▪ Abstract Manganese(IV) oxides produced through microbial activity, i.e., biogenic Mn oxides or Mn biooxides, are believed to be the most abundant and highly reactive Mn oxide phases in the environment. They mediate redox reactions with organic and inorganic compounds and sequester a variety of metals. The major pathway for bacterial Mn(II) oxidation is enzymatic, and although bacteria that oxidize Mn(II) are phylogenetically diverse, they require a multicopper oxidase-like enzyme to oxidize Mn(II). The oxidation of Mn(II) to Mn(IV) occurs via a soluble or enzyme-complexed Mn(III) intermediate. The primary Mn(IV) biooxide formed is a phyllomanganate most similar to δ-MnO2 or acid birnessite. Metal sequestration by the Mn biooxides occurs predominantly at vacant layer octahedral sites.

Biogenic manganese oxides: Properties and mechanisms of formation

Geomycology: biogeochemical transformations of rocks, minerals, metals and radionuclides by fungi, bioweathering and bioremediation

Rational design of non-noble materials as highly efficient, economical, and durable bifunctional catalysts for oxygen evolution and reduction reactions (OER/ORR) is currently a critical obstacle for rechargeable metal-air batteries. A new route involving S was developed to achieve atomic dispersion of Fe-Nx species on N and S co-decorated hierarchical carbon layers, resulting in single-atom bifunctional OER/ORR catalysts for the first time. The abundant atomically dispersed Fe-Nx species are highly catalytically active, the hierarchical structure offers more opportunities for active sites, and the electrical conductivity is greatly improved. The obtained electrocatalyst exhibits higher limiting current density and a more positive half-wave potential for ORR, as well as a lower overpotential for OER under alkaline conditions. Moreover, a rechargeable Zn-air battery device comprising this hybrid catalyst shows superior performance compared to Pt/C catalyst. This work will open a new avenue to design advanced bifunctional catalysts for reversible energy storage and conversion devices.

Atomically Dispersed Iron–Nitrogen Species as Electrocatalysts for Bifunctional Oxygen Evolution and Reduction Reactions

Role of assisted natural remediation in environmental cleanup

The bioaccumulation of arsenic by plants may provide a means of removing this element from contaminated soils and waters. However, to optimize this process it is important to understand the biological mechanisms involved. Using a combination of techniques, including x-ray absorption spectroscopy, we have established the biochemical fate of arsenic taken up by Indian mustard (Brassica juncea). After arsenate uptake by the roots, possibly via the phosphate transport mechanism, a small fraction is exported to the shoot via the xylem as the oxyanions arsenate and arsenite. Once in the shoot, the arsenic is stored as an AsIII-tris-thiolate complex. The majority of the arsenic remains in the roots as an AsIII-tris-thiolate complex, which is indistinguishable from that found in the shoots and from AsIII-tris-glutathione. The thiolate donors are thus probably either glutathione or phytochelatins. The addition of the dithiol arsenic chelator dimercaptosuccinate to the hydroponic culture medium caused a 5-fold-increased arsenic level in the leaves, although the total arsenic accumulation was only marginally increased. This suggests that the addition of dimercaptosuccinate to arsenic-contaminated soils may provide a way to promote arsenic bioaccumulation in plant shoots, a process that will be essential for the development of an efficient phytoremediation strategy for this element.

