Tailored design of well-defined hierarchical nitrogen-doped carbon via salt-confined strategy for selective Cd(Ⅱ) adsorption

Abstract

Efficient cadmium (Cd) removal is vital to ensure freshwater safety, yet it still lacks high-efficiency treatment technologies, especially for the technique with simple-operation and eco-friendliness. Herein, three different carbon-based nanomaterials of hierarchical nitrogen-doped carbon (h-NC-750, h-NC-800 and h-NC-850) were successfully synthesized, via carbonizing the sealed ZIF-8 particles in NaCl crystals at various carbonization temperatures of 750, 800 and 850 °C in Ar atmosphere. Amongst them, the acquired dual-carbon of h-NC-800 harvesting a total nitrogen content of 15.5% rendered the maximum Cd(Ⅱ) adsorption capacity of 356.4 mg g−1, which was 12.5 and 48.3% higher than that of h-NC-750 and h-NC-850 counterparts. The density functional theory (DFT) simulations in combination with characterizations unveiled that the exceptional Cd(Ⅱ) removal of h-NC-800 was derived from the harmonized edge- to graphitic-nitrogen ratio that strengthened the binding energies between Cd(Ⅱ) and h-NC. Impressively, thus-optimized adsorbents afforded the favorable and stabilized removal efficiency (>92%) toward Cd(Ⅱ) in realistic water and five-consecutive regeneration cyclicality. This work is anticipated to offer an innovative insight into the molecular-level architecture design of h-NC with well-defined nitrogen doping and controllable edge- to graphitic-nitrogen ratio, targeting high performance in aqueous Cd(Ⅱ) removal.