Fabrication of TiO₂-doped ZrO₂ nanofiltration membranes by using a modified colloidal sol-gel process and its application in simulative radioactive effluent

TiO₂-doped ZrO₂ (hereafter denoted as TDZ) nanofiltration (NF) membranes with stable tetragonal phases are efficiently fabricated via a modified colloidal sol-gel process using a mixture of Zr-inorganic salts and Ti-alkoxides. Nanometer-sized TiO₂-ZrO₂ (hereafter denoted as TZ) colloidal sols with an average hydrodynamic diameter of ~2 nm are synthesized, showing good stability and reproducibility. The resulting TDZ materials are characterized by XRD, TEM, XPS, CA, mapping and nitrogen sorption. It is shown that the incorporation of Ti⁴⁺ restrains the t→m phase transition, decreases the tetragonal crystallite size, enhances the hydrophilicity, increases the specific surface area and narrows the pore size distribution. Furthermore, these changes are promising for fabricating high performance NF membranes. The as-prepared TDZ NF membranes exhibit high performances with a low MWCO of ~500 Da and a high pure water permeability of 35~40 L m^-2 h^-1 bar^-1, as well as desired retention rates of 99.6% for Co²⁺, 99.2% for Sr²⁺ and 75.5% for Cs⁺, in simulative radioactive waste water treatment.