, with particles of 100 nm sintered at 900 C and massive,micron-sized particles at 1100 C.Fig. 2. IR spectra of plain quantitative filter paper and Zno thin film prepared atThe Zn(CH3 CO2 h2 ethanol precursor solution fills the filter paperpores, and upon firing at high temperature undergoes evaporationof ethanol, decomposition of acetate and the formation of particlesEven though the filter paper pore size is on the order of a micron,The IR spectra of Zno thin films prepared at higher temperaturesZno nanoparticles are obtained, which is also observed using otherare shown in Fig 3. The absorption peaks from the filter paper fiber, template with large pores( Liu et al, 2009). At low temperatures,such as C-O, C-H, C-CH2", and-CH2-peaks, become very weakthe nucleation speed of Zno particles is much higher than theircompletely disappear, indicating the decomposition of the cellu- growth speed, and consequently, a large amount of small particlesare obtained in the product. At high temperature the probabillose component. At 1583 cm", there is no carbonyl(C-O)group ity of ion collision may increase due to the acceleration of Brownabsorption peak for calcination temperatures of 400-1100 C, indi-movement, causing the formation of large size particles In addcating complete decomposition of acetate at these temperatures. tion, when sintering Zno ceramics at temperatures higher thanFor calcination temperatures between 400 and 500 C, the Zn-Otial zinc may be formed. The excess interstitial zinc can transfer tothe particle boundaries, where it can react with oxygen to form ZnOagain, leading to particle sintering( Lee Parravano, 1959: Weyl,1100°C3.2. Precursor solution concentrationFig 5 shows the morphology of Zno nanoparticles comprisi900Cfilms prepared from different concentrations of Zn( CH3 CO2h pre-cursor,with0.0456.0.228,0456,0.912,1.5and2.0 mol/L for(a(b),(c), (d),(e), and(f), respectively. The calcination temperaturewas fixed at600°C700°CDifferent samples prepared from different concentrations ofprecursor solution have large differences in appearance. Sampleswith a denser surface are generated by the higher concentra-tion of precursor solution, while small pieces instead of particles600°Care prepared with a lower solution concentration, such as 0.0456and 0.228 mol/L (Fig. 5(a)and(b)). with a gradual increase inconcentration, the particle size gradually becomes smaller, andagglomeration becomes worse. Fig. 6 is a large magnitude SEMimage of Zno thin film prepared using a precursor concentrationof 1.5 mol/L. The resulting film comprises approximately 30nmhomogeneous quasi-spherical particles. Only when the loadingdosage of the precursor solution on certain kind of paper arrivesthe optimal value, small Zno nanoparticles can be obtained. When400°C中国煤化工 was too low and the paperpaper fiber was completely5001000150020002500300035004000CNMHGperature, resulting in greatWavenumber(cmu particies. As a result, Zno thin films of highdensity cannot be obtained because particles cannot be closelyFig. 3. IR spectra of Zno thin films prepared at different temperatures spaced. When the precursor solution concentration is too high,too(400-1100many Zno particles can easily result in hard agglomeratesB. Wang et al Particuology 9(2011)253-259bECefFig 4. SEM images of Zno thin films prepared at different temperatures: (a)400 C (b)500 C (c)600 C (d)700 C (e)900 C and(0 C.3.3. Zno thin films obtained using different types of filter papering in more free space left after calcination and large gaps betweenZno particles, as shown in Fig. 7(a). In contrast, fast-speed filterFig. 7 shows SEM images of Zno thin films obtained using paper has larger pores and less fiber, causing increased contactslow-speed and medium-speed quantitative filter paper templates. between Zno particles and ultimately leading to the formation ofBoth samples were prepared using a precursor concentration of dense films with small size particles after calcination. Medium-1.5 mol/ L and a calcination temperature of 600 C Zno nanopar- speed filter paper has characteristics between the other two papersticles comprising the film prepared from slow-speed filter paper The relationship between paper porosity and resulting particlehave the highest inter-particle porosity(Fig. 