Nuclear Magnetic Resonance Study of Hydrated Bentonite

Abstract

Impedance spectroscopy and nuclear magnetic resonance (NMR) were used to investigate the mobility of water molecules located in the interlayer space of H⁺ – exchanged bentonite clay. The conductivity obtained by ac measurements was 1.25 × 10⁻⁴ S/cm at 298 K. Proton (¹H) lineshapes and spin-lattice relaxation times were measured as a function of temperature over the temperature range 130–320 K. The NMR experiments exhibit the qualitative features associated with the proton motion, namely the presence of a ¹H NMR line narrowing and a well-defined spin-lattice relaxation rate maximum. The temperature dependence of the proton spin-lattice relaxation rates was analyzed with the spectral density function appropriate for proton dynamics in a two-dimensional system. The self-diffusion coefficient estimated from our NMR data, D ∼ 2 × 10⁻⁷ cm²/s at 300 K, is consistent with those reported for exchanged montmorillonite clay hydrates studied by NMR and quasi-elastic neutron scattering (QNS).

Keywords:

• Bentonite
• clays
• EPR
• impedance spectroscopy
• NMR
• proton conduction
• water adsorbed

Acknowledgments

Partial support of CNPq and Fapesp (Brasil) are gratefully acknowledged. The authors are grateful to Dr. J. F. Lima for the EPR analysis. Research partially financed by FONDECYT (Contracts 1090282, 1070195), Basal Financing Program CONICYT, FB0807 (CEDENNA), Millenium Science Nucleus P06-022-F.