Biochar-based adsorbents have attracted increasing attention as sustainable materials for low-concentration CO₂ capture in air filtration and direct air capture (DAC) applications. Among various biomass resources, bamboo-derived biochar is particularly attractive due to its rapid renewability and favorable carbon framework. However, the effects of chemical activation severity on pore structure evolution and practical CO₂ adsorption performance are not yet fully understood, especially under conditions relevant to air filtration.

In this study, bamboo-derived biochar samples activated under different potassium hydroxide (KOH) conditions were systematically investigated to elucidate the relationship between activation severity, structural evolution, and CO₂ adsorption behavior. Textural and physicochemical properties were characterized using nitrogen adsorption (BET analysis), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). CO₂ adsorption isotherms were measured at ambient temperature to evaluate adsorption performance in the low-pressure range relevant to air-based CO₂ capture.

The results revealed a non-monotonic [...] adsorption performance on activation severity. Moderate activation promoted pore development and enhanced CO₂ uptake, whereas intermediate activation conditions resulted in a temporary decrease in surface area and adsorption performance, likely due to pore blockage or reduced accessibility during structural transition. With further activation, surface area and CO₂ adsorption performance were recovered, indicating the formation of newly accessible pore networks. These structural transitions were qualitatively supported by SEM observations and changes in inorganic residue distribution identified by EDS analysis.

Overall, the findings demonstrate that ...