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ceo2 纳米粒子的合成英文回答：Synthesis of CEO2 Nanoparticles.Cerium oxide nanoparticles (CEO2) are versatile materials with a wide range of applications, including in catalysis, sensors, and biomedicine. Their unique properties, such as their high oxygen storage capacity, redox activity, and low toxicity, make them particularly attractive for various applications.There are several methods for synthesizing CEO2 nanoparticles, including chemical precipitation, sol-gel, hydrothermal, and combustion synthesis. Each method has its own advantages and disadvantages, and the choice of method depends on the desired properties of the nanoparticles.Chemical Precipitation.Chemical precipitation is a simple and cost-effective method for synthesizing CEO2 nanoparticles. In this method, a cerium salt, such as cerium nitrate or cerium chloride,is dissolved in water and then precipitated by adding a base, such as sodium hydroxide or ammonium hydroxide. The precipitate is then washed and dried to obtain the CEO2 nanoparticles.The chemical precipitation method is versatile and allows for the control of the size, shape, andcrystallinity of the nanoparticles. However, this methodcan be sensitive to the reaction conditions, and it can be difficult to obtain nanoparticles with uniform properties.Sol-Gel.The sol-gel method involves the hydrolysis and condensation of a cerium precursor, such as cerium alkoxide, in a solvent. The resulting sol-gel is then heated to form the CEO2 nanoparticles.The sol-gel method offers good control over the sizeand shape of the nanoparticles. However, this method can be time-consuming and can require specialized equipment.Hydrothermal.Hydrothermal synthesis is a method for synthesizing CEO2 nanoparticles in a closed vessel under high temperature and pressure. In this method, a cerium precursor is dissolved in water and then heated in a sealed vessel. The high temperature and pressure promote the formation of CEO2 nanoparticles.The hydrothermal method is a versatile method that allows for the control of the size, shape, andcrystallinity of the nanoparticles. However, this method can be expensive and can require specialized equipment.Combustion Synthesis.Combustion synthesis is a method for synthesizing CEO2 nanoparticles by rapidly heating a mixture of ceriumnitrate and a fuel, such as glycine or urea. The rapidheating causes the fuel to combust, which provides the energy for the formation of CEO2 nanoparticles.Combustion synthesis is a simple and cost-effective method. However, this method can be difficult to control, and it can be difficult to obtain nanoparticles withuniform properties.中文回答：CEO2 纳米粒子的合成。
Studies in Synthetic Chemistry 合成化学研究, 2016, 4(4), 29-37 Published Online December 2016 in Hans. /journal/ssc /10.12677/ssc.2016.44004文章引用: 苏琳峰, 巩金峰, 孟凡明. 纳米CeO 2的合成及其光催化性质的研究进展[J]. 合成化学研究, 2016, 4(4):Research Progress of Preparation and the Photocatalysis Properties of Nanoparticle CeO 2Linfeng Su, Jinfeng Gong, Fanming Meng *School of Physics & Material Science, Anhui University, Hefei AnhuiReceived: Dec. 2nd , 2016; accepted: Dec. 16th , 2016; published: Dec. 21st , 2016Copyright © 2016 by authors and Hans Publishers Inc. This work is licensed under the Creative Commons Attribution International License (CC BY)./licenses/by/4.0/AbstractAs the photodegradation method was gradually applied to every aspect of our life, the CeO 2 be-came the favoured material for its excellent photocatalytic performance. The research achieve-ments of domestic and overseas scholars in recent years about the origins of the photocatalysis performance of CeO 2 were discussed in this paper briefly, mainly including method of precipita-tion, sol-gel method and hydrothermal method. The essay introduces the photocatalytic mechan-ism and the influence factor of the CeO 2, and also briefly introduces the application status of the CeO 2. Meanwhile this article looked into the distance in the research about the photocatalytic per-formance of CeO 2. KeywordsNanoparticle CeO 2, Synthesis, Photocatalysis纳米CeO 2的合成及其光催化性质的研究进展 苏琳峰，巩金峰，孟凡明*安徽大学物理与材料科学学院，安徽 合肥*通讯作者。
第28卷㊀第3期2023年6月㊀哈尔滨理工大学学报JOURNAL OF HARBIN UNIVERSITY OF SCIENCE AND TECHNOLOGY㊀Vol.28No.3Jun.2023㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀溶剂热法制备CeO 2/BiOI 复合光催化剂及性能米世新,㊀牟红旭,㊀王剑浩,㊀杨陆娟,㊀吴鹏伟,㊀刘子薇,㊀庄艳丽(哈尔滨理工大学材料科学与化学工程学院,哈尔滨150080)摘㊀要:针对提高单体BiOI 的可见光催化降解效率的问题,采用煅烧法在不同温度下制备出了CeO 2三维花型结构,然后将CeO 2加入到BiOI 前驱体溶液中,通过溶剂热法制备出不同复合比例的BiOI /CeO 2复合光催化剂㊂运用X 射线粉末衍射(XRD )㊁扫描电子显微镜(SEM )㊁紫外-可见漫反射光谱(UV-Vis DRS )㊁电化学等对制备样品进行表征,利用对罗丹明B (RhB )的降解实验评价了不同CeO 2煅烧温度㊁不同复合比例对光催化降解效率的影响,并通过自由基捕获实验对复合材料的光催化机理进行了分析㊂结果表明,当BiOI 与CeO 2(煅烧温度为400ħ)的质量比为1ʒ1时,复合材料对RhB 的降解率最佳,约为38.1%㊂相比于BiOI (约为24%)和CeO 2(约为23%)其降解率有了一定的提高㊂这可能归因于两种材料复合后在界面处形成的异质结结构有效地抑制了光生电子-空穴的复合速率,实现了光催化性能的提高㊂关键词:CeO 2;BiOI ;溶剂热法;光催化性能DOI :10.15938/j.jhust.2023.03.015中图分类号:TQ135.3+2;TQ136.1+3文献标志码:A文章编号:1007-2683(2023)03-0119-10Preparation and Photocatalytic Dye DegradationProperties of CeO 2/BiOI HeterojunctionMI Shixin,㊀MU Hongxu,㊀WANG Jianhao,㊀YANG Lujuan,㊀WU Pengwei,㊀LIU Ziwei,㊀ZHUANG Yanli(Harbin University of Science &Technology,School of Materials Science and Chemical Engineering,Harbin 150080,China)Abstract :In order to improve the visible light catalytic degradation efficiency of monomer BiOI,the three-dimensional floralstructure of CeO 2was prepared by calcination at different temperatures.Then,CeO 2was added to BiOI precursor solution and BiOI /CeO 2composite photocatalysts with different composite ratios were prepared by solvothermal method.X-ray powder diffraction (XRD),scanning electron microscope (SEM),ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS)and electrochemistry were used to characterize the prepared samples,and the effects of CeO 2calcination temperatures and different mass ratios on the photocatalytic degradation efficiency were evaluated by the degradation experiments of rhodamine B (RhB).The photocatalytic mechanism of the composites was analyzed by radical trapping experiments.The results showed that when the mass ratio of BiOI to CeO 2(400ħ)was 1ʒ1,the degradation rate of RhB was the best,which was about 38.1%.Compared with BiOI (about 24%)andCeO 2(about 23%),the degradation rate was improved.This may be attributed to the heterojunction structure formed at the interface after the composite of the two materials,which effectively inhibits the photoelectron-hole recombination rate and improves the photocatalytic performance.Keywords :CeO 2;BiOI;hydrothermal method;photocatalytic performance㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀收稿日期:2022-02-28基金项目:国家自然科学基金青年科学基金(52105332);先进焊接与连接国家重点实验室开放课题基金面上项目(AWJ-22M15);有色金属及材料加工新技术教育部重点实验室开放基金(20KF14);黑龙江省大学生创新性实验计划资助项目(8105/218200003).作者简介:米世新(2000 ),男,本科生;牟红旭(2000 ),男,本科生.通信作者:庄艳丽(1984 ),女,博士,讲师,E-mail:zhuangyanli@.0㊀引㊀言三次技术革命在推动世界工业化扩展和科学技术提升的同时,也打破了大自然长期稳定的自净能力,造成了众多的环境问题,其中工业污水处理成为国家关注的重点问题之一[1]㊂伴随着科技的发展,越来越多的污水处理技术被发掘出来,相较于传统的处理技术,半导体光催化技术因其能耗低㊁反应速度快㊁催化降解完全等特点在污水处理领域备受关注[2]㊂半导体光催化技术是以可再生环保的太阳能作为能源对有机污染物进行降解,过程中的中间产物没有危害性且不存在二次污染,这些特性使它能够很好地解决能源短缺和生态环境污染问题,但是半导体催化技术在对大量工厂污水处理时仍存在一定的限制[3],所以提高半导体光催化剂的性能势在必行㊂在1972年日本学者藤岛和本田提出纯的TiO2材料在日光照射条件下能够被用作电极对水进行分解,电极旁产生的气泡经检测后发现是氢气和氧气[4],光催化领域自此拉开序幕㊂众多学者对TiO2材料深入地进行探究㊁开拓,它本身无毒㊁价格低廉㊁具有较强的氧化能力和相当良好的化学稳定性,本应成为最佳光催化材料的它因自身的禁带宽度相对较大(~3.2eV),使其只在紫外光(太阳光谱的5%左右)下才可以显示出光催化响应,因此极大程度地限制了该种材料在实际应用过程中对太阳光的高效利用[5-8]㊂所以,开发高效稳定的半导体光催化材料并拓宽其应用是光催化领域研究的发展趋势[9-11]㊂Zhang等[12]在2006年指出了具有高光催化活性的BiOCl材料,从此,卤氧化铋这类材料[BiOX (X=I㊁Br㊁Cl)]进入了人们的视野中[13-14]㊂BiOX 是一种具有层状开放式晶体和间接跃迁带隙结构的高度各向异性的半导体光催化剂,这种结构拥有足够空间可以极化相应的原子和原子轨道,诱导光生载流子的有效分离[15]㊂卤氧化铋体系中BiOI的窄禁带宽度(1.72~1.92eV)最小,经过大量实验后判定BiOI可以作为一种光催化性能良好的材料进行使用[16]㊂但因为BiOI的光生电子-空穴对极易结合㊁对可见光的吸收能力也十分有限㊁量子效率相对较低,限制了它的实际应用[17]㊂当前,光催化材料的合成方法主要有化学沉淀法㊁溶胶-凝胶法和水热法(溶剂热法)等,其中最为常用的方法是溶剂热法,该方法的优点是制备方法简便,缺点是制备周期较长,产率较低㊂研究者们采用该种方法对BiOI进行了改性研究,如CdSQDs/BiOI/WO3[18]㊁BiOI/TiO2[19]㊁AgI/BiOI[20]等㊂将一种或两种以上半导体材料或具有不同能带结构的光催化材料与BiOX复合制备成异质结或同质结,改变自身的光生载流子的迁移率,以提高光催化活性㊂作为一种典型的n型半导体材料和稀土氧化物,CeO2由于其宽禁带宽度(2.8~3.1eV)㊁高稳定性㊁优异的光学和催化性能以及成本效益而被认为是一种新型的光催化材料㊂据报道,材料的带隙结构和电子转移过程受其可调形态㊁晶体结构的极大影响[21]㊂到目前为止,已经开发了许多技术来合成具有各种形态的CeO2纳米材料,例如一维纳米棒/纳米线/纳米管[22-23]㊁二维纳米片[24]和三维纳米立方体/纳米球/空心纳米球[25-29]㊂CeO2作为催化剂的助剂和催化剂载体的良好添加剂,在催化剂和载体的双重作用下,具有2D薄层结构的氧化铈通过与共催化剂偶联表现出更有效的光活性㊂例如,Sul-tana等[30]报道了一种CeO2基的2D-2D纳米复合材料,用于在光照下对RhB染料进行脱色,其显著的光催化性能主要是由于BiOI和CeO2纳米片之间通过异质结的构建从而达到电荷的高效输运㊂因此,为提高单体BiOI的可见光催化降解效率,本文选择对材料进行复合的方法,以碘氧化铋为前驱体,拟采用溶剂热法制备CeO2/BiOI复合材料,改变二氧化铈的制备温度以及两者不同质量掺比对复合材料的光催化性能进行探讨㊂1㊀实㊀验1.1㊀CeO2/BiOI复合催化剂的制备1.1.1㊀实验试剂六水合硝酸铈(上海麦克林生化科技有限公司,99.95%)㊁碳酸氢铵(上海麦克林生化科技有限公司,99.995%)㊁五水合硝酸铋(天津福晨化学试剂有限公司,分析纯,99.0%)㊁碘化钾(上海银典化工有限公司,99.0%)㊁乙二醇(天津富宇精细化工有限公司,分析纯)㊁无水乙醇(天津富宇精细化工有限公司,分析纯)㊁去离子水(永昌化学试剂,分析纯)㊁罗丹明B(天津福晨化学试剂有限公司,分析纯)㊂1.1.2㊀催化剂的制备1)煅烧法制备CeO2:称取1.39g的Ce(NO3)3㊃6H2O溶解在200mL去离子水中进行搅拌㊂接下来称取0.75g的NH4HCO3溶解在200mL去离子水021哈㊀尔㊀滨㊀理㊀工㊀大㊀学㊀学㊀报㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀第28卷㊀中,随后快速加入至Ce(NO3)3㊃6H2O的水溶液中,在0ħ环境下搅拌30min㊂使用滤纸进行产物收集,去离子水进行3次离心洗涤㊂恒温60ħ下干燥12h,最后在不同温度(350ħ㊁400ħ㊁450ħ㊁500ħ)下煅烧4h,取出后便得到纯CeO2㊂2)溶剂热法制备BiOI:称取0.97g的Bi(NO3)3㊃5H2O溶解在20mL无水乙醇和20mL乙二醇的混合溶液中,搅拌10min㊂接下来称取0.332g的KI,将其溶解在20mL的去离子水中,进行5min搅拌,待KI完全溶解,将KI水溶液缓慢滴加到硝酸铋醇溶液中,并且搅拌10min使材料充分混合,充分混合后的溶液移至聚四氟乙烯内衬的反应釜中,加热炉中加热到180ħ,反应12h㊂冷却至室温,用去离子水和无水乙醇对产物进行离心洗涤,最后恒温60ħ下干燥12h,样品最后经过研磨得到Bi(NO3)3㊃5H2O与KI摩尔比为1ʒ1的BiOI样品㊂3)溶剂热法制备CeO2/BiOI复合材料:取0.97g 