Microstructure Regulation Of Graphitic Carbon Nitride Photocatalyst For Photocatalytic Antibiotic Degradation And Bacteria Inactivation

Due to the overuse of antibiotics in the 21st century,water pollution has become increasingly serious.Owing to its strong treating capacity,no secondary pollution,and mild reaction condition,photocatalytic technology has shown great application prospects in water pollution control.Graphitic carbon nitride(g-C₃N₄),as a semiconductor photocatalyst with good visible light absorption,suitable energy band structure and non-metallic property,has received extensive attention in the field of photocatalysis.However,due to the intense exciton effect,severe charge carrier recombination process and large bulky structure,the photocatalytic activity of the pristine g-C₃N₄ is weak,which greatly limits its utilization in photocatalysis.For the sake of improving the efficiency of the photocatalytic reaction,it is extremely important to rationally modulate the microstructure of semiconductor photocatalyst.Therefore,from the perspective of optimizing the bulky structure,promoting exciton dissociation and accelerating charge carrier separation,a series of novel g-C₃N₄photocatalysts with high activity w ere prepared through the regulation of microstructure(morphology optimization,heterogeneous element doping,functional group functionalization and heterojunction constr uction),and the regulated g-C₃N₄was applied for the degradation of antibiotic and inactivation of bacterial.By analyzing the material structure and electron behavior,the internal reaction mechanism for the enhanced performance of g-C₃N₄ photocatalyst was explored,and the photocatalytic reaction mechanism was revealed.The main research contents and results are as follows:(1)Through the strategy of hydrothermal oxidation coupled secondary calcination,the O-substituted ultrathin porous g-C₃N₄ nanosheets(OCN-24-550)were prepared and applied for the degradation of oxytetracycline hydrochloride(OTC).The results of structural analysis and density functional theory(DFT)calculations show that internal O substitution and ultrathin porous structure contr ibute to the performance improvement of OCN-24-550.Specifically,O-substitution can promote the dissociation of exciton,while the ultrathin porous structure accelerates the separation of charge carrier.Then,the separated photogenerated electron will combine with molecular oxygen and activate it,producing reactive oxygen species to participate in the decomposition of OTC.As a result,OCN-24-550 can effectively degrade 85.76%of OTC under 120 min of visible light irradiation.The degradation process well fits the pseudo-first-order kinetic model,and the reaction rate constant is0.0164 min^-1,which is 11.71 times that of the initial BCN.(2)The highly crystalline porous g-C₃N₄(CPCN)with electron accumulation capacity was prepared by a KCl-confined calcination method and applied for the degradation of ciprofloxacin(CIP).The experimental results show that during the preparation of CPCN,KCl can provide the inter-crystal confined space for the polymerization process and introduce-C?N and K⁺,while the decomposition of supramolecular precursors will guide the formation of porous structures.Specifically,the electron withdrawing group-C?N will distort the structure of g-C₃N₄,so that the electron in the exciton is quickly extracted by-C?N,and then stabilized by K⁺,giving CPCN the electron accumulation ability.The electron accumulation process promotes the dissociation of exciton and the separation of charge carrier,and the separated electron will activate molecular oxygen to generat e ROS(such as·O₂^-,H₂O₂ and·OH)to participate in the degradation of CIP.As a result,after 90 min of visible light irradiation,CPCN can effectively degrade 85.8%of CIP,which is significantly higher than that of BCN(48.1%).(3)In order to study the driving force of the electron withdrawing group in the process of extracting electron,causing exciton dissociation and carrier separation,carbonyl and carboxyl groups functionalized few-layer ultrathin g-C₃N₄(FCN-12)was prepared through an acid oxidation method,and the obtained FCN-12 was applied for the degradation of chlortetracycline hydrochloride(CTC)through the photocatalytic activation of peroxymonosulfate(PMS).Experimental results show that the carbonyl and carboxyl groups will creat e an upward energy band bending with the height of?0.17 e V in the space charge region of FCN-12.Acted as a driving force,the energy band bending can quickly extract photogenerated electron,and achieve effective photogenerated exciton dissociation and photoge nerated charge carrier separation by preventing its backflow.After adding PMS,the photogenerated electron accumulated on the carbonyl and carboxyl groups of FCN-12 will activate PMS to generate ROS(SO₄^·-,·OH,¹O₂ and·O₂^-)to participate in the degradation of CTC.As a result,the FCN-12/PMS/vis system can efficiently degrade 83.4%of CTC within120 min.In addition,the FCN-12/PMS/vis system has a good anti-interference ability,and can effectively degrade CTC in a certain range of p H variation and the coexistence of some anions.(4)In order to further study the role of energy band bending in exciton dissociation and charge carrier separation,a co-catalyst Co B with strong electron-withdrawing ability was introduced into g-C₃N₄ nanosheets(CNs)by electrostatic self-assembly coupled calcination method,and the obtained Co B/CNs Schottky junction photocatalyst was applied for the photocatalytic inactivation of Staphylococcus aureus(S.aureus).Experimental results show that the difference in work function between CNs and Co B will creat e an upward energy band bending of0.26 e V in the Co B/CNs Schottky junction.In Co B/CNs,the strong electron-withdrawing ability of Co B promotes the dissociation of photogenerated exciton in CNs,while the upward band bending can prevent electron from flowing back to CNs and then realize the spatial separation of photogenerated charge carrier.In addition,the interface Co-N bond can effectively adjust the electron transfer kinetics,so that Co B/CNs-2 exhibits a more efficient two-step single-electron O₂reduction reaction,which improves the ROS generation ability of Co B/CNs-2.As a result,Co B/CNs-2 can not only completely inactivate 7×10⁷ CFU/m L S.aureus under125 min of visible light irradiation,but also can effectively degrade the intermediate produced in the process of bacterial inactivation.