N, S co-doped porous carbon for ultra-selective and cost-effective capture of palladium from highly acidic solution

Abstract

The selective capture of palladium from highly acidic solutions is critical for sustainable resource utilization and environmental remediation. This study presents a nitrogen/sulfur co-doped porous carbon (NSPC) derived from glucose and melamine via a green synthesis route, offering ultrahigh selectivity and cost-effectiveness for the capture of Pd(II) in extreme acidic conditions (1 M HNO₃). Guided by the hard–soft acid–base (HSAB) principle, the dual N/S doping strategy creates abundant soft-base sites (S > N > O) that synergistically enhance Pd(II) affinity through strong coordination interactions, achieving an exceptional adsorption capacity of 103.5 mg g⁻¹ with >99% efficiency within 30 minutes. The sorbent demonstrates remarkable selectivity over 25 coexisting metal ions (e.g., Fe³⁺, Zr⁴⁺, Ru³⁺) and retains >99% Pd(II) removal efficiency after 10 regeneration cycles, attributed to the coordination of Pd–N/O (CN = 2.2 ± 0.2), Pd–S (CN = 0.2 ± 0.1), and Pd–Pd (CN = 2.3 ± 0.5) confirmed by X-ray photoelectron spectroscopy and X-ray absorption fine structure spectroscopy. With a production cost of only 3.5 RMB g⁻¹ and scalable synthesis, NSPC outperforms state-of-the-art sorbents (e.g., MOFs, silica, POPs) in both economic viability and acid stability, positioning it as a transformative solution for palladium reclamation from highly acidic solutions.