的Bi(NO3)3㊃5H2O溶解在20mL无水乙醇和20mL 乙二醇的混合溶液中,搅拌10min㊂取0.332g的KI,将其溶解在20mL去离子水中并搅拌5min,待KI完全溶解,将KI水溶液缓慢滴加到硝酸铋醇溶液中,并且搅拌10min,使材料充分混合后加入0.704g的CeO2成品,搅拌溶解后转移到聚四氟乙烯内衬的反应釜中,加热炉中加热到180ħ,反应24 h㊂冷却至室温,用去离子水和无水乙醇对产物进行离心洗涤,最后恒温60ħ下干燥12h,样品最后经过研磨得到BiOI与CeO2质量比为1ʒ1的CeO2/ BiOI样品㊂改变二氧化铈加入质量,制备出BiOI与CeO2质量比为1ʒ0.5㊁1ʒ1㊁1ʒ1.5和1ʒ2的4组复合样品㊂1.2㊀样品的性能及表征对所制备样品的物相以及组成的研究是使用以Cu-Ka作为发射源的日本东京ModelD/MaX-3B的XRD衍射仪(λ=0.154nm)进行表征分析,确定扫描速率为4ʎ/min,扫描角度2θ=10ʎ~80ʎ;对制备完成的材料选择扫描电子显微镜(SEM,FEI Sirion200)进行形貌和尺寸大小的观察;利用紫外-可见分光光度计(UV-vis DRS,UV-757CRT)对样品的光学性质进行了表征;并用具有标准的三电极系统的法国Bio-Logic VPM3多通道电化学工作站上进行电化学阻抗谱(EIS)测试和莫特肖特基测试(MS)㊂通过将制备好的材料置于25ħ室温下降解模拟染料废水的程度来对材料的光催化性能进行评估,光降解实验使用产于上海田颖特种电光源厂生产的400W氙灯作为照明源,实验中选择一定浓度的罗丹明B(RhB)溶液进行染料废水的模拟㊂相关的操作流程为:量取50mL的20mg/L的RhB溶液置于烧杯中,首先对RhB溶液初始吸光度进行测试,将测量数值作为初始数值A0㊂随后称量0.05g 制备好的光催化材料放入其中,在黑暗环境下进行吸附搅拌,时间持续1h使染料和水分子在材料表面达到吸附-脱附平衡㊂每半小时取8mL搅拌溶液进行离心,取离心后的样品上清液约5mL至石英比色皿中,利用UV-757CRT型的紫外-可见分光光度计进行吸光度测试㊂1h暗环境下吸附搅拌后,打开氙灯进行模拟太阳光照,每隔30min重复操作,利用式(1)计算光催化降解效率:D=(A0-A t)/A0ˑ100%(1)式中:D为模拟染料废水 罗丹明B的降解率;A0为未加入样品的RhB的初始吸光度;A t为样品在经过各个不同时间段的光催化降解反应后测得的吸光度㊂为了阐明复合材料中光催化过程的活性成分,通过活性氧捕获实验对可能的光催化机理进行研究㊂在光催化活性实验的基础上,活性氧捕获实验中加入1mmol/L的清除剂,分别使用对苯醌(BQ)㊁草酸钠(Na2C2O4)㊁异丙醇(IPA)作为牺牲剂捕获超氧自由基(㊃O2-)㊁空穴(h+)和羟基自由基(㊃OH),其余步骤与光催化活性实验相同㊂2㊀结果与讨论2.1㊀物相分析图1~3为所制备的BiOI㊁CeO2以及CeO2/BiOI 复合材料的XRD谱图㊂由图1可见,在2θ=29.6ʎ㊁31.6ʎ和45.4ʎ处的特征峰分别与四方相BiOI的(012)㊁(110)和(020)晶面相互对应(JCPDS No.10-0445),这表明所合成的试样为BiOI㊂此外,从图1中还可以看出,不同煅烧温度下得到的CeO2,其在2θ=28.5ʎ㊁33.1ʎ㊁48.1ʎ㊁56.8ʎ处的峰值分别与立方萤石结构CeO2的(111),(200),(220),(311)晶面相对应(JCPDS No.43-1002),且无其它特征峰出现,这表明合成的CeO2纯度较高㊂由图2可见,当用不同煅烧温度下制备的CeO2与BiOI复合,所有复合样品的XRD图谱中均出现了CeO2与BiOI特征峰,这表明两种物质成功复合㊂图3为不同比例下CeO2/BiOI复合材料的XRD衍射图谱㊂可以看121第3期米世新等:溶剂热法制备CeO2/BiOI复合光催化剂及性能出,随着CeO 2含量增加,其特征峰逐渐明显,进一步表明两种材料成功复合㊂图1㊀纯BiOI ㊁纯CeO 2(不同煅烧温度)的XRD 图Fig.1㊀XRD patterns of Pure BiOI ,CeO 2(differentcalcination temperatures)图2㊀质量比1ʒ1的CeO 2/BiOI (不同煅烧温度)复合材料的XRD 图Fig.2㊀XRD patterns of CeO 2/BiOI (different calcinationtemperatures )composites with a mass ratio of1ʒ1图3㊀不同质量比的CeO 2/BiOI (400ħ)复合材料的XRD 图Fig.3㊀XRD patterns of CeO 2/BiOI (400ħ)compositeswith different mass ratios2.2㊀SEM 分析图4为BiOI㊁CeO 2的微观形貌图㊂如图4(a)所示,所制备的BiOI 主要由片状结构组成的三维花球形貌,且花球的直径约为1~3μm㊂如图4(b)㊁(c)㊁(d)㊁(e)所示,以Ce(NO 3)3㊃6H 2O 为原料在不同煅烧温度为下制备出的CeO 2均是由片组装成的三维花状结构,其长度约为5~8μm㊂图5为质量比为1ʒ1的CeO 2/BiOI 复合材料的微观形貌图㊂图4㊀所制备材料的SEM 图Fig.4㊀SEM images of the preparedmaterials图5㊀质量比1ʒ1的CeO 2/BiOI 的SEM 图Fig.5㊀SEM images of CeO 2/BiOI with a mass ratio of 1ʒ1221哈㊀尔㊀滨㊀理㊀工㊀大㊀学㊀学㊀报㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀第28卷㊀由图可见,BiOI 负载在CeO 2的三维花状结构上,复合后的材料大小约为5~8μm,花球状BiOI与的CeO 2紧密接触有助于电荷载流子的分离,并且两者复合后片状结构相互交错有利于光催化反应过程中更好地与染料废水接触起到吸附和分散作用,因此有助于提高材料的光催化降解性能㊂图6为不同质量比的CeO 2/BiOI 复合材料的微观形貌图㊂由图6可见,随着BiOI 的比例增加,负载在CeO 2上的BiOI 逐渐增多㊂图6㊀不同质量比的CeO 2(400ħ)/BiOI 的SEM 图Fig.6㊀SEM images of CeO 2(400ħ)/BiOI withdifferent mass ratios图7与表1为质量比1ʒ1的CeO 2(400ħ)/BiOI 的EDS 图和测定的相对元素含量表㊂由图7可见,CeO 2(400ħ)/BiOI 复合材料中含有Bi㊁O㊁Ce 和I 元素㊂结合表1㊁图7和XRD 测试结果,进一步表明了所制备的试样为CeO 2/BiOI 复合材料㊂表1㊀质量比1ʒ1的CeO 2(400ħ)/BiOI 的相对元素含量Tab.1㊀Relative element content of CeO 2(400ħ)/BiOIwith mass ratio of 1ʒ1元素质量分数/%体积分数/%O 18.3469.55I 3.74 1.79Ce 42.3518.34Bi35.5710.33图7㊀质量比1ʒ1的CeO 2(400ħ)/BiOI 的元素面分析Fig.7㊀Elements maps analysis of CeO 2(400ħ)/BiOIat a mass ratio of 1ʒ12.3㊀UV-Vis DRS 分析材料的光催化性能,在一定程度上受其吸收光能力的影响㊂通常选用紫外-可见漫反射对材料吸收光的能力进行测试,分析材料的表层结构等㊂因此使用紫外可见漫反射光谱对样品进行了光吸收特性测试,结果如图8㊁9所示㊂由图8可见,纯BiOI 的吸收边缘约为682nm,CeO 2/BiOI 的吸收边缘约为677nm,材料复合后对光吸收范围基本无影响,吸光度相对纯物质有小幅下降㊂从图9中得到复合材料CeO 2/BiOI 的带隙宽度为1.92eV,相比于两种纯物质,其复合后得到的带隙宽度更小,表明了两种材料的复合可以减小带隙宽度,使复合材料更容易被可见光激发产生载流子,也就是更利于在可见光下响应,得到更优异的光催化活性㊂321第3期米世新等:溶剂热法制备CeO 2/BiOI 复合光催化剂及性能图8㊀BiOI ㊁CeO 2㊁CeO 2/BiOI 材料的UV-Vis 谱图Fig.8㊀UV-Vis reflectance spectrum of BiOI ,CeO 2andCeO 2/BiOImaterials图9㊀BiOI ㊁CeO 2㊁CeO 2/BiOI 材料的禁带宽度Fig.9㊀Energy gap of BiOI ,CeO 2and CeO 2/BiOI materials2.4㊀电化学分析为了明确材料的能带结构,在固定频率下对材料进行了Mott-Schottky 电化学测试,如图10所示㊂由于线型图表现为正斜率,所以显示了n 型半导体的特性,即BiOI㊁CeO 2均为n 型半导体㊂其中莫特-肖特基曲线的切线与横轴(y =0)的交点是样品的平带电势㊂由于平带电势与导带电势相差约0.1eV,所以可以凭此来确定BiOI 和CeO 2的的导带电势(E CB )分别为-1.8eV 和-0.9eV㊂再根据式(2)对BiOI 与CeO 2的价带㊁导带位置进行计算:E CB =E VB -E g (2)式中:E CB 为导带电位;E VB 为价带电位㊂结合图9中BiOI 与CeO 2带隙宽度(E g )1.97eV 和2.83eV,进一步计算得到BiOI 和CeO 2的E VB 分别为0.17eV 和1.93eV㊂图11为BiOI㊁CeO 2㊁CeO 2/BiOI 材料的电化学阻抗测试(EIS)㊂众所周知,EIS 谱图中较小的半圆直径代表着较低的电荷转移电阻,这表明成功阻止了光诱导电子和空穴的复合,界面处发生的有效电荷转移也就越高㊂所以从图11中可以看到CeO 2/BiOI 复合材料的半圆直径比的CeO 2和BiOI 更小,也就说它具有更低的电子传输阻力,这也是其具有最佳的光催化性能的前提㊂综上所述,与两个纯的CeO 2和BiOI 光催化材料相比,CeO 2/BiOI 复合材料具有更多的光生载流子,以及更低的电子传输阻力,并更有效地分离和转移,以此提高电子空穴对的分离效率,因此,CeO 2/BiOI 复合材料具有优异的光催化活性㊂图10㊀CeO 2㊁BiOI 材料的莫特-肖特基曲线Fig.10㊀Mott-Schottky curves of BiOI and CeO 2materials图11㊀BiOI ㊁CeO 2㊁CeO 2/BiOI 材料的EIS 谱图Fig.11㊀EIS reflectance spectrum of BiOI ,CeO 2andCeO 2/BiOI materials421哈㊀尔㊀滨㊀理㊀工㊀大㊀学㊀学㊀报㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀第28卷㊀2.5㊀光催化分析图12为在不加入任何光催化材料下的罗丹明B 自降解情况,可以看到其前2.5h 并未发生自降解,实验结束时由于罗丹明B 在氙灯的照射下温度上升,使其发生轻微的自降解(小于1%),对降解率影响甚微㊂图13为氙灯照射下纯物质CeO 2和BiOI 降解罗丹明B(RhB)污染物的降解速率图㊂由图13(a)可见,在相同条件下,BiOI 的降解率约为24%(暗吸附16%),主要表现为暗吸附,光催化降解效果不明显㊂CeO 2进行4h 降解实验后的降解率约为23%(暗吸附8%),材料降解效率低㊂图12㊀罗丹明B 自降解率图Fig.12㊀The self degradation rate images ofRhB图13㊀CeO 2、BiOI 对罗丹明B 的降解率图Fig.13㊀The degradation rate images of RhB图14为两种材料进行1ʒ1质量比复合后的降解速率图,其变量为二氧化铈的煅烧温度,通过图14(a)观察当二氧化铈煅烧温度为400ħ时,复合材料的降解效率最高,具体表现为暗吸附效果21%,光催化过程中降解了约18%㊂其它3组在加入氙灯照射后,材料的降解效率基本不变,均以暗吸附为主,经过分析为400ħ的CeO 2与BiOI 复合后形成的异质结结构效果最好㊂图15为BiOI /CeO 2(400ħ)不同质量比时的降解速率图,通过观察图15(a)可以确定两种材料复合的最优质量比为1ʒ1㊂图14㊀质量比为1ʒ1的CeO 2/BiOI 复合材料对罗丹明B 的降解率图及一阶动力学k 值图Fig.14㊀The degradation rate images of RhB and the first-order kinetic k value images by CeO 2/BiOI composite material with a mass mixing ratio of1ʒ1521第3期米世新等:溶剂热法制备CeO 2/BiOI 复合光催化剂及性能图15㊀煅烧温度为400ħ的CeO 2/BiOI 复合材料对罗丹明B 的降解率图及一阶动力学k 值图Fig.15㊀The degradation rate images of RhB and the first-order kinetic k value images by CeO 2/BiOIcomposite material calcined at400ħ图16㊀不同捕获剂存在下质量比1ʒ1的CeO 2(400ħ)/BiOI 复合材料可见光降解RhB 图Fig.16㊀Visible light degradation of RhB in CeO 2(400ħ)/BiOI composites with a mass ratio of 1ʒ1in thepresence of different scavengers采用式(3)L-H 动力学模型公式:-ln(c t /c 0)=kt (3)对多组降解数据进行拟合来探究光催化剂在降解过程中的反应动力学,模拟污染物初始浓度在式中用c 0表示,c t 则代表污染物经过t 时刻的反应时间后的浓度,单位均为mol /L,k 为反应速率常数(min -1),结果如图13㊁14㊁15(b)所示㊂图中质量比1ʒ1的CeO 2(400ħ)/BiOI 的反应速率常数要显著高于其它各组数据的,表明煅烧温度为400ħ的CeO 2与BiOI 以质量比为1ʒ1的复合是提升材料的光催化活性效果最佳的㊂一般来说,活性物质是在光催化过程中产生的,并且在光照下可以降解染料,包括超氧自由基(㊃O 2-)㊁光生空穴(h +)和羟基自由基(㊃OH)㊂为了研究CeO 2/BiOI 复合材料在RhB 溶液中的光催化反应机理,如图16所示使用自由基捕获实验来识别主要自由基㊂不同的清除剂分散在有光催化剂存在的染料溶液中,会影响降解效率㊂对苯醌(BQ)㊁草酸钠(Na 2C 2O 4)㊁异丙醇(IPA)作为牺牲剂分别捕获超氧自由基(㊃O 2-)㊁空穴(h +)和羟基自由基(㊃OH),当在反应过程中加入1mmol /L BQ 和1mmol /L IPA 时,CeO 2/BiOI 复合材料的最终降解效率存在小幅下降,这表明㊃O 2-和㊃OH 参与RhB 光催化降解过程㊂与之相比,添加1mmol /L 草酸钠对光催化效率的抑制作用更明显,这证明h +在光降解过程中起关键作用㊂所以,CeO 2/BiOI 异质结的构建显著改善了电子-空穴对的分离,从而产生更多的活性基团,增强了对RhB 的光催化降解效率,使材料的光催化性能得到提升㊂2.6㊀光催化机理分析经过各种测试中多组平行数据的分析,复合材料光催化性能提高的大概率因素是形成了异质结结构,能带理论中提出电子会从高费米能级向低费米能级持续运动,直到两侧费米能级相等才停止㊂从测得的Mott-Schottky 曲线中可以得知本次材料复合中BiOI 的费米能级更靠近价带,而n 型半导体CeO 2的费米能级更靠近导带,从电化学测试结果可知对于纳米片组装成的花球状BiOI,其导带电势和价带电势分别为-1.8eV 和0.17eV,CeO 2的导带电势和价带电势分别为-0.9eV 和1.93eV㊂在模拟太阳光照射下,材料内部电子与空穴的转移情况如图17所示㊂根据图17中能带位置推断,结合自由基捕获实验结果,综上推断CeO 2与BiOI 复合形成了传统的Ⅱ型异质结㊂复合材料在进行拟太阳光照射后,两组份都会对能量高于自身能带隙的光子进行吸收,电子吸收能量后从价带激发到导带上,价带产生空穴,不断积累的电子与空穴就会作用于另一材料的导带与价带产生强氧化还原作用,由于CeO 2晶体具有较强的吸附氧能力,吸附氧脱附可以进一步抑制电子-空穴复合速率,因此这种异质结结构可以延长所产生空穴的存在时间,促进光催化降解效率㊂621哈㊀尔㊀滨㊀理㊀工㊀大㊀学㊀学㊀报㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀第28卷㊀图17㊀光催化过程示意图Fig.17㊀Diagram of photocatalytic process3㊀结㊀论综上所述,首先制备BiOI前驱体溶液,加入不同煅烧温度㊁不同质量比的CeO2,采用溶剂热法合成CeO2/BiOI复合光催化剂,然后利用氙灯模拟太阳光下CeO2/BiOI对罗丹明B的降解效率表征复合材料的光催化性,能得到质量比1ʒ1的CeO2 (400ħ)/BiOI复合材料光催化性能最优越㊂通过SEM㊁EDS图像和相应的元素图谱证实在CeO2的三维花球状结构上成功负载了片状的BiOI㊂紫外可见漫反射光谱对样品进行光吸收特性测试,结果表明复合后的材料带隙宽度明显减小,复合后更容易被可见光激发产生载流子㊂最后通过电化学测试明确复合材料由于异质结的构建使其光生电荷的分离效率得到显著的提高,并确定了其价带㊁导带位置,然后利用捕获实验证明h+是降解罗丹明B的主要自由基,根据上述结果提出了合理的复合机理㊂我们认为CeO2/BiOI复合材料是一种具有光明前景的可见光驱动光催化剂,还有更多的开发潜力㊂所以,对有机污染物的光降解方面我们还会有更深的探索㊂参考文献:[1]㊀刘光石.