Polyol-functionalized thin-film composite membranes with improved transport properties and boron removal in reverse osmosis

Thin-film composite membranes comprising modified polyamide layers were cast on an ultrafiltration polysulfone support using sequential interfacial polymerization, thus obtaining bilayer membranes with a final layer of polyols at the surface. A traditional polyamide layer made by interfacial polymerization of trimesoyl chloride and m-phenylene diamine, as well as a reference bilayer membrane with a topmost layer of m-phenylenediamine, were compared with novel bilayer membranes containing N-Methyl-D-glucamine, (+/-) 3-amino-1,2-propanediol, or serinol functionalizations. Filtration experiments performed with pure water, or with solutions containing 2000 mg/L NaCl and 5 mg/L boric acid, indicated that the water permeance of the modified membranes was improved with no associated loss of salt rejection compared to reference membranes. In particular, functionalization using (+/-)-3-amino-1,2-propanediol allowed achievement of the highest water flux and the best rejection (NaCl permeance, B, of 0.18 L m(-2) h(-1)) with 40% reduction in salt passage compared to the reference membranes (B of 0.26 L m(-2) h(-1)). Bilayer membranes also showed enhancement in boron removal, performing about 90% observed boron rejection at pH 5.2, condition under which boron is mostly present as neutral boric acid. The strategy employed in the present work allows for robust design of TFC membrane consisting of active layers with improved water permeance and boron rejection performances.