An aqueous sol-gel process for the fabrication of high-flux YSZ nanofiltration membranes as applied to the nanofiltration of dye wastewater

Ceramic nanofiltration (NF) membranes are becoming increasingly important for the recovery and purification of dyes and salts (e.g., NaCl) in high salinity waste streams. This work reports an aqueous sol-gel process for the preparation of high-flux yttria-stabilized-zirconia (YSZ) NF membranes derived from zirconium oxychloride, and the procedure is completely free of organic solvents. The use of zirconium oxychloride as a precursor dissolved in deionized water was expected to contribute to environmental protection and reduce cost. A crack-free thin YSZ layer was fabricated on α-Al₂O₃ supported ZrO₂ ultrafiltration membranes. The YSZ NF membrane exhibited a great water permeability of 28 L m^-2 h^-1 bar^-1 and a low molecular weight cut-off of 800 Da. Furthermore, the desalination and recovery were examined with fluorescent brightener wastewater in different operation parameters by YSZ NF membranes. The filtration results revealed that the fluorescent brightener retention increased slightly with increasing transmembrane pressure and cross-flow velocity. When the filtration was operated at 60°C, the fluorescent brightener recovery value of 99% was obtained while the NaCl removal was greater than 98%, meanwhile the flux was up to 89 L m^-2 h^-1 under suitable conditions, indicating that ceramic NF membranes were the technology of choice in treatment of high temperature dye wastewater.