Design Of Polymeric Carbon Nitride And Their Performance And Mechanism In Catalytic Degradation Of Antibiotic Contamina Nts In Water Under Visible Light

In recent years,with the rapid development of poultry and aquaculture,a large number of antibiotics have entered the water environment.This causes serious pollution to the water body,even to human health.Therefore,the search for efficient,easy-to-operate,and low-cost techniques to remove antibiotic pollution in water bodies has become a research hotspot and frontier in the environmental field.Photocatalytic technology has the advantages of energy saving and easy operation,but the performance of photocatalysts is restricted by the limit light absorption and photogenerated electron-hole separation.Therefore,the development of a catalyst with a wide light absorption range and good charge separation efficiency is an important issue for water pollution control.Carbon nitride(PCN)is an organic polymer photocatalytic material.It has the advantages of a wide range of raw materials,easy structure modification,and good bio-friendliness.This paper aims to control the chemical structure,morphology and electronic structure of PCN through element doping,heterojunction,molecular self-assembly copolymerization and other methods.This paper focus on the mechanism of PCN-based photocatalytic materials for the removal of sulfamethazine and tetracycline in water,with a view to providing theoretical guidance for the development of efficient,environmentally friendly and feasible water pollution control technologies.The paper is divided into five chapters:Melamine,cyanuric acid,and barbituric acid were used as raw materials for prepared carbon-doped carbon nitride by self-assembly copolymerization and calcination.Carbon-doped carbon nitride used as a photocatalyst to degrade sulfamethazine in water.The results show that carbon-doped carbon nitride has a higher specific surface area(179 m² g^-1),wider visible light absorption,lower fluorescence intensity,and higher photocurrent than carbon nitride.These characteristics are favorable for the degradation of sulfamethazine.The carbon-doped carbon nitride can remove 98%of sulfamethazine in 1 hour,and the removal rate of pure carbon nitride is 20%.Free radical capture experiments showed that the active species were mainly·O₂^-and h⁺.In addition,the study found that carbon-doped carbon nitride has good stability,and after 4 cycles of expe riments,the activity of the catalyst did not decrease significantly.This research can provide a new perspective for the design and utilization of highly efficient and stable non-metal photocatalysts,which can be used to improve the catalyst's degradatio n performance of pollutants.(Chapter 2)A CCN/Bi₁₂O₁₇Cl₂ heterojunction composite was constructed based on the carbon-doped carbon nitride(CCN)and Bi₁₂O₁₇Cl₂.The composite was used to degrade tetracycline under visible light.The results show that the 2 0%CCN/Bi₁₂O₁₇Cl₂composite has the highest photocatalytic activity,and the degradation constant rate for tetracycline is 0.0409 min^-1,which is approximately 2.9,1.5,and32.1 folds than that of pristine Bi₁₂O₁₇Cl₂,CCN,and Bi OCl,respectively.The results of photocurrent response and electrochemical impedance spectroscopy showed that the addition of Bi₁₂O₁₇Cl₂ greatly improved the photogenerated carrier separation efficiency of CCN.The main active species in the reaction system are^·O₂^-,h⁺and·OH.This result shows that CCN/Bi₁₂O₁₇Cl₂ heterojunction composite can be used as an excellent photocatalyst,and it may be used in the degradation of refractory pollutants and environmental remediation applications in the future.(Chapter 3)L-cysteine and dicyandiamine were used as raw materials for prepared nitrogen vacancy carbon nitride(LCN)by self-assembly copolymerization.The addition of L-cysteine increased the specific surface area of LCN and expanded the light absorption range.In addition,the nitrogen vacancies caused by L-cysteine are beneficial for the separation and transfer of photo-generated carriers,which is conducive to improving the activity of the photocatalyst.The degradation rate constant of LCN-0.015 for sulfamethazine is about 12 tim es that of DCN.LCN can also produce H₂O₂ under visible light,such as LCN-0.015 with a H₂O₂production rate of 73?mol h^-1.The HPLC-MS results found two intermediates for the degradation of sulfamethazine.Based on the results of free radical capture experiments and ESR,it was found that^·O₂^-and h⁺are the main free radical species.The above results show that the introduction of L-cysteine is conducive to the improvement of the photocatalytic performance of carbon nitride,and this self-assembly experience provides technical support for the future design of efficient photocatalysts.(Chapter4)Salicylic acid(SA)was introduced as a monomer to react with urea to form the modified carbon nitride(CN-SA-x)by self-assembly copolymerization.The doping of SA distorts the planar structure of carbon nitride,thereby causing electrons to migrate from???*of the planar structure to n??*of the distorted structure,expanding the range of light absorption.The porous structure of CN-SA-x also provides abundant active sites for the degradation of pollutants.The degradation rate constant of tetracycline by CN-SA-x reaches 0.0327 min^-1,which is more than 2 times higher than PCN.In addition,the degradation rate constant of CN-SA-x for sulfamethazine reached 0.0823 min^-1,which is about 3 times that of PCN.After 4 cycles of modified CN-SA-x,the activity and structure remains stable.This study shows that CN-SA-x has good photocatalytic performance and has great potential for degradation of tetracycline and sulfamethazine.(Chapter 5)Based on the research in Chapter 5,the pyrazine and its derivative s were used to introduce into the framework of PCN to obtain a series of modified carbon nitride(PCN-DP).Pyrazine,as an electron transfer channel,promotes the separation of photo-generated carriers.Compared with the traditional PCN based on urea,the degradation rate constant of sulfamethazine by pyrazine-modified PCN-DP reaches0.087 min^-1,which is 4 times higher than that of PCN.The degradation efficiency in the reaction system mainly depends on the concentration of reactive oxygen species(such as^·O₂^-,H₂O₂and·OH)and the interface interaction between the pollutant and the photocatalyst.In addition,the prepared photocatalyst also has better performance in water spiliting.The rate of H₂ production by PCN-DP reaches 63?mol h^-1,which is6 times higher than that of PCN,and it can continuously and stably produce H ₂.Finally,through phytotoxicity experiments,it was shown that the toxicity of the sulfamethazine solution was greatly reduced after degradation;the prepared PCN and PCN-DP series photocatalysts were non-toxic to plants.This work broadens the method of modifying carbon nitride and provides researchers with a new idea for modification,which improves the performance of sulfamethazine degradation and H₂production.In addition,this work has certain potential to be applied to the environmental remediation of actual water bodies and the utilization of wastewater resources.(Chapter 6)...