Enhancement Of Visible Light Photocatalytic Activities Of Heterojunction Semiconductor Photocatalysts

Semiconductor photocatalysis technology is a promising environmental remediation technology which can be used to treat the inorganic or organic pollutants in the environment.The two key issues in the development of this technology are improving the photocatalytic activity and spectral response.To construct a heterojunction semiconductor with phase matching,which can not only expand the wide range of semiconductor response to the visible light,but also promote the separation of the light induced charge.In this study,three kinds of g-C₃N₄ as well as g-C₃N₄/BiVO₄,g-C₃N₄/TiO₂,CeO₂/TiO₂,Bi₂MoO₆/TiO₂ and Bi₂O₃/TiO₂ composite catalysts were prepared,respectively.The purpose is to build photocatalytic materials with low-cost,high efficiency,wide range of application,and phase matching,hoping to be widely used in environmental restoration.The Graphitic-like carbon nitride?g-C₃N₄?photocatalysts were synthesized by a facile chemical pyrolysis method,which was based on the self-condensation of melamine,urea and thiocarbamide,respectively,to generate g-C₃N₄.Heterojunctions of g-C₃N₄ and BiVO₄ were synthesized using a facile solvent evaporation method.The formation of BiVO₄/g-C₃N₄ composites was confirmed by XRD,FT-IR,SEM and UV-vis DRS analyses.The photocatalytic activities for?Rhodamine B?degradation were investigated under visible light irradiation.The photocatalytic activity of g-C₃N₄ prepared by urea was higher than that of g-C₃N₄ prepared by melamine and thiourea,which was attributed to its larger specific surface area and higher oxidation capacity.The heterojunction composites exhibited higher photocatalytic activity than pure g-C₃N₄ or BiVO₄.The results showed a obvious removal efficiency for RhB,and the optimal sample with a BiVO₄ content of 10% exhibited high efficiency than pure BiVO₄ and g-C₃N₄,and 10wt% BiVO₄/CN-U showed the highest photocatalytic activity.The enhanced photocatalytic activity of BiVO₄/g-C₃N₄ composite can be attributed to the intimate coupling between the two host substrates,resulting in an efficient charge separation.g-C₃N₄/TiO₂,CeO₂/TiO₂,Bi₂MoO₆/TiO₂ and Bi₂O₃/TiO₂ heterojunction photocatalysts were prepared by a solvent thermal method.The formation of composite catalysts was confirmed by XRD,UV-vis DSR.The photocatalytic activities for Cr???reduction or phenol oxidation were investigated under visible light irradiation.Compared with the pure catalysts,the composite photocatalysts exhibited excellent photocatalytic activities in both Cr???reduction and phenol oxidation.This is mainly due to the closely contacted semiconductor photocatalyst material and good matching band position,thus the photo-induced carriers were separated effectively and improved the activity of the composite photocatalyst.In the case of photocatalytic redox reaction,heterojunction photocatalyst with composited by TiO₂ and semiconductor with narrow band gap,had a certain regularity for phenol oxidation or Cr???reduction.The composite photocatalyst had higher reducing capacity when the conduction band position of the narrow band gap semiconductor was more negative,while it had higher oxidizing capacity when the valence band position was more positive.