Molten salt-assisted synthesis of coal gangue-derived hierarchical porous carbon: Structural regulation and adsorption performance

A carbon-rich precursor was extracted from coal gangue by gradient purification. • Molten salt-assisted activation regulated pore structure and surface chemistry. • The optimized porous carbon exhibited high surface area and defect density. • High-capacity cationic dye adsorption was achieved by CGC-124. • DFT revealed enhanced binding by oxygen-containing functional groups. Coal gangue is a massive coal-based solid waste containing intrinsic carbonaceous matter that remains underutilized for the preparation of high-value functional carbon materials. Herein, coal gangue was converted into hierarchically porous carbon through gradient purification and molten salt-assisted KOH activation. Flotation followed by sequential HF/HCl leaching effectively removed mineral impurities and enriched the carbonaceous fraction. During activation, the NaCl/KCl molten salt medium promoted more uniform KOH etching and moderated excessive corrosion of the carbon framework, facilitating hierarchical pore development while retaining oxygen-containing surface functionalities. The optimized porous carbon, CGC-124, exhibited a specific surface area of 2964.39 m 2 /g, abundant defects, and surface hydroxyl/carboxyl groups. Using methylene blue (MB) as a representative cationic dye, CGC-124 achieved an adsorption uptake of 2798.48 mg/g at 318 K. Kinetic analysis was consistent with a surface-controlled process with chemisorption-like characteristics, whereas the better Freundlich fitting reflected the heterogeneous nature of the carbon surface. Experimental characterization and DFT calculations indicated that pore filling, electrostatic attraction, hydrogen bonding, π–π interactions, and interactions involving oxygen-containing groups jointly contributed to MB adsorption. This work provides a route for converting coal gangue into high-surface-area porous carbon and offers insight into molten salt-assisted pore engineering for cationic dye adsorption. Download: Download high-res image (160KB) Download: Download full-size image