Titania membranes for liquid phase separation: effect of surface charge onflux

Titania membranes were prepared by sol-gel processes. Molecular weight cut- offs (MWCO) were successfully controlled in the range from 500 to 1000 with pure water permeabilities of 0.6-1.5 x 10(-11) m(3) m(-2) s(-1) Pa-1. Nano filtration experiments were carried out for various types of electrolytes ( NaCl, Na2SO4, MgCl2 MgSO4) using several membranes having different MWCOs ( 400, 500, > 1000). Rejection showed the minimum values near the isoelectric point (IEP) which were determined by streaming potential measurements. Lar ger rejections were obtained for the case where electrolytes having divalen t co-ions were nanofiltrated, while low rejection were observed for the cas e of electrolytes having divalent counterions. On the other hand, permeate volume fluxes were maximized near IEP and the fluxes were almost the same i rrespective of types of electrolytes. However, permeate volume fluxes decre ased at pH higher than IEP. The dependency was pronounced for the case of d ivalent counterions and smaller pore diameters, probably because of larger hydrodynamic resistance by ionically-adsorbed counter ions. (C) 2001 Elsevi er Science BN. All rights reserved.