Preparation Of G-C₃N₄-Based Composites And Their Photocatalytic Properties

Tetracycline antibiotics not only pollute the environment,but also pose a serious threat to human health.In recent years,the theoretical research and practical technology of photocatalysis have been continuously developing and innovating,especially in the modification of photocatalytic materials to improve the degradation efficiency.Photocatalysis is the most important way in the degradation method of tetracycline antibiotics,which mainly realizes the degradation of tetracycline antibiotics through a series of reactions.g-C3N4 has a very suitable semiconducting band edge position and is a common photocatalyst.In order to improve the photocatalytic activity of g-C3N4,many scholars have proposed many strategies at this stage.On this basis,g-C3N4-based photocatalytic composites were prepared by modifying the g-C3N4 substrate material with the aim of creating a dual synergistic catalyst.The optimal photocatalyst was identified by degrading tetracycline under visible light to overcome material defects and improve the photocatalytic efficiency of the composites.The structural morphology and optical properties of the g-C3N4 based composites were analyzed by relevant characterization methods,and the stability experiments were used to verify the stability of the prepared materials.In addition,the capture experiment of composite photocatalytic materials was carried out to determine the key active species in the photocatalytic reaction and analyze the specific catalytic mechanism,providing data and theoretical support for exploring the modification methods of g-C3N4 based catalysts.The main contents are as follows:(1)A new Ag/BN/g-C3N4 ternary composite photocatalytic material was prepared by photoreduction method.The structure and morphology of the composite material were investigated by TEM,XRD,XPS and FT-IR,and the optical properties of Ag/BN/g-C3N4 were investigated by UV-DRS,PL and EIS.Compared with single g-C3N4,the degradation rate of tetracycline by Ag/BN/g-C3N4 reached 79.64%within 2 h,showing the highest reaction rate constant,which was 2.68 and 2.02 times for g-C3N4 and BN/g-C3N4,respectively.The excellent photocatalytic performance of Ag/BN/g-C3N4 is mainly due to the following two aspects:on the one hand,the surface plasmon resonance effect of nano-Ag metal particles brings about the enhancement of the local electric field,which helps to improve the visible light absorption range of the catalyst.On the other hand,Ag acts as an electron capture agent,h-BN acts as a hole transport agent,and the double-promoted photocatalyst increases the unpaired electron-holes.Cycling experiments prove that Ag/BN/g-C3N4 is an efficient and structurally stable photocatalyst.In addition,h+ and·O2-were the main active species in Ag/BN/g-C3N4 degradation process,which was verified by the capture experiment.(2)A novel K-g-C3N4/WO3 ternary composite photocatalyst was synthesized by calcination method.This Z-type heterojunction with visible light response enables the material to have excellent photocatalytic activity.The photocatalytic degradation of tetracycline was evaluated.The results showed that the photocatalytic performance of K-g-C3N4/WO3 was the best when the K content was 9.5%and the WO3 loading was 5%.After 120 min of illumination,87.04%of tetracycline can be degraded,which is 40.5%more than that of single g-C3N4.The structure and optical properties of K-g-C3N4/WO3 were analyzed by SEM,XRD,XPS,FT-IR,UV-DRS,PL and EIS.During the degradation of K-g-C3N4/WO3,the active species that played a role were verified by trapping experiments and ESR characterization.After five degradation experiments,the degradation rate of K-g-C3N4/WO3 photocatalyst for TC can still reach more than 80%,showing good photocatalytic stability.Furthermore,based on HPLC-MS and experimental results,the degradation pathways and reaction mechanisms were investigated in more detail.(3)The I-g-C3N4/MoS2 composite material was successfully synthesized by the method of impregnation and calcination.SEM,XRD,FT-IR,UV-DRS and PL characterization methods showed that the materials modified by I and MoS2 were favorable for g-C3N4 to adsorb more tetracyclines.By degrading TC under visible light,the optimal contents of I and MoS2 for g-C3N4 modification were determined,and then the photocatalytic performance of the prepared materials was evaluated.Compared with g-C3N4 and I-g-C3N4,I-g-C3N4/MoS2 has higher photocatalytic performance,and the removal rate of TC can reach 72.34%after 100 min of illumination,which was 1.73 and 1.38 times for g-C3N4 and I-g-C3N4,respectively.