Application of solid-state electrochemistry techniques to polyfunctional organic-inorganic hybrid materials: The Maya Blue problem

摘要

The time evolution of indigo plus palygorskite powdered mixtures during isothermal heating at different temperatures between 120 and 180 °C to form Maya Blue-type materials has been monitored by means of infrared spectrometry, diffuse reflectance spectrometry in the visible region and solid state electrochemical techniques. The kinetics of the formation process of such materials can be described in terms of two consecutive reactions, the first one consisting of the loss of zeolitic water of the palygorskite coupled with clay-indigo attachment and partial indigo to denydroindigo oxidation. The palygorskite dehydration acts as a rate-determining step fitting to a 3D Avrami-Erofe'ev kinetics. The second step would consist of the diffusion-controlled penetration of the different dye molecules in the palygorskite channel system. This kinetic analysis is consistent with the view of Maya Blue-type materials as organic-inorganic hybrid polyfunctional nanostructured systems.