No abstract

Poly(vinylidene fluoride) (PVDF) membranes without any additives were fabricated by a vapor-induced phase separation method and applied to the adsorption separation of vitamin B12 (VB12) from aqueous solution. The effects of preparation conditions including PVDF concentration in dope, vapor humidity, and exposure time on the morphologies, mechanical strength, adsorption, and permeation performances are investigated in detail. The results indicate that the PVDF membranes have a uniform spongy structure without macrovoids. The lower polymer concentration, relatively higher humidity, and longer exposure time easily leads to the formation of larger polymer nodules in the membrane matrix and lower mechanical strength of membranes. The resulted PVDF membranes exhibit superior separation efficiency for both static and dynamic adsorption for VB12. In the ultrafiltration (adsorption)-regeneration cycles, the permeation flux remains above 2500 L m −2 h −1 bar −1 and the VB12 removal ratio is above 92% after six cycles. The prepared PVDF membranes show superior adsorption capacities to other traditional adsorbents (such as activated carbons, nanoclay, etc.) for VB12 removal.