Thermal analysis of the adsorption of rhodamine 6G by smectite minerals

DTA, TG and DTG curves of montmorillonite and laponite treated with various amounts of rhodamime 6G were run in air. The evolved gases were simultaneously determined by mass spectrometry and gas evolution curves of H₂0, CO₂, NO₂, H₂, CH₃, and C₂H₆ were recorded. Each thermal analysis curve can be divided into three regions. The first region represents the dehydration of the clay. The second region represents the oxidation of the organic cation and is characterized by two or three exothermic peaks. The first peak is due to the oxidation of H atoms. The second and third peaks are mainly due to the oxidation of C and to some extent also N atoms. The third region represents the dehydroxylation of the smectite mineral. The resulting DTA curve of montmorillonite in this region is affected by the oxidation of organic matter which remains in the heating cell throughout the second region, whereas with laponite only traces of the organic material remain.