Preparation Of Single-atom Photocatalyst Based On Polymeric Carbon Nitride Toward Antibiotics Degradation

Due to the improper use of antibiotics,the global water pollution caused by antibiotics is becoming increasingly serious.Conventional water treatment technology is difficult to efficiently remove antibiotics with stable structure.In contrast,photocatalytic water treatment technology is more ideal and has the prospect of industrial application.As the core of photocatalytic technology,it is quite vital to develop stable,efficient and low-cost photocatalysts.Among various photocatalysts,polymeric carbon nitride（PCN）has been widely studied by virtue of plentiful merits like simple preparation,low cost and stable structure.However,the drawbacks such as poor utilization of visible light and severe recombination of photo-generated carriers limit the practical application of PCN.Recently,single-atom catalysts（SACs）have attracted much attention in various catalytic reactions due to their high atomic utilization rate and excellent catalytic performance.However,most SACs still require further optimization ascribed to their stringent preparation conditions and high preparation costs.In view of the above situation,in this thesis,stable,efficient,low-cost and easily amplified monatomic photocatalysts using PCN as the basic material had been prepared successfully via facile in-situ thermal polymerization method,and then had been applied to the photodegradation of tetracyclines（TCs）.The specific research contents are as follows:（1）Single manganese（Mn）atoms decorated PCN photocatalyst had been prepared via a convenient one step in-situ thermal polymerization method.Single Mn atoms within PCN have a salutary effect on adjusting the band gap,boosting the transfer and separation of photo-generated carriers,and optimizing the utilization of visible light.Consequently,the optimized MCN-2 exerts a superior pseudo-first-order kinetic rate constant k of 0.041 min^-1 in visible-light-driven TC photodegradation,with 13.7 folds higher than that of the pristine PCN.MCN-2 still maintained benign catalytic performance and structural stability after five cycles.Further,the intermediates and reactive oxygen species generated in the TC photodegradation process are experimentally manifested and a plausible mechanism for TC degradation over MCN is proposed.This work confirms and proves the universality of the in-situ polymerization strategy to synthesize single transition metal atom photocatalyst and provides a feasible way to prepare SACs based on PCN.（2）Considering the merits of aluminum（Al）such as high abundance and low environmental toxicity,a kind of single-atom Al modified PCN photocatalyst was prepared via in-situ polymerization method successfully.The introduction of single Al atoms narrows the intrinsic band gap of PCN,improves the response ability to visible light,and promotes the migration of photogenerated electron-hole pairs.As a consequence of visible-light-driven degradation of TC,oxytetracycline（OTC）and chlortetracycline（CTC）,the optimal ACN-2 exhibits superb TC removal rate as 82%within 20 min,and the k values of three pollutants’degradation reactions can reach 0.084 min^-1,0.051min^-1 and 0.067 min^-1,respectively,which are much better than that of bulk PCN.Additionally,ACN-2 can still retain excellent performance in high TCs concentration.Moreover,ACN-2 exerts superior structure stability and photocatalytic activity after 10 cycles.The scale-up-produced ACN-500catalyst can still maintain good structure and excellent catalytic activity.This work provides an idea for industrial large-scale production of single-atom photocatalysts with high efficiency for photodegradation pollutants.