Activated carbons prepared from peanut shell and sunflower seed shell for high CO₂ adsorption

Biomass wastes are considered as cost-effective and sustainable precursors to prepare activated carbons for CO₂ capture. In this study, two biomass-derived activated carbons were prepared using peanut shell and sunflower seed shell, and the optimal activated carbons were obtained at low KOH/carbon ratio of about 1. The peanut shell derived activated carbon (P-973-1.00) and sunflower seed shell derived activated carbon (S-973-1.25) exhibited CO₂ uptake of 1.54 and 1.46 mmol/g, respectively, at 298 K and 0.15 bar, among the activated carbons with the highest CO₂ adsorption. Although P-973-1.00 had much lower surface area and micropore volume than S-973-1.25, it possessed higher CO₂ uptake at 298 K and 0.15 bar due to the higher volume of micropores in the range of 0.3–0.44 nm. The calculated higher isosteric heat values at lower CO₂ uptake indicated the strong affinity of CO₂ in these micropores. The ordered micro-sized pores in the activated carbons were favorable for CO₂ diffusion into the porous materials and adsorption in the inner micropores. The activated carbons had moderate CO₂ selectivity over N₂ at 1 bar, but the selectivity was significantly enhanced at 0.15 bar. The spent activated carbons after vacuum regeneration exhibited stable CO₂ adsorption in five cycles, showing the high reusability for CO₂ capture.