Biomass-Derived Activated Biochars to CO₂ Adsorption

The development of low-cost and sustainable adsorbents for carbon dioxide (CO₂) capture has gained increasing attention as a strategy to mitigate greenhouse gas emissions. In this study, activated biochars produced from babassu, elephant grass, and Pinus elliottii were evaluated as CO₂ adsorbents after different activation treatments. The biochars were produced by slow pyrolysis at 400 °C and subsequently modified using three activation routes: steam activation, chemical activation with KOH, and KOH activation followed by acid washing. The materials were characterized by proximate analysis, specific surface area measurements, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, and CO₂ adsorption tests. Steam activation produced the highest specific surface areas, reaching 1270.53, 1027.28, and 907.87 m² g^-1 for babassu, elephant grass and Pinus, respectively. Despite the superior textural properties achieved through steam activation, the highest CO₂ adsorption capacities were obtained for the samples subjected to chemical activation followed by acid washing. These results indicate that adsorption performance is governed not only by the development of surface area but also by pore accessibility and the surface chemistry of the adsorbent. Maximum adsorption capacities of 82.78, 81.19, and 85.24 mg g^-1 were obtained for ACKAW B, ACKAW CE, and ACKAW P, respectively. Adsorption-desorption cycling experiments demonstrated regenerability and stable performance over repeated cycles. The results indicate that KOH activation followed by acid washing is an effective strategy for producing high-performance biochar-based adsorbents for CO₂ capture.