对环境工程污水处理的几点思考[J].环境与发展,2017,29(5):77.LIU Guangshi.Some Thoughts on Wastwater Treament ofEnvironmental Engineering[J].Environment and Devel-opment,2017,29(5):77.[2]㊀CHEN Chuncheng,MA Wanhong,ZHAO Jincai.Semi-conductor-mediated Photodegradation of Pollutants UnderVisible-light Irradiation[J].Chemical Society Reviews,2010,39(11):4206.[3]㊀吴乾威,祝媛媛.基于半导体光催化剂研究[J].当代化工研究,2021(3):14.WU Qianwei,ZHU Yuanyuan.Research on Semiconduc-tor Photocaatalyst[J].Modern Chemical Research,2021(3):14.[4]㊀FUJISHIMA A,HOND A K.Electrochemical Photolysisof Water at a Semiconductor Electrode[J].Nature,1972,238(5358):37.[5]㊀李大玉,张文韬,张超.不同种类金属掺杂改性TiO2材料光催化性能的研究进展[J].材料导报,2019,33(23):3900.LI Dayu,ZHANG Wentao,ZHANG Chao.Research Pro-gress in Improving the Photocatalytic Properties of TiO2Materials by Doping with Different Metals[J].MaterialsReports,2019,33(23):3900.[6]㊀王骜,仪修佶.TiO2光催化应用综述[J].当代化工研究,2021(8):1.WANG Ao,YI Xiuji.Review on Application of TiO2Photocatalysis[J].Modern Chemical Research,2021(8):1.[7]㊀汪克富.二氧化碳光催化还原材料的制备与性能研究[D].中国科学院大学:中国科学院上海硅酸盐研究所,2018.[8]㊀ZHANG Liwu,FU Hongbo,ZHU Yongfa.Efficient TiO2Photocatalysts from Surface Hybridization of TiO2Particleswith Graphite-like Carbon[J].Advanced Functional Ma-terials,2008,18(15):2180.[9]㊀孙海杰,陈凌霞,张晓锋,等.Ru-B-BiOI催化剂光催化降解甲基橙性能研究[J].水处理技术,2019,45(6):48.SUN Haijie,CHEN Lingxia,Zhang Xiaofeng,et al.Study on Performance of Ru-B-BiOI Catalyst for Photocat-alytic Degradation of Methyl Orange[J].Technology ofWater Treatment,2019,45(6):48.[10]杨帆,盛亮,岳晓霞.工业水处理技术的发展概况与技术进步[J].中国资源综合利用,2020,38(4):140.YANG Fan,SHENG Liang,YUE Xiaoxia.Developmentof Industrial Water Treatment Technology and Reasearchon Technical Progress[J].China Resources Comprehen-sive Utilization,2020,38(4):140.[11]GIL J J,AGUILAR M O,PINA P Y,et al.Efficient ZnSZnO/ZnAILDH Composite for H2Production by Photoca-talysis[J].ACS Applied Materials&Interfaces,2019,11(39):35702.[12]ZHANG Kelei,LIU Cunming,HUANG Fuqiang,et al.Study of the Electronic Structure and Photocatalytic Activ-ity of the BiOCl Photocatalyst[J].Applied Catalysis B:Environmental,2006,68(3/4):125. [13]ZHAO Yang,TAN Xin,YU Tao,et al.SDS-assistedSolvothermal Synthesis of BiOBr Microspheres with High-721第3期米世新等:溶剂热法制备CeO2/BiOI复合光催化剂及性能ly Visible-light Photocatalytic Activity[J].Materials Let-ters,2016,164:243.[14]LI Baoying,HUANG Hongwei,GUO Yuxi,et al.Diat-omite-immobilized BiOI Hybrid Photocatalyst:FacileDeposition Synthesis and Enhanced Photocatalytic Activity[J].Applied Surface Science,2015,353:1179. [15]鲍玥,周旻昀,邹骏华,等.C3N4/BiOBr复合可见光催化剂的性能及其作用机制[J].环境科学,2017,38(5):2182.BAO Yue,ZHOU Minyun,ZOU Junhua,et al.Perform-ance and Mechanism Study of Visible Light-driven C3N4/BiOBr Composite Photocatalyst[J].Environmental Sci-ence,2017,38(5):2182.[16]HE Rongan,CAO Shaowen,GUO Daipeng.3D BiOI-GOComposite with Enhanced Photocatalytic Performance forPhenol Degradation Under Visible-light[J].Ceramics In-ternational,2015,41(3):3511.[17]孙艳娟,廖佳珍,董帆,等.Bi/BiOI/(BiO)2CO3异质结可见光催化净化NO的性能增强[J].催化学报,2019,40(3):362.SUN Yan Juan,LIAO Jiazhen,DONG Fan,et al.A Bi/BiOI/(BiO)2CO3Heterostructure for Enhanced Photocat-alytic NO Removal Under Visible Light[J].ChineseJournal of Catalysis,2019,40(3):362. [18]BI Qiang,GAO Yu,WANG Zengqiang,et al.Prepara-tion of a Direct Z-scheme Thin-film Electrode Based onCdS QD-sensitized BiOI/WO3and Its Photoelectrocatalyt-ic Performance[J].Colloids and Surfaces A:Physico-chemical and Engineering Aspects,2020,599:124849.[19]ZHANG Xi,ZHANG Lizhi,XIE Tengfeng,et al.Low-temperature Synthesis and High Visible-light-inducedpho-tocatalytic Activity of BiOI/TiO2Heterostructures.TheJournal of Physical Chemistry C,2009,113(17):7371.[20]CHENG Hefeng,HUANG Baibiao,DAI Ying,et al.One-step Synthesis of the Nanostructured AgI/BiOI Com-posites with Highly Enhanced Visible-light Photocatalyticngmuir,2010,26(9):6618. [21]YU Jiaguo,YU Yanfang,ZHOU Peng,et al.Morpholo-gy-dependent Photocatalytic H2-production Activity of CdS[J].Applied Catalysis B:Environmental,2014,156:184.[22]MA Zhaoxia,SHENG Liping,WANG Xinwei,et al.Ox-ide Catalysts with Ultrastrong Resistance to SO2Deactiva-tion for Removing Nitric Oxide at Low Temperature[J].Advanced Materials,2019,31(42):1903719.[23]PENG Honggen,DONG Tao,ZHANG Li,et al.Activeand Stable Pt-Ceria Nanowires@Silica Shell Catalyst:Design,Formation Mechanism and Total Oxidation of COand Toluene[J].Applied Catalysis B:Environmental,2019,256:117807.[24]LIU Ying,MA Chao,ZHANG Qinghua,et al.Phos-phate-functionalized CeO2Nanosheets for Efficient Cata-lytic Oxidation of Dichloromethane[J].EnvironmentalScience&Technology,2018,52(22):13430. [25]HILLARY Brendan,SUDARSANAM Putla,AMIN Mo-hamad Hassan,et al.Nanoscale Cobalt-manganese OxideCatalyst Supported on Shape-controlled Cerium Oxide:Effect of Nanointerface Configuration on Structural,Red-ox,and Catalytic Properties[J].Langmuir,2017,33(8):1743.[26]DAI Qiguang,ZHANG Zhiyong,YAN Jiaorong,et al.2D Electron Gas and Oxygen Vacancy Induced High Oxy-gen Evolution Performances for Advanced Co3O4/CeO2Nanohybrids[J].Advanced Materials,2019,31(21):1900062.[27]LIANG Xizhuang,WANG Peng,GAO Yugang,et al.Design and Synthesis of Porous M-ZnO/CeO2Micro-spheres as Efficient Plasmonic Photocatalysts for NonpolarGaseous Molecules Oxidation:Insight Into the Role ofOxygen Vacancy Defects and M=Ag,Au Nanoparticles[J].Applied Catalysis B:Environmental,2020,260:118151.[28]ZHENG Ningchao,OUYANG Ting,CHEN Yibo,et al.Ultrathin CdS Shell-sensitized Hollow S-doped CeO2Spheres for Efficient Visible-light Photocatalysis[J].Ca-talysis Science&Technology,2019,9(6):1357.[29]WANG Haiyan,YANG Weipeng,WANG Xiaoxia,et al.A CeO2@MnO2Core-shell Hollow Heterojunction asGlucose Oxidase-like Photoenzyme for Photoelectrochemi-cal Sensing of Glucose[J].Sensors and Actuators B:Chemical,2020,304:127389.[30]SULTANA S,MANSINGH S,PARIDA K M.Facile Syn-thesis of CeO2Nanosheets Decorated Upon BiOI Micro-plate:A Surface Oxygen Vacancy Promoted Z-scheme-based2D-2D Nanocomposite Photocatalyst with EnhancedPhotocatalytic Activity[J].The Journal of PhysicalChemistry C,2018,122(1):808.(编辑:温泽宇)821哈㊀尔㊀滨㊀理㊀工㊀大㊀学㊀学㊀报㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀第28卷㊀。
OriginalarticleHydrothermal synthesis of single-crystal CeCO3OH and their thermal conversion to CeO2Kun Gao a,Yi-Yang Zhu a,Da-Qing Tong a,Li Tian a,Zhao-Hui Wang a,b,Xiao-Zu Wang a,*a College of Chemistry and Chemical Engineering,Nanjing University of Technology,Nanjing210009,Chinab State Key Laboratory of Materials-Oriented Chemical Engineering,Nanjing University of Technology,Nanjing210009,China1.IntroductionIn recent years,cerium compounds have been widely used incatalysis[1–4],fuel cells[5]and chemical materials[6–8]due totheir specific4f energy levels of the Ce-element[9,10].Among allthe cerium compounds,cerium carbonate hydroxide,as animportant functional material,has been attracted much attentionbecause of its novel electronic properties,optical properties andchemical characteristics arising from their4f electrons[9–12].Recently,cerium carbonate hydroxide with different morphol-ogies was synthesized by different methods,such as self-assembly,sonochemical[13,14],hydrothermal[15–18],and microwave-assisted hydrothermal route[19].Among all the preparationmethods,the hydrothermal process is considered to be an effectiveand economical route due to its merits of low synthesistemperature,high powder reactivity and versatile shape control[20–23].In a hydrothermal system,CeCO3OH with differentstructures corresponding to distinct morphologies have beensynthesized[18,24,25].There have been sufficient studies report-ing on the synthesis of different morphologies,for example,Guoet al.reported the synthesis of triangular micro-plate,bundle-like,shuttle-like andflower-like structures of CeCO3OH by hydrother-mal method[15,16,18].Li and Zhao synthesized single-crystallineCeCO3OH with dendrite-like structures through a facile hydro-thermal method and obtained CeO2by heating CeCO3OH at5008Cfor6h[26].Zhang et al.synthesized CeCO3OH rhombic micro-plates by the precipitation method in the presence of3-aminopropyltriethoxysilane[28].However,most of these reportson the synthesis of CeCO3OH micro/nanoparticles were preparedusing CO(NH2)2or HMT as the alkaline and carbon resource[13–18]and added surfactant or template to adjust the