Synthesis of MoVTeNb Oxide Catalysts with Tunable Particle Dimensions

DOI:10.1002/cctc.201100089SynthesisofMoVTeNbOxideCatalystswithTunableParticleDimensions

YuryV.Kolen’ko,[b]WeiZhang,[c]RaoulNaumannd’Alnoncourt,[a]FrankGirgsdies,[a]ThomasW.Hansen,[d]TillWolfram,[a]RobertSchlçgl,[a]andAnnetteTrunschke*[a]

IntroductionDuringthelastthreedecades,complexmultimetaloxideshavecapturedtheinterestofresearchersaspotentialcatalystsforalkaneactivation.[1–5]Intheoxidativedehydrogenationofethane[5]andtheselectiveoxidationofpropanetoacrylicacid,[6]selectivitiesofapproximately80%havebeenachievedathighalkaneconversionovermixedoxidesbasedonMo,V,Te,andNb.Theactivecatalystsaretypicallycomposedofthetwodifferentbronze-likecompoundsMo7.8V1.2Te0.937NbO28.9andMo4.31V1.36Te1.81Nb0.33O19.81,whicharereferredtointheliteratureastheM1andM2phases,respectively.[7–13]TheactivationoftheCÀHbondsinthealkanemoleculehasbeenattributedpri-marilytotheM1phase.[6,14–18]AsynergisticeffectofM2inM1–M2phasemixtureshasalsobeendiscussed.[19]Highcrystallini-tyofthecatalystisrequiredtoachievetheutmostcatalyticperformance,implyingthehypothesisthatthedevelopmentofactiveensemblesonthesurfaceofM1isgovernedbywell-de-finedstructuralfeatures.Accordingly,thecatalyticrelevanceofthecrystallographic(001)planes(basalplanesofelongatedM1particles)hasbeenintensivelydiscussedintheliterature.[10,20–25]However,restrictedapplicabilityandresolutionofspectroscop-icandcrystallographicmethodsstronglylimittheknowledgeregardingthemolecularstructureandelectronicdetailsoftheM1surfacetermination.ThesituationisfurthercomplicatedbythefactsthattheM1phaseisonlyaccessibleinacertaincom-positionalrangeandthatthesurfacecompositionoftheactivecatalystisextremelysensitivetowardsoperationconditions.[26]Becauseofthebroadparameterspacethatdeterminesthecat-alyticresponseofM1,developmentofcontrolledsynthesismethodstoproducewell-defined,phase-purematerialsisstronglyrequired.Thisisimportantforgainingadeeperin-sightintothecatalyticversatilityofM1,whichwouldprovideauniqueguidetodesignanddiscovernewcatalystsforselec-tiveoxidation.Ingeneral,MoVTeNboxidecatalystsarepreparedbycopre-

cipitationwithsubsequentrapidevaporationofthesolvent[3,27]orbyhydrothermalsynthesis.[6,16,28–35]Subsequentannealinginaninertatmosphereisnecessarytocrystallizethesolidsandtoderivebalancedoxidationstatesofthekeyelements.[36,37]At

thestateoftheart,itisstillanontrivialexperimentaltasktosynthesizephase-pureM1catalystsinacontrolledmanner.Particularly,itisdifficulttoavoidanintrinsicformationofthebyproducts,suchastheM2phase,Te,(Mo0.93V0.07)5O14,

[a]Dr.R.N.d’Alnoncourt,Dr.F.Girgsdies,T.Wolfram,Prof.R.Schlçgl,Dr.A.TrunschkeDepartmentofInorganicChemistryFritzHaberInstituteoftheMaxPlanckSocietyFaradayweg4–6,14195Berlin(Germany)Fax:(+49)30-8413-4405E-mail:trunschke@fhi-berlin.mpg.de

[b]Dr.Y.V.Kolen’koPresentaddress:InternationalIberianNanotechnologyLaboratoryAv.MestreJosØVeiga,s/n,4715-330Braga(Portugal)

[c]Dr.W.ZhangPresentaddress:RisøNationalLaboratoryforSustainableEnergyTechnicalUniversityofDenmarkFrederiksborgvej399,4000Roskilde(Denmark)

[d]Dr.T.W.HansenPresentaddress:CenterforElectronNanoscopy,TechnicalUniversityofDenmarkFysikvejBuilding30,2800KongensLyngby(Denmark)

SupportingInformationforthisarticleisavailableontheWWWunderhttp://dx.doi.org/10.1002/cctc.201100089.

Reliableproceduresforthecontrolledsynthesisofphase-pureMoVTeNbmixedoxideswithM1structure(ICSD55097)andtunablecrystaldimensionsweredevelopedtostudythestruc-turesensitivityoftheselectiveoxidationofpropanetoacrylicacid.AseriesofpowderedM1catalystswassuccessfullypre-paredonagramscalebyusingahydrothermal-basedroute,purificationofbiphasicM1-M2(M2phase–ICSD55098)oxidesystems,andaninnovativeapproachutilizingasuperheatedwatervaportreatmentofcalcinedprecursors.Theinfluenceofthepreparationtechniqueontheparticlemorphologyandthesizeisdiscussed.Detailedexperimentalstudieshighlightthattheas-derivedcatalyticmaterialswereindeedphase-pureandcompositionallyuniformMoVTeNboxideM1powders,com-posedofsingle-crystallineandstructuraldefect-freecrystalsgrownalongthecaxis.Themorphologicallydifferentcatalystswerestudiedintheselectiveoxidationofpropanetoacrylicacid,revealingthatactivesitesappearontheentireM1surfaceandillustratingthehighsensitivityofcatalystperformanceonthecatalystsynthesismethod.

