Mechanistic Investigation Of Enhanced CoWO₄/g-C₃N₄ Heterojunction Photocatalytic Charge Transfer By Energy Level Modulation Strategy

The photocatalytic system based on graphitic carbon nitride（g-C₃N₄）activating peroxymonosulfate（PMS）under visible light irradiation has been widely used for treating emerging pollutants.However,the high recombination rate of photogenerated carriers severely inhibits the degradation efficiency of photocatalysts.Constructing heterojunctions can effectively promote the separation of photogenerated electrons and holes.Previous studies have shown that Co WO₄ is a semiconductor material with a narrow band gap and high carrier mobility,which can form heterojunctions with g-C₃N₄,thereby achieving the expansion of spectral response range and the promotion of charge transfer.However,an interfacial potential barrier will be generated at the interface after the two contacts,and the high carrier complexation rate inside g-C₃N₄ greatly hinders the transmission of electrons and holes.Therefore,based on the Fermi level matching principle,this paper has successively modified the energy band structure of Co WO₄and g-C₃N₄,and strengthened the charge transfer capability between the interfaces of heterojunction and the internal of g-C₃N₄.This work has established a theoretical foundation for the directional construction of efficient photocatalysts for activating PMS.The specific contents are as follows:（1）In order to enhance the charge transfer capability between the heterojunction interfaces,Co WO₄/g-C₃N₄ heterojunction catalyst with matched band structure was precisely constructed by adjusting the energy band position of Co WO₄ through the introduction of ammonia.According to a series of characterizations,the morphology,structure and chemical composition of the composite materials were studied.The degradation experiment results showed that the degradation performance and mineralization performance of tetracycline hydrochloride（TCH）could respectively reach 99.9%and 59.8%within 10 min in PMS/vis system.The above-mentioned excellent decontamination performance was attributed to the strong photogenerated carrier separation and transfer induced by the band-matched Co WO₄ and g-C₃N₄.In addition,the degradation performance of band-matched Co WO₄/g-C₃N₄ for ciprofloxacin（CIP）and norfloxacin（NOF）was more excellent than that of non-band-matched Co WO₄/g-C₃N₄ reported in the literature.A series of experimental results showed that·O₂^-,¹O₂ and SO₄^·-were the main active species.（2）In order to enhance the charge transfer capability inside g-C₃N₄,Co WO₄/GD-C₃N₄ catalyst was successfully constructed by gradient doping of graphitic carbon rings(C_gra)in g-C₃N₄ based on the previous experiment.Theoretical calculations and experimental results show that the gradient doping results in the gradual rearrangement of the energy level structure in GD-C₃N₄.The built-in electric field（BIEF）formed between different layers promoted the transfer of photogenerated charges from the inner layer to the surface,thereby achieving efficient separation of internal photogenerated carriers.Compared with the degradation efficiency of TCH by Co WO₄/g-C₃N₄ within5 min（88.3%）,the degradation efficiency of Co WO₄/GD-C₃N₄ increased to 99.9%。...