Preparation And Photocatalytic Properties Of G-C₃N₄/TiO₂/NiWO₄ Composite Photocatalyst

TiO₂ is the most widely studied and applied semiconductor photocatalyst.However,due to its own defects（wide forbidden band can not be excited by visible light,high charge recombination rate,etc.）,it is necessary to improve the photocatalytic efficiency of TiO₂ by means of modification.Constructing heterojunction with other semiconductor materials is a simple and efficient method.In this paper,NiWO₄/TiO₂,g-C₃N₄/TiO₂ and g-C₃N₄/TiO₂/NiWO₄ composite photocatalysts were successfully prepared by a simple hydrothermal method.The characterization of composite photocatalysts were examined XRD,scanning electronic microscopy（SEM）,energy dispersive X-ray analysis spectroscopy（EDS）,transmission electron microscope（TEM）,Fourier Translation Infrared spectroscopy（FT-IR）,X-ray photoelectron spectroscopy（XPS）,ultraviolet-visible（UV-vis）absorption spectra,Photoluminescence（PL）and electrochemical impedance spectroscopies（EIS）.The results show that the NiWO4/TiO2 composites were successfully prepared by simple hydrothermal method.NiWO₄ nanoparticles encapsulated the surface of TiO₂microspheres to form a core-shell structure,forming a heterojunction between them,which effectively reduced the photo-generated electron-hole pair recombination and improved the separation efficiency of photogenerated electrons and holes.Compared with pure NiWO₄and TiO₂,NiWO₄/TiO₂ composites exhibit excellent photocatalytic degradation properties for RhB.Under visible light irradiation,5%NiWO4/TiO2 was used to degrade 96%of rhodamine B in water for 60 min,while only 37%of rhodamine B was removed at the same time under the catalysis of P25-TiO₂.Studies have shown that superoxide radicals are the main active species in the reaction system,and NiWO4/TiO2 composite photocatalysts have good chemical stability.The research shows that the composite composite g-C₃N₄/TiO₂ is a peanut-shaped heterojunction composite photocatalyst composed of two TiO2 microspheres combined with g-C₃N₄ as the connection point.During the photocatalytic reaction,the electrons on g-C₃N₄are transferred to the TiO₂ on both sides,which effectively inhibits the photo-generated electron-hole recombination and enhances the photocatalytic efficiency.Due to the presence of the heterojunction,the photoresponse range of the composite material is extended to the visible light region,which improves the utilization of sunlight by the material.Under visible light irradiation,99%of rhodamine B in water was degraded in 40 min.The results of the cycle experiments show that the g-C₃N₄/TiO₂ composite has good stability and can be recycled many times.The g-C₃N₄/TiO₂ composite photocatalyst was further compounded with NiWO₄,and the ternary heterojunction g-C₃N₄/TiO₂/NiWO₄ composite was successfully prepared.Good visible light absorption ability of NiWO₄ further enhances the photo-responsive ability of the ternary heterojunction composite in the visible region,and the ternary heterojunction further promotes charge transfer between materials and improves the separation of photogenerated electron-hole pairs.The efficiency in turn increases the visible light catalytic activity of the composite.Under visible light irradiation,the prepared ternary heterojunction can degrade 99%of rhodamine B in water for 30 min.Cyclic experiments show that the g-C₃N₄/TiO₂/NiWO₄ ternary heterojunction photocatalyst has good stability and shows potential application value.