Efficient removal of metal ions by capacitive deionization with straw waste derived graphitic porous carbon nanosheets

Capacitive deionization (CDI) is considered to be an energy-efficient and cost-effective technology for ion removal from saline or waste water. However, its implementation remains challenging due to low ion adsorption capacity of the commonly used electrode materials. It is thus desirable to develop highly efficient CDI electrode materials for ion removal. Herein, graphitic porous carbon nanosheets (GPCSs) were originally prepared from straw waste via a combined activation and graphitization process. Being composed of graphitic carbon sheets with abundant pores in the framework, the obtained GPCSs had a large specific surface area and good conductivity and wettability, which can provide sufficient adsorption sites and promote efficient ion transport. The GPCS electrodes presented a higher specific capacitance, good stability and low inner resistance in electrochemical tests. Moreover, the GPCSs showed a high deionization capacity of 19.3 mg g^-1 at 1.2 V in a 500 mg L^-1 NaCl solution. Repeated adsorption-desorption experiments demonstrated the good regeneration performance of the GPCS electrodes. Furthermore, the removal efficiency towards Cd²⁺, Ni²⁺ and Cu²⁺ of the GPCS electrodes is 91.5%, 97.0% and 100% at 1.2 V in a 100 mg L^-1 CdCl₂, NiCl₂ or CuCl₂ solution, respectively. This work offers a promising solution to efficient removal of ions from saline or waste water and a new route to the utilization of straw waste.