Preraration And Application Of Hydrophilic/Hydrophobic Composite Membranes For Membrane Distillation

Membrane distillation（MD）is a new kind of liquid separation technology combining distillation technology with membrane separation technology,which is driven by a vapor pressure drop caused by the temperature difference between the both side of membrane.MD technology has been widely applied in domestic,industrial wastewater treatment,pharmaceutical concentrating and seawater desalination.During the long-term operation of MD,the membrane pores were easily wetted and fouled and resulted in the efficiency reduction of MD.In this paper,commercial polyvinylidene fluoride（PVDF）membrane was modified to be superhydrophobic to impove the ability of anti-fouling and wetting,and provided a theoretical bases to promote the industrialization of MD technology.In this paper,the Si O₂was hydrophobically modified by vinyltrimethoxysilane（VTMOS）,and the modified Si O₂was grafted onto the surface of commercial PVDF（polyvinylidene fluoride）membrane by self-assembly method.Meanwhile the VTMOS produced highly monodisperse spherical polyvinylsilsesquioxane（PVSQ）particles by selfhydrolysis and condensation reaction.The achievement of the superhydrophobic composite membrane,named PVDF-Si O₂/PVSQ,was attributable to the hierarchical micro/nano rough structure constructed by the random distribution of Si O₂particles and spherical.When the mass fraction of Si O₂reached 1.5 wt%,the results showed that the maximum water of contact angle modified membrane surface was up to 159.5°,and the sliding angle could reach 8.1°.The anti-fouling property of the commercial and modified membrane were investigated by direct contact membrane distillation（DCMD）experiments with feed solution containing Na Cl,HA and Ca Cl₂,the anti-wetting property was also tested with feed solution containing SDS and Na Cl.In this paper,the thiol-ene click reaction was induced by ultraviolet irradiation,so that the octa-vinyl polyhedral oligomeric silsesquioxane（OVPOSS）was grafted on the commercial PVDF surface,successfully fabricated the superhydrophobic composite membrane PVDF-OVPOSS.OVPOSS is highly crystalline,hierarchical rough structure with low surface energy composed of hexagonal OVPOSS crystals was formed on the modified membrane sureface in the process of grafting.The anti-fouling property of the commercial and PVDF-OVPOSS were investigated by DCMD experiments with feed solution containing foulants,such as HA,SA and BSA,the anti-wetting property was also investigated with feed solution containing surfactants,such as SDS,DTAC and LEO.In this paper,superhydrophobic composite PVDF membranes were fabricated through the above two method.A variety of techniques were performed to examine the difference in hydrophobicity,surface morphology,chemical composition,anti-fouling and anti-wetting properties between modified membrane and origin membrane.The results indicated that the superhydrophobic membrane prepared in this paper owned ideal anti-fouling and anti-wetting properties under the premise of ensuring the membrane flux.In summary,the methods provided in this papar was facile,environmentally friendly,low cost and offered great theoretical support in the industrialization of MD technology...