110th Anniversary: Liquid Separation Membranes Based on Nanowire Substrates for Organic Solvent Nanofiltration and Membrane Distillation

Ceramic nanowire-based flat porous membranes allow development of organic-inorganic membranes. Two types of surface modifications of alumina nanowire-based membranes were implemented. The first one involved reaction of hydroxyl groups on an alumina surface with silicone oil at a higher temperature, developing a grafted coating yielding a nonporous or a porous hydrophobic membrane. The hydrophobicity was verified via a contact angle comparable to that of a porous hydrophobic ethylene chlorotrifluoroethylene membrane. The membrane porosity was demonstrated by running vacuum membrane distillation with a 1 wt % salt-containing brine. The process yielded satisfactory water vapor flux with 98% salt rejection. The silicone oil's reaction with the alumina surface could also block the pores, yielding a nonporous membrane for organic solvent nanofiltration (OSN). Interfacial polymerization was also carried out on the porous nanowire membrane to yield a nonporous polyamide membrane. The developed membrane was tested for OSN using the dyes Safranin O (MW, 351 g/mol) and Brilliant Blue R (MW, 826 g/mol) in methanol. Rejections of 68.1% and 76.7% were achieved for Safranin O and Brilliant Blue R, respectively, at a relatively low pressure of 551 kPag (80 psig). The methanol permeabilities were higher than those of a few nanofiltration membranes described in the literature.