ChemCatChem2011,3,1597–1606󰀂2011Wiley-VCHVerlagGmbH&Co.KGaA,Weinheim1597

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金属性二维过渡金属硫化物的溶剂热合成及电催化析氢性能

Vol.42 2021年2月No.2654~661 CHEMICAL JOURNAL OF CHINESE UNIVERSITIES高等学校化学学报金属性二维过渡金属硫化物的溶剂热合成及电催化析氢性能余强敏1，张致远1，罗雨婷1，李洋2，成会明1，3，刘碧录1（1.清华大学深圳盖姆石墨烯中心,清华⁃伯克利深圳学院/清华大学深圳国际研究生院,深圳518055；2.伍伦贡大学超导和电子材料研究中心,伍伦贡2500,澳大利亚；3.中国科学院金属研究所,沈阳材料科学国家实验室,沈阳110016）摘要采用溶剂热法制备了多种二维过渡金属硫化物(TMDCs),在合成过程中通过调控反应前驱体的滴加速率来控制所得TMDCs的形貌和结构.然后采用高温热处理来提高TMDCs的结晶性,从而提升了其电催化活性.在酸性电解液中进行电催化析氢性能测试.结果表明,“花状”结构的金属性二维二硫化铌(NbS2)具有最佳的催化活性和稳定性,在电流密度为10mA/cm2时,其过电位仅为146mV,持续工作24h后电流密度几乎不衰减.研究发现,可充分暴露面内活性位点的“花状”结构以及高温处理后材料导电性的提高是二维NbS2具有优异电催化性能的主要因素.关键词二维材料；二硫化铌；溶剂热合成；电催化析氢；电流密度中图分类号O646文献标志码A氢能具有能量密度高、产物零碳排放且可再生等优点，被认为是最理想的能量载体之一，开发和利用氢能对能源的可持续发展具有重要意义［1，2］.在众多的制氢技术中，电解水制氢优势显著，具有能量转换效率高、氢气（H2）纯度（>99.99%）高及无需苛刻制备条件等优点［3~5］.在电解水反应中，电极反应动力学直接关系到整个电解水能量转换效率的高低［6，7］.因此，具有高催化活性的电极材料是提高电解水效率的决定性因素.商用贵金属铂基（Pt）催化剂被认为是最理想的析氢反应（HER）电催化材料，因为Pt催化剂的氢吸附自由能（ΔG H*）接近于0eV，非常有利于反应中间体的吸附和反应产物的脱附.此外，金属Pt催化剂具有良好的导电性，可以实现催化过程中高效的电子转移［8，9］.然而，贵金属Pt资源稀缺、价格昂贵，难以满足工业析氢催化材料的大规模使用要求.因此，需要寻求资源丰富、价格低廉、性能优异的材料来替代现有的Pt材料以满足工业化需求.廉价的过渡金属化合物，如金属氧化物（CoO x，FeO x，NiO x）［10，11］、金属磷化物（CoP x，FeP x）［12~14］、金属氮化物（MoN x）［15］、金属碳化物（Mo x C y）［16］以及金属合金（Ni x Mo y）［17］等，均被用作电解水催化剂，然而，这些材料的本征活性差、活性位点数有限及耐腐蚀性差等缺点严重制约了它们在规模化制氢应用中的潜力.近年来，二维材料，尤其是二维金属性过渡金属硫化物（TMDCs）材料在电催化析氢应用中逐渐受到关注，具有工业化应用前景［18~20］.与其它二维材料相比，金属性TMDCs具有很多独特优势.首先，金属性TMDCs是零带隙材料，导电性好，有利于电化学过程中的电荷传输.其次，金属性TMDCs具有丰富的面内活性位点，密度泛函理论计算表明，一些金属性TMDCs的ΔG H*也与Pt接近［21］，是现有材料体系中少有的与Pt性能相当的材料，故而无需其它缺陷或掺杂修饰来增加其催化活性位点的数目［22~25］.目前，金属性TMDCs主要是通过化学气相沉积（CVD）法制备，该方法制备的样品质量高，但产量低，doi：10.7503/cjcu20200454收稿日期：2020-07-14.网络出版日期：2020-10-13.基金项目：国家自然科学基金(批准号:51722206,51920105002)、广东省创新创业研究团队项目(批准号:2017ZT07C341)和深圳市工业和信息化局项目(批准号:201901171523)资助.联系人简介：刘碧录,男,博士,副教授,主要从事二维材料的可控制备及其在光电器件和能源转换领域的应用研究.E-mail:********************655 No.2余强敏等：金属性二维过渡金属硫化物的溶剂热合成及电催化析氢性能因而难以在电催化剂中获得规模化应用.相比于CVD法，液相法合成通常具备规模化制备的优点，是可大量制备金属性TMDCs的潜在重要方法.本文采用溶剂热法制备不同导电属性的TMDCs催化剂.以金属性NbS2为主要研究对象，研究了反应前驱体的滴加速率对催化剂形貌结构的影响和高温退火处理对催化剂结晶性的影响，考察了其在酸性条件下的电催化析氢活性及稳定性，为金属性TMDCs在高效电解水制氢中的应用提供了新思路.1实验部分1.1试剂与仪器五氯化铌（NbCl5，纯度99.5%）、五氯化钼（MoCl5，纯度99.5%）、三氯化钒（VCl3，纯度99.5%）、十二硫醇（DDT，纯度99.0%）和油胺（OLA，纯度85.0%）均购于上海阿拉丁生化科技股份有限公司；硫酸（H2SO4，质量分数98.0%）、丙酮（C3H6O，纯度99.5%）和乙醇（C2H6O，纯度99.8%）均购于国药集团化学试剂有限公司.SU-8010型场发射扫描电子显微镜（SEM，日本日立公司）；Tecnai F30型透射电子显微镜（TEM，美国FEI公司）；PHI5000VersaProbeII型X射线光电子能谱仪（XPS，日本Ulvac公司）；D8Advance型X射线衍射仪（XRD，德国布鲁克公司）；LabRAM HR型拉曼光谱仪（Raman，激发波长532nm，日本Horiba 公司）；VMP-300型电化学工作站（法国Biologic公司）.1.2实验过程不同导电属性的二维TMDCs电催化剂通过溶剂热法和高温热处理制备.首先，将25g油胺和138 mg NbCl5依次加入到100mL的圆底烧瓶中，向圆底烧瓶中的油胺通入氮气（流量为30sccm）直至反应结束，使得NbCl5处于氮气环境下避免空气进入，在此过程中通过施加搅拌使NbCl5均匀分散在油胺溶液中.然后将装有油胺溶液的圆底烧瓶加热至280℃恒温后，以不同速度（5.0，1.0，0.2和0.1mL/min）滴加3.0mL DDT，继续反应1h后冷却至室温，加入过量的丙酮洗涤产物，通过离心分离作用洗涤固体样品（重复3次）.样品再次用乙醇和去离子水依次清洗并真空干燥烘干.最后将干燥的样品置于管式炉中在不同温度（650，750和850℃）下退火处理2h，退火升温速率为10℃/min，退火过程中通入氩氢混合气（95sccm Ar+5sccm H2）；退火处理后冷却至室温取最终产物（NbS2）待用.在相同条件下分别合成出NbS2、二硫化钼（MoS2）和二硫化钒（VS2）3种二维材料.此外，采用相同制备过程将NbS2生长在钼箔（Mo foil）上用作自支撑电极，在样品洗涤过程中，将NbS2/Mo foil浸泡在丙酮和乙醇中12h后烘干，最后将烘干的样品置于管式炉中，在750℃下通入氩氢混合气（95sccm Ar+5sccm H2）退火处理2h，然后冷却至室温获得最终产物（NbS2/Mo foil）.1.3电化学析氢性能测试不同电催化剂的催化性能在室温下采用标准三电极体系进行测试.其中将TMDC催化剂（负载量约为0.3mg/cm2）负载在玻碳电极上作为工作电极，石墨棒为对电极，饱和银/氯化银为参比电极，0.5 mol/L H2SO4溶液为电解液.向电解液中通30min氮气（流量为50sccm），以排除溶液中的其它气体.线性扫描伏安曲线（LSV）的工作电压为0.1~‒0.5V，扫描速率为5mV/s；电化学阻抗谱（EIS）的电压设为‒0.2V，交流频率范围为0.1~105Hz，振幅为5mV；循环伏安（CV）曲线以不同扫描速率在相对标准氢电极电位为0.05~0.15V范围内进行测试；电化学活性面积（ECSA）通过不同扫描速率（10，20，40，60和80mV/s）下的循环伏安曲线转化得到.采用恒电位法在不同电位下进行长时稳定性（I-t）测试.电化学电位（E）均根据可逆氢电极进行校正（V vs.RHE），在0.5mol/L H2SO4溶液中，E（RHE）=E（Ag/AgCl）+0.20V. 2结果与讨论2.1催化剂的形貌与结构表征在退火温度为750℃下，不同DDT滴加速率下合成的NbS2如图1所示.由图1（A~D）可见，随着DDT滴加速率的减小，NbS2逐渐由微米颗粒转变为片层结构，最终呈现出二维纳米片组成的“花状”形Vol.42高等学校化学学报貌.DDT 作为反应还原剂，其滴加速率直接影响到NbS 2成核的快慢.当DDT 大量滴加（滴加速率快）时，由于反应速率过快，形成的晶核因高的表面能导致其相互聚集而形成块体结构.将DDT 滴加速率减慢，成核反应速率也相应变慢，团聚现象逐渐减弱，从而更易形成二维纳米片状晶体结构.采用电化学循环伏安法对以上4种不同DDT 滴加速率条件合成的NbS 2材料的电化学活性面积进行了测试（图S1，见本文支持信息）.图1（E ）给出了4种NbS 2电催化剂的充放电电流差（ΔJ ）与扫描速率的线性关系，根据公式换算后所得的催化剂电化学活性面积如图1（F ）所示.当DDT 滴加速率为5.0mL/min 时，其电化学活性面积仅为20.2cm 2，随着DDT 滴加速率逐渐减至0.1mL/min 时，其电化学活性面积增大至159.5cm 2，展现出二维材料的高比表面积特征，有利于电催化反应过程中的反应前驱体与催化位点充分接触，图1（G ）所示为二维NbS 2材料及其HER 过程示意图.进一步对具有高比表面积的NbS 2材料（DDT 滴加速率为0.1mL/min ，退火温度为750℃下合成）进行元素分析及晶体结构和原子结构的表征.图S2（见本文支持信息）为NbS 2材料的EDS 元素成分分布图及相应的谱线，测试结果显示材料成分中S/Nb 的原子比为1.93∶1，与理论值2∶1相近.图2（A ）为NbS 2材料的XRD 谱图，4个强衍射峰对应于NbS 2的（002），（100），（110）和（200）晶面，与NbS 2标准卡片（PDF#41-0980）的衍射峰一致［26，27］，表明所制备的NbS 2是2H 相晶体结构.图2（B ）为NbS 2材料的Raman 光谱图，3个Raman 特征峰（E 1g ，278cm －1；E 2g ，330cm －1；A 1g ，382cm －1）与文献［28］报道的2H 相NbS 2材料一致，与XRD 所得的结构相吻合.为进一步确定合成产物的价态，采用XPS 测定了NbS 2的Nb 和S 元素的结合能，结果如图S3（见本文支持信息）和图2（C ，D ）所示.首先，由图S3可见，合成的样品中仅含有Nb ，S ，C 和O 4种元素.图2（C ）中Nb 3d 谱图存在3组峰，分别对应于Nb 5+（210.5eV ）、Nb 4+（3d 3/2，207.7eV ；3d 5/2，204.3eV ）以及阴离子插层Nb （4‒δ）+（3d 3/2，206.5eV ；3d 5/2，203.7eV ）［27］；图2（D ）S 2p 谱图的2组峰分别对应于S —O（164.7eV ）和S 2‒（2p 1/2，163.3eV ；2p 3/2，162.0eV ［29］）.以上结果表明，溶剂热合成的主要产物是NbS 2材料.对产物进行TEM 表征，如图2（E ）所示，NbS 2呈现二维层状结构；高分辨透射电子显微镜（HRTEM ）照片显示NbS 2材料具有高质量晶态结构［图2（F ）］，晶格间距为0.30nm ，对应于2H 相NbS 2的（100）晶面.此外，对其它2种溶剂热合成的MoS 2和VS 2材料也进行了HRTEM 表征，均呈现出高质量的晶体结构（图S4，见本文支持信息）.以上结果表明，溶剂热法及后续Fig.1SEM images of two⁃dimensional(2D)NbS 2with different injecting rates of DDT precursors(A —D),capacitive currents at the potential of 0.10V against the scan rate calculated from Fig.S1(E),ECSAof NbS 2samples with different injecting rates of DDT precursors(F)and schematic of 2D NbS 2forHER(G)Injecting rate of DDT/(mL ·min -1):(A)5.0;(B)1.0;(C)0.2;(D)0.1.656No.2余强敏等：金属性二维过渡金属硫化物的溶剂热合成及电催化析氢性能高温处理对合成高质量的2H 相TMDCs 晶体具有普适性.2.2电化学析氢性能为评价不同条件下合成的二维NbS 2材料的电催化析氢性能，测试了其催化活性和动力学特性，结果见图3.图3（A ）为DDT 滴加速率为0.1mL/min 时不同退火温度处理的NbS 2的线性扫描伏安曲线.与未经退火处理的材料相比，退火处理后的NbS 2材料的催化活性大幅提高；在退火处理温度为750℃时性能达到最佳，该样品在电流密度为10mA/cm 2时过电位仅为146mV ，远小于同等条件下未经退火处Fig.2XRD pattern(A),Raman spectrum(B),XPS spectra of Nb 3d (C)and S 2p (D),TEM(E)and HRTEM(F)images of metallic 2D NbS 2materialsFig.3LSV curves(A)and corresponding Tafel curves(B)of NbS 2with different annealing temperatures,LSV curves(C)of NbS 2with different injecting rates of DDT precursors and overpotentials(D)ofNbS 2at 10and 50mA/cm 2under different injecting rates of DDT precursors657Vol.42高等学校化学学报理的样品（在10mA/cm2时过电位为305mV）.当退火温度高于或低于750℃时，样品的催化活性均减弱.进一步评价了不同退火温度处理的NbS2电催化剂在HER中的动力学特性，如图3（B）所示.根据塔菲尔方程η=a+b lg J［其中，a（mV）为电流密度为单位数值（1mA/cm2）时的过电位值；J（mA/cm2）为电流密度；b（mV/dec）为塔菲尔常数，b值越小，催化剂活性越高］计算了其在HER过程的塔菲尔斜率.在电催化析氢过程中，750℃退火处理后的NbS2催化剂的塔菲尔斜率为45mV/dec，远小于未经退火处理的NbS2材料的116mV/dec，表明750℃退火处理的NbS2表现出优异的动力学特性.此外，对不同退火温度处理的NbS2电催化剂的电荷传输能力进行评价，结果如图S5（见本文支持信息）所示，可见，750℃退火条件下NbS2的电荷传输电阻约为30Ω，小于850℃的35Ω，远小于650℃的63Ω和未退火样品的106Ω，表明750℃退火条件下的NbS2具有更快的电子转移速率.根据以上结果可知，高温退火处理可提升材料的导电性和结晶度，提高材料的催化活性.相反，过高温度的还原气氛处理不利于保持材料原始的本征结构，如图S6（见本文支持信息）所示，与750℃下退火后的NbS2样品相比，850℃退火后的样品其Nb3d峰整体向低结合能方向偏移约1.0eV，表明NbS2中的Nb从本征的+4价态转变为更低价态，从而改变了NbS2的本征结构；另外，金属性NbS2本征结构的改变使得NbS2的导电性降低，进而使其催化活性降低.除了退火条件，对不同DDT滴加速率下制备的NbS2的析氢催化活性进行了电催化性能表征，其具体变化趋势如图3（C）所示.随着DDT滴加速率的减小，NbS2的催化活性逐渐提高，原因在于：一方面滴加速率慢有利于二维薄层结构的形成，从而暴露更多催化活性位点；另一方面，“花状”多孔结构的形成有利于反应中质子的传输及气体扩散，可进一步提高HER速率.此外，由图3（D）可见，当电流密度从10mA/cm2增加到50mA/cm2时，“花状”多孔结构NbS2所需电位只增加了102mV，远小于微米颗粒NbS2的140mV，进一步表明“花状”多孔结构NbS2具有更快的HER反应动力学.基于以上研究结果，通过优化实验参数制备了不同种类的TMDCs材料，包括金属性的二维NbS2和VS2，以及半导体性的二维MoS2.对优化后的3种不同TMDCs进行了HER电催化活性表征.如图4（A ）Fig.4LSV curves(A)and corresponding Tafel curves(B)of MoS2,VS2,NbS2and Pt/C catalysts,EIS curvesof MoS2,VS2and NbS2catalysts(C)and the stability curve of NbS2catalysts at the potential of-0.146V(vs.RHE)(D)The inset of(C)is the equivalent circuit used to fit the impedance spectra.The inset of(D)is the LSV curves of NbS2 catalyst before and after5000cycles of CV scans from‒0.3V to0.1V(vs.RHE).658No.2余强敏等：金属性二维过渡金属硫化物的溶剂热合成及电催化析氢性能所示，在电流密度10mA/cm 2下，NbS 2、VS 2和MoS 2的过电位分别为145，148和201mV ，表明金属性TMDCs 具有更高的反应活性，与文献报道一致［21］；图4（B ）为NbS 2、VS 2和MoS 23种催化剂的塔菲尔曲线，其斜率分别为45，50和63mV/dec ，说明3种不同TMDCs 催化剂的HER 过程均遵循Volmer -Heyrovsky 的反应机理［30］.图4（C ）为3种TMDCs 催化剂的Nyquist 图，图中半圆直径表示电极电荷转过移电阻R ct ，插图为实际测试电化学阻抗的拟合模型.测试结果显示，NbS 2和VS 2的R ct 分别为30和32Ω，远低于MoS 2的64Ω，表明金属性TMDCs 催化剂具有良好的电子传输能力和HER 动力学.除电催化活性外，电极材料的稳定性和耐久性也是评价电催化剂实际应用价值的重要依据.图4（D ）为NbS 2催化剂的稳定性和耐久性测试曲线，在恒电压下连续工作24h 后，NbS 2催化剂的电流密度几乎未衰减.此外，在循环5000次后，NbS 2催化剂在10mA/cm 2电流密度下所需过电位基本没有增大.对电化学循环后的NbS 2催化剂进行形貌结构表征，如图S7（见本文支持信息）所示，样品在经过电化学循环后无明显团聚现象，其晶格结构无明显变化，该结果表明NbS 2催化剂具有良好的电化学稳定性.以上结果均表明，相较于半导体性TMDCs ，金属性TMDCs 在HER 中具有更高的催化活性和应用前景.为进一步验证溶剂热法制备的金属性TMDCs 在实际析氢反应中的应用前景，将生长在钼箔基底上的NbS 2（NbS 2/Mo foil）自支撑电极置于高电流密度析氢条件下进行测试，结果如图5（A ）所示.在400mA/cm 2的高电流密度下，NbS 2/Mo foil 所需过电位仅为386mV ，略高于同等条件下Pt 催化剂的303mV.为验证制备的NbS 2/Mo foil 自支撑电极的稳定性，对其进行了长时间计时电流测试.如图5（B ）所示，在过电位为225mV 下持续工作24h ，NbS 2/Mo foil 的电流衰减率仅为0.1mA/h ，该结果证明NbS 2/Mo foil 自支撑电极具有良好的电化学稳定性.催化材料的规模化制备是衡量其工业应用中的重要指标［31，32］，基于此，不同催化剂制备方法的产能需进一步评价.目前制备金属性TMDCs的方法包括CVD 法、溶剂热法和化学气相输运（CVT ）法.不同方法制备的金属性TMDCs展现出不同的析氢活性，如图6和表1所示，在电流密度为10mA/cm 2时，CVD 法和溶剂热法制备的金属性TMDCs 在电流密度为10mA/cm 2下的析氢过电位均小于200mV ，优于同等条件下CVT 法制备样品的过电位（300~1000mV ）.从表1可见，CVT 和溶剂热法制备的金属性TMDCs 可实现10~100mg/h的生产速率，高出CVD 法2~3个数量级.综上，溶剂热法是规模化制备高性能金属性TMDCs 电催化剂的最佳方法，具有潜在的工业化应用前景.Fig.5LSV curves(A)and I ⁃t curve(B)of self⁃supporting electrode of NbS 2/MofoilFig.6Performance and production rate of diffe -rent TMDCs by CVT,CVD and solvother⁃mal methods 659Vol.42高等学校化学学报3结论采用溶剂热法制备出不同导电属性的TMDCs 析氢电催化剂.通过调控DDT 反应前驱体的滴加速率和产物高温退火处理，可显著提高NbS 2的催化性能.酸性电解质中，当电流密度为10mA/cm 2时，NbS 2所需的析氢过电位仅为146mV 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Yuting1，LI Yang2，CHENG Huiming1，3，LIU Bilu1*（1.Shenzhen Geim Graphene Center，Tsinghua⁃Berkeley Shenzhen Institute&Tsinghua Shenzhen InternationalGraduate School，Tsinghua University，Shenzhen518055，China；2.Institute for Superconducting and Electronic Materials，University of Wollongong，Wollongong2500，Australia；3.Shenyang National Laboratory for Materials Sciences，Institute of Metal Research，Chinese Academy of Sciences，Shenyang110016，China）Abstract Different kinds of transition metal disulfides（TMDCs）were prepared via solvothermal method.The morphologic structure of TMDCs were controlled by tuning the injecting rates of the reaction precursor.The crystallization of the products could be improved by annealing treatment at high-temperature，and thus impro-ving the electrocatalytic activity of TMDC catalyst.The results of electrocatalytic hydrogen evolution in acidic electrolyte show that the metallic"flower-like"niobium disulfide（NbS2）exhibits excellent catalytic activity and stability.It possess a small overpotential of only146mV to achieve a current density of10mA/cm2.The current density almost shows no decays after24h continuous working at10mA/cm2.The excellent perfor⁃mance of NbS2catalyst is attributed to the"flower-like"structure that can expose abundant active sites，and to the improvement of electrical conductivity and material quality after annealing treatment.Keywords2D Material；NbS2；Solvothermal synthesis；Electrocatalytic hydrogen evolution；Currentdensity(Ed.:Y,K,S)Science Foundation of China（Nos.51722206，51920105002），the Program of Guangdong Innovative（No.2017ZT07C341）and the Program of Bureau of Industry and Information Technology of Shen⁃zhen，China（No.201901171523）.661。

