Construction and adsorption performance of coal fly ash-based hierarchical porous zeolite A

Driven by the synergistic advancement of the Dual Carbon Strategy and the circular economy， the high-value resource utilization of coal fly ash from coal-fired power plants and the multiscale remediation of environmental pollutants have emerged as critical research topics. However， the direct construction of hierarchical porous zeolite A，which integrates a microporous framework with mesoporous mass-transfer channels，from coal fly ash remains a significant challenge. This is largely due to the complex impurity background of the raw material and the difficulty in synergistically controlling crystalline phase growth and pore architecture. To address the inherent bottlenecks of conventional microporous zeolite A， such as narrow pore channels， severe mass-transfer limitations， and inefficiencies in removing larger pollutant molecules， this study successfully synthesized a hierarchical porous zeolite A featuring a three-dimensionally interconnected mesoporous network. This was achieved via a soft-template-assisted alkali fusion-hydrothermal method， utilizing acid-treated coal fly ash as the silica-alumina source. The underlying mechanisms governing the effects of template type and dosage on the crystalline phase， morphological evolution， and pore structure of the products were systematically investigated. The results demonstrated that using 3 % dimethyloctadecyl［3-（trimethoxysilyl）propyl］ ammonium chloride （TPOAC） as the template，the prepared zeolite yielded a step-like， rough cubic morphology formed by the self-assembly of nanocrystals. Its specific surface area and total pore volume reached 57.0 m²/g and 0.1351 cm³/g， respectively， representing approximately three- and four-fold increases compared to conventional microporous zeolite A. Furthermore， aqueous ammonia nitrogen， and gaseous acetone were employed as probe pollutants to elucidate the differential response mechanisms of the hierarchical pore structure toward contaminants with distinct adsorption mechanisms. For ammonia nitrogen， which primarily relies on an ion-exchange mechanism， the hierarchical pores mainly served to improve mass transfer， yielding an adsorption capacity comparable to that of microporous zeolite A. In contrast， for larger acetone molecules restricted by the molecular sieving effect， the hierarchical porous zeolite A leveraged its highly developed mesoporous volume to effectively overcome steric diffusion hindrance. This induced highly efficient capillary condensation， resulting in a dramatic surge in acetone adsorption capacity from 12 mg/g （for conventional microporous zeolite） to 59 mg/g， a nearly four-fold increase. This study elucidates the structure-activity relationship between pore architecture evolution and differential adsorption behaviors， providing robust theoretical and technical support for the large-scale utilization of coal fly ash and the targeted design of advanced remediation materials for complex environmental pollutants.