Thermal analytic study of the adsorption of crystal violet by montmorillonite

The adsorption of crystal violet by montmorillonite was investigated by visible spectroscopy. X-ray diffraction and thermal analysis. DTA, TG and DTG curves were run in air. The evolved H₂O, CO₂, NO₂, CH₃ and C₂H₆ were simultaneously determined by mass-spectrometry. The spectroscopic study showed that the adsorption of crystal-violet may result in four different types of adsorption. In one type π interactions occur between the dye cation and the alumino-silicate layer. This type of interaction increases the thermal stability of the dye cation. The oxidation of this dye cation occurs only together with or after the dehydroxylation of the montmorillonite, whereas the oxidation of other adsorbed dye species occurs at lower temperatures. The oxidation gives rise to exothermic peaks and to CO₂ evolution peaks.