MaterialsLetters

Chemical synthesis of mesoporous CoFe2O4nanoparticles as promising bifunctional electrode materials for supercapacitorsLeilei Lv a,b,Qun Xu a,n,Rui Ding b,nn,Li Qi b,Hongyu Wang ca College of Material Science and Engineering,Zhengzhou University,No.75University Road,Zhengzhou450052,Chinab State Key Laboratory of Electroanalytical Chemistry,Changchun Institute of Applied Chemistry,Chinese Academy of Sciences,5625Renmin Street,Changchun130022,Chinac Changzhou Institute of Energy Storage Materials&Devices,No.9Hehai Eastern Road,Changzhou213000,Chinaa r t i c l e i n f oArticle history:Received8May2013Accepted12August2013Available online22August2013Keywords:CoFe2O4NanoparticlesPseudocapacitanceMesoporousMetallic compositesa b s t r a c tA promising mesoporous cobalt iron oxide(CoFe2O4)electrode material for supercapacitors has beensynthesized via a chemical co-precipitation method using aluminum nitrate(Al(NO3)3)as a precursor ofaluminum oxide(Al2O3)hard template.The as-prepared CoFe2O4materials were spherical-likenanoparticles with diameter of around25nm.Moreover,the as-prepared CoFe2O4materials exhibiteda high speciﬁc surface area(140.6m2gÀ1)and high porosity(0.23cm3gÀ1).The fabricated CoFe2O4electrode showed typical pseudocapacitive behavior with a broad potential window(1.5V),a highspeciﬁc capacitance(142F gÀ1,2mV sÀ1)and a long cycling life(71.8%retention after1000cycles).&2013Elsevier B.V.All rights reserved.1.IntroductionWith worldwide increasing warmth in the energy storageﬁeldof supercapacitors,3d transition metal oxides ranging from noblemetal oxides to inexpensive metal oxides,characterized by highlyreversible capacities,long cycle performance and high powerdensity,have been extensively studied[1].Among them,RuO2could exhibit prominent performance with pseudocapacitance ashigh as720F gÀ1[2],but the expensive cost and high toxicityapparently hinder its commercial application,which made MnO2,Co3O4,Fe3O4,V2O5and NiO,especially binary system materialsCo–Ni,Fe–Mn,Co–Mn,Mn–Ni oxides environmental and econom-ical alternatives of choice for improved applicability[1].Ferrosoferric oxide(Fe3O4)and cobalt oxide(Co3O4)of spinelseries are both attractive candidates for the application in super-capacitors owning to their low-cost and environmental friendlynature,as well as excellent electrochemical capacitive behavior[3,4].Their binary compound cobalt iron oxide(CoFe2O4),as anefﬁcient magnetic material on demand inﬁelds of electronics,photomagnetism,catalysis,has widely been studied[5].In2005,Kuo and Wu[6]had a report of CoFe2O4with a speciﬁc capacitanceof7.1F gÀ1in neutral NaCl electrolyte,which shed light on itselectrochemical properties by improving inherent structure.Herein,we employ a hard template of Al2O3derived from co-precipitating Al(NO3)3precursor solution to fabricate the porouscapacitive CoFe2O4.And the artiﬁcial porous structures are provedto largely enhance the electrochemical performance of theCoFe2O4materials.2.ExperimentalIn a typical procedure,ﬁrst,2.25g Al(NO3)3Á9H2O,4.85g Fe(NO3)3Á9H2O and1.75g Co(NO3)2Á6H2O were dissolved in120mLdeionized water to form a well-mixed solution.ExcessiveNH3ÁH2O was subsequently added to the solution dropwise untila pH level of10was reached.The obtained dark brown precipita-tion was further vigorously stirred at501C for4h with a constantspeed in a water-jacketed reaction vessel using circulating ther-mostatic bath.Then,the as-prepared sample was obtained bycentrifugalﬁltration and dried at701C for10h,afterwardannealed in a mufﬂe stove at4501C under air for2h at a heatingrate of21C minÀ1.Subsequently,the product was etched in2MKOH solution at501C for24h to remove Al2O3template,after-wardﬁltrated by centrifugation and washed with distilled waterseveral times until a neutral pH level,andﬁnally dried at701Cfor10h.For comparison,the experiment without Al(NO3)3Á9H2Oaddition was also conducted.Theﬁnal products with andwithout Al2O3template are named T-CoFe2O4and CoFe2O4,respectively.Contents lists available at ScienceDirectjournal homepage:/locate/matletMaterials Letters0167-577X/$-see front matter&2013Elsevier B.V.All rights reserved./10.1016/j.matlet.2013.08.055n Corresponding author.Tel.:þ8637167767827.nn Corresponding author.Tel.:þ8643185262915.E-mail addresses:*************.cn(Q.Xu),***************.cn(R.Ding).Materials Letters111(2013)35–38X-ray diffraction (XRD)patterns of the samples were recorded on a Rigaku D/max-2500diffractometer equipped with monochromated Cu K α(λ¼0.15406nm)radiation.Scanning electron microscopy (SEM)images were taken using Philips XL 30and a JEOL JSM-6700F microscope.N 2adsorption –desorption measurements were performed on a Micromeritics ASAP 2020apparatus.Electrochemical examinations were carried out with a CoFe 2O 4working electrode,a Pt mesh counter electrode and a Hg/HgO (2M KOH aqueous solution)reference electrode.The working electrodes were prepared by pressing the homogenous mixture of 70wt%CoFe 2O 4active materials,15wt%acetylene black,and 15wt%poly(tetra ﬂuoroethy-lene)(Sigma Aldrich)onto a stainless steel mesh collector.Cyclic voltammetry (CV)and cyclic stability were collected on CHI700D electrochemical workstation and land CT2001A tester,respectively.The gravimetric speci ﬁc capacitance (C m )is calculated accord-ing to the following equation:C m ¼12vm ðΔV ÞZ V bV a I d V ð1Þwhere m ,νand (V a –V b )i.e.ΔV denote the mass of CoFe 2O 4or T-CoFe 2O 4active powders,scan rate and the potential window (1.5V),respectively.3.Results and discussionFig.1a displays the XRD patterns of T-CoFe 2O 4and CoFe 2O 4materials.All the resultant peaks can be indexed as a face-centered-cubic spinel phase.The identi ﬁed eight diffraction peaks at 2θvalue of 30.211,35.701,37.131,43.161,54.131,57.361,62.961and 74.321correspond to the (220),(311),(222),(400),(422),(511),(440)and (533)crystal planes,respectively,which is in well agreement with the standard patterns for CoFe 2O 4(JPCDS No.22-1086).No signals of Al 2O 3phase (JCPDS No.10-0425)aredetected in the patterns [7].Moreover,neither does Al emerge in XPS nor in EDAX spectra of T-CoFe 2O 4(seen in Fig.S1and S2).All suggested the successful removal of the template.Furthermore,it is clearly seen that diffraction peaks of T-CoFe 2O 4are duller indicating T-CoFe 2O 4comprises of smaller nanoparticles than CoFe 2O 4and this inference is further con ﬁrmed by their SEM images (Fig.1b and c).The CoFe 2O 4in Fig.1b,shows basically microsized agglomerate particles with few pores and voids,and a smooth surface,whereas the T-CoFe 2O 4exhibits basically dis-persed and uniform spherical-like particles of around 25nm size with rough surface and high porosity,as can be seen in the domain of Fig.1c.Thus by etching the hard template,T-CoFe 2O 4exhibits a porous framework with smaller granular size rather than bulk.To accommodate super ﬁcial electroactive species as much as possible,it is essential for the electrode material to enrich its inner surface area and pores so as to ease the mass transfer of electrolytes [8].The surface area and porosity of the T-CoFe 2O 4and CoFe 2O 4were further veri ﬁed by nitrogen sorption measurements which are shown in Fig.1d.The N 2adsorption –desorption isotherms of CoFe 2O 4and T-CoFe 2O 4representative of type II and IV curves with distinct hyster-esis loops.The BET surface area of T-CoFe 2O 4is 140.6m 2g À1which is far larger than the value of 27.6m 2g À1for CoFe 2O 4.The main pore size distributes narrowly in the range of 4–8nm centered at 5.6nm and 2–4nm centered at 2.2nm for the T-CoFe 2O 4and CoFe 2O 4,respectively,(shown in the insets of in Fig.1d).Besides,average pore size and mesoporous volume of T-CoFe 2O 4are quantitatively eval-uated as 6.53nm and 0.23cm 3g À1,and the corresponding values of CoFe 2O 4are 2.2nm and 0.225cm 3g À1,respectively.High speci ﬁc surface area and porosity is critical to enhance the electrochemical performances of electrode materials for supercapacitors [1].Thereby,improved electrochemical properties for the porous T-CoFe 2O 4,such as speci ﬁc capacitance,high-rate capability,and longer cycling life,can be expectedaccordingly.Fig.1.XRD patterns (a)and N 2adsorption –desorption isotherms with insets of BJH pore size distribution (d)of CoFe 2O 4and T-CoFe 2O 4;SEM images of CoFe 2O 4(b)and T-CoFe 2O 4(c).L.Lv et al./Materials Letters 111(2013)35–3836The CV plots of CoFe 2O 4and T-CoFe 2O 4electrodes tested in the potential range of À1.0–0.5V were plotted in Fig.2a and b.Two obvious pseudocapacitive blocks are observed in the positive (À0.1–0.5V)and negative (À0.5–À1.0V)potential regions which contribute to most of the capacitance.While the middle intervals (À0.1–À0.5V)contribute to the minor EDL capacitance [9].Here,the observed redox couples well elucidate the pseudocapacitive properties of CoFe 2O 4electrodes.The three couples of redox peaks located at around 0.28/0.05V,0.5/0.38V,À0.75/À0.85V indicate the reversible redox processes of Co 3þ/Co 2þ,Co 4þ/Co 3þ,Fe 3þ/Fe 2þredox couples in alkaline electrolytes [4,9,10],which can be expressed as the following equations:1/3Co 3O 4þ1/3OH Àþ1/3H 2O 2CoOOH þ1/3e À(2)CoOOH þOH À2CoO 2þH 2O þe À(3)2/3Fe 3O 4þ2/3OH ÀþH 2O 22FeOOH þ2/3e À(4)Even though a series of reports have studied the capacitive properties of M Fe 2O 4(M ¼Mn,Fe,Co,Ni),CoFe 2O 4in our work may draw fresh attention as it can both act as anode and cathode electrode materials by virtue of the broad potential window area.The speci ﬁc capacitance values of CoFe 2O 4and T-CoFe 2O 4electrodes are shown in Fig.2c,both speci ﬁc capacitance decreases with increasing scan rate because of insuf ﬁcient active material involved in the redox reactions under higher scan rate.The CoFe 2O 4electrode exhibits a low speci ﬁc capacitance range of 44–13F g À1while the T-CoFe 2O 4electrode exhibits a much higher and considerable speci ﬁc capacitance range of 142–23F g À1in the scan rate range of 2–50mV s À1.Obviously,the porous T-CoFe 2O 4has much higher electrochemical activity than the bulk CoFe 2O 4thanks to suf ﬁcient electroactive sites for electrochemical reac-tions and easy ion diffusion pathways for electrolyte ions transfer process.Long cycle life is a crucial parameter for electrode materials used for supercapacitors.The cyclic performances of CoFe 2O 4and T-CoFe 2O 4electrodes are shown in Fig.2d.The CoFe 2O 4electrodeshowed a capacitance ′s decay in the ﬁrst 200cycles,then gradually went up with the increasing cycle numbers and ﬁnally a retention rate of 68.7%was obtained.The speci ﬁc capacitance of T-CoFe 2O 4,which is nearly three times of CoFe 2O 4,slightly decreased before 200cycles and remained almost stable in the subsequent cycles.A retention rate of 71.8%was obtained after 1000cycles for the T-CoFe 2O 4electrode.Here,the decline in the speci ﬁc capacitance with cycle number may be ascribable to the loss of active material caused by the dissolution and/or detach-ment during early cycle number [11].Further work on searching the most appropriate ratio of template to improve the cycling behavior is currently under progress.4.ConclusionsIn summary,the mesoporous CoFe 2O 4materials for super-capacitors have been successfully synthesized with assistance of co-precipitating Al 2O 3template.High BET speci ﬁc surface and porosity of 140.6m 2g À1and 0.23cm 3g À1were obtained which facilitate the Faradaic pseudocapacitive performance by virtue of suf ﬁcient electroactive sites and easy ions pathways.The unique mesoporous CoFe 2O 4electrode delivered a wide potential window of 1.5V and a high speci ﬁc capacitance of 142F g À1at 2mV s À1,which can be expected to take important roles in both anode and cathode materials for supercapacitors.AcknowledgmentsWe gratefully acknowledge the ﬁnancial support of this research by National Basic Research Program of China (2012CB932800),Scienti ﬁc Research Foundation for the Returned Overseas Chinese Scholars and State Education Ministry (SRF for ROCS,SEM).Fig.2.CV plots of CoFe 2O 4electrode (a)and T-CoFe 2O 4electrode (b);speci ﬁc capacitance values under different scan rates (c)and cycling performances (d)of CoFe 2O 4and T-CoFe 2O 4electrodes.L.Lv et al./Materials Letters 111(2013)35–3837Appendix A.Supporting informationSupplementary data associated with this article can be found in the online version at /10.1016/j.matlet.2013.08.055. References[1]Wang GP,Zhang L,Zhang JJ.Chemical Society Reviews2012;41:797–828.[2]Zheng JP,Cygan PJ,Jow TR.Journal of the Electrochemical Society1995;142:2699–703.[3]Xu JA,Gao L,Cao JY,Wang WC,Chen ZD.Electrochimica Acta2010;56:732–6.[4]Du X,Wang CY,Chen MM,Jiao Y,Wang J.Journal of Physical Chemistry C2009;113:2643–6.[5]Li XH,Xu CL,Han XH,Qiao L,Wang T,Li FS.Nanoscale Research Letters2010;5:1039–44.[6]Kuo SL,Wu NL.Electrochemical and Solid State Letters2005;8:A495–9.[7]Shang XF,Wang XG,Nie WX,Guo XF,Zou XJ,Ding WZ,et al.Materials Letters2012;83:91–3.[8]Wei TY,Chen CH,Chien HC,Lu SY,Hu CC.Advanced Materials2010;22:347–51.[9]Li YH,Huang KL,Yao ZF,Liu SQ,Qing XX.Electrochimica Acta2011;56:2140–4.[10]Wu JB,Lin Y,Xia XH,Xu JY,Shi QY.Electrochimica Acta2011;56:7163–70.[11]Lokhande CD,Gujar TP,Shinde VR,Mane RS,Han SH.ElectrochemistryCommunications2007;9:1805–9.L.Lv et al./Materials Letters111(2013)35–38 38。

PET合成用钛锑复合催化剂的制备及其性能

研究与开发CHINA SYNTHETIC RESIN AND PLASTICS合成树脂及塑料， 2023， 40（5）： 7随着纺织印染行业的快速发展，聚对苯二甲酸乙二酯（PET）行业作为排污和耗水大户引起了社会的高度重视［1］。

其中，含锑化合物价格低廉、活性高、副反应较少，常被用作PET生产过程中的催化剂。

但是在PET后处理（如纺丝、碱减量、染色）过程中，由于高温会使大量锑离子被释放出来，导致废水中重金属锑含量超标［2-4］，严重威胁环境安全及人体健康。

目前，PET合成用催化剂的主要制备方法为复配法、水解法、稳定化法等［5-6］。

其中，通过复配法制备的钛锑复合催化剂不仅可以弥补钛系催化剂在应用中的缺陷，而且可以有效提高催化剂中锑的利用率，对新型PET催化剂DOI：10.19825/j.issn.1002-1396.2023.05.02 *PET合成用钛锑复合催化剂的制备及其性能王泽男1，杨淑娟1，来雷2，杨飞3，崔科丛1，张秀梅1，张勇1*（1. 浙江理工大学先进纺织材料与制备技术教育部重点实验室，浙江杭州 310018；2. 浙江传化华洋化工有限公司，浙江杭州 311231；3. 浙江宇博新材料有限公司，浙江台州 318000）摘要：以氯化锑为原料，活化后坡缕石（HATP）为载体，聚乙二醇和异丙基三（二辛基焦磷酸酰氧基）钛酸酯混合溶液为助剂，制备了聚对苯二甲酸乙二酯合成用钛锑复合催化剂Sb/Ti/HATP，对其进行表征，并利用“FWO法”和“等转化率法”评估其催化性能。

