Preparation Of Manganese Cadmium Sulfur-based Photocatalysts And Hydrogen Evolution Performance

New ternary sulphides combining broadband semiconductors with narrow-band photocatalysts are attracting attention for their superior light absorption properties and tunable forbidden band positions.The Mn_xCd_1-xS composite system,formed by combining Mn S with Cd S,is one of the most promising materials for photocatalytic hydrogen production due to its tunable energy band structure,excellent visible light absorption capacity and strong photocatalytic properties.However,photocatalytic hydrogen evolution performance of Mn_xCd_1-xS photocatalysts under visible light irradiation is still limited by the rapid complexation of photo-induced electron-hole pairs.Various strategies have been employed to further improve the photocatalytic hydrogen production performance of Mn_xCd_1-xS,such as transition metal doping,heterostructure building and co-catalyst modification.In this thesis,NiCo₂Se₄/Mn_0.5Cd_0.5S,CuSe/Mn S/Mn_0.5Cd_0.5S,Cu₂MoS₄/Mn S/Mn_0.5Cd_0.5S composites were prepared by constructing heterojunctions and co-catalyst modification strategies with the aim of obtaining efficient and stable Mn_xCd_1-xS-based composite photocatalysts to enhance the Mn_xCd_1-xS photocatalytic hydrogen production performance.The main research elements of this thesis are as follows:（1）NiCo₂Se₄/Mn_0.5Cd_0.5S（NCS/MCS）composite photocatalysts were synthesized using a two-step hydrothermal method.The results show that the NCS/MCS photocatalytic system has good photogenerated carrier separation and transfer capability.The photocatalytic hydrogen evolution efficiency of the NCS/MCS composite was strongest when the molar ratio of NCS reached 4%,and the hydrogen evolution efficiency reached 20 mmol h^-1 g^-1,which was higher than that of pure MCS(12.2 mmol h^-1 g^-1).The composite exhibited excellent cycling and structural stability in three hydrogen production cycle stability experiments and in a comparison of pre-and post-cycle XRD patterns.（2）CuSe/Mn S/Mn_0.5Cd_0.5S（CS/MCS-0.5）composites were prepared by in situ synthesis.The prepared materials showed highly efficient photocatalytic hydrogen evolution efficiency under visible light and in aqueous Na₂S-Na₂SO₃ solution,with photocatalytic hydrogen evolution efficiency reaching up to 24.7 mmol g^-1 h^-1,4.1times higher than that of MCS-0.5(5.99 mmol h^-1 g^-1)and 6.9 times higher than that of pure Cd S(3.59 mmol h^-1 g^-1).The addition of CuSe effectively improves the photogenerated carrier separation efficiency of the CS/MCS-0.5 composite as well as weakening the composite of photogenerated electron-hole pairs.This work provides an effective way to improve the photocatalytic activity of MCS-0.5 using transition metal selenide co-catalysts.（3）Cu₂MoS₄/Mn S/Mn_0.5Cd_0.5S（CMS/MMCS）composites were synthesised using a hydrothermal impregnation method.The photocatalytic hydrogen evolution performance of MMCS was improved by combining CMS in lamellar form with MMCS in short rods.The hydrogen evolution efficiency of the CMS/MMCS composite reached 9.7 mmol g^-1 h^-1,which is 2.3 times higher than that of MMCS.The addition of CMS reduces the complexation of photogenerated carriers and enhances the separation and transport of photogenerated carriers.Figure[36]table[6]reference[130]...