Layered manganates from soft-templates: preparation, characterization and enhanced dyedemethylation capabilities

Abstract

A soft-template method for the synthesis of layered manganate (K_xMnO₂, birnessites) compounds with a relatively good control at the nanoscale regime on the number of octahedral layers (thickness) is described. The soft-template method is based on the stabilization of reverse micelles at moderate temperatures and the optimization of parameters to modulate the size of the templates while still preserving their stability during the formation of layered manganates. Degradation experiments of a model system (methylene blue) using the birnessites here reported have shown efficient demethylation in the absence of oxidants for aqueous suspensions made of non-dried birnessites containing the fewest number of layers. The observed strong thickness and aggregation dependence (i.e. dependence on exposed surfaces) for demethylation explains why particulate birnessites have only been considered for dye sequestration and not as an efficient demethylation agent in the absence of oxidants. Finally, when compared to electrodeposited thin films, the higher loading capabilities of the colloidal suspensions here prepared have made it possible to demethylate larger amounts of methylene blue at a similar time.