Activated carbon from tea twig waste via KOH activation and carbonization by conventional furnace or ultrafast arc plasma for CO2 capture

Tea twig waste (Camellia sinensis), a lignocellulosic by-product of the tea industry, represents a promising renewable precursor for the production of high-performance activated carbon for CO2 capture. In this study, activated carbon was prepared from tea twig biomass via chemical activation with potassium hydroxide (KOH), followed by two distinct heating methods: conventional furnace activation and rapid Arc Plasma activation. The plasma process, employing argon as the working gas and operated at 700 °C with a current of 70 A for 10 min, selectively removed non-carbon species and promoted the development of microporosity together with oxygen- and nitrogen-containing surface functionalities. The sample activated using Arc Plasma under optimised conditions (AC2-B8C10) exhibited a high specific surface area of 1236 m2 g-1 and a micropore volume of 0.597 cm3 g-1, with ultramicropores well matched to the kinetic diameter of CO2. In contrast, samples activated by conventional heating (AC1-B8C7, 700 °C for 2 h) displayed lower surface areas and more pronounced mesoporosity. CO2 adsorption performance was evaluated using temperature-programmed desorption of CO2 (TPD-CO2), revealing an adsorption capacity of up to 6.6 mmol g-1 at 40 °C and 1 bar for the plasma-activated sample, significantly outperforming its furnace-activated counterpart. Comprehensive characterisation by XRD, SEM, and FTIR confirmed an essentially amorphous carbon structure with abundant microporosity and polar surface functional groups favourable for CO2 physisorption. These findings demonstrate that Arc Plasma activation enables ultrafast processing while enhancing pore development and CO2 capture performance, and, based on a semi-quantitative laboratory-scale assessment, offers the potential for reduced specific energy input compared with conventional furnace activation.