含过渡元素LDHs的电子结构及可见光催化性能第一性原理研究
发布时间：2018-11-05 13:18
【摘要】：由于层状双金属氢氧化物(LDHs)具有层板金属元素的可替换性、原子级均匀分散性等特点使之成为光催化的研究热点。本文采用密度泛函理论的第一性原理计算,对部分含过渡元素的LDHs的电子结构进行计算,探讨含过渡元素LDHs中层板金属元素、表面缺陷位点及其复合材料等因素和可见光催化性能的关系,为构筑新型高分散催化剂提供了一定的理论基础。主要创新性研究内容及结论包括：1、根据LDHs层板金属元素的可替换性,将Zn、Ti等过渡元素和常见的LDHs替换,使得TiO6等基元在LDHs介质中高度分散,解决了传统催化剂在应用过程中活性组分易团聚、分散度低的问题。同时发现,过渡元素调节了LDHs的禁带宽度,可对太阳光中的可见光部分响应,Mm+或Nn+对LDHs催化性能的影响程度取决于M、N金属元素本身。同时,OH=基团易捕获空穴而产生自由基,LDHs表面的OH基团有效地提升了载流子的传输效率。2、通过建立含H和OH缺陷位点的LDHs模型,探讨不同价态的Mm+或Nn+对可见光催化分解H2O性能的影响。结果表明,不同价态的Mm+或Nn+元素对光催化性能有一定影响,H或OH缺陷位点作为光生e-的受限位抑制了e-和h+复合,使得更多的e-和h+参与氧化还原反应中,从而使得可见光催化性能进一步提升。3、通过建立LDHs-X(X:石墨烯、还原氧化石墨烯、TiO2、g-C3N4)复合模型,采用第一性原理计算探讨LDHs复合材料催化剂的催化性能。结果表明,LDHs与还原氧化石墨烯、TiO2、g-C3N4等通过氢键或者C-0-M键连接,形成了电子迁移的通道。LDHs与还原氧化石墨烯、TiO2、g-C3N4等的能带差异和氧化还原电位错位,造就异质结,使得LDHs光激发的电子通过两者间的氢键或者C-0-M键迁移到还原氧化石墨烯、TiO2、g-C3N4等基材上,减少e-和h+复合,从而提升了光催化性能。
[Abstract]:Layered bimetallic hydroxide (LDHs) has become a hotspot in photocatalysis due to its substitutability of metal elements in laminates and the homogeneity of atomic dispersion. In this paper, the first principle calculation of density functional theory is used to calculate the electronic structure of LDHs with transition elements, and the laminated metal elements in LDHs with transition elements are discussed. The relationship between the surface defect sites and their composite materials and their visible light catalytic properties provides a theoretical basis for the construction of novel highly dispersed catalysts. The main innovative research contents and conclusions are as follows: 1. According to the substitutability of metal elements in LDHs laminates, the transition elements such as Zn,Ti and common LDHs are replaced, so that TiO6 and other elements are highly dispersed in LDHs medium. The problem of easy agglomeration and low dispersity of active components in the application of traditional catalysts was solved. It is also found that the transition element adjusts the band gap of LDHs and can respond to the visible light in the solar light. The influence of Mm or Nn on the catalytic performance of LDHs depends on the metal element Mon itself. At the same time, the OH= group is easy to capture holes and produce free radicals, and the OH group on the LDHs surface can effectively improve the transport efficiency of carriers. 2. By establishing the LDHs model with H and OH defect sites, The effect of Mm or Nn in different valence states on the catalytic decomposition of H2O by visible light was investigated. The results show that different valence elements of Mm or Nn have a certain effect on photocatalytic performance. The defect sites of H or OH, as the restricted sites of photogenerated e-, inhibit the combination of e- and h, and make more e- and h participate in the redox reaction. Thus, the catalytic performance of visible light was further improved. 3. By establishing LDHs-X (X: graphene, reduced graphene, TiO2,g-C3N4) composite model, the first principle calculation was used to study the catalytic performance of LDHs composite catalyst. The results show that LDHs is connected with reduced graphene oxide and TiO2,g-C3N4 by hydrogen bond or C-0-M bond to form electron transport channel. LDHs is associated with reduced graphene oxide, TiO2, and so on. The energy band difference of g-C3N4 and the dislocation of redox potential make the photoexcited electrons of LDHs migrate to the reduced graphene, TiO2,g-C3N4 and other substrates through the hydrogen bond or C-0-M bond between them. The photocatalytic performance was improved by reducing the composition of e- and h.
【学位授予单位】：北京化工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：O611.2;O643.3
本文编号：2312208
[Abstract]:Layered bimetallic hydroxide (LDHs) has become a hotspot in photocatalysis due to its substitutability of metal elements in laminates and the homogeneity of atomic dispersion. In this paper, the first principle calculation of density functional theory is used to calculate the electronic structure of LDHs with transition elements, and the laminated metal elements in LDHs with transition elements are discussed. The relationship between the surface defect sites and their composite materials and their visible light catalytic properties provides a theoretical basis for the construction of novel highly dispersed catalysts. The main innovative research contents and conclusions are as follows: 1. According to the substitutability of metal elements in LDHs laminates, the transition elements such as Zn,Ti and common LDHs are replaced, so that TiO6 and other elements are highly dispersed in LDHs medium. The problem of easy agglomeration and low dispersity of active components in the application of traditional catalysts was solved. It is also found that the transition element adjusts the band gap of LDHs and can respond to the visible light in the solar light. The influence of Mm or Nn on the catalytic performance of LDHs depends on the metal element Mon itself. At the same time, the OH= group is easy to capture holes and produce free radicals, and the OH group on the LDHs surface can effectively improve the transport efficiency of carriers. 2. By establishing the LDHs model with H and OH defect sites, The effect of Mm or Nn in different valence states on the catalytic decomposition of H2O by visible light was investigated. The results show that different valence elements of Mm or Nn have a certain effect on photocatalytic performance. The defect sites of H or OH, as the restricted sites of photogenerated e-, inhibit the combination of e- and h, and make more e- and h participate in the redox reaction. Thus, the catalytic performance of visible light was further improved. 3. By establishing LDHs-X (X: graphene, reduced graphene, TiO2,g-C3N4) composite model, the first principle calculation was used to study the catalytic performance of LDHs composite catalyst. The results show that LDHs is connected with reduced graphene oxide and TiO2,g-C3N4 by hydrogen bond or C-0-M bond to form electron transport channel. LDHs is associated with reduced graphene oxide, TiO2, and so on. The energy band difference of g-C3N4 and the dislocation of redox potential make the photoexcited electrons of LDHs migrate to the reduced graphene, TiO2,g-C3N4 and other substrates through the hydrogen bond or C-0-M bond between them. The photocatalytic performance was improved by reducing the composition of e- and h.
【学位授予单位】：北京化工大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：O611.2;O643.3
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，本文编号：2312208
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