Preparation Of Graphite Carbon Nitride Composites And Study On The Photocatakytic Mechanism By The Degradation Of PPCPs

With the improvement of industry and living standards,drugs and personal care products(PPCPs)have been widely used in various fields.The half-life of PPCPs is low,but they are used extensively by individuals and the livestock industry,leading to the formation of pseudo-persistent phenomena in PPCPs.Therefore,PPCPs were frequently detected in natural water,drinking water,and effluent from sewage treatment plants.The long-term existence of PPCPs had threatened the ecological environment of water and human health.Photocatalytic oxidation technology is a method that can directly use sunlight to efficiently degrade PPCPs in wastewater.Therefore,it is of great significance to study and design new photocatalysts to degrade PPCPs in water.Graphite carbon nitride(g-C3N4),as a non-metallic visible light photocatalytic material,has a suitable band structure and stable chemical structure,and became a research hotspot in the environmental field in recent years.However,g-C3N4 prepared by traditional methods has disadvantages such as poor absorption of visible light,smaller specific surface,and higher recombination rate of photo-generated electron-hole pairs.Therefore,its photocatalytic activity under visible light is not ideal,which limits its use in various fields.In this study,in order to improve the photocatalytic performance of g-C3N4 under visible light,g-C3N4 was modified by nonmetal doping and compounding with other semiconductors.The novel photocatalysts with high photocatalytic activity were designed and applied to photocatalytic degradation of typical PPCPs.The photocatalytic mechanism of materials,the photocatalytic degradation mechanism of pollutants,and the effects of coexisting ions in water on photocatalytic degradation are systematically studied through various characterizations and experiments,providing a theoretical basis for its future applications.The main contents and results of this study are as follows:(1)A novel phosphorus and oxygen co-doped graphitic carbon nitride(POCN)was successfully synthesized through a one-step thermal polymerization method and exhibited remarkable photocatalytic activity for the photocatalytic degradation of fluoroquinolones(FQs).Under simulated visible light irradiation,the enrofloxacin(ENFX)degradation rate of POCN0.01 was 6.2 times higher than that of pure g-C3N4.Based on the results of X-ray photoelectron spectroscopy(XPS)and nuclear magnetic resonance spectroscopy(NMR),P atoms replaced the corner and bay C sites,whereas O atoms replaced the N sites in the g-C3N4 framework.The improvement of the photocatalytic effect of POCN0.01 was attributed to its narrow bandgap,effective charge separation and enhanced specific surface area.It was the first report that phosphorus doping could promote the generation of reactive oxygen species(ROS).ROS scavenging tests revealed that O2·-was the primary active species during the degradation of ENFX.Furthermore,ENFX degradation pathways were proposed via the detection of intermediate products via HRAM LC-MS/MS and the prediction of active sites using the Fukui function.(2)Anatase TiO2 nanoparticles coated with P and co-doped g-C3N4 were prepared via a single-step procedure using polyvinylpyrrolidone,hexachlorocyclotriphosphazonitrile,guanidine hydrochloride and anatase TiO2.The resulting POCN/anatase TiO2 demonstrated remarkable performance in the degradation of enrofloxacin(ENFX).Under simulated visible light irradiation,the photocatalytic activity of the heterojunction photocatalyst was 3.60 and 3.71 times better than that of the POCN0.01 and TiO2,respectively.According to the results of transmission electron microscope,it was found that hydrophilic anatase TiO2 was successfully loaded on the surface of POCN0.01 to form heterojunction.Co-doping with P and O increased the visible light adsorption capacity and the separation efficiency of photoinduced carriers of the g-C3N4,whereas the anatase TiO2 nanoparticles enhanced hydrophilicity,the adsorption properties of the ENFX,and the separation of the photoinduced carriers of the POCN/anatase TiO2.The results of the H2O2 detection test and electron paramagnetic resonance(ESR)confirmed that POCN/anatase TiO2 was a type Z-scheme photocatalyst.The O2·-and h+were the main reactive oxidative species in the photocatalytic degradation of ENFX.The effects of coexisting ions in water and different pH values on the degradation of ENFX by POCN/TiO2 1-1 were also considered.In addition,the photocatalyst still maintains excellent photocatalytic performance after three times cyclic experiments and has an excellent application prospect in the field of photocatalytic degradation of PPCPs.(3)P-doped g-C3N4(PCN)was successfully prepared via a single step thermal polymerization technique using phytic acid biomass and urea,which exhibited remarkable photocatalytic activity for the degradation of indometacin(IDM).The results of photocatalytic degradation experiments show that the degradation rate of IDM by PCN under visible light is 7.1 times greater than that of pure g-C3N4(CN).According to the analysis of the chemical binding state of PCN,it was found that,P atoms replaced carbon atoms in the CN structure.According to the analysis of the electronic positioning function,P-N has a lower value of the electronic positioning function(ELF),which promotes the transfer of photoelectrons.Furthermore,Ag2WO4 with a high valence band was loaded onto the surface of the PCN,which formed a Z-scheme heterostructure.The heterostructure photocatalyst not only promotes the separation of photogenerated carriers,but also improves the oxidation capacity of h+.The h+generated by 30%Ag2WO4/PCN could directly oxidize H2O and OH-to form OH.The results of active species scavenging experiments confirmed that O2·-was the primary active specie in the photocatalytic degradation system.The photocatalytic degradation pathways of IDM were proposed through the identification of by-products and prediction of IDM reaction sites.The results of photocatalytic experiments in natural water,cycling tests,and the effect of coexisting ions in water showed that 30%Ag2WO4/PCN has great application prospects in photocatalytic degradation of IDM wastewater.