Coal fly ash-ZIF composites for enhanced and stable carbon capture—an in-depth study†

Composites possess significant potential to mitigate the shortcomings of their individual components, offering a measure of reinforcement. In this study, composites based on CFA based Na-A and ZIF-8 were synthesized and subjected to CO₂ adsorption tests. The composites were identified as a class of ZIF-8@Na-A. These composites retained the physical attributes of their parent materials. Notably, the CO₂ uptake performance of ZIF-8@Na-A (1 : 5) was particularly high, recording values around 3.48 mmol g⁻¹ at 298 K and 1 bar. Hierarchical three step process optimization has been done to achieve the highest carbon capture and stability. Different synthesis protocols have been compared too. TGA studies have been used to validate the amine loading on the adsorbent. Among the factors influencing CO₂ uptake, temperature and pressure emerged as the most influential, while the time of carbonation exhibited minimal impact. Kinetic analysis revealed that the optimized adsorbent adhered to Avrami kinetics, displaying high R² values of 0.994. The Sips adsorption model demonstrated the best fit for explaining the adsorption behavior of the adsorbents. The average heat of adsorption for ZIF-8@Na-A was measured at −11 kJ mol⁻¹. During a 50-cycle stability assessment, the adsorbent exhibited robust performance, retaining approximately 92% of its initial CO₂ uptake. However, a subtle change in appearance was observed in the ZIF-8@Na-A adsorbent, which turned slightly pale yellowish after the completion of 50 cycles.