Preparation Of Monolithic G-C₃N₄ Supported CoO Photocatalyst Modified By Quantum Dots With Spongelike Structure And The Research Of Its Degradation Performance Of Tetracycline

Tetracycline antibiotics have been frequently detected in the surface water and groundwater environment,and their long-term accumulation poses a great threat to the ecological environment and human health.Photocatalysis is a new technology which is environmentally friendly and can effectively degrade toxic pollutants in the environment.Carbon nitride（g-C₃N₄）has been widely used in the photocatalytic degradation of pollutants due to its advantages of metal-free,easy preparation,low cost and high stability.However,most studies focus on powdered g-C₃N₄,which is not only difficult to recover,but also has shortcomings such as low photoresponse range,small specific surface area,and easy recombination of photogenerated carriers.Therefore,in this paper,the floating spongelike structure g-C₃N₄ prepared by thermal condensation method was used as the substrate material,and Co O was loaded onto the floating spongelike structure g-C₃N₄ to construct the Co O/g-C₃N₄（Co O/HPNCN）p-n heterojunction with matched energy band structure,and then carbon quantum dots were added to the Co O/HPNCN heterojunction.The CQDs/Co O/HPNCN composite material is formed.The photocatalytic properties of tetracycline wastewater were investigated by degrading simulated tetracycline wastewater.The degradation of tetracycline intermediates by photocatalysis and the possible photocatalytic reaction mechanism were discussed.The research content is as follows:（1）The floating spongelike structure g-C₃N₄（FSCN）was prepared by one-step thermal condensation method.The phase composition,morphology size and chemical elements of FSCN were studied by XRD,SEM,XPS and UV-Vis.Under the irradiation of xenon lamp,the removal rate of 40 mg/L TC by FSCN was 76%,which was 1.2 times of that by powder g-C₃N₄.Under clear natural light,the removal rate of TC by FSCN was70.4%,only 5.6%lower than that under xenon lamp irradiation.In addition,the removal rates of FSCN and powder g-C₃N₄ samples decreased by 4.1%and 5.4%,respectively,after being reused for five times.FSCN showed better stability and reusability.（2）Co O/HPNCN p-n heterojunctions were successfully prepared by one-step heat shrinkage method and solvothermal method.The physicochemical properties were studied by a series of characterizations.Among them,30%Co O/HPNCN p-n heterojunction showed the best photocatalytic degradation effect（88.1%,90min）in TC photocatalytic degradation.The reaction rate constants(0.02066 min^-1)were 1.58 and 2.62 times higher than those of pure HPNCN(0.01311 min^-1)and Co O(0.00788 min^-1),respectively.The degradation rate of the prepared Co O/HPNCN p-n heterojunction decreased less than 5%after five cycles of use,indicating that the prepared Co O/HPNCN p-n heterojunction has good stability.The reason is that after Co O and HPNCN form p-n heterojunctions,Co O nanoparticles are dispersed and distributed on the surface of HPNCN,thus improving the separation rate of photogenerated electron hole pairs.（3）Different proportions of CQDs/Co O/HPNCN composites were designed and synthesized by one-step heat shrinkage method and solvothermal method.The physicochemical properties were studied by a series of characterizations.The CQDs-2/Co O/HPNCN composite showed the best photocatalytic degradation effect of TC（94.7%,90min）.The reaction rate constants(0.0288 min^-1)were 2.33,3.65 and 1.48 times that of pure HPNCN(0.01237 min^-1),Co O(0.00788 min^-1)and Co O/HPNCN(0.01944min^-1),respectively.This is due to electron storage and transfer by the added CQDs and the formation of CQDS-2/Co O/HPNCN TYPE II heterojunctions,which promote the separation of photogenerated charge carriers.