Thermogravimetry and differential thermal analysis of montmorillonite treated with 1,4-diaminoanthraquinone

Neat organic dye 1,4-diaminoanthraquinone (DAAQ) was investigated by TG, DTG, and DTA in air and under nitrogen up to 900°C. Total mass loss was 79.1 and 38.3 % in air and under nitrogen, respectively. The residues in both heating cells were dark black, suggesting that they were charcoals which required temperatures higher than 900°C for oxidation or pyrolysis. Complexes of montmorillonite (MONT) with this organic dye were investigated by TG, DTG, and DTA in air and under nitrogen up to 900°C. Aqueous solubility of DAAQ is very low (0.33 mg/1 l) and consequently the loading of the clay by the dye is very small (5-24 mmol DAAQ/100 g clay). Five saturated dye solutions were prepared for the synthesis of five complexes, (i) in distilled water and (ii-v) in 0.1, 0.5, 1.0, and 2.0 molar HCl. The DTA and DTG peaks of the thermal reactions of the organoclay complexes (oxidation in air and pyrolysis under nitrogen) were very weak and many were not detectable. On the other hand, inflections were detected in the TG curves and were considered as upper and lower borders of mass-loss steps. Conclusions on reaction steps which are responsible for mass loss were based on previous knowledge of the thermal reactions of organoclays. Six mass-loss steps were identified in air and seven steps under nitrogen. Mass-loss steps in air were attributed to evolution of interlayer water, H-bonded water, dehydroxylation of MONT, and to three steps of oxidation of intercalated DAAQ. Under nitrogen, steps were attributed to evolution of interlayer water, H-bonded water, dehydroxylation of MONT, and four steps of pyrolysis of DAAQ.