Insertion of isatin molecules into the nanostructure of palygorskite

Abstract

Palygorskite has unique a groove-and-channel nanostructure to protect inserted molecules from ruin, and Maya blue is a perfect example of this phenomenon. In this paper, a new hybrid pigment prepared by inserting isatin into palygorskite was synthesized and analyzed. The hybrid retained its vivid color even after being boiled for 5 h in 30% H₂O₂ aqueous solution. Protected by palygorskite, 59% of the isatin successfully survived 72 h of CHCl₃ Soxhlet extraction of the hybrid. Ultraviolet-near infrared spectroscopy (UV-NIR) and Fourier transform infrared spectroscopy (FT-IR) indicated that the conjugate plan of isatin might be distorted when inserted to palygorskite, just like indigo did in Maya blue. X-ray diffraction analysis (XRD) and high-resolution transmission electron microscopy (HRTEM) pointed out that palygorskite exhibited a certain degree of lattice distortion after hybridization. Thermal gravity and differential thermal gravity analysis (TG-DTG) showed further that the small-size isatin could go deeper into the channels of palygorskite and block the channel entrance better than indigo did in Maya blue. All analyses indicated that isatin inserted deeply into the clay, and the insertion is much deeper than that of indigo.