Preparation Of WS₂/TiO₂ Nanocomposites And Study On Photogenerated Carriers Transport Properties

The solution of environmental pollution problems cannot be ignored,and semiconductor photocatalysis technology is a pollution control method which does not bring secondary pollution,and can be operated simplely with mild reaction conditions.TiO₂ is the most commonly used photocatalytic material,but its wide band gap and low quantum efficiency will cause low photocatalytic efficiency.The researchers found that the formation of TiO₂-based nanocomposites is an effective way to improve the solar utilization and photocatalytic efficiency of TiO₂photocatalysts.As a new two-dimensional material,the larger specific surface area of WS₂ nanosheets will provide more pairs of adsorption and reaction sites;its narrower band gap can greatly expand the light absorption range of photocatalyst.The good conductivity and the transport capacity of the photo-generated carriers inside the catalyst can be greatly improved;more importantly,due to the matching of the band structure,the formation of the WS2/TiO2 semiconductor heterojunction can effectively suppress the secondary recombination of the photo-generated carriers,making more photo-generated carriers participate in the photocatalytic reaction,so the photocatalytic efficiency of the material can be greatly improved.So far,there have been a lot of researches on heterojunction preparation and photocatalytic performance improvement,but the complex dynamics of photogenerated electrons and holes in heterojunctions have not yet been elucidated,especially at the interface of heterojunctions.The effects of the relaxation process,the capture process,the transfer process,and the composite process have not been studied at all.Therefore,this thesis mainly studies the internal carrier transport kinematics by constructing a structure-controlled WS₂/TiO₂ nanocomposites.The main contents are as follows:?1?In this study,the WS₂/TiO₂ nanocomposites structure control experiment was carried out to study the influence of growth conditions on the structure and morphology of nanocomposites during the synthesis of WS₂/TiO₂ nanocomposites by hydrothermal method.Then,the microstructure controlled WS₂/TiO₂ nanocomposites was successfully prepared by growth condition control.?2?The photocatalytic properties of WS₂/TiO₂ nanocomposites under visible and ultraviolet light were studied.The results show that the photocatalytic performance of WS₂/TiO₂ nanocomposites increases with the increase of WS₂ content under different illumination conditions.The difference is that under ultraviolet light,the introduction of a smaller amount??3%wt?of WS₂ can improve the photocatalytic performance of the composites,and the composites exhibits the best when the amount of WS₂ is 0.5%wt.Under visible light,when the amount of WS₂ is 5%,the composite exhibits the excellent visible light catalytic performance.?3?The defects of characterization,steady state and transient luminescence spectra were tested by the TW0.5 with the best UV-catalytic performance,TW5 with the best visible-light catalytic performance as representative with pure TiO₂ and pure WS₂ as reference.Further exploring the transport of internal carriers in nanoheterojunctions,the separation of photogenerated electron-hole pairs,and the lifetime of composites and carriers.The heterojunction are excited in different illumination environments to study the transport process and photocatalytic mechanism.It is found that there are a large number of oxygen defects at the interface of the heterojunction,and the existence of the defect state makes the migration,capture and secondary recombination processes of the photogenerated electron-hole pairs at the interface of the heterojunction in different light environments greatly different,so as the photocatalytic performance.Under ultraviolet light,the holes generated on TiO2 and the electrons generated on WS2 will flow to the heterojunction interface,and the defect state will capture electrons and holes in a large amount,thus increasing the probability of secondary quadratic.In this case,the defect state acts as a role of the new composite center is not conducive to the improvement of photocatalytic performance.While under visible light,since TiO₂ cannot be excited by visible light to generate electron-hole pairs,only the electrons generated on WS₂will swell at the heterojunction interface.In this case,the electrons captured by the defect state do not be secondary recombination,thus effectively suppressing the secondary recombination of photogenerated electron-hole pairs on WS₂,and the trapping of electrons by the defect state can extend the life of the electrons to"wait"until participating in the photocatalytic reaction,so the photocatalytic performance can be greatly improved.