7(a)), while the film quality is similar to that of different concentrations of Zn(CH3 CO2hmade from fast-speed filter paper have smaller inter-particle precursor and particle quality( Fig. 5 ): if there is less Zn( CH3CO2h2.pores and more uniform particles(Fig. 6) Samples prepared from then the particle gap is large, and vice versamedium-speed filter paper displayed porosity and particle size inIn Fig. 8, Zno thin films prepared from fast-speed, medium-between those of the other two filter papers(Fig. 7(b).Different speedfilm densities and particle sizes might result from different porosi. XRD中国煤化工 er papers display the sameties and pore size distributions in the filter papers. The pore sizes of ondarfast-speed, medium-speed and slow-speed papers are 12-25 um, the SclCNMHGze(d) was calculated usingnotnedifraction peak: d=kA/Bcos B4-12 um and 2 um, respectively(Table 1). Because of the small where k is a constant(usually 0.89). A is the wavelength of the inci-pore size, slow-speed paper contains a large amount of fiber, result- dent X-ray(0.15406 nm). 0 is the Bragg diffraction angle and B isB Wang et al. Particuology 9(2011)253-259aeFig. 5. SEM images of Zno nanoparticles comprising films prepared from different Zn( CH3 COz) precursor concentrations: (a)0.0456. (b)0. 228, (c)0. 456. (d)0.912 (e)1.5and(0 2.0 mol/Lthe full width at half maximum(Borchert et al., 2005 ). The sizes of tors. Formaldehyde is commonly postulated to be oxidized by theZnO particles prepared from fast-speed, medium-speed, and slow- adsorbed oxygen ion, shown as follows(Lv et al., 2008: Wu, 1992well agreeing with the SEMresults. As can be seen from the SEM andXRD analysis results, the most ideal Zno thin films were prepared O2(g)+2e-20adsby fast-speed quantitative filter paper, so fast-speed quantita-tive filter paper was used to prepare the material in the coming HCHo+ 20 ads-CO2+H20+2esectionswhere O2(g) is oxygen in air and o is the adsorbed oxygen ion.3. 4. Study of gas-sensing propertiesThus, the electron extracted by oxygen returns to the bulk, and theFor a material to be used in gas-sensing applications, one orFi中国煤化工 re was determined using themore material's properties should change in response to the envi- fast-CNMHGwn in Fig 9. The maximumronmental change in gas composition to be measured (Lee Reedy, respHILu us wv . ere the formaldehyde con-2000). For Zno thin films, the resistivity changes significantly with centration is between 120 and 205 ppm At low temperatures. thechanges in gas composition In the gas-sensing process, adsorbed adsorbed HCHO and free electrons may not be excited in ZnO effecoxygen first behaves as an electron extractor for bulk semiconduc- tively while at high temperatures, HCHo does not adsorb easily.B Wang et al Particuology 9(2011)253-259Table 2Comparison of the response of Zno thin hlms prepared from fast-speed quantitative filter paper with literature informationMaterialPreparation methodLiterature065pFire wood templateHigh to H2S, low to HCHOLiu et al. (2009Precipitationan, Tian, Wei, et aL. (2009)and Han Tian, Wu, et al. (2009)0.825 mV/ppmSno2-NiOCo-precipitation-O5 ppmChen et al. (2008)In O,-CdoCalcination80-10 ppm(nonlinear)Lv et al. (2008)Slow2030405060702 Theta(degree)Fig 8. XRD patterns of Zno thin films prepared by fast, medium- and slow-speedquantitative filter papers.Fig. 6. Large magnitude SEM image of a Zno thin film prepared from 1.5 mol/L ofactive surface state might occur with a decrease in particle size.leading to a higher gas response. The response of the Zno nanoparand oxygen might desorb, thus decreasing the influence on the ticles prepared from fast paper is linearly related (-0.65 ppm-)film resistance. The formaldehyde gas-sensing properties of fast, with the formaldehyde concentration, as shown in Fig 10 inset Amedium-and slow-speed paper Zno particles were also tested at comparison of the response of these particles with the literature400C, as shown in Fig. 10. The Zno prepared by fast-speed paper is made in Table 2. The response of these particles is higher thanexhibited the highest response, and Zno prepared using slow paper or comparable to those of commonly used materials(NiO, SnOzexhibited the lowest response. It is well known that the gas sens- and Zno), but lower than the most sensitive material, which mighting ability of a material is surface-controlled. It is possible that be a result of the catalytic effect of Cdo Chen, Liu, Zhou, & Wangthe surface activity is higher for smaller Zno particles, as more 2008)a中国煤化工CNMHGIOFig. 