Positively charged membranes constructed via complexation for chromium removal through micellar-enhanced forward osmosis

[Display omitted] •Positively charged membranes were developed via a Fe3+-ligand complexation protocol.•Substantial improvements in membrane properties were achieved after modification.•The PA-Fe-Bet membrane increased the water permeability by 142% compared to that of the PA membrane.•The PA-Fe-Bet membrane achieved complete CrO42- removal with improved water fluxes and fouling resistance. It is challenging to purify wastewater containing heavy metals at low concentrations. Forward osmosis (FO) is promising to remove most of contaminants from wastewater. However, the lack of suitable membranes disables FO to achieve its full potential. Here we designed positively charged PA-Fe-H2O and PA-Fe-Bet membranes for efficient chromium (CrO42-) removal through micellar-enhanced FO (MEFO) separation. These membranes were developed by functionalizing the ready-made polyamine (PA) membrane via eco-friendly complexation between Fe3+ and carboxyl groups of the PA layer and/or betaine (Bet). A Fe3+-bridged hydration or quaternary ammonium layer was formed which imbued the membrane with desirable properties for FO separation. The water permeability of the PA-Fe-H2O and PA-Fe-Bet membranes was increased by 92% and 142%, respectively, compared to that of the PA membrane when 0.5 M MgCl2 as the draw solution. The PA-Fe-Bet membrane greatly improved CrO42- removal efficiency by increasing the water flux from 6.2 to 12.0 LMH along with complete CrO42- retention in the cetylpyridinium chloride (CPC) facilitated MEFO process. Moreover, this membrane exhibited enhanced antifouling properties when exposed to CPC solutions. The environmentally benign synthesis approach, high CrO42- removal efficiency and fouling resistance of the PA-Fe-Bet membrane demonstrate its potential for contaminants removal.