Preparation and performance of MOFs@FMH composites

Coal-fired power generation dominates the current energy landscape, but it generates fly ash as a by-product of power generation not only takes up land, but also may cause dust and pollution. Concurrently, substantial CO₂ emissions from the greenhouse effect are exacerbating. Carbon capture and storage (CCS) technology is one of the effective solutions to mitigate the greenhouse effect. Metal-organic frameworks (MOFs) have great potential for CO₂ capture due to their controllable porous structure and high specific surface area. In this study, MOFs@FMH composites were synthesized via a solution method using fly ash and waste polyethylene terephthalate (PET) as raw materials., and characterized by XRD, SEM, FTIR, TGA and N₂ physisorption (BET). The results demonstrate that the porous architecture of fly ash facilitates the outward growth or surface loading of MOFs crystals. 25%Fe-MOF@FMH composite has good crystallinity, complete crystal structure, specific surface area and micropore volume of 104.5 m²/g and 0.078 cm³/g, which are 48 times and 52 times those of fly ash, respectively. Under identical atmospheric pressure conditions, 25%Fe-MOF@FMH composite exhibited the highest CO₂ adsorption capacity among the synthesized series, reaching 1.48 mmol/g at 25℃ and 0.91 mmol/g at 80℃, respectively. The CO₂ adsorption capacity showed a trend of first increasing and then decreasing with increasing Fe-MOF loading. This non-monotonic trend is primarily attributed to the evolution of pore structure: an optimal loading facilitates the formation of abundant and well-defined micropores, maximizing accessible adsorption sites; whereas insufficient loading results in limited active sites, and excessive loading induces pore blockage and structural disorder, both of which are detrimental to adsorption performance.