Separation properties of γ-alumina nanofiltration membranes compared to charge regulation model predictions

Electrolyte retention of supported bi-layered nanofiltration membranes

“…5 clearly indicate that separation performance of the bi-layered membrane is considerably better than for systems with only a ␥-alumina layer. For ␥-alumina membranes NaCl retentions of about 40% at pH ≈ 9.5 were reported (at 1.6 MPa, see [9]) while in the bi-layered system R ≈ 95% in the alkaline region. This higher retention of the silica/␥-alumina system stems of course partly from the fact that the pore size of the silica layer is twice as small as that of the ␥-alumina, but is also a direct result from the high (negative) membrane charge of the silica at neutral and alkaline pH.…”

“…Those films were then ground and suspended in 1, 10 and 100 mol/m 3 electrolyte solutions of NaCl at various pH. A detailed description of the preparation procedure of the solutions for the electrophoresis experiments is given elsewhere [9]. The potentiometric titration experiments were performed at the Physical Chemistry and Colloid Science Group of the University of Wageningen.…”

“…For ␥-alumina this method has already been used previously and a pore size of 2.0 nm was obtained [9]. An explanation of this procedure is described in Appendix A.…”

“…The ion retention experiments were performed at 25 ± 1 • C on a dead-end permeation set-up with a volume of 2 dm 3 under rapid stirring [9]. The retention experiments were conducted with aqueous solutions of 1 mol/m 3 NaCl at various pH.…”

“…A NF membrane performs ion separation best at pH values far from its iso-electric point (IEP), as this corresponds to a high membrane potential. Apart from the pH, the membrane potential and charge is also a strong function of the type of ions present in the electrolyte solution and their concentration [1][2][3][4][5][6][7][8][9].…”