MOF基光催化剂的合成、电荷分离与分解水产氢性能研究

发布时间：2018-04-29 23:27

本文选题：金属-有机框架材料 + 金属纳米颗粒　；参考：《中国科学技术大学》2017年博士论文

【摘要】：金属-有机框架材料(Metal-Organic Frameworks,MOFs)是由金属离子或者金属簇合物与有机配体桥连构成的一类新颖的结晶性多孔固体材料。这类材料一般具有高比表面积、可剪裁性、可功能化、多活性位点等特点,被发现至今在气体吸附和储存、分子分离、荧光传感、催化、超级电容器、药物载体或多孔模板等领域都具有极其重要的应用价值。MOFs的次级结构单元是金属氧簇结构,能够表现出类半导体的行为,因而在光催化研究中引起了广泛兴趣。由于MOFs无/少缺陷的晶态有序结构和多孔特性使其在电子空穴有效分离上具有独特的优势,理性设计合成MOFs及其复合材料在光催化中的应用己呈现了非常迷人的前景。以此为突破口,基于MOFs明确且方便调控的结构,对理解光催化反应的构效关系、发展新型多孔光催化剂材料也具有十分重要的意义。本论文在所在实验室近年来的工作基础上:包括发展了 MOFs材料的设计合成及在有机催化领域的应用,集中阐述了基于MOF复合和衍生材料对太阳光的增强光吸收,通过理性设计合成策略促进了此类基于MOFs的光催化剂的电荷有效分离,并应用于高效光催化分解水产氢领域。通过将金属纳米颗粒与MOFs进行复合,得到新颖的金属@MOFs的复合结构,这种复合结构有利于光生电子和空穴的快速转移和分离,促进对光生电荷的有效利用,极大的改善了光催化产氢性能。另外,本文还深入探讨了形貌和尺寸对所制备的MOF基光催化剂的性能影响。本论文所取得的主要研究成果如下:1.金属纳米颗粒,尤其是铂(Pt)纳米颗粒,被认为是特别好的电子受体,因此金属纳米颗粒与MOF的复合材料一般会显示出比纯MOF更高的光催化性能。基于MOF的多孔性不影响质子传输以及对纳米颗粒的限域作用,MOF可以作为理想的模板来研究电子受体位置对光催化性能的影响。我们设计合成了平均粒径为3nm的铂(Pt)纳米颗粒,并将其均匀分散在MOF材料UiO-66-NH2的内部或表面,分别得到Pt@UiO-66-NH2和Pt/UiO-66-NH2材料,并用于可见光解水制氢的性能研究。与单纯的UiO-66-NH2相比较,两个负载Pt的复合材料显示出明显提高但显著不同的光解水制氢性能,表明了 Pt在MOF材料中的相对位置对光催化效率的影响。其中,Pt@UiO-66-NH2极大的缩短了电子传输距离,更利于电子-空穴的分离,因此显现出相对Pt/UiO-66-NH2更高的光催化效率。蕴含的催化机理进一步通过超快光谱测试和荧光光谱测试得到揭示。2.设计合成含有两种金属-MOF界面的新型光催化产氢体系,促进光生电子流的形成和高效产氢性能。要实现半导体材料高的产氢性能,有两个特别重要的I要求:一是较宽的光吸收范围;二是该半导体材料被光激发产生的光生电子和空穴能得到有效分离并利用。基于MOF与Pt纳米颗粒的肖特基结构有利于电子传输和分离;同时Au和Ag等金属颗粒具有很好的等离子共振效应,能实现在可见及近红外区的光吸收,将其与MOF复合可以拓宽MOF的光吸收范围。而将这种肖特基结构和等离子共振效应同时设计结合到同一 MOF材料中,将能实现光生电子和空穴的更有效转移和分离,减少光生电子和空穴在体相中的复合,从而达到更好的光催化产氢效果。3.选用超高热稳定的MOF材料,MIL-53(A1),作为硬模板,向其孔道中引入各种金属硝酸盐,通过高温煅烧纳米刻蚀的办法成功指引生成多孔金属氧化物材料。使用该模板法得到的金属氧化物材料具有高比表面积,并且可大体复制MOF的孔结构。合成过程中,金属氧化物可进一步转化成金属硫化物,MOF模板去除后即可得到多级孔道金属硫化物。相对于传统的体相的硫化镉和纳米尺寸硫化镉而言,该方法得到的纳米尺寸多级孔道硫化镉在光催化裂解水产氢反应中具有更优异的光催化性能。
[Abstract]:Metal-Organic Frameworks (MOFs) is a kind of novel crystalline porous solid material composed of metal ions or metal clusters and organic ligand bridges. These materials generally have high specific surface area, can be tailored, functionalized and multi active sites, and have been found to be adsorbed and stored in gas so far. Molecular separation, fluorescence sensing, catalysis, supercapacitors, drug carriers, or porous templates, which are of great importance to the application of.MOFs, are metal oxygen cluster structures, which can show the behavior of semiconductor like semiconductors, and thus have aroused wide interest in the study of photocatalytic research. Due to the amorphous structure of MOFs with no / less defects, the structure of the crystalline ordered structure has been found. And the porous properties have unique advantages in the effective separation of electron holes. Rational design and synthesis of MOFs and its composites have been very attractive in the application of photocatalysis. Based on the structure of clear and convenient MOFs regulation, the structure of the photocatalytic reaction is understood and the new porous photocatalyst is developed. On the basis of the recent work in the laboratory, this paper includes the development of the design and synthesis of MOFs materials and the application in the field of organic catalysis, focusing on the enhanced optical absorption of solar light based on MOF composite and derivative materials, and through the rational design synthesis strategy to promote this type of MO The charge of Fs's photocatalyst is effectively separated and applied to the field of high efficiency photocatalytic decomposition of aquatic hydrogen. By combining the metal nanoparticles with MOFs, the composite structure of the novel metal @MOFs is obtained. This composite structure is beneficial to the rapid transfer and separation of photoelectron and hole, and the effective use of the photogenerated charge. The properties of photocatalytic hydrogen production are good. Furthermore, the effects of morphology and size on the properties