On the positions of rare earth cations in Y zeolites as studied by NMR relaxation of adsorbed molecules

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

“…2,[10][11][12][13][14][15][16][17] Organic species are of comparable interest, but molecular scale study of their adsorption and confinement is more limited. 1,2,[18][19][20] Many of these organic species, including amino acids, carboxylic species, peptides, and larger proteins and molecules of natural organic matter (NOM), occur as anions at neutral to basic pH values and are thus expected to interact strongly with solids having positive structural or pH dependent charges. Many silicate minerals, such as clays, normally have negative structural charges, but layered double hydroxides (LDHs) have a large, permanent positive structural charge and are known to effectively exchange many organic species.…”

“…We present here an experimental NMR study of the relative humidity (RH) dependence of the 1 H spin-lattice relaxation times (T 1 ) and 1 H spectral line widths of the prototypical LDH, hydrotalcite [HT; nominally (Mg 2 Al)(OH) 6 A -• nH 2 O, where Ais a counteranion which may bear different charges] containing surface and interlayer glutamate (GA), and for comparison similar data for HT with small inorganic anions. To our knowledge, this is the first such investigation of LDHs containing an organic anion.…”

“…To our knowledge, this is the first such investigation of LDHs containing an organic anion. The only previous 1 H T 1 study of the dynamical behavior of anions, water molecules, and -OH groups in LDH compounds is for Zn-Al hydrotalcite-like compounds with inorganic anions. 21 In our previous NMR, X-ray diffraction (XRD), and thermal analysis (TGA-DTA) study of HT containing glutamate, we showed that much of the adsorbed GA is not intercalated in the HT interlayer but occurs on external particle surfaces.…”

“…NMR Experiments. 1 H T 1 measurements were carried out under static conditions using the saturation recovery pulse sequence (π/2, τ, π/2), 31 at a frequency of 599.819 MHz on a Varian Infinity-Plus wide bore spectrometer using a 4 mm Triple-resonance MAS probe (Varian). The 90°pulse width was 3 µs, and each spectrum was obtained from the average of 16 transients.…”

“…These frequencies are all much greater than the Larmor frequency, and association with the solid increases the density of states at the Larmor frequency and also allows for greater interaction with paramagnetic centers. 1,2,15,18,35 For instance, the T 1 relaxation times of bulk water are of the order of 2000 to 4000 ms at room temperature [36][37][38] and published T 1 values for water associated with solids are of the order of a few milliseconds to a few tens of milliseconds depending on the magnetic field and the substrate, e.g., zeolites, 2,18 carbon powders, 39 aluminum phosphates, 15 coal, 6 clays 10,17 and other minerals. 12 However, in some cases the T 1 values may reach a few hundred milliseconds.…”