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 mgCO2/gA. 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 mgCO2/gA and 73.2 mgCO2/gA, respectively, for AGWS and APP.