Molecularly imprinted organic solvent nanofiltration membranes – Revealing molecular recognition and solute rejection behaviour

Abstract

A new class of organic solvent nanofiltration (OSN) membranes featuring molecular recognition sites has been fabricated by a phase inversion molecular imprinting technique. Polybenzimidazole (PBI) was employed as a functional polymer for molecular imprinting for the first time. Apart from acting as a functional polymer, PBI exhibits excellent chemical and solvent stability and can be used as a nanofiltration membrane, acting both as shape-specific adsorbent and size-exclusion membrane. The molecularly imprinted organic solvent nanofiltration (MI-OSN) membranes fabricated in this study showed both nanofiltration membrane performance, and excellent molecular recognition ability. The model system comprised roxithromycin pharmaceutical, 2-aminopyrimidine building block and N,N-dimethylaminopyridine catalyst, which are retained, adsorbed and permeated through the MI-OSN membrane, respectively. The effect of both dope solution concentration and applied pressure on the molecular recognition behaviour of MI-OSN membranes has been investigated by employing Sips and Freundlich adsorption isotherms, as well as examining the physical morphology of the membranes. The rate of adsorption was investigated, revealing that the adsorption follows second-order kinetics and is not limited by diffusion. The imprinted membrane exhibited fourfold higher flux whilst maintaining the same rejection performance in comparison to the control membrane. It is shown that increasing the transmembrane pressure across the MI-OSN membrane irreversibly suppresses the molecular recognition whilst maintaining the rejection and flux performance.