Effect of Vegetable Feedstock Minerals on Biochar Structure and CO₂ Uptake

Agricultural residues represent a renewable resource for producing functional carbon materials. Biochars are prepared from nine vegetable-derived feedstocks and characterized for their structural, compositional, and CO₂ adsorption properties. X-ray diffraction reveals distinct crystal structures and mineral phases, including KCl, while scanning electron microscopy (SEM)-energy-dispersive X-ray spectrometer (EDS) confirms differences in morphology and elemental distribution. CO₂ adsorption isotherms show that banana, Japanese sweet potato, and onion biochars exhibit uptake capacities comparable to activated carbon. Desorption profiles indicate that biochars with lower carbon content, such as green pepper, sweet potato skin, and potato skin, are dominated by chemisorption, whereas others primarily exhibit physisorption. These results highlight that carbon ordering, residual minerals, and feedstock composition collectively govern CO₂ adsorption mechanisms, offering insight into the rational design of low-cost, biomass-derived sorbents for carbon capture applications.