Sustainable valorization of coal gasification fine slag into hierarchical porous carbon-zeolite composites for efficient CO2 capture and separation

Coal gasification fine slag (CGFS) represents a significant category of coal-based solid waste characterized by its vast reserves and substantial disposal challenges. Guided by the “waste-to-resource” philosophy, this study utilized four CGFS samples from diverse sources as substrates to successfully synthesize a series of X-type carbon-zeolite composites with three-dimensional interconnected porous structures via a sequential “acid leaching-alkali fusion-hydrothermal crystallization” process. These composite materials have demonstrated excellent performance in carbon dioxide capture and separation. The results demonstrate that the composite materials achieve a specific surface area of 550–650 m 2 /g with both ultramicroporous and mesoporous structures. At 298 K and 1 bar, the highest CO 2 adsorption capacity among the four samples reached 4.07 mmol/g, complemented by exceptional selectivity for CO 2 /N 2 (141.21) and CO 2 /CH 4 (67.58). Furthermore, the composite retained more than 95% of its initial CO 2 adsorption capacity after eight adsorption-desorption cycles, suggesting promising short-term regenerability. Molecular simulations further elucidated the underlying adsorption mechanism, revealing that the strong electrostatic interactions of Na + cations dominate microporous adsorption, while the synergistic effect of the hierarchical pore structure optimizes both adsorption kinetics and mass transfer efficiency. This study provides a novel pathway for the high-value utilization of coal-based solid waste and the development of cost-effective materials for CO 2 capture.