以无机亚磷酸为牺牲剂光化学法制备无定形Ni(OH)2助催化剂用于光催化产氢

随着环境污染和能源危机的加剧,发展可持续能源迫在眉睫.氢气被认为是可以替代化石能源的最有前途的能源之一,且光催化分解水产氢是一种可以将太阳能转化为氢能的环境友好的方法.n型半导体材料石墨C3N4 (g-C3N4)是一种被广泛用作光催化产氢的吸光材料,然而,纯g-C3N4的光生电子–空穴对会迅速重组,其光催化活性非常低.负载助催化剂能够有效抑制光生载流子的复合,是提高光催化产氢速率的有效方法.助催化剂的作用是将电子和空穴转移给相应的反应物,因此除了助催化剂和光吸收材料之间的能级匹配之外,助催化剂负载的位置也是非常重要的.通过常规方法制备的助催化剂一般是随机分布的,而光化学方法可以将助催化剂沉积在电子和空穴的出口处,从而有利于下一步的光催化反应.使用光化学沉积法,可以通过光化学氧化制备氧化型助催化剂,也可以通过光化学还原制备还原型助催化剂.光化学法是还原贵金属助催化剂的一种常用方法,但是对于制备非贵金属助催化剂来说,它仍然是一种相对新颖的方法.光化学法目前正处于发展阶段,依然缺乏成分调控的手段,因此我们致力于发展相对准确、可控的光沉积方法.H2PO2^–由于其特殊的性质被用于光化学还原过渡金属,然而,在H2PO2^–存在下形成的颗粒非常大且高度结晶,这可能抑制光催化剂的活性.本文设计了一种利用其他磷酸盐光沉积合成光催化剂的新方法,旨在制备可控的弱结晶和小尺寸的助催化剂,以提高产氢活性.首先以不同磷酸盐为原料制备催化剂,发现以H2PO3^–为无机牺牲剂制得的催化剂的光催化产氢活性非常突出,而且制得的催化剂具有无定形结构并且平均尺寸约为10 nm.通过XRD, XPS等多种表征,证实了该条件下得到的产物是Ni(OH)2/g-C3N4.同时,通过设计对照实验,发现在使用H2PO3^–作为牺牲剂, NiCl2作为镍源, g-C3N4作为光吸收材料条件下才能制得效果最好的催化剂.然后对光沉时间,原料添加量,产氢牺牲剂等多组条件进行了优化,得到最优的复合光催化剂Ni(OH)2/g-C3N4(4.36wt%)的光催化产氢速率为13707.86μmol·g^-1·h^-1,甚至高于Pt–4.36wt%/g-C3N4的活性(11210.93μmol·g^-1·h^-1).最后,通过PL, TR-PL, SPV, I-V等多种表征对反应机理进行探究,结果表明,光催化产氢性能提升主要原因是Ni(OH)2的负载可以有效提高光生电荷的分离和转移效率,抑制光生电子对的重组.

Controllable photochemical synthesis of amorphous Ni(OH)2 as hydrogen production cocatalyst using inorganic phosphorous acid as sacrificial agent

Loading of cocatalysts can effectively inhibit the recombination of photogenerated carriers in photocatalysts and greatly improve the photocatalytic hydrogen production rate. Cocatalysts can be deposited at the outlet points of electrons using a photochemical method, which is beneficial for the following photocatalytic hydrogen production reaction. H2PO2^– has been used in the photochemical reduction of transition metals because of its special properties. However, the particles formed in the presence of H2PO2^– are very large and highly crystalline, which may inhibit the activity of photocatalysts. In this study, we designed a new method for synthesizing photocatalysts by photodeposition using some other phosphates, aiming to prepare controllable weakly crystalline and small-size cocatalysts to improve the hydrogen production activity. The cocatalyst prepared using H2PO3^– as an inorganic sacrificial agent has an amorphous structure and an average size of about 10 nm. The optimal photocatalytic hydrogen production rate of the obtained Ni(OH)2/g-C3N4(4.36 wt%) is 13707.86 μmol·g^-1·h^-1, which is even higher than the activity of Pt-4.36 wt%/g-C3N4(11210.93 μmol·g^-1·h^-1). Mechanistic studies show that loading of Ni(OH)2 can efficiently accelerate the separation and transfer efficiency of photogenerated charge carriers.