Electronic Structure And Photoelectrocatalytic Properties Of MoS₂/TiO₂ Heterostructures

The two-dimensional layered material MoS₂ exhibits excellent semiconducting properties in transition metal dichalcogenides(TMDCs),and its band gap is adjustable from 1.3 to 1.8 e V.MoS₂ absorbs a wide range of wavelengths,therefore compensates for the shortcomings of other semiconductor materials for low absorption of visible light.In addition,MoS₂ nanomaterials have a larger specific surface area and expose more catalytically active sites,so there is great potential in the field of photoelectrocatalysis.However,the traditional MoS₂ has fewer active sites and poor conductivity,which limits its application in the field of catalysis.MoS₂,which is designed more catalytic active sites and possesses high electron transport efficiency,has become the focus of researchers.In order to overcome these problems,MoS₂ is often combined with other semiconductor materials or precious metal materials to modify MoS₂,so that the prepared MoS₂ has the properties of composite materials.TiO₂ material has the characteristics of chemical stability,strong corrosion resistance and low cost,but its band gap is wide,and it is only limited to absorb the ultraviolet part of natural light.Therefore,MoS₂ and TiO₂ materials are compounded to make up for their respective shortcomings.Synergistic effect of heterojunction can significantly improve the catalytic ability.In addition,in order to improve the conductivity of MoS₂,the Au nanorods are used to modify the MoS₂ nanomaterials,and the Au nanorods can accelerate the electron transport rate,thereby significantly improving the catalytic performance.After Au nanorod modification,the change of interface electronic structure and the catalytic mechanism of the material are studied.(1)The TiO₂ nanotubes are successfully prepared by anodic oxidation method.The effect of growth time and growth voltage on the morphology of TiO₂ nanotubes is studied.It is found that the longer the growth time,the longer the nanotube length and the larger the growth voltage,the larger the nanotube diameter.At the same time,the effect of annealing temperature on TiO₂ is studied by annealing of TiO₂ nanotubes.By comparison,the catalytic performance of nanotubes is best when the annealing temperature is 500°C.(2)The MoS₂/TiO₂ heterostructures is prepared by hydrothermal synthesis,and the loading of MoS₂ nanosheets can be changed by adjusting the growth time.It is found that when the amount of MoS₂ is small,the photocatalytic performance of the heterojunction is better.The MoS₂/TiO₂ heterostructures is prepared by chemical vapor deposition(CVD),and the morphology of the MoS₂ nanosheet is changed by controlling the amount of precursor and the growth temperature.It is found that the size and quantity of MoS₂nanosheets will affect the catalytic ability.When the size of the nanosheet is about 800 nm and the amount is large,it has better catalytic performance and higher catalytic ability than the hydrothermal method.It is indicates that the coupling of MoS₂ and TiO₂ prepared by CVD is very good,which enhances the photoelectrocatalytic ability of MoS₂/TiO₂heterostructures.(3)After the Au nanorods modified the MoS₂/TiO₂ heterostructures,the electrocatalytic performance is improved and the overpotential is reduced by 130 m V.From the XPS results,it is found that when the MoS₂/TiO₂ sample is annealed in the S atmosphere,the Fermi level shifts in the conduction band direction.After the Au nanorods modified the a-MoS₂/TiO₂-S sample,the Fermi level shifts toward the valence band,which causes the Fermi level shifts due to the n-type doping of the Au nanorods modified heterojunction,indicating that electrons in the Au nanorods are transferred to the MoS₂nanosheets.The recombination of MoS₂ with the Au plasma structure results in a rearrangement of the Fermi level between Au and MoS₂,which changes the transmission path of excitons and"hot"electrons.The charge separation efficiency of the Au/MoS₂/TiO₂sample is significantly improved by the auxiliary action of Au plasma.