The Effect of the Molar Mass of Ammonium Cations on the Thermal Behavior of Organomontmorillonites

The effect of the size of different ammonium cations on thermal stability of ammonium-montmorillonites was investigated. Montmorillonite in the form of K-, Na-, Ca- and Mg-montmorillonites were intercalated with mono-, di- and triethanolammonium cations via ion-exchange process. The examined samples were characterized by TGA, XRD and FTIR techniques. The thermogravimetric analysis show three thermal transitions which attributed to desorption of physically adsorbed and bounded water, decomposition of ammonium cations in the interlayer space and dehydroxylation of structural water of the clay. From the thermograms, the type of ammonium cation used affected the position and the intensity of the adsorbed and bounded water peak. Triethanolammonium-montmorillonites showed smaller desorption temperature value and water content than that for diethanolammonium and monoethanolammonium-montmorillonites, which is consistent with less hydrophilic nature of triethanolammonium-montmorillonites. XRD results show an increase in the basal spacing of the clay with the size of ammonium cation, indicating a monolayer arrangement of alkyl chains in the interlayer spacings of the clay. From FTIR results of the examined samples, the presence of the common IR peaks of ammonium compounds confirms the intercalation of such compounds in the interlayer space of montmorillonites