基于SiC的优良新型可见光响应分解水催化材料的研究

发布时间：2018-04-15 17:09

  本文选题：碳化硅 + 分解水　； 参考：《北京科技大学》2016年博士论文

【摘要】：在半导体催化剂的作用下,利用太阳能分解水制备清洁能源氢能被认为是解决化石能源短缺和环境问题的有效途径之一。碳化硅(SiC)作为重要的非金属材料半导体,具有化学性质稳定、高电子迁移率等优良性质。其导带、价带的位置完全满足光分解水的要求,是理想的可见光响应分解水的催化剂。本工作以SiC为主体催化剂,围绕两个问题,一是SiC的光生电子和空穴在催化剂内部的分离、转移、复合是如何进行的,二是如何能更好延长SiC光生电子和空穴的存在时间,促进其光生电荷的分离,抑制其复合。通过BiVO4及其量子点、还原石墨烯以及金属助剂的定向负载对SiC进行表面修饰,探究上述两个问题在这些催化剂中的作用行为,从而深入地了解SiC自身在光催化分解水反应过程中的催化反应机理。具体研究结果如下：(1)采用化学沉淀法利用BiVO4对SiC进行修饰,复合物中异质结的构建促进了其光生电子和空穴的分离,增加了复合物中光生电子的寿命,催化性能最佳的样品SiC/BiVO4(1:1)的光生电子寿命达到4.34 ns,相比SiC光生电子寿命3.56 ns,提高了21%。通过Pt分子探针实验检测,复合物中的光生电子按照Z型电子转移体系进行传输。在FeCl3为牺牲剂,可见光(L420nm)下反应4h,SiC/BiVO4(1:1)催化剂的产氧量为131.7 μmol,产氧速率为658.8μmol·h-1·g-1,其在420nm处的量子效率达到了1.04%。(2)将GO引入SiC/BiVO4复合物催化剂中。此催化剂中,光生电子仍以Z型传导路径进行传输。GO的引入,进一步增加了光生电子寿命,催化性能最佳的样品SiC/GO-1%/BiVO4的达到4.67 ns,相比SiC,提高了31.2%。引入的GO,在反应过程中被部分还原为RGO,其优异的导电性能,提高了光生电子在此复合物中的转移速率。相同反应条件下,SiC/GO-1%/BiVO4的产氧量为195.7 μmol,产氧速率为988.2 pmol·h·g-1,在420 nm处的量子效率达到了1.56%。(3)采用水热法将量子点QD-BiVO4定向沉积于SiC的C面上。这种定向沉积进一步增加了复合物中光生电子的寿命,催化性能最佳的样品SiC/BiVO4(1:0.1)的光生电子寿命达到4.96 ns,相比SiC提高了39.5%。在复合物催化剂中,光生电子仍然按照Z型电子转移体系进行传输。QD-BiVO4定向沉积在SiC的C面上,缩短了Z型电子传导路径的距离,传输效率更高。相同反应条件下,SiC/QD-BiVO4(1:0.1)催化剂的分解水产氧量为413.8 μmol,产氧速率为2069μmol·h-1·g-1,其在420nm处的量子效率达到了3.1%。(4)采用光沉积法利用Pt修饰了SiC, Pt在SiC表面是定向分布的,呈正价态Ptδ+。其在SiC的表面与Si相互作用形成Pt-Si键。Pt-Si键的形成构建了一个电子转移的通道,促进了光生电子由SiC表面加速、定向转移到Pt的表面参与光还原产氢反应,从而有效地抑制了光生电荷的复合。在Na2S和Na2SO3作为牺牲剂,可见光(λ420 nm)下反应3h, Pt/SiC (PD)催化剂的分解水氢气的最大产量为41.3μL,产氢速率为1376 μL·h-1·9-1,在420 nm处的量子效率为1.81%。(5)通过第一性原理计算和实验结果,SiC的Si面是光生电子的富积面,C面是光生空穴的富积面。利用Pt、MnO2(Pt作为还原反应助剂,MnO2作为氧化反应助剂)作为目标物进行了验证。Pt定向沉积在SiC的Si面上,充当光生电子的捕获中心和光还原反应的活性中心,MnO2定向沉积在SiC的C面上,充当光生空穴的捕获中心和光氧化反应的活性中心。Pt和MnO2在SiC的表面上实现了空间分离,有利于地促进了SiC表面光生电子和空穴的分离。在牺牲剂的存在下,光催化产氢反应,Pt/SiC/MnO2,3 h的反应中,氢气的最大产量为396μL,产氢速率为2640 μL·h-1·g-1。光催化产氧反应,Pt/SiC/MnO2样品3h的反应中,氧气的最大产量为36.8μL,产氧速率为245.7 μL·h-1·g-1。(6)将Z型光催化体系引入SiC中,以Pt/SiC为产氢催化剂,WO3为产氧催化剂,I-/IO3-为氧化还原离子对,构建了Z型光催化全解水的反应体系。负载的Pt的最佳含量为0.5%(wt),反应溶液的最佳pH值为3。在整个Z型光催化体系反应过程中,还原H+产氢反应步骤是整个催化反应过程的决速步。此Z型光催化反应体系在4h的光照反应中,其催化分解水产生氢气的最大产量为25.1μL,氧气的产量为12.4μL,在420nm处的量子效率为0.021%。氢气和氧气按照体积比为2:1的计量比产出,实现了以SiC为基的可见光下的全解水。
[Abstract]:In the semiconductor catalyst, using solar energy water decomposition preparation of hydrogen energy is considered to be one of the effective ways to solve the shortage of fossil energy and environmental issues. Silicon carbide (SiC) as an important semiconductor non metallic materials, has stable chemical properties, excellent properties of high electron mobility. The conduction band and the valence band fully meet photodecomposition water requirement is the ideal response to visible light catalyst. The decomposition of water using SiC as the main catalyst, about two issues, one is the separation of SiC, the photogenerated electrons and holes in the catalyst transfer inside the composite, is how the two is how to extend the SiC light time better the electron and hole, promote the separation of photogenerated charges, inhibition of the composite. Through the BiVO4 and quantum dots, reduced graphene and directed metal additives load on the SiC surface modification, the inquiry Two problems in the behavior of these catalysts, and in-depth understanding of SiC itself in the catalytic reaction mechanism of water in the reaction process of photocatalytic decomposition. The main results are as follows: (1) precipitation of SiC was modified by BiVO4 using the chemical construction, promote the separation of photogenerated electrons and holes heterojunction in the compound, increases the lifetime of photogenerated electrons in the compound, the best