Synthesis of large mesoporous silica for efficient CO2 adsorption using coal gasification fine slag

Coal gasification fine slag (CGFS), a byproduct of the coal gasification process, is currently being recognized as a resource with significant potential for value addition and sustainable applications, especially in synthesizing CO2 adsorbents. The overarching challenges in this domain include the attainment of high-efficiency, environmentally benign transformation of CGFS into useful products, and the development of cost-effective adsorbent materials featuring precisely engineered pore structures. In this study, a hierarchical porous nanostructured silica material is synthesized rapidly, efficiently, and cost-effectively through acid leaching and alkaline dissolution-assisted hydrothermal treatment, employing CGFS as the precursor. The mass ratios of sodium hydroxide (NaOH) to CGFS range from 0.4 to 1, resulting in varying morphologies and adsorption properties. Specifically, the sample with the NaOH to CGFS ratio of 0.6 (CGFS-0.6) shows the best adsorption performance. The adsorption capacities are 2.87 mmol/g and 8.49 mmol/g at 20 °C with 15 % and 45 % CO2 concentration, respectively. The material is characterized by a well-developed pore structure shaped like a bouquet of flowers, with a specific surface area of 457 m2/g and pore volume reaching 2.34 cm3/g. During the hydrothermal processing, silicate/aluminosilicate entities self-organized into a Si-O-Na/Al network structure, endowing the synthesized adsorbent with optimal internal porosity and silanol functionalities. The adsorption equilibrium is achieved rapidly within 10 min, and CO2 adsorption stability remains robust across 20 successive cycles. All isothermal models of the adsorbents conform to the Sips model. This study offers a promising pathway for the value-enhanced utilization of coal-derived solid wastes.