Novel Ionic Grafts That Enhance Arsenic Removal via Forward Osmosis

Current forward osmosis (FO) membranes are unsuitable for arsenic removal from water because of their poor arsenic selectivity. In this study, we designed and synthesized a series of novel imidazolium-based ionic liquids via one-step quaternization reactions and grafted these novel compounds on to conventional thin-film composite FO membranes for treatment of arsenic-containing water. The newly developed ionic membranes contained a functionalized selective polyamide layer grafted with either carboxylic acid/carboxylate or sulfonate groups that drastically enhanced membrane hydrophilicity and thus FO water permeation. Ionic membranes modified with sodium 1-ethanesulfonate-3-(3-aminopropyl) imidazolium bromide (NH2-IM-(CH2)(2)-SO3Na) outperformed pristine membranes with higher water recovery efficiency. Exceptional performance was achieved with this ionic membrane in FO arsenic removal with a water flux of 11.0 LMH and a rejection higher than 99.5% when 1000 ppm arsenic (HAsO42-) as the feed with a dilute NaCl solution (0.5 M) as the draw solution under the FO mode. Ionic membranes developed in this work facilitated FO for the treatment of arsenic-containing water while demonstrating its superiority over incumbent technologies with more efficient arsenic removal.