Preparation Of Carbon Nitride Homoheterojunction Materials And Research On Pollutant Degradation

C₃N₄ is a kind of photocatalyst with good photocatalytic performance.In the field of environmental governance,it is widely used in the degradation of pollutants due to its non-toxic and stable chemical properties.But the poor carrier separation ability and wide band gap restriction on its application.By combining the two functionalized C₃N₄into an isotype heterojunction,the carrier can be effectively separated,the carrier life can be prolonged,and the non-toxic and harmless characteristics of C₃N₄ can be guaranteed.Therefore,it is a very practical method to improve the performance of C₃N₄by combining the two functionalized C₃N₄ into an isotype heterojunction.1.In this work,phosphorus-doped carbon nitride/phosphorus and sulfur co-doped carbon nitride(P-C₃N₄/PS-C₃N₄)isotype heterojunction was prepared by a two-step calcination method.The composite displayed asheet-like structure with a surface area of 23 m²/g.Compared with pure C₃N₄,band gaps of P-C₃N₄and PS-C₃N₄ were only slightly modified during the heteroatom-doping process.Therefore,a wellmatched band alignment was constructed,which not only improved the separation efficiency of photogenerated electron-hole pairs,but also well preserved the high oxidizability of holes on valance band and good reducibility of electrons on conduction band.Because of the similarity in physicochemical properties,the interface resistance between P-C₃N₄ and PS-C₃N₄ was low,which accelerated the electron transfer and prolonged the lifetime of charge carriers.Although the visible-light utilization was somewhat low in comparison with P-C₃N₄ and PS-C₃N₄,by taking advantage of above merits,P-C₃N₄/PS-C₃N₄ exhibited high photocatalytic activity in the degradation of rhodamine B with the reaction rate constant of 0.183 min^-1,which was 8.7 times and 4.0 times of P-C₃N₄ and PS-C₃N₄,respectively.Besides high catalytic activity,isotype heterojunction displayed good recyclability,since 95.3%of catalytic activity was maintained after the 5th cycle.This method is simple,economical and environmentally friendly,and has a broad application prospect in environmental remediation.2.Herein,a type I phosphorus-doped carbon nitride/oxygen-doped carbon nitride(P-C₃N₄/O-C₃N₄)isotype heterojunction is designed.The photoinduced charge carriers are effectively separated and the high reducibility of electron is well preserved in P-C₃N₄ with the help of internal-electric-field near the interface,ensuring the high H₂O₂yield.As a result,the production rate of H₂O₂ for P-C₃N₄/O-C₃N₄ in an air-saturated solution is 168?M·h^-1,about 5.6 times higher than that of carbon nitride(C₃N₄).Due to the cascade mode(continuous H₂O₂ production and following Fenton reaction),the H₂O₂ utilization efficiency is remarkably improved to 82.8%,about 10 times higher than that of traditional Fenton reaction.Befitting from the high yield and utilization efficiency,the degradation performance of P-C₃N₄/O-C₃N₄ is undoubtedly superior than other photocatalysts.The mechanisms of photocatalytic H₂O₂ production and pollutant degradation are proposed,and the contributions of radicals are investigated.This work well addresses two bottlenecks in traditional Fenton reaction:source of H₂O₂and their low utilization efficiency,and the findings is beneficial to understand the mechanism and advantage of the photocatalysis-self-Fenton system in environmental remediation.