Preparation Of Highly Dispersed Heterometallic Sulfides For Hydrogen Production Application Of Photocatalytic Decomposition Of Water

The development of photocatalysts with wide spectral response and high carrier separation efficiency is the key to realize the efficient conversion of solar energy and large-scale hydrogen production.The MoS₂is a potential ideal photocatalyst due to its low hydrogen adsorption free energy,high absorption of visible light and low price.However,the characteristics of its multilayer stacking resulted in less exposure of the catalytic active center of MoS₂and the poor alkaline resistance of a single MoS₂.These defects greatly hinder the application of such catalysts in the field of photocatalytic water decomposition and hydrogen production.An effective strategy to improve the catalytic activity and stability of a single MoS₂material is formed by introducing a high dispersion,thereby increasing the number of effective active sites and optimizing the morphology of the MoS₂material.In the conventional technical route for the preparation of heterometal sulphides,it is difficult to obtain highly dispersed hetermetal sulfides because the selected isometal salt materials are discrete from each other and have different sulfur nucleation rates,so that different metal sulfide components are isolated during growth.POMs（Polyoxometalates）can simultaneously provide multiple metal sources at the molecular level by regulating their constituent metal elements,which is an ideal pre-assembly platform for heterometallic materials（precursor）.Accordingly,using molybdenum-based polyacid as the precursor and introducing secondary metal materials with high photocatalytic activity such as Cd or Ni,we obtain"one-step"or"step-by-step"water thermal sulfide catalysts,and study the systematic structure and morphology of characterization,and photocatalytic decomposition of water hydrogen production performance test.The main work is listed as follows:On the one hand,composite（CdS-MoS₂-1）was prepared by a“one-step”hydrothermal synthesis technology with Keggin phosphomolybdic acid,metal salt cadmium nitrate and sulfur source thiourea as raw materials.On the other hand,an unprecedent crystalline was prepared by hydrothermal synthesis from phosphomolybdic acid,cadmium nitrate and 2,2’-bipyridyl(C₁₀H₈N₂):[Cd(C₁₀H₈N₂)₃](HPMo₁₂O₄₀)(abbreviated as Cd ^II-PMo₁₂).Then,we used it as a preassembly platform and prepared a composite（CdS-MoS₂-2）by a“step-by-step”hydrothermal vulcanization procedure.The structure,morphology,optical properties and band gap width of the two composites were systematically characterized.Under the 350 nm to 780 nm light,the photocatalytic experiment results show that CdS-MoS₂-1 and CdS-MoS₂-2 composites have high hydrogen production rates(1190μmol g^-1h^-1and 1815.5μmol g^-1h^-1),however,the catalytic hydrogen production rate of MoS₂and CdS was only 479μmol g^-1h^-1and 889μmol g^-1h^-1.The excellent photocatalytic activity of CdS-MoS₂-2 is mainly due to the selection of Cd ^II-PMo₁₂precursor,which promotes the vulcanreaction of Cd and Mo metals in a certain proportion,so as to control the formation of highly dispersed heterometallic sulfide,which helps to play the synergistic effect between CdS and MoS₂.At the same time,the unique nanotube morphology of CdS-MoS₂-2 is composed of a large number of nanosheets,which can fully expose the reactive reaction sites and provide more reaction interfaces,effectively promote the transmission of photogenerated electrons,and finally makes the composite have excellent catalytic properties.The classical Waugh type polyacid crystal（NH₄）₆(NiMo₉O₃₂)·8H₂O（abbreviated as NiMo₉）is directly used as the bimetallic source,a composite precursor（Ni₃S₂-MoS₂）was prepared.Then,on this basis,CdS was loaded into Ni₃S₂-MoS₂to obtain Ni₃S₂-MoS₂-CdS three metal composites.The structure,morphology,optical properties and band gap width of the composites were characterized.Namely,the hydrogen production rate of the NiMo₉catalyst is only800μmol g^-1h^-1,the Ni₃S₂-MoS₂and Ni₃S₂-MoS₂-CdS composites have excellent hydrogen production rates and excellent stability(up to 2770μmol g^-1h^-1and 2873μmol g^-1h^-1,respectively).Among them,the excellent photocatalytic activity of Ni₃S₂-MoS₂-CdS can be attributed to the composite has high catalytic performance due to the synergistic effect of CdS,MoS₂and Ni₃S₂.