nucleation andcrystal growth of CeCO3OH particles[13,15–18,28],which makesthe process complex and raw materials more costly.So it isimportant to explore a facile method to synthesize morphology-controlled CeCO3OH micro/nanomaterials.In this paper,we report a simple method to synthesize dendrite-like CeCO3OH crystallites using CeCl3Á7H2O as the cerium source,triethylenetetramine as both an alkaline and carbon source.Thepolycrystalline CeO2was obtained by calcination of the precursor at5008C for4h,partly maintaining the dendrite-like morphology.Theoptical absorption properties of CeO2were also investigated.2.ExperimentalAll chemical reagents were of analytical grade without furtherpurification.In a typical synthesis,0.001mol of CeCl3Á7H2O wasdissolved in60mL deionized water to form a clear solution,andthen0.30mL triethylenetetramine was added to the transparentsolution in order to completely react with Ce3+at258C for about0.5h with continued stirring.The resulting homogenous solutionChinese Chemical Letters25(2014)383–386A R T I C L E I N F OArticle history:Received10August2013Received in revised form8September2013Accepted26September2013Available online1December2013Keywords:CeCO3OHHydrothermalCerium carbonate hydroxideNanostructuresA B S T R A C THexagonal single-crystalline cerium carbonate hydroxide(CeCO3OH)precursors with dendritemorphologies have been synthesized by a facile hydrothermal method at1808C using CeCl3Á7H2O asthe cerium source,triethylenetetramine as both an alkaline and carbon source,with triethylenete-tramine also playing an important role in the formation of the dendrite structure.Polycrystalline ceria(CeO2)have been obtained by calcining the precursor at5008C for4h.The morphology of the precursorwas partly maintained during the heating process.The optical absorption spectra indicate the CeO2nano/microstructures have a direct band gap of2.92eV,which is lower than values of the bulk powderdue to the quantum size effect.The high absorption in the UV region for CeO2nano/microstructureindicated that this material was expected to be used as UV-blocking materials.ß2013Xiao-Zu Wang.Published by Elsevier B.V.on behalf of Chinese Chemical Society.All rightsreserved.*Corresponding author.E-mail address:wangxiaozu@(X.-Z.Wang).Contents lists available at ScienceDirectChinese Chemical Lettersj o u rn a l h om e p a g e:w w w.e l s e v i e r.c o m/l o c a t e/c c l e t1001-8417/$–see front matterß2013Xiao-Zu Wang.Published by Elsevier B.V.on behalf of Chinese Chemical Society.All rights reserved./10.1016/let.2013.11.047was transferred to a 100mL Teflon-line stainless steel autoclave,which was sealed and maintained at 1808C for 24h,and cooled to room temperature naturally.The white precipitate was collected by centrifugation,washed several times with distilled water and ethanol,and dried at 708C for 6h.The as-synthesized CeCO 3OH was calcined to produce straw-yellow CeO 2in air at 5008C for 4h.The XRD measurements were performed on a Bruker-D8Advanced X-ray diffractometer,equipped with graphite-monochromatizedhigh-intensity Cu K a radiation (l =1.5418A˚).The morphologies and sizes of the resulting products were examined by field-emission scanning electron microscopy (FESEM,Hitachi S-4800)and transmission electron microscopy (TEM,JEM2000EX),respec-tively.The thermal behavior of the resulting products was carried out by differential scanning calorimetric analysis (DSC)and thermogravimetric analysis (TG)with a Netzsch-449C simulta-neous TG/DSC apparatus heating from room temperature to 6008C (108C/min)in flowing air.UV/vis absorption spectra were acquired on a spectrophotometer (Shimadzu)and the analyzed range was 200–800nm.3.Results and discussionFig.1presents the typical XRD pattern of the as-synthesized CeCO 3OH products.All of the diffraction peaks in Fig.1can be exactly indexed to the pure hexagonal crystalline phase ofCeCO 3OH with lattice constants a =7.2382A˚,c =9.9596A ˚,which are in good agreements with the literature values (JCPDS 32-0189).No impurity peaks are detected,indicating the high purity of the final product.The strong and sharp diffraction peaks suggest that the products are highly crystallined.Fig.2shows a typical SEM image of the CeCO 3OH dendrite structure synthesized at 1808C for 24h.As shown in Fig.2,it reveals most of the as-prepared CeCO 3OH products display twofold-symmetric structures with a length of 1–2m m along the trunk.The detailed morphology of the structures of CeCO 3OH dendrites is further studied using TEM and SAED (Select-area electron diffraction).A typical high magnification TEM image of the structure of CeCO 3OH dendrites is shown in Fig.3.It reveals that the product is composed of a long central trunk with secondary and tertiary sharp branches,which are parallel to each other and emerge at 608angles with respect to the central trunk.The SAED pattern in the inset of Fig.3taken from an individual dendrite-like nanostructure is indexed to hexagonal CeCO 3OH,indicating that the individual is a single crystal.The diffraction pattern indicates the individual dendrite-like CeCO 3OH is well crystallized.The typical TG pattern of the as-prepared CeCO 3OH dendrite structure is shown in Fig.4a.The TG curve shows that CeCO 3OH begins to decompose at about 2808C and finishes at 6008C.Thetotal weight loss between 2808C and 6008C is measured at about 21.70%,which is close to the results in the theoretical value calculated from following reaction:4CeCO 3OH þO 2!4CeO 2þ2H 2O þ4CO 2(1)The DSC curve (Fig.4b)shows one endothermic peak with a maximum at 300.08C.The temperature range of the endothermic peak in the DSC curve agrees well with the weight loss in the TG curve,corresponding to endothermic behavior during the thermal decomposition/oxidation of CeCO 3OH to CeO 2.Fig.5shows the XRD pattern of CeO 2obtained by calcinations of as-prepared CeCO 3OH.All of the peaks are well assigned to pure face-centered cubic (fcc)structure of CeO 2with lattice constantsa =5.412A˚,which is in good agreement with the JCPDS card (No.43-1002).No obvious peaks for other elements or impurities were observed.The strong and sharp reflection peaks suggest that the as-prepared products are well crystallized.After the CeCO 3OH dendrites are calcined in air at 5008C for 4h,CeO 2dendrites are formed.As shown in Fig.6a,SEM image of CeO 2reveals that the dendrite morphology was partly sustained after thermal decomposition/oxidation to CeO 2.Fig.6b presents a typical TEM image of CeO 2dendrite and its corresponding ED pattern (Fig.6b inset).The discontinuous rings in ED pattern indicate that it could consist of CeO 2polycrystals with an oriented crystallographic axis.In our experiment,since triethylenetetramine was not used,noting products were obtained.Fig.7shows the SEM image of raw material (CeCl 3Á7H 2O),only erose particles were observed,indicating the triethylenetetramine plays an important role in the formation of CeCO 3OH dendrite structures.As is well known,triethylenetetramine at the room tempera-ture will release OH Àin the aqueous solution.Meanwhile,triethylenetetramine has large average capacities for the absorp-tion CO 2[27].So the CO 32Àanions in the solution may result from1020304050602θ (° )(002)(110)(112)(004)(300)(114)(302)(220)(222)(304)Fig.1.XRD patternof the CeCO 3OH dendrite-like nanostructure.Fig.2.SEM image of the as-synthesized CeCO 3OH.Fig.3.TEM image of the as-synthesized CeCO 3OH.K.Gao et al./Chinese Chemical Letters 25(2014)383–386384the possible oxidation of triethylenetetramine,the absorption andslight dissolution of CO 2from air.In the hydrothermal process,the C—N bond in triethylenete-tramine is the easiest bond to break,so upon heating to a certain temperature,triethylenetetramine hydrolyzes to form NH 4+and CO 32À.The cerium ions can exist in the form of [Ce(H 2O)n ]3+in aqueous solution,and then [Ce(H 2O)n ]3+is changed into [Ce(OH)(H 2O)n +]2+,and finally CeCO 3OH is obtained by the reaction between [Ce(OH)(H 2O)n À1]2+and CO 32À.It is proposed that dendrite structures are obtained through a seed-mediated growth in the presence of micelles of triethylenetetramine.The CeCO 3OH nuclei were created and used as seed center,these random moving nuclei in the environment can aggregate with each other to form anisotropic morphology.In our experiment,we consider that triethylenetetramine used as the alkaline and surfactant in the