Use of organic media to modify the surface and porosity properties of hydrotalcite-like compounds

Abstract

In this paper we have focused on the surface and porosity properties of [Mg-Al-CO₃] and [Mg-Al-Cl] obtained by the coprecipitation method. Different synthetic routes are used as well as post-synthesis treatments in order to measure how far textural modifications can be induced in these materials. For example, by performing the direct synthesis of [Mg-Al-CO₃] in mixtures composed of water and an organic solvent, or by regenerating calcined samples in similar mixtures, the surface areas, pore volumes and pore sizes are shown to be greatly affected by some solvents: synthesis in ethylene glycol causes an increase of 81% in the surface area, while in glycerol it results in the induction of microporosity (30%). On the other hand, we have also investigated the influence of these organic solvents on the textural properties during anion exchange reactions. Through analysis of their BET nitrogen adsorption/desorption isotherms, unpillared [Mg-Al-CO₃] proved to be mostly mesoporous, while [Mg-Al] hydrotalcite pillared with hexacyanoferrate (III) exhibited high microporosity, this characteristic being greatly influenced when the exchange reactions were carried out in organic media. SEM images provided evidence of the microtextural modifications undergone by the products throughout these different treatments.