of MOF based photocatalysts are also discussed. The main achievements in this paper are as follows: 1. metal nanoparticles, especially platinum (Pt) nanoparticles, are considered to be a particularly good electron acceptor, so the composite of metal nanoparticles and MOF The material generally shows higher photocatalytic performance than pure MOF. The porosity based on MOF does not affect proton transfer and the confinement effect on the nanoparticles. MOF can be used as an ideal template to study the effect of electron acceptor position on the photocatalytic performance. We designed and synthesized platinum (Pt) nanoparticles with an average particle size of 3nm and divided them evenly. The Pt@UiO-66-NH2 and Pt/UiO-66-NH2 materials were obtained separately on the internal or surface of the MOF material UiO-66-NH2 and used to study the performance of hydrogen production by visible photolysis. Compared with the simple UiO-66-NH2, the two Pt loaded composites showed significantly improved but significantly different photodissociation properties of hydrogen, indicating the relative position of Pt in MOF materials. The effect of Pt@UiO-66-NH2 on the photocatalytic efficiency has greatly shortened the electron transport distance and is more conducive to the separation of electron holes. Therefore, the higher photocatalytic efficiency of the relative Pt/UiO-66-NH2 is revealed. The implication of the catalytic mechanism further reveals that the.2. design and synthesis of two kinds of metals are further revealed by the ultrafast spectral and fluorescence spectra tests. A new type of photocatalytic hydrogen production system at the -MOF interface promotes the formation of optical electron flow and the performance of high hydrogen production. To achieve high hydrogen production performance of semiconductor materials, there are two special important I requirements: one is wide optical absorption range, and two is the effective separation and utilization of photogenerated electrons and holes produced by the semiconductor material by light excitation. The Schottky structure of MOF and Pt nanoparticles is beneficial to the electron transport and separation; meanwhile, the metal particles such as Au and Ag have good plasma resonance effect, and can realize the optical absorption in the visible and near infrared regions. The composite can widen the optical absorption range of MOF with MOF, and the Schottky structure and the plasma resonance effect are designed simultaneously. Combined with the same MOF material, the more effective transfer and separation of photogenerated electrons and holes will be achieved, and the recombination of photogenerated electrons and holes in the body phase can be reduced to achieve better photocatalytic hydrogen production by using the super high thermal stable MOF material, MIL-53 (A1), as a hard mold plate, and the introduction of all kinds of metal nitrate to its channel through high temperature. The method of temperature calcining nano scale etching has successfully guided the formation of porous metal oxide material. The metal oxide material obtained by this template has high specific surface area and can reproduce the pore structure of MOF in general. In the process of synthesis, the metal oxide can be further converted into metal sulfide, and the multistage channel metal can be obtained after the MOF template is removed. Sulfides. Compared with cadmium sulfide and nanoscale cadmium sulfide, the nanoscale multilevel channel cadmium sulfide obtained by this method has better photocatalytic performance in the reaction of photocatalytic cracking of aquatic hydrogen.

【学位授予单位】：中国科学技术大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O643.36;TQ116.2

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