Study On The Effective Construction Of Self-cleaning Surface Of PVDF Composite Microfiltration Membrane And Its Oil-water Separation Performance

Membrane separation technology has the advantages of high efficiency,low energy consumption and low cost.Microfiltration membrane is one of the core membrane types of membrane separation technology,which is susceptible to contamination during daily use.With the development of industry and urbanization level,the discharge of wastewater is increasing,and there are often a large number of pollutants in wastewater,such as oil,dyes and other organic pollutants,which will adhere to the membrane surface during the separation process and cause irreversible contamination to the membrane.Therefore,membrane cleaning is extremely important in the membrane separation process,however,excessive cleaning can also cause damage to the membrane,so there is a preference to produce a microfiltration membrane that can be self-cleaning.Photocatalytic technology has the advantages of being environmentally friendly and pollution-free,and is an efficient and environmentally friendly method for treating printing and dyeing wastewater,but it also has some problems,such as the catalyst is difficult to recycle and reuse.In this context,it is of practical application to combine photocatalysis technology with membrane separation technology to prepare photocatalytic oil-water separation membranes with dual functions of separation and dye degradation.In this study,polyvinylidene fluoride（PVDF）was blended with ethylene-co-maleic anhydride copolymer（PEMA）,which is a hydrophobic polymer,and PEMA is a maleic anhydride copolymer,which can be decomposed into carboxyl groups and has high hydrophilicity.We also perform photocatalytic experiments by depositing substances with photocatalytic properties on the blended membrane to degrade oil and water contaminants on the membrane,and to perform dye adsorption degradation to verify the self-cleaning ability of the membrane.（1）Using the prepared PVDF/PEMA blended membrane as the main body,after acid-base treatment,the membrane was enriched with carboxyl ions,and Zn S was deposited in situ on the membrane by using the coordination effect between the carboxyl ions on the membrane and Zn²⁺to prepare a composite PVDF/PEMA membrane with Zn S loading carboxyl-rich ions.The results showed that with the increase of PEMA content,the water contact angle of the composite membrane tended to decrease and then increase,and the water flux tended to increase and then decrease,and the hydrophilic performance of the carboxyl-rich PVDF/PEMA composite membrane was optimal when the content of PEMA accounted for 20%of PVDF.The water contact angle of the membrane decreased from 91.16°to 42.7°,and the pure water flux increased from1120.30 L·m^-2·h^-1·MPa^-1 to 3570 L·m^-2·h^-1·MPa^-1;after in situ deposition of Zn S,the hydrophilic performance of the membrane improved again,in which the best hydrophilic performance was obtained after four cycles of mineralization with a water contact angle of 16°and a pure water flux of The surface morphology of the prepared membranes was analyzed using field emission scanning electron microscopy（SEM）and X-ray diffractometer（XRD）,as well as the elements contained in them.By EDS and Mapping,it can be concluded that Zn S was uniformly deposited on the surface and cross-section of the composite microfiltration membrane,indicating that the composite membrane with Zn S-loaded carboxyl-rich PVDF/PEMA was successfully prepared.Moreover,the diffraction peaks of Zn S on the membranes were obtained by XRD and were consistent with previous reports,further indicating that Zn S was successfully deposited on the composite membranes.The oil-water separation experiments on the prepared composite membrane can be concluded that the composite membrane exhibits super oleophobicity in water,and the separation efficiency of the oil-in-water emulsion containing vegetable oil reaches more than 97%.In addition,the membrane has self-cleaning property and anti-pollution property.The degradation efficiency of methylene blue was more than 98%,and five repetitions of adsorption-degradation experiments showed that the membrane has excellent reusability.Therefore,the membrane has potential applications in emulsion separation and dye degradation.（2）Using the prepared PVDF/PEMA blended membrane as the main body,the surface of PVDF/PEMA blended membrane is rich in carboxyl groups,which can ligated with Fe³⁺and then formedβ-Fe OOH nanoparticles.Subsequently,Fe³⁺was mineralized intoβ-Fe OOH nanoparticles and deposited on the PVDF/PEMA membrane to obtain the composite microfiltration membrane withβ-Fe OOH-loaded carboxyl-rich PVDF/PEMA.β-Fe OOH has excellent hydration ability and can react with H₂O₂ under UV light irradiation to give the membrane superwetting and photocatalytic self-cleaning properties.The surface morphology as well as elemental content of the composite membranes were analyzed by Fourier infrared spectroscopy（ATR-FTIR）,SEM,XRD,X-ray photoelectron spectroscopy（XPS）,etc.It can be concluded by ATR-FTIR that PEMA and PVDF were mixed uniformly,and under the analysis of EDS,Mapping,XPS,XRD,β-Fe OOH was successfully prepared on the membrane.When the Fe³⁺concentration was0.1 mol/L,the hydrophilic performance of the co-blended membrane was optimal with a water contact angle of 20.34±0.65°and a pure water flux of 1845.65±19.68 L·m^-2·h^-1·bar^-1.The M@β-Fe OOH（0.1）prepared under the optimized conditions could be rapidly wetted within 6 s and the pure water flux could be maintained at 1845.65±19.68 L·m^-2·h^-1·bar^-1,and the retention rate of vegetable oil could be maintained at 98.4%.The M@β-Fe OOH（0.1）membrane contaminated with vegetable oil has a fast and stable self-cleaning performance by UV light photo-Fenton self-cleaning experiment.The degradation rate of methylene blue could reach more than 99%at p H=2 and H₂O₂concentration of 9 mmol·L^-1,and the degradation rate of methylene blue by this composite microfiltration membrane was still above 90%under 10 replicate experiments.It indicates that the prepared membranes are reusable.