LAUSR

Abstract SiO 2 -ZrO 2 (5/5, 3/7) nanofiltration membranes with a low molecular weight cut-off (MWCO) were fabricated by coating different Si/Zr molar ratios of 5/5 and 3/7 sols from large to small colloidal sol sizes on cylindrical α-alumina porous supports with firing at 550 °C. The pore sizes of the membranes were controlled by the SiO 2 -ZrO 2 colloidal sol sizes used for the top layer. SiO 2 -ZrO 2 membranes with a MWCO of less than 60, and 160–180 for neutral solutes, showed water permeabilities of (0.2–0.4)×10 –12 and (1.9–2.7)×10 –12  m 3 /(m 2  s Pa), respectively. The solute rejections were strongly dependent on the type of solute; the rate of rejection for alcohols was much higher than that for either glycols or sugars. SiO 2 -ZrO 2 membranes with a low MWCO showed hydrothermal stability and high nanofiltration performance in water at 90 °C. The water permeabilities of membranes increased from 2.5×10 –12 to 11.9×10 –12  m 3 /(m 2  s Pa) in operating temperatures from 25 to 90 °C, while the MWCO increased slightly from 150 to 210. This indicates that SiO 2 -ZrO 2 membranes with a low MWCO showed excellent nanofiltration performance at high temperatures. The permeation properties for nanofiltration membranes were analyzed using the Spiegler-Kedem equation.