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 CO 2 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 CO 2 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 m 2 g −1 and a CO 2 uptake of 2.24 mmol g −1 at 25°C and 1 bar under a 5 vol% CO 2 /He mixture (P_CO 2 = 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 CO 2 adsorbents for post-combustion capture applications. • CA and AC routes were systematically compared for tea-twig-derived porous carbon adsorbents. • The CA route achieved the highest CO 2 uptake of 2.24 mmol g −1 at 25°C in 5 vol% CO 2 /He). • Optimal performance was achieved at 450°C with a 1:1 KOH-to-biomass ratio. • The best CA sample retained 82.1% of its initial CO 2 uptake after five cycles. • KOH post treatment at 80°C enabled microporous carbon formation undermild conditions.