碳化硅基复合材料的设计、制备及可见光催化产氢性能研究

发布时间：2018-03-23 14:16

本文选题：碳化硅　切入点：异质结　出处：《北京科技大学》2017年博士论文

【摘要】：随着人类社会中能源的大量消耗和环境污染问题的出现,探索清洁无污染的可持续发展能源成为解决该问题的希望之路。在半导体作用下,利用太阳能催化分解水制备氢能被认为是解决能源危机和环境问题的有效途径之一。为更好地利用太阳光,发展可见光响应的半导体则成为研究的焦点。碳化硅(SiC)作为一种重要的无机非金属半导体材料,具有化学性质稳定、高电子迁移率等优良性质。同时,其价带导带位置能够满足分解水的要求,是一种具有发展潜力的可见光分解水的催化剂。本课题以SiC为主体催化剂,致力于研究SiC及其复合物的可见光催化产氢性能。通过与CdS复合形成促进载流子顺利转移的直接Z型光催化体系,之后通过改变合成方法优化异质结的接触界面,并探讨了半导体不同晶格匹配程度对于异质结结构构建的影响。在此基础上,继续引入有机偶联剂作为载流子转移桥梁促进光生电子空穴的分离。取得的研究结果如下:(1)采用化学沉淀法用CdS对SiC进行修饰。CdS的负载改变了 SiC表面过电势较高,不易发生化学反应的问题,与SiC之间形成Z型载流子转移体系促进光生载流子的传输。该催化剂在可见光下产氢速率达到555μmol·h-1·g-1,负载3 wt%Pt颗粒作为共催化剂后,产氢效率进一步提高至5460μmol·h-1·g-1,且在420nm处的量子效率达到了 2.1%。该异质结能够有效促进电子和空穴的分离,提高载流子的利用率。(2)通过理论计算优化了 CdS在SiC表面的负载量,并通过水热控制CdS的异质形核过程优化了二者的接触界面及CdS的分散程度。该催化剂的可见光催化产氢效率是普通沉淀法制备复合物产氢量的两倍。同时,该催化剂具有更好的结晶性、均匀的分散性和良好的光吸收性能。其体相也具有较长的光生电子寿命,有利于载流子转移到复合物的表面产氢,从而促进了光催化效率的提升。(3)通过改变水热温度制备了一系列不同晶型匹配的SiC/CdS复合物异质结光催化剂。六方相CdS(H-CdS)和六方相SiC(H-SiC)具有一致的空间群,且晶格参数之间存在3aaH-CdS=4aH-SiC的恒比关系,在水热环境中H-CdS以H-SiC为核进行外延式生长,形成的异质结的缺陷较少,从而有更好的接触界面。其可见光催化产氢性能为259μmol·h-1·g-1,是立方相CdS(C-CdS)负载的晶型不匹配的复合物C-CdS/H-SiC的四倍,且具有更强的光电流响应。H-CdS与H-SiC更为匹配的价带导带位置也更有助于电子空穴的分离。(4)将有机硅烷偶联剂(3-巯基丙基三甲氧硅烷)引入到SiC/CdS无机复合体系中作为链接键桥促进载流子转移。偶联剂和SiC之间能够形成Si-O-Si键,使得SiC体相中的载流子易于顺利转出,并延长了光生电子的寿命,促进产氢效果相比于未加偶联剂的样品有三倍的提升,为制备新型复合半导体研究提供了新思路。
[Abstract]:With the large consumption of energy and the emergence of environmental pollution in human society, exploring clean and pollution-free sustainable development energy becomes a promising way to solve this problem. The preparation of hydrogen energy by catalytic decomposition of water from solar energy is considered to be one of the effective ways to solve the energy crisis and environmental problems. The development of visible light responsive semiconductors has become the focus of research. As an important inorganic nonmetallic semiconductor material, sic has many excellent properties, such as chemical stability, high electron mobility and so on. The valence band conduction band position can meet the requirements of water decomposition, and it is a potential catalyst for water decomposition by visible light. In this paper, SiC is used as the main catalyst. In order to study the visible light catalytic hydrogen production of SiC and its complexes, a direct Z-type photocatalytic system was formed by combining with CdS to facilitate the smooth transfer of carriers, and then the contact interface of the heterojunction was optimized by changing the synthesis method. The influence of different lattice matching degree on the structure of heterojunction is discussed. Organic coupling agent was continuously introduced as carrier transfer bridge to promote the separation of photogenerated electron holes. The results obtained are as follows: 1) the loading of SiC modified with CdS by chemical precipitation method changed the surface overpotential of SiC. The formation of Z type carrier transfer system with SiC promotes the transport of photogenerated carriers. The hydrogen production rate of the catalyst reaches 555 渭 mol h-1 g-1 under visible light. The supported 3 wt%Pt particles are used as co-catalysts. The efficiency of hydrogen production was further increased to 5460 渭 mol h-1 g-1, and the quantum efficiency at 420nm reached 2.1. The heterojunction can effectively promote the separation of electrons and holes and improve the carrier utilization. The heterogeneous nucleation process of CdS was controlled by hydrothermal method. The contact interface and the dispersion of CdS were optimized. The hydrogen production efficiency of the catalyst was twice as high as that of the conventional precipitation method. The catalyst has better crystallinity, uniform dispersion and good photoabsorption performance, and its bulk phase also has a longer photoelectron lifetime, which is favorable for the carrier transfer to the surface of the complex to produce hydrogen. Therefore, a series of heterojunction photocatalysts of SiC/CdS complexes with different crystal types were prepared by changing the hydrothermal temperature. The hexagonal and hexagonal SICP H-CdS) and hexagonal SICP H-SiC have a consistent space group. Moreover, there is a constant ratio of 3aaH-CdS=4aH-SiC among lattice parameters. In hydrothermal environment, H-SiC is used as the core for epitaxial growth of H-CdS, and the defects of heterojunction are less. The visible photocatalytic activity of hydrogen production is 259 渭 mol h-1 g-1, which is four times higher than that of cubic CdS- C-CdS- supported complex C-CdS/H-SiC. The valence band position, which has stronger photocurrent-response. H-CdS and H-SiC, is also more helpful for the separation of electron holes. (4) the organic silane coupling agent, 3-mercapto propyl trimethoxysilane, is introduced into the SiC/CdS inorganic composite system as a kind of inorganic compound system. The link bridge facilitates carrier transfer. Si-O-Si bonds can be formed between the coupling agent and the SiC. The carrier in the bulk phase of SiC is easy to be transferred out, and the lifetime of photogenerated electrons is prolonged. The hydrogen production efficiency is three times higher than that of the sample without coupling agent, which provides a new idea for the preparation of new composite semiconductors.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O643.36;TQ116.2

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