An ‘Eco-friendly’ all aqueous sol gel process for multi functional ultrafiltration membrane on porous tubular alumina substrate

An all aqueous sol gel process for developing photoactive titania ultrafiltration membranes on tubular macroporous commercial alumina substrate is presented. The precursor for titania was titanylsulfate and a multilayer approach was adopted for developing the membrane on substrates with average pore sizes of 1.4 μm. Substrate pore size was systematically reduced by an initial alumina slurry coating followed by a boehmite sol coating and finally a titania nano sol coating. The alumina suspension had an average particle size of 350 nm, boehmite sol, a particle size of 147 nm and the titania sol, 27 nm. After calcinations, the phase composition of the interlayer was α-alumina, that of boehmite layer was γ-alumina and the ultrafiltration top titania layer consisted of a mixture of anatase, rutile and brookite. The membranes were photoactive as observed from methylene blue degradation studies. Pore size reduction occurred from 1.4 μm to <100 nm by the multilayer coating. Highly uniform membrane layers on multichannel tubes of length 20 cm have been demonstrated. The presented method is an all aqueous process and no organic solvent was required for any step in the coating procedure. These membranes have a retention efficiency of 98% for ∼11 nm sized bovine serum albumin (BSA).