CO2 adsorption in biochars obtained from soursop (Anonna muricata) seeds by chemical activation with metallic salts

Environment remediation is one of the primary goals of sustainable development and anthropogenic activities, and the use of fuels in various industrial processes through combustion has led to an increase in CO₂ as well as big damage to the atmosphere by the greenhouse effect. Biochar has been used for the capture of carbon dioxide due to its high surface area. In this study, we obtained biochar from soursop seeds. The materials were synthesized by pyrolysis of precursor materials and chemical activation with chlorides of Ca and Mg at a concentration of 5% w/v. The effect of the defatting process of the soursop seeds on the obtained carbon was also researched. The absorbed solids were characterized through thermogravimetric analysis, X-ray diffraction, and CO₂ adsorption, followed by infrared spectroscopy, N₂-physisorption, CO₂-physisorption, CO₂, XPS, DRIFTS and TPD of NH₃. The type of activating agent and pretreatment conditions used were more favorable than the defatted process at obtaining carbons with N₂ surface areas between 26 and 220 m²g⁻¹. The biochars were analyzed by CO₂ surface area to describe the microporous framework, and the solid with the best CO₂ surface area was the one with the highest CO₂ adsorption. According to the statistical analyses conducted, the evaluated models Langmuir, Freundlich, and Redlich-Peterson presented good fits to the experimental data. However, the Redlich-Peterson model showed the lowest values for the residual variance, which were of the order of 0.001 or less in all cases based on the CO₂ adsorption isotherms on the studied activated carbons. However, the carbons obtained by defatting showed favorable hydrophilic behavior along with adsorption capacities in the bioremediation process and affinity towards of this GHG.