NIR and MIR spectroscopic characteristics of hydrophilic and hydrophobic bentonite treated with sulphuric acid

Abstract

Near-infrared (NIR) and mid-infrared (MIR) spectroscopy are irreplaceable methods for characterization of bentonites. The paper presents work on bentonites modified with inorganic Na + and organic HDTMA + (hexadecyltrimethylammonium) cations and treated by 1.5, 3, 4.5 and 6 M H 2SO 4. The characterization was based on the assignment of the stretching (ν) and bending (δ) vibrations observed in the MIR region and the first overtone [2ν(R-H)] and combination [ν(R-H) + δ(R-H)] modes of R-H groups (R = O, C) in the NIR region. NIR spectrum shows the characteristic OH and CH bonds for organomontmorillonite. The effect of larger alkylammonium cations on the vibrations of Si-O and OH bonds in montmorillonite layers is observed. A few key-bands in the NIR region show the change of water in the interlayer montmorillonite. The intensities of the overtone (7080 and 6840 cm -1) and combination (5242 cm -1) bands of H 2O have considerably decreased as a result of hydrophobic character of the NaOM. Spectra of acid-treated samples show a gradual decrease in the intensities of the OH overtone (near 7100-7000 cm -1) and combination bands (4600-4300 cm -1) reflecting a fewer number of octahedral atoms. This paper also points out that ATR technique and the 2nd derivative spectrum enables much precise band assignment. © 2011 Elsevier B.V. All rights reserved.