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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 (CH3Hg+) 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 Hg2+ (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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Abstract: This study addresses the critical challenge associated with the removal of reactive yellow dyes from aqueous media and industrial wastewater streams. Owing to their pronounced chemical stability and resistance to conventional degradation techniques, such dyes constitute a substantial environmental concern. In this context, the present work investigates the efficacy of unmodified magnetite nanoparticles (plate-like rounded structures 6–23 nm in size), synthesised under rigorously controlled conditions and well characterised, as high-performance adsorbents for the sequestration of persistent dye species exhibiting limited susceptibility to rapid degradation. The effects of key operational parameters on dye removal efficiency were systematically evaluated to establish optimal treatment conditions. Complete removal of reactive yellow dye (100%) was achieved within 30 min at low initial dye concentrations (20 mg/L) under mildly acidic conditions and continuous agitation. Adsorption equilibrium studies, interpreted using the Langmuir isotherm model, revealed a maximum adsorption capacity of 33 mg/g under optimised conditions. Thermodynamic analysis indicated that the adsorption process is spontaneous (−ΔG° ≈ 46–54 kJ/mol) and endothermic (ΔH° = 21.12 kJ/mol), accompanied by an increase in system disorder (ΔS° = 0.2 kJ/mol × K). Importantly, experiments conducted using real wastewater matrices demonstrated performance comparable to that obtained in deionised water, thereby underscoring the practical applicability of the proposed system. Furthermore, the nanoparticles retained more than 90% removal efficiency after five consecutive adsorption–desorption cycles, employing a basic eluent for dye desorption and surface regeneration. The intrinsic magnetic properties of the adsorbent additionally enable facile recovery and potential reutilisation in secondary applications, including asphalt production. Collectively, these findings highlight the considerable potential of magnetite nanoparticles as effective and reusable adsorbents for wastewater remediation and support further investigation toward pilot-scale implementation.

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Abstract: Sulfur isotopes in mantle plume-derived magmas show heterogeneities attributed to recycling of material from the Earth's surface. The sedimentary sulfur isotope record exhibits dramatic temporal variations over Earth history, raising the question of whether its secular evolution is echoed in mantle plume-derived magmas. We present new secondary ion mass spectrometry and X-ray absorption near-edge structure measurements of δ34S and Fe3+/ΣFe in naturally glassy melt inclusions from the 2.7 Ga Belingwe komatiites. We find that δ34S of Belingwe melt inclusions is relatively homogeneous (+3.2 ± 0.9) and elevated relative to the depleted upper mantle. We evaluate explanations for elevated magmatic δ34S including degassing, sulfide fractionation, assimilation, subduction-like processes, and mantle recycling. We find no evidence for significant sulfur isotope fractionation via degassing or sulfide saturation. The elevated δ34S in the Belingwe komatiites could reflect late-stage assimilation of sediments or seawater. Alternatively, Belingwe komatiites may have formed in a subduction-like setting, as modern arcs display a bias toward positive δ34S. However, we find these scenarios less favorable. Instead, our preferred interpretation is that elevated δ34S was supplied to the komatiite mantle source via recycled lithologies such as sediments, altered oceanic crust, and/or pyroxenite. Combined with δ34S data from mantle plume-derived magmas spanning a wide age range, our results resemble the secular evolution of δ34S in surface reservoirs. We suggest that the δ34S record in mantle plume-derived magmas may echo secular evolution in the surficial sulfur reservoir with a delay of several hundred million years, linking Earth's surface and interior sulfur cycles.

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Abstract: Local and regional museums often rely on cost-effective handheld equipment to undertake non-destructive pigment assessment. When preserved colourants are only microscopic, however, these methods’ limits may be encountered. This becomes acute with fragile objects, as is often the case for organic materials. Using a reconstructed decorated ostrich eggshell vessel, an elite grave good in 7th–6th C BCE Etruria, this study compares the efficacy of portable X-ray fluorescence spectrometry; handheld Fourier-transform infrared spectroscopy; Raman spectroscopy; visible-induced luminescence imaging; multispectral multi-light reflectance analysis; synchrotron radiation X-ray fluorescence; and X-ray absorption near edge structure analysis to distinguish microscopic pigment traces. The portable device results were inconclusive, but Egyptian blue and malachite were positively identified via synchrotron analyses. This outcome supports museums to further develop protocols regarding minimal pigment residue identifications on fragile objects, including assessing risk with external analysis, and informs our understanding of pigments used on organic objects during this period.

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Abstract: Arc magmas have long been considered significantly more oxidised than their ocean island and mid-ocean ridge counterparts, a characteristic widely attributed to infusion of the mantle wedge by fluids from subducted lithologies. However, here we show that at comparable degree of differentiation and sulfur content, arc magmas have comparable oxidation state to ocean island magmas. Our study is based on measurements of Fe3+/∑Fe along with major and volatile elements in olivine and plagioclase hosted melt inclusions and matrix glasses from eleven volcanic systems located in arc settings worldwide. Accounting for fractional crystallisation (to MgO = 6 wt. %) we find that all systems lie on a reducing trend accompanying sulfur degassing, from QFM +0.9 (±0.2, 1σ) when S > 2000 ppm to QFM −0.2 (±0.6, 1σ) when S < 100 ppm (where QFM stands for the Quartz-Fayalite-Magnetite buffer). These findings reconcile the observed discrepancy between the oxidation states of xenoliths in arc magmas and gas emissions from arc volcanoes. We further show that fractional crystallisation influences the redox evolution of arc magmas to a comparable extent as, and sometimes counteracting, sulfur degassing.