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

•3 salt-sealed N-doped carbon (NC) derived from MOFs are prepared for Cd(Ⅱ) removal.•h-NC-800 render a qm of 356.4 mg g−1, which is 13–48% higher than counterparts.•Harmonized edge- to graphitic-nitrogen ratios strengthen Cd(Ⅱ) adsorption on h-NC.•Cd(Ⅱ) adsorption mechanisms of h-NC are verified by DFT calculation.•h-NC-800 afford the stabilized Cd(Ⅱ) removal efficiency (>92%) in realistic water.