Green dual-organic salt activation synthesis of hierarchical N, S co-doping artificial humic acid-derived porous carbon toward superior cadmium capture in asymmetric capacitive deionization

Efficient hierarchical porous carbon (HPC) and heteroatom doping electrode materials remain a formidable challenge for advanced capacitive deionization (CDI) systems for cadmium-containing wastewater purification. This study reports the successful preparation of asymmetric CDI cathodes for the electrosorption of Cd 2+ by a controlled dual-organic-salt activation strategy, and its adsorption performance and underlying mechanism were comprehensively investigated. Compared with a single K 2 C 2 O 4 activation strategy, incorporating C 8 H 16 N 2 O 6 S 2 K 2 during activation induced a chain activation–gas etching reaction, resulting in a carbon material with high heteroatom doping, exceptional specific surface area an optimized pore distribution, and abundant edge defects. Further, the optimized N, S-doped HPC2 exhibited a high specific capacitance (118 F g −1 ), enhanced reversibility, and efficient electron transfer, contributing to an exceptional electrochemical Cd 2+ adsorption capacity (125.13 mg g −1 at 1.2 V). Meanwhile, it exhibited outstanding selectivity ( K d  = 18,179 mL g −1 ), remarkable cycling stability (91 % retention over 20 cycles), and superior practical performance, achieving ultralow Cd 2+ concentrations (<1 μg L −1 ) in real desulfurization wastewater via multi-stage asymmetric CDI. This work exemplifies the effectiveness of the one-step method to achieve accurate regulation of pore architecture and heteroatom co-doping, thereby providing novel insights into the mechanism of cadmium removal.