Study on composite membranes with high selective permeance properties

Flavonoids are natural products having several biological and physiological properties depending upon their molecular configurations. Flavonoids with similar configuration cannot be separated by traditional separation method and membrane separation technology whose selectivity is lower. This work investigates composite membranes with structural and functional molecular recognition properties prepared according to molecular imprinted technology. Functional silica sol was synthesized by taking luteolin as the template (or imprinting) molecule, γ-aminopropyltriethoxysilane (γ-APTS) as the functional monomer, and tetraethoxysilane (TEOS) as the cross-linker. The resultant functional silica sol was coated on Al₂O₃ microporous substrate followed by the removal of the template molecule. Scanning electron microscope micrographs showed a 5 μm thickness composite membrane with uniformly distributed porosity. Steady state flux was reached at ∼70 min at 215 L m⁻² h⁻¹ for the composite membrane, while a lower value of 168 L m⁻² h⁻¹ was measured for the blank membrane (i.e. non-templated). Further, in an aqueous mixture containing similar template molecules, the selectivity factor of luteolin to rutin was 14.1, thus suggesting that the imprinting process allowed for preferential permeance and affinity selectivity to the template molecule (i.e. luteolin). These results strongly suggest the formation of cavities, which are joined by channels to deliver the percolative effect for the permeation of luteolin. In addition to structural formation, further site recognition properties were accomplished by the functional silica sol in the composite matrix by electrovalent bonds. Considering the percolative effect in tandem with electrovalent bonds and under the influence of a concentration gradient (i.e. driving force), a mechanism of molecular recognition was proposed based on the molecular bond, followed by bond cutting and jumping to another site to form another molecular bond. The preparation method of the composite membrane was applied to other template molecules, and the template molecules can selectively permeate the membrane. So the method was universal for other substance. So it made it possible for the separation of the natural products exactly and efficiently. At the same time, it had great potential for the resolution of the chiral drugs and the preparation of the new membrane reactor.