Synergistic Removal of Methylene Blue and Cr(VI) by Aminated Gasification Slag

Coal gasification fine slag (CGFS) provides a stable, hierarchically porous framework, but its use as an adsorbent precursor is limited by energy-intensive, CO₂-emitting, high-temperature activation. Herein, we propose a low-energy, three-step route-hydrothermal acid leaching, mild alkali treatment, and tetraethylenepentamine functionalization-to prepare an amine-modified bifunctional adsorbent (CSM-T5%). CSM-T5% delivers exceptional single-solute capacities (862.06 mg/g for methylene blue [MB] and 233.10 mg/g for Cr(VI)), which are further enhanced in binary systems to 1206.27 and 243.90 mg/g, respectively, through synergistic interactions. The material exhibits good reusability, retaining 71.37% MB and 63.68% Cr(VI) removal after five adsorption-desorption cycles. Mechanistic analysis shows that Cr(VI) removal involves adsorption coupled with in-situ reduction, while MB uptake is governed by electrostatic attraction, hydrogen bonding/π anchoring, and pore confinement; in binary systems, charge compensation and spatial site complementarity reinforce these pathways. This study unlocks the latent porosity of CGFS without high-temperature activation, offering a sustainable and cost-effective strategy for converting industrial residues into efficient adsorbents for complex wastewater treatment.