The CO2 capture method using porous solid materials for adsorption is considered more eco-friendly than absorption using amine solutions. In this study, activated carbon was chosen as the adsorbent for CO2 capture, utilizing tea twig waste biomass as a precursor. After initial treatment, the tea twigs were carbonized at 400°C for 1 hour to create biochar. The biochar was then chemically activated with KOH, using different ratios of KOH solution to biochar. The findings revealed that the KOH-activated biochar from tea twigs had the highest specific surface area, ranging from 206-253 m2 g-1, and exhibited a mesoporous structure. The highest CO2 adsorption capacity at 40°C was achieved by the biochar activated with a 4:1 ratio (3.073 mmol CO2 g-1), outperforming the biochar activated at the 2:1 ratio (2.697 mmol CO2 g-1) and 6:1 ratio (2.842 mmol CO2 g-1). The adsorption occurred through physical sorption via pore diffusion, involving Van der Waals forces, along with chemisorption, where covalent bonds formed between the adsorbent surface and CO2, aiding in CO2 adsorption. The results, along with relevant literature, indicate that the pore structure development on activated carbon surfaces plays a significant role in CO2 adsorption capacity. The sizes of micro- and mesopores provide effective pathways for adsorption, ensuring CO2 molecules are effectively captured within the pore structure. Future research will focus on improving CO2 adsorption capacity by further enhancing these pore structures. © 2026 American Institute of Physics Inc.. All rights reserved.