Facile preparation of stable palygorskite/cationic red X-GRL@SiO2 “Maya Red” pigments

Abstract

Inspired by Maya Blue, we report the fabrication of stable “Maya Red” pigments with a purple-red hue by adsorption of cationic red X-GRL (CR-X-GRL) onto palygorskite (PAL), which is followed by hydrolysis and polycondensation of tetraethoxysilane (TEOS) via a modified Stöber method to form a layer of SiO₂. The parameters influencing the adsorption of CR-X-GRL onto PAL (e.g., m_CR-X-GRL/m_PAL and the ball milling time) and polycondensation of TEOS (e.g., concentrations of TEOS and ammonia, and volume ratio of ethanol to water) were investigated by using stability of the pigment as the probe. The CR-X-GRL content in the PAL/CR-X-GRL pigments can be as high as 12%, which is higher than all the state-of-the-art Maya Blue-like pigments. Since the stability of the PAL/CR-X-GRL pigments is not very high, a layer of SiO₂ was introduced to further improve the stability. The SEM, TEM, FTIR and BET data prove the presence of silica on the surface of the PAL/CR-X-GRL pigment. The PAL/CR-X-GRL@SiO₂ “Maya Red” pigments show excellent chemical (1 M HCl, 1 M NaOH and ethanol), thermal and UV stability.