锡基、钽基半导体光催化材料制备及光解水制氢性能研究

发布时间：2018-03-25 12:23

本文选题：光催化　切入点：光解水制氢　出处：《内蒙古大学》2017年硕士论文

【摘要】：能源危机和环境污染是当今人类面临的两大主要挑战,尤其是化石燃料的需求量逐渐增加,探索和开发清洁、安全、可持续新型能源迫在眉睫。氢能作为清洁能源受到广泛关注,在众多制氢方法中,半导体光解水制氢具有环境友好、高效等优点,存在潜在应用价值。SnO2作为一种典型n型半导体,由于其优异的光学性能在光催化和太阳能电池领域中受到广泛关注。然而SnO2用于光解水产氢领域的研究报道寥寥无几,主要是由于其光生电子空穴复合率较高、带隙较宽。因此抑制光生载流子复合率、减小禁带宽度,对提高SnO2可见光制氢催化活性是极为重要的。CsTaWO6是一种高效光催化剂,但是纯相的CsTaWO6带隙较宽,限制了其在可见光催化中的实际应用。通过掺杂、复合、贵金属沉积等方法调控其光催化性能使其对见光响应已成为半导体光催化领域的研究热点之一。本论文以锡基氧化物和CsTaWO6为研究对象,通过离子掺杂和半导体复合来提高材料的光学性能及光催化活性,结合实验及理论计算研究了半导体能带结构和光催化活性调控机制。主要内容如下:(1)通过调控反应温度合成一系列非化学计量比SnOx,实现了可见光下高效分解水制氢。合成样品的化学组成和元素价态通过XPS测试得以确认,测试结果表明SnOx样品中同时存在Sn2+和Sn4+。室温合成的SnOx样品产氢活性最好,而随着反应温度升高,SnOx样品产氢性能逐渐降低。这是由于催化剂中减少的Sn2+导致还原驱动力降低。非化学计量比SnOx中较多的表面羟基和Sn2+以及相对较负的导带电位,是实现可见光响应和高效分解水制氢的关键因素。本研究为设计开发可见光产氢新型材料提供有效指导。(2)沉淀法合成了不同比例Sn2+自掺杂SnO2纳米材料,对制备的SnO2-x样品进行红外和拉曼等测试,结果表明SnO2-x与未掺杂SnO2(Sn4+)样品相比晶体结构并未发生明显改变。瞬态光电流测试表明SnO2-x具有较强的可见光响应能力。可见光下分解水制氢测试结果表明,随着Sn2+掺杂量增加,SnO2-x光解水产氢量逐渐增加。Sn2+自掺杂SnO2可以有效减小SnO2的禁带宽度,同时催化剂中大量的表面羟基氧使得催化剂的导带位置上移,催化剂的还原能力增强,因此光解水产氢活性增强。(3)采用简单的高温固相法合成了纯相的CsTaWO6光催化剂,进一步合成了 CsTaWO6/g-C3N4复合光催化剂。CsTaWO6/g-C3N4光电流明显强于CsTaWO6,且阻抗较小。在可见光照射下光解水制氢实验结果证明,复合型光催化剂的光催化活性有明显提高。由于二者能级匹配,光致激发g-C3N4产生的光生电子可有效的转移到CsTaWO6的导带上,从而实现了光生电荷有效分离,提高了光催化活性。
[Abstract]:The energy crisis and environmental pollution are the two major challenges facing mankind today, especially the increasing demand for fossil fuels, the exploration and development of clean and safe, As a clean energy source, hydrogen energy has received extensive attention. Among many hydrogen production methods, semiconductor photolysis water hydrogen production has the advantages of environmental friendliness, high efficiency and so on. There are potential applications of .SnO2 as a typical n-type semiconductor, which has attracted extensive attention in the field of photocatalysis and solar cells due to its excellent optical properties. However, there are few reports on the application of SnO2 in the field of photodissociation of aquatic hydrogen. The main reason is that the photogenerated electron hole recombination rate is higher and the band gap is wider. Therefore, it is very important to increase the catalytic activity of SnO2 visible light hydrogen production by inhibiting the photogenerated carrier recombination rate and decreasing the band gap. CsTaWO6 is a kind of high efficiency photocatalyst. However, the wide band gap of pure phase CsTaWO6 restricts its practical application in visible light catalysis. The photocatalytic response of noble metals to photocatalytic properties has become one of the hot topics in semiconductor photocatalysis. In this thesis, tin based oxides and CsTaWO6 were used as research objects. The optical properties and photocatalytic activity of the materials are improved by ion doping and semiconductor recombination. The regulation mechanism of semiconductor energy band structure and photocatalytic activity was studied in combination with experiments and theoretical calculations. The main contents are as follows: 1) A series of non-stoichiometric SnOxs were synthesized by controlling the reaction temperature, and the efficient decomposition of water under visible light was achieved. Hydrogen. The chemical composition and valence states of the synthesized samples are confirmed by XPS, The results show that both Sn2 and Sn4 exist in the SnOx samples. The SnOx samples synthesized at room temperature have the best hydrogen production activity. However, with the increase of reaction temperature, the hydrogen production performance of Sno _ x samples decreases gradually, which is due to the decrease of Sn2 in the catalyst resulting in a decrease in the reduction driving force. There are more surface hydroxyl groups and Sn2 and a relatively negative conduction band potential in non-stoichiometric SnOx than in SnOx. This study provides an effective guide for the design and development of novel visible light hydrogen production materials. Different ratios of Sn2 self-doped SnO2 nanomaterials were synthesized by precipitation method. The prepared SnO2-x samples were tested by IR and Raman spectroscopy. The results show that the crystal structure of SnO2-x is not obviously changed compared with that of undoped SnO2(Sn4. The transient photocurrent measurement shows that SnO2-x has a strong visible light response. With the increase of doping amount of Sn2, the hydrogen content of hydrolysate increases gradually. Sn2 self-doped SnO2 can effectively reduce the band gap of SnO2. Meanwhile, a large amount of surface hydroxyl oxygen in the catalyst can make the conduction band position of the catalyst move up, and the reduction ability of the catalyst is enhanced. Therefore, a pure phase CsTaWO6 photocatalyst was synthesized by a simple high temperature solid state method. The photocurrent of CsTaWO6/g-C3N4 composite photocatalyst, CsTaWO6 / g-C3N4, was obviously stronger than that of CsTaWO6, and the impedance was lower. The photocatalytic activity of the composite photocatalyst was obviously improved under visible light irradiation. The photogenerated electrons generated by photoexcited g-C3N4 can be transferred to the conduction band of CsTaWO6 effectively, thus realizing the effective separation of photogenerated charges and improving the photocatalytic activity.
【学位授予单位】：内蒙古大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36;TQ116.2

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