hydrothermal process.Therefore,existing triethylenetetramine,as a capping agent in the reaction system,is absorbed selectively on the different planes of CeCO 3OH seeds,helps to lower the surface energy and results in the different growth rate of different planes to form the dendrite structures.The real formation mechanism of CeCO 3OH dendrite structure needs further investigation.Fig.8shows the UV/vis diffuse absorption spectra of CeCO 3OH and CeO 2.Fig.8a shows the UV/vis absorption spectra for CeCO 3OH.The spectra displayed a strong absorption band below 400nm in the spectra.As seen in Fig.8b and 8c,when the synthesized particles were calcined to produce straw yellow CeO 2by heating at 5008C for 4h,the CeO 2has a stronger absorption band below 480nm in the spectra,which is originated from change-transfer transition between O 2p and Ce 4f bonds [28–30].The optional band gap E g can be determined based on the absorbance spectrum of the powders by the following equation:E g =1240/l AE ,where l AE is the edge wavelength of absorbance.The onset of absorption for CeO 2is at 425.3nm,which corresponds to the band gap energy (E g )of 2.92eV,lower than the values of bulk100200300400500600700800024681012←b. DSC cur veH e a t f l o w (m W /m g )Temerature (oC)← a . TG curve80859095100W e i g h t l o s s(%)Fig.4.TG-DSC pattern of the as-synthesized CeCO 3OH.10203040506070802θ (° )(111)(200)(220)(311)(222)(400)(311)(420)Fig.5.XRD pattern of the CeO 2sample.Fig.6.The typical SEM and TEM images of CeO 2obtained from thermal decomposition/oxidation of CeCO 3OH dendrite structure.Fig.7.SEM image of CeCl 3Á7H 2O powders.800700600500400300200b A b s o r b a n c e (a .u )Wavelength (nm)a800700600500400300200A b s o r b a n c e (a .u )Wavelength (nm)cFig.8.UV/vis absorption spectra of CeCO 3OH (a)and CeO 2(b),(c).K.Gao et al./Chinese Chemical Letters 25(2014)383–386385powders(3.19eV).In general,reduction in crystal size would increase the band gap width because of the quantum size effect [31].Hence,the high absorption in the UV region for CeO2show that the materials can be used as UV-blocking,shielding materials to avoid damage from ultraviolet rays and optical devices.4.ConclusionIn summary,we have successfully synthesized CeCO3OH dendrite structures by a facile hydrothermal method in the presence of triethylenetetramine.After annealing the CeCO3OH precursor powders at5008C for4h,CeO2nano/microstructures with dendrite morphology could be obtained with the morphology partly kept.It is believed that triethylenetetramine plays an important role in the growth of CeCO3OH dendrite structures.The optical absorption spectra indicate that the CeO2nano/microstruc-ture have a direct band gap of2.92eV,which is lower than the values of bulk powders.It is expected that these materials canfind potential application in catalysis and UV-blocking material. AcknowledgmentsThis work was supportedfinancially by the Program for Innovative Research Team in Jiangsu Province(No.SZK[2011]87), Creative and Innovative Talents Introduction Plan(No.SZT[2011]43) and Special Research Foundation of Young teachers of Nanjing University of Technology(No.39701007).References[1]D.Andreeva,I.Ivanov,L.Ilieva,et al.,Nanosized gold catalysts supported on ceriaand ceria–alumina for WGS reaction:influence of the preparation method, Powder Technol.333(2007)153–160.[2]rese,M.L.Granados,F.C.Galisteo,et al.,TWC deactivation by lead:a study ofthe Rh/CeO2system,Appl.Catal.B62(2006)132–143.[3]Y.Dai,B.D.Li,H.D.Quan,et al.,CeCl3Á7H2O as an efficient catalyst for one-potsynthesis of b-amino ketones by three-component Mannich reaction,Chin.Chem.Lett.21(2010)31–34.[4]M.Hajjami,A.G.Choghamarani,M.A.Zolfigol,et al.,An efficient and versatilesynthesis of aromatic nitriles from aldehydes,Chin.Chem.Lett.23(2012) 1323–1326.[5]G.Jacobs,L.Williams,U.Graham,et al.,Low-temperature water–gas shift:in-situDRIFTS reaction study of a Pt/CeO2catalyst for fuel cell reformer applications,J.Phys.Chem.B107(2003)10398–10404.[6]M.S.Tsai,Powder synthesis of nano grade cerium oxide via homogenous precipi-tation and its polishing performance,Mater.Sci.Eng.B110(2004)132–134. [7]D.S.Lim,J.W.Ahn,H.S.Park,et al.,The effect of CeO2abrasive size on dishing andstep height reduction of silicon oxidefilm in STI–CMP,Surf.Coat.Technol.200 (2005)1751–1754.[8]Y.H.Kim,S.K.Kimb,N.Kimb,et al.,Crystalline structure of ceria particlescontrolled by the oxygen partial pressure and STI CMP performances,Ultramicro-scopy108(2008)1292–1296.[9]A.W.Xu,Y.Gao,H.Q.Liu,The preparation,characterization,and their photo-catalytic activities of rare-earth-doped TiO2nanoparticles,J.Catal.207(2002) 151–157.[10]D.C.Koskenmaki,K.A.Gschneidner Jr.,Handbook on the Physics and Chemistry ofRare Earths,vol.1,North-Holland,Amsterdam,1978,pp.338–340.[11]Y.G.Sun,B.Mayers,Y.N.Xia,Template engaged replacement reaction:a one stepapproach to the large scale synthesis of metal nanostructures with hollow interiors,Nano Lett.3(2003)675–679.[12]A.P.Alivisatos,Semiconductor clusters,nanocrystals,and quantum dots,Science271(1996)933–937.[13]K.Li,P.S.Zhao,Synthesis and characterization of CeCO3OH one-dimensionalquadrangular prisms by a simple method,Mater.Lett.63(2009)2013–2015.[14]Z.Y.Guo,F.F.Jian,F.L.Du,Sonochemical synthesis of luminescent CeCO3OH one-dimensional quadrangular prisms,Mater.Res.Bull.207(2011)35–41.[15]Z.Y.Guo, F.L.Du,G.C.Li,et al.,Synthesis and characterization of single-crystal Ce(OH)CO3and CeO2triangular microplates,Inorg.Chem.45(2006) 4167–4169.[16]Z.Y.Guo,F.L.Du,G.C.Li,et al.,Synthesis and Characterization of bundle-likestructures consisting of single crystal Ce(OH)CO3nanorods,Mater.Lett.61(2007) 694–696.[17]M.Y.Cui,J.X.He,N.P.Lu,et al.,Morphology and size control of cerium carbonatehydroxide and ceria micro/nanostructures by hydrothermal technology,Mater.Chem.Phys.121(2010)314–319.[18]Z.Y.Guo,F.L.Du,G.C.Li,et al.,Hydrothermal synthesis of single-crystallineCeCO3OHflower-like nanostructures and their thermal conversion to CeO2, Mater.Chem.Phys.113(2009)53–56.[19]E.L.Qi,L.Y.Man,S.H.Wang,et al.,Microwave homogeneous synthesis andphotocatalytic property of CeO2nanorods,Chin.J.Mater.Res.25(2011)221–224.[20]L.Yan,R.B.Yu,J.Chen,et al.,Template-free hydrothermal synthesis of CeO2nano-octahedrons and nanorods:investigation of the morphology evolution,Cryst.Growth Des.8(2008)1474–1477.[21]X.J.Yang,X.P.Li,X.T.Bai,et al.,Facile synthesis and characterization of uniformCdS colloidal spheres,Chin.Chem.Lett.23(2012)1091–1094.[22]W.T.Yao,S.H.Yu,Recent advances in hydrothermal syntheses of low dimensionalnanoarchitectures,Int.J.Nanotechnol.4(2007)129–162.[23]D.Zhao,J.S.Tan,Q.Q.Ji,et al.,Mn2O3nanomaterials:facile synthesis andelectrochemical properties,Chin.J.Inorg.Chem.26(2010)832–838.[24]Z.H.Han,N.Guo,K.B.Tang,et al.,Hydrothermal crystal growth and characteri-zation of cerium hydroxycarbonates,J.Cryst.Growth219(2000)315–318. [25]C.H.Lu,H.C.Wang,Formation and microstructural variation of cerium carbonatehydroxide prepared by the hydrothermal process,Mater.Sci.Eng.B90(2002) 138–141.[26]K.Li,P.S.Zhao,Synthesis of single-crystalline Ce(CO3)(OH)with novel dendritemorphology and their thermal conversion to CeO2,Mater.Res.Bull.45(2010) 243–246.[27]Z.Wang,M.X.Fang,Y.L.Pan,et al.,Amine-based absorbents selection for CO2membrane vacuum regeneration technology by combined absorption–desorp-tion analysis,Chem.Eng.Sci.93(2013)238–249.[28]Y.W.Zhang,R.Si,C.S.Liao,et al.,Facile alcohothermal synthesis,size-dependentultraviolet absorption,and enhanced CO conversion activity of ceria nanocrystals, J.Phys.Chem.B107(2003)10159–10167.[29]N.Imanaka,T.Masui,H.Hirai,et al.,Amorphous cerium–titanium solid solutionphosphate as a novel family of band gap tunable sunscreen materials,Chem.Mater.15(2003)2289–2291.[30]S.Tsunekawa,T.Fukuda,A.Kasuya,Blue shift in ultraviolet absorption spectra ofmonodisperse CeO2Àx nanoparticles,J.Appl.Phys.87(1999)1318–1321. [31]Y.B.Yin,X.Shao,L.M.Zhao,et al.,Synthesis and characterization of CePO4nanowires via microemulsion method at room temperature,Chin.Chem.Lett.20(2009)857–860.K.Gao et al./Chinese Chemical Letters25(2014)383–386 386。
