Soft template synthesis of high selectivity mesoporous SnO2 gas sensors Soft template synthesis of high selectivity mesoporous SnO2 gas sensors

Soft template synthesis of high selectivity mesoporous SnO2 gas sensors

  • 期刊名字:上海大学学报(英文版)
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  • 论文作者:LIU Gang,TAN Zhi-jin,WANG Cong
  • 作者单位:School of Environmental and Chemical Engineering
  • 更新时间:2020-09-15
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论文简介

J Shanghai Univ (Engl Ed), 2010, 14(4): 297-300Digital Object Identifier(DOI): 10.1007/s11741-010-0647-3Soft template synthesis of high selectivity mesoporous SnO2 gas sensorsLIU Gang(刘刚), TAN Zhi-jin (谈志金),WANG Cong(王丛), WU Ruo-fei (吴若飞),ZHANG Hai-jiao (张海娇)School of Environmental and Chemical Engineering, Shanghai University, Shanghai 20444,4 P. R. China(Communicated by WU Ming-hong)⑥Shanghai University and Springr-Verlag Berlin Heidelberg 2010A bstract Mesoporous SnO2 was synthesized using cetyltrimethyl ammonium bromide (CTAB) as supermolecule templateby hydrothermal method fllowved by calcining under diferent temperature in air. X-ray difraction analysis (XRD) andtransmission electron microscopy (TEM) techniques were used to characterize the structure of mesoporous SnO2. The resultsindicated that the gas sensors prepared by using mesoporous SnO2 after calcination at 400 °C showed quick response andrecovery to ethanol at 200。C. It was also found that the mesostructure SnO2 with small particle size had higher sensitivityand seletivity to CzHgOH than the SnO2 nanoparticles the particle size of which is 20 nm syntheized by sol-gel method.Keywords tin dioxide, mesoporous nanostructure, cetytrimethyl ammonium bromide (CTAB), gas sensing propertiesIntroductionbecome ideal candidates in many fields, such becomecatalysis, batteries, water treatment, etc.15-17] After-As an n-type semiconductor, tin dioxide (SnO2)wards, a number of related synthetic strategies havehas a lot of technological applications.It has beeneen developed and a variety of materials have beenused in, for instance, rechargeable Li-batteries, gas sen-synthesizedl8- 19]. Up to date, several approaches utiliz-sors, catalysis, photoelectrochemical cells, etc.1-4 Ating a supramolecular templating mechanism have beenpresent, various morphologies of SnO2 nanostructuredreported for the preparation of mesoporous SnO2. How-materials such as nanoparticles, nanorods, nanobelts,ever, previous studies focused mainly on the microstruc-and nanowires have been synthesizedl2,5-7. Althoughtures of the synthesized SnO2, and paid little attentionit has various structures and operating mechanisms,to the subsequent crystallization and high temperaturemost of the applications need the similar propertiescalcination processes120-21.such as high surface areas and good crysallinity18-10).In our work, mesoporous SnO2 was synthesized byRecently, SnO2 gas sensors are increasingly demandedintroducing cetytrimethylammonium bromide (CTAB)for fammable- gas inspection, air-quality monitoring andinto a homogenous SnCl4 solution. The thermal stabil-explosive-gas detection. It is well known that the sens-ity is critical for gas sensing application. Thus long-terming mechanism of SnO2 is the surface controlled type.microstructural stability is needed under high tempera-The response based on the reaction between adsorbedture conditions. Especially, the efect of different caici-oxygen species on the surface of SnO2 materials and thenation temperature on the properties of the mesoporousgas molecules may be detectedl11-13]. Hence, the syn-SnO2 is also investigated in detail.thesis of thermally stable mesoporous SnO2 with highsurface areas is of great importance.1 ExperimentMCM family of mesoporous silicates using thesupramolecular templating approach was firstly discov-1.1 Synthesis of mesoporous SnO2ered in 199214. Since mesoporous materials have at-AIl the