Vacancy-regulation And Photocatalytic Performance Of Ultrathin Two-dimensional Molybdenum Disulfide Based

The increasingly serious problem of global environmental pollution urgently needs to be solved by efficient and environmental protection technologies.Among all these environmental remediation technologies,photocatalytic technology stands out because of its advantages of low energy consumption,low cost,cleanness and high efficiency.Photocatalysis can achieve the purpose of deep cleaning of contaminants by the redox-reaction with the photogenerated electrons or holes produced from semiconductor excited by solar energy.Based on the advantages of abundant reserves,adjustable band gap and excellent adsorption capacity,MoS₂ has broad application prospects in environmental purification.In this thesis,MoS₂ is selected as the research object.The ultrathin two-dimensional（2D）MoS₂nanosheets and corresponding composites were prepared by the solid phase micro domain method.Their phases and micro-structures are optimized and their vacancy regulations were performed.The defect-rich ultrathin 2D MoS₂ nanosheets and MoS₂/Mo O_X composites were obtained by mechanical force solid state method.Subsequently,by characterizing the phase composition,microscopic morphology,photocatalytic performance and photoelectrochemical performance of above photocatalysts,the types,distribution,relative concentration of defects were analyzed,and photocatalytic mechanisms were studied.1.Preparation of ultrathin 2D MoS₂ nanosheets and MoS₂/Mo O_X composites using solid phase micro domain method.Mo O₃ powders and S powders were used as the source of molybdenum and sulfur,respectively.The effects of Mo/S raw material molar ratio,ball-to-powders mass ratio,annealing temperature,and annealing atmosphere on the phase and morphology of these products were investigated.The results show that ultrathin 2D MoS₂nanosheets with approximately 12 layers were obtained through the optimized process,which is that the mixed materials with a Mo/S raw material molar ratio of 1:6 and a ball-to-material ratio of 45:1,were milled for 24 h at a speed of 580 rpm·min^-1,finally annealed in a nitrogen atmosphere at 600°C for 2 h.In addition,in the process of adjusting the molar ratio of Mo/S raw materials,when the amount of the reducing agent S is insufficient,the MoS₂/Mo O_Xcomplex can also be harvested.2.Research on vacancy regulation and photocatalytic performance of ultrathin 2D MoS₂nanosheets.The mechanical force solid phase method is used to construct the vacancy of the ultrathin 2D MoS₂ nanosheets,the types and concentration ratios of defects can be adjusted by modulating the amount of ascorbic acid.When the molar ratio of MoS₂/ascorbic acid is 1:1,Optimized as D-MoS₂-3,it was able to reduce Cr（Ⅵ）at an efficiency of 98.9%in 3 h via visible light photocatalysis.And the normalized apparent photocatalytic rate constant is 15.4times higher than that for P-MoS₂.In addition,the S defects have two forms:S point-defects and stripping-defects.The S point-defects with high-concentration are more likely to become the recombination centers of photo-generated carriers,while S stripping-defects can become electron-rich centers so as to promote the separation of photo-generated carriers.3.Research on the vacancy regulation and photocatalytic performance of MoS₂/Mo O_Xcomposites.The MoS₂/Mo O_X composites were prepared at the molar ratio of Mo/S raw materials of 1:4,and the vacancy regulation was achieved by the mechanical force solid phase method.By adjusting the amount of ascorbic acid,the type and ratio of S and O vacancies can be adjusted accordingly.When the mass ratio of MoS₂/Mo O_X composite to ascorbic acid is1:1.1,D-MS-2 with an O vacancy concentration of 52.6%can be obtained.Optimized as D-MS-2,it was able to reduce Cr（Ⅵ）at an efficiency of 80.9%in 3 h via visible light photocatalysis.Its apparent photocatalytic rate constant is around 12.6 times higher than that for MS,and its normalized photocatalytic apparent rate constant is approximately 1.7 times as that of D-MoS₂-3.The results show that the coupling of O vacancies and photogenerated carriers play an important role in promoting the process of photocatalysis.