NaClO post-treatment: A specific strategy to boost RO performance of PE-based TFC-PA RO membranes from RIP processes

A post-treatment strategy, involving immersion in sodium hypochlorite solution, was found to be specifically effective in improving the reverse osmosis (RO) performance of polyethylene (PE) based thin film composite (TFC) polyamide (PA) membranes prepared from reverse phase interface polymerization (RIP) processes. RIP processes produced abundant amine groups on the PA surfaces to allow the formation of abundant PA-N(H)Cl intermediates, while the inertness of the PE substrates preserved them for self-coupling into azo linkages, -N N-. Due to the formation of the azo cross-linking structure, the salt rejection rate of the PA layer was enhanced, while the degradation of part of the -C( O)-NH- groups increased surface ionic groups at pH 8, improving water permeance. Experiments were conducted to determine the most suitable concentration, pH value, and treatment time of the sodium hypochlorite solution. Treatment with a sodium hypochlorite solution at 500 ppm and pH 8 for 4 min increased the permeance of the PA/PE TFC membrane from 1.59 ± 0.02 L·m −2 ·h −1 ·bar −1 to 1.63 ± 0.03 L·m −2 ·h −1 ·bar −1 , while the salt rejection rate increased from 98.64 ± 0.06% to 99.24 ± 0.08%. The membrane also maintained good operational stability, antifouling property, and enhanced alkaline stability.