CuO/TiO2复合材料制备与光催化性能研究

2023-07-06 06:36陈顺洪胥巧陈鸿锦刘佳伟王牟博朱晓东
关键词:溶胶

陈顺洪 胥巧 陈鸿锦 刘佳伟 王牟博 朱晓东

(文章编号:1004-5422(2023)02-0184-05

DOI:10.3969/j.issn.1004-5422.2023.02.012

收稿日期:2022-11-14

基金项目:四川省科技厅应用基础研究项目(19YJ0664);四川省高等教育人才质量和教学改革项目(JG2021-1104、JG2021-1105);成都大学大学生创新计划项目(CDUCX2022013、CDUCX2022070、CDUCX2022086)

作者简介:陈顺洪(1993—),男,硕士,助教,从事智能材料设计研究.E-mail:chenshunhong@cdu.edu.cn

摘要:采用溶胶—凝胶法在550 ℃热处理条件下制备纯TiO2及CuO/TiO2复合光催化材料.通过X射线衍射、扫面电子显微镜和荧光光谱等方法对催化剂的晶体结构、微观形貌,以及光生电子和空穴复合率进行表征,并以亚甲基蓝作为目标污染物,研究其光催化性能.结果表明,采用550 ℃热处理工艺制备的纯TiO2为锐钛矿结构,Cu元素加入后,TiO2中出现了微量的金红石,促进了锐钛矿向金红石转变,并且产生了CuO相,形成了CuO/TiO2复合材料.CuO的产生有利于抑制光生电子与空穴的复合,但CuO/TiO2对亚甲基蓝的降解率低于纯TiO2,这可能是CuO/TiO2复合材料的纳米颗粒团聚现象增强,比表面积降低所致.

关键词:溶胶—凝胶法;CuO/TiO2复合材料;光催化性能

中图分类号:TB332;O643.36

文献标志码:A

0引言

利用光解催化剂处理污水因其方式简单,效果明显而受到极大地关注[1-7].为提高光催化性能,研究人员采用多种方式对光催化剂进行改性处理.其中,包括光敏化处理[8-9]、半导体复合[10-13]、引入助催化剂[14-16]和掺杂处理[17-20]等.TiO2因其化学性质稳定、无毒无害、廉价易得和可重复使用等优点在光催化领域备受青睐[21-23].但纯TiO2光生电子—空穴对极易复合,并且可见光利用率较低[24-25],因此需要对TiO2进行改性以提高光催化性能.半导体复合是近年来改性的一个研究热点,当其他半导体与TiO2复合后,由于复合材料中半导体价带和导带能级位置不同,当受到光照产生光生电荷后,可以在界面间加快转移,抑制复合,从而提高光催化性能[26-28].Kusior等[29]采用溶胶—凝胶法制备SnO2/TiO2复合材料,光生电子由锐钛矿导带向SnO2迁移,空穴从SnO2转移到TiO2,从而有效抑制电子与空穴的复合,延长载流子寿命,相比纯TiO2拥有更高的光催化活性.

本研究采用溶胶—凝胶法在550 ℃热处理下制备纯TiO2及CuO/TiO2復合材料光催化剂,对光催化材料进行晶体结构、微观形貌,以及光生电子和空穴复合率分析,以亚甲基蓝(MB)为目标污染物,对其进行光催化降解实验,研究纯TiO2及CuO/TiO2复合材料的光催化性能.

1材料与方法

1.1仪器

UV-6100A型紫外可见分光光度计(上海元析仪器有限公司),Solar-350型氙灯光源(北京纽比特科技有限公司),DHG-9030型电热恒温鼓风干燥箱(上海鸿都电子科技有限公司),HC-2064型高速离心机(安徽中科中佳科学仪器有限公司),DX-2700型X射线衍射仪(XRD)(上海精密仪器仪表有限公司),F50型扫描电子显微镜(SEM)(美国FEI公司),F-4600型荧光光谱分析仪(PL)(日立高新技术有限公司).

