One-step synthesis of hierarchically porous fly ash-based NaX zeolite as assisted by CTAB for low-concentration CO2 adsorption

Despite significant attention being drawn to the synthesis of zeolites from fly ash for CO 2 adsorption, few studies have focused on hierarchical porous NaX zeolites derived from fly ash. The existing synthesis methods are often complex, and the role of CTAB in zeolite formation remains unclear. To address these research gaps, we employed a one-step method for synthesizing hierarchically porous fly ash-based NaX zeolites with tunable mesoporosity. Utilizing CTAB as a template agent, we conducted a comprehensive investigation into the effects of varying CTAB dosages and aluminum source types on zeolite formation. The synthesized materials were fully characterized through XRD, FTIR, SEM, TEM, and N 2 adsorption/desorption analysis. The results showed that the mesoporous volume of the zeolites can be effectively controlled by adjusting the CTAB/Al 2 O 3 ratio. At an optimal ratio of 0.04, the synthesized zeolite has a surface area of 422 m 2 /g and a mesoporous volume of 0.116 cm 3 /g, which represents a two-fold increase compared to the NaX synthesized without CTAB. This improvement of mesoporosity significantly reduces the resistance to CO 2 diffusion, thereby enhancing the adsorption performance with a maximum adsorption capacity of 3.37 mmol/g and a high cyclic stability. A further investigation reveals the crucial role of CTAB in promoting mesopore formation and inhibiting crystal growth during zeolite synthesis. These findings provide valuable insights into the one-step synthesis of hierarchical porous zeolites.