chemical reagents used in the experimentstracted considerable attention because of their remark-were obtained from commercial sources 88 guaranteed-ably large surface areas, chemical inertness, thermal sta-grade reagents and used without further purification.bility and narrow pore distribution, which make themIn a typical syathesis, 2.2 g CTAB was used asReceived Dec.9, 2009; Revised Jan.10, 2010Project supported by the Shanghai Leading Academic Discipline Projec中国煤化工1 Science FoundationofShanghai Municipality (Grant No.08ZR1407800), the Research FoundeChemical Engineering(ECUST), and the Shanghai Key Laboratory of Green Chemnistry andMYHCNMHGCorresponding author ZHANG Hai-jiao, Ph D, Assoc Prof, E-mail: hjzhang128@shu.edu.cn298J Shanghai Univ (Engl Ed), 2010, 14(4): 297 -300the surfactant and dissolved in 60 mL water undercalcination. Significant grain growth is evidenced after60。C, and a solution of 1.4 g SnCl4:5H2O in 60 mLcalcination at 300 °C and 400 °C, which is accordancewater was added to CTAB solution.The resultingrith XRD results. The diameter of SnO2 particles ismixture stirred for 3 h at 60 °C and then heated togrowing but the mesoporous structure of SnO2 is not160 °C in a Teflon-lined autoclave for 16 h. Thendestroyed. When the temperature increases to 500。C,the solid product was filtered, dried and calcined atthe mesoporous structure of SnO2 is destroyed and the300 °C, 400 °C and 500 °C, respectively, for 2 h in orderparticles grow together.to remove the surfactant CTAB.1.2 Characterizations of samplesX-ray powder diffraction (XRD) patterns were ob-tained on the Japan Rigakul D/max 2550 instrumentoperating at 40 kV and 40 mA using CuKa radiation(入=0.154 nm). The structural properties and the mor-phology of samples were studied by a JEOL 200CX,旨transmission electron microscopy (TEM), and all sam-ples were first dispersed in ethanol, and then collectedusing copper grids covered with carbon films for analy-sis.1.3 Fabrication and performance of sensors20/(°)The chemical sensors were constructed with synthesized mesoporous SnO2 as building blocks by dispers-Fig.1 XRD patterns of mesoporous SnO2 before (a)and after calcination at 300 °C (b), 400 °C (c),ing the nanomaterials into water to form a slurry sus-and 500 °C (d)pension. The mixture was then coated onto the sur-face of ceramic tubes with two Pt electrodes to obtain thick films. Side-heating type devices were aged at300。C for 3-5 d to improve the stability prior to test-ing. The gas sensing properties were characterized u8-ing a computer-controlled gas sensing characterizationsystem (WS-30A. Zhengzhou). Special software was developed to collect the data and govern the whole systemby computers automatically.2 Results and discussions100 nm200 nm(a) Before calcination(b) After calcination at 300 CFigure 1 displays XRD patterns of mesoporous SnO2before and after calcination at different temperature. Asseen from Fig.1(a), the SnO2 sample exhibits low crys-tallinity before calcination. By a certain heat treatment,the SnO2 samples have significant changes. By increas-ing the calcined temperature from 300 °C to 500 °C,SnO2 samples show higher crysallinity. When the tem-perature improves to 400。C, the SnO2 sample is com-pletely crystallized. The prominent peaks corresponding200mto (110), (101) and (211) crystal lattice planes and other(C) Ater calcinationat 400 C (d) After caleination at 500 Csmaller peaks coincide with the corresponding peaks ofFig.2 TEM images of mesoporous SnOzthe rutile structure of SnO2 given in the standard datafile (JCPDS No. 41-1445). With increasing the calcinedCombining the XRD with TEM images results, wetemperature to 500 °C, the peaks become narrower andcan find that the pore structure is still thermally stablethe intensity of peaks become higher. This implies theeven at 400。