锌镉基硫化物光催化剂的制备及制氢性能研究

1、 博士学位论文锌镉基硫化物光催化剂的制备及制氢性能研究PREPARATION OF ZINC- AND CADMIUM-BASED SULFIDE PHOTOCATALYSTS FORPHOTOCATALYTIC HYDROGEN PRODUCTION于耀光哈尔滨工业大学2014年 6月 国内图书分类号：O614.51国际图书分类号：661.881学校代码：10213密级：公开工学博士学位论文锌镉基硫化物光催化剂的制备及制氢性能研究博 士 研 究 生：于耀光 导 师 ：陈刚 教授 申 请 学 位：工学博士 学科：化学工程与技术 所 在 单 位 ：理学院化学系 答 辩 日 期 ：2014年 6月

2、 授予学位单位 ：哈尔滨工业大学 Classified Index: O614.51U.D.C: 661.881Dissertation for the Doctoral Degree in EngineeringPREPARATION OF ZINC- AND CADMIUM-BASED SULFIDE PHOTOCATALYSTS FORPHOTOCATALYTIC HYDROGEN PRODUCTIONCandidate：Yaoguang YuSupervisor：Prof. Gang ChenAcademic Degree Applied for：Speciality：Doctor o

3、f EngineeringChemical Engineering and TechnologyDepartment of Chemistry Affiliation：June, 2014 Date of Defence：Degree-Conferring-Institution：Harbin Institute of Technology 摘 要摘 要利用一种既不释放温室气体，也不产生其它污染物的方式来为世界提供能源是一项极具挑战的课题，而通过半导体光催化剂分解水制氢无疑是最吸引人的手段之一。在众多的光催化材料中，以 ZnS 及 CdS 为代表的硫化物光催化剂因其优异的光催化制氢性能受到了研

4、究者的广泛关注，在此领域的研究也取得了很多深受瞩目的成果。本论文利用简单方法合成了一系列具有优异光催化制氢性能的锌镉基硫化物光催化材料，系统的研究了晶体结构、微观形貌、光生电荷分离与光催化制氢性能之间的关系。采用水热法首次合成了具有分级多孔结构的 Cd、In 共掺 ZnS 光催化剂，其 BET 比表面积最高可达 127 m2g1。FESEM 及 TEM 测试结果表明光催化剂是由纳米片随机自组装的花状微球构成，通过调节 Cd与 In的含量可使 Cd，In共掺 ZnS 纳米片的晶体生长过程处于奥斯特瓦尔德熟化与侧向定向聚集晶体生长机制的竞争中，从而使得纳米片具有六方纤锌矿 /立方闪锌矿异质结构，该

5、异质结构对光生电子空穴分离具有促进作用。 Cd，In共掺 ZnS 光催化剂对可见光的吸收主要源于 Cd元素的掺杂。负载 2 wt% Pt的 Cd，In 共掺 ZnS 光催化剂的制氢活性最高可达 3.7 mmolh1，是一种具有潜在应用价值的光催化材料。采用水热法合成了 ZnIn2S4/CdIn2S4复合光催化剂， ZnIn2S4与 CdIn2S4的形貌分别对应于纳米片紧密堆积的大花球与纳米片松散堆积的小花球。由于 Cd与 Zn 在 ZnIn2S4与 CdIn2S4间的交互掺杂，复合光催化剂紫外可见吸收光谱的吸收边集中在 540550 nm 范围内。通过在 ZnIn2S4/CdIn2S4复合光催

6、化剂中引入还原助催化 Pt 及氧化助催化剂 PdS，确定了光催化制氢过程中的速度控制步骤为光催化氧化半反应。负载 PdS 助催化剂后的复合光催化剂的光催化制氢活性最高可达 780 molh1，相比于纯相 ZnIn2S4光催化剂性能提高近 3倍。通过简便、快捷的微波辅助液相法合成了一系列 CdxZn1xS 固溶体光催化剂，15 min 内便能完成反应过程。所制备的光催化剂是由纳米晶团聚而成的无规则二次颗粒。通过在反应过程中引入阴离子表面活性剂十二烷基苯磺酸钠(SDBS)，使得所制备的纳米晶具有孪晶结构，纳米晶中的孪晶结构可使光生电子空穴有效地分离。当 SDBS 浓度为 0.6 molL1时，所合

