Fabrication and characterization of Y-doped ZrO₂ nanofiltration membranes by aqueous sol-gel process

Crack-free tubular yttria-stabilized-zirconia (YSZ) nanofiltration membranes was fabricated via an aqueous Sol-Gel process, using zirconium oxychloride as precursor and water as solvent. This procedure was completely free of organic solvent and thus was environmentally friendly. The influences of precursor concentration and calcination temperature on the particle size of sols, crystal and pore structure were investigated. The results revealed that the sol prepared with lower precursor concentration and calcined at 400℃, has higher content of monoclinic phase, thus leading to the increase of pore size. Subsequently, addition of 8mol% yttrium into the sol inhibits phase transformation from tetragonal to monoclinic and grain growth, as well as avoid membrane cracking. In addition, retention experiment result shows that the YSZ nanofiltration membrane exhibits a molecular weight cut-off (MWCO) of 860 Da and a water permeability of 200 L/(m²·h·MPa). Furthermore, ions retention properties of YSZ nanofiltration membrane towards four solutions like NaCl, Na₂SO₄, CaCl₂, and MgCl₂, were conducted at pH 6 and a transmembrane pressure of 0.8 MPa. The retention properties of YSZ nanofiltration membrane towards CaCl₂ and MgCl₂ solutions reach maximum values of 65% and 78%, respectively.