BACKGROUND: Ceramic membranes have received more attention than polymeric membranes for the separation and purification of bio-products owing to their superior chemical, mechanical and thermal properties. Commercially available ceramic membranes are too expensive. This could be overcome by fabricating membranes using low-cost raw materials. The aim of this work is to fabricate a low-cost γ -Al 2 O 3 -clay composite membrane and evaluate its potential for the separation of bovine serum albumin (BSA) as a function of pH, feed concentration and applied pressure. To achieve this, the membrane support is prepared using low-cost clay mixtures instead of very expensive alumina, zirconia and titania materials. The cost of the membrane can be further reduced by preparing a γ -alumina surface layer on the clay support using boehmite sol synthesized from inexpensive aluminium chloride instead of expensive aluminium alkoxide using a dip-coating technique.
This work addresses the advantages of the ultrasound stimulation method over the conventional heating method for the preparation of nanosized γ-Al 2 O 3 . The γ-Al 2 O 3 obtained by calcination of boehmite at 600 °C is derived from the inexpensive aluminum chloride salt by the precipitation route. Thermal evolution, phase transformation, surface area, and particle size distribution of the boehmite and γ-Al 2 O 3 are characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared analysis (FT-IR), nitrogen adsorption-desorption isothermal data, and dynamic light scattering analysis (DLS). The γ-Al 2 O 3 prepared by ultrasound stimulation has higher surface area (256 m 2 g -1 ), bigger pore diameter (6.06 nm) and larger cumulative pore volume (0.388 cm 3 g -1 ) than the conventional heating method (surface area, pore diameter, and pore volume of 219 m 2 g -1 , 5.61 nm, 0.307 cm 3 g -1 , respectively), which are even higher than the value reported in the literature for γ-Al 2 O 3 synthesized at 100 °C for 24 h aging (pore diameter of 4.27 nm and pore volume of 0.26 cm 3 g -1 ). The sonication applied during the aging of boehmite sol reduces the crystallite size (or particle size) and increases the porosity. The boehmite and γ-Al 2 O 3 obtained by sonication have the highest porosity of 46% and 59%, respectively, without using any structure directing agent. The crystallite size calculated from XRD analysis using Scherrer's equation is found to be 2.32 and 3.13 nm for boehmite and γ-Al 2 O 3 obtained by ultrasound stimulation, respectively, which is due to the formation of microjets during sonication. The particle size analysis result reveals the formation of nanosized γ-Al 2 O 3 particles by ultrasonication with a mean particle size of 51 nm. In conclusion, the boehmite and γ-Al 2 O 3 prepared by ultrasound stimulation are better than the samples synthesized by the conventional method.
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