Cadmium　(Cd)　removal　is　imperative　to　ensure　the　safety　of　aquatic-ecosystem,　yet　its　effective　removal　technology　has　remained　elusive　by　far.　To　address　this　concern,　three-dimensional　N-doped　carbon　(NC)　polyhedrons　affording　ample　porosity　is　fabricated　based　upon　the　thermal　carbonization　and　KOH　activation　of　zeolitic　imidazolate　framework-8　(ZIF-8)　precursor.　Thus-derived　activated　NC　(a-NC)　adsorbent　not　only　overcomes　the　inherent　instability　of　ZIF-8　but　also　harvests　a　maximum　Cd(II)　adsorption　capacity　of　370.2　mg　g-1,　which　evidently　surpasses　those　of　bare　NC　counterpart　as　well　as　previously　reported　adsorbents.　Impressively,　a-NC　achieves　ca.　100%　removal　of　aqueous　Cd(II)　in　a　broad　working　pH　range　(5-9),　and　particularly　attains　stable　performances　(81-92%)　in　various　realistic　water.　Theoretical　calculations　in　combination　with　experimental　characterizations　further　offer　mechanistic　insight　into　the　enhanced　removal　exerted　by　a-NC.　Notably,　owing　to　the　increased　specific　surface　area　(3041　vs.　389　m2　g-1)　and　enhanced　sp2　carbon　content　(91.7　vs.　68.8%)　of　a-NC　as　compared　to　NC,　advanced　Cd(II)　adsorption　via　a-NC　can　be　exhibited.　Our　designed　a-NC　material　harnessing　favorable　recycling　capability　would　be　in　particular　attractive　in　the　realm　of　practical　Cd(II)　remediation.