Controlling membrane ionization with bifunctional alendronates to benefit desalination through forward osmosis

Gradual ionizing forward osmosis (FO) membranes were synthesized through tailoring modifications with alendronate materials on polyamide thin film composite (TFC) membrane surfaces. The newly developed membranes have gradually ionized surfaces and are more hydrophilic after introducing amino, hydroxyl and phosphate groups derived from the alendronates. Significantly improved performance was achieved with the alendronate-modified membranes relative to the unmodified membrane. With DI water as the feed and 0.5 M MgCl2 as the draw solution, the novel membranes yielded water fluxes 35-60% higher than the nascent one. When MgCl2 (2.0 M) as the draw solution, alendronate tetrasodium (A-4Na) modified membrane had a water permeation rate of 17.3 LMH under FO mode (feed solution faced the membrane active layer) in seawater desalination, a 25% increase compared to that of the pristine membrane and surpasses many other recently-developed FO membranes, remarkably increasing water filtration efficiency.