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Two-dimensional (2D) materials and phenomena attract huge attention in modern science. Herein, we introduce a family of layered materials inspired by the minerals valleriite and tochilinite, which are composed of alternating "incompatible", and often incommensurate, quasi-atomic sheets of transition metal chalcogenide (sulfides and selenides of Fe, Fe-Cu and other metals) and hydroxide of Mg, Al, Fe, Li, etc., stacked via electrostatic interaction rather than van der Waals forces. We survey the data available on the composition and structure of the layered minerals, laboratory syntheses of such materials and the effect of reaction conditions on the phase purity, morphology and composition of the products. The spectroscopic results (Mössbauer, X-ray photoelectron, X-ray absorption, Raman, UV-vis, etc.), physical (electron, magnetic, optical and some others) characteristics, a specificity of thermal behavior of the materials are discussed. The family of superconductors (FeSe)·(Li,Fe)(OH) having a similar layered structure is briefly considered too. Finally, promising research directions and applications of the valleriite-type substances as a new class of prospective multifunctional 2D materials are outlined. [ABSTRACT FROM AUTHOR]

The interaction of aqueous solutions bearing platinum-group elements (PGEs) with sulfides is important for understanding the formation and weathering of PGE ore deposits, mineral processing, and synthesis of nanomaterials. Here, the surface species formed upon the contact of the main sulfide minerals (pyrite, pyrrhotite, galena, chalcopyrite and valleriite) with the solutions of H2PtCl6 (pH 1.5, 20 °C) have been studied using X-ray photoelectron spectroscopy (XPS). Uptake of Pt increased gradually with increasing interaction time, and depended, as well as the composition of immobilized products, on the mineral nature and the state of its surface, e.g., the chemical pre-treatment. The highest rate of Pt deposition was observed on galena and valleriite and the lowest on pyrite and pyrrhotite. The preliminary moderate oxidation of pyrrhotite promoted Pt deposition, which, however, was hindered under harsh reaction conditions. The pre-oxidation of pyrite in all cases resulted in a decrease of the Pt deposition. Initially, Pt(IV) chloride complexes adsorb onto the mineral surface, and then the reduction of Pt(IV) to Pt(II) and substitution of chloride ions with sulfide groups occur forming sulfides of Pt(II) and then, Pt(IV). The reduction of Pt species to the metallic state was observed at valleriite after 24 h, probably due the negative charge of the sulfide nanolayers of this sulfide-hydroxide composite mineral. [ABSTRACT FROM AUTHOR]

Abstract: Stable sols of copper nanoparticles from 10nm to 50nm in diameter synthesized in aqueous solutions using several reducing agents and immobilized on pyrographite were characterized by XPS, Cu L3MM Auger and X-ray absorption spectroscopy (Cu L-edge TEY XANES and Cu K-edge XANES and EXAFS in transmission mode) along with UV–vis spectroscopy, AFM, TEM. It was found that the nanoparticles produced in the hydrazine hydrate and sodium borohydride assisted synthesis are composed of surface Cu(II) oxyhydroxides, and the shells formed by cuprite Cu2O and distorted Cu(I) oxide, which showed the Cu L-edge peak shifted to higher energies, above the metallic core. The relative amount of cuprite was usually larger in the hydrazine systems, but it depended on the sample preparation protocol. The nanoparticles prepared using ascorbic acid as a reactant consisted of rather thick Cu(II) overlayer and largely distorted Cu(I) oxide underneath. The post-synthetic sample handling notably affected the results; in particular, sedimentation (instead of drying of the colloidal solution) favored reduction of the oxide layers to metallic copper and agglomeration of the Cu particles in the precipitate, even in the case of ascorbic acid, while the colloidal particles in the supernatant were oxidized. [Copyright &y& Elsevier]