Synthesis of TiO_2 Ultrafilter Membranes on Functionally Graded Porous Alumina

摘要

For the first time defect-free titania ultrafilter monolayers with the thickness of <2 μm were deposited on graded porous alumina supports without intermediate layers through optimizing the conditions of the sols and using proper supports with low roughness (< 0.4 μm). The disc shaped supports with the mean pore size of 0.5 μm were prepared via centrifugal casting with the acceleration of 3000 g. The mean pore size and porosity of the upper side of the supports were 0.38 μm and 10.7%, respectively. The sols were prepared via peptization using tetra iso propyl ortho titanat. Unlike other reported researches, the colloidal sols were prepared without heating and their average particle sizes (12-22 nm) were smaller than the ones prepared by similar methods (>35 nm). By applying preheat-treatment on the hydrogel, a new method was invented to control the sol particle size. Unsupported titania membranes in the form of thin films with the pore diameter of approximately 3 nm and the porosity of 49 to 57% were synthesized. Porosity and average pore sizes of the titania ultrafilters were studied by BET as a function of sintering temperature, concentration of zirconia as impurity (0, 1, 2 wt%) and presence of PVA. In addition, the effect of the presence of zirconium ions on delaying the anatase to rutile transformation was evaluated by insitu-XRD. The lack of microcracks in the titania ultrafilter layers deposited on the supports were confirmed by gas permeability tests and SEM.