Electro-Enhanced Membrane Sorption: A New Approach for Selective Ion Separation and Its Application to Phosphate and Arsenic Removal

We describe a new electro-enhanced sorption approach, where an electric field is applied across an ion-selective nanocomposite membrane. Unlike capacitive deionization, here, the membrane rather than the electrode functions as the sorbent, whereas the electrodes are inert. This electrode-sorbent decoupling extends the space of suitable sorption materials, currently constrained to conductive materials. Here, we synthesized ferric oxyhydroxide (FeO) nanocomposite membranes (FeOm) using diffusion-controlled growth of FeO nanoparticles within porous track-etched membranes, resulting in a high-capacity sorbent. The use of FeOm to study the electro-enhanced sorption of phosphate revealed that the electric potential (5–15 V) accelerates both the adsorption and desorption steps. Furthermore, desorption at pH ∼10–11—much lower than the current practice for FeO regeneration (pH 13–14)—was demonstrated, potentially enabling 2–3 orders of magnitude savings on chemical consumption. Lastly, a highly selective uptake of arsenate from simulated groundwater was demonstrated, pointing at the potential of the new approach to intensify sorption processes.