结果表明：Sb/Ti/HATP的比表面积可达156.8013 m2/g，平均表观活化能可降至42.84 kJ/mol，催化剂活性和热稳定性显著提高。

关键词：聚对苯二甲酸乙二酯钛锑复合催化剂坡缕石表观活化能催化剂活性中图分类号：TQ 342+.21；TQ 426.64文献标志码： B 文章编号：1002-1396（2023）05-0007-05 Preparation and properties of titanium-antimony composite catalystfor PET synthesisWang Ze′nan1，Yang Shujuan1，Lai Lei2，Yang Fei3，Cui Kecong1，Zhang Xiumei1，Zhang Yong1（1. Key Laboratory of Advanced Textile Materials and Manufacturing Technology of the Ministry of Education，Zhejiang Sci-Tech University，Hangzhou 310018，China；2. Company Limited of Zhejiang Transfar Whyyon Chemical，Hangzhou 311231，China；3. Company Limited of Zhejiang Yubo New Material，Taizhou 318000，China）Abstract：A titanium-antimony composite catalyst（Sb/Ti/palygorskite［HATP］） for polyethylene terephthalate syntheis was prepared with antimonous chloride as raw material，activated HATP as carrier，polyethylene glycol and Isopropyl tri（dioctylpyrophosphate） titanate mixed solution as assistant，which was characterized and whose catalytic performance was evaluated by FWO method and equal conversion method. The results show that the specific surface area of Sb/Ti/HATP is as high as 156.8013 m2/g，and its average apparent activation energy can be reduced to 42.84 kJ/mol，its catalytic activity and thermal stability are significantly improved.Keywords：polyethylene terephthalate； antimony-titanium composite catalyst； palygorskite； apparent reaction activation energy； catalytic activity收稿日期：2023-03-27；修回日期：2023-06-26。

聚乙二醇修饰ZIF-8 的合成及对活性艳红的吸附

聚乙二醇修饰ZIF-8的合成及对活性艳红的吸附曹占平，武鑫霞，李岚（天津工业大学环境科学与工程学院，天津300387）摘要：由于ZIF-8材料孔径较小，制约了其对大分子染料活性艳红的吸附，为了调节其孔径，结合有机膜制备中聚乙二醇（PEG ）常作为孔调节剂，因此选择PEG 作为软膜板剂对ZIF-8进行修饰复合，获得了一种新型的ZIF-8/PEG 多孔纳米复合材料；采用XRD 、SEM 和氮气吸附-脱附等方法对ZIF-8/PEG 进行表征。

结果表明：合成了孔径有所增加的分级孔，形成了5~10nm 的介孔孔径，发现添加PEG 改性后材料粒度变小，但比表面积不增反降，这是因为其介孔孔径的存在；考察了其对液相污染物偶氮废水———活性艳红X-3B 的吸附性能，发现分子质量为2ku 的PEG 改性其吸附量较未改性前提高26.7%，吸附量可达38.5mg/g 。

关键词：改性ZIF-8；介孔吸附；活性艳红；表面活性剂中图分类号：TB331文献标志码：A文章编号：员远苑员原园圆源载（圆园20）园6原园园40原07第39卷第6期圆园20年12月Vol.39No.6December 2020DOI ：10.3969/j.issn.1671-024x.2020.06.007天津工业大学学报允韵哉砸晕粤蕴韵云栽陨粤晕GONG 哉晕陨灾耘砸杂陨栽再收稿日期：2019-05-27基金项目：国家自然科学基金资助项目（51078265）；国家级大学生创新创业训练计划（201710058032）通信作者：曹占平（1970—），男，博士，副教授，主要研究方向为生物降解污染物的处理。

E-mail ：caozhanping2012@126援com Synthesis of polyethylene glycol modified ZIF-8and adsorption ofreactive brilliant redCAO Zhan-ping ，WU Xin-xia ，LI Lan（School of Environmental Science and Engineering ，Tiangong University ，Tianjin 300387，China ）Abstract ：Due to the small pore diameter of ZIF-8material袁its adsorption to reactive brilliant red of macromolecular dyesis restricted.In order to adjust the aperture袁considering that the polyethylene glycol 渊PEG冤is often used as a pore regulator in the preparation of organic membranes袁so PEG is selected as a soft diaphragm agent to modify ZIF-8袁a new type of ZIF-8/PEG porous nanocomposite was obtained.XRD袁SEM and nitrogen adsorption-des鄄orption methods were used to characterize ZIF-8/PEG.The results show that the synthesized aperture increases the classification of hole袁the mesoporous aperture of 5-10nm was formed.It was found that the particle size of the material became smaller fater the addition of PEG袁but the specific surface area did not increase but de鄄creased because of the mesoporous pore diameter.The adsorption of azo wastewater-reactive brilliant red X-3Bwas investiated.It was found that the adsorption capacity of the modified PEG with a molecular weight of 2ku was26.7%higher that that before modification袁and the adsorption capacity was up to 38.5mg/g.Key words ：modified ZIF-8曰mesoporous adsorption曰active brilliant red曰surfactant金属有机骨架材料（metal -organic frameworks ，MOFs ）是一种有机配体和金属离子或团簇通过配位键自组装形成的具有分子内孔隙的有机-无机杂化材料。

外文翻译钼磷酸铵SBA15介孔分子筛催化剂制备用4,6二甲基二苯并噻吩加氢脱硫发生

钼磷酸铵SBA-15介孔分子筛催化剂的制备用4,6-二甲基二苯并噻吩的加氢脱硫的发生摘要:4,6 –二甲基二苯并噻吩加氢脱硫超过钼磷酸铵催化剂和NiMoP/<x）TiSBA-15催化剂使用杂多酸制备<多酸H3PMo12O40）和柠檬酸镍<C12H10Ni3O14）作为Mo，Ni的前体进行了研究。

分析煅烧温度对加氢脱硫活性的影响，在催化剂和焙烧温度为773 K下制备。

不同性能的4,6 - 二甲基加氢脱硫过程中的催化剂与参考催化剂进行了比较通过用含七钼酸铵和硝酸镍的溶液浸滞后来制备。

4,6 –二甲基二苯并噻吩加氢脱硫的动力学参数采用简化的动力学模型来估算。

催化剂采用N2物理吸附，X-射线衍射，拉曼和红外CO吸附光谱在100K下进行表征。

结果表明，对于催化剂负载在纯SBA-15分子筛的准备用钼磷酸铵催化剂<NiMoP<H-NC）/ SBA-15）呈现次数最多的活性中心，较高的表观反应速率常数为氢化路线，因此4,6-二甲基二苯并噻吩的加氢脱硫活性最好。

相反，对于改性的钛催化剂，镍钼磷的Ti-SBA-15分子筛加氢脱硫活性最高，当15%TiO2被合并到SBA-15分子筛并且将催化剂在773 K温度下焙烧，这种催化剂呈现最高的催化性能，镍钼磷的Ti-SBA-15分子筛加氢脱硫活性最高。

引言：随着重质原油的加工日益增加的需求以及关于硫含量严格的环保法例在燃料的加氢脱硫发展中要求催化剂具有高活性和选择性。

要获得超低含硫量的柴油，有必要消除最难治的化合物如4,6 –二甲基二苯并噻吩. 该化合物的脱硫反应通过以下几种途径：直接脱硫 <DDS），加氢<HYD），和<ISO）异构化。

该催化剂的性能取决于各路线反应的贡献，这显著是由该组合物和催化剂的制备方法的影响，即，镍和钼的前体，辅助条件，添加剂或改性剂，催化剂活化预处理之前，硫化条件等。

b5E2RGbCAP多种策略已经被提出以提高加氢脱硫催化剂的性能，例如，最近提出的杂多酸与羟基铝离子的盐类。

层状金属氧化物用于二氧化碳吸附及其催化加氢转化的研究进展

王君雅等㈤、Sidek等㈣以石墨烯为碳材料，对不同复
合方式合成的材料进行了研究，其中，静电自组装法合成的LDO/氧化石墨烯(LDO-NS/GO )复合材料，方镁石中的Mg被Al替代或者八面体水镁石中A1原子的空缺导致活性物质M g-O键出现，从而展现出优于纯类水滑石材料的CO?吸附性能。通过对其合成条件、吸附条件、CO?吸附性能、热稳定性、再生循环
Abstract： In this paper, the application of layered metal oxide (LDO) in CO2 adsorption and catalytic hydrogenation was reviewed, and its advantages and possible problems were discussed. It is found that LDO has abundant pore structure and adjustable alkaline sites on the surface, which enhances the adsorption capacity of CO2. Meanwhile, its special layered structure can promote the uniform dispersion and interaction of active metals, which improves the catalytic activity of CO2 hydrogenation. Based on its precursor layered double hydroxides (LDHs) with adjustable chemical composition, intercalated anion exchangeability and thermal stability, and by selecting preparation methods and controlling reaction conditions, the catalytic materials with stronger CO2 adsorption capacity and higher hydrogenation activity can be obtained. However, most of the existing studies are limited to the adsorption of CO2 by LDO, and the hydrogenation products are also relatively single. In the future work, LDO materials can be further studied in order to combine the adsorption, activation and hydrogenation of CO2 to obtain more abundant target products.

