Study On The Synthesis And Photocatalytic Performance Of POMs/g-C₃N₄ Composites

Recently,the great capacity of semiconductor photocatalyst to solve the problem of environmental pollution has been widely recognized.As a novel metal-free polymer,g-C₃N₄ is considered to be an ideal photocatalyst of handling with water pollution,due to advantages of facile synthesis,suitable band structure?².7 eV?,nontoxicity,good thermal stability and chemical stability.It has applications in many fields,such as produce H₂,biomedical detection,solar cells,and so on.It has been a hotspot in the field of photocatalysis research.However,pure g-C₃N₄ has a lot of shortcomings including low quantum efficiency,rapid recombination of photo-generated electron–hole pairs,a small specific surface area,which restrain its photocatalytic performance.Polyoxometalates?POMs?are a class of transition metal-oxygen cluster compounds,has specially physical and chemical properties,and can be used as good electron trapping agent.So we are looking forward to g-C₃N₄ combine with POMs.Polyoxometallates can act as good electron capture agent due to its unique structural features.The photogenerated electrons on the conduction band of g-C₃N₄ can be captured by polyoxometallates to promote the effectively segregation of the photogenerated electron-hole pairs.And thereby enhanced the photocatalytic activity of g-C₃N₄.In this work,g-C₃N₄ powder was synthesized by thermal condensation method with urea as the precursor.Two novel SiW12/g-C₃N₄ and PMo₁₂/g-C₃N₄ composite photocatalyst fabricated by impregnation of polyoxometallates on g-C₃N₄ surface were presented.The structure,morphology and optical absorption properties of PMo₁₂/g-C₃N₄ composite photocatalysts were well characterized by TGA,XRD,UV-vis-DRS,SEM,FT-IR,TEM,XPS and PL.Results showed that the PMo₁₂ nanoparticles equably dispersed on the surface of g-C₃N₄,and primary Keggin structure remained intact.Under visible-light irradiation???420 nm?,the PMo₁₂/g-C₃N₄ photocatalyst displays higher photocatalytic activity than pure g-C₃N₄ for the degradation of methyl orange.Among,It was found the PMo₁₂/g-C₃N₄ hybrid(mass ratio of PMo₁₂/g-C₃N₄=15:1)and H₂O₂ can completely degrade MO nearly 100 % within only 12 min.A conceivable photocatalytic mechanism was speculated.The enhancement of photocatalytic activity could put down to effectively hinders the recombination of electron-hole pairs of g-C₃N₄ by the loading of PMo₁₂.And the decomposition of H₂O₂ can furnish plentiful the hydroxyl radical?·OH?.The structure and properties of SiW12/g-C₃N₄ photocatalysts were also characterized by a series of characterization methods.The photocatalytic testing result indicates that the SiW12/g-C₃N₄ composite displays higher photocatalytic activity than pure g-C₃N₄ under visible-light irradiation???420 nm?.Among the hybrid composites,the SiW12/g-C₃N₄?1:3?catalysts possesses the optimum activity for the decolorization of RhB.The decolorization of RhB was 98.0% for 120 min of visible-light irradiation.Under the mediation of H₂O₂?2 mL,30 wt.%?,the decolorization of RhB was 97.7% for only 24 min of visible-light irradiation.The enhanced photocatalytic activity of SiW₁₂/g-C₃N₄ hybrids could be ascribed to effectively retards the recombination of electron-hole pairs of g-C₃N₄ by the loading of SiW₁₂.And the decomposition of H₂O₂ produced the hydroxyl radical?·OH?also played a vital role.