Preparation and intercalation reactions of nano-structural materials, Mn-Al LDH

Abstract

Hydrotalcite (HT) or hydrotalcite-like compounds (HTlc) are layered double hydroxides belonging to the class of anionic clays. The structure of these compounds are very similar to that of brucite, Mg(OH)2, where some of Mg2+ represented as [M(II)] are isomorphously replaced by Al3+ represented as [M(III)] and the net positive charge is compensated by the inter-layered exchangeable anion (An-). LDH has been receiving increasing attention in recent years, owing to its potential technological applications such as catalysis, electrode, optical memory, separator, adsorbent, precursor for composite materials, and ion exchange. The general formula of these compounds can be represented as: [M(II)1-xM(III)x(OH)2]·Anx/n·mH2O with M(II) and M(III) as metal cations and An- as exchangeable anion. LDHs also possess relatively large surface areas and high anion-exchange capacities. Because of these properties, LDHs have been studied for removing toxic anionic species from aqueous systems. Thermal decomposition of these materials by calcination above 420°C results in the formation of high surface area basic mixed oxides which are reported to be potential candidates in catalyzing various reactions involved in the synthesis of a variety of fine chemicals. Indeed at this temperature, the as formed mixed oxides solid solution can regenerate upon rehydratation the HT structure with the suitable anions present in solution. Therefore, this so-called reconstruction process may be used to improve the sorption of anionic species. The LDH has been synthesized by the coprecipitation method at pH constant. The material has been obtained with [Mn/Al] molar ratio of 2.0. The product is characterized by X-ray diffraction (XRD), spectroscopy infra red (FTIR), and differential thermal analysis / thermo gravimetric analysis (DTA/TG). Dosages of polluted solutions have been realized by spectrometry UV visible.