Ferrihydrite formation : the role of Fe13 Keggin clusters

Ferrihydrite is the most common iron oxyhydroxide found in soil and is a key sequester of contaminants in the environment. Ferrihydrite formation is also a common component of many treatment processes for clean-up of industrial effluents. Here we characterize ferrihydrite formation during the titration of an acidic ferric nitrate solution with NaOH. In-situ SAXS measurements supported by ex situ TEM indicate that initailly Fe13 Keggin clusters (radius ~0.45 nm) form in solution at pH 0.5 - 1.5, and are persistant for at least 18 days. The Fe13 clusters begin to aggregate above ~ pH 1, initially forming highly linear structures. Above pH ~ 2 densification of the aggregates occurs in conjunction with precipiation of low molecular weight Fe(III) speices (e.g. monomers, dimers) to form mass fractal aggregates of ferrihydrite nanoparticles (~ 3 nm) in which the Fe13 Keggin motif is preserved. SAXS analysis indicates the ferrihydrite particles have a core-shell structure consisting of a Keggin center surrounded by a Fe-depleted shell, supporting the surface depleted model of ferrihydrite. Overall, we present the first direct evidence for the role of Fe13 clusters in the pathway of ferrihydrite formation during base hydrolysis, showing clear structural continuity from isolated Fe13 Keggins to the ferrihydrite particle structure. The results have direct relevance to the fundamental understanding of ferrihydrite formation in environmental, engineered and industrial processes

An Amorphous Teflate Doped Aluminium Chlorofluoride: A Solid Lewis‐Superacid for the Dehydrofluorination of Fluoroalkanes

An anion‐doped aluminium chlorofluoride AlCl0.1F2.8(OTeF5)0.1 (ACF‐teflate) was synthesized. The material contains pentafluoroorthotellurate (teflate) groups, which mimic fluoride ions electronically, but are sterically more demanding. They are embedded into the amorphous structure. The latter was studied by PDF analysis, EXAFS data and MAS NMR spectroscopy. The mesoporous powder is a Lewis superacid, and ATR‐IR spectra of adsorbed CD3CN reveal a blue‐shift of the adsorption band by 73 cm−1, which is larger than the shift for SbF5. Remarkably, ACF‐teflate catalyzes dehydrofluorination reactions of monofluoroalkanes to yield olefins in C6D6. In these cases, no Friedel‐Crafts products were formed

Editorial for Special Issue “Formation of Sulfate Minerals in Natural and Industrial Environments”

Sulfate is abundant in the environment and, as a result, sulfate-containing minerals constitute a large and important focus of research [...

Editorial for Special Issue “Formation of Sulfate Minerals in Natural and Industrial Environments”

Sulfate is abundant in the environment and, as a result, sulfate-containing minerals constitute a large and important focus of research [...

Nanoparticle Assembly Leads to Mackinawite Formation

Iron sufides are important mineral phases in natural environments where they control global elemental cycles. Fe–S phases have been suggested to form through the transformation of several possible precursors to finally reach stable crystalline structures. Mackinawite is a metastable intermediate, of which a full chemical and structural characteristization of various possible intermediate stages in its formation pathways, or the chemical conditions that affect the transformations to the metastable mackinawite, are well understood. Here we report, the various steps of mackinawite formation via oriented aggregation (OA) from a nanoparticulate precursor. During OA, the formation of aggregates is a crucial stage for self-assembly of primary particles to reach stable structures. The formation occurs in five steps: (1) homogeneous nucleation of primary FeSnano particles; (2 and 3) formation of mass fractal-like aggregates from the FeSnano as precursor toward the transformation to mackinawite; (4) oriented alignment and self-assembly of these mackinawite-like aggregates; and (5) transformation to a still metastable but typical layered mackinawite structure

Towards automation of the polyol process for the synthesis of silver nanoparticles

Metal nanoparticles have a substantial impact across different fields of science, such as photochemistry, energy conversion, and medicine. Among the commonly used nanoparticles, silver nanoparticles are of special interest due to their antibacterial properties and applications in sensing and catalysis. However, many of the methods used to synthesize silver nanoparticles often do not result in well-defined products, the main obstacles being high polydispersity or a lack of particle size tunability. We describe an automated approach to on-demand synthesis of adjustable particles with mean radii of 3 and 5 nm using the polyol route. The polyol process is a promising route for silver nanoparticles e.g., to be used as reference materials. We characterised the as-synthesized nanoparticles using small-angle X-ray scattering, dynamic light scattering and further methods, showing that automated synthesis can yield colloids with reproducible and tuneable properties.Comment: Main text pages 1-16; SI pages 17-22; All the supporting files not, which are not included in this pre-print can be downloaded from here: https://doi.org/10.5281/zenodo.591061

