Preparation Of Non-metallic Element-doped Carbon Nitride And Study On Its Photocatalytic Performance

Graphitic carbon nitride（g-C₃N₄）has attracted extensive attention due to its high chemical and thermal stability properties,easy synthesis and environmental friendliness.However,the low photogenerated carrier mobility and specific surface area of g-C₃N₄limit its wide range of applications.In this paper,carbon doped carbon nitride（CL）and carbon doping-defects co-modified carbon nitride（CE）were synthesized by non-metallic element doping method,and bisphenol A（BPA）was selected as the target contaminant to prove that the photocatalytic performance of the prepared materials.The main studies are as follows.（1）Carbon doped carbon nitride（CL）was successfully synthesized by thermal copolymerization of ammonium citrate and urea,and used CL for photocatalytic degradation of BPA.The results showed that the addition of a small amount of ammonium citrate could introduce additional carbon in the form of C-O-C bond on the carbon nitride,but without destroying the crystal structure and surface morphology of the prepared material.The carbon doping expands the visible light absorption range of carbon nitride and improves its utilization of visible light as well as photocatalytic activity.The results showed that the catalyst prepared using urea of 20 g and ammonium citrate of 0.02 g had the best photocatalytic activity.Under the given conditions（catalyst dosage of 0.5 g/L,p H 6 of the original solution）,the optimal CL（0.02CL）has the highest BPA degradation rate of 93.2%,and its degradation rate constant was 6.7times higher than that of g-C₃N₄,and the TOC removal rate was also significantly higher than that of g-C₃N₄.Further study of the radical scavenging experiments revealed that superoxide radicals（·O₂^-）play a major role in the visible light degradation of BPA,followed by vacancies（h⁺）,while hydroxyl radicals（·OH）play no significant role.（2）Carbon doping-defects co-modified carbon nitride（CE）was prepared via a one-step thermal polymerization of urea and EDTA-2Na.Compared with the g-C₃N₄,the CE catalyst introduced additional C-C bonds and defects,resulting in a loosely folded structure.UV-vis DRS results showed that the CE has a lower band gap and a wider response range for visible light.PL and photoelectrochemical analyses show that CE has a low recombination rate of photogenerated electron-hole pairs,which can improve its utilization for visible light.Therefore,the degradation efficiency of CE catalysts for BPA was higher under visible light irradiation,where the best catalyst（0.02CE）showed a degradation efficiency of 98.6%,and its degradation rate constant was 8.7 times higher than that of g-C₃N₄.In addition,0.02CE showed excellent stability during the photocatalytic process,and its degradation efficiency of BPA was still higher than 86%after three consecutive catalytic cycles.Meanwhile,0.02CE also exhibited high mineralization rate and was able to degrade BPA into CO₂ and H₂O by the generation of active species,like superoxide radicals（·O₂^-）and holes（h⁺）.（3）In this paper,the catalysts with the visible photocatalytic activity（0.02CE,prepared by calcination of urea was 20 g and ammonium citrate was 0.02 g）were selected for the degradation of four different charged forms of endocrine disruptors.（EDCs）.The results showed that 0.02CE can effectively degrade EDCs under visible light irradiation.After 150 min of visible light irradiation,the degradation efficiency reached 98.6%,92.9%,78.1%and 93.2%for bisphenol A（BPA,nature）,diclofenac sodium（DCF-Na,anions）,doxepin hydrochloride（DOX,cations）and amitriptyline hydrochloride（AMI,cations）,respectively.By exploring the effect of the initial p H of the solution,it was demonstrated that the best photocatalytic activity of 0.02CE was achieved at p H 11.The radical scavenging experiments confirmed that superoxide radicals（·O₂^-）play a major role and photogenerated holes（h⁺）play a minor role during the BPA,DCF-Na,and DOX degradation process.However,h⁺play a major role and·O₂^-play a minor role during the AMI degradation process.