Reduction and Coordination of Arsenic in Indian Mustard

More than a century of non-ferrous metallurgical activities have had a severe impact on the natural environment leading, in most heavily contaminated sites, to a complete loss of the vegetation cover (that is, desert-like areas) or to the selection of metal-hyperaccumulator plant species. Identifying the chemical forms of toxic metals is of vital importance for a realistic assessment of the chemical risk posed by their presence in soils and selecting effective remedia- tion technologies. In this study, X-ray diffraction (XRD), X-ray texture goniom- etry, and powder and polarized extended X-ray absorption fine structure (EXAFS, P-EXAFS) have been used to investigate quantitatively the speciation of Zn in soils contaminated by three smelters from northern France and Belgium, and coupled synchrotron-based micro-X-ray radiation fluorescence (SXRF) and mi- cro-EXAFS (EXAFS) were also used for one of these soils. Of these techniques, the application of P-EXAFS and EXAFS to molecular environmental science was unprecedented, and we show that their complementarity greatly improves the sensitivity of powder EXAFS to identify the nature of metal-containing minerals in soils. Franklinite (ZnFe2O4), willemite (Zn2SiO4), hemimorphite (Zn4Si2O7(OH)2 ·H 2O), and Zn-containing magnetite ((Fe,Zn)Fe2O4) were identi- fied in dense soil fractions by XRD and powder EXAFS. These primary minerals originate from atmospheric fallout of Zn dusts emitted during the pyrometallurgi- cal smelting process, and they act as the main source of Zn in contaminated soils. In all soil samples, Zn released in solution during the weathering of these high-temperature minerals is taken up partly by phyllosilicates and, to a lesser extent, by Mn and Fe (oxyhydr) oxides. Zn-containing phyllosilicates were identi- fied by comparing powder EXAFS spectra to a library of model compounds and from the noteworthy angular dependence of EXAFS spectra collected on self- supporting films of clay soil fractions. Analysis of higher correlations in EXAFS spectra suggests that the local structure around Zn in phyllosilicates is trioctahe- dral. The phyllomanganate Zn-sorbed birnessite and Zn-containing Fe grains having a FeOOH-like local structure were unambiguously identified bySXRF— EXAFS. In birnessite Zn is sorbed in the interlayer space above/below vacant sites and can be either 4-fold or 6-fold coordinated depending, presumably, on the anionic stacking of birnessite layers. Based on this micro-mineralogical investiga- tion, a satisfactory fit of the three identified Zn species (that is, phyllosilicate, Mn, and Fe (oxyhydr)oxides) to experimental powder EXAFS spectra of all clay soil fractions was obtained. The significance, origin, and stability of Zn-phyllosilicates are discussed. Specifically, we show that the formation of Zn-containing phyllosili- cates is consistent with calculated thermodynamic solubilities. For the range of measured Zn 2 (D10 ppm), Si(OH)4 (10-20 ppm), and H (5.6 F pH F 7.5) concen- trations, soil solutions are supersaturated (pH G 6) or near saturation (pH F 6) with respect to the trioctahedral Zn phyllosilicate, Zn-kerolite. Finally, the plausi- bility of the formation of (Zn,Al) hydrotalcite-like species contemplated by Julliot (1999) is critically assessed.

Quantitative zn speciation in smelter-contaminated soils by exafs spectroscopy

Fungal cell walls possess strong complexing properties, which make them valuable biosorbents to remove heavy metals from wastewaters. The binding mechanisms of Zn and Pb to Penicillium chrysogenum ...

Structural Determination of Zn and Pb Binding Sites in Penicillium chrysogenum Cell Walls by EXAFS Spectroscopy

Some lichens have a unique ability to grow in heavily contaminated areas due to the development of adaptative mechanisms allowing a high tolerance to metals. Here we report on the chemical forms of...

Mechanisms of Lichen Resistance to Metallic Pollution

Chemical forms of sulfur in geological and archeological asphaltenes from Middle East, France, and Spain determined by sulfur K- and L-edge X-ray absorption near-edge structure spectroscopy

Laurent Eybert-Bérard

Papers

Quantitative zn speciation in smelter-contaminated soils by exafs spectroscopy

Structural Determination of Zn and Pb Binding Sites in Penicillium chrysogenum Cell Walls by EXAFS Spectroscopy

Mechanisms of Lichen Resistance to Metallic Pollution

Chemical forms of sulfur in geological and archeological asphaltenes from Middle East, France, and Spain determined by sulfur K- and L-edge X-ray absorption near-edge structure spectroscopy