Ultra-high flux ceramic hollow fiber membranes for nanofiltration

High permeation is a prerequisite for the practical applications of nanofiltration membranes. In this work, gamma-Al2O3 hollow fiber nanofiltration membranes with high permeation have been fabricated by a single-step coating and sintering process. alpha-Al2O3 asymmetric hollow fiber supports with a smooth surface, which is featured as a surface roughness of 147 nm and mean pore size of 218 nm are first prepared by a phase inversion technique, using two types of Al2O3 powder with different particle-size ranges. A boehmite sol with colloidal particle size ranging from 220 nm to 825 nm is then coated and sintered on the outer surface of the hollow fibers to form the separation top-layer. Permeability can be improved by eliminating the membrane interlayer and controlling the thickness of gamma-Al2O3 separation layer via adjusting the viscosity of colloidal sol. Water permeance of the gamma-Al2O3 membrane with a thickness of 1 mu m reaches 47.03 L m(-2) h(-1) bar(-1) at the molecular weight cut-off (MWCO) of similar to 4750 Da at room temperature and 82.07 L m(-2) h(-1) bar(-1) at 60 degrees C, respectively. So far, this membrane reveals the highest water permeation at a similar MWCO compared with other reports. The present gamma-Al2O3 hollow fiber membrane also demonstrates superior separation performance for divalent ions with >85 % retention and for dyes of MW < 1000 Da, showcasing great potential in textile wastewater treatment and desalination applications.