Copolymerization Of Carbon Nitride And The Mechanism Of Photocatalytic Degradation Of Sulfonamides

In recent years,sulfonamides（SAs）is one of the most widely used antibiotics in animal husbandry,medical and food-related fields.Excessive use of sulfonamide antibiotics has caused serious environmental impacts,directly posing a substantial threat to human and environmental"health".The SAs entering the ecological environment can cause harm to aquatic organisms and humans,and may even induce antibiotic resistance genes in the environment.To date,various techniques have been conducted to remove sulfonamides in water environment,such as adsorption,advanced oxidation techniques（AOPs）and biological treatment.Among them,photocatalytic oxidation is a green and efficient technology of AOPs,which is expected to be a feasible method to degrade antibiotics.As a non-metallic polymer photocatalyst,graphitized carbon nitride（g-C₃N₄）has attracted extensive attention of scholars due to abundant raw materials,high cost-effectiveness,facile synthesis and intrinsic properties controllability.Due to these advantages,polymer g-C₃N₄ is expected to be a strong candidate for photocatalytic remove residual antibiotics.Furthermore,modification of g-C₃N₄ is an effective way to further improve its photocatalytic efficiency.In this work,the removal effect of SAs was optimized via material modification of g-C₃N₄.The main research contents are as follows:（1）4-phenoxyphenol-modified g-C₃N₄（PCN）was preliminarily prepared by the copolymerization of dicyandiamide and 4-phenoxyphenol（POP）.The bond of C-O-C was introduced into the g-C₃N₄ framework,which was beneficial to the generation of more reactive oxygen species(O₂^·-and·OH).The photocatalytic degradation activity of optimized PCN towards sulfisoxazole（SIZ）under blue light（LED）irradiation was 4.5 times higher than that of pure g-C₃N₄.The successful introduction of C-O-C bonds was confirmed by X-ray photoelectron spectroscopy（XPS）and Fourier transform infrared spectroscopy（FT-IR）.Active species trapping experiments,electron spin resonance（ESR）and photoelectrochemical characterization experiments demonstrated that the faster charge separation of PCN promotes the formation of additional reactive oxygen species.Among them,sulfapyridine（SPD）,sulfadiazine（SDZ）and sulfamethazine（SMZ）in light/PCN system,SIZ and SMZ were more vulnerable to attack due to the methyl groups in their structures.The potential transformation pathway of SIZ was speculated by frontier molecular orbital theory and HRAM LC-MS/MS.（2）For the first time,three-dimensional hollow porous vesicle-like carbon nitride（HPCN）was synthesized from low-cost cyanuric acid and thiocyanate,and further applied to photocatalytic degradation of sulfamethoxazole（SMX）.The optimized HPCN_1.0photocatalytic“reactor”exhibits desirable photocatalytic performance on SMX under blue LED irradiation,which is significantly superior to that of pristine g-C₃N₄（CN,11.4 times）and3D hollow vesicle-like g-C₃N₄（HCN,4.8 times）.The HPCN_1.0 was observed to present porous hollow vesicles by scanning electron microscope（SEM）.The successful doping of S atoms was confirmed by XPS,combined with Ultraviolet-Visible absorption diffuse emission spectroscopy（UV-vis DRS）and electrochemical experiments to confirm that the unique hollow porous geometry and sulfur doping.Moreover,these morphological changes were beneficial to the multiple reflections of visible light inside HPCN,enabling more efficient electron-hole separation and exposing more reaction sites.The active species quenching experiments proved that O₂^·-and h⁺were the active species in the photocatalytic degradation system.The HRAM LC-MS/MS was conducted to identify the conversion intermediate,and further speculate on the potential transformation pathway.