Metal oxides modified Carbon electrode materials for Fluoride and Paraquat removal from water by capacitive deionization

Abstract

Capacitive deionization (CDI) is an emerging water treatment technology with many advantages, including low energy consumption, high efficiency, low cost, green and pollution free electrode regeneration. However, the electrode material is the main controlling factor for achieving high CDI performance. For a long time, activated carbon (AC) has been a preferred electrode material for CDI due to its availability, ease of preparation, low cost, and tunable textural properties. However, the pristine AC lacks selectivity towards the targeted ions, resulting in unnecessary energy consumption for treating polluted water and decreasing the removal efficiency (RE) of the targeted pollutant. To improve ion selectivity, in this study, composites of AC with metal oxides have been synthesized through a simple and one-step co precipitation method at ambient temperature (23-27°C) for defluoridation and removing paraquat (PQ) from water. The composite properties were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, energy-dispersive X ray spectroscopy, and Brunauer-Emmett-Teller analysis. In competitive fluoride (Fˉ) removal CDI experiments, AC–Al4Fe2.5Ti4 composite reduced the Fˉ concentration from 5.15 to 1.18 mg/L, below the allowable limit of 1.5 mg/L set by the World Health Organization while pristine AC reduced the Fˉ concentration to 4.5 mg/L. Also, AC–Al4Fe2.5Ti4 composite demonstrated a high RE of 79% and excellent regeneration performance after continuous electric adsorption–desorption cycles. Furthermore, CDI batch experiments compared the electrosorption of paraquat (PQ) herbicide by the composite electrodes (AC-Al2O3: 1:1) and pristine AC. The performance of the composite electrodes showed that PQ RE and electrosorption capacity (EC) depend on aluminium content loading, applied potential, flow rate, and charging time. At 1.2 V, a flow rate of 15 mL/min, and a charging time of 3 h, the composite electrode demonstrated a RE, EC, and energy consumption of 95.5%, 1.27 mg/g, and 0.055 kWh/m3 , respectively, compared to 62%, 0.83 mg/g, and 0.11 kWh/m3 for the pristine AC. The presence of other ions/pollutants was found to have negligible interference on PQ pesticide removal as the RE of the AC/Al2O3-1:1 composite in both artificial and natural water were 95.5 and 87.5% while EC was 1.27 and 1.17 mg/g, respectively. Therefore, the modified AC-metal oxides electrodes are promising and efficient materials for removing inorganic pollutants from water, such as Fˉ and organic pollutants, including PQ pesticides for CDI technology