Bioadsorbents from Household Biowastes: A Sustainable Solution for CO₂ Capture

Bioadsorbents derived from food waste can not only help reduce the amount of such waste but also demonstrate significant potential for CO₂ capture from both the energy sector and other industries. This study evaluates the feasibility of using bioadsorbents obtained from various types of household biowaste-including black and green coffee grounds, tea grounds, potato peels, walnut shells and green walnut shells-for CO₂ capture from flue gas. The bioadsorbents were produced through a two-step process consisting of carbonization followed by KOH activation. The physicochemical properties of the bioadsorbents were characterized using SEM, FTIR, XRD, TGA and BET techniques. The CO₂ sorption capacity was examined for bioadsorbents and for the original biowaste and the biocarbons obtained after carbonization. Isothermal CO₂ adsorption tests were carried out at 25 °C under 100% CO₂ atmosphere. The influence of porous properties-such as specific surface area, total pore volume, micropore volume and average pore diameter-on the CO₂ sorption capacity was assessed for bioadsorbents, biocarbons and raw biowastes. The results showed that the most effective bioadsorbent for CO₂ capture was derived from spent dark roast coffee grounds, with a sorption capacity of 115.8 mg_CO2/g_A. The favorable sorption performance of this bioadsorbent was attributed to its high specific surface area (1580 m²/g), the largest total pore volume (0.84 cm³/g) and micropore volume (0.5 cm³/g) among the tested materials, as well as an optimal average pore diameter (0.96 nm). Similarly favorable structural properties were observed for the potato peel-derived bioadsorbent (APP-1604 m²/g; 0.65 cm³/g) and the bioadsorbent derived from green walnut shells (AGWS-1376 m²/g; 0.64 cm³/g). Their CO₂ adsorption capacities reached 104.1 mg_CO2/g_A and 73.2 mg_CO2/g_A, respectively, for AGWS and APP.