Au_NiO催化剂的XRD_TEM_TPR及XPS表征研究

第16卷第3期分子催化V ol.16,N o.3 2002年6月J O U RN A L O F M O L ECU L A R CA T A L YSI S(CHIN A)J un.　2002　文章编号:1001-3555(2002)03-0209-04Au/NiO催化剂的XRD、TEM、TPR及XPS表征研究齐世学1,邹旭华1,徐秀峰1,安立敦1*,李树本2(1.烟台大学　应用催化研究所,山东烟台264635;　2.中国科学院兰州物理化学研究所,甘肃兰州730000)摘　要:采用X RD、T EM、T PR及X PS等表征手段,对共沉淀法制备的Au/NiO催化剂的活性中心、载体的结构及状态进行了研究.结果表明,活性中心金以纳米尺寸高度分散于载体表面,部分金可能呈现氧化状态,载体结晶适度.关　键　词:负载型金催化剂;一氧化碳;催化氧化;结构表征中图分类号:O643.32 文献标识码:A 催化CO低温氧化的负载型金催化剂已用于:封闭式CO2激光器、CO气体防毒面具、从空气中移除CO以制取高纯度的O2和N2、CO气体传感器等,并且对其在有毒废气(如NO x、CO)的催化治理、烃类的催化燃烧、不饱和烃的选择加成、水-汽置换反应、CO2加氢制甲醇以及氯氟烃的催化分解等环保、化工领域中的应用亦进行了实验研究,显示出广阔的应用前景.已有研究[1～3]表明,用不同方法制备的Au/ NiO催化剂在常温和低温下对CO的催化反应显示出良好的活性.我们采用XRD、T EM、T PR和X PS等表征手段,着重研究其活性中心和载体的结构及状态,并与其活性相关联.1实验部分1.1催化剂的制备于搅拌下将K2CO3的水溶液慢慢滴加到一定浓度的HAuCl4和Ni(NO3)2·6H2O的水溶液中,等沉淀完全后,过滤、充分洗涤至无Cl-离子,于真空、60℃下干燥,将所得样品在流动的空气中进行程序升温焙烧,得到催化剂Au/NiO.1.2反应装置流程采用小型固定床连续流动反应装置,反应管为硬质玻璃管,内径为 3.5mm,将其放置于加热炉或冷阱内以便控制反应温度.由反应管出来的气体经流量计计量后放空,在反应管后有取样点.1.3催化剂活性的评价方法称取制备好的催化剂0.2g(粒径为0.45～0.90m m),将其装入反应管中,调节原料气(1% CO、10%O2、89%N2)流量为25m L/min,进行CO 的氧化反应.催化剂的活性以最低全转化温度(T1/1)表示,此温度越低,表明催化剂的活性越好.使用GC-1102型气相色谱仪,热导池检测器在线分析反应混合气中CO的含量,CO最少可检测体积浓度为5.0×10-5.1.4催化剂的XRD、TEM、TPR和XPS测试X射线粉末衍射(X RD)测试仪器为日本Riga ku公司产RU-200B型旋靶式X-射线衍射仪,入射光源为Cu Kα靶,入射波长为0.15405nm,测试时将粉末样品于载玻片上加压制成片状.扫描范围2θ=5～80°,扫描速率8°/min.透射电镜(TEM)测试在美国Philips公司产CM-120型电子显微镜上进行,加速电压100kV,放大倍数 1.0×105,采用研磨悬浮法制备试样.程序升温还原(TPR)测试仪器为为天津先权应用技术研究所产TP-5000型多用吸附仪.称取收稿日期:2001-08-13;修回日期:2001-09-24.基金项目:国家自然科学基金资助项目(29873041)部分工作及中国科学院大连化学物理研究所催化基础国家重点实验室基金资助项目.作者简介:齐世学,男,37岁,副教授,博士研究生,主要从事应用催化和化学工程方向的研究工作.DOI:10.16084/ k i.i ssn1001-3555.2002.03.011约0.10g 样品,在200℃温度下用高纯氮气吹扫1h ,然后降至室温,用H 2/N 2(5/95)混合气进行程序升温还原,升温速度为5℃/min,气体流量为60m L /min.X 射线光电子能谱(X PS )分析使用仪器为德国Ley bo ld -Heraeus 公司产HLS -12型表面分析仪.测试时将粉末样品制压成片送入样品室,当仪器真空度达到 1.0×10-9Pa 后进行测试.2结果与讨论2.1催化剂的活性评价2.1.1不同焙烧温度制备的催化剂活性将共沉淀物在不同的焙烧温度下处理,得到的催化剂的活性评价结果示于图 1.可以看出,焙烧温度对催化图1不同温度焙烧制备的催化剂的活性Fig.1Activities o f ca talysts prepa red at differ ent ca lcinatio n tempera tures Reactio n co nditio ns :CO concentra tio n in feed g as :1%;space v elocity:7500m L ·g -1·h -1剂的活性影响显著,于300℃焙烧得到的催化剂活性最好,焙烧温度过低或过高均会使催化剂的活性下降,经500℃焙烧的催化剂活性更低.2.1.2不同负载量的催化剂活性以最佳焙烧温度300℃制备了不同负载量的Au /NiO 催化剂,其活性评价结果示于图 2.由图2可见,金负载量在1%～5%的范围内,Au /NiO的活性随着金负载量图2不同金负载量的催化剂的活性Fig.2Activ ities of cataly sts w ithdifferent g old loa ding sReactio n conditio ns a re the same as in Fig .1.的增加而提高.金负载量为5%的Au /NiO 催化剂可于-32℃将1%(体积分数)的CO 完全转化.2.2催化剂的X RD 表征为探究焙烧温度对催化剂活性的影响,对不同温度焙烧制得的催化剂进行了X RD 表征,结果示于图 3.由图3(a)可见,以不同温度焙烧制备的1%Au /NiO 催化剂,仅其载体NiO 的特征衍射峰强度不同,即载体的结晶程度不同.随焙烧温度的升高,NiO 的特征衍射峰强度增强,说明载体的结晶度提高.经200℃焙烧的催化剂,其NiO 的衍射峰出现包络和宽化,表明在较低的温度条件下图3以不同温度焙烧制备的Au /N iO 的X RD 谱图Fig.3X RD pat terns of Au /N iO calcina ted at diffe rent tempera tures210分子催化第16卷　Ni(OH)2的分解不完全,生成的NiO 量很少,所以结晶的NiO 也很少,催化剂的催化活性较低;于300℃焙烧的催化剂,其载体NiO 的衍射峰强度中等,说明载体结晶适度,催化剂的活性最好;焙烧温度高于400℃的催化剂,其载体的结晶程度进一步提高,但催化剂的活性反而下降.在图3(a )中未出现活性中心金的特征衍射峰,可能是由于金的负载量太低,或金高度分散于载体表面.为探究焙烧温度对活性中心金颗粒大小的影响,将催化剂的负载量提高至5%后再作XRD 表征,结果见图3(b).可以看出,经500℃焙烧处理的、含金5%的催化剂,其X RD 图谱上NiO 的特征衍射峰强度高、峰形窄,而且在2θ为38.34°和44.38°处(分别对应d 值为0.236和0.204nm )出现了金的特征衍射峰,说明高温焙烧导致催化剂的烧结,使载体和活性中心金的晶粒均长大,催化剂的活性下降;而于300℃焙烧处理的金含量为5%的催化剂,其NiO 的特征衍射峰强度中等,说明载体NiO 结晶适度;但没有出现金的衍射峰,说明金仍然是高度分散于载体表面的,表明在较高负载量条件下,仍然可以制得高分散度的金催化剂.2.3催化剂的TEM 表征为进一步研究催化剂中高分散的金颗粒的大小,对催化剂进行了TEM 测试,结果示于图 4.可以看出,对于高活性的Au /NiO 催化剂,其活性中心金颗粒的大小约在10nm 以内.结合X RD 表征结果,可以认为,金颗粒确实是以纳米尺寸高度分散于金属氧化物载体表面,表现出与宏观的金属金图41%Au /NiO 的T EM 照片(×100000)Fig .4T EM pho tog ra ph o f 1%Au /NiO 完全不同的反应性能,从而保证了其对CO 氧化的高催化活性.2.4催化剂的TPR 表征结果为探讨所制备的Au /NiO 上金的化学状态与其催化CO 氧化活性之间的关系,对以最佳条件制备的成品催化剂3%Au /NiO 进行了TPR 测试,作为对比,将同样方法制得的未负载金的载体NiO 也进行了TPR 试验,结果示于图 5.由图5a 可以看出,载体NiO 有两个还原峰,显示出NiO 逐步被还原成Ni 0;而在图5b 中,除了Au /NiO 的载体NiO 的两个还原峰以外,在约90～150℃还有一个还原图5NiO 和Au /N iO 的T PR 谱图Fig.5T P R pr ofiles of N iO and Au /N iO峰,这是负载于载体NiO 上氧化态金的还原信号,说明在该温度范围内催化剂中氧化态的金被完全还原为零价态的金属金.由此可以推测,催化剂Au /NiO 中部分金可能以氧化态的形式存在.211第3期齐世学等:Au /NiO 催化剂的XRD 、T EM 、TPR 及XPS 表征研究2.5催化剂的XPS表征结果有研究[4]认为,在高活性的金催化剂中,活性中心金以零价态的金属金的形式存在.为进一步研究Au/NiO催化剂中金的化学状态,对3%Au/ NiO催化剂进行了X PS表征,结果列于表1.表1表13%Au/N iO催化剂的XPS结果T able1X PS results fo r3%Au/NiO cataly stsB inding energ y(eV)Au4f7/2Au4f5/283.884.586.087.588.189.7中,83.5eV为Au04f7/2的结合能,86.0eV处的峰可能是尚存Au1+的4f7/2结合能峰,84.5eV可能是部分氧化态Auδ+的4f7/2结合能.结合前述的TPR 结果,可以认为,Au/NiO中的活性组分金,除了零价态的金属金外,部分金可能以氧化态的形式存在.3结论3.1焙烧温度影响到催化剂中活性中心金颗粒的大小和载体的结晶程度,从而影响了催化剂的活性;高活性的催化剂中,载体适度结晶.3.2催化剂上的金颗粒尺寸约在10nm以下,金高度分散于金属氧化物载体表面上,使其对CO 的氧化具有高催化活性.3.3催化剂中活性组分金除了Au0的形式以外,部分金可能呈氧化态.参考文献:[1]　邹旭华,齐世学,安立敦,等.以Au(PPh3)(N O3)为前体的Au/NiO催化剂的制备及其对CO的催化氧化[J].分子催化,2000,6(3):171～174[2]　Har uta M,Yamada N,Ko baa yashi T,et al.Go ldCa talysts Pr epa red by Coprecipitatio n for Lo w-tempera tur e Oxidatio n o f Hy drog en a nd Ca rbonM o no xide[J].J Catal,1989,115:301～309[3]　张文详,陶玉国,吴通好,等.不同方法制备的纳米Au/NiO上CO常温常湿催化氧化性能的研究[J].高等学校化学学报,1998,19:1317～1319[4]　吴世华,黄唯平,张守民,等.溶剂化金属原子浸渍法制备高分散Au/TiO2低温CO氧化催化剂[J].催化学报,2000,21(5):419～422XRD,TEM,TPR and XPS Characterization Studieson Au/NiO CatalystsQI Shi-x ue1,ZO U Xu-hua1,XU Xiu-feng1,AN Li-dun1,LI Shu-ben2(1.Institute of Applied Catalysis,Yantai University,Yantai264005,China;nzhou Institute of Chem ical Physics,The Chinese Academy of Sciences,Lanzhou730000,China)Abstract:XRD,TEM,T PR and X PS characterizatio n m eans w ere used to study the structure and state of activ e center a nd suppo rt in Au/NiO catalysts prepared by coprecipitatio n.The results sho w tha t the size o f gold particles highly dispersed o n the surface of suppo rt is in the rang e of sev eral na nom eters,and it is possible that a certain fractio n o f gold particles has a positiv e ox idation state,w hile the suppo rt possesses a pro per cry stallinity.Key words:Suppo rted go ld catalyst;Carbo n mo noxide;Cataly tic oxidatio n;Structural characterizatio n 212分子催化第16卷　。

