Preparation Of Layered Double Hydroxides Research Articles

Preparation of Layered Double Hydroxides and Their Applications as Additives in Polymers, as Precursors to Magnetic Materials and in Biology and Medicine

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Preparation and characterization of rare earth-containing layered double hydroxides

Abstract Novel Layered Double Hydroxide (LDH) phases containing Rare Earth Elements (Ce3+ and Eu3+) have been prepared by ion exchange method using Ln ( dipic ) 3 3 − complexes as guest anions ([C7H3NO4]2−=dipic ligand). Intercalation of Ce3+ and more generally of rare earth cations in the opened structure of LDH displays many interests for applications as catalysts or catalyst precursors and materials with luminescence properties. The influence of various experimental conditions were investigated for the optimisation of the intercalation reaction, including the host layer composition and charge density and other synthesis parameters such as temperature, pressure, reagent concentration, and reaction time. Moreover, the adsorption isotherm of Na3[Ce(dipic)3] on Zn2Al-LDH was recorded in order to study the ion-exchange process. The different products were characterized using ICP, XRD, FTIR, TG and UV solid. The results confirmed the intercalation of [Ce(dipic)3]3− anions and the preparation of Ce-containing LDHs. The interlayer spacing of [Ce(dipic)3]3− containing ZnAl LDH was 1.24 nm, in agreement with the mean size of the complex (0.9 nm) and a slanted orientation between the layers. This study was extended to the intercalation of [Eu(dipic)3]3− complexes and preliminary results on luminescence properties have been recorded. Hereafter, rare-earth element will be noted (REE).

Hydrolysis in Polyol: New Route for Hybrid-Layered Double Hydroxides Preparation

A new route has been investigated for layered double hydroxides (LDH) preparation using hydrolysis of metal salt precursors in polyol medium (ethylene glycol and diethylene glycol) under reflux. It constitutes a simple way to prepare hybrid LDH in soft chemistry conditions. The process of LDH formation rests on progressive extraction of aluminum from an insoluble complex, which is conditioned by water addition and presence of divalent metallic cations. We focused on the preparation of LDH with cation compositions NiAl and CoAl. Many advantages are demonstrated over the standard coprecipitation method, in terms of phase purity and morphology. Indeed, this method avoids the use of any other precipitation reagents and pH or atmosphere control. The formation of LDH and presence of acetate in the interlayer region was confirmed by X-ray data, IR spectroscopy, and ionic chromatography. Moreover, controlled calcinations of as-prepared LDH allow preparing mixed oxides with enhanced specific surface area properties (up to 250 m 2 /g) and narrow pore range distributions in the mesoporous region of interest for catalytic applications.

Preparation of Layered Double Hydroxides

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Comparative study of the coprecipitation methods for the preparation of Layered Double Hydroxides

Coprecipitation is the method most frequently applied to prepare Layered Double Hydroxides (LDHs). Two variations of this method can be used, depending on the pH control conditions during the precipitation step. In one case the pH values are allowed to vary while in the other they are kept constant throughout coprecipitation. Although research groups have their preferences, no systematic comparison of the two variations of the coprecipitation method is available in the literature. On this basis, the objective of the present study was to compare the properties of LDHs prepared using the two forms of pH control in the coprecipitation method. The results showed that even though coprecipitation is easier to perform under conditions of variable pH values, materials with more interesting properties, from the point of view of technological applications, are obtained at constant pH. Higher crystallinity, smaller particle size, higher specific surface area and higher average pore diameter were found for materials obtained by coprecipitation at constant pH, when compared to the materials obtained at variable pH.