Synthesis Of Cadmium Sulfide Composites With Dual Co-catalysts And Their Photocatalytic Performance For Hydrogen Evolution

As the development of society with the increasing economic activities,environmental pollution and resource scarcity are serious problems.In order to solve these problems,photocatalytic technology has made great progresses in water splitting and pollutant degradation.Photocatalysis can convert solar energy into clean energy and eliminate most of pollutants.CdS is a promising photocatalyst due to its suitable band gap energy for absorbing light and negative conduction band potential for hydrogen generation from water.CdS has poor photocatalytic stability because of its rapid photochemical corrosion.To improve photocatalytic activity and stability of CdS,many effective ways have been taken including element doping and composite formation with co-catalysts.2D transition metal dichalcogenides(TMDs)such as ReS2 and MoS2 have suitable band gap and special nonlinear optics,which can be used as efficient co-catalysts.This thesis focused on syntheses and photocatalytic performance of ternary composites photocatalysts of CdS with MoS2,ReS2 and NiS as co-catalysts.The main contents are as follows:(1)CdS@ReS2 composites were synthesized with cadmium acetate Cd(CH3COOH)2,ammonium perrhenate(NH4ReO4)and thiourea(CH4N2S)as precursors by a one-step hydrothermal method.Photocatalytic activities of CdS@ReS2 composites were studied for hydrogen generation from water via adjusting the amount of rhenium precursor.Known from photocatalytic reaction results and DRS characterization,the CdS@ReS2 composite(7.5%,the molar percentage of Re/Cd)exhibited the highest hydrogen production rate and the strongest absorption ability of light.(2)NiS@CdS@ReS2 composites were synthesized by a one-step hydrothermal method.Different amounts of Re and Ni introduced were compared on photocatalytic activities of the composites.With the molar ratio of nickel acetate Ni to Cd precursor as 1/9 and the molar percentage of Re to Cd precursor as 5%,the NiS@CdS@ReS2 composite demonstrated the highest hydrogen production rate as 138.96 mmol·g-1h-1.These ternary composites exhibited the increased absorption intensity of visible light.A dual Z-scheme pathway mechanism was proposed to illustrate the rapid separation and transfer of photo-excited electron-hole pairs in NiS@CdS@ReS2 composite.(3)Several MoS2/CdS@ReS2 composites were prepared via a two-pot hydrothermal method.MoS2 formed in the first stage and then CdS@ReS2 nanoparticles in-situ formed on it.When the molar ratio of ammonium molybdate(NH4)6MO7O24 to Cd precursor was 3/7 and the molar percentage of Re to Cd precursor was 5%,the MoS2/CdS@ReS2 composite exhibited the highest hydrogen generation rate up to 171.96 mmol·g-1h-1 and good stability in four recycle reactions.The formed heterojunctions between ReS2,CdS and MoS2 provided a dual Z-scheme structure to improve photocatalytic activity for hydrogen generation.