Synthesis And Photocatalytic Activity Study Over Contaminants Of G-C₃N₄-based Photocatalysts

As a non-metallic semiconductor material with narrow bandgap?2.6 eV?,graphite carbon nitride?g-C₃N₄?has attracted tremendous attention in environmental applications owing to its nontoxicity,low cost,thermal and chemical stability.But the photocatalyst also has some problems of low quantum efficiency due to high photoelectron-hole recombination rate,low oxidation capacity and photogenerated holes mobility.In this paper,g-C₃N₄ was modified by semiconductor composites and chemical exfoliation method to promote the separation efficiency of photogenerated electrons and holes and improve its photocatalytic activity.Ultrathin g-C₃N₄ nanosheets with different bandgaps were prepared by a simple chemical exfoliation method at room temperature and were characterized by various techniques.The obtained ultrathin nanosheets performed the lateral size from hundreds of nanometers to several micrometers with the thickness from 2 nm to 3 nm.The optimal ultrathin nanosheets?CN4h?could decompose 100%of phenol in 90 minutes while the corresponding phenol degradation of bulk g-C₃N₄ is only 43%,and its apparent photocurrent density was 1.5 times higher than that of the bulk g-C₃N₄ under visible-light irradiation.It was considered that the enhanced photocatalytic activity of CN4h sample may benefit from the appropriate band structure and the high efficiency of photons absorption of ultrathin nanosheets.g-C₃N₄/Ag/Ag₃PO₄ was synthesized by a simple in situ precipitation method at room temperature and was characterized by various techniques,XRD,FT-IR,SEM,TEM,DRS and PL.The XRD and FT-IR patterns revealed that the composite consisted of g-C₃N₄,Ag and Ag₃PO₄.The SEM results showed that rhombic dodecahedron of Ag₃PO₄ finely coated on the surface of the g-C₃N₄ sheet.The photocatalytic activity of the composite with different g-C₃N₄/Ag/Ag₃PO₄ ratio was evaluated by the degradation of phenol and gaseous isopropanol under visible-light irradiation.Most composites exhibited enhanced photocatalytic activity than that of either g-C₃N₄ or Ag₃PO_4,in which the optimal g-C₃N₄/Ag/Ag₃PO₄ photocatalyst(AC_1.0)could dramatically decompose phenol in five minutes with a degradation rate of 1.13 min^-1,almost 60 and 2.5 times higher than that of pure g-C₃N₄ and Ag/Ag₃PO₄,respectively.After three cycling runs,the AC_1.0photocatalyst still maintained high photocatalytic activity.It was further verified that the g-C₃N₄/Ag/Ag₃PO₄ composite worked under Z-scheme mechanism in the process of the photocatalysis by the reactive species trapping experiments.The photocatalytic activity of AC_1.0 sample towards gaseous organic compound such as isopropanol was tested as well,which obtained 63%removal and 45%transformation of acetone upon 4 hours irradiation.