| One of the key issues to ensure the sanitation and safety of drinking water is the control of pathogens in the water,which is particularly important in today's epidemic of viral infectious diseases.Traditional disinfection technologies,including chlorine disinfection,ozone disinfection,and ultraviolet disinfection,are prone to produce toxic and harmful disinfection by-products,and have problems such as incomplete disinfection,high resurrection rates,and high operating costs.The photocatalytic disinfection technology can efficiently inactivate pathogens such as viruses and significantly increase the disinfection efficiency.It has the advantages of cleanliness,high efficiency,low energy consumption,and simple operation,is the current focus of the field of disinfection.However,most of the photocatalysts are currently limited to metal semiconductors and cannot fully utilize visible light as energy.Moreover,the most widely used "metal-free" visible-light-driven photocatalytic material g-C3N4 also has the problems of few specific binding sites and high photogenerated electron-hole recombination rate.Therefore,this paper intends to design a covalent organic framework(COF)material with large specific surface area,high stability,and high conjugation,and couple it with the green,low-cost photocatalyst g-C3N4 to form a new type of COF@g-C3N4 composite with heterogeneous structure.Then it was used to achieve the synergistic inactivation of virus in water by adsorption and visible-light-driven photocatalysis.Using the bacteriophage MS2 as the indicator virus,the photocatalytic inactivation performance of COF@g-C3N4 composite on waterborne viruses was clarified,the stability and reusability of COF@g-C3N4 composite was evaluated,and the synergistic inactivation mechanism of adsorption and visible-light-driven photocatalysis on waterborne viruses was revealed.The main research results of this paper are as follows:(1)In this paper,the COF@g-C3N4 composite material was synthesized by a two-step method of high temperature calcination and solvothermal method.It is a lamellar structure covered by a surface nano-network structure.Such a microstructure makes its specific surface area as high as 90.883 m2/g(4.4 times that of g-C3N4),giving it more adsorption and photocatalytic reaction sites.In addition,the two monomers in the COF@g-C3N4 composite are connected by a stable imine bond,which increases the degree of conjugation of the photocatalysis and the degree of separation of photogenerated electrons and holes,making it have a wider visible light absorption range,a narrower band gap(2.38 eV),and a stronger ability to the generation,separation,and migration of electron-hole pair.(2)Using the bacteriophage MS2 as the indicator virus,the visible-light-driven photocatalytic inactivation performance of COF@g-C3N4 composite on waterborne viruses was evaluated.1.0 g/L composite with the ratio of 1/6 can inactivate 1×107 PFU/mL phage MS2 by 5.8 log within 60 min under visible light irradiation,its inactivation rate(0.2502 min-1)was 7.36 times higher than g-C3N4(0.0340 min-1),and the inactivation process was found to be adsorption-visible-light-driven photocatalysis synergistic inactivation.In addition,the stability of the COF@g-C3N4 composite was investigated through cyclic experiments.After 5 cycles of repeated use,no significant reduction in the efficiency of phage inactivation was observed,which was in line with the 4 log inactivation requirements of the U.S.Environmental Protection Agency(EPA)(3)The large number of surface functional groups and large specific surface area in the COF@g-C3N4 composite provide a large number of sites for the adsorption of phage,and the adsorption of the COF@g-C3N4 composite to the phage is mainly physical adsorption.Adsorption is achieved through hydrogen bonding.The appropriate amount of adsorption shortens the mass transfer path of the reactive species(RS)produced by visible-light-driven photocatalysis,thereby ensuring that it can efficiently inactivate bacteriophages within a limited half-life.(4)In the COF@g-C3N4 composite,g-C3N4 and COF form a Type ?heterostructure at the interface,which significantly enhances the spatial separation of photo-generated electrons-holes,prolongs the life of photo-generated electrons-holes,and facilitates the progress of photocatalytic reactions.The ·O2-and ·OH generated by the reduction of dissolved oxygen by photogenerated electrons at the conduction band(CB),and the photogenerated holes(h+)at the valence band(VB)work together to achieve the inactivation of bacteriophages,where ·O2-plays a major role in inactivation.(5)During the inactivation process,the total protein concentration of the phage was reduced by approximately 65.3%,the TOC concentration was reduced by approximately 34.6%,and the RNA content was reduced by approximately 3.3 log.It proves that the inactivation mechanism of bacteriophage is that the oxidative damage of its surface protein leads to the leakage and rapid destruction of its internal material,that is,RNA,which ultimately leads to its complete loss of biological activity and no generation.In short,this paper designed a new type of COF@g-C3N4 composite,using the"Bait hook&Destroy" strategy to achieve efficient inactivation of phage in water via synergistic adsorption and visible-light-driven photocatalysis of phage.It provides new technical ideas and theoretical support for the disinfection of viral pathogens in water,and has important theoretical and practical significance for reducing the health risks caused by viruses in drinking water and ensuring water quality and safety. |
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