Cu_SiO2

Journal of Catalysis257(2008)172–180Contents lists available at ScienceDirectJournal of Catalysis/locate/jcatCu/SiO2catalysts prepared by the ammonia-evaporation method:Texture,structure,and catalytic performance in hydrogenation of dimethyl oxalate to ethylene glycolLiang-Feng Chen a,Ping-Jun Guo a,Ming-Hua Qiao a,∗,Shi-Run Yan a,He-Xing Li b,Wei Shen a,Hua-Long Xu a,∗, Kang-Nian Fan aa Department of Chemistry and Shanghai Key Laboratory of Molecular Catalysis and Innovative Materials,Fudan University,Shanghai200433,PR Chinab Department of Chemistry,Shanghai Normal University,Shanghai200234,PR Chinaa r t i c l e i n f o ab s t r ac tArticle history:Received7February2008 Revised3April2008 Accepted23April2008 Available online27May2008Keywords:Cu/SiO2Ammonia-evaporation Copper phyllosilicate Dimethyl oxalateEthylene glycol Hydrogenation Cu/SiO2catalysts prepared by the ammonia-evaporation(AE)method have been systematically characterized focusing on the effect of the AE temperature during catalyst preparation.It is found that the texture, composition,and structure of the calcined and reduced Cu/SiO2catalysts were profoundly affected by the AE temperature.Based on characterizations and previousﬁndings,the copper species on calcined Cu/SiO2samples and reduced Cu/SiO2catalysts were assigned.In gas-phase hydrogenation of dimethyl oxalate(DMO)to ethylene glycol(EG),the evolution of the catalytic activity with the Cu0and Cu+ surface areas suggested that Cu+also participated in the hydrogenation process.The cooperative effect between Cu0and Cu+is proposed to be responsible for the highest hydrogenation activity of the Cu/SiO2 catalyst prepared at the AE temperature of363K,on which an EG yield of98%was obtained under the optimized hydrogenation conditions.©2008Elsevier Inc.All rights reserved.1.IntroductionEthylene glycol(EG)is an important chemical widely used as antifreezer and in polyester manufacture[1].At present,ethylene oxidation is a universal industrial approach to produce EG.How-ever,as crude oil resource shrinks,synthesis of EG from syngas attracts more and more interest.This indirect synthesis process includes two steps:the coupling of CO with nitrite esters to ox-alates,and the hydrogenation of oxalates to EG[2–7].Considerable works have been devoted to the hydrogenation of oxalates since the1970s.Matteoli et al.[8–13]have investigated the homoge-neous hydrogenation of oxalates,and obtained an EG yield of82% under H2pressure of20MPa at453K using Ru(CO)2(Ac)2(PBu)3 as the catalyst.Recently,Teunissen and coworkers[14,15]applied Ru-based homogeneous catalysts in the hydrogenation of dimethyl oxalate(DMO);an EG yield of95%was obtained under milder con-ditions(7MPa,373K).Being aware of the diﬃculties in the catalyst–product separa-tion for the homogeneous catalysts,Cu-based heterogeneous cat-alysts have been investigated in the hydrogenation of dialkyl ox-alates.Although on CuCr catalysts a high yield of EG was ob-*Corresponding authors.Fax:+862165641740.E-mail addresses:mhqiao@(M.-H.Qiao),shuhl@(H.-L.Xu).tained[16–20],the toxicity of Cr severely limits its practical ap-plication.Therefore,Cr-free Cu-based catalysts supported on dif-ferent carriers(SiO2,Al2O3,ZnO,and La2O3)were studied[4,21–26],among which the Cu/SiO2catalyst afforded the highest yield of EG in the hydrogenation of DMO[25]and diethyl oxalate[4] due to the weak acidic and basic properties of SiO2.It is known that strong acid sites induce the intermolecular dehydration of EG to ethanol,whereas strong basic sites catalyze the Guerbet reac-tion into the formation of1,2-butanediol(1,2-BDO)[27,28],both of which deteriorate the selectivity to EG.In above-mentioned works,the Cu/SiO2catalysts were mainly prepared by the homogeneous deposition–precipitation method, but the effect of the deposition–precipitation temperature remains to be explored.Van der Grift et al.[29]identiﬁed the formation of copper phyllosilicate on Cu/SiO2catalyst prepared by the homo-geneous deposition–precipitation method.However,the inﬂuences of the deposition–precipitation temperature on the kinds of cop-per species formed and on the catalytic activity were not studied. It should be mentioned that for the Ni/SiO2catalyst prepared by the deposition–precipitation method,the preparation temperature and time determined the crystallinity and even the type of nickel phyllosilicate[30].The present work was built on previous studies on the prepara-tion of Cu/SiO2catalysts by the ammonia-evaporation(AE)method, a kind of the homogeneous deposition–precipitation method which0021-9517/$–see front matter©2008Elsevier Inc.All rights reserved. doi:10.1016/j.jcat.2008.04.021L.-F.Chen et al./Journal of Catalysis257(2008)172–180173can conveniently and effectively disperse copper species on sil-ica[21],with the added dimension of exploring the inﬂuences of the AE temperature on the texture and phase composition of the calcined Cu/SiO2samples.The catalytic performance of the reduced Cu/SiO2catalysts was evaluated using gas phase hydro-genation of DMO as the probe reaction.The nature of the active sites on the reduced Cu/SiO2catalysts was discussed and corre-lated with the characterization and activity results.2.Experimental2.1.Catalyst preparationThe Cu/SiO2catalysts were prepared by the AE method de-scribed as follows.15.25g of Cu(NO3)2·3H2O(A.R.,Sinopharm Chemical Reagent Ltd.)was dissolved in150ml of deionized water. 46ml of28%ammonia aqueous solution(A.R.,Sinopharm Chemi-cal Reagent Ltd.)was added and stirred for30min.Then40.0g of silica sol(Ludox AS-40)was added to the copper ammonia com-plex solution and stirred for another4h.The initial pH of the suspension was11–12.All the above operations were performed at room temperature.The suspension was transferred to an oil bath preheated at333,343,353,363,and373K,respectively,to allow for the evaporation of ammonia and the decrease of pH and con-sequently,the deposition of copper species on silica.When the pH value of the suspension decreased to6–7,the evaporation process was terminated.Theﬁltrate was washed with500ml of deion-ized waterﬁve times and dried at393K overnight.The catalyst precursors were calcined in static air at723K for4h,pelletized, crushed,sieved to40–60meshes,and denoted as CuSiO-T,where T represents the AE temperature in Kelvin.The reduced catalysts were denoted as CuSi-T correspondingly.2.2.Catalyst characterizationThe bulk composition was analyzed by inductively coupled plasma-atomic emission spectroscopy(ICP-AES;IRIS Intrepid).The BET surface area(S BET)was measured using N2physisorption at 77K on a Micromeritics TriStar3000apparatus.The X-ray diffrac-tion(XRD)patterns were collected on a Bruker AXS D8Advance X-ray diffractometer using Cu Kαradiation(λ=0.15418nm).The tube voltage was40kV,and the current was40mA.For the re-duced catalyst,Ar was used to protect the sample from oxidation during data acquisition.IR spectra were recorded on a Nicolet Nexus470spectrom-eter equipped with a DTGS detector.The samples wereﬁnely grounded,dispersed in KBr,and pelletized.The spectral resolution was2cm−1,and32scans were recorded for each spectrum.The particle size and distribution were observed by transmission elec-tron microscopy(TEM;JEOL JEM2011).The surface species were detected by X-ray photoelectron spectroscopy(XPS;Perkin Elmer PHI5000C).The spectrum was recorded with Mg Kαline as the excitation source(hν=1253.6eV).The binding energy(BE)val-ues were referenced to the C1s peak of contaminant carbon at 284.6eV with an uncertainty of±0.2eV.Temperature-programmed reduction(TPR)was carried out on a home-made apparatus.20mg of the calcined Cu/SiO2sample was outgassed at473K under Ar for1h.After cooling to room temperature under Ar,the gas was switched to5%H2/Ar,and the sample was heated to723K at a ramping rate of10K min−1.The amount of H2consumed was monitored by a thermal conductivity detector(TCD).The metallic Cu surface area was measured by N2O decomposition at363K using a pulsed method with N2as the carrier gas[31].The consumption of N2O was detected by a TCD. An adsorption stoichiometry of two Cu atoms per O atom and a Cu surface density of1.46×1019Cu atom m−2were assumed.2.3.Activity test and product analysisThe activity test was conducted on a continuousﬂow unit equipped with a stainless-steelﬁxed-bed tubular reactor.The cat-alyst bed had an inner diameter of10mm with a height of ap-proximately40mm.Both sides of the catalyst bed were packed with quartz powders(20–40meshes)to ensure a plugﬂow proﬁle of the feed.The catalyst was activated in a5%H2/Ar atmosphere at623K for4h at a ramping rate of2K min−1.After cooling to the reaction temperature of473K,20wt%DMO(purity>99%)in methanol and H2were fed into the reactor at a H2/DMO molar ra-tio of50and a system pressure of2.5MPa.The room-temperature space velocity(LHSV)of DMO was varied from0.10to0.50h−1. The products were condensed and analyzed by a gas chromato-graph(Finnigan TraceGC ultra)ﬁtted with a30m HP-5capillary column and aﬂame ionization detector(FID).3.Results3.1.Characterization of calcined samples3.1.1.Chemical composition and porosityThe Cu contents in the calcined Cu/SiO2samples are summa-rized in Table1.The Cu contents are14.7and15.7wt%at AE temperatures of333and343K,respectively,which are lower than those at higher AE temperatures(∼17.6wt%).At low AE tempera-tures,theﬁltrate was deep blue-colored,indicating the incomplete precipitation of the Cu species.The N2adsorption–desorption isotherms of the calcined Cu/SiO2 samples and their pore size distribution curves are illustrated in Fig.1.The BET surface area,pore volume,and average pore diame-ter are summarized in Table1.It is found that the BET surface area increased from156to326m2g−1when the AE temperature in-creased from333to373K.The pore shape of the calcined Cu/SiO2 samples changed from“spherical”to“slit-like”with the increase of the AE temperature.The change was especially prominent when the samples prepared at333and363K were compared.The pore size distribution curves derived from the desorption branch using the BJH algorithm(Fig.1B)show that at elevated AE tempera-tures,the contribution of pores at ca.3.0and11.1nm to the total pore volume increased considerably at the expense of pores at ca.18.3nm,which is consistent with the decrease of the average pore diameter from11.6to ca.8.2nm.It is noted that the pore vol-ume and average pore diameter of the CuSiO-363sample deviated from the trend displayed by other samples.3.1.2.Crystalline phase and morphologyFig.2shows the XRD patterns of the calcined Cu/SiO2samples, in which the feature at2θof around22◦came from amorphous silica.At the AE temperature of333K,the calcined Cu/SiO2sample exhibited diffractions characteristic of CuO(tenorite)at2θof35.6 and38.7◦(JCPDS05-0661),which were dramatically weakened at 343K andﬁnally vanished at elevated temperatures.The CuO crys-tallite sizes of the CuSiO-333and CuSiO-343samples are11.7and 10.1nm,respectively,based on the Scherrer formula.Although theTable1Physicochemical properties of the calcined Cu/SiO2samplesSample Cu loading(wt%)S BET(m2g−1)V p(cm3g−1)d p(nm)d CuO a(nm) CuSiO-33314.71560.5611.611.7 CuSiO-34315.72090.8011.510.1 CuSiO-35317.32740.989.5–CuSiO-36317.63200.838.2–CuSiO-37317.83260.988.3–a CuO crystallite size calculated by the Scherrer formula.174L.-F.Chen et al./Journal of Catalysis 257(2008)172–180Fig.1.N 2adsorption–desorption isotherms (A)and pore size distribution curves calculated by BJH equation in desorption branch (B)of the calcined Cu/SiO 2samples prepared at the AE temperature of (a)333K,(b)343K,(c)353K,(d)363K,and (e)373K.Fig.2.XRD patterns of the calcined Cu/SiO 2samples.(a)CuSiO-333,(b)CuSiO-343,(c)CuSiO-353,(d)CuSiO-363,and (e)CuSiO-373.weak and broad diffraction peaks at ca.31.2and 35.8◦suggest the presence of copper phyllosilicate with poor crystallinity [32],more unambiguous evidence supporting the formation of this phase is given below.The disappearance of the CuO phase and the increased disper-sion of copper species with the increase of the AE temperature can be directly observed in Fig.3.In the TEM image of the cal-cined CuSiO-333sample (Fig.3a),light gray spherical silica par-ticles are identiﬁed along with dark ones assignable to CuO.The latter reduced in amount at higher AE temperatures,suggesting the improved dispersion of CuO and/or the formation of phases other than CuO.For CuSiO-353,CuSiO-363,and CuSiO-373sam-ples,randomly oriented ﬁlandrous structure was observed,with the amount of the ﬁlandrous species in the CuSiO-363sample be-ing the most abundant.IR technique has been adopted to determine the ﬁlandrous compounds of phyllosilicates [32–34].In this work,as shown in Fig.4,the formation of copper phyllosilicate is supported by the appearance of the δOH band at 663cm −1and the νSiO shoulderpeak at 1040cm −1on the low frequency side of the νSiO asym-metric stretching band of SiO 2at 1110cm −1[32].The relative amount of copper phyllosilicate in calcined Cu/SiO 2samples is cal-culated by considering the integrated intensity of the δOH band at 663cm −1normalized to the integrated intensity of the νSiO sym-metric stretching band of SiO 2at 800cm −1,which is termed as I 663/I 800[32].It is worthwhile to note that the I 663/I 800ratio only gives a qualitative estimation of the amount of copper phyllosili-cate,because the extinction coeﬃcients of the corresponding IR bands are not known.Inset in Fig.4clearly shows that the rela-tive amount of copper phyllosilicate in calcined Cu/SiO 2samples increased with the AE temperature and maximized at 363K.3.1.3.Chemical state of copper and reduction behaviorXPS analysis was carried out to elucidate the chemical states of copper.Typically,the Cu 2p 3/2BE of CuO is found at ca.933.5eV [35],and the Cu 2p 3/2BE of supported copper phyllosil-icate is 934.9eV [29].Fig.5shows that in all calcined Cu/SiO 2samples copper existed in the oxidation state of Cu 2+,as evi-denced by the Cu 2p 3/2peak at 933.1–935.6eV and the 2p →3d satellite at 942–944eV characteristic of Cu 2+with electron con-ﬁguration of d 9[36].The variation of the Cu 2p 3/2BE values with the AE temperatures is an indication of the formation of different copper species in calcined Cu/SiO 2samples.Fig.6shows the TPR proﬁles of the calcined Cu/SiO 2samples.For the CuSiO-333sample,besides the main reduction peak at 516K,there was a shoulder peak at ca.540K,which was at-tenuated for the CuSiO-343sample,and vanished at higher AE temperatures.Based on the XRD and TEM characterizations,this shoulder peak is assigned to the reduction of large CuO particles to metallic Cu.The assignment is in compliance with the fact that the reduction of bulk CuO usually occurs at 528–573K [37–39].On the other hand,the main reduction peak at lower temperature is assigned to the reduction of other Cu species but not conﬁned to copper phyllosilicate.A detailed assignment of the Cu species relating to the main reduction peak will be given in Section 4.3.3.2.Characterization of the reduced catalysts3.2.1.BET surface area and porosityThe N 2adsorption–desorption isotherms of the reduced Cu/SiO 2catalysts and their pore size distribution curves are plotted inL.-F.Chen et al./Journal of Catalysis257(2008)172–180175Fig.3.TEM images of the calcined Cu/SiO2samples.(a)CuSiO-333,(b)CuSiO-343,(c)CuSiO-353,(d)CuSiO-363,and(e)CuSiO-373.(f)is the TEM image for the reduced CuSi-363catalyst.Fig.7.The BET surface area,pore volume,and average pore di-ameter are summarized in Table2.After reduction,the isotherms and pore size distribution curves still resembled those of calcined Cu/SiO2samples,except for the shift of the peak with the smallest pore size from ca.3.0to2.4nm and the decreased contribution of this peak to the total pore volume.As a result,the average pore diameter increased.In addition,the BET surface area and the total pore volume decreased,while their evolution with the AE temper-ature followed that of calcined Cu/SiO2samples.It is again noticed that similar to the CuSiO-363sample,the CuSi-363catalyst has pore volume and average pore diameter not in line with the trend held by other reduced catalysts.3.2.2.Crystalline phase and morphologyThe XRD patterns(Fig.8)of the reduced Cu/SiO2catalysts show a strong diffraction peak at2θof43.3◦along with two weak ones at50.4and74.1◦characteristic of fcc Cu(JCPDS04-0836).The Cu crystallite sizes calculated by the Scherrer formula are listed in Ta-ble2.For the CuSi-333catalyst,the Cu crystallite size showed a bimodal distribution at5.2and22.1nm,which was also observed but not as obvious for the CuSi-343catalyst,as identiﬁed byﬁtting the Cu(111)diffraction peak at43.3◦.The bimodal distribution of the Cu particle size for the CuSi-333and CuSi-343catalysts is visi-ble by TEM as well,as listed in Table2.On other reduced Cu/SiO2 catalysts,only Cu crystallites with size of ca.4nm were identiﬁed.176L.-F.Chen et al./Journal of Catalysis257(2008)172–180Fig.4.IR spectra of the calcined Cu/SiO2samples.(a)CuSiO-333,(b)CuSiO-343, (c)CuSiO-353,(d)CuSiO-363,and(e)CuSiO-373.Inset shows the I663/I800intensityratio representing the relative amount of copper phyllosilicate in theprecursors.Fig.5.XPS spectra of the calcined Cu/SiO2samples.(a)CuSiO-333,(b)CuSiO-343, (c)CuSiO-353,(d)CuSiO-363,and(e)CuSiO-373.In addition,all reduced catalysts showed a weak and broad peak at around36.4◦ascribable to the Cu2O(111)plane(JCPDS05-0667), indicating that a portion of copper exists as Cu+after reduction in H2at623K.Among the reduced Cu/SiO2catalysts,the CuSi-363 catalyst showed the most distinct Cu2O(111)diffraction peak.The TEM image of the CuSi-363catalyst is shown in Fig.3f as an example for the reduced Cu/SiO2catalysts.A comparison with the TEM image of the CuSiO-363sample(Fig.3d)clearly demon-strates that after reduction the typicalﬁlandrous morphology of copper phyllosilicate was eliminated substantially,whereas black spherical particles attributable to metallic Cu emerged.The metal-lic Cu particle size observed by TEM is larger than the crystallite size derived from XRD,indicating the polycrystalline nature of the metallic Cu particles.3.2.3.Surface chemical statesThe XPS and X-ray induced Auger spectra(XAES)of the reduced Cu/SiO2catalysts are illustrated in Figs.9and10,respectively.As Fig.6.H2-TPR proﬁles of the calcined Cu/SiO2samples.(a)CuSiO-333,(b)Cu-SiO-343,(c)CuSiO-353,(d)CuSiO-363,and(e)CuSiO-373.Table2Physicochemical properties of the reduced Cu/SiO2catalystsCatalyst S BET(m2g−1)V p(cm3g−1)d p(nm)d Cu a(nm)d Cu c(nm) CuSi-3331320.5014.022.1,5.2b30.2,6.4 CuSi-3431810.7513.515.7,4.8b14.3,6.1 CuSi-3532480.7712.34.17.1 CuSi-3632810.719.03.67.3 CuSi-3733090.9610.33.97.2a Cu crystallite size calculated by the Scherrer formula.b Bimodal size distribution of Cu crystallites calculated byﬁtting the(111)diffrac-tion peak of fcc Cu.c Cu particle size measured by TEM.compared to the calcined samples,the Cu2p3/2BE of the reduced catalysts shifted to ca.932.7eV,and the2p→3d satellite dis-appeared due to the reduction of Cu2+to Cu0or/and Cu+.The modiﬁed Auger parameterα ,which represents the summation of the kinetic energy(KE)of the Cu LMM Auger electron and the BE of the Cu2p3/2photoelectron,was employed to distinguish be-tween the Cu0and Cu+species.In general,α is ca.1851.0eV for Cu0and1849.0eV for Cu+[40].In Fig.10,it is obvious that each Cu LMM spectrum contains one more component as inferred by the broad and asymmetrical peak shape;the deconvolution results are listed in Table3.Theα value at ca.1851.0eV is ascribed to Cu0and ca.1847.0eV to Cu+.The smallerα value for Cu+than the bulk value is attributed to the strong interaction between Cu+ and SiO2.It is reported that when copper(in+2,+1,and0va-lence)is in the highly dispersed state and in intimate contact with the supports,α can be2–3eV lower than the bulk values[41].As listed in Table3,the Cu+/(Cu++Cu0)intensity ratio derived byﬁtting the Cu LMM peak increased with the AE temperature, and maximized at363K with the Cu+/(Cu++Cu0)ratio of54.9%. It has been shown that CuO species weakly interacting with the support can be readily reduced to Cu0at623K[42,43].The high Cu+/(Cu++Cu0)ratios(>40%)for the reduced Cu/SiO2catalysts signify the hindrance for Cu2+reduction in calcined Cu/SiO2sam-ples prepared by the AE method.The metallic Cu surface areas measured by N2O titration are listed in Table3.The Cu0surface area increased from 3.6to 9.8m2g−1as the AE temperature increased,with the exception of the CuSi-363catalyst having a Cu0surface area of9.2m2g−1,L.-F.Chen et al./Journal of Catalysis 257(2008)172–180177Fig.7.N 2adsorption–desorption isotherms (A)and pore size distribution curves calculated by BJH equation in desorption branch (B)of the reduced Cu/SiO 2catalysts prepared at the AE temperature of (a)333K,(b)343K,(c)353K,(d)363K,and (e)373K.Fig.8.XRD patterns of the reduced Cu/SiO 2catalysts.(a)CuSi-333,(b)CuSi-343,(c)CuSi-353,(d)CuSi-363,and (e)CuSi-373.Fig.9.XPS spectra of the reduced Cu/SiO 2catalysts.(a)CuSi-333,(b)CuSi-343,(c)CuSi-353,(d)CuSi-363,and (e)CuSi-373.Fig.10.Cu LMM Auger spectra of the reduced Cu/SiO 2catalysts.(a)CuSi-333,(b)CuSi-343,(c)CuSi-353,(d)CuSi-363,and (e)CuSi-373.The Auger features due to Cu 0and Cu +are indicated.Table 3Cu species on the reduced Cu/SiO 2catalyst derived from Cu LMM XAES spectra CatalystKE (eV)α (eV)X Cu +a (%)S Cu 0b(m 2g −1)S Cu +c(m 2g −1)Cu +Cu 0Cu +Cu 0CuSi-333914.4918.41847.01851.040.4 3.62.4CuSi-343914.2918.21847.01851.040.57.85.3CuSi-353914.2918.01846.91850.745.79.68.1CuSi-363914.3918.41846.91851.054.99.211.2CuSi-373914.2918.01846.81850.652.09.810.6aIntensity ratio between Cu +and (Cu ++Cu 0)by deconvolution of Cu LMM XAES spectra.bMetallic Cu surface area determined by N 2O titration.c Calculated based on X Cu +and S Cu 0assuming that Cu +ion occupies the same area as that of the Cu 0atom,and has the same atomic sensitivity factor as that of Cu 0.which is smaller than its neighboring catalysts.As revealed by the Cu LMM XAES results,the Cu species on the reduced Cu/SiO 2cat-alysts are Cu 0and Cu +.Assuming that the Cu +ion occupies the same area as that of the Cu 0atom,and has the same atomic sen-178L.-F.Chen et al./Journal of Catalysis 257(2008)172–180Scheme 1.Reaction pathway for the hydrogenation of DMO to MG,EG,and ethanol.Table 4The catalytic performance of the Cu/SiO 2catalysts prepared by the AE method in gas-phase hydrogenation of DMO a CatalystDMO conversion (%)Selectivity (%)MG EG Ethanol 1,2-BDO CuSi-3333482180.70.2CuSi-343467326 1.50CuSi-353656533 1.70CuSi-363795743 1.80CuSi-3737374251.10.1aReaction conditions:p =2.5MPa,T =473K,H 2/DMO =50(mol mol −1),and LHSV of DMO =0.50h −1.Fig.11.Effect of the LHSV of DMO on the catalytic performance of the CuSi-363cat-alyst.Reaction conditions:p =2.5MPa,T =473K,and H 2/DMM =50(mol mol −1).sitivity factor as that of Cu 0,the Cu +surface area was estimated according to the Cu 0surface area and the surface Cu +/(Cu ++Cu 0)LMM intensity ratio.In Table 3,it is found that different from the evolution of the Cu 0surface area,the Cu +surface area maximized at the AE temperature of 363K,with the value of 11.2m 2g −1.3.3.Gas-phase hydrogenation of DMOThe catalytic performance of the Cu/SiO 2catalysts prepared at different AE temperatures was investigated in gas-phase hy-drogenation of DMO.Steady-state product compositions were ob-tained after about 8h on stream.It is known that the hydrogena-tion of DMO proceeds via methyl glycolate (MG)to EG,while EG can dehydrate further to ethanol (Scheme 1).The reaction between EG and ethanol on basic sites yields 1,2-BDO [28].Under the re-action condition speciﬁed under Table 4,the conversion of DMO increased steadily from 34%on the CuSi-333catalyst to 79%on the CuSi-363catalyst,and then dropped to 73%on the CuSi-373cata-lyst.Almost all the converted DMO had been turned into MG and EG.The selectivities to ethanol and 1,2-BDO remained low (<2%),attributable to the lacking of acid and basic sites on SiO 2.Over the CuSi-363catalyst which exhibited the highest hy-drogenation activity,while keeping other reaction conditions un-changed,the LHSV of DMO was adjusted to optimize the yield of EG.In Fig.11,the conversion of DMO and selectivities to ethanol and 1,2-BDO decreased with the increase of LHSV,whereas the se-lectivity to MG increased only slightly below LHSV of 0.25h −1,then grew up drastically.As a result,the EG selectivity reached a maximum of 98%at the LHSV of 0.25h −1when the DMO conver-sion still remained at about 100%.4.Discussion4.1.Formation of copper phyllosilicate on calcined Cu/SiO 2samples Copper phyllosilicate (Cu 2Si 2O 5(OH)2),also called chrysocolla,is a kind of copper silicate with lamellar structure that consists of layers of SiO 4tetrahedra sandwiched between discontinuous layers of CuO 6octahedra.Copper phyllosilicate is known to form during the preparation of Cu/SiO 2catalyst by the deposition–precipitation method using urea hydrolysis [29]and by selective adsorption ofCu(NH 3)2+4on SiO 2[32].Our work showed that copper phyllosil-icate can also be formed using the AE method.Van der Grift et al.[29]reported that the BET surface area of the Cu/SiO 2catalyst prepared by the urea hydrolysis method increased with the in-crease of the Cu loading,and ascribed it to the formation of more ﬁlandrous copper phyllosilicate which enhanced the BET surface area.In the present work,the BET surface areas of the calcined Cu/SiO 2samples increased with the AE temperature.The forma-tion of copper phyllosilicate is also corroborated by IR.TEM images showed that the ﬁlandrous structure characteristic of copper phyl-losilicate became predominant on samples with higher AE temper-atures.Therefore,the change in the pore shape from “spherical”to “slit-like”and the decrease in the average pore size can be at-tributed to the formation of a new pore system arising from the ﬁlandrous copper phyllosilicate.For both the calcined Cu/SiO 2samples and the reduced Cu/SiO 2catalysts,N 2physisorption,TEM,IR,XPS,and TPR characteriza-tions all point to the similar character of the samples prepared at AE temperatures of 353and 373K.As reported by Burattin et al.[30],the formation of nickel phyllosilicate during deposition–precipitation by urea hydrolysis was facilitated by longer prepa-ration time and higher temperature.In the present case,although the preparation method and the formed phyllosilicate are different,the synthesis time may also play an important role in the forma-tion of copper phyllosilicate.But for the AE method used here,a higher preparation temperature means more rapid evaporation of ammonia,thus a shorter time for the pH of the suspension decreasing from 11–12to 6–7.The similarity between calcined Cu/SiO 2samples prepared at AE temperatures of 353and 373K can be rationalized in terms of the interplay between the AE tem-perature and the AE time.At the optimal AE temperature,363K,the amount of copper phyllosilicate became the most abundant,as supported by TEM and IR results shown in Figs.3and 4,respec-tively.4.2.Copper species on calcined Cu/SiO 2samples prepared by the AE methodThe ion-exchange method reported by Kobayashi et al.[44]and Kohler et al.[41]resembles to some extent with the AE methodused here.For both methods,SiO 2was immersed in the Cu(NH 3)2+4solution at the pH value of 11–12at room temperature until ad-sorption and ion-exchange reached a dynamic equilibrium.The difference is that evaporation of ammonia instead of ﬁltration was followed in the AE method.The Cu species on the calcined Cu/SiO 2catalyst prepared by the ion-exchange method are present in two forms.One is the immobilized single Cu ions on SiO 2surface by exchanging with two silanol group,the other is a well dispersed CuO layer over the ion-exchanged Cu–O–Si layer,which originates from the calcination of Cu(OH)2formed during washing by waterthat hydrolyzes Cu(NH 3)2+4trapped in the ﬁlter cake [41].Using。