7、成的 Cd0.6Zn0.4S固溶体光催化剂无负载条件下制氢活性亦可达 3.6 mmolh1。根据以纳米晶团聚而成的 Cd0.6Zn0.4S 光催化剂在首次循环后活性升高的现象，首次提出了聚集体系光催化剂初始反应阶段的 “活化机制 ”，为合理评价聚集体系光催化剂的制氢性- I - 哈尔滨工业大学工学博士学位论文能提供了理论依据。通过溶剂热法首次将 La 掺入 Cd0.6Zn0.4S 固溶体的空间电荷层中，MottSchottky 测试表明调节 La 的掺入量可调控 Cd0.6Zn0.4S 固溶体空间电荷层的厚度，XPS 测试结果表明 La 原子以 LaSZn 键的形式存在。由于 La 的掺杂，C

8、d0.6Zn0.4S固溶体对光的吸收明显增强，350 nm单色光下 CZS: 2% La的表观量子产率高达 93.3%。而 CZS: 2% La 光催化剂在模拟太阳光 (AM 1.5)的可见波段下的制氢活性最高可达 1.39 mmolh1。此外，La 修饰对光催化分解水制氢的促进作用在红色 TiO2体系中也得到了验证。关键词：光催化剂；分解水制氢；固溶体；异质结构- II - 哈尔滨工业大学工学博士学位论文AbstractPowering the world without emitting greenhouse gases or producing additionalpollutants

9、is a challenging issue. Photocatalytic H2 evolution through solar watersplitting using semiconductor photocatalyst is one of the most attractive routes toachieve this goal. Among the photocatalysts, sulfide photocatalysts, including ZnS,CdS, received much attention because of their outstanding perfo

10、rmance forphotocatalytic H2 production. Research in this field have received remarkableachievements. In this thesis, a series of Zinc- and Cadmium-based sulfidephotocatalytic materials have been synthesized through facile routes. Therelationship between crystal structure, morphology, separation of p

11、hoto-generatedcharges and performance of photocatalytic H2 production has been investigatedsystematically.Hierarchical porous Cd, In co-doped ZnS photocatalyst was firstly synthesizedthrough the hydrothermal method. BET specific surface area of the as-preparedsamples was up to 127 m2g1. FESEM and TE

12、M results demonstrated that thephotocatalysts were composed of flower-like microsphere by assembly ofnanoflakes. By adjusting the amount of Cd and In components in Cd, In co-dopedZnS photocatalyst, the crystal growth process would be in a competition betweenOstwald ripening and orientation attachmen

13、t, which makes the nanoflakes presentwurtzite/sphalerite heterostructures. The wurtzite/sphalerite heterostructures couldcontribute to the separation of photo-generated charges. The visible-light absorptionwas mainly attributed to the doping of Cd element. Performance of photocatalystwith 2% Pt load

14、ed for photocatalytic H2 production reached 3.7 mmolh1, which isa good candidate for potential applications.ZnIn2S4/CdIn2S4compositephotocatalystsweresynthesizedthroughhydrothermal method. Morphologies of ZnIn2S4 and CdIn2S4 corresponding tobigger flower-like microspheres with denser packed nanoflak

15、es and smallerflower-like microspheres with looser packed nanoflakes. Due to the cross-doping ofCd and Zn into the ZnIn2S4 and CdIn2S4, the absorption edges of compositephotocatalysts were mainly located between 540 and 550 nm. Through introducingthe Pt reduction cocatalyst and PdS oxidation cocatal

16、yst into the ZnIn2S4/CdIn2S4composite photocatalyst, the rate-determining step of the total photocatalytichydrogen evolution reaction was confirmed to the photocatalytic oxidative halfreaction. Performance of the composite photocatalyst for photocatalytic H2production could reach 780 molh1 after loa

17、ding PdS cocatalyst, which is 3 times- III - Abstracthigher than the pure ZnIn2S4 photocatalyst.A series of CdxZn1xS solid solution photocatalysts have been synthesizedthrough a facile, fast microwave-assisted route, the photocatalyst powder could beobtained in 15 min. The as-prepared photocatalyst

18、was composed of irregularsecondary particles by assembly of nanocrystals. Through introducing sodiumdodecyl benzene sulfonate (SDBS) as the anionic surfactant, the nanocrystalspresented twin structures which could effectively separate the photo-generatedelectrons and holes. The photocatalytic H2 pro

19、duction performance of Cd0.6Zn0.4Ssolid solution photocatalyst synthesized in the presence of 0.6 molL1 of SDBSreached 3.6 mmolh1 even without loading any cocatalyst. According to thephenomenon that the performance of Cd0.6Zn0.4S photocatalyst composed ofnanocrystals increased after first cycle, an

