Preparation of zirconia nanofiltration membranes through an aqueous sol-gel process modified by glycerol for the treatment of wastewater with high salinity

ZrO₂ nanofiltration (NF) membranes are attracting increasing interest for the treatment of wastewater with high salinity owing to the material stability and processing efficiency. This work presents an approach to synthesize zirconyl oxalate aqueous sols through a straightforward sol-gel route by introducing glycerol to modify zirconium oxychloride for fabricating a pure tetragonal ZrO₂ NF membrane with high permeable and separation performance. The glycerol, acting as a capping agent, binds to the surface of the sol particles resulting in stable nano-sized sol particles and then inhibiting the t→m phase transformation when calcination at 400°C. A crack-free ZrO₂ NF membrane with a molecular weight cut-off of 750Da and a permeability of 13Lm^-2h^-1bar^-1 was prepared. By comparing to the reference system with polymeric NF membrane for the treatment of model wastewater with high salinity, we demonstrate that, both ZrO₂ and polymeric NF membranes show similar retention performance (higher than 90%) of pure polyethylene glycol (molecular weight=1000). However, at the high NaCl mass fraction varying from 0% to 24.92%, the ZrO₂ NF membrane displays much better retention performance at about 68% while only 36% for polymeric NF membrane. Our results indicate the potential application of ZrO₂ NF membranes in the wastewater with high salinity.