A comparative study of acid‑activated non‑expandable kaolinite and expandable montmorillonite for their CO2 sequestration capacity

This study aims to improve the pore volume and specific surface area of kaolinite (Kaol) and montmorillonite (Mt) through low-temperature acid treatment to address their limited adsorption capacity. Clay mineral samples underwent sulfuric acid activation at various concentrations and durations. SEM analysis indicated acid activation improved kaolinite pore structure, increasing specific surface area, while montmorillonite exhibited reduced grain size and higher porosity, resulting in greater pore volume and surface area. EDX analysis revealed changes in chemical composition, including a 10% increase in silica and a 13% reduction in aluminium in kaolinite, whereas montmorillonite exhibited a 13% aluminium increase and 9.5% higher silica content. Kaolinite’s XRD pattern remained unchanged, resisting 2.5 M acid activation, while montmorillonite displayed modified patterns, indicating interlayer conversion with increased acid concentration. BET analysis confirmed higher sulfuric acid concentration increased pore volume and surface area, while FTIR analysis showed stable Si–O stretching peaks with changing intensity after 8 h. Montmorillonite exhibited Al–OH and Mg–OH bands, decreasing with higher acid concentration, and Si–O–Fe and Si–O–Al bonds disappeared with acid activation. Thus, the results indicate significantly enhanced pore volume and specific surface area after acid activation, accelerating CO ₂ adsorption rates. This activation demonstrates a direct relationship between acid concentration and reaction time with clay minerals’ pore characteristics. These clay minerals can be used as adsorbents for CO ₂ in carbon capture technology, aiding the global goal of achieving ‘net zero’ emissions by 2050.