Preparation of Acid Red73 adsorbed on chitosan-modified sepiolite with SiO₂ coating as a highly stable hybrid pigment

The application of organic dyes in industry is severely limited due to its insolubility and instability. The adsorption of organic dyes by inorganic materials to form hybrid pigment is a valid method to improve its stability, thus widening its applications in industries. A simple method for preparing stable hybrid pigment by adsorpting Acid Red 73 (AR73) on the chitosan (CTS) modified sepiolite with a SiO2 coating is explored in this work. Sepiolite modified by the CTS was used to immobilize AR73 (CTS-sep/AR73) uniformly to form a hybrid pigment. The effects of the dosage of CTS, the concentration of acetic acid (HAc) and the pH of AR73 solution for CTS-sep adsorption of AR73 were investigated. CTS-sep/AR73 was further coated with a layer of SiO2 to form the CTS-sep/AR73@SiO2 pigment, which enhanced the stabilities of the hybrid pigment. The CTS-sep/AR73@SiO2 pigment shows excellent stability in strong acid, strong alkali and anhydrous ethanol environment, along with the improved thermal ageing, intensified UV resistance, and enhanced thermal stability (more than 220 °C) which is higher than that of CTS-sep/AR73 hybrid pigment.