1.2材料

钛酸四丁酯(C16H36O4Ti,分析纯)、无水乙醇(C2H6O,分析纯)、冰乙酸(CH3COOH,分析纯)、三水硝酸铜(Cu(NO3)2·3H2O,分析纯),均购自成都市科隆化学品有限公司.

1.3样品制备

首先量取一定量的C16H36O4Ti和C2H6O,配制成溶液A;再取适量的去离子水、CH3COOH和C2H6O,配制成溶液B;随后称取一定量的Cu(NO3)2·3H2O溶于溶液B中,超声5 min,得到溶液C.将所得C液滴加入A液中,搅拌30 min使溶液混合均匀,静置24 h后,在100 ℃烘箱中干燥.将得到的粉体在550 ℃条件下进行热处理,制备得到CuO/TiO2复合材料,其中Cu/Ti摩尔比为20%.其他条件相同,不加Cu(NO3)2·3H2即可制得纯TiO2.

1.4表征技术

采用XRD表征样品晶体结构,采用SEM分析样品表面形貌,采用PL检测光生电子与空穴的复合率.

1.5光催化实验

以10 mg/L MB为目标污染物,量取100 mL MB溶液,加入0.1 g光催化剂(TiO2或CuO/TiO2).超声5 min后在闭光环境中搅拌30 min,然后以250 W氙灯作为光源,光照下1 h后取4~5 mL MB溶液于离心管中,离心后取上层清液,在波长λ为664 nm的条件下测试其吸光度A,降解率计算公式为,     Φt =(A0-At)/A0×100%(1)

式中,Φt 为t时刻的降解率,A0和At分别为初始和t时刻溶液吸光度.

2结果与分析

2.1晶体结构分析

图1为样品的XRD图谱.纯TiO2在25.3°、37.8°和48.1°等位置出现了衍射峰,分别对应锐钛矿晶型的(101)、(004)和(200)等晶面.图谱中并未出现金红石衍射峰,表明此时纯TiO2为单一锐钛矿结构.当Cu加入后,在27.3°处出现了金红石(110)晶面衍射峰,表明有金红石的产生,此时为锐钛矿与金红石组成的混晶结构.不仅如此,在XRD图谱中,35.6°、38.7°、48.9°和61.8°处出现了CuO的相关衍射峰,对应氧化铜的(11-1)、(111)、(20-2)和(11-3)等晶面.表明Cu元素加入后,形成了CuO/TiO2复合材料.Cu元素的加入促进了锐钛矿向金红石的转变,这与王保伟等[30]的研究结果一致.TiO2 和 CuO/TiO2 平均晶粒尺寸计算公式[31]为,

D= kλ /(βcosθ)(2)

式中,D 为 TiO2 平均晶粒尺寸;λ 为 X 射线入射波长,k 为常数,0.89;β 为XRD 衍射峰的半高宽;θ为布拉格衍射角度的1/2.计算结果显示,纯TiO2的锐钛矿晶粒尺寸为23.5 nm,CuO/TiO2中锐钛矿的晶粒尺寸为32.3 nm.

混晶中金红石质量百分数的计算公式[32]为,

XR=1/(1+0.8IA /IR )(3)

式中,XR 为 TiO2 混合物中金紅石质量百分数;IA为锐钛矿(101) 晶面衍射峰的相对强度;IR为金红石(110)晶面衍射峰的相对强度,计算可知,金红石质量分数为4.9%,锐钛矿质量分数为95.1%.

2.2表面形貌分析

图2为纯TiO2与CuO/TiO2复合材料的SEM图,图2(A)中纯TiO2颗粒尺寸分布在30 nm~200 nm.CuO复合后所得材料出现了进一步的团聚,颗粒尺寸大致分布在100~500 nm,如图2(B)所示.TiO2光催化材料尺寸范围在纳米级,而纳米材料中位错、孪晶和层错等晶体缺陷会在晶界处堆积,产生很大的畸变能与缺陷,易与其他粒子结合形成团聚体[33-35].

