Preparation And Performance Study Of PVDF Nanofiltration Catalytic Composite Membrane

With the rapid development of industry,the problem of water pollution has become increasingly serious,and water treatment technology has received widespread attention.It is difficult to remove the small molecular pollutants such as 4-nitrophenol and organic dyes from industrial wastewater by traditional polymer membrane technology.In this study,nanofiltration and precious metal catalysts are combined to prepare membranes with both nanofiltration and catalytic functions.The removal of pollutants in wastewater through the coupling of retention and catalysis achieves an efficient decontamination effect.The prepared membrane and main research contents are as follows:1.PA/PVDF-Ag membrane:PVDF powder and polymethacrylic acid(PMAA)microspheres prepared by distillation precipitation polymerization are blended to prepare a membrane,and then Ag ion chelation,in-situ reduction was performed to obtain a catalytic membrane loaded with silver nanoparticles(Ag NPs).Afterwards,the interfacial polymerization method is used to form a polyamide nanofiltration layer on the catalytic membrane to obtain a novel membrane combining catalysis and nanofiltration.Fourier infrared spectrometer(FTIR),X-ray photoelectron spectrometer(XPS),scanning electron microscope(SEM)and true color confocal microscope(CSM)were used to characterize the element composition,morphology and surface roughness of the composite membrane.In addition,the paper also investigated the effects of temperature,pressure and Ag nanocatalyst loading on the catalytic removal of 4-nitrophenol.Studies have shown that the conversion rate of 4-nitrophenol catalyzed by the composite membrane is 65.05%when the load of Ag NPs is at a maximum of 0.814mg/g at 25?,pressure of 0.1 MPa.Combined with the retention part,the removal rate of 4-nitrophenol in the solution can reach 96.61%.With the increase of pressure,the removal rate of 4-nitrophenol by the composite membrane decreased slightly,but the removal rate could still reach 91.04%at 0.6 MPa.2.PA-Ag/PVDF membrane:With PVDF/PMAA membrane as the supporting layer,the polyamide layer is prepared by interfacial polymerization,and then the polyamide layer of the composite membrane is soaked with a mixed solution of silver nitrate and m-phenylenediamine,and the amino group is fixed by the polymerization of the amino group and the excess acid chloride on the polyamide layer.The complex formed with silver ions is then reduced in situ to obtain a nanofiltration composite membrane with Ag nanocatalyst on the surface.FTIR,XPS,SEM and CSM were used to characterize the composition membrane.The retention rate of Congo red dye by composite membrane can reach 100%.Further,Congo red dye(0.5 L,10 mg/L)was catalyzed for degradation by cross-flow mode circulating on the surface of the composite membrane with an effective area of 17.9 cm².At the tangential flow rate of752.16 ml/min,100%degradation of dye could be achieved within 18min.The effects of temperature,Congo red concentration,Na BH₄ concentration and Ag nano-catalyst load on catalytic degradation were also investigated.The increase of temperature,Na BH₄ concentration and Ag NPs load are conducive to the catalytic reaction,while the increase of Congo red concentration reduces the reaction rate.The composite membrane catalyzed Congo red has good cyclic stability,and the degradation rate of the dye is still over 94.83%after five cycles.The results showed that composite membrane catalyzed Congo red has good cycling stability.