英文翻译

一步制备降解罗丹明B的掺杂银、氧化铟的二氧化钛光催化剂夏阳，徐磊磊，于晓丹，郭一洋摘要开发新颖的共掺杂银、氧化铟的二氧化钛光催化剂，通过一个单步溶胶 - 凝胶法，随后通过溶剂热三嵌段共聚物表面活性剂的存在下处理。

该产品表现出非常小的颗粒尺寸（12±2纳米）与金属银集群分布的产品的表面上，在同一时间，该产品主要是在具有高结晶度的锐钛矿相。

对于掺杂银、氧化铟的光催化活性评价染料罗丹明B（RB）的水溶液中的降解，获得显着的光催化活性高，可以归因于掺杂贵金属银的同时作用电子的影响和半导体氧化铟作为窄带隙增敏剂的影响。

此外，独特的形态和纳米尺寸的产品也发挥了重要作用，这种可以增强的光催化活性。

2007年由Elsevier BV公司发布关键词：银，氧化铟；共掺杂二氧化钛；光催化溶胶 - 凝胶；罗丹明B1.介绍由于其潜在的有机化合物的总破坏活动污染的空气和废水，设计和制备高效多相光催化材料仍然备受关注。

为了设计和制备高效多相光催化材料，已经提出了各种方法，以提高涉及二氧化钛（带隙为3.2 EV）的光催化效率主要包括掺杂，表面官能化的金属颗粒，并且把粒径减少为纳米级。

因此，二氧化钛的带隙能减少和/或光生电子的复合空穴对（E·小时），可以有效防止催化活性的降低。

在这些方法中，掺杂的两个组成部分成锐钛矿型二氧化钛晶格产生共掺杂的二氧化钛光催化剂是用于提高二氧化钛的光催化活性最有效的方法之一。

例如，共掺杂氮和三价铁的纳米级二氧化钛光催化剂比铁 - 二氧化钛光触媒的光催化剂分解可见光催化活性高得多；具有较高的磷-氮共掺杂的二氧化钛奈米光触媒应用于厕所光催化活性的可见光区域;银相氧化铟共掺杂复合薄膜与掺杂1％银的染料甲基橙表现出较高的可见光活性分解。

