Preparation And Catalytic Performance Study Of G-C₃N₄ Composites

With the development of industry and urbanization of human beings,environmental pollution problems are becoming more and more serious,among which dye wastewater discharge and antibiotic pollution are the most significant problems.Photocatalysis,which uses green solar energy to degrade organic pollutants,is considered to be one of the most promising technologies.Finding suitable catalytic materials and promoting the separation of photogenerated carriers is one of the methods to improve the catalytic performance of catalysts.The graphitic phase carbon nitride material g-C₃N₄ has been widely concerned in the field of catalysis due to its unique energy band structure and stable physicochemical properties,but its potential direct application is greatly limited by its wide band gap for visible light response,high photogenerated electron-hole recombination rate and low carrier migration rate.In this work,a facile way of doping graphitic phase carbon nitride g-C₃N₄ with carbon quantum dots CQDs,metal Cu elements,and metal oxides Ni Co₂O₄,respectively,was proposed to prepare three composite catalysts to explore their photocatalytic applications.（1）The carbon quantum dot-doped g-C₃N₄ composite catalysts CQDs/g-C₃N₄were prepared by a co-precipitation calcination method.and the catalytic activity of CQDs/g-C₃N₄under dark conditions was investigated by taking advantage of the intrinsic piezoelectric properties of g-C₃N₄.The experimental results demonstrated that the CQDs/g-C₃N₄ composite catalyst achieved 92.5%degradation of methylene blue within 30 min.The catalytic effect was enhanced relative to the pure g-C₃N₄ catalyst.The effects of different CQDs contents and different stirring speeds on the catalytic activity of CQDs/g-C₃N₄ were investigated.The piezoelectric effect of g-C₃N₄ was verified by PFM.FPT and VASP calculations confirmed the synergistic charge transfer effect of CQDs.（2）A one-step calcination method was employed to prepare the metal Cu element-doped composite catalyst Cu/g-C₃N₄.and the catalytic activity of the Cu/g-C₃N₄composite catalyst was evaluated by the degradation of tetracycline under light conditions.The degradation efficiency of the Cu/g-C₃N₄ composite catalyst for tetracycline reached 85%within one hour,and the catalytic activity was enhanced compared to that of pure g-C₃N₄.（3）The composite catalyst of Ni Co₂O₄/g-C₃N₄ doped with metal oxide Ni Co₂O₄was prepared by the ball milling method,and the catalytic activity of Ni Co₂O₄/g-C₃N₄composite catalyst was investigated under ultrasonic,light and ultrasonic synergistic light conditions.The degradation efficiency of Ni Co₂O₄/g-C₃N₄ on tetracycline was 90%under the condition of ultrasonic synergistic light irradiation in fifteen minutes.The microstructure and physicochemical properties of the three g-C₃N₄ composite catalysts were analyzed by TEM,XRD,FT-IR,XPS,and specific surface area analysis tests.To investigate the reasons for the enhancement of catalytic efficiency of the three composite catalysts,the optical properties of the three g-C₃N₄ composite catalysts were studied by photoluminescence test and UV-vis diffuse reflection,and the carrier separation efficiency of the three composite catalysts was measured by electrochemical test,and the results proved that the construction of composite structures accelerated the photogenerated electron-hole transfer and effectively improved the three g-C₃N₄composite catalysts’catalytic activity.The catalytic efficiency of graphite-phase carbon nitride g-C₃N₄ was greatly improved by three different doping strategies,and the prepared g-C₃N₄ composite catalysts have broad application prospects in dye degradation,antibiotic degradation and other water pollution treatment.