Comprehensive studies of membrane rinsing on the physicochemical properties and separation performance of TFC RO membranes

Transport behaviour of thin film composite (TFC) reverse osmosis (RO) membrane is highly dependent on the physicochemical property of the uppermost polyamide (PA) layer. In this work, we provide a comprehensive understanding of the impacts of post interfacial polymerization (IP) rinsing using either organic solvents (i.e., hexane, cyclohexane and isoparaffin-G) or aqueous solution on the structure and chemistry of PA layer and correlate the properties change to membrane performance. Evidently, the desalination performance of the aqueous-rinsed membrane is better than the organic solvents-rinsed membrane. Compared to the un-rinsed membrane, the aqueous-rinsed membrane also showed 28% higher pure water flux and 13% lower water contact angle (i.e., greater hydrophilicity) with least compromised NaCl rejection (97.70%). This is possibly caused by its reduced PA cross-linking degree and/or hydrolysis of acyl chloride monomers that alter the membrane surface chemistry. It is also found that the introduction of air-drying prior to the rinsing process could improve the membrane reproducibility as a result of extensive polymerization. The findings from this experimental work confirmed that aqueous solution is the best rinsing solution for TFC RO membrane fabrication, improving both physicochemical properties and water permeability of membrane.