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.