Quaternized graphene oxide modified PVA-QPEI membranes with excellent selectivity for alkali recovery through electrodialysis

Composite anion exchanges membranes are prepared by incorporating quaternized graphene oxide (QGO) within poly(vinyl alcohol) (PVA) or the mixture of PVA and quaternized polyethyleneimine (QPEI), followed by cross-linking with formaldehyde. The PVA-QGO series of membranes have low ion exchange capacities (IECs) of 0.10–0.37   mmol/g and low water uptakes ( W R ) of 16.1%–22.0%, leading to high area resistances (>60   Ω   cm 2 ). The PVA-QPEI-QGO series of membranes show much lower area resistances of 2.47–6.04   Ω   cm 2 , which is ascribed to the improved IECs (0.86–1.37   mmol/g) and W R (46.8%–71.4%). Both series of membranes show higher alkali resistance than commercial membrane AMV. Their weight losses are in the range of 0.5%–8.9% after immersion in 60   °C 2   mol/L NaOH alkaline solution for 32 days, while the value of AMV membrane is 19.2%. When utilized for electrodialysis (ED) application to recover NaOH from NaOH/Na 2 WO 4 mixture, the prepared membranes exhibit high selectivity, as evidenced by the low leakage ratio of Na 2 WO 4 . The leakage ratio of the optimized composite membrane to WO 4 2− is only 5.1%, while the leakage ratio of AMV membrane is up to 61.4%. To explore this reason, the composite membranes are selected for the ED separation of monovalent ions. The separation efficiency ( S ) of the optimized membrane is 83.9%, which is similar to the value of commercial anion selective membrane NEOSEPTA® ACS (88.7%), confirming further the selectivity of the composite membranes.