Construction Of Mesoporous G-C₃N₄/Transition Metal?Fe,Co,Cu?/Ag₃PO₄ Heterojunction System And Study On The Mechanism Of Visible Light Catalytic Oxidation

g-C₃N₄ as a visible light catalyst for degrading pollutants has some shortcomings,such as small BET surface area,high photoelectron-hole pair recombination rate and weak catalytic oxidation ability of g-C₃N₄ heterojunction.In order to solve these problems and improve photocatalytic performance and stability,in this paper,some strategies were proposed,such as g-C₃N₄ synthesized by a specific preparation methods with large BET surface area,Z-type heterojunction with strong oxidant and doped transition mental.The catalytic performance of the g-C₃N₄ photocatalyst can be improved by changing the preparation method and compounding with a strong oxidized semiconductor.In this paper,the"second calcination+acid deep treatment"method was used to construct a visible light catalyst carrier with large BET surface area mesoporous g-C₃N₄,which provided sufficient adsorption and reaction sites for catalytic degradation,and was combined with Ag₃PO₄ to obtain strong oxidizing ability.The g-C₃N₄/Ag₃PO₄ heterojunction found room for improvement in its stability.The degradation effect of methyl orange showed that the photocatalytic degradation performance of the catalyst was improved.The TOC analysis showed that the methyl orange was mineralized after combined with Ag₃PO₄.Further,mesoporous g-C₃N₄/M?Fe,Co,Cu?/Ag₃PO₄ heterojunction system was synthesized by an oil bath method.The transition metal doping valence state and the optimal doping amount are explored.It has been found that the loading of transition metals can broaden the visible light absorption range,inhibit the photo-generated electron-hole recombination,and increase the specific surface area,thereby improving the photocatalytic performance.Cyclic experiments show that transition metal doping can improve photocatalyst stability.The mechanism of transition metal?Fe,Co,Cu?in heterojunction system was analyzed,and the catalytic degradation mechanism of mesoporous g-C₃N₄/M?Fe,Co,Cu?/Ag₃PO₄heterojunction system was investigated.The role of transition metals in photocatalytic heterojunction systems is explained by the direction of the electron orbit.The electron energy system of the transition metal itself is proportional to the activity and the performance of the photocatalytic material,and also transition mentals provide more adsorption and reaction sites for the degradation dye.In order to better explain the photocatalytic mechanism,the active substance capture tests were carried out,and it was found that the active substances in the photodegradation process had h⁺and O₂^-·,and a possible photocatalytic reaction process was proposed.The conduction band edge of g-C₃N₄ is-1.36 eV,which can utilize O₂^-·oxidized methyl orange;the conduction band edge of Ag₃PO₄ is 2.68 eV,which has strong oxidizing property and can be directly used to oxidize methyl orange;transition metal in catalyst system becomes an electron capture center while reducing the recombination of photogenerated electron-hole pairs of materials.Thereby the photocatalytic performance has been improved.