The Design Of Carbon Nitride Microtube Photocatalyst And Their Photocatalytic Degradation And Water Splitting Performance

Increasing environmental pollution and energy problems have seriously hindered the sustainable development of human society.Exploring clean energy and green pollution-free technologies is an effective way to solve these two challenges.Sunlight-driven semiconductor photocatalysis technology has the advantages of green,clean,and non-toxic in the degradation of pollutants,complete water solution and hydrogen production,and is considered to be an effective way to solve these two challenges.The key challenge for this technology is to design and prepare a high-performance photocatalyst rationally to enhance the absorption and utilization of sunlight by its photocatalytic reaction.Graphite carbon nitride（g-C₃N₄）is an excellent candidate due to its simple synthesis,metal-free properties,adjustable band gap,and high stability.However,pure g-C₃N₄ has some inherent shortcomings,such as easy recombination of electrons and holes,limited specific surface area,and low visible light absorption efficiency,which seriously hinder its photocatalytic efficiency.To solve the above problems,a carbon nitride microtube photocatalyst system was constructed in this paper.Through morphology and energy band adjustment,and further compounding with other materials,a series of characterization and photocatalytic performance experiments were carried out to explore the reaction mechanism,aiming to enhance The photocatalytic activity improves its efficiency in pollutant degradation,hydrogen production,and total water solution.The main findings are as follows:By adopting the method of first hydrothermal and then a polymerization,the carbon nitride microtubes（TCN）and phosphorus-doped carbon nitride microrods（PCN）photocatalysts were prepared,which achieved stable and efficient performance of complete water dissolution and hydrogen production.The results show that,compared with g-C₃N₄,TCN’s total water-decomposing performance is improved by 31 times.Besides,compared with g-C₃N₄ and PCN,the hydrogen production performance of TCN is improved by 11.6times and 2 times,respectively.The improvement of TCN performance is attributed to the fact that the hollow form changes the light scattering and causes a significant enhancement in the electric field,which is considered to be an important contribution to the excellent total water solution performance,which is confirmed by the finite element modeling calculation（FEM）.At the same time,the improvement of the charge separation efficiency,the increase of the specific surface area,the increase of the exposed active sites,and the optimized band structure also play a key role in improving the photocatalytic performance.Based on the first hydrothermal and then polymerization method,combined with sodium borohydride to prepare nitrogen defect and boron-doped carbon nitride microtubes（D-CCN）,which achieves stable degradation of tetracycline hydrochloride（TC）and high efficiency of hydrogen evolution.Characterization and analysis showed that the electron-hole recombination rate of D-CCN composite photocatalyst was significantly reduced,the light absorption range was broadened,and the characteristics of larger photocurrent and lower electrical impedance significantly improved the photocatalytic performance.When the calcination temperature is 450℃,the photocatalytic degradation activity of D-CCN is the highest.After 80 minutes of visible light irradiation,the degradation rate of TC reaches68.2%,and the generation rate of H₂ also reaches 789.2μmol h^-1g^-1.Compared with g-C₃N₄,the degradation and hydrogen production rates are increased by 9.3 times and 4.2 times,respectively.The improvement of D-CCN performance is due to the introduction of doping and defects that increase the charge separation efficiency and specific surface area,which improves the photocatalytic activity.Density functional theory calculations（DFT）results show that the asymmetric HOMO and LUMO orbitals of nitrogen defects and boron-doped D-CCN help to separate the redox sites from each other,thereby reducing the recombination of charge carriers.The photocatalytic activity is improved,and the contribution of the 2s orbital of D-CCN to the conduction band and valence band is increased,which helps to make the band gap narrower.