One-step controllable synthesis of N-doped porous carbon derived from ZIF-8 for efficient capacitive deionization

Metal-organic framework (MOF)-derived carbon-based electrodes have demonstrated outstanding capacitive deionization (CDI) performance, owing to their special structures and configurations. Developing novel low-cost controllable protocols to obtain highly efficient Nitrogen-doped carbon-derived MOFs is the most challenging factor to transfer widely the application of these materials at real world. This work aims to develop a low-cost one-step growth route to produce N-doped carbon (NGZC) utilizing N-doped graphene quantum dots (N-GQDs) and zeolitic imidazolate frameworks-8 (ZIF-8) as starting substrates. The surface chemistry, morphology and CDI performance of the as-synthesized NGZC electrode were investigated, compared with conventional materials. The authors found that the introduction of N-doped graphene quantum dots dramatically enhances the mesopore volume (0.742 cm 3 /g) and pyrrolic-N ratio (19.21 %) for NGZC. These improvements effectively shorten the electron and sodium ion transport paths which in turn facilitate the pseudocapacitive activity and charge transfer in NGZC. The specific capacitance and salt adsorption capacity were found to be 283.16 F/g and 17.86 mg/g, respectively, demonstrating superior values than commonly used electrodes. NGZC shows a high stability over 30 adsorption-desorption cycles with a capacity retention of 90 %. DFT results further demonstrate the pseudocapacitive superiority of pyrrolic-N to reinforce the Na + capture. This finding provides new insights into the design of an economical and controllable N-doped carbon electrode for efficient CDI desalination.