A Comparative 1H –29Si Cross-Polarization Solid-State Nuclear Magnetic Resonance Study of Opal-A and Opal-CT

IF 2.9 3区化学 Q2 CHEMISTRY, MULTIDISCIPLINARY ACS Earth and Space Chemistry Pub Date : 2024-12-05 DOI:10.1021/acsearthspacechem.4c0023310.1021/acsearthspacechem.4c00233

Martin R. Johnston*, Neville J. Curtis and Jason R. Gascooke,

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Abstract

We report an extensive ¹H to ²⁹Si cross-polarization (CP) nuclear magnetic resonance (NMR) investigation of a wide range of opal-AG, opal-AN and opal-CT samples, including both spectra and contact time dependent kinetics. After an extensive study of Hartmann–Hahn optimization, spin rates and power levels we are forced to conclude that the kinetics of the system is only amenable to comparative analysis rather than determination of absolute values. Q₃ peaks showed both signal growth (T_IS) and decay (T_1ρ^I) while Q₄ centers only showed the T_IS component for all opals studied, consistent with isolated proton sources in the latter. Q₂ centers are only a minor factor in most cases. Initial ¹H–²⁹Si 2D-HETCOR spectral evidence suggests that multiple Q₃ and Q₄ sites, with differing chemical shifts, are involved in the CP process. Active silicate centers and water sites may differ for single pulse (SP) and CP modes. Both SP and CP techniques are best used for comparative studies within each and between opal classes. Differing geometries are implied for all three types of opal.

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来源期刊

ACS Earth and Space Chemistry Earth and Planetary Sciences-Geochemistry and Petrology

CiteScore

5.30

自引率

11.80%

发文量

249

期刊介绍： The scope of ACS Earth and Space Chemistry includes the application of analytical, experimental and theoretical chemistry to investigate research questions relevant to the Earth and Space. The journal encompasses the highly interdisciplinary nature of research in this area, while emphasizing chemistry and chemical research tools as the unifying theme. The journal publishes broadly in the domains of high- and low-temperature geochemistry, atmospheric chemistry, marine chemistry, planetary chemistry, astrochemistry, and analytical geochemistry. ACS Earth and Space Chemistry publishes Articles, Letters, Reviews, and Features to provide flexible formats to readily communicate all aspects of research in these fields.