C, and complete crystallization appears af-crystallization and growth of SnO2 nanoparticles.ter treatment at this temperature. Therefore, we choseTEM images of synthesized samples before and af-the sample calcined at 400 °C and carried on gas sensingter calcining at different temperature are shown inperfor中国煤化工onse of mesoporousFig.2. As can be seen, the synthesized powder has dis-ordered mesoporous structure and the diameter of poresSnO2fYHC N M H Gt operation temper-is similar with that of SnO2 particles about 3 nm beforeature with exposure to 50x10-6 ethanol. The re-J Shanghai Univ (Eng! Ed), 2010, 14(4): 297- 300299sponse, defined as号,where Rair and Rg are thealso compared with SnO2 nanoparticles synthesized byelectrical resistance in dry air and ethanol gas, re-Yang, et al122, whose diameter is about 20 qm. Thespectively, increases with increasing the temperature tosensors show higher sensitivity with the improvement200 °C and then decreases.of ethanol concentration, and mesoporous SnO2 alsoshows higher response than SnO2 nanoparticles underthe same concentration of ethanol and work tempera-ture. We think that surface reactions are dependent on10the ethanol concentration 88 long 88 adsorption sites are3enough. However, when the ethanol concentration be-comes high compared with the available adsorption siteson the surface of SnO2, ethanol molecules have to com-pete for adsorption sites, which may become the rate-determining step in a high gas concentration region. Thelinear dependence of gas sensitivity on target gas CoD-140 160 180 200 220 240 260centration between gas sensitivity and the ethanol con-Temperature /ccentration was previously reported in an ethanol sensorFig.3 Temperature dependence of sensor sensitivity tousing SnO2 nanorodsl.ethanol at 50x10-Figure 4 shows response and recovery curves of meso-porous SnO2 sensors exposed to 50x 10-6 ethanol after3 cycles of gas on and off at 200 °C. The sensor showsfast response and recovery time under this temperature,which is only 5 s and 9 s, respectively. In addition, thesensor shows excellent response and recovery properties,2.n。and the sensitivity reaches almost the same level everyotime in 3 cycles of gas on and off.H2co Ethanol Gasoline AcetoneGases2.4FFig.5 Sensitivity of mesoporous SnO2 sensors to diferent.0gases (50x10-6) at 200 °C.6 +50 r-Mesoporous SnO25t- SnOz nanoparticles40 t亨o.8-s5上30 t.4几几5L0t50 100 150 200 250 300 350Time /sFig.4 Response and recovery curves of mesoporous SnO2to 50x10-6 ethanol alfter 3 cycles of gas on and off100 200 300 400 500at 200 °CConcentration /10*Fig.6 Response of mesoporous SnO2 and SnO2Especially, the response of these sensors to othernanoparticles to different concentrations ofgases including CO, H2, gasoline and acetone is alsoethanol at 200 °Cmeasured. The sensitivities of sensors to the tested gases3 Conclusionsat 50x10-6 are shown in Fig.5. They are all lower thanthe response to ethanol. It can be concluded that theMesoporous SnO2 nanomaterial is prepared success-chemical sensors made by mesoporous SnO2 exhibit se-fully_ using SnCl45H2O as the stannum source andlectivity to ethanol vapor on the basis of good sensitivityCTA中国煤化工olar template by by-and quick response and recovery time for practical ap-drotHsized SnO2 has highplications.crystfHC N M H Gorous nanostructureFigure 6 shows the response of mesoporous SnO2 tofor calcination at 400 °C. The sensor synthesized by thediferent concentrations of ethanol at 200 °C, and it ismesoporous SnO2 shows better response and recovery300J Shanghai Univ (Engl Ed), 2010, 14(4): 297- 300properties than SnO2 nanoparticle with 20 nm diame-[11] HYoDo T, ABE S, SHIMIZU Y, EGASHIRA M. Gaser. In addition, it also shows better ethanol selectivitysensing properties of ordered mesoporous SnO2 and ef-and sensitivity to gasoline, acetone, H2 and CO at op-fects of coatings thereof [J]. Sensors and Actuators B,erating temperature 200 °C. 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