Electro-enhanced adsorption of ammonium ions by effective graphene-based electrode in capacitive deionization

Capacitive deionization (CDI) offered a promising electrosorption technology for desalination. This study presented the feasibility of CDI for removing and recovering NH₄⁺ from low-strength wastewater. The three-dimensional and porous reduced graphene oxide/titanium dioxide (rGO/TiO₂) materials were successfully synthesized and investigated as potential material for CDI system. The structural and electrochemical properties of rGO and rGO/TiO₂ composites were analyzed, while the incorporated TiO₂ was anatase phase and TiO₂/rGO mass ratio 20% delivered the best property. The effects of applied voltage, circulating flow rate, initial NH₄⁺ concentration and regeneration conditions were investigated. The results demonstrated that rGO/20%TiO₂ electrode performed much better electrosorption capacity and regeneration ability than the reference electrode (rGO electrode). Furthermore, NH₄⁺ electrosorption onto CDI electrode followed the Freundlich adsorption isotherm and indicated a physisorption process according to kinetic studies. Additionally, hydrated radius and valence notably affected the alternative electro-behavior of CDI. In a co-existed system, electrosorption of ion highly depended on the ion charge rather than hydrated radius.