Spectral characteristics of the bentonite loaded with benzyldimethyloctadecylammonium chloride, hexadecyltrimethylammonium bromide and dimethyldioctadecylammonium bromide

Abstract

The spectral characterization, including the FTIR, DRIFT (diffusive reflectance), SWAXS (small and wide angle X-ray scattering) spectra comparison of the sodium bentonite modified by BDMODA–Cl (benzyldimethyloctadecylammonium chloride), HDTMA–Br (hexadecyltrimethylammonium bromide), DDA–Br (dimethyldioctadecylammonium bromide) is presented in the paper. The FTIR spectra show the shift of C–H stretching vibrations: ν sym(CH2), ν asym(CH2) of surfactants methylene chains toward lower frequencies (from 2855 to 2851 cm −1 for ν sym(CH2) and from 2927 to 2918 cm −1 for ν ansym(CH2) with the surfactant concentration in bentonite phase. The bending vibrations δ H–O–H in water molecules change their positions in the direction of higher frequencies (from 1634 to 1647 cm −1) with the surfactant concentration for bentonite–BDMODA and bentonite–DDA contrary to bentonite–HDTMA, where the constant position δ H–O–H is explained as the consequence of the lower concentration of the hydrogen bonded water in bentonite–HDTMA phase when compared with the remaining forms of bentonite. The DRIFT spectra reveal dramatic shift of the ν Si–O stretching vibration toward higher frequencies upon intercalation of the sodium bentonite with the surfactant cations. The SWAXS spectra and SEM images of the bentonite are the evidence of somewhat different sorption mechanism of DDA–Br when compared with the BDMODA–Cl and HDTMA–Br, including remarkable external surface sorption contribution in the overall sorption.