Controlled Synthesis Of Polymetallic Sulide And Its Perfomance In Photocatalytic Hydrogen Evolution From Water

Hydrogen energy has become the most ideal green energy in this century because of its green environmental protection,high energy and renewable advantages.Photocatalytic hydrogen production technology is a widely studied green hydrogen production measure,which can convert endless solar energy into environmentally friendly hydrogen by using semiconductors.Among various semiconductor materials for photocatalytic hydrogen production,polymetallic sulfides stand out due to their narrow band gaps,suitable conduction band positions and unique photoelectric properties.Among them,the most studied materials are ZnIn₂S₄,Cu In₂S₄,Cd In₂S₄,Ag In₅S₈,Mn_xCd_1-xS,etc.However,the high recombination rate of photogenerated carriers and photocorrosion phenomenon limit their further development.In this thesis,ZnIn₂S₄,Cd In₂S₄ and Mn_0.5Cd_0.5S,as the research objects,are modified by means of morphology control,construction of heterojunctions,and loading of cocatalysts to improve their photocatalytic hydrogen production performance.The main research contents and conclusions are as follows:1.The Mn_0.5Cd_0.5S/Ti₃C₂ photocatalyst is composed of Ti₃C₂ nanosheets with Mn_0.5Cd_0.5S particles on its surface.First,Ti₃C₂ nanosheets are obtained by etching commercial Ti₃Al C₂ with hydrofluoric acid and ultrasonic stripping process.Then Mn_0.5Cd_0.5S particles were deposited on the surface of Ti₃C₂ by hydrothermal method to obtain Mn_0.5Cd_0.5S/Ti₃C₂ composites.The hydrogen production test results show that the hydrogen production rate of the optimal composite(Mn_0.5Cd_0.5S/Ti₃C₂-10)is 9 times higher than that of Mn_0.5Cd_0.5S particles,which is because the introduction of Ti₃C₂nanosheets can promote the separation of photogenerated carriers and increase the specific surface area of the composites,which can provide more active sites for photocatalytic reactions.2.The Co₉S₈/ZnIn₂S₄ heterojunction is composed of ZnIn₂S₄ nanoflowers and Co₉S₈nanoparticles dispersed on its surface.First,ZnIn₂S₄ nanoflowers assembled from nanosheets were prepared by solvothermal method,and then Co₉S₈ nanoparticles were deposited on the surface of ZnIn₂S₄ by further hydrothermal process to obtain Co₉S₈/ZnIn₂S₄ heterojunction.The characterization results show that the loaded Co₉S₈nanoparticles can promote the migration of photogenerated electrons from ZnIn₂S₄ to Co₉S₈ in the composites,which improved the separation efficiency of photogenerated electrons and holes,inhibited the recombination of photogenerated carriers,and thus improved the hydrogen evolution performance of catalysts.The hydrogen evolution test results show that all Co₉S₈/ZnIn₂S₄ composites have higher performance of hydrogen evolution than that of ZnIn₂S₄,and the best photocatalyst（3%Co₉S₈/ZnIn₂S₄）has a hydrogen evolution rate of 126.7μmol h^-1 and a quantum yield of 8.28%.And additionally,3%Co₉S₈/ZnIn₂S₄ has extremely high stability where its hydrogen evolution rate had hardly any decreased after 6 cycles.3.The Ni（OH）₂/Cd In₂S₄ photocatalyst is composed of Cd In₂S₄ hollow flower ball and Ni（OH）₂ particles.Cd In₂S₄ hollow flower ball were obtained by solvothermal method,then Cd In₂S₄ was added to the alkaline solution containing nickel precursor.Then,Ni（OH）₂/Cd In₂S₄ composites were obtained through co-precipitation process.The photocatalytic hydrogen evolution test results show that the hydrogen evolution rate of Ni（OH）₂/Cd In₂S₄ is 5.9μmol h^-1,which is 8.55 times that of Cd In₂S₄.As a cocatalyst,Ni（OH）₂ increases the specific surface area and light absorption intensity of the catalyst,improves the separation efficiency and transfer ability of charge carriers,and thus improves the photocatalytic activity.