catalytic performance of sample SiC/BiVO4 (1:1) of the photogenerated electron lifetime reached 4.34 ns, compared to the SiC electron lifetime of 3.56 ns, increased by 21%. through experimental inspection of Pt molecular probe, complexes of photoinduced electron transfer in Z type of electron transfer system. As the sacrificial agent in FeCl3, visible light (L420nm) under the reaction of 4h, SiC/BiVO4 (1:1) catalysts for oxygen production is 131.7 mol, oxygen production rate of 658.8 mol - H-1 - g-1, the 420nm in the quantum efficiency of 1.04%. (2) GO The introduction of SiC/BiVO4 composite catalyst. This catalyst, the photogenerated electrons to the conduction path of Z type transmission.GO, further increase of the electron lifetime, sample SiC/GO-1%/BiVO4 best catalytic performance of up to 4.67 ns, compared to SiC, 31.2%. increased the introduction of GO, in the reaction process was partially reduced to RGO and its excellent conductive properties, improve the photoinduced electron transfer rate in this complex. Under the same reaction conditions, SiC/GO-1%/BiVO4 oxygen production is 195.7 mol, oxygen production rate was 988.2 pmol - H - g-1, the quantum effect at 420 nm rate of 1.56%. (3) by hydrothermal method quantum dots QD-BiVO4 directional deposition in SiC C surface. The directional deposition further increases the life of the photogenerated electron compound, sample SiC/BiVO4 best catalytic performance (1:0.1) of the photogenerated electron lifetime reached 4.96 ns, compared to SiC increased 39.5%. in Composite catalyst, the photogenerated electrons are still in accordance with the Z type electron transfer system for transmission directional.QD-BiVO4 deposited on SiC C face, shorten the Z electronic conduction path distance, higher transmission efficiency. Under the same conditions, SiC/QD-BiVO4 (1:0.1) decomposition of aquatic oxygen catalyst is 413.8 mol, the rate of oxygen production 2069 mol - H-1 - g-1, the 420nm in the quantum efficiency of 3.1%. (4) by using Pt modified by SiC light deposition method, Pt is a directional distribution on the surface of SiC positive valence Pt 8. The SiC with Si on the surface of the interaction between the formation of Pt-Si bond formation of.Pt-Si bond construction an electron transfer channel, promotes photogenerated electrons by SiC surface acceleration, directional transfer to the surface of Pt in light hydrogen reaction, so as to effectively suppress the recombination of photogenerated charge. As a sacrificial agent in Na2S and Na2SO3, visible light (a 420 nm) under the reaction of 3H, Pt/Si C (PD) catalyst for decomposition of hydrogen water maximum output is 41.3 L, the hydrogen production rate of 1376 L - H-1 - 9-1, the quantum efficiency at 420 nm 1.81%. (5) by first principle calculation and experimental results, Si SiC is the accumulation of surface electron, C surface is photohole rich area. By using Pt, MnO2 (Pt as a reaction agent, MnO2 as oxidation additives) as the object is verified.Pt directional deposition on SiC Si surface, acting as electron capture center and photoreduction activity center, MnO2 SiC C in directional deposition on the surface, a photohole capture center and photooxidation of the active center of.Pt and MnO2 in SiC on the surface to realize spatial separation, is conducive to promote the separation of SiC surface photoinduced electrons and holes. In the presence of a sacrificial agent, photocatalytic reaction, Pt/SiC/MnO2,3 h reaction. The maximum hydrogen production 閲忎负396渭L,浜ф阿閫熺巼涓，

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