Proton Dynamics in Layered Double Hydroxides: A 1H T1 Relaxation and Line Width Investigation

Abstract

The investigation of the dynamics of water and organic species confined in minerals or adsorbed at their surface is of significant geochemical, environmental, catalytic, biomedicine, and life’s growth interests but is poorly understood on the molecular scale. This work explores the behavior of water molecules and glutamate species adsorbed on and between the double hydroxide layers of hydrotalcite [HT; (Mg2Al)(OH)6A−·nH2O, where A− is a counteranion which may bear different charges] and compares the results to those for HT containing small inorganic anions. The relative humidity (RH) dependence of the 1H T1 relaxation rates for all samples reveals the existence of two separate spin systems with 1/T1 relaxation rates differing by a factor of approximately 2 × 103. The static 1H spectral line widths allow assigning the fast relaxing protons to the fixed “static” interlayer and adsorbed species—i.e. bound water, bound organic species, and most of the structural hydroxyl groups (-OH)—and the slow ones to the ...