Study of KOH-activated hydrochar for CO2 adsorption

The use of solid porous materials for CO capture is a more environmentally benign approach than conventional wet scrubbing using amine-based solutions. Therefore, in this study, porous carbon materials were prepared using sawdust through hydrothermal carbonization (HTC) to produce hydrochar, followed by KOH activation. The results showed that KOH-activated hydrochar had a specific surface area of 646–1195 m/g, and a micropore area of 547–1059 m/g, indicating a microporous structure was developed. The highest CO adsorption capacity at tested adsorption temperatures was achieved from activated hydrochar obtained at 750 °C (40 °C: 0.95 mmol/g; 75 °C: 0.80 mmol/g), which is higher than pristine hydrochar (40 °C: 0.05 mmol/g; 75 °C: 0.04 mmol/g). Physisorption through pore diffusion and surface coverage and chemisorption involving formation of covalent bonds between adsorbent’s surface functionality and CO both contributed to CO adsorption. Importantly, the presence of N-containing chemicals, particularly the presence of N-containing functional groups on the surface, played an important role in CO adsorption capacity. Based on the current results and relevant literature, the development of ultra-micropore and the introduction of more N-containing functional groups to the surface would be the research focuses to further increase the CO adsorption capacity.