Selective phosphate removal using layered double hydroxide/reduced graphene oxide (LDH/rGO) composite electrode in capacitive deionization

Phosphate removal is a critical issue in water treatment because excess levels of phosphate can cause severe eutrophication. Capacitive deionization (CDI), which has several advantages, such as simple, eco-friendly, and energy efficient operations, has gained attention as a potential alternative over conventional phosphate removal technologies like activated sludge, chemical precipitation, and adsorption processes. However, CDI suffers from a lack of selectivity for phosphate, resulting from non-selective anion removal of positively biased electrodes. Herein, the layered double hydroxide/reduced graphene oxide (LDH/rGO) composite electrode in the CDI process was examined for selective phosphate removal. LDH/rGO showed the selective phosphate removal performance with sustained phosphate removal efficiency even in the presence of excess chloride. In addition, the selective phosphate removal in the CDI process with the LDH/rGO was successfully demonstrated in the simulated water, fabricated by adding a significantly low concentration of phosphate (0.4 mg∙L⁻¹) into real river water matrix (Han River, Seoul, Korea). This result was explained by the high electrochemical selectivity of the LDH/rGO for phosphate.