Preparation And Dye Removal Performance Of PVDF Composite Graphene-based Catalytic Membrane

In recent years,photocatalytic technology has received widespread attention,among which semiconductor photocatalytic technology has become one of the research hotspots due to its green and efficient chemical degradation.Among semiconductor materials,zinc oxide(ZnO)is widely used in the field of photocatalysis due to its rich microscopic morphology,good biocompatibility and environmental safety.However,ZnO still has problems such as easy recombination of electrons and holes generated on the surface and low dispersion.In recent year,many studies on photocatalytic nanomaterials have shown that the photocatalytic efficiency of ZnO can be improved by inhibiting the light-induced recombination of electron-hole pairs or increasing the dispersibility.Therefore,we improve the catalytic efficiency by adjusting the microstructure of zinc oxide and combining it with modified graphene materials to construct binary and ternary composite catalysts.Furthermore,the composite catalyst is combined with a polyvinylidene fluoride(PVDF)separation membrane to prepare a composite graphene-based catalytic membrane and the catalytic mechanism and separation performance are studied.Nano-spherical ZnO was prepared on the surface of amination modified graphene(NGO)by in-situ growth method,and ZnO-NGO composite material was successfully prepared by solvothermal reaction.NGO can not only effectively contact ZnO particles,but also prevent ZnO from agglomerating,which can effectively increase the specific surface area of the composite material.In the photodegradation process,NGO provides multiple chelating sites for the photocatalysis of the composite material,which in turn enabled the composite material to have a higher adsorption rate for dyes.In addition,NGO could also significantly increase the lifetime of ZnO photoelectron-hole pairs,thereby increasing the photocatalytic removal rate of ZnO-NGO composites.Therefore,the ZnO-NGO composite material had a good photocatalytic removal rate for both methyl orange(MO)and methyl blue(MB),and the degradation effect of MB could reach 99%under a 300 W xenon lamp.Studies had found that rod-shaped ZnO had better catalytic performance.Using graphene oxide/zinc peroxide(GO/ZnO₂)as the precursor,a binary reduced graphene oxide/zinc oxide rod composite(RGO/ZnO)was prepared by a simple hydrothermal method.Under hydrothermal conditions,spherical ZnO₂ nanoparticles could be transformed into rod-shaped ZnO.The addition of RGO was significantly improved the photocatalytic ability of ZnO by enhancing the dispersion of ZnO and inhibiting the recombination of ZnO photogenerated electron pairs.The photodegradation rate of RGO/ZnO composites for MB and MO were both higher than 90%.Moreover,it was calculated that the apparent kinetic reaction rate constant(k)of RGO/ZnO composites was much higher than that of ZnO,ZnO₂ and RGO/ZnO₂ composites.In addition,the method also provided a possibility to combine with other materials to prepare rod-shaped ZnO.Potassium hydroxide(KOH)was mixed with RGO/ZnO₂,and the RGO/ZnO-ZnO₂ternary composite photocatalyst was prepared by solvothermal method.The addition of KOH was conducive to the formation of intermediates and can promote the conversion of ZnO₂,enabling the ternary composite structure contains both rod-shaped ZnO and spherical ZnO₂-supported flake graphene.Under xenon lamp irradiation,the degradation and removal rate of MO by RGO/ZnO-ZnO₂ was 99.82%in 100 min.This was because ZnO₂ participates not only as a semiconductor material in photocatalytic degradation,but also promoted the photocatalytic reaction by generating hydrogen peroxide.Moreover,the special two-dimensional structure and excellent conductivity of RGO could also enhance the catalytic performance of the composite material.In addition,the photocatalytic performance of RGO/ZnO-ZnO₂ was not affected by p H.In order to avoid the difficult recovery of RGO/ZnO nanoparticles after photodegradation,the PVDF/RGO-ZnO casting solution was mixed into the surface of the pure PVDF membrane to prepare a double-layer PVDF&PVDF/RGO-ZnO composite membrane.The addition of hydrophilic PEG and RGO/ZnO nanorods increased the porosity and hydrophilicity of the top layer PVDF/RGO-ZnO membrane,but did not significantly change the surface morphology of the PVDF membrane.The bottom layer PVDF membrane ensured the separation ability of the double layer membrane for dyes.Compared with pure PVDF membrane and single-layer composite membrane,double-layer composite membrane has better dye separation ability:the rejection rates for Acid Fuchsin(AF)and MO were 96.3%and 33.58%,respectively.The separation efficiency of the two-layer composite membrane for the mixture dyes was 41.4%.Under light conditions,the RGO/ZnO on the surface functional membrane can effectively degrade the dye adsorbed on the pores and surface of the membrane,and has recyclable use and anti-fouling properties.The synergy of the top and bottom membranes makes the prepared double-layer PVDF&PVDF/RGO-ZnO membranes show great potential application prospect in the field of water treatment.