Advances in Condensed Matter Physics 凝聚态物理学进展, 2014, 3, 28-32Published Online August 2014 in Hans. /journal/cmp/10.12677/cmp.2014.33004Research Progress of Preparation ofNano CeO2Li Cui1, Yaqin Hu1, Fanming Meng1,2*1School of Physics and Materials Science, Anhui University, Hefei2Anhui Key Laboratory of Information Materials and Devices, Anhui University, HefeiEmail: *mrmeng@Received: Jul. 2nd, 2014; revised: Aug. 3rd, 2014; accepted: Aug. 12th, 2014Copyright © 2014 by authors and Hans Publishers Inc.This work is licensed under the Creative Commons Attribution International License (CC BY)./licenses/by/4.0/AbstractCeO2 is a kind of cheap industrial materials widely used; it has a broad market prospect. CeO2 has been widely used in catalysis, solid oxide fuel cell, functional ceramics, and UV absorption mate-rials. In this paper, by analyzing the structure characteristics, the electron energy and the charac-teristics of cerium oxide, four kinds of preparation of cerium oxide are introduced which are solid phase method, liquid phase method, gas phase method, and hydrothermal method.KeywordsCeO2, Solid Phase Method, Liquid Phase Method, Gas Phase Method, Hydrothermal Method纳米CeO2的制备研究进展崔丽1，胡雅琴1，孟凡明1,2*1安徽大学物理与材料科学学院，合肥2安徽大学安徽省信息材料与器件重点实验室，合肥Email: *mrmeng@收稿日期：2014年7月2日；修回日期：2014年8月3日；录用日期：2014年8月12日*通讯作者。
摘要本文简要介绍目前二氧化锆的制备方法（共沉淀法、溶胶—凝胶法、喷雾热解法、金属有机物水解法、水热法、反向胶团法等），主要以水热法为例,详细介绍其制备过程及步骤，并检测制得二氧化锆的各项性能（红外、XRD)。
本文采用水热法制备氧化钇稳定氧化锆（YSZ ）纳米粉术，以Zr 4+和Y 3+的氢氧化物为热前驱体，氢氧化钾和碳酸钾作矿化剂，研究水热处理温度、PH 值和矿化剂浓度对水热合成纳米氧化锆晶型结构的影响。
实验的各项性能结果表明:高的反应温度有利于立方氧化锆的生成,矿化剂的加入对合成产物晶化度和晶粒大小有显著的影响，体系pH 值会影响水热前驱体的结构,进而影响水热合成纳米氧化锆的晶型.在Y 2O 3 掺杂量比较大的时候,PH 值的变化对氧化锆晶型的影响不明显，晶型由掺杂量决定。
在本文中还附有二氧化锆制备步骤及其性能检测的各种实验数据，用到的实验仪器，可操作性强，从而为制备粒度和晶型可控的纳米二氧化锆粉末提供实验依据.关键词： 二氧化锆 制备方法 水热法 性能检测Title Preparation and properties of zirconium dioxide detectionAbstractThis paper introduces the preparation methods of the present zirconia（Coprecipitation、Sol - gel method、Spray pyrolysis、Hydrolysis of metal organic、Hydrothermal、Reverse micelles and so on）. Case Study of the main hydrothermal. Details of their preparation process and steps，and detection system was the performance of zirconia （XRD). In this paper, hydrothermal yttria stabilized zirconia nano—powder technique to Zr4+ and Y3+in the hydroxide precursor for the heat，potassium hydroxide and potassium carbonate as a mineralizer of hydrothermal treatment temperature，PH value and mineralizer concentration on the hydrothermal synthesis of nano-zirconia crystal structure。
2017年第36卷第12期 CHEMICAL INDUSTRY AND ENGINEERING PROGRESS·4501·化 工 进展纳米CeO 2/水性聚氨酯复合材料的制备及性能赵艳娜，姬定西（陕西科技大学化学与化工学院，陕西 西安 710021）摘要：采用溶胶-凝胶法合成了纳米CeO 2溶胶，然后将合成的纳米CeO 2溶胶与水性聚氨酯（MWPU ）共混，制备了一系列纳米CeO 2/水性聚氨酯（CMWPU ）复合材料。
采用DLS 、UV-Vis 、SEM 、XRD 、TGA 等表征了CMWPU 复合材料的结构和性能，探讨了纳米CeO 2溶胶质量分数对CMWPU 复合乳液及其膜性能的影响。
结果表明：加入纳米CeO 2溶胶后成功制备了CMWPU 复合材料，纳米CeO 2溶胶在CMWPU 复合体系中分散均匀。
当纳米CeO 2溶胶质量分数为7.0%时，复合乳液紫外吸收效果较好，其吸光度值达到0.63。
与MWPU 相比，CMWPU 复合膜耐热性得到提高，最大热分解速率对应的温度提高了63.4℃，拉伸强度达到52.63MPa 。
关键词：纳米材料；二氧化铈；水性聚氨酯；复合材料；聚合物中图分类号：TQ630.4 文献标志码：A 文章编号：1000–6613（2017）12–4501–07 DOI ：10.16085/j.issn.1000-6613.2017-0319Preparation and properties of nano CeO 2/waterborne polyurethanecompositesZHAO Yanna ，JI Dingxi（College of Chemistry and Chemical Engineering ，Shaanxi University of Science and Technology ，Xi’an 710021，Shaanxi ，China ）Abstract ：The nano CeO 2 sol was synthesized by sol-gel method ，and then a series of nano CeO 2/waterborne polyurethane composites （CMWPU ）were prepared by blending the nano CeO 2 sol with waterborne polyurethane （MWPU ）. The structure and properties of CMWPU composites were characterized by DLS ，UV-Vis ，SEM ，XRD ，TGA and so on. The effects of the content of nano CeO 2 sol on the properties of CMWPU composite emulsion and its film were also discussed. The results showed that CMWPU composites were successfully prepared by adding nano CeO 2 sol ，and the nano CeO 2 sol was dispersed evenly in the CMWPU composite. When the content of nano CeO 2 sol was 7.0%，the UV absorption effect of composite emulsions was the best and the absorbance value reached 0.63. Compared with MWPU ，the thermal stability of CMWPU film has been improved. The temperature corresponding to maximum thermal decomposition rate increased by about 63.4℃，and the tensile strength of the composite film was up to 52.63MPa.Key words ：nanomaterials ；cerium oxide （CeO 2）；waterborne polyurethane ；composites ；polymers水性聚氨酯（WPU ）是一类具有良好耐磨性、耐化学性及柔韧性的环境友好型材料，被广泛应用于纺织涂层、皮革涂饰、造纸等领域[1-2]。
Journal of Materials Processing Technology190 (2007) 217–222Hydrothermal synthesis of CeO2nano-particlesA.I.Y.Tok∗,F.Y.C.Boey,Z.Dong,X.L.SunSchool of Materials Science&Engineering,Nanyang Technological University,Nanyang Avenue,639798Singapore,SingaporeReceived7February2006;received in revised form23January2007;accepted24February2007AbstractNano-crystalline particles of CeO2have been synthesized via a low temperature hydrothermal synthesis process.Two types of precursors were studied—cerium hydroxide and ceria acetate.The precursors were adjusted to a basic(pH10)and acidic(pH4)medium before hydrothermal treatment at various durations of6,12,18,and24h at250◦C using a Teflon-lined hydrothermal bomb.The synthesized samples were characterized using DTA/TGA,XRD and TEM.Based on the characterization results,both precursor systems produced crystalline ceria nano-particles after6h of hydrothermal synthesis at250◦C.The average crystallite sizes were6and15nm for the hydroxide and acetate system,respectively.The acetate precursor system appeared to produce better particles in terms of crystallinity and morphology.Based on the DTA/TGA analysis,hydrothermal synthesis had been effective in reducing the amount of intermediate products.With increasing hydrothermal treatment duration of up to24h,the samples did not exhibit a remarkable improvement in properties.The synthesized nano-particles were subsequently heat treated at500and1000◦C for2h.After the heat treatment,enhanced crystallinity and growth in crystallite size was observed,but particles appeared more agglomerated.© 2007 Elsevier B.V. All rights reserved.Keywords:Hydrothermal synthesis;CeO2;Nano-particles;Rare earth oxide1.IntroductionRare earth oxide nano-particles have exceptional lumines-cence,magnetic and electronic properties due to their unfilled 4f electronic structure.As such,rare earth-based phosphors, magnetic materials,hydrogen storage material and high sur-face area support catalyst are being widely developed.Most of the applications require the use of non-agglomerated nano-particles,as aggregated nano-particles lead to inhomogeneous mixing,poor sinterability and compromised quantum proper-ties[1].However,nano-crystallites with a primary particle size <5nm have a stronger tendency to agglomerate,making pro-cessing very difficult.As such,the benefits expected from highly crystalline nano-particles are easily lost during the manufacture of components unless weakly agglomerated nano-particles can be produced[2].Ceria(CeO2)is widely used as an oxygen ion conductor in solid oxide fuel cells,oxygen pumps and amperometric oxygen monitors because of its high oxygen ion conductiv-ity[3–8].Ceria has also received much success in redox and combustion catalysts due to its ability to shift between ∗Corresponding author.Tel.:+6567904935;fax:+6567904935.reduced and oxidized state as a result of change in gas phase oxygen concentration[9].As an oxygen storage component, ceria act as an oxygen buffer providing oxygen under lean conditions and removing it under rich conditions for optimal conversion in three-way catalyst system[4,5].Under working conditions,the catalysts are exposed to alternating O2defi-cient to excess O2environment.Ceria,in this situation,has the ability to donate its oxygen for the removal of CO and hydrocarbons during the O2deficient part of the cycle while absorbing and storing oxygen from O2,NO and water during the excess O2environment[6].This unique feature of ceria is thus termed as oxygen storage capacity(OSC).It derives from the ability to be easily and reversibly reduced to several CeO2−x stoichiometries when exposed to O2deficient atmo-spheres[6].Hydrothermal processing studies on the synthesis of nano-particles have focused on particle size,morphology and crystal polymorph.The pH of the reaction medium is a significant parameter affecting the nature and crystallinity of the nano-particles.Wu et al.