An integrated capacitive deionization and photocatalysis system for efficient ammonium removal from low-concentration wastewater

Following the concept of high effectiveness, environmental friendliness and good stability, an integrated capacitive deionization and photocatalysis system was first time applied to enable high performance ammonium removal from low-concentration wastewater. Due to synergistic effect of CeO₂ nanoparticles along with graphene support, the novel reduced graphene oxide/cerium dioxide (rGO/CeO₂) composites were prepared and studied as the potential material for this integrated system. The incorporated CeO₂ was cubic fluorite structure and rGO/20%CeO₂ composite delivered the best structural and physicochemical properties. As a pretreatment, capacitive deionization with rGO/20%CeO₂ electrode exhibited high electrosorption capacity (7.66 mg g⁻¹) on ammonium removal. Meanwhile, suitable electrosorption operation conditions (1.2 V applied voltage, 1.0 mmol L⁻¹ initial concentration, 30 mL min⁻¹ flow rate, and 20 °C temperature) were obtained. Additionally, rGO/20%CeO₂ catalyst showed excellent photocatalysis potential and stability due to significant synergistic effect. The photocatalysis efficiency of ammonia reached 88.0 %, which achieved the advanced treatment effect. Importantly, the total ammonium can steadily be reduced to 1.35 mg L⁻¹ under low initial concentration (1.0 mmol L⁻¹), which met the guidelines for Chinese surface water quality standard (Grade IV). Based on the obtained results, combining capacitive deionization with photocatalysis technology for low-concentration ammonium wastewater treatment was proved practicable and can be extended to full-scale environmental samples application.