Eco-friendly and energy efficient flowable surface modified carbon electrode materials in flow electrode capacitive deionization for heavy metal adsorption and energy recovery

With the rapid growth of the world's population, the global demand for clean and safe water has become increasingly critical. Capacitive deionization (CDI) has emerged as a promising technology for desalination due to its high energy efficiency, environmental friendliness, and operational convenience. However, its low desalination capacity, poor water wettability, and discontinuous desalination process have limited its application in desalination and large-scale implementation. To address these issues, flow-electrode capacitive deionization (FCDI) has been developed to enhance the desalination performance of traditional CDI systems. Optimizing the activated carbon (AC) materials that form the flow-electrodes is a primary focus of research to improve the desalination performance of FCDI. In this work, AC was modified using varying concentrations of Tollens' reagent and sodium alginate (SA) solutions. Due to the interaction between heavy metal ions and the silver (Ag) and SA groups on the surface of the synthesized materials, this experiment was conducted to remove lead ions (Pb²⁺) from simulated wastewater. Experimental results showed that, compared to flow-electrodes made from commercial AC, the average desalination rate for Pb²⁺ increased from 0.00238 mmol/m²/s to 0.00831 mmol/m²/s. The adsorption performance also increased from 0.4454 mg/g to 0.9501 mg/g. Additionally, due to the electrochemical flow capacitor-like properties of the FCDI system, the energy recovery and charging efficiency of the FCDI system were evaluated. The energy recovery potential may reduce the energy consumption of FCDI-based seawater desalination, making FCDI more advantageous compared to other traditional seawater desalination technologies.