An FTIR investigation of hexadecyltrimethylammonium intercalation into rectorite

Rectorite is an interstratified clay mineral made at 1:1 ratio of an orderly arrangement of a nonswelling component illite and a swelling component smectite. Due to the presence of two distinct types of components, it is of great interest to study the adsorption of long chain alkylammonium in rectorite. In this study, we conducted batch experiments and used X-ray diffraction (XRD) and Fourier Transform infrared (FTIR) spectroscopy to characterize the interlayer configuration of intercalated long chain hexadecyltrimethylammonium (HDTMA) in rectorite. The FTIR results showed that a monomer-like intercalation with extensive gauche conformers was formed at surfactant loading less than the cation exchange capacity (CEC) of the mineral. At a higher surfactant loading the CH₂{single bond} symmetric and anti-symmetric vibrations shifted to lower frequencies, suggesting a more ordered all-trans surfactant interlayer configuration. The thermogravimetric and derivative of thermogravimetric analayses showed a high pyrolysis temperature for the monomer-like gauche conformers and lower pyrolysis temperature for the all-trans configuration of the intercalated HDTMA. The XRD analysis confirmed the monomer-like conformation with a d-spacing of 25.2 Å at the low surfactant intercalation and a vertical all-trans configuration with a d-spacing of 49.5 Å at an HDTMA intercalation of 3.20 CEC. In addition to conformation analyses of intercalated surfactant in the interlayer using FTIR, the absorbance measured by peak height at 1470, 2850, and 2917 cm^-1 increased linearly with surfactant loading, providing a faster, yet efficient method to quantify the amount of surfactant adsorbed.