Time-Resolved Small-Angle X-Ray Scattering

This chapter focuses on time-resolved studies of nanostructure development in sol-gel liquids, that is, diluted sols, wet gels, and drying thin fffilms. The most commonly investigated classes of sol-gel materials are silica, organically modified silica, template-directed mesostructured silica, titania and titania-based materials, zirconia and zirconia-based materials, and few others. After a brief overview of small-angle X-ray scattering (SAXS) theory and some experimental details, the chapter discusses separately each of these classes of sol-gel materials. Nearly all time-resolved SAXS studies on silica have been carried out starting with alkoxysilanes. The chapter discusses studies of systems with a single precursor under acidic and basic conditions, respectively, and reviews combinations of alkoxysilanes with other metal precursors and mixed organic-inorganic systems

Ni- and Co-struvites: Revealing crystallization mechanisms and crystal engineering towards applicational use of transition metal phosphates

Industrial and agricultural waste streams, which contain high concentrations of NH4+, PO43- and transition metals are environmentally harmful and toxic pollutants. At the same time phosphorous and transition metals constitute highly valuable resources. Typically, separate pathways have been considered to extract hazardous transition metals or phosphate, independently from each other. Investigations on the simultaneous removal of multiple components have been studied only to a limited extent. Here, we report the synthesis routes for Co- and Ni-struvites (NH4MPO4.6H2O, M = Ni2+, Co2+ ), which allow for P, ammonia and metal co precipitation. By evaluating different reaction parameters, the phase and stability of transition metal struvites, as well as their crystal morphologies, and sizes could be optimized. Ni-struvite is stable in a wide reactant concentration range and at different metal/phosphorus (M/P) ratios, whereas Co-struvite only forms at low M/P ratios. Detailed investigations of the precipitation process using ex situ and in situ techniques provided insights into the crystallization mechanisms/crystal engineering of these materials. M-struvites crystallize via intermediate colloidal nanophases, which subsequently aggregate and condense to final crystals after extended reaction times. However, the exact reaction kinetics of the formation of a final crystalline product varies significantly depending on the metal cation involved in the precipitation process: several seconds (Mg) to minutes (Ni) to hours (Co). The achieved level of control over the morphology and size, makes precipitation of metal struvites a promising method for direct metal recovery and binding them in the form of valuable phosphate raw materials. Under this paradigm, the crystals can be potentially upcycled as precursor powders for electrochemical applications, which require transition metal phosphates (TMPs).Comment: Main manuscript 22 pages, SI 27 page

Misères et richesses archivistiques : la gendarmerie et la sortie de la Seconde Guerre mondiale

Entre misère regrettable et richesse inattendue, la situation archivistique de la gendarmerie en guerre est pleine de contrastes. En s’appuyant sur l’expérience de notre thèse de doctorat, nous désirons les éclairer, et présenter les matériaux avec lesquels nous tâtonnons pour dresser l’histoire de la gendarmerie. Pour enrichir le propos, des comparaisons sont établies avec les situations archivistiques de la gendarmerie française ou de la Koninklijke marechaussee néerlandaise. Nous structurons ces sources en réintégrant le corps dans la dynamique des régulations sociales de la fin de l’Occupation. De cette façon, il est aisé d’en démontrer l’intérêt mais aussi les limites face à notre problématique de thèse et pour la recherche dans son ensembl

Electron microscopy study of intragranular nanoporosity and the occurrence of local structural disorder in cubic BaTiO3BaTiO_3 nanopowders from alkoxide–hydroxide precipitation process

The evolution of phase and defect structure in BaTiO 3 nanopowders synthesized by an alkoxide–hydroxide process in benzyl alcohol under reflux conditions were investigated. As-prepared powders were heat-processed at temperatures ranging from 250 to 850 1 C. X-ray powder diffraction (XRD) showed that BaTiO 3 remained cubic with crystallite size below 30 nm after heat treatment up to 850 1 C. Internal pores of 1–2 nm diameter inside the crystallites were well visible with transmission electron microscopy (TEM) at processing temperatures between 250 and 600 1 C. Their presence was confirmed by infrared spectroscopy (FT-IR) and is attributed to accumulation and curing of lattice hydroxyl defects. No tetragonal phase was detected by XRD up to 700 1 C. However, Raman spectroscopy (FT-RS) revealed Raman activity in all cubic materials. This was attributed to local tetragonal and orthorhombic distortions, resulting from the presence of internal nanopores. Considering that the nanopores constitute a relatively large fraction of the total volume of the nanocrystals, the internal strain may be substantial. Hence, a relatively high temperature is necessary not only to cure the hydroxyl defects, but also to release the internal strains accumulated in the crystals upon volume diffusion and sintering. Therefore, the cubic-to- tetragonal phase transition was observed only after heat treatment at 850 1 C, when the occurrence of a tetragonal phase was accompanied by substantial grain growth to 100 nm siz