Preparation And Application Of MoS₂ QDs And MoS₂ QDs/rGo Composites

Molybdeum disulfide（MoS₂）is one of transition metal dichalcogenides（TMDs）with graphene-analogous structure.When the size is controlled to be less than 10 nm,zero-dimensional MoS₂ quantum dots（MoS₂ QDs）can be obtained.Because of quantum confinement and edge effects,MoS₂ QDs possess unique optoelectronic and catalysis properties.Graphene is a hexagonal lattice structure two-dimensional carbonaceous material composed of a single layer of carbon atoms.Due to its special physical,chemical and excellent structural properties,it is widely used in optoelectronics,biomedicine and environmental protection.At present,it is still necessary to optimize the preparation method of MoS₂ QDs and MoS₂ QDs/rGO composites to overcome the problems in the preparation process,such as complicated operation,time consuming,low quantum yield and so on.In this thesis,MoS₂ QDs was prepared by bottom-up photo-induced oxidation etch-assisted hydrothermal method for the first time,and one pot method was used to synthesize MoS₂QDs/rGO composites.The morphology and size of MoS₂ QDs and MoS₂ QDs/rGO composites were characterized and applied to photocatalytic degradation of organic dyes.The main research contents and results of thesis are shown as follows:1.Photoinduced oxidation etching-assisted hydrothermal method to prepare MoS₂ QDsA series of MoS₂ QDs were prepared with sodium molybdate and L-cysteine as precursors,reaction time and illumination time were controlled,and MoS₂ QDs were characterized by SEM,TEM,AFM,EDS,FTIR,UV-vis and PL.The results showed that the dot-plate hybrid structure of nanosheet and spherical QDs were obtained respectively by the hydrothermal reaction method for 4 h and 36 h（average particle size of 2.12 nm）.After being subjected to ultraviolet light for 5 h,the nanosheet was etched to a spherical structure with an average particle size of 1.74 nm and a thickness of about 0.8 nm.The relative fluorescence quantum yield of MoS₂ QDs prepared by photoinduced oxidation etching-assisted hydrothermal method was 9.2%,which was higher than that of 5.7%obtained by hydrothermal reaction for 36 h.2.Application of MoS₂ QDs in photodegradation of organic dyesAs-prepared MoS₂ QDs were used as catalysts to simulate visible light degradation of dye methylene blue（MB）.For MoS₂ QDs obtained from photoinduced oxidation etching-assisted hydrothermal method,MoS₂ QDs and MoS₂ nanosheet prepared by hydrothermal method,the photodegradation behaviors exhibited first order kinetics,and the slope of kinetics curve were 0.0282 min^-1,0.0182 min^-1 and 0.0098 min^-1,the degradation rate of MB were 97%,85%and 79%within 90 min respectively.The possible reason was that the MoS₂ QDs had smaller size,resulting in the improvement of catalytic capacity.3.MoS₂ QDs/rGO composites were prepared by one-pot solvothermal method and used for catalytic degradation of organic dyesThe MoS₂ QDs/rGO composites were prepared by one-pot solvothermal method using sodium molybdate,L-cysteine,N,N-dimethylacetamide and graphene oxide（GO）as raw materials.The results of SEM and TEM graph analysis showed that MoS₂ QDs were uniformly attached to rGO surface,and the average size of MoS₂ QDs on rGO surface was1.18 nm.The photocatalytic results showed that the degradation rate of Rh B reached 97%within 80 min and that of MB reached 98%within 60 min.The slopes of the first-order reaction kinetic curves were 0.0236 min^-1 and 0.0313 min^-1.In addition,MoS₂ QDs/rGO composites catalyst can be cyclic used,and the degradation rate can still reach above 90%after 10 cycles.