Design Of G-C₃N₄-based Photocatalyst And Its Photocatalytic Performance For Degradation And Hydrogen Production

In recent years,with the exploitation and consumption of fossil fuels in nature,energy sources have gradually decreased and environmental pollution has become more and more serious.Therefore,Energy shortages and environmental pollution are major issues facing and urgently to be resolved in today’s society.The development of photocatalytic technology is of great significance for solving the above-mentioned problems and realizing sustainable development strategies.Designing and preparing high-performance photocatalysts is a key challenge faced by this technology.Graphite carbon nitride（g-C₃N₄）has become an excellent candidate due to its simple synthesis,strong stability,easy adj ustment of the band gap,and low price.However,pure g-C₃N₄ has some inherent shortcomings,such as high electron-hole recombination rate,small specific surface area and low visible light absorption efficiency.These shortcomings seriously hinder its pho tocatalytic efficiency.In order to solve the above problems,this article carried out a modification study on carbon nitride,and carried out a series of characterization and photocatalytic performance experiments,and explored the reaction mechanism,aiming to enhance the photocatalytic activity and improve its performance in pollutant degradation and hydrogen production.First,using melamine as the raw material,combining the acidification method and the bubble template method,a series of loose and porous carbon nitride（HC l-CNU-X）composite photocatalysts were successfully synthesized after high-temperature polymerization.The results of photocatalysis experiments show that under the irradiation of visible light,the degradation rate of HC l-CNU-3 to tetracycline hydrochloride（TC）can reach 72%within 60 minutes,and its degradation rate constant is 7.5 times that of g-C₃N₄.In addition,the photocatalytic reduction performance has also been improved.HC l-CNU-5 has the highest H₂ production,reaching 32.5μmol h^-1,which is 4.2 times that of g-C₃N₄.And after 4 cycles,HC l-CNU-3 and HCl-CNU-5 can still maintain high catalytic degradation activity for TC.The enhanced photocatalytic activity of HC l-CNU-X is attributed to the formation of its porous structure.These pores can increase the specific surface area of the catalyst and increase the reactive sites,thereby promoting the separation of photo-generated electrons and holes and enhancing the photocatalytic activity.Using urea and PCDots as raw materials,the ultrathin PCDots-C₃N₄composite material was synthesized through a one-step thermal synthesis method.Characterization by SEM mapping,XPS and NMR proved that PCDots were implanted into g-C₃N₄ through P-N bond.Combined with DFT calculation,the influence of PCDots implantation on the electronic structure and band gap is analyzed.The photocatalytic experiment results show that PCDots-C₃N₄ not only has the best oxidation ability,but also the best reduction ability.Under visible light irradiation,the degradation rate of PC Dots to TC can reach 76%within 60 min,and the degradation of bisphenol A can reach 100%.In addition,the hydrolysis of PCDots-C₃N₄ under visible light in 4 hours can reach 11615μmol g^-1,which is about twice the hydrogen production of pure g-C₃N₄.The enhancement of the photocatalytic activity of PCDots-C₃N₄ is attributed to the fact that the implantation of PCDots will change the quantum confinement effect and electronic structure of PCDots-C₃N₄,make the electron transfer rate faster,and reduce the recombination rate of photogenerated electrons and holes.The catalytic activity becomes stronger.