Construction and Adsorption Performance of Coal Fly Ash-Based Hierarchical Porous Zeolite A
Under the synergistic advancement of the Dual Carbon Strategy and circular economy, high-value utilization of coal fly ash and multiscale pollutant remediation are critical. Direct synthesis of hierarchical porous zeolite A from coal fly ash, integrating microporous framework and mesoporous channels, faces challenges due to complex impurities and difficulty in controlling crystal growth and pore architecture. To overcome bottlenecks of conventional microporous zeolite A—narrow pores, mass-transfer limitations, and inefficiency in removing larger pollutants—this study used acid-treated coal fly ash as silica-alumina source and a soft-template-assisted alkali fusion-hydrothermal method to synthesize hierarchical porous zeolite A with three-dimensionally interconnected mesoporous network. Effects of template type and dosage on crystalline phase, morphology, and pore structure were systematically investigated. With 3% dimethyloctadecyl[3-(trimethoxysilyl)propyl]ammonium chloride (TPOAC) as template, the zeolite exhibited step-like rough cubic morphology formed by self-assembly of nanocrystals. Its specific surface area and total pore volume reached 57.0 m²/g and 0.1351 cm³/g, respectively, approximately three- and four-fold increases over conventional microporous zeolite A. Using aqueous ammonia nitrogen and gaseous acetone as probe pollutants, differential responses were revealed: for ammonia nitrogen (ion-exchange mechanism), hierarchical pores mainly improved mass transfer, yielding adsorption capacity comparable to microporous zeolite A; for acetone (molecular sieving effect), hierarchical zeolite leveraged developed mesoporosity to overcome steric hindrance and induce capillary condensation, increasing adsorption capacity from 12 mg/g (microporous) to 59 mg/g—a 3.9-fold enhancement. This study elucidates structure-activity relationships and provides theoretical and technical support for large-scale fly ash utilization and design of materials for complex pollutant remediation.