Permanganate-mediated dissolution of hydroxy-Cr interlayers from montmorillonite

Expandable layer silicates may be intercalated with a variety of hydrolyzed metal cations. Chromium is among those metals that have received the most attention, due to its presence in many polluted environments and toxicity when present as Cr(VI). Of all potential oxidants of Cr(III), high-valence Mn remains one of the most potent. Manganese(VII) species were, therefore, introduced to suspensions of hydroxy-Cr(III) interlayered montmorillonite to: (i) establish the role that Mn(VII) plays in the oxidation of intercalated Cr(III) and, (ii) attempt to intercalate Mn species that would impart catalytic activity to the montmorillonite. The oxidation of intercalated hydroxy-Cr(III) polymers by Mn(VII) was rapid initially then decreased sharply due, in part, to accumulation of residual Mn within the interlayer. As this intercalated Mn was present as Mn(II), the oxidative capacity of the clay was not enhanced. Furthermore, the hydroxy-Cr(III) pillars readily collapsed upon oxidation, eliminating much of the gallery space required for effective catalysis. However, the intercalation of Mn onto montmorillonite by means of reduction, described for the first time in this paper, may find application in the synthesis of related pillared clay catalysts.