2.3光生电子和空穴复合率分析

半导体价带上的电子受到光子激发时,由价带跃迁至导带,形成导带上的光生电子,同时在价带留下相应的光生空穴.但是导带上的光生电子容易返回价带与光生空穴复合,同时释放出光子,从而产生荧光,称为“光致发光”.因此,光致发光(PL)光谱强度越低,则表明光生电子和空穴的复合率越低.图3为纯TiO2及CuO/TiO2复合材料的PL光谱图.纯TiO2的PL光谱的最强峰在398 nm附近,此峰可归因于光生电子从导带返回到价带而引起,位于波长450~470 nm区间内的峰可能是晶体表面缺陷引起的[36-37].纯TiO2 PL峰强度相较于CuO/TiO2更高,这表明CuO的生成明显地降低了材料光生电荷的复合率.CuO与TiO2复合后,促进了光生电荷在两相界面间转移,抑制了复合,因此表现出了更低的PL峰强度[38].图3TiO2和CuO/TiO2的PL光谱

2.4光催化结果分析

图4为纯TiO2和CuO/TiO2复合材料的光降解结果柱状图.纯TiO2在1 h时对MB的降解率Φ为31.2%,而CuO/TiO2复合材料的降解率出现了一定幅度的下降,降解率Φ为5.8%.实验结果表明,CuO/TiO2的光催化活性低于纯TiO2.有研究表明,复合材料光催化活性与Cu/Ti的摩尔比例有关,低浓度的Cu有利于促进电子—空穴对的分离,而较高浓度的Cu会导致晶格缺陷和氧空位的增加,形成新的电子—空穴复合中心,降低光催化活性[39].本研究中,当在TiO2中引入Cu时,其PL光谱较纯TiO2表现出更低的峰强度,虽然Cu/Ti摩尔比达到20%,但并未形成新的复合中心.因此,这不是光催化活性下降的原因.结合SEM图观察结果,CuO/TiO2团聚现象较纯TiO2更严重,颗粒尺寸明显增大,这会减小催化剂的比表面积,使光催化降解反应的活性位点减少,导致光催化活性降低.

3结论

本研究采用溶胶—凝胶法制备了纯TiO2和CuO/TiO2复合光催化材料.Cu加入有利于锐钛矿向金红石的转变,同时生成了CuO相,形成了CuO/TiO2复合材料.PL光谱结果表明,CuO/TiO2加快了光生电荷在两相界面的迁移,明显降低了光生电子—空穴的复合.形貌分析表明,CuO/TiO2颗粒团聚现象比纯TiO2严重,团聚体尺寸增加.CuO/TiO2复合材料对亚甲基蓝染料的降解率较纯TiO2出现了下降,这可能是团聚增加,减小了比表面积所致.

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Study on Preparation of CuO/TiO2 Composite Material and Its Photocatalytic Performance

CHEN Shunhong,XU Qiao,CHEN Hongjin,LIU Jiawei,WANG Mubo,ZHU Xiaodong

(School of Mechanical Engineering,Chengdu University,Chengdu 610106,China)

Abstract:

Pure TiO2 and CuO/TiO2 composite photocatalytic materials were prepared by sol-gel method at 550 ℃.X-ray diffractometer,scanning electron microscope,fluorescence spectroscopy were used to analyze the crystal structure,surface morphology,and recombination rate of photogenerated electron and holes of the samples.Methylene blue,as a photocatalytic degradation target,was used to evaluate the photocatalytic performance of the prepared photocatalysts.The results show that the pure TiO2 exists as anatase crystalline phase at 550 ℃.Cu adding makes the emergence of a small amount of rutile,promoting the transformation of anatase to rutile.In addition,CuO phase is yielded,forming CuO/TiO2 composite material.The formation of CuO is useful to inhibit the recombination of photogenerated electrons and holes;however,the photocatalytic activity of CuO/TiO2 is lower than that of pure TiO2.This may be caused by the increased aggregation of nanoparticles of CuO/TiO2 composite material and the decrease in specific surface area.

Key words:

sol-gel method;CuO/TiO2 composite materials;photocatalytic performance

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