An improved synthesis of ultrafiltration zirconia membranes via the sol–gel route using alkoxide precursor

Crack-free ultrafiltration zirconia membranes were synthesized using zirconium butoxide via the sol–gel route. Unlike the conventional technique, the esterification of anhydrous butanol and glacial acetic acid provided the hydrolyzing water. In addition, acetic acid also served as a chelating ligand to stabilize the hydrolysis–condensation process and minimize the agglomeration of zirconia. Esterification was verified by its product, butyl acetate, as identified by a GC/Mass. FTIR spectrum confirmed the presence of bidental ligand. HNO3 was used to perform the peptization, creating a stable particulate sol with pH near 1. The sol was spin-coated on anodic alumina discs, dried under programmed temperature and humidity, then calcined at 500°C to remove organics. Grazing incident XRD verified that the zirconia membrane was partially transformed to the tetragonal phase. SEM showed a uniform layer 0.15 μm thick on top of the support. Based on nitrogen permeation, the flow-average pore diameter of the ZrO2 membrane was estimated near 3.6 nm. The pore size distribution of unsupported zirconia was measured from nitrogen adsorption/desorption indicating two modes, centered at 1.5 and 3.6 nm, respectively. TEM revealed that the particle size of zirconia ranged from 5 to 10 nm. Our results illustrate that ZrO2 layer is the closed-packing of nano-size spherical particles. Supported zirconia membrane was tested by a cross-flow ultrafiltration. The rejection of soybean oil/hexane solution achieved 37% which was much better than that of bare disc.