Study On The Preparation Of Cs⁺ Modified G-C₃N₄ Materials And Their Photocatalytic Oxidative Degradation Performance Of Tetracycline

The O₂ and H₂O in the environment media can be activated into active species e.g.superoxide anion radicals（·O₂^-）and hydroxyl radicals（·OH）,etc.via the photocatalytic technology under the light irradiation,which makes the photocatalysis as a potential strategy for environmental remediation.Graphitic carbon nitride（g-C₃N₄）is a kind of non-metallic and layered material,which has a suitable energy structure bringing it excellent ability in photocatalytic activation of O₂ and H₂O.Therefore,herein,Cs⁺-doped g-C₃N₄（labeled as CN-x Cs）and g-C₃N₄ with rich N vacancies promoted by Cs⁺（CN-NV_R）were prepared by modulating the physicochemical interactions between CsCl and g-C₃N₄.Moreover,their performance and the related mechanism were also studied here for photocatalytic generation of reactive oxygen species and oxidative degradation of tetracycline（TC）.The specific research contents in detail are as follows:（1）The Cs⁺doped g-C₃N₄ photocatalyst（labeled CN-x Cs,x=0.2,0.8,1）was prepared by mixing CsCl with g-C₃N₄powder and then heat-treating at 550℃.The results showed that the doping of Cs⁺allowed O atoms to enter the structure of g-C₃N₄to form N vacancies and cyano groups,which promoted the activation of molecular oxygen（O₂）.A proper amount of Cs⁺doping could reduce the band gap,increasing the light absorption range,and had better charge separation and transfer performance,so it could significantly promote the generation of·O₂^-.Therefore,CN-0.8Cs could produce a large quantity of·O₂^-（179.30μM）,which was much higher than that of g-C₃N₄（6.22μM）,and exhibited excellent photocata-lytic degradation performance of tetracycline.The rate constant k of TC degradation was0.020 min^-1,which is 6.7 times compared with that of g-C₃N₄(k=0.003 min^-1).（2）The LiCl was mixed with CsCl as the fluxing agent,therefore the molten Cs⁺formed at 550℃ could fully interact with g-C₃N₄.The resulting product was washed with hydrochloric acid to prepare g-C₃N₄ with rich N vacancies（labeled as CN-NV_R）.As a con-trol,after washing CN-0.8Cs with hydrochloric acid,g-C₃N₄（labeled CN-NV_S）with a small amount of N vacancies was also obtained.The results showed that the doping of Cs⁺was beneficial to reduce the band gap of g-C₃N₄,thereby broadening its light absorption range;and N vacancies played an important role in promoting the photoexcited charge separation and transfer as well as inhibiting the charge recombination.In addition,CN-NV_R had a valence band potential of 2.86 V vs.NHE,so it can react with H₂O to produce the·OH（24.15μM）,while the presence of·OH was basically undetectable in CN-0.8Cs（0.42μM）.Therefore,CN-NV_R also showed excellent performance in photocatalytic degradation of tetracycline.The rate constant k for TC degradation was 0.032 min^-1,which was 10.7 times compared with that of the g-C₃N₄(k=0.003 min^-1).Moreover,after five cycles,the photo-catalytic degradation performance of CN-NV_R still remained 94.3%compared with that of the first cycle,indicating that it had relative good photocatalytic stability.