Artificial colouration of smectite through adsorbing dyes from wastewater to make a hybrid pigment

Abstract Artificially coloured smectites (smectite pigments) were prepared via the sorption of anionic dyes on smectite saturated with ferric ions (Fe-smectite). Fe-smectite has a surface charge and is capable of decolourizing aqueous solutions containing single-component anionic dyes (Amaranth, Brilliant blue FCF and Tartrazine) or multi-component dyes (dye mixtures). Kinetic and equilibrium models were used to describe the sorption of individual dyes, whereas the decolourization of the multi-component system was studied by monitoring the reduction in the intensity of the absorption bands in the visible light region. The Langmuir–Freundlich dual-site model presented the best fit to the experimental data, and the sorption kinetics followed the pseudo-second order model. The smectite pigments were dispersed in colourless paint (10%, w/w), acting as organic–inorganic hybrid pigments. Colorimetric measurements of the powdered smectite pigments dispersed in colourless real-estate paint showed chemical compatibility without the need for solvents as dispersants. These properties allow the application of coloured smectites as pigments in a sustainable circular economy.