CO₂ Adsorption and Storage on Ca-Modified Biochar Derived from Coconut Endocarp

Carbon capture and storage are technologies capable of reducing atmospheric CO₂ levels, contributing to mitigating the problems caused by global warming and climate change. Biochar has been widely investigated as an adsorbent for CO₂ capture due to its low cost and wide availability. However, research on CO₂ capture followed by storage using biochar is still limited. Therefore, this work aimed to investigate the capture and storage of CO₂ in physically activated and Ca-modified biochars derived from coconut endocarp. The adsorption and carbonation performances were evaluated at different temperatures and moisture conditions. The maximum adsorption capacity was observed at 30 °C and among the Ca-modified samples, the biochar with the lowest Ca content (3.5 wt %) exhibited the highest specific surface area (577 m²/g) and adsorption capacity (46.1 mg/g). The adsorption kinetics were evaluated using three kinetic models, with the Avrami model showing the best fit to the experimental data. Thermal treatment at 510 °C led to the formation of CaCO₃ particles deposited throughout the porous carbon structure; the sample with the highest Ca content (23.9 wt %) and the lowest specific surface area (242 m²/g) showed the highest carbonation capacity (104.6 mg/g). Carbonation of the Ca-modified biochars was also affected by moisture, being significantly faster in humid environments as compared to dry ones at room temperature. The results of this study demonstrated that Ca-modified biochars are environmentally friendly hybrid adsorbents capable of adsorbing and storing CO₂ in the form of carbonates, potentially serving as a sustainable alternative to help achieving the goals set by the Paris Agreement.