Removal of ammonium ions in wastewater by electrosorption with TiO2 modified graphene electrode

In this study, the TiO₂ modified graphene composite material (RGO/ TiO₂) was prepared by hydrothermal method, and its morphological structure and electrochemical properties were investigated. Then RGO/TiO₂ material was assembled into electrode, and NH₄⁺ ions electrosorption efficiencies of unmodified graphene (RGO) electrode and the RGO/TiO₂ electrode were compared. The effects of applied voltage, circulating velocity and initial concentration on NH₄⁺ ions electrosorption by RGO/TiO₂ electrode were investigated. The characteristics of NH₄⁺ ions electrosorption and the effect of advanced NH₄⁺ ions removal from simulated actual wastewater containing NH₄⁺ ions were also studied. The results showed that the RGO/TiO₂ composite material had a three-dimensional pore structure with specific surface area of 382.08 m²·g^-1 and specific capacitance of 325.80 F·g^-1 at a scan rate of 0.01 V·s^-1, which were better than those of the RGO material. The initial adsorption capacity of RGO/TiO₂ electrode was 28.3% higher than that of RGO electrode. After 10 cycles of regeneration adsorption, the adsorption capacity of NH₄⁺ ions of RGO/TiO₂ electrode only decreased 5.87%, and its cyclic regeneration adsorption property was better than that of RGO electrode. In addition, the applied voltage 2.0 V, circulating velocity 35 ml·min^-1 and initial concentration 1.0 mmol·L^-1 were the optimal NH₄⁺ ions electrosorption conditions for RGO/TiO₂ electrode. The electrosorption process of NH₄⁺ ions by RGO and RGO/TiO₂ electrodes was in accordance with the quasi-first-order kinetic model and the Freundlich isothermal adsorption model. The electrosorption of NH₄⁺ ions was a multi-layer adsorption behavior on heterogeneous surface and physical adsorption was the dominant. When the RGO/TiO₂ electrode was connected in 4-stage series, the removal efficiency of simulated actual NH₄⁺ refining purified water reached 86.84%.