Thermal decomposition behavior and de-intercalation kinetics of kaolinite/quaternary ammonium salt complexes

Abstract

Kaolinite/quaternary ammonium salt complexes were prepared by intercalation and displacement of kaolinite–N-methylformamide (Kaol–NMF) with methanol (Me) and quaternary ammonium salt. The samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetry and differential scanning calorimetry (TG–DSC) analysis. The d-values of the kaolinite/quaternary ammonium salts complexes increase with the alkyl chain length of the quaternary ammonium salts. Based on the results and the available evidence pointing toward the interlayer structure of kaolinite intercalation complexes, the most possible structural model for the kaolinite/quaternary ammonium salt intercalation complexes was proposed. For the kaolinite–dodecyl trimethyl ammonium chloride, kaolinite–trimethyl tetradecyl ammonium chloride and kaolinite–hexadecyltrimethylammonium chloride, the intercalation molecules are oriented perpendicular to the kaolinite surface in a single layer. However, for kaolinite–stearyl trimethyl ammonium chloride, the cationic head of intercalated stearyl trimethyl ammonium chloride molecules may be partially hydrated and arrayed aslant in the interlayer space of kaolinite with an inclination angle of 35°. Thermal analysis results revealed that the thermal decomposition of kaolinite/quaternary ammonium salt complexes occurs in two main steps. The function of the most probable mechanism, activation energy E and pre-exponential factor were obtained by mutual authentication using KAS and Ozawa methods, Satava integral method and Achar–Brindley–Sharp–Wendworth methods. The average activation energy E of four kaolinite/quaternary ammonium salt intercalation complexes is 108.147, 153.478, 125.723 and 88.008 kJ mol−1, respectively. The optimized mechanism function for de-intercalation process of quaternary ammonium salt is f(α) = 1 − α and G(α) = −ln(1 − α).