Preparation Of Nano ZnO/PVDF Ultrafiltration Membrane And Its Photocatalytic Degradation Performance Of PNP

P-nitrophenol(PNP)has been accumulated in the surrounding environment because of its poor biodegradability,stable physicochemical properti es,high toxicity and bioaccumulation,which seriously endangered the living environment and health of human beings..Photocatalysis combined with membrane separation technology exerting the function of membrane separation,meanwhile the presence of photocatalyst improves the hydrophilicity and self-purification of the membrane.It solves the problems of membrane fouling and the difficulty in degradation of concentrated solution and the difficulty recovery of photocatalyst in every single process.It has broad research prospects.In this paper,nano-ZnO photocatalysts were prepared by microwave hydrothermal method.Then,the dominant active species in the photodegradation process of PNP by ZnO were explored by free radical trapping experiment,then the degradation products and mechanism of this system were inferred.Besides,the PVDF ultrafiltration membrane was prepared by immersion precipitation phase inversion method.Then the Nano-ZnO/PVDF ultrafiltration membrane was prepared with PVDF and ZnO by blending method,which combines dual functions of photocatalysis and membrane separation.The effect of the addition of ZnO on the properties of ZnO/PVDF ultrafiltration membrane and the photocatalytic degradation of PNP in water were investigated..Then the process conditions of the PNP treated by the ZnO/PVDF ultrafiltration membrane and membrane cleaning were investigated..During the experiment,PNP was used as the target pollutant on the photocatalytic performance test of the catalyst and membranes.In additi on,X-ray diffraction(XRD),scanning electron microscope(SEM),Fourier transform infrared spectrometer(FTIR),ultraviolet-visible diffuse reflectance spectrometerz(UV-vis DRS),thermogravimetric analyzer(TG/DTG),water contact angle tester were used to evaluate the catalysts and composite membrane.The results showed that the optimal conditions for preparation of ZnO nanoparticles by microwave hydrothermal method were as follows: hydrothermal temperature was 180 °C and hydrothermal time was 30 min.The ZnO prepared under the optimal conditions was the hexagonal wurtzite crystal structure with nanosheet-like and it is a mesoporous material with an average pore diameter of 17.92 nm and a large specific surface area.When it was put under the simulated visible light for 3 h,the removal rate of PNP was 94.43%;The free radical trapping experiment showed that the main active species in the photocatalytic degradation of PNP by ZnO was positive hole.Therefore,it was speculated that the intermediate products of PNP degradation were hydroquinone,1,2,4-Trihydroxybenzene,3,4,5-Trihydroxynitrobenzene,p-nitro catechol,para-benzoquinone,etc.The optimal conditions for the preparation of pure PVDF ultrafiltration membrane by phase inversion method were as follows: the concentration of PVDF was 18%,the content of PVP was 6%,and the water bath temperature was 50 °C.Pure PVDF membranes prepared under these conditions have the highest pure water flux and the retention of bovine serum albumin could up to 100%;The ultrafiltration performance,hydrophilicity,mechanical properties and thermal stability of the membrane can be improved by adding appropriate amount of photocatalyst to the PVDF membrane.When the mass ratio of ZnO/PVDF was 0.15,the pure water flux of the ZnO/PVDF ultrafiltration membrane was 23.08% higher than that of the pure membrane.The addition of ZnO nanoparticles has improved the removal rate of PNP in water by ZnO/PVDF ultrafiltration membrane.The removal efficiency of PNP was 57.44% when it was put under simulated sunlight irradiation for 3 h,which was 5 times higher than that of pure PVDF membrane.After 9 cycles,it still maintains good photocatalytic stability.Nano-ZnO/PVDF ultrafiltration membrane has a 20% reduction in flux attenuation of BSA,compared to non-irradiated,when it was put under simulating solar irradiation.Therefor it had a certain degree of self-purification capability.The chemical method was used to clean the contaminated ultrafiltration membrane.It was found that the use of strong alkali cleaners had the best cleaning effect on contaminated ultrafiltration membranes,in which the flux recovery rate of BSA was 94.67%.