{sup 2}H solid-state NMR investigation of terephthalate dynamics and orientation in mixed-anion hydrotalcite-like compounds
- Pacific Northwest National Lab., Richland, WA (United States). Environmental Molecular Sciences Lab.
The dynamics and orientations of interlayer terephthalate (TA) anions in mixed-anion hydrotalcite-like compounds [Mg{sub 1{minus}x}Al{sub x}(OH){sub 2}](A{sub y}B{sub 1{minus}y}){sub x/s}{center_dot}nH{sub 2}O, where A = p-C{sub 6}D{sub 4}(COOO){sub 2}{sup 2{minus}} and B = CO{sub 3}{sup 2{minus}} were investigated by {sup 2}H variable-temperature solid-state nuclear magnetic resonance (NMR) spectroscopy. Two dominant 003 d spacings, 7.6 and 14.2 {angstrom}, were observed by X-ray diffraction (XRD) in these samples, suggesting that there were at least two interlayer environments. Over the range of layer charges studied (0.37 {ge} x {ge} 0.29), the intensity of the 7.6 {angstrom} XRD peak increased with decreasing x, while the intensity of the 14.2 {angstrom} peak increased with increasing x. Analysis of {sup 2}H NMR line shapes indicated that the motion of some of the TA anions in every sample could be described as rotational diffusion (RD) about the C-COO{sup {minus}} axis at temperatures ranging from 245 to 355 K, with the remainder being essentially immobile. The fraction of TA anions exhibiting rotation (X{sub RD}), as estimated by {sup 2}H NMR, was positively correlated with the TA content of the interlayer and thus seemed to correspond to the fraction of TA molecules in the 14.2 {angstrom} phase. A large difference in X{sub RD} was observed between compounds having similar layer charge but different TA mole fractions. At temperatures of {le}330 K, X{sub RD} increased with temperature. A secondary minimum in X{sub RD}, however, was observed for each of the compounds at temperatures between 330 and 350 K. The authors conclude that the presence of CO{sub 3}{sup 2{minus}} anions in the interlayer regions, rather than layer charge, is the dominant factor affecting the dynamics and orientation of interlayer TA anions.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 682096
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Journal Name: Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical Journal Issue: 25 Vol. 103; ISSN 1089-5647; ISSN JPCBFK
- Country of Publication:
- United States
- Language:
- English
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