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

• An aqueous sol–gel method for crack-free ZrO2 NF membrane is presented.
• The tetragonal ZrO2 could be stabilized at 400 °C by introducing glycerol.
• ZrO2 NF membranes show a permeability of 13 L m−2 h−1 bar−1 with a MWCO of 750 Da.
• The membranes show a good performance for the PEG retention in the presence of NaCl.

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 750 Da and a permeability of 13 L m−2 h−1 bar−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.