Preparation And Photocatalytic Redox Reaction Properties Of Metal Sulfide Nanocomposites

Nowadays,photocatalysis is considered to be one of the most potential ways to deal with the energy and environmental crisis.However,traditional photocatalysis has low efficiency and tends to be catalyzed with a single function,resulting in low utilization of photogenerated electrons and holes.In recent years,in addition to using different methods to improve photocatalysts and improving photocatalytic efficiency,the research on dual-functional catalytic systems that can increase the utilization of photogenerated electrons and holes has also attracted more and more attention.The thesis taked metal sulfide nanocomposites(CdS/g-C₃N₄,NiS/Zn₃In₂S₆ and Ni₁₂P₅/Zn In₂S₄)as the research objects,and explored its photocatalytic redox activity under visible light.The monomer and the catalyst with the best activity were also characterized in detail.In addition,the influencing factors of the activity,the reason for the enhancement of photocatalytic activity and the possible transfer mechanism of photogenerated carriers are concluded combined with experiments and theoretical calculations.The main research is as follows:1.Novel 2D/2D relative p-n heterojunction CdS/g-C₃N₄ with Z-scheme（orS-scheme）was fabricated by in-situ growing ultrasmall 2D CdS nanoflakes on the surface of 2D g-C₃N₄ nanosheets.2D/2D CdS/g-C₃N₄ composites show high photocatalytic reduction（H₂ evolution）and oxidation（selective oxidation of5-hydroxymethylfurfural（HMF）into 2,5-diformylfuran（DFF））activities,which are about 26.8 timesand 3.51 times higher than individual g-C₃N₄ and are about 4.4 times and 2.39 times higher than individual CdS,respectively.The optimized 2D/2D heterojunction structure with proper band configuration and suitable heterojunction interfacecan improve photoexcited charge carriers separation spatially and transfer to the ideal reaction sites.Furthermore,the mechanisms including direction and inner impetus of the photoexcited charge separation and transfer in the composite photocatalyst are proposed and verified by experimental and computational analyses.2.We have fabricated noble metal-free 2D/2D-3D NiS/Zn₃In₂S₆（NiS/ZIS）hierarchical architecture by one-step method for efficiently visible-light-driven dehydrogenation of HMF into H₂ and DFF with high selectivity.The separation of photoexcited electrons（e^-）and holes（h⁺）can be promoted in this dual-function photocatalysis process,both e^-and h⁺are involved in the desired conversions,i.e.the generation of H₂ and the production of value-added chemicals,respectively.The rates of H₂ evolution and DFF production for 1%NiS/ZIS can reach up to 120 and 129μmol g^-1 h^-1,around 41.4 and 35.8 times higher than that of pure ZIS,respectively.The conversion was favored not only by thermodynamics,but also kinetics.The H₂-evolution rate in HMF solution was up to 1090.9 times than in water.Additionally,the DFF selectivity could reach up to 94.1%.Moreover,the photocatalytic H₂-evolution rate of 1%NiS/ZIS is about 3.9,4.6 and 1090.9 times higher than those of 1%Pt/ZIS,1%NiS-ZIS（prepared by the traditional two-step method）and 1%NiS/ZIS for water splitting,respectively.The PEC and TRPL tests together with theoretical calculationstrongly demonstrate that the advantages of NiS as a cocatalyst.3.2D/2D-3D Ni₁₂P₅/Zn In₂S₄（NP/ZIS）heterostructures are prepared via zinc vacancies(V_Zn)engineering and cocatalyst modification.NP/ZIS showed remarkable reactivity and stability for benzaldehyde production and H₂evolution by the photocatalytic selective conversion of benzyl alcohol.Under simulated sunlight illumination,the rates of benzaldehyde production（selectivity of 91.5%）and H₂evolution could increase up to 1190.3 and 1104.9μmol h^-1,respectively.Compared to pure water splitting and individual ZIS,the thermodynamics and kinetics of H₂production over 7%NP/ZIS are enhanced by 15825.6 and 12.2 times,respectively.Moreover,notably,NP/ZIS also shows promising capability for photocatalytic CO₂reduction and N₂ fixation coupled with organic synthesis.