Polysulfone/graphene quantum dots composite anion exchange membrane for acid recovery by diffusion dialysis

The advancement in membrane-based separation technologies offers advantages over traditional ways. Recovery of acid from acidic waste stream is an important issue to be solved by greener route. Diffusion dialysis using anion exchange membranes (AEMs) is an energy-intensive and environment friendly process to be taken forward. Herein, we report the eco-friendly route for chloromethylation of polysulfone using chloromethyl ethyl ether (CMEE). Effect of chloromethyl ethyl ether concentration, reaction temperature, and reaction time are investigated to get maximum tethered chloromethyl group and high yield of product. Series of chloromethylated polysulfone membranes are prepared with different concentrations of graphene quantum dots (GQDs) followed by quaternization using trimethylamine. The prepared membranes are characterized by their water content, transport properties, and stabilities. Composite membranes show enhanced water uptake, ion exchange capacity, and mechanical stability compared to that of pristine membrane. Interestingly, to address the environmental impact of acids present in industrial waste, AEMs are employed for acid recovery from model waste at higher concentrations of acid and salt using diffusion dialysis. For prepared membranes, 35.5-47.5% acid recovery has been achieved in presence of metal ions. SCE-1.0 (1.0 wt % GQD/ QPSU) membrane shows the highest acid recovery (47.5%) among the membranes. Composite membranes suggest their potential utility in acidic effluent treatment via diffusion dialysis.