由这些结果作为动力，本工作演示了一个新的共掺杂银、氧化铟的二氧化钛纳米复合材料。

由于其在纳米贵金属中显著的催化活性，银是一个非常有吸引力的金属，它的大小和形状依赖于它的光学性能。

晶带轴

In Situ Growth of Self-Assembled and Single In2O3Nanosheets onthe Surface of Indium GrainsHeqing Yang,*,†Ruigang Zhang,†Hongxing Dong,†Jie Yu,†Wenyu Yang,†andDichun Chen‡Key Laboratory of Macromolecular Science of Shaanxi Pro V ince,School of Chemistry and MaterialsScience,Shaanxi Normal Uni V ersity,Xi’an710062,China,and Ad V anced Material Analysis and TestCenter,Xi’an Uni V ersity of Technology,Xi’an710048,ChinaRecei V ed January7,2007;Re V ised Manuscript Recei V ed May15,2008ABSTRACT:Self-assembled In2O3nanosheet networks andﬂowerlike nanoarchitectures,as well as single In2O3nanosheets,have been grown in situ on indium substrate by heating indium grains at900-950°C under theﬂow of O2in the presence of a small quantity of P2O5.The as-synthesized In2O3nanosheets were characterized by transmission electron microscopy,scanning electron microscopy,and Raman spectrum.It was found that the In2O3nanosheets were single crystals with body-centered cubic structure and dimensions of about0.5-3µm.A possible mechanism for the In2O3nanosheet growth was also proposed on the basis of the results of the present and previous works.This mechanism not only can explain all the experimental observations but also helps to clarify the growth mechanism of other nanostructures in the gas phase.A strong and narrow photoluminescent(PL)peak at428nm was observed from the nanosheets,which is attributed to radiative recombination between an electron on an oxygen vacancy and a hole on an indium-oxygen vacancy center in the In2O3nanosheets.1.IntroductionSynthesis of different dimensional(D)nanostructures,such as0D quantum dots,1D nanowires and nanotubes,or2D nanosheets and nanodisks are of great importance in studying the physical properties of nanomaterials or constructing func-tional nanodevices.1Indium oxide(In2O3),an n-type semicon-ductor with a wide bandgap of about3.6eV,has been widely used as window heater,solar cell,andﬂat-panel display materials2and gas sensors.3Since the discovery of indium oxide nanobelts in2001,4research in In2O3nanostructures,including nanowires,nanotubes,nanobelts,octahedrons,nanocubes,and core-shell nanoparticles has been rapidly expanded due to their potential application in high sensitivity sensor,optoelectronic,ﬁeld emission,and electronic devices.The indium oxide nanowires have been used to fabricatedﬁeld-effect transistors,5,6 nanoscale chemical sensors,7and biosensing devices.8Up to now,many kinds of In2O3nanostructures have been synthesized via thermal evaporation of In2O3,chemical vapor deposition(CVD),pulsed laser deposition(PLD),and wet chemical methods.In2O3nanobelts were synthesized via a thermal evaporation of In2O3powders at1400°C4or via a CVD using thermal oxidation reactions of In.9In2O3nanowires can be obtained by the CVD of thermal oxidations10–12and reductions,6,13,14by a laser ablation of InAs target,15or by triblock copolymer and porous alumina template methods.16 Additionally,single-crystalline In2O3nanotubesﬁlled with metallic In,17In2O3nanocrystal chains,and nanowire networks18 were synthesized by evaporating a mixture of In/In2O3or C/In2O3.Hollow In2O3nanotubes were grown in porous alumina membranes by a sol-gel process.19Aligned1D In2O3structures with a triangular cross-section were synthesized by a metal-organic chemical vapor deposition method(MOVCD).20In addition to the quasi-1D nanostructures,0D quantum dots such as quasi-monodisperse In2O3nanoparticles,21,22nanocubes,23In2O3octahedron,24,25and highly ordered In2O3coated In core-shell nanoparticles26were prepared via wet chemical methods,21–23CVD,24,25and a three-step oxidation process of In nanoparticle arrays.26However,to our knowledge,synthesis of2D In2O3nanostructures except for thinﬁlms has not been reported until now.Herein we report the synthesis of self-assembled and single In2O3nanosheets by an in situ thermal oxidation method.These sheet-like nanostructures were directly grown on the surfaces of indium grains by heating indium metal at900-950°C in an oxygen gas atmosphere in the presence of a small quantity of pared with CVD,MOCVD,and PLD,this procedure does not include In or In2O vapor transport and condensation processes and does not require very high temperature and low pressure.Growth mechanism and photoluminescence of the In2O3nanosheets were investigated in detail.2.Experimental Procedures2.1.Sample Preparation.The In2O3nanosheets were synthesized by a simple thermal oxidation of indium metal in a conventionalhorizontal tube furnace.In a typical experiment,In metal grains(purity99.999%)were treated in an aqueous1.0M HCl solution for30s andthen washed with absolute ethanol in an ultrasonic bath for15min.The grain was placed on a silicon wafer,and the silicon wafer wasplaced in a quartz boat containing a small quantity of P2O5(formed byheating a quartz boat containing about2-5mg of red phosphorus to500°C and then maintaining it at500°C for0.5h in an O2gasatmosphere).The boat was placed at the center of a quartz tube thatwas inserted in a horizontal tube furnace,where the temperature andgrowth time were controlled.Prior to heating,high-purity N2(99.999%)was introduced into the quartz tube with a constantﬂow rate of3.0L/h to purge the O2inside.After20min,the system was heated to900°C for60min under a constantﬂow of N2gas at a rate of1.0L/h. Afterward,1.0L/h O2was introduced into the chamber,and thetemperature was kept at900°C for2h.After the system cooled toroom temperature under a constantﬂow of N2gas at a rate of1.0L/h,a large amount of ashen products were found on the surface of theindium grains.2.2.Characterization.The synthesized products were characterized and analyzed by X-ray diffraction(XRD;Rigaku DMX-2550/PC X-ray diffractometer),Raman spectra(Jobin Yvon LabRAM HR800and*Corresponding author.Fax:+86-29-85307774.Tel:+86-29-85303943.E-mail address:hqyang@.†Shaanxi Normal University.‡Xi’an University of Technology.10.1021/cg070019e CCC:$40.75 XXXX American Chemical SocietyPublished on Web 07/23/2008Nicolet Alemga dispersive Raman spectrometer),scanning electron microscopy (SEM;FEI Quanta 200),and high-resolution transmission electron microscopy (HRTEM;JEOL JEM-3010at 300kV).Samples for HRTEM were prepared by dispersing a powdered In 2O 3product on a carbon-coated copper grid.An energy-dispersive X-ray spectros-copy (EDS)facility attached to the SEM and TEM was employed to analyze the chemical composition.Photoluminescent (PL)spectra were measured at room temperature in an Edinburgh FLS920ﬂuorescence spectrophotometer with a Xe lamp using excitation at 380nm.3.Results and DiscussionFigure 1a -c shows typical SEM images of as-prepared samples grown at 900°C for 2h at low and high magniﬁcations.These In 2O 3nanosheets were randomly and fairly uniformly distributed on the surface of the In grain.Figure 1c clearly shows that In 2O 3nanosheets are oriented upward with respect to the underlying substrate and have irregularly shaped morphologies with maximum dimension of about 0.5-3.0µm on the bottom,gradually narrowing to the top.The minimum thickness of the In 2O 3sheets on the top is tens of nanometers.In addition to the dispersed In 2O 3nanosheets,a small quantity of intercrossed In 2O 3nanosheet networks are also observed in some areas on the surface of the In grains.The typical morphology of these self-assembled In 2O 3nanosheets is shown in Figure 2.Figure 2a-b shows the low-and high-magniﬁcation SEM images,respectively.Figure 2b clearly shows that the network is constructed of nanosheets with heights ranging from 0.5to 1.2µm.The nanosheets intercross with each other to form complicated networks.When the reaction temperature was increased from 900to 950°C,a few interesting ﬂowerlike In 2O 3nanoarchitectures were observed on the surface of the In grains.Typical SEM micrographs of the ﬂowerlike In 2O 3nanoarchi-tectures at low and high magniﬁcations are presented in Figure 3a,b.From Figure 3a,b,it is evident that In 2O 3nanoﬂowers consist of sheetlike nanostructures.The In 2O 3nanosheets possessmainly fan-shaped morphologies and are 0.5-5.5µm in length and 0.6-3.2µm in height.Figure 4a shows the XRD pattern of the samples grown at 900°C for 2h in an O 2gas atmosphere.Sixteen peaks at 2θ)30.5°,32.8°,35.3°,37.6°,41.7°,43.6°,45.5°,49.1°,50.9°,52.8°,56.0°,59.0°,60.5°,62.1°,63.5°,and 64.4°are observed from Figure 4a.According to JCPDS card no.06-0461,the products are In 2O 3with body-centered cubic structure,and these peaks are assigned to (222),(321),(400),(411),(332),(422),(431),(521),(440),(433),(611),(541),(622),(631),(444),and (543)diffraction lines of cubic In 2O 3phases,respectively.RamanFigure 1.SEM images of as-prepared samples grown at 900°C for 2h at differentmagniﬁcations.Figure 2.Low-(a)and high-magniﬁcation (b)SEM images of the intercrossed In 2O 3nanosheetnetworks.Figure 3.Low-(a)and high-magniﬁcation (b)SEM micrographs of the ﬂowerlike In 2O 3nanoarchitectures grown at 950°C for 2h.Figure 4.XRD pattern (a)and Raman spectrum (b)of the samples grown at 900°C for 2h.B Crystal Growth &Design,Vol.xxx,No.xx,XXXX Yang et al.scattering,due to its sensitivity to crystallization in nanostruc-tures,was also measured for the In 2O 3nanosheets.Figure 4b shows the Raman spectrum of the samples grown at 900°C for 2h excited with an Ar +laser at 514nm at room temperature.The ﬁve peaks at 126,301,358,489,and 622cm -1can be identiﬁed to be those of the cubic In 2O 3.27XRD and Raman indicate that the products obtained are In 2O 3nanosheets with cubic structure.The characterization of individual In 2O 3nanosheets was achieved in further detail using TEM.Figure 5a shows the TEM image of a quasi-rectangular In 2O 3nanosheet.The nanosheet is 650nm in length and 520nm in width.The contrast on a whole sheet is inhomogenous,which indicates that the thick-nesses of the sheet at the root and the center are greater than that at the top and side edges,as observed by SEM.The corresponding selected area electron diffraction (SAED)pattern is shown in Figure 5b;it can be indexed as a cubic In 2O 3along the [125]axis,consistent with the XRD and Raman results.The HRTEM image of the In 2O 3nanosheet is displayed in Figure5c.The fringe spacing is about 0.42nm,corresponding to the (121j )crystal planes of the cubic In 2O 3.The chemical composi-tion of the In 2O 3nanosheet was veriﬁed by an EDS facility attached to the TEM.The EDS data curve is shown in Figure 5d,in which In,O,and Cu elements were marked.The Cu-related peak is due to the presence of the Cu grids.So,the nanosheet consists of indium and oxygen.These results indicate that the nanosheets are a single-crystalline with body-centered cubic structure.To identify whether there was P 2O 5on the surface of the In 2O 3nanosheets,an EDS facility attached to the SEM was employed to analyze the chemical composition of the In 2O 3nanosheets obtained by heating indium grains at 900°C for 2h in an O 2gas atmosphere in the presence of a small quality P 2O 5,and the results are shown in Figure 6.Figure 6b-c shows EDS spectra from the marked region and dot in panel a,respectively.The peaks of In,P,and O elements were observed from the EDS spectra.It indicates that there was P 2O 5on the surface of In 2O 3nanosheets.The P-related peak was not found in the EDS spectrum (Figure 5d)obtained by using an EDS facility attached to the TEM.The disappearance of the P-related peak may because that the P 2O 5was dissolved in ethanol during prepara-tion of the samples for TEM analysis.To illuminate the role of P 2O 5in the formation of In 2O 3nanosheets,the products obtained by heating indium grains at 900°C for 2h in an O 2gas atmosphere in the absence of P 2O 5were characterized with SEM and Raman,and results are shown in Figure 7.We found that there are octahedra instead of nanosheets on the surface of the indium grain in the SEM image (Figure 7a),indicating that P 2O 5plays an important role in the growth process of In 2O 3nanosheets.Figure 7b is Raman spectra of the sample.In the Raman spectra,we observed ﬁve scattering peaks at 130,306,366,495,and 628cm -1,which can be identiﬁed to be those of the cubic In 2O 3.27It indicates that metallic In was oxidized to form an In 2O 3octahedral layer on the surface of In grains when indium grains were heated at 900°C in an O 2gas atmosphere without P 2O 5.In order to understand the formation process of the In 2O 3nanosheets,time-dependent experiments were carried out,and the resultant products were analyzed by SEM and Raman spectra.The representative SEM images of the products prepared at certain reaction time intervals are shown in Figure 8.A large quantity of spherical particles was seen on the surface of the In grains obtained by heating at 900°C for 2min (Figure 8a).When the reaction time was prolonged to10min,these particles aggregated with each other to form large congeries (Figure 8b).In addition to the congeries,a small quantity of In 2O 3nanosheets was observed on the surface of the congeries (Figure 8c).When the reaction time was increased to 30min,a large quantity of In 2O 3nanosheets were observed on the surface of the In grains (Figure 8d).Figure 9shows the Raman spectra from the samples reacted for 2,10,and 30min excited with an Nd:YVO 4laser at 532nm at room temperature,which indicates that the nanoparticles and nanosheets are In 2O 3with a cubic structure.27The growth process for the In 2O 3is similar to the growth of BN nanowires through the reaction of a mixed gas of N 2and NH 3over R -FeB particles 28and the growth of In 2O 3nanowires through the reaction of an O 2gas over indium grains coated on a Au ﬁlm.29The P 2O 5may be a catalyst for the growth of In 2O 3nanosheets.On the basis of the investigations described above,a possible mechanism to form In 2O 3nanosheets was proposed with reference to the preparation of Ti-doped CeO 2nanopar-ticles,30growth of carbon tubes via surface diffusion,31and growth of silicon nanowires via a solid -liquid -solid(S-L-S)Figure 5.TEM images and SAED pattern of the In 2O 3nanosheets synthesized at 900°C for 2h:(a)typical image of a single In 2O 3nanosheet;(b)corresponding SAED pattern;(c)HRTEM image;(d)EDS spectrum.Self-Assembled and Single In 2O 3Nanosheets on In Grains Crystal Growth &Design,Vol.xxx,No.xx,XXXX Cmechanism.32As illustrated in Figure 10,during heating under the ﬂow of N 2,the In metal was melted to form liquid In (the melting point of In metal is 156.6°C);P 2O 5was vaporized and reacted with surface In of In grains to produce In -P -O liquid-phase layers.When the temperature was increased to 900°C,O 2gas was introduced into the chamber and reacted with the surface In rapidly to produce In 2O 3.According to Feng,30Tian,31a and Hofmann 31b and their co-workers,the In 2O 3congregated,nucleated,and grew into In 2O 3nanoparticles coated with an In -P -O liquid-phase layer on the liquid In surface via surface diffusion (Figure 10c).The In 2O 3nanoparticles coated with an In -P -O liquid-phase layer evolved into large particles driven by the minimization of surface energy.The In -P -O liquid-phase layers reacted with the In 2O 3core to form In -P -O droplets (Figure 10e)on the surface of the large particles.When the In 2O 3in the droplets reach a saturated concentration,crystalline In 2O 3nanosheets begin to grow from the droplets via the S-L-S mechanism (Figure 10f).The growth mechanism may be characterized by the growth at the roots of the nanosheets.The underlying In 2O 3core provides the neces-sary feeding materials for the nanosheet growth.The surrounding In 2O 3of the In 2O 3core was consumed and transported through the surface of In metal for the continuous growth of the In 2O 3nanosheets.The oxidation reaction of the surface In of indium grains provides In 2O 3to maintain the surface diffusion and nanosheet growth.After the reaction,the shape of the In grain is also spherical (Figure 1a),which indicates that the oxidation of metallic In as well as nucleation and growth of In 2O 3nanosheets occurred on the metallic In surface.During the growth of In 2O 3nanosheets in addition to the S-L-S growth mechanism,surrounding In 2O 3of the In 2O 3sheets was trans-ported through the surface of In 2O 3particles and nanosheets to the top and side edges of nanosheets,and nucleated and grew (Figure 10g).There is a concentration gradient of In 2O 3between the top and roots of the In 2O 3sheets to maintain the surface diffusion.The thicknesses of the sheet at the root and center are bigger than those on the top and side edges due to the presence of the In 2O 3concentration gradient.During nucleation and growth of In 2O 3nanostructures,the initially formed nuclei in the droplets are dispersed,and subsequent growth from the nuclei results in the nanosheets.Agglomeration of neighboring nanoscale nuclei is likely to be responsible for self-assembled nanosheets.The initially formed nuclei aggregate to form nuclei with a network structure and nucleus arrays,and subsequent growth from the assembled nuclei results in the intercrossed nanosheet networks and ﬂowerlike nanoarchitectures.When the reaction temperature was increased from 900to 950°C,the agglomeration of neighboring nanoscale nuclei was aggrandized,and thus the ﬂowerlike nanoarchitectures were obtained.As the In 2O 3nanosheets formed,an In 2O 3layer is also obtained on the surface of the In metal.The In 2O 3layer protects the In metal from further oxidation.Therefore,after the reaction,the shape of the In grain is also spherical (Figure 1a).Without P 2O 5during the heating under the ﬂow of N 2,the In metal was melted and vaporized.As O 2gas was introduced into the chamber at 900°C,the In vapor reacted rapidly with O 2to form In 2O 3.TheFigure 6.SEM image and EDS spectra of the products obtained at 900°C for 2h:(a)SEM image;(b,c)EDS spectra from the selected area and spot in panela.Figure 7.SEM image (a)and Raman spectrum (b)of products prepared at 900°C for 2h without P 2O 5.D Crystal Growth &Design,Vol.xxx,No.xx,XXXX Yang et al.In 2O 3directly deposited on the In grain and grew into octahedra via a vapor -solid process.4It is known that bulk In 2O 3cannot emit light at room temperature.33However,Recently,Seo 22and Liu 21and their co-workers observed PL peaks at 325-332,392,and 423nm from In 2O 3nanoparticles.Lee et al.34observed PL peaks at 360,400,and 470nm from In 2O 3nanocubes.Liang 10and Guha 35et al.reported a peak at 470nm from nanoﬁbers and octahedrons of In 2O 3.Lee 36and Li 17and their co-workers observed PL peaks at 637and 617nm from thin ﬁlms and nanotubes of In 2O 3,respectively.The PL spectra of the In 2O 3nanosheets obtained at 900°C at room temperature are shown in Figure 11a.As can be seen from Figure 11a,a strong and narrow PL peak at 428nm is observed from the nanosheets under excitation at 380nm,which is different from broad blue PL emission spectra observed from In 2O 3nanoparticles and nanowires.21,22,10The full width at half-maximum intensity of the PL peak is 28nm.Figure 11b shows the excitation spectra for blue light emission monitored at 428nm.The excitation spectra have three maximum around 300,322,and 385nm.In general,The UV emission would correspond to the near-band-edge emission.The visible emission matches the deep-level emission,which originated from defects or oxygen vacancies in the lattice sites of the In 2O 3crystals produced in the preparation of thesamples.Figure 8.SEM images of the products prepared at 900°C for different reaction times:(a)2min;(b,c)10min;(d)30min.Figure 9.Raman spectra of the products synthesized at 900°C for different reaction times:(a)2min;(b)10min;(c)30min.Figure 10.Schematic illustration of a possible mechanism for the In 2O 3nanosheet growth:(a)indium grain;(b)formation of In -P -O liquid-phase layers on the In surface;(c)formation of In 2O 3spherical particles coated with a In -P -O liquid-phase layer;(d)congregation of the In 2O 3particles into large particles;(e)formation of In -P -O droplets on the surface of the In 2O 3particles;(f)the nanosheet growth starts from the In -P -O droplets;(g)diffusion of In 2O 3on the surface of the In 2O 3particles and nanosheets;(h)ﬁnal state of the nanosheets.Self-Assembled and Single In 2O 3Nanosheets on In Grains Crystal Growth &Design,Vol.xxx,No.xx,XXXX EThe intensive blue light emission can be attributed to oxygenvacancy (V O x )and indium -oxygen vacancy centers (V In ,V O )x .35The (V In ,V O )x and the (V O x)may act as the acceptors and thedonors,respectively.An electron in donor level (V O x)may becaptured by a hole on an acceptor {(V In ,V O )x}to form a trapped exciton.The trapped exciton recombines radiatively to produce the observed blue emission.The oxygen vacancy and indium -oxygen vacancy centers should be generated because of partial crystallization during the growth process of In 2O 3nanosheets.4.ConclusionsWe have successfully synthesized self-assembled In 2O 3nanosheet networks and ﬂowerlike nanoarchitectures,as well as single In 2O 3nanosheets,by direct thermal oxidation of In metal with a small quantity of P 2O 5for the ﬁrst pared with CVD,MOCVD,and PLD,this procedure does not include In or In 2O vapor transport and condensation processes and does not require very high temperature and low pressure.The growth process has been clearly illuminated,which starts from the oxidation of In followed by the sequential growth of the In 2O 3nanoparticles and nanosheets,and a schematic elucidation is presented.This mechanism not only can explain all the experimental observations but also helps to clarify the growth mechanism of other nanostructures in the gas phase.The In 2O 3nanosheets exhibited strong PL emission in the blue region of the spectrum.This emission can be attributed to oxygen vacancy and indium -oxygen vacancy centers.The methodology dem-onstrated here for synthesizing 2D nanosheets may be employed for synthesis of other semiconductor 2D nanostructures and might offer unlimited possibilities in a broad range of ﬁelds such as photonics,chemical sensors,catalysis,and nanodevices.Acknowledgment.This work was supported by the National Natural Science Foundation of China (Grant 20573072)and Specialized Research Fund for the Doctoral Program of Higher Education (Grant 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