Sequential activation-carbonization strategy for engineering porous carbon from tea twigs biomass toward enhanced CO2 capture

The conversion of tea twig biomass into porous activated carbon presents a sustainable pathway for mitigating CO2 emissions. This study systematically compares two thermo-chemical synthesis routes, activation-carbonization (AC) and carbonization-activation (CA), to elucidate their effects on the structural, chemical, and adsorptive properties of tea-twig-derived activated carbons. Samples were prepared across two synthesis routes, three KOH-to-biomass ratios (0.5:1–2:1), and three carbonization temperatures (250–450°C). Across the conditions investigated, the CA route yielded higher surface areas, enhanced microporosity, and improved CO2 adsorption performance relative to the AC route. The best-performing condition (CA route at 450°C with a 1:1 KOH-to-biomass ratio) achieved a BET surface area of 740.2 m2 g−1 and a CO2 uptake of 2.24 mmol g−1 at 25°C and 1 bar under a 5 vol% CO2/He mixture (P_CO2 = 0.05 bar), attributed to its optimized microporous structure, low O/C and H/C ratios, and nitrogen-enriched surface. Regeneration over five adsorption-desorption cycles demonstrated good stability, with ∼17.8% capacity loss. Dynamic breakthrough behavior was well described by the Thomas and Yoon–Nelson models under the tested conditions. These findings highlight tea twigs as a low-cost precursor and demonstrate the effectiveness of the CA strategy for developing high-performance, regenerable CO2 adsorbents for post-combustion capture applications.