Near-infrared spectroscopic analysis of acid-treated organo-clays

Jana Madejová, Helena Pálková, Martin Pentrak, Peter Komadel

Research output: Contribution to journalArticlepeer-review

Abstract

The potential use of near-infrared (NIR) spectroscopy as a characterization tool for organo- clays would be a great asset but little work has been done in this regard because the application ofNIR to clay mineral studies is a relatively new phenomenon. The purpose of this study was to use NIR spectroscopy to investigate the effect of alkylammonium cations on the acid dissolution of a high-charge montmorillonite (SAz-1). Detailed analysis ofthe spectra of Li+-, TMA+- (tetramethylammonium), and HDTMA+- (hexadecyltrimethylammonium) saturated SAz-1 montmorillonite in the NIR region was achieved by comparing the first overtone (2v) and combination (v+δ) bands of XH groups (X = O, C) with the fundamental stretching (v) and bending (δ) vibrations observed in the mid-infrared (MIR) region. Comprehensive analysis ofthe vibrational modes of CH 3-N, CH3-C, and CH2-C groups of TMA+ and HDTMA+ cations detected in the MIR and NIR regions was also performed. Both MIR and NIR spectra demonstrated that exchange of Li+ by TMA+ only slightly improved the resistance of SAz-1 layers to dissolution in 6 M HCl at 80°C, while exchange by the larger HDTMA+ cations almost completely protected the montmorillonite layers from acid attack. Use of NIR spectra in reaching these conclusions was crucial. Only in the NIR region could the creation of SiOH groups be monitored, which is an important indicator of the acidification of the montmorillonite surface. The OH-overtone region in the spectra of Li- SAz-1 and TMA-SAz-1 revealed that the SiOH band near 7315 cm-1 increases in intensity with enhanced acid treatment. In contrast, no SiOH groups were identified in the NIR spectra of HDTMA-SAz-1 treated in HCl, indicating that HDTMA+ completely covers the inner and outer surfaces of the montmorillonite and hinders access of protons to the Si O bonds created upon acid treatment.

Original languageEnglish (US)
Pages (from-to)392-403
Number of pages12
JournalClays and Clay Minerals
Volume57
Issue number3
DOIs
StatePublished - Jun 1 2009
Externally publishedYes

Keywords

  • Acid treatment
  • Alkylammonium cations
  • NIR spectroscopy
  • Organo-clays
  • Structural modifications

ASJC Scopus subject areas

  • Water Science and Technology
  • Soil Science
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)

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