Abstract
A new approach to describe the composition of Maya blue (MB), an ancient organic–inorganic hybrid material, is presented. It is based on the analysis of attenuated total reflection-Fourier transform infrared (ATR-FTIR), Raman spectroscopy, UV–visible (vis) spectroscopic, and electrochemical data for indigo and dehydroindigo plus palygorskite hybrids, including a novel methodology using electrocatalytic effects on the oxygen reduction reaction. As a result, it is concluded that MB results from the tautomerization of indigo-to-indigo hemienol and the subsequent oxidation of these isomeric forms to dehydroindigo, all associated with the palygorskite clay framework, at temperatures above 100 °C. This model is also consistent with 13C NMR data on indigo plus sepiolite hybrids. A consistent set of thermochemical parameters is obtained from ATR-FTIR, solid-state electrochemistry, and UV–vis diffuse reflectance spectra for the successive isomerization and redox tuning processes experienced by palygorskite-associated indigo.
Highlights
Maya blue (MB), an ancient pigment used by the Mayas and other ancient Mesoamerican people in pre-Columbian times, can be considered as the precursor of a wide series of inorganic−organic hybrid materials.[1]
A novel approximation to the nature of MB where, upon heating indigo plus palygorskite mixtures above 100 °C, indigo isomerizes to indigo hemienol, which in turn is oxidized to clay-associated dehydroindigo at higher temperatures is presented
This view is based on UV−vis diffuse reflectance spectra, ATR-FTIR, and solid-state electrochemistry of MB
Summary
Maya blue (MB), an ancient pigment used by the Mayas and other ancient Mesoamerican people in pre-Columbian times, can be considered as the precursor of a wide series of inorganic−organic hybrid materials.[1] Its remarkable stability, brightness, and hue variability have promoted a continuous interest in the pigment, which is surrounded by an atmosphere of mystery due to the absence of historical sources describing the preparation of the pigment by the Mayan people.[2,3]. 1 wt %) plus palygorskite mixtures up to 100 °C to promote the (more or less extensive) loss of water weakly bound to the clay channels. Indigo@palygorskite hybrids are prepared by this “dry” method but the Mayans possibly used “wet” routes.[4,5]
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