Examining the thermal synthesis conditions of Maya blue: Insights into colors, stability and clay-dye interactions

Abstract

Maya blue can be synthesized by heating a mixture of indigo and palygorskite, yet the impact of preparation conditions on its properties is not fully understood. This study investigates the effects of heating temperature (100–500 °C) and duration (1–72 h) on the color, acid resistance, solvent resistance, and photostability of Maya blue, as well as the pigment's structure and the indigo-palygorskite interaction. The reflectance spectra and CIE color parameters indicate that the optimal synthesis temperature for Maya blue lies between 100 and 200 °C, with a recommended heating time not exceeding 8 h. Increasing the temperature (up to 200 °C) enhances the green hue while diminishing the blue hue; however, temperatures above 200 °C result in significant color saturation loss. At 150 °C, extending the heating duration increases the green hue while maintaining stability after 8 h, with a corresponding reduction in the blue hue. The specific surface area, micropore volume, and X-ray diffraction results suggest that indigo molecules diffuse deeply into the palygorskite channels under heating. The infrared spectra indicate that the interaction between indigo and palygorskite appears weak, with indigo being encapsulated as stabilized monomers through intramolecular hydrogen bonding, which contributes to the greenish-blue hue and exceptional stability of Maya blue. High-resolution transmission electron microscope images confirmed the identical microstructure of Maya blue and raw palygorskite. These findings enhance the understanding of Maya blue’ preparation mechanism and may contribute to the development of organic-inorganic hybrid materials.