Preparation And Mechanism Of Metal Modified Carbon Nitride Photocatalyst

Graphite-phase carbon nitride（g-C₃N₄ or CN）photocatalysts has been widely used in the degradation of organic pollutants in water.To address the underutilization of solar energy and high photogenerated carriers’recombination rate for this type of catalyst,three kinds of g-C₃N₄ based photocatalysts have been prepared by means of element doping and heterojunction construction.Their morphology,structure,photochemical properties,degradation properties and mechanism have been studied.Compared with the CN-based photocatalysts reported in other literatures,the three CN-based photocatalysts prepared in this paper all show better photocatalytic activity.The contents are as follows:（1）K⁺doped g-C₃N₄（CN-K_x）have been fabricated via one-step thermal condensation through the simultaneous heating of urea and KOH.XRD,SEM,TEM and EDX mapping analysis demonstrate that K⁺is successfully doped into g-C₃N₄.The FTIR and XPS analysis results confirm the formation of cyano groups on the surface of the g-C₃N₄.PL spectroscopy,EIS and the transient photocurrent response indicate the synergistic effect of the cyano groups and K⁺,which obviously enhances the separation of carriers.As results,the optimized sample of CN-K_0.009 exhibits the Rhodamine B（Rh B）degradation rate is 0.0542 min^-1,which is 4.14 times that of pristine CN.Further band analysis indicates that the bandgap of CN-K_0.009 is reduced from 2.67 e V（for CN）to 2.59 e V,leading to the enhanced light absorption capacity.Trapping experiments reveal that superoxide radicals（?O₂^-）and holes（h⁺）dominate the oxidation process of Rh B.More importantly,the CN-K_0.009 can also be expanded to efficient degradation of many organic pollutants,such as basic fuchsin（91.7%）,Congo red（85.7%）,and tetracycline（74.0%）.（2）Mo-Ni bimetallistic sulfide/g-C₃N₄ nanosheets（MNS/CNNS-x）Schottky junction is constructed via a facile ultrasound-assisted method.Photoelectrochemical investigations indicate that the bandgap alignments of CNNS and MNS favor the formation of Schottky junction between the two materials,which facilitates separation and accumulation of carriers via Schottky barriers for boosting the transformation of O₂ toward superoxide radicals.As a result,the optimal MNS/CNNS-10 exhibits a good Rh B degradation rate(0.0950 min^-1),which is 3.6 times higher than that of CNNS.The Rh B removal rate is as high as 100%within 30 min,outperforming many CN-based photocatalysts reported.（3）Ag modified Bi₂Mo O₆/g-C₃N₄ all-solid-state Z-scheme heterojunction（Ag/BMO/CN）is prepared by solvothermal and photodeposition methods with the help of nickel foam.The Ag/BMO/CN has been used for the degradation of Rh B under visible light.The photodeposition of Ag nanoparticles on the surface of BMO/CN prepared in-situ effectively enhance the visible light absorption and improve the charge transfer efficiency.Ag/BMO/CN shows excellent catalytic activity in Rh B degradation,and its degradation rate reaches to0.0739 min^-1.The trapping experiments show that?O₂^-,h⁺and hydroxyl radicals（?OH）decisive roles in the catalytic reaction,and the Ag nanoparticles act as the charge transfer medium between BMO and CN.Moreover,the Ag/BMO/CN also displays good stability after five consecutive degradation cycles.