Activated carbon from tea twig waste via low-temperature KOH activation for efficient CO ₂ capture: Development mesoporous structures under mild conditions

The development of low-energy and sustainable materials for carbon capture is critical to climate change mitigation. In this study, activated carbon was synthesized from tea twigs waste ( Camellia sinensis ) via pyrolysis at 300 °C followed by KOH chemical activation at an ultra-low temperature of 200 °C. The optimized sample (AC-A 2 B 4 ) exhibited a high BET surface area of 542 m 2 g −1 , narrow average pore diameter (1.936 nm), and a CO 2 adsorption capacity of 2.867 mmol g −1 at 25 °C—surpassing many adsorbents produced under conventional high-temperature conditions. Characterization using BET, FTIR, XRD, and SEM-EDX confirmed the presence of abundant polar surface functionalities (e.g. –OH, C = O), high carbon content (83.5%), and an amorphous mesoporous structure conducive to CO 2 physisorption and chemisorption. Although the initial N 2 uptake at low P/P 0 (< 0.1) suggests the presence of narrow pores, the overall isotherms exhibited Type IV characteristics, indicative of dominant mesoporosity. Isotherm modeling showed strong agreement with the Langmuir model (R 2 = 0.994), indicating monolayer adsorption on a surface with uniform high-affinity sites. Regeneration experiments over five cycles demonstrated minimal capacity loss (<5%), while life cycle analysis revealed ∼70% lower energy consumption compared to traditional activation routes. This study introduces a novel, energy-efficient pathway to produce mesoporous, high-performance CO 2 adsorbents from agro-industrial waste under mild processing conditions, offering scalable potential for decentralized carbon capture and sustainable manufacturing.