Mechanisms of mercury (Hg) and methylmercury (CH3Hg+) removal by pristine and thiol-modified açaí waste nanobiochar

Abstract

Mercury (Hg) contamination remains a global environmental challenge, driven by sources such as artisanal gold mining, industrial emissions, and coal combustion. Developing efficient and sustainable remediation strategies is therefore critical. Here we evaluate for the first time the mechanisms controlling Hg and methylmercury (CH 3 Hg + ) removal using nanobiochar derived from açaí ( Euterpe oleracea Mart) seed residues and its thiol-functionalized counterpart. Nanobiochar (< 50 nm) was produced via pyrolysis at 600 °C and chemically modified to enhance sorption performance. Thiol functionalization increased maximum sorption capacities by 29% for Hg 2+ (from 299 to 385 mg g −1 ) and 61% for CH₃Hg⁺ (from 102 to 164 ng g −1 ), while also reducing desorption. Spectroscopic analyses (XPS and EXAFS) revealed that Hg immobilization was primarily driven by the formation of stable Hg–S species, including metacinnabar (β-HgS), highlighting a shift from weaker ionic interactions to covalent bonding. This mechanistic evidence demonstrates that surface functionalization not only enhances sorption capacity but also promotes long-term stability of retained Hg species. By coupling waste valorization with advanced spectroscopic insights, this study provides a novel framework for designing high-performance materials for Hg remediation in contaminated environments.

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