[10]reported on the effects of pH of the reaction medium on the crystallization of ceria grains under hydrothermal conditions when cerium hydroxide was used as the precursor.The synthesis mechanism was thought to be by Ostwald ripening,where in an acidic medium and0924-0136/$–see front matter© 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2007.02.042218 A.I.Y.Tok et al./Journal of Materials Processing Technology 190 (2007) 217–222 with the dissolution of the precursor,grain growth is faster incontrast to a basic medium.This paper describes the hydrothermal synthesis of CeO2nano-particles derived from two types of precursors—ceriumhydroxide and ceria acetate,discusses the thermal degradationof the precursors as well as the effects of synthesis duration onthe crystallinity and morphology of the nano-particles.2.Experimental procedureHydrothermal synthesis was employed to synthesize cerium oxide nano-particles from two types of precursors(cerium hydroxide and ceria acetate),andthe effects of hydrothermal time and subsequent heat treatment were studied.Raw materials used were cerium carbonate(Ce2(CO3)3·3H2O,Ce2O3/TREO60.5%),hydrous cerium oxide stabilized by acetate ions(CeO2·x H2O),bothfrom Advanced Materials Resources,acid(65%HNO3),acetic acid(100%CH3COOH),ammonia hydroxide(28%NH3)and hydrogen peroxide(30%H2O2),all of which were from Merck.In stock solution preparation,cerium car-bonate was dissolved in nitric acid to yield cerium(III)nitrate,hydrous ceriumoxide stabilized by acetate ions(cerium acetate gel)was dissolved in deionizedwater to yield‘acetate stabilized colloidal ceria’and will be identified as ceriaacetate for the following discussions.Ammonia hydroxide was diluted to7Mto be used as the precipitating agent and the adjustment of pH.The synthesiswas done using a45ml PTFE-lined Acid Digestion Bomb from Parr InstrumentCompany.2.1.Cerium(IV)hydroxide precursorCerium(III)nitrate,Ce(NO3)3·6H2O,was diluted to[Ce4+]=0.5M usingdeionized water.Hydrogen peroxide in the molar ratio(H2O2:Ce4+)of1:2wasadded to cerium(III)nitrate solution and stirred for5min under heat on a mag-netic hotplate to convert Ce3+to Ce4+.Diluted ammonia solution(7M)in themolar ratio(NH4OH:Ce4+)of3was then added to this mixture.Upon addingammonia solution,the precipitation reaction occurred.Excess ammonia solu-tion was added drop-wise until a pH of8.8was achieved.The mixture was leftto stir continuously at80◦C for1h for the reaction to complete.After an hour,the pale yellow precipitates(Ce(OH)4)were washed several times with deion-ized water until the conductivity of the supernatant solution was less than orequal to2milli-Siemens(mS).After adjusting to pH10using ammonia solu-tion,30ml of the washed precipitates were placed into the Teflon vessel ofthe hydrothermal bomb.The bomb was then placed in the oven and heatedat the respective durations(0–24h).Thefinal products were re-washed withdeionized water to achieve conductivity of less than or equals to2mS,anddried at75◦C.Dried powders were ground and set aside for heat treatment orcharacterization.2.2.Ceria acetate precursorCeria acetate was diluted to[Ce4+]=0.5M using deionized water.The con-ductivity and pH of the solution were noted before placing30ml of the solutioninto the Teflon vessel.The bomb was then placed in the oven and heated to250◦Cat different treatment times.After recovery of thefinal products,conductivityand pH of the products were recorded.The products were later centrifuged anddried at75◦C.Dried powders were ground and set aside for heat treatment andcharacterization.XRD analysis(Shimadzu6000)was used to determine the phase compositionand to estimate the crystallite size of the nano-particles.Cu K␣radiation in the2θrange of20–80◦at4◦2θ/min was used for measurement.The crystallite sizeof the powders was estimated using the Scherrer equation:D hkl=0.89λβhkl cosθ(1)whereλis the wavelength of the incident X-rays(0.15406nm);θthe diffraction angle;βhkl the measured half-width.Lattice parameter(a)was calculated by the following lattice parameter formula(Eq.(2).d=a√2+k2+l2(2)a refers to the CeO2FCC lattice parameter,and h,k,l are the crystalline face indexes while d is the crystalline face space.Powder morphology,state of agglomeration and crystalline state were observed via TEM(Jeol JEM2010).Differential thermal analysis and thermo-gravimetric analysis(TG-DTA, Netzsch STA449C)was done in dry-air atmosphere up to1000◦C using a heating rate of10◦C/min.3.Results and discussionThe DTA/TG spectrum in Fig.1shows the thermal decompo-sition process for the cerium(IV)hydroxide.The total measured weight loss from25to900◦C was11.64%,while the theoreti-cal weight loss for the decomposition of cerium hydrate oxide is17.3%,i.e.Ce(OH)4/CeO2·2H2O to CeO2.Ce(OH)4is a hydrous oxide,represented by CeO2·x H2O which dehydrates progressively.Therefore,the decomposition of the precursor is a form of dehydration process of the hydrated CeO2.It is suggested that the difference in weight loss observed could be due to the following reasons:(a)precipitate consist-ing of a partially hydrated form of ceria,(i.e.CeO2·x H2O),for which a11.64%weight loss on decomposition corresponds to x=1.35or(b)the precipitate consisted of a mixture of phases like CeO2·2H2O+CeO2[2].The DTA/TG traces for ceria acetate precursor are shown in Fig.2.The precursor measured a total weight loss of12.55% with four distinct temperature peaks.The theoretical weight loss to be observed for pure cerium acetate with the chemical for-mula of Ce(CH3COO)3·1.5H2O is50%[11].However,it is not expected for the precursor used in this study to have similar weight loss but the acetate groups will still undergo similar chemical reactions thermally.Thefirst endothermic peak was detected at around100◦C.This is attributed to the release of the water molecules present in the precursor.From100to200◦C, the weight loss was attribute to the removal of the surface acetate groups and later the formation of the acetic acid when surface acetate hydrolysis occurs[12].This also explains the veryweakFig.1.DTA/TG of Ce(OH)4precursor.A.I.Y.Tok et al./Journal of Materials Processing Technology 190 (2007) 217–222219Fig.2.DTA/TG of ceria acetate precursor. endothermic peak detected at200◦C.There was a sharp weight loss from200to400◦C and a corresponding exothermic peak. This exothermic peak suggests the formation of oxyacetate and dioxocarbonate complexes with cerium,Ce(OH)(CH3COO)and Ce2O2CO3.The formation of these complexes during thermal decomposition have been reported for the Lanthanide acetates [11,12].As temperature increased to700◦C,the Ce2O2CO3 decomposed endothermally to produce thefinal product,CeO2 suggesting that the complete formation on CeO2occurs after 700◦C.In Fig.3,after6and24h of hydrothermal treatment,weight loss is dramatically reduced to2.64and1.37%.The distinct temperature peaks are similar to that of the precursor.How-ever,the distinct exothermic peak for the hydrothermal treated samples is no longer as pronounced as that of the precursor. This could be due to the amount of acetate complexes forma-tion being reduced considerably after hydrothermal treatment. Traces of cerium acetate complexes were still present in the samples after hydrothermal treatment.The amount is however, significantly lower than that found in the precursor.Figs.4and5show the XRD patterns of the ceria produced from cerium(IV)hydroxide precursor and ceria acetate precur-sor,respectively,at various hydrothermal treatment durations. Figs.6and7show their lattice constant values,respectively.In Fig.4,the nano-particles exhibited some degree of crystallinity and displayed all of the major peaks of CeO2with a cubic structure(JCPDF34-0394)after6h treatment.However,no significant improvement in crystallinity was observed between 6and24h,and the peaks were broad with weak intensities. This trend is similar with the ceria acetate system.However,the peaks are significantly narrower with higher intensities suggest-ing larger crystallite sizes at an average of15.5nm as calculated and larger degree of crystallinity as compared to the cerium(IV) hydroxide system.The peaks at higher2θangles can also be clearly observed for all samples.The lattice constants were calculated using Rietveld refine-ment method(Topas software),and the obtained data are included in Table1.For CeO2obtained using Ce(OH)4pre-cursor,the lattice parameter decreased by about0.2%after hydrothermal treatment at250◦C for6h(Fig.6).Whenthe Fig.3.DTA/TG for CeO2synthesized from ceria acetate:(a)after6h treatment;(b)after24h treatment.treatment duration increased from6to12h at the same tem-perature,the lattice expanded.The lattice constant only varied