Sulfur-enhanced nitrogen-rich polymer for ultrafast adsorption of precious metals

The recovery of precious metals (PMs) from secondary resources has gained significant attention, driving the need for efficient adsorbents. In this work, we designed two high-performance adsorbents (TPA@PEI and SA@PEI) prepared by cross-linking polyethyleneimine (PEI) with 3,3'-thiodipropionic acid (TPA, sulfur-containing) or succinic acid (SA, sulfur-free) for selective Au(III) and Pd(II) recovery. Both materials demonstrate striking adsorption capacities for Au(III) and Pd(II), with TPA@PEI reaching 2319.34 ± 5.98 mg/g Au(III) and 572.81 ± 8.70 mg/g Pd(II) at pH 3, and SA@PEI achieving 2068.04 ± 68.88 mg/g Au(III) and 346.28 ± 2.56 mg/g Pd(II). TPA@PEI exhibits ultrafast adsorption kinetics, achieving equilibrium within 0.5 min for both Au(III) and Pd(II), significantly outperforming SA@PEI (10 min for Au(III), 5 min for Pd(II)). Crucially, TPA@PEI shows superior selectivity (>99 % recovery) for both PMs in quaternary ion mixtures. Comparative tests and theoretical simulations and reveal that the incorporating sulfur atoms into the adsorbent structure enhances key performance metrics, including ion selectivity, adsorption capacity, kinetics, and long-term reusability. This work not only presents a practical nitrogen-rich, sulfur-containing adsorbent platform for precious metal recovery but also fundamentally clarifies the previously underappreciated role of sulfur in optimizing the efficiency of such processes.