Al2O3 nanofiltration membranes fabricated from nanofiber sols: Preparation, characterization, and performance

Abstract Al2O3 nanoporous membranes for nanofiltration were successfully prepared from nanofiber sols (4 nm in diameter and 1400 nm in length) by controlling the number of sol coats and the firing temperature of the membrane. The effects of the number of sol coats and the firing temperature were characterized via X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2 adsorption-desorption, scanning electron microscope (SEM), transmission electron microscopy (TEM), nanopermporometry, and nanofiltration. A crack-free and continuous separation layer of the membranes, which is composed of Al2O3 nanofibers overlapping in the same direction on the membrane surface, was achieved. A greater number of sol coats greatly reduced the N2 permeance and water permeability of the membrane, but had no significant effect on either the average pore size or the molecular weight cut-off (MWCO). Meanwhile, firing temperature greatly affected the structure and separation performance of the membranes due to a transformation of the crystalline phase from boehmite to γ-Al2O3 under high temperatures. Al2O3 nanofiber-derived membranes had an average pore size and a MWCO that tended to be constant at 1.0 nm and 870–990 g/mol via firing at 200 °C, irrespective of the number of sol coats. Those values were increased, however, with increases in the firing temperature.