Study On Preparation Of N-deficient G-C₃N₄-based Composite And Its Performance For Photocatalytic Degradation Of Antibiotics In Water

The abuse of antibiotics in agriculture,aquaculture,animal husbandry and other industries has resulted in a large amount of antibiotic residues in water.It is urgent to find a simple,efficient,and green method to degrade antibiotics in water.Semiconductor photocatalysis technology has been widely used in the degradation of organic pollutants in water.Graphite phase carbon nitride?g-C₃N₄?is a non-metallic semiconductor photocatalyst with promising application.In order to overcome the defects of the pure phase g-C₃N₄ such as insufficient light absorption,small specific surface area and rapid recombination of photo-generated electron-hole pairs to improve its photocatalytic efficiency for degrading antibiotics.In this study,g-C₃N₄ was modified by coupling structural defects of the catalyst with the constructing heterojunction.Dy VO₄ with a narrow band gap,KNb O₃ with a wide band gap and co-catalyst Co P nanoparticles were selected to be combined with nitrogen defects g-C₃N₄?g-C₃Nx?to construct the three heterojunction composite Dy VO₄/g-C₃Nx,KNb O₃/g-C₃Nx and Co P/g-C₃Nx.The as-prepared catalysts were characterized by scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,ultraviolet-visible diffuse reflectance spectroscopy?DRS?and photoluminescence spectroscopy?PL?.The photocatalytic degradation of TC under visible-light irradiation was conducted to evaluate the photocatalytic activity of the obtained catalyst.The possible charge transfer mechanism and degradation path of TC were speculated.The results are as follows:?1?Dy VO₄/g-C₃Nx composite photocatalyst was successfully synthesized by simple precipitation calcining.Dy VO₄/g-C₃Nx has a narrow band gap,high conductivity and obvious visible light collection capacity,showing good visible-light driven activity for the degradation of TC.Especially,10%Dy VO₄/g-C₃Nx own the best photocatalytic performance,resulting in 92%of degradation efficiency of TC within 60 min under visible light irradiation.which exhibits significantly higher photocatalytic activity than pure phase g-C₃N_4,Dy VO₄,g-C₃Nx and complex Dy VO₄/g-C₃N₄.The improvement of photocatalytic activity is mainly due to its defect structure and formation of heterojunction,which improves the absorption of visible light and the separation efficiency of photogenerated electron-hole pairs.?2?KNb O₃/g-C₃Nx composite was prepared by impregnation.The band gap energy of the composite catalyst is reduced from 3.3 e V of pure phase KNb O₃ to 2.78 e V,which greatly enhances the absorption ability of visible light and overcame the shortcoming that the broad band gap semiconductor KNb O₃ was only excited by ultraviolet light.KNb O₃/g-C₃Nx has excellent photocatalytic activity for degradation of TC under visible light.It can degrade 84%of TC within 120 min.The kinetic constants of degradation of KNb O₃/g-C₃Nx are 125 times,10.71 times and 3.75 times as high as that of KNb O₃,g-C₃N₄ and g-C₃Nx,respectively.?3?N-defective g-C₃N₄ and Co P co-catalyst were combined to synthesize Co P/g-C₃Nx composite photocatalyst by in-situ precipitation-phosphorylation method.The synergistic effect of N-defects in g-C₃N₄ structure and Co P cataly not only effectively expand the visible light absorption range,but also greatly improve the separation efficiency of photogenerated electron-hole pairs,thus significantly enhances its photocatalytic activity.Within 120 min,the degradation rate of TC catalyzed by Co P/CNx under visible light irradiation was 97%,which are 6.84 and 4.33 times as high as that of pure g-C₃N₄ and N defect g-C₃N₄,respectively.