within a narrow range(| a|/a≈0.03%)after12h,indicating that the structure became stable.For CeO2samples obtained using ceria acetate precursor,the lattice constant decreased by about0.5%after hydrothermal treatment at250◦C for6h as shown in Fig.7.Further changes of lattice constant were very small when treatment duration was increased.The variation of lattice constant was less than0.03%.From Table1,it can be seen that crystallite size remained relatively constant with respect to the change inhydrothermal Fig.4.CeO2using Ce(OH)4precursor(250◦C)as a function of time.220 A.I.Y.Tok et al./Journal of Materials Processing Technology190 (2007) 217–222Fig.5.CeO 2using ceria acetate precursor (250◦C)as a function oftime.ttice constant of CeO 2after hydrothermal treatment at 250◦C using Ce(OH)4precursor.treatment time.The crystallite size of the ceria acetate precursor is half the size of the hydrothermal treated crystallite sizes.It appears that hydrothermal treatment did contribute to the growth in crystallite size and increase in crystallinity of the precursors.Both precursors employed were in the form of CeO 2·x H 2O.Acetate anion groups used to stabilize the ceria for the ceria acetate gel dissociated easily in the form of acetic acid;dis-sociation of acetic acids occurs very easily.Similarly,the use of acetate-based precursors reduced the time needed to achieve the same degree of crystallinity under the same hydrothermal conditions.Hydroxide precursors underwent the hydrothermal crystal-lization mechanism,where precipitated solid hydroxide samples are placed into the hydrothermal autoclave and further trans-formed into its oxide form.The hydroxide precipitateswillttice constant of CeO 2after hydrothermal treatment at 250◦C using ceria acetate precursor.T a b l e 1L a t t i c e t y p e a n d c r y s t a l l i t e s i z e o f C e O 2b a s e d o n X R D d a t a /r e fin e m e n tS t a r t i n g m a t e r i a l sT r e a t m e n t t i m e (h )A s s y n t h e s i z e dH e a t t r e a t e d a t 500◦CH e a t t r e a t e d a t 1000◦CL a t t i c e t y p e L a t t i c e c o n s t a n t D h k l (n m )L a t t i c e t y p e L a t t i c e c o n s t a n t D h k l (n m )L a t t i c e t y p e L a t t i c e c o n s t a n t D h k l (n m )C e (O H )4P r e c u r s o r A m o r p h o u s 5.42575.5––––––C e (O H )46C u b i c 5.41525.5––––––C e (O H )412C u b i c 5.42085.9––––––C e (O H )418C u b i c 5.42266.7––––––C e (O H )424C u b i c 5.42216.0C u b i c 5.40948.8C u b i c 5.40688.8C e r i a a c e t a t e P r e c u r s o r A m o r p h o u s 5.43396.14––––––C e r i a a c e t a t e 6C u b i c 5.407513.8––––––C e r i a a c e t a t e 12C u b i c 5.406115.4––––––C e r i a a c e t a t e 18C u b i c 5.407315.8––––––C e r i a a c e t a t e 24C u b i c5.406817.2C u b i c5.407117.7C u b i c 5.406517.7A.I.Y.Tok et al./Journal of Materials Processing Technology 190 (2007) 217–222221Fig.8.CeO2from Ce(OH)4(24h)heat treated at(a)500◦C,(b)1000◦C. experience a dissolution–re-precipitation process or the Ostwald ripening process.It has been reported that pH of the medium used in hydrothermal synthesis has a critical and significant influence in the crystallinity of thefinal products[10].When Ostwald ripening occurs,smaller grains dissolve faster, the diffusion of solute is slower and larger grains grow more slowly.Hence,it can be assumed that the growth kinetics is controlled by diffusion or surface reaction.This is true for substances where their solubility products are big such as K sp (AgCl)=1.8×10−10and K sp(BaSO4)=1.1×10−10.However, the solubility product of Ce(OH)4is2×10−48and is much smaller than the precipitated substances.Therefore,an opposite phenomenon where smaller grains dissolved slower with the solute diffusing faster and larger grains growing more quickly is observed.Thus,it is assumed the growth kinetics is controlled by dissolution.Ce(OH)4is a basic precipitate,therefore increasing[OH−] will result in a decrease in solubility of Ce(OH)4and increasing [H+]will result in a dramatic increase in solubility of Ce(OH)4. For Ostwald ripening,there is an equilibrium value for grain size, r*.When r is smaller than r*,smaller grains will dissolve and disappear.When r is greater than r*,larger grains will continue to grow.Under a basic medium,concentration of hydroxideions Fig.9.CeO2from ceria acetate(24h)heat treated at(a)500◦C,(b)1000◦C. becomes very high with small solubility values of Ce(OH)4,the dissolution of the precursor grains become very limited.Hence, Ostwald ripening proceeds to a very small extent,and the size of the grains increased only slightly.The opposite would have occurred if the medium was adjusted to acidity.Figs.8and9show the XRD patterns for the24h-synthesized ceria from cerium(IV)hydroxide and ceria acetate precursors, respectively,heat treated at500and1000◦C with holding time of2h.In bothfigures,it can be seen that the characteristic peaks are sharper and narrower.The higher2θpeaks for the hydroxide system can also be observed after heat treatment.This crystal-lite size after heat treatment at500and1000◦C grew to8.8 and47.4nm,respectively.In comparison,the samples from the ceria acetate system exhibited a larger degree of crystallinity than cerium hydroxide system.The crystallite size for the ceria acetate system after heat treatment was17.7and53.6nm at500 and1000◦C,respectively.The ceria synthesized from cerium(IV)hydroxide in Fig.10(a)after24h hydrothermal treatment exhibited very fine particles,which were agglomerated.Crystallinity could be observed based on the particles and its corresponding elec-tron diffraction pattern.Its crystallite size is about5–6nm as estimated from the TEM micrographs.The particlesgenerally Fig.10.TEM and electron diffraction pattern of CeO2from cerium(IV)hydroxide(a)and ceria acetate(b)after24h hydrothermal treatment.222 A.I.Y.Tok et al./Journal of Materials Processing Technology 190 (2007) 217–222shown rounded edges but they are not well-defined due to its small size.For the ceria synthesized from the acetate system after24h in Fig.10(b),particles are very well-defined and relatively dis-persed.Good crystalline faces and crystallinity state could be observed.The particle sizes,at about10–15nm,are slightly bigger compared to the cerium(IV)hydroxide system,agrees well to the calculated crystallite sizes using the XRD results. The ceria acetate system appears to be less agglomerated than the cerium(IV)hydroxide system.However,agglomeration of the particles still appears to be a problem.4.ConclusionNano-particles of ceria have been synthesized using low tem-perature hydrothermal synthesis.Cubic-fluorite ceria structure can be easily hydrolyzed under hydrothermal conditions in6h at250◦C with relatively good crystallinity.Small crystallite sizes in the range of6–15nm were obtained and they appeared to be independent on the hydrothermal treatment times at the given temperature.The choice of precursors in the synthesis of ceria has yielded relatively different results in terms of crys-tallinity,crystallite size and specific surface area.The‘acetate stabilized colloidal ceria’has been able to give particles with good crystallinity and good morphology when viewed under the TEM.Both ceria systems experienced relatively agglomer-ated particles when synthesized under hydrothermal conditions. Further studies and experiments are being done to reduce the agglomeration of the nano-particles via the use of surfactants.References[1]Y.Chen,N.Glumac,B.H.Kear,G.Skandan,Nanostruct.Mater.9(1997)101–104.[2]B.Djuricic,S.Pickering,J.Eur.Ceram.Soc.19(1999)1925–1934.[3]M.Hirano,E.Kato,J.Am.Ceram.Soc.79(1996)777–780.[4]S.Colussi,C.de Leitenburg,G.Dolcetti,A.Trovarelli,J.Alloys Compd.374(2004)387–392.[5]T.Masui,T.Ozaki,K.Machida,G.Adachi,J.Alloys Compd.303–304(2000)49–55.[6]A.Trovarelli,M.Boaro,E.Rocchini,C.de Leitenburg,G.Dolcetti,J.Alloys Compd.323–324(2001)584–591.[7]M.Boaro,A.Trovarelli,J.H.Hwang,T.O.Mason,Solid State Ionics147(2002)85–95.[8]L.F.Liotta,G.Pantaleo, A.Macaluso,G.Marc`ı,S.Gialanella,G.Deganello,J.Sol–Gel Sci.Technol.28(2003)119–132.[9]A.Trovarelli,Catal.Rev.Sci.Eng.38(1996)439–509.[10]N.C.Wu,E.W.Shi,Y.Q.Zheng,W.J.Li,J.Am.Ceram.Soc.85(2002)2462–2468.[11]M.J.Fuller,J.Pinkstone,Thermal Analysis of the Oxalate Hexahydratesand Decahydrates of Yttrium and the Lanthanide Elements,J.Less-Common Metals70(1980)127.[12]G.A.M.Hussein,Powder Technol.118(2001)285–290.。
