The dehydration mechanism of Na and K birnessites: a comprehensive multitechnique study.

The structural, spectroscopic and electronic properties of Na and K birnessites were investigated from ambient conditions (bir) to complete dehydration, and the involved mechanisms were scrutinized. Density Functional Theory (DFT) simulations were employed to derive structural models for lamellar AMnO·HO (A = Na or K, = 0 or 0.66), subsequently compared with the experimental results obtained for NaMnO·0.

Synthesis and characterization of a new monometallic layered double hydroxide using manganese.

This article reports for the first time the synthesis of an LDH using only manganese as the divalent and trivalent metallic ion. Analysis of the pH, redox potential, and chemical composition during the oxidation of a manganese basic salt using persulfate indicates the oxidation of 1/3 of the initial Mn ions, in agreement with the paramagnetic structure and XPS analysis. Infrared, Raman spectra and thermogravimetric analysis results were similar to the ones obtained with Fe-LDH also known as green rust.

As(V) and As(III) sequestration by starch functionalized magnetite nanoparticles: influence of the synthesis route onto the trapping efficiency.

We report the effect of the synthesis route of starch-functionalized magnetite nanoparticles (NPs) on their adsorption properties of As(V) and As(III) from aqueous solutions. NP synthesis was achieved by two different routes implying the alkaline precipitation of either a mixed Fe/Fe salt solution (MC samples) or a Fe salt solution in oxidative conditions (MOP samples). Syntheses were carried out with starch to Fe mass ratio (R) ranging from 0 to 10.

Birnessite: A New Oxidant for Green Rust Formation.

Iron and manganese are ubiquitous in the natural environment. Fe-Fe layered double hydroxide, commonly called green rust (), and Mn-Mn birnessite () are also well known to be reactive solid compounds. Therefore, studying the chemical interactions between Fe and Mn species could contribute to understanding the interactions between their respective biogeochemical cycles.

Solid-State NMR and DFT Combined for the Surface Study of Functionalized Silicon Nanoparticles.

Silicon nanoparticles (NPs) serve a wide range of optical, electronic, and biological applications. Chemical grafting of various molecules to Si NPs can help to passivate their reactive surfaces, "fine-tune" their properties, or even give them further interesting features. In this work, (1) H, (13) C, and (29) Si solid-state NMR spectroscopy has been combined with density functional theory calculations to study the surface chemistry of hydride-terminated and alkyl-functionalized Si NPs.

Unusual two-stage kinetics of ethylene adsorption on Si(100) unraveled by surface optical spectroscopy and Monte Carlo simulation.

The adsorption of ethylene on a Si(100)-2×1 surface in an ultrahigh vacuum has been monitored at room temperature by use of real-time surface differential reflectance spectroscopy, which clearly demonstrated that the adsorption follows a two-stage process. About half a monolayer is obtained for 1 L, while the second stage is much slower, yielding the complete monolayer for an exposure of ∼400  L. The kinetics over the full range has been successfully reproduced by a Monte Carlo calculation.

Thermodynamic factors limiting the preservation of aromaticity of adsorbed organic compounds on Si(100): example of the pyridine.

Using pyridine as an example, a thermodynamic analysis of the low temperatures adsorption of aromatic organic molecules with a N atom on the Si(100) surface is presented. This study is restricted to the case of an equilibrium with the gas phase. Dative attachment which is the only way to preserve aromaticity is the more stable form of adsorbed pyridine in dilute solutions at low temperatures.

Adsorption of phenylacetylene on Si(100)-2 x 1: kinetics and structure of the adlayer.

Direct adsorption of phenylacetylene on clean silicon surface Si(100)-2 x 1 is studied in ultrahigh vacuum (UHV). The combination of scanning tunnel microscopy (STM) and surface differential reflectance spectroscopy (SDRS) with Monte Carlo calculations are put together to draw a realistic kinetic model of the evolution of the surface coverage as a function of the molecular exposure. STM images of weakly covered surfaces provide evidence of two very distinct adsorption geometries for phenylacetylene, with slightly different initial sticking probabilities.