20、“activation effect” of the photocatalyst inassemble system at the initial stage of photocatalytic reaction was proposed, whichprovides theoretical evidence for the rational evaluation of the photocatalytichydrogen evolution performance of the photocatalysts in assemble system.La was firstly doped in

21、to the space charge layer of Cd0.6Zn0.4S solid solutionthrough solvothermal method. MottSchottky test indicated the depth of spacecharge layer of Cd0.6Zn0.4S solid solution could be adjusted by changing the amountof La doped. XPS results demonstrated La was doped into the space charge layer inthe fo

22、rm of LaSZn bonds. Attributed to the La doping, light-absorbing property ofCd0.6Zn0.4S solid solution was greatly improved. Furthermore, the apparent quantumyield of CZS: 2% La was up to 93.3% under the irradiation of 350 nmmonochromatic light. And the photocatalytic performance for H2 production of

23、 CZS:2% La photocatalyst under the irradiation of the visible region of simulated sunlight(AM 1.5) could reach 1.39 mmolh1. Moreover, the promotion of La modificationon the photocatalytic H2 production performance has also been verified in the redTiO2 system.Keywords: photocatalyst, H2 production fr

24、om water splitting, solid solution,heterostructure- IV - 目录目 录摘 要 . IAbstract . III第 1章 绪 论 . 11.1 课题背景及研究的目的和意义 . 11.2 光催化分解水制氢反应基本原理 . 21.2.1 半导体光催化剂中电荷分离机制 . 21.2.2 氧化物光催化体系牺牲剂反应机制 . 31.2.3 硫化物光催化体系牺牲剂反应机制 . 31.3 光催化分解水制氢材料研究现状 . 41.3.1 TiO2光催化材料 . 41.3.2 氮(氮氧)化物光催化材料 . 61.3.3 非金属光催化材料 . 71.3.4 硫

25、化物光催化材料 . 91.4 构筑高效光催化分解水制氢材料的有效途径 . 121.4.1 控制暴露高活性晶面 . 131.4.2 负载助催化剂及表面等离子效应 . 141.4.3 构筑异相(质)结构 . 151.4.4 稀土掺杂及修饰 . 161.4.5 能带工程 . 171.5 本文的主要研究内容 . 18第 2章 实验材料及表征方法 . 192.1 实验试剂及实验仪器 . 192.1.1 实验试剂 . 192.1.2 实验仪器 . 202.2 样品的表征方法 . 202.2.1 X射线衍射(XRD) . 202.2.2 紫外-可见吸收光谱 (UV-vis) . 212.2.3 X射线光电子

26、能谱 (XPS) . 212.2.4 电感耦合等离子体原子发射光谱 (ICP-AES) . 21- V - 哈尔滨工业大学工学博士学位论文2.2.5 傅里叶变换 -红外光谱(FT-IR). 212.2.6 扫描电镜(SEM) . 222.2.7 透射电子显微镜 (TEM) . 222.2.8 比表面积分析 (BET) . 222.2.9 莫特-肖特基(Mott-Schottky）测试 . 222.3 光催化分解水制氢材料的性能评价 . 222.3.1 光催化材料分解水制氢活性 . 222.3.2 光催化材料分解水制氢稳定性 . 232.4 表观量子产率的计算 . 23第 3章 含铟的锌镉基硫化

27、物的制备及性能研究 . 253.1 引言. 253.2 水热合成含铟的锌镉基硫化物 . 253.3 分级多孔 Cd，In共掺 ZnS 光催化剂的表征及制氢性能研究 . 263.3.1 元素组成与晶体结构分析 . 263.3.2 形貌分析 . 283.3.3 异质结构形成机理 . 313.3.4 BET 分析 . 343.3.5 紫外可见吸收光谱及能带结构 . 353.3.6 光催化制氢性能及电子传输机制 . 363.4 ZnIn 2S4/CdIn 2S4复合光催化剂的制备及制氢性能研究 . 393.4.1 元素组成与晶体结构分析 . 393.4.2 形貌分析 . 413.4.3 BET 分析 . 433.4.4 紫外可见漫反射光谱及能带结构 . 433.4.5 光催化制氢性能 . 443.4.6 光生电荷传输机制及多次循环测试 . 483.5 本章小结 . 50第 4章 微波辅助合成 CZS 固溶体光催化剂及其制氢性能研究 . 524.1 引言. 524.2 样品的制备 . 524.3 晶体结构分析 . 534.4 形貌分析 . 544.5 BET 及紫外-可见吸收光谱分析 . 56- VI - 目录4.6 光催化制氢性能 . 594.7 多次循环测试及活化效应 . 624.8 本章小结 . 64第 5章 镧改性 CZS 光催化剂的制