7. SEM images of Zno thin films prepared with: (a)slow-speed quantitative filter paper and (b) medium-speed quantitative filter paper259205 ppmhighest gas-sensing ability, which is between 120 and 205 ppmformaldehyde(linearly related)at 400 C, depending on the particleAcknowledgementhe authors thank National 863 Program(No. 2007AA061401)for financial support.12040090ReferencesBae, H. Y.& Choi, G. M. (1999). Eleducing gas sensing properties ofn0 and Zno-Cuo thin films fabricated by spin coating method. Sensors and151931-1936Caglar, M, llican, S, Caglar, Y (2009). Influence of dopant concentration on theproperties of Zno in films by sol-gel method. Thin Solid Films, 517(17).023-5028Chen, T, Liu, Q J, Zhou, Z L, Wang Y D (2008). The fabrication and gas-sensingcharacteristics of the formaldehyde gas sensors with high sensitivity Sensorsand Actuators B: ChemicaL, 131(1)301-305hien, E.S. S, Wang, C R, Chan, Y. L Lin, H L, Chen, M. H, wu, R ]. (2010).Fast051015202530response ozone sensor with Zno nanorods grown by chemical vapor deposition.Time(min)Dirksen, J. A Duval, K, Ring, T A(2001). Nio thin-film formalHan, N, Tian, Y. Wei, L, Wang, C, Chen, Y (2009). NiO thin film fabricFig 9. Effect of test temperature on the response of Zno prepared from fast-speedretic deposition and formaldehyde gas sensing property therquantitative filter paper at 70% relative humidityHan, N Tian, Y. Wu, x.& Chen, Y(2009) Improving humidity selectivity inand Actuators B: Chemical, 138(1). 228-23Low-speedKhatko, V Gorokh, G, Mozalev, A, Solovei, D, Llobet, E, Vilanova, X, et al. (2006).Medium-speedKrunks, M. Katerski, A, Dedova, T, Oja Acik, L, Mere, A(2008). Nanostructuredsited Zno nanorod array. Solar Energy120Lee, A P, Reedy B J (2000). Application of radiometric temperaturetion methods to semiconductor gas sensors, Sensors and Actuators69(1-2)37-45.85Lee, V J, Parravano, G (1959). Sintering reactions of zinc oxide Jourmal of AppliedPhysics,3o11).1735-1740.T, Zhang, D, Gong, X,& Xu. ](2009). Hierarchically porous Zno wihigh sensitivity and selectivity to H2S derived from biotemplates. Sensors andActuators B: Chemical 136(2), 499-509.32Lv, P, Tang, Z, Yu. J, Zhang, F Wei, G Huang, Z, et al. (2008). Study on a micro-gasand Actuators B: Chemical, 132(1) 74-80Min, Y K. Tuller, H L Palzer, S. wallenstein. ], Bottner, H (2003). Gas response⊥⊥,f reactively sputtered ZnO films on Si-based micro-array Sensors and Actuators103435-4Mofor, A C. Bakin, A S. Postels, B Suleiman, M, Elshaer, A Waag. A(2008).Time(min)Growth of Zno layers for transparent and flexible electronics. Thin Solid Films.Fig. 10. Gas sensing properties of Zno particles prepared from fast, medium- and Moseley, P. T.& Tofield, B. C(1987). Solid state gas sristol: Adam-Hilger.slow-speed quantitative filter papers tested at 400 C and 70% relative humidity.Wang, C, Chu, X,& Wu, M (2007). Highly seWeyl, W.A(1952). Atomistic iation of mechanism of solid state reactionsand of sintering Ceramic Ag28-38.4. ConclusionsWu, x (1992). Sensors and materials. Beijing: Publishing House of Electronics indus-Sahal, M, Hartiti, B, Ridah, A, Mollar, M,& Mari, B (2008). Structural, electrical andZno thin films with uniform particle size can be prepared usinguantitative filter paper as a template and a 1.5 mol/L precursorJouma,3912)1425-1428zinc acetate dihydrate ethanol solution followed by calcinationSeiyama, T, Kato, A Fujiishi, K, Nagatani. M. 1962). A new detector for gaseousat 600 C. Under these conditions, the sizes of ZnO nanoparticlesomponents using semiconductive thin films. Analytical Chemomprising films prepared from fast, medium- and slow-speed Xu,J.JiYHaHan. L& Gan. 0.(0n7) Selective detection of HCHOuantitative filter papers are approximately 30, 40 and 50nm. The中国煤化工 and actuators B: Chemical.1202formaldehyde gas-sensing properties of the different ZnO nanopar- Xu, J. Palticles were tested, and the 30 nm Zno nanoparticles have theCNMHGemical.6(18-3.27-279operties

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