A two-pronged strategy to boost the capacitive deionization performance of nitrogen-doped porous carbon nanofiber membranes

Abstract

Carbon-based capacitive deionization (CDI) systems are universally subject to the limited desalination capacity, due to the electrosorption characteristics and undesirable pore structures. Herein, a two-pronged strategy is proposed to boost the desalination performance of the electrospun carbon nanofibers (CNFs), where silicalite-1 nanoparticles as the internal porogen create mesopores and macropores, and layered zeolitic imidazolate framework (ZIF-L) leaves as the external carbon source provide micropores and mesopores. This combination results in the large surface area, well-developed graded pore structure, and increased nitrogen content of the core-shell polyacrylonitrile/silicalite-1@ZIF-L-derived CNFs (defined as PCNFs-SZ) electrode, which delivers a superior specific capacitance of 145.4 F g⁻¹ in a neutral electrolyte. The symmetric CDI cell assembled by the self-supporting PCNFs-SZ membrane electrodes holds a prominent desalination capacity of 37.09 mg g⁻¹ and a rapid salt removal rate of 10.36 mg g⁻¹ min⁻¹ at 1.2 V (initial NaCl concentration: 500 mg L⁻¹), and demonstrates significant potential for real-world applications in the desalination and purification of reclaimed water. Furthermore, theory calculations confirm the enhanced Na⁺-capture capability of PCNFs-SZ. The present work highlights an effective and viable approach to enhance the desalination performance of carbon-based CDI cells.