Montmorillonite treated with rhodamine-6G mechanochemically and in aqueous suspensions. Simultaneous DTA-TG study

The mechanochemical solid-state adsorption of the cationic dye rhodamine-6G (R6G) by montmorillonite was investigated by XRD and simultaneous DTA-TG. Five different mixtures of R6G and montmorillonite were investigated. They contained 10, 20, 35, 50 and 100 mmol R6G per 100 g clay. The solid R6G was ground with the clay for five minutes. Mixtures were ground both in the absence of water (dry grinding) and with the adding of drops of water periodically, (wet grinding). There were no differences between samples obtained by wet or dry grinding. X-ray and DTA data were compared with those of R6G-montmorillonite obtained from aqueous suspensions. The mechanochemical products were different from those obtained from aqueous suspensions. The X-ray and DTA studies suggest that the mechanochemical adsorption of organic cations takes place on the external surfaces of the clay whereas in suspensions the adsorption takes place into the interlayer space. In the latter case the final stages of oxidation occur in temperatures higher than those of the neat dye whereas in the former they occur at lower temperatures.