Polydopamine-Assisted Modification of Anion-Exchange Membranes with Nanomaterials for Improved Biofouling Resistance and Electrodialysis Performance

The present study is the first to systematically investigate the impact of membrane modification on antifouling propensity and desalination performance of anion-exchange membranes (Ionics AR204) by codeposition of polydopamine (PDA) and TiO2 or graphene oxide (GO) nanomaterials. Ion-exchange capacity (IEC), surface hydrophilicity, overall desalting performance, and biomass accumulation on the membranes during biofouling experiments were analyzed to elucidate the impact of PDA and nanomaterials coating on membrane performance. All modified membranes exhibited marginal differences in IEC ranging between 2.19 and 2.45 mequiv/g as compared to the AR204 membrane of 2.40 mequiv/g. The modified membranes showed exceptional antifouling properties by the codeposition of PDA and nanomaterials (GO or TiO2). The cell attachment decreased by more than 98% at the TiO2 dosage of 5-10 wt %. The PDA-assisted TiO2 membranes observed a higher reduction in extracellular polymeric substances (88.6%-96.5%, the highest reduction at 10 wt %) than the PDA-assisted GO membranes (73.3%-88.7%, the highest reduction at 7.5 wt %). Bench-scale electrodialysis experiments revealed that membrane modification had a minor impact on the overall desalting performance, slightly reduced the energy consumption, and noticeably enhanced the monovalent permselectivity. The transport time for SO42- ions to pass through the interface between the modification layer and the membrane was significantly longer than for Cl- ions. The PDA-GO coating resulted in improved steric hindrance caused by the GO nanosheets because no change of impedance spectra was observed by electrochemical impedance spectroscopy compared to the unmodified AR204 membrane.