CO₂ Capture Using Zeolite Synthesized from Coal Fly Ash and Its Subsequent Utilization for Fire Retardation and Dye Removal

This study explores an effective synthesis of zeolite Na P1 (SynZ) from coal fly ash (CFA) to capture carbon dioxide (CO2) and subsequent utilization for potential fire retardation and methylene blue (MB) removal. Compared to raw CFA, SynZ exhibited extensively improved physicochemical properties, including a high surface area (94 m2/g), cation exchange capacity (447 cmol(+)/kg), and functionalities (Na+, −O, −OH, and −Si–O–Al–O–Si−) within its pore architecture. These properties synergistically expedited CO2 sorption, leading to a 30-fold higher CO2 sorption capacity using SynZ compared to CFA. However, sorption was temperature- and pressure-dependent, with 45 °C contributing to higher sorption (151 mg/g) than other studied temperatures (<95.5 mg/g). Isosteric heat, regeneration, and kinetics of sorption also proved that low-pressure conditions had a role in chemisorption and high-pressure conditions for physisorption. SynZ with captured CO2 (SynZCO2) showed excellent fire retardation behavior by preserving over 81% char residue, which is nearly 10% more than that for raw SynZ. The activation of Na2CO3 and/or NaHCO3 in the spent material could be antiflammable. Furthermore, SynZCO2 exhibited higher MB removal (85%) than SynZ (78%), potentially as a result of a strong carbonate (HCO3–/CO32–)-to-dye (MB+) interaction in SynZCO2_MB. This research finding underscores the utilization of industrial solid waste in sustainable applications.