Adsorption studies of cetyltrimethylammonium on an acid-activated smectite, and their thermal stability

The intercalation of the cationic surfactant cetyltrimethylammonium (C16TMA) intothe interlayer of an acid-activated clay in the presence of different anions has been studied in detail.When Br or OH anions were used, the basal spacing increased significantly, the increase beingrelated to the loading concentration of the surfactant solution. For intercalated compounds preparedfrom the hydroxide form, the basal spacing at room temperature varied from 1.6 to 3.8 nm. However,for organoclays prepared from the surfactant bromide, the basal spacing is almost loading-independent (1.9 nm). The use of hydroxide and bromide at higher pH is crucial to intercalatinglarger amounts of C16TMA cations and, hence, to improving the exfoliation of the silicate sheets.Magic-angle spinning 13C nuclear magnetic resonance spectroscopy indicates that the intercalatedsurfactants exhibit a significant degree of gauche conformation. According to in situ powder X-raydiffraction, an increase of the basal spacing to 4.08 nm is observed at intermediate temperatures of50 to 150ëC for organoclay with an initial basal spacing of 3.7 nm. At higher temperaturesdecomposition of the surfactant occurs and the basal spacing decreases to ~1.4 nm