Fabrication of a sol–gel derived microporous zirconia membrane for nanofiltration

This paper reports the fabrication and nanofiltration properties of a sol–gel derived microporous zirconia membrane. Effects of synthesis parameters, including hydrolysis time, hydrolysis temperature, hydrolysis ratio and chelating agent dopant, on the state and size of polymeric zirconia sol, were investigated. Highly reproducible and stable zirconia sol after refluxing at 40 °C for 180 min, with an average particle size of approximately 8.6 nm, was synthesized with a recipe of [Zirconium n-propoxide]: [Diethanolamine]: [1-propanol]: [H2O] being 1: 2.2: 28.7: 9.4 (in molar ratio). The sol was subsequently used for the fabrication of microporous ZrO2 membranes onto alumina supported mesoporous γ-Al2O3 layers. ZrO2 membranes with molecular weight cut-off (MWCO) of 354, 1,195, corresponding to the pore size of 0.94 and 1.75 nm, were successfully fabricated. Ionic retention properties of such ZrO2 membranes with respect to electrolyte solutions, like MgCl2, CaCl2, NaCl and Na2SO4, were also determined. Effects of parameters such as concentration of salt solutions and trans-membrane pressure on retention rates of microporous ZrO2 membranes were studied in detail. Results showed that zirconium n-propoxide derived microporous ZrO2 membranes exhibited comparatively high retention rates towards divalent ions like Mg2+ and Ca2+, while much lower retention rates were observed for mono-valent ion (Na+) in the present study, which are the characteristics of nanofiltration membranes.