Preparation Of Visible-light Catalysts Based Porous G-C₃N₄ And Its Degradation Of TCH And MB In Water

In the process of modernization,the rapid advancement of pharmaceutical,printing and dyeing,chemical and other industries has produced a large amount of refractory organic wastewater.Therefore,it is of great significance to develop deep reduction technologies to efficiently treat harmful wastewater.Photocatalytic technology is an economical,efficient and environmentally friendly water treatment technology.It uses sunlight to degrade and even mineralize refractory organics.It has great application prospects in the field of water purification.In this paper,tetracycline hydrochloride（TCH）in common pharmaceutical wastewater and methylene blue（MB）in dye wastewater are selected as representatives of refractory organics,and photocatalytic degradation technology is used to efficiently treat both.Although there are many researches on photocatalytic technology in the treatment of refractory wastewater,the technology still has problems such as insufficient use of visible light and easy shedding of composite photocatalyst nanoparticles.In this paper,a new type of porous graphite phase carbon nitride（porous g-C₃N₄）matrix is prepared,which uses the abundant amino groups at the edges of the pores to assist in anchoring transition metal nano-semiconductor materials to form a heterogeneous structure.Modification by this method improves the firmness of semiconductor nanoparticles and improves the visible light catalytic performance of porous g-C₃N₄.Further,the degradation efficiency,degradation mechanism and application of the based porous g-C₃N₄ composite material were explored,and the following results were obtained.First,using dicyandiamide as a raw material,the porous g-C₃N₄ was synthesized by template-free thermal polymerization.The semiconductor nanoparticles were successfully loaded on the porous g-C₃N₄ matrix to construct a heterogeneous structure.When the porous g-C₃N₄ and Cd S mass ratio is 1:2,the composite material Cd S/g-C₃N₄-2 has the best photocatalytic performance.The degradation rate of TCH is81.46%within 60 minutes,and the degradation rate of MB is 85.30%within 180minutes.Characterizing the composite material Cd S/g-C₃N₄-2,its specific surface area is 140 m²/g,which is 3 times that of porous g-C₃N₄ and nearly 14 times that of ordinary g-C₃N₄.In addition,the light absorption of the Cd S/g-C₃N₄-2 composite material is broadened from 525 nm to 620 nm relative to the porous g-C₃N₄,and the fluorescence intensity is also significantly reduced,indicating that the composite material has a wider light absorption range and more efficient photo-generated carriers Separation efficiency.The thesis explores the specific influencing factors of the based porous g-C₃N₄photocatalyst in the degradation of pollutants in the system through single factor experiments.The results show that the dosage of the catalyst is 0.2 g/L more suitable;the composite photocatalyst is more suitable for treating neutral and alkaline wastewater;Interfering hetero ions HCO₃^-,Cl^-,NO₃^-and humic acid（HA）have very little effect on photocatalytic degradation（the degradation rate varies within 2%）.Cyclic degradation test shows that the composite photocatalyst has high physical and chemical stability,and its degradation rate can still maintain more than 70%after five cycles.In summary,it can be seen that based porous g-C₃N₄ composite materials can adapt to complex environmental conditions and have great potential in applications.Exploring the degradation mechanism of based porous g-C₃N₄ composite materials.The results show that the main active groups in the photocatalytic degradation system are·O₂^-and h⁺.Two strong oxidizing substances gradually destroy the structure of pollutants,and finally produce non-toxic and harmless small molecular substances.The system mineralization level is about 20%after 3 h.Because the powder material is difficult to recycle,The experiment load the based porous g-C₃N₄ powder material on the graphene aerogel carrier and designed a reaction device for the degradation experiment of flowing wastewater.The continuous degradation of the reaction system for 20 h can maintain a stable and high degradation rate,which indicates that the porous g-C₃N₄ composite photocatalyst has great practical application potential in the removal of refractory organics.