Morphology Control Of Transition Metal Sulfides By Silica And Study On Their Photocatalytic Properties

Two-dimensional transition metal sulfides(TMDs)have unique electrical and optical properties.But their band gaps are usually 1-2 eV.The narrow band gaps are not conducive to their photocatalytic activity and are often used as the cocatalysts.In this paper,the morphology of TMDs was improved to prepare a porous structure to increase the active sites and to study the photocatalytic activity of the composite photocatalysts by compounding with the currently studied metal sulfide CdS.In our work,porous TMDs(WS2,MoS2)were prepared by SiO2 as the hard template and then combined with CdS procatalyst.And the conditions in the compounding process were optimized.Two kinds of different composite photocatalysts including porous WS2/SiO2-CdS and porous MoS2/SiO2-CdS were prepared,and then their photocatalytic properties were investigated by photocatalytic hydrogen production experiments under visible light irradiation.The research contents are as follows:1)Firstly,SiO2 microspheres,tungsten trioxide,thiourea and anhydrous sodium sulfite were mixed uniformly in different mixing modes,then WS2/SiO2 was prepared by high temperature calcination,and SiO2 not completely wrapped by WS2 was removed by concentrated alkali to obtain porous WS2/SiO2.The morphologies of the WS2/SiO2 porous structure were controlled by varying the molar amounts of the silicon source and the particle sizes of the hard template.The results showed that when the ultrasonic dispersion assisted method was used,the ratio of tungsten to silicon was 1/5,and the particle size of SiO2 was 350 nm,the hydrogenation activity of the composite catalyst by the porous WS2/SiO2 with CdS increased the most.2)The porous WS2/SiO2-CdS was prepared by combining the optimized porous WS2/SiO2-350 with the CdS precursors under hydrothermal conditions.Investigated the influencing factors in the composite process,including the loadings of porous WS2/SiO2-350,the amounts of potassium hydroxide added.And explored the effect of the volume concentrations of lactic acid.After optimizing these conditions,the highest hydrogen production activity of the porous WS2/SiO2-CdS composite samples was up to 51.82 mmol·h-1·g-1.3)Based on the above high temperature calcination method to prepare porous TMDs,the hydrothermal method was introduced for comparison.It was found that the MoS2/SiO2 porous cocatalyst prepared by hydrothermal method had higher photocatalytic activity after compounding with CdS,when compared with the high temperature calcination method.Then the morphologies of porous MoS2/SiO2 were further adjusted.When the molar ratio of molybdenum to silicon was 1/10 and the particle size of SiO2 was 350 nm,the porous morphology of MoS2/SiO2 made the performance of the composite catalyst achieve the best results.The optimized porous MoS2/SiO2-350 and CdS precursors were combined by hydrothermal reaction,and then some factors affecting the composite process were investigated,including porous MoS2/SiO2-350 loadings,CdS morphologies,and composite modes.The results showed that when the loading was 30%,the CdS was nanoparticle,and the one-step hydrothermal composite method was used,the hydrogen production activity of the synthesized porous MoS2/SiO2-CdS could reach 54.08 mmol·h-1·g-1.