Basic Properties of MgAl-Mixed Oxides in CO2 Adsorption at High Temperature.

The increase of consciousness towards global warming and the need to reduce greenhouse gas emissions lead to the necessity of finding alternative applications based on easy-to-use materials in order to control and reduce global CO2 emissions. Layered Double Hydroxides (LDHs) and LDH-derived materials are potentially good adsorbents for CO2, thanks to their low cost, easy synthesis, high sorption capacity, and surface basicity. They have been intensively studied in CO2 capture at high temperature, presenting variable sorption capacities for MgAl LDHs with the same composition, but prepared under different synthesis conditions. The ambient temperature coprecipitation synthesis method is an attractive one-step procedure to synthesize LDHs under mild conditions, with low energy consumption and short synthesis time. The present study is based on the synthesis and characterization of hydrotalcites by a mild-conditions coprecipitation process and the production of derived mixed oxides to be used as CO2 adsorbents. A critical comparison to similar materials is reported. Moreover, the effect of the surface basicity of the derived mixed oxides (measured by adsorption calorimetry) and the CO2 sorption capacity are discussed, showing a linear correlation between the amount of weak and very strong basic sites and the CO2 adsorption behavior.

In situ preparation of compounds using silanized mPEG inspired by talc-like structures.

Composite materials show improved properties compared to pristine materials, in particular when the filler is dispersed homogeneously in the matrix. For polymer-clay composites, different strategies exist to improve clay mineral dispersion in the polymer matrix. In this study, an innovative approach is suggested which consists of forming a talc-like structure directly in a polymer matrix using a silanized polymer as the silicon source. Poly(ethylene glycol) methyl ether of different average molar masses (Mn = 350, 500, 750, 1900 g mol-1) were functionalized with (3-isocyanatopropyl)triethoxysilane and added to the ethanolic solutions of magnesium nitrate. 1H-29Si CPMAS solid state NMR experiments revealed partial condensation of silane compounds, and FTIR analysis confirmed the presence of both Si-O and Mg-O bonds, but an additional proof of the Si-O-Mg bond is needed to prove the formation of such a structure.

Review: Clay-Modified Electrodes in Heterogeneous Electro-Fenton Process for Degradation of Organic Compounds: The Potential of Structural Fe(III) as Catalytic Sites.

Advanced oxidation processes are considered as a promising technology for the removal of persistent organic pollutants from industrial wastewaters. In particular, the heterogeneous electro-Fenton (HEF) process has several advantages such as allowing the working pH to be circumneutral or alkaline, recovering and reusing the catalyst and avoiding the release of iron in the environment as a secondary pollutant. Among different iron-containing catalysts, studies using clay-modified electrodes in HEF process are the focus in this review. Fe(III)/Fe(II) within the lattice of clay minerals can possibly serve as catalytic sites in HEF process. The description of the preparation and application of clay-modified electrodes in the degradation of model pollutants in HEF process is detailed in the review. The absence of mediators responsible for transferring electrons to structural Fe(III) and regenerating catalytic Fe(II) was considered as a milestone in the field. A comprehensive review of studies investigating the use of electron transfer mediators as well as the mechanism behind electron transfer from and to the clay mineral structure was assembled in order to uncover other milestones to be addressed in this study area.

Crystal structure control of aluminized clay minerals on the mobility of caesium in contaminated soil environments.

Radioactive caesium pollution resulting from Fukushima Dai-ichi and Chernobyl nuclear plant accidents involves strong interactions between Cs+ and clays, especially vermiculite-type minerals. In acidic soil environments, such as in Fukushima area, vermiculite is subjected to weathering processes, resulting in aluminization. The crystal structure of aluminized clays and its implications for Cs+ mobility in soils remain poorly understood due to the mixture of these minerals with other clays and organic matter. We performed acidic weathering of a vermiculite to mimic the aluminization process in soils. Combination of structure analysis and Cs+ extractability measurements show that the increase of aluminization is accompanied by an increase in Cs+ mobility. Crystal structure model for aluminized vermiculite is based on the interstratification of unaltered vermiculite layers and aluminized layers within the same particle. Cs+ in vermiculite layers is poorly mobile, while the extractability of Cs+ is greatly enhanced in aluminized layers. The overall reactivity of the weathered clay (cation exchange capacity, Cs+ mobility) is then governed by the relative abundance of the two types of layers. The proposed layer model for aluminized vermiculite with two coexisting populations of caesium is of prime importance for predicting the fate of caesium in contaminated soil environments.

Nature of the sites involved in the process of cesium desorption from vermiculite.

Three particle size fractions of sodium-saturated vermiculite (10-20, 1-2 and 0.1-0.2 µm), differing only in their ratios of external-to-total sorption sites, were used to probe the nature of the sites involved in desorption of cesium ions. The sorption was investigated for initial aqueous concentrations of cesium ranging from 5.6×10(-4) to 1.3×10(-2) mol/L, and the cesium desorption was probed by exchange with ammonium ions. The results showed that (1) the amounts of desorbed cesium were strongly dependent on the particle size for a given initial aqueous cesium concentration and (2) the amounts of desorbed cations (Na(+) and Cs(+)) strongly decreased with increasing initial cesium aqueous concentration, irrespective of the particle size investigated. Quantitative analysis of these results suggested that cesium ions sorbed on external (edge+basal) sorption sites can be desorbed by ammonium ions. As a contrast, most of cesium ions sorbed on interlayer sites remain fixed due to the collapse of the structure under aqueous conditions. This study provides important information, such as the nature of the sites involved in the exchange process, when the thermodynamic formalism is considered to describe the ion-exchange process involving cesium and high-charge swelling clay minerals in polluted soil environments.