Fabrication And Research Of Poly (Vinylidene Fluoride) Composite Membrane With Anti-fouling Property For Membrane Distillation

In this paper,using poly?vinylidene fluoride??PVDF?flat sheet microporous membranes as support membranes,hierarchical micro/nano-composite membranes with superhydrophobicity were fabricated by the immersion-deposition method and the surface grafting method.As a simple and practical surface modification way,the immersion-deposition was applied to immobilize silica?SiO₂?nanoparticles on the membrane surface with the aid of PVDF binder,in order to increase the roughness of the membrane surface.The surface grafting method was performed to graft the fluoroalkylsilane coupling agents 1H,1H,2H,2H-perfluorooctyltrichlorosilane?PFOTS?on the nanoparticles,so that the solid surface energy of the membrane surface decreased.A variety of techniques were carried out to characterize and analyze the effects of surface modification on surface morphology,cross-section structure,chemical composition and hydrophobicity of composite membranes,such as scanning electron microscopy?SEM?,atomic force microscopy?AFM?,attenuated total reflectance-Fourier transform infrared spectroscopy?ATR-FTIR?,X-ray photoelectron spectroscopy?XPS?and contact angle goniometry.Meanwhile,the stability,non-wetting property and antifouling performance of derived composited membranes were investigated in the process of membrane distillation.The results showed that PVDF flat sheet microporous membranes were prepared by non-solvent induced phase separation?NIPS?.The optimum conditions were that there were 12 wt%PVDF,5 wt%LiCl and 5 wt%PEG-400 in the casting solution,in addition,the first coagulation bath was composed of 70 vol%isopropanol and 30 vol%deionized water and the second coagulation bath was pure water.Besides,the coagulation bath temperature was controlled at 25°C.In the process of surface modification,the micro/nano dual structure made up of PVDF crystalloid microspheres and SiO₂ nanoparticles was formed on the composite membrane surface uniformly when the immersion solution included 0.5 wt%PVDF resin,2.5 wt%SiO₂ nanoparticles?or the mass ratio of SiO₂ and PVDF was 5:1?.In addition,the mixture of N,N-dimethyl formamide?DMF?and acetone?AC?was used as the solvent in the immersion solution and the volume ratio of DMF and AC was 5:5.After a series of direct contact membrane distillation?DCMD?tests,it could be found that derived composite membrane presented excellent anti-fouling performances for inorganic salts and organic substances with the rejection rate above 99.99%.The prepared composite membrane with outstanding anti-fouling property is suitable for membrane distillation and there is a great application potential in the membrane distillation operation.