Fabrication And Photocatalytic Antibacterial Performance Of GO/g-C₃N₄/TiO₂ Heterojunction

The marine biofouling will cause the increase of ship weight and energy consumption,the loss of functions of marine instrument sensors,the destruction of oil platform,and the blockage of meshes leading to the decline of marine aquaculture production and so on.TiO₂photocatalyst antibacterial agent has attracted extensive attention in the field of marine antifouling due to its advantages of broad spectrum,excellent chemical stability and environmental friendliness.However,it can only absorb the ultraviolet light,which accounts for 4%of the sunlight,and there is a problem of high recombination rate of photogenerated charge carriers.So,the photocatalytic antibacterial efficiency is limited,making it difficult to meet practical needs.This article focuses on the issues of poor visible light absorption ability and high recombination rate of photogenerated carriers in TiO₂.The visible light responsive g-C₃N₄ and zero bandgap GO are introduced,and different types of GO/g-C₃N₄/TiO₂ ternary heterojunctions are constructed using alkali thermal and in situ synthesis methods,respectively.The GO/g-C₃N₄/TiO₂ heterostructure is optimized through controlling group distribution ratio and process parameter.The morphology,phase,element composition and molecular structure were characterized and analyzed,and the visible light catalytic antibacterial properties of GO/g-C₃N₄/TiO₂ were systematically evaluated.Moreover,the relationship between the optical absorption and response characteristics,the activity and lifetime of photogenerated carriers and the antibacterial properties was clarified.The charge transfer mechanism of GO/g-C₃N₄/TiO₂ was revealed by combining experimental studies with theoretical calculations of DFT.Finally,in order to meet the requirements of marine antifouling,GO/g-C₃N₄/TiO₂ modified PVA hydrogel flocking layer was prepared,its suitability for photocatalyst powder immobilization was established.The GO/g-C₃N₄/TiO₂ was prepared using P25,g-C₃N₄,and monolayer GO as raw materials using alkali-heating.The optimal ratio was TiO₂:g-C3N₄:GO=100:2.5:2.5,and the photocatalytic degradation rate of MB under visible light conditions was as high as 97.7%.The sharp decrease in the transmission resistance of photogenerated carriers indicates that the introduction of GO can significantly accelerate the transfer of photogenerated carriers.However,the spectral absorption range is only expanded to 440.49 nm.The bactericidal rates to E.coli and S.aureus are 18.1%and 43.2%,respectively.So,the photocatalytic bactericidal effect needs to be improved.TBOT was used as the titanium source to prepare GO/g-C₃N₄/TiO₂ternary S-scheme heterojunction photocatalyst by three-step in situ synthesis.The optimal calcination temperature was 500°C,and the optimal mass ratio was TiO₂:g-C₃N₄:GO=100:80:2.5.The photocatalyst exhibited excellent bactericidal performance to E.coli,S.aureus and Marinobacter lipolyticus SM19（T）,with bactericidal rates of 98.2%,98.7%,and 99.0%,respectively;The spectral absorption range of GO/g-C₃N₄/TiO₂ has been extended to 595.02nm,and the bandgap value Eg has sharply decreased to 2.55 e V,significantly improving its absorption ability for visible light.Moreover,its visible light induced current density is 4.29times that of GO/TiO₂,16.85 times that of TiO₂,and 48.39 times that of g-C₃N₄.It also has the smallest EIS Nyquist arc radius and the lowest PL peak intensity,indicating that GO/g-C₃N₄/TiO₂ has the best photogenerated carrier generation and separation rate,the carrier transmission ability,and can effectively suppress the carrier recombination.The GO/g-C₃N₄/TiO₂ ternary S-scheme heterojunction photocatalyst achieves interface bonding through hydrogen bonding N····H–O,C^–≡Ti⁺between TiO₂ and g-C₃N₄,and N–sp³C between g-C₃N₄ and GO.The band bending at the interface between g-C₃N₄ and TiO₂ promotes band rearrangement,and photogenerated electrons transfer from the conduction band of g-C₃N₄ to GO.GO participates in the formation of the S-scheme heterojunction with band arrangement.The successful construction of the S-Scheme GO/g-C₃N₄/TiO₂ heterojunction achieved the space separation of photogenerated electrons and hole.The photogenerated electrons of g-C₃N₄ CB reduced O₂ to·O₂^-,resulting in improved photocatalytic antibacterial activity.The GO/g-C₃N₄/TiO₂ modified PVA hydrogel flocking layer was designed and prepared by using PVA hydrogel as the suspended photocatalyst immobilization carrier with its self-cleaning and anti-adhesion.It has excellent visible light photocatalytic bactericidal performance,and the bactericidal rates to E.coli,S.aureus and Marinobacter lipolyticus SM19（T）were 98.4%,99.7%,and 98.5%,respectively.The gap value of GO/g-C₃N₄/TiO₂composite PVA hydrogel tape is 2.50 e V,and the energy band edge is 636.53 nm,indicating that PVA is a good immobilization carrier for GO/g-C₃N₄/TiO₂ photocatalysis powder.