Design of amine-functionalized fly ash-based hierarchically porous SiO₂ adsorbents and mechanistic insights into CO₂ adsorption

Owing to their cost-effectiveness and high efficiency, solid amine adsorbents derived from solid waste are deemed highly promising for CO₂ capture. Nevertheless, traditional solid waste-based adsorbents are predominantly limited by their uniform pores structure, which significantly hampers the kinetics of CO₂ adsorption-desorption. In this study, we innovatively introduce an efficient method for recovering Si elements via alkali leaching and subsequently synthesize hierarchical porous SiO₂ through gas-phase-assisted precipitation and self-assembly, forming a distinctive "lamellar-spherical stacking structure". This unique hierarchical porous architecture enables the efficient incorporation of pentaethylenehexamine (PEHA) organic amines, thereby minimizing pore blockage due to amine functionalization and alleviating mass transfer resistance during adsorption and desorption. The resultant solid amine-functionalized hierarchical porous structures exhibit a CO₂ adsorption capacity of 4.815 mmol/g at 70 °C and maintain remarkable stability over 10 cyclic tests. Thus, the rational design of pore effects and functionalized molecular configurations synergistically enhances the CO₂ adsorption capacity in flue gas and stability, offering robust technical support for the application of solid amine CO₂ adsorbents.