Valorization of Amazonian Sacha Inchi shells into carbonaceous materials for efficient mercury removal from multiple water matrices

Mercury ion (Hg 2+ ) is a global pollutant that poses a significant threat to human health and wildlife, particularly in aquatic environments. In this study, the outer shell of Sacha-Inchi, an agro-industrial residue from the Amazon region, was used to prepare carbonaceous materials for the adsorption of Hg 2+ from water. Carbonaceous materials were obtained using different preparation strategies, including pyrolysis at different temperatures (300, 400, and 500°C), chemical modification with KOH and H 3 PO 4 , and hydrothermal treatment. The performance of all materials in Hg 2+ removal was then evaluated to assess the influence of the synthesis approach employed. The results show that the carbonaceous material prepared at 300°C (SE-300) was the most effective, as it maintained a high Hg 2+ adsorption (≥95%). This is attributed to the fact that the lower temperature prevents the collapse of the material's porosity, allowing the formation of functional groups such as C=C bonds and oxygenated groups that favored the removal of Hg 2+ through free electron-cation interactions, complex formation and π-cation interactions. Adsorption isotherm analysis indicated that the process best fits the Langmuir model, suggesting monolayer behavior with a maximum adsorption capacity of 120.6 mg of Hg 2+ per gram of SE-300. Kinetic and thermodynamic analyses revealed that adsorption follows a pseudo-second order model and is a spontaneous and endothermic process. Finally, the study demonstrated the process's economic viability, pH stability, the ability to reuse the material and the effectiveness of the material for removal of heavy metal in domestic wastewater and river water.