Preparation Of Molecularly Anchored G-C₃N₄-based Nanomaterials For Efficient Photocatalytic Inactivation Of E.coli

In recent years,with the deepening of urban modernization,various pollution problems have become prominent,among which the problem of water pollution and microbial pathogens are the most prominent.More seriously,due to the widespread use of antibiotics,a large number of antibiotic resistant bacterias（ARBs）in the aquatic environment has caused frequent outbreaks of diseases.The traditional chemical and physical disinfection methods have the disadvantages of poor killing effects,incomplete sterilization,low sterilization efficiency,easy to produce disinfection by-products（DBPs）,etc.Photocatalytic sterilization technology has become a most notable subject with its extensive inactivation effect on pathogenic bacteria.Among the various photocatalysts,carbon nitride（g-C₃N₄）has attracted attentions due to its excellent visible light response and ease of modification adjustment.However,g-C₃N₄ still has some specific defects,such as small specific surface area,poor interfacial contact,low absorption efficiency,fast recombination of photogenerated electron-hole（e^--h⁺）pairs,lagging of proton and charge transfer,short lifetime of reactive oxygen species（ROS）and so on.Based on the above existing problems,it is imperative to develop g-C₃N₄-based photocatalytic materials with better optical performance.In this paper,a variety of carbon nitride-based photocatalytic materials which can efficiently inactivate drug-resistant E.coli in water were explored.The carbon nitride-based photocatalytic materials were modified by combination of various strategies to improve the responsiveness and range to visible light,achieve molecular anchoring and promote redox reactions.The strategies included element doping,molecular modification,noble metal deposition,and quantum dot heterostructure fabrication.At the same time,as the efficient photocatalytic inactivation of drug-resistant E.coli materials,the experimental and theoretical basis of the prepared material was analyzed by studying means of physics,chemistry and biology.The main research contents and conclusions were as follows:（Ⅰ）The cationic polymer polyethyleneimine（PEI）grafted and O-doped g-C₃N₄（PEI-OCN）was successfully prepared by one-pot thermal polymerization and subsequent covalent cross-linking reaction for the first time.It is found that PEI-OCN can integrate various photocatalytic sterilization properties such as regulating the intrinsic electronic structure of the material,prolonging the photogenerated charge lifetime,improving the charge transfer efficiency,and enhancing the bacteria-composites electrostatic adsorption.In the photocatalytic inactivation of drug-resistant E.coli,PEI-OCN showed good photocatalytic inactivation effects.At the concentration of 0.10 mg/m L,it could completely kill more than 7.00 log(CFU?m L^-1)drug-resistant E.coli within 30 min of visible light irradiation.The ROS including h⁺and·O₂^-played a major role in the reaction process.（Ⅱ）The structure and performance results found that Ag was successfully loaded onto the surface.At the same time,Ag promoted the generation of more ROS through its own SPR effect.Compared with PEI-OCN,the optical performance was further improved.Ag-PEI-OCN-5showed the best comprehensive performance,which had more appreciable sterilization performance.It is also an effective and rapid bactericide even under lower concentration and shorter illumination time.After being irradiated with visible light for 30 min,Ag-PEI-OCN-5showed a bactericidal performance over 7.00 log(CFU?m L^-1).The generation of ROS（such as h⁺,·O₂^-and so on）had increased obviously during the photocatalytic process.（Ⅲ）The heterojunction structure materials（CD-PEI-OCN）were obtained by loading N-CQDs quantum dots onto PEI-OCN surfaces.As an effective carrier of photogenerated electrons,N-CQDs had improved the photocatalytic performance of nanomaterials.For example,CD-PEI-OCN had stronger light absorption,lower electron-hole recombination rate and higher photo-generated carrier separation efficiency.Compared with PEI-OCN,CD-PEI-OCN-2 could produce more active species（·O₂^-and·OH）.At the concentration of 0.05 mg/m L,it could achieve 100%complete sterilization for drug-resistant E.coli within 30 min.