Comment on “Exploring Dynamics and Cage–Guest Interactions in Clathrate Hydrates Using Solid-State NMR”

Comment on “Exploring Dynamics and Cage–Guest Interactions in Clathrate Hydrates Using Solid-State NMR

Magnetic Resonance Imaging of Gas Hydrate Formation in a Bed of Silica Sand Particles

The formation of methane hydrate in an unconsolidated bed of silica sand was investigated and spatially resolved by employing the magnetic resonance imaging technique. Different sand particle size ranges (210–297, 125–210, 88–177, and <75 μm) and different initial water saturations (100, 75, 50, and 25%) were used. It was observed that hydrate formation in such porous media is not uniform, and nucleation of hydrate crystals occurs at different times and different positions inside the bed. Also, hydrate formation was found to be faster in a bed with lower water content and smaller particle size. Decomposition of hydrate by thermal stimulation at constant volume showed that the dissociation front moves radially inward starting from the external surface of the hydrate formation vessel

Toward Fluorinated Spacers for MAPI-Derived Hybrid Perovskites: Synthesis, Characterization, and Phase Transitions of (FC₂H₄NH₃)₂PbCl₄

The intrinsic moisture sensitivity of the hybrid perovskite methylammonium lead iodide (MAPI) calls for new synthetic strategies to enhance moisture resistance and, thus, long-term stability. Here, we combine two strategies: (i) transitioning from 3D to 2D hybrid perovskites by inserting larger A-site cations as spacers and (ii) using fluorinated linkers to enhance the hydrophobicity of the materialand identify two new hybrid perovskite-type compounds, (FC₂H₄NH₃)₂­PbCl₄ and (FC₂H₄NH₃)­PbBr₃·DMF, carrying 2-fluoroethylammonium (FC₂H₄NH₃)⁺ as a promising organic cation for the synthesis of moisture-resistant hybrid perovskites. (FC₂H₄NH₃)₂­PbCl₄ features a two-dimensional structure and pronounced long-term stability as confirmed by single-crystal and powder X-ray diffraction. The observed reversible phase transitions at 87 and 107 °C investigated with thermal analysis, temperature-dependent powder X-ray diffraction measurements, and ¹H, ¹³C, and ²⁰⁷Pb solid-state NMR spectroscopy can be assigned to changes in the inorganic lead chloride and organic sublattices, respectively, both having clearly observable fingerprints in the solid-state NMR spectra. DFT calculations trace the origin of the observed severe distortion of the inorganic sublattice in (FC₂H₄NH₃)₂­PbCl₄ back to structural features including the formation of hydrogen bonds. The optical properties of (FC₂H₄NH₃)₂­PbCl₄ were characterized by optical absorption spectroscopy and time-resolved photoluminescence measurements with a view toward the interaction between the organic and inorganic sublattices. The broad photoluminescence spectrum as well as specific absorption characteristics are assigned to exciton self-trapping due to a strong coupling of the excited states to lattice distortions

Assembling Photoluminescent Silicon Nanocrystals into Periodic Mesoporous Organosilica

A contemporary question in the intensely active field of periodic mesoporous organosilica (PMO) materials is how large a silsesquioxane precursor can be self-assembled under template direction into the pore walls of an ordered mesostructure. An answer to this question is beginning to emerge with the ability to synthesize dendrimer, buckyball, and polyhedral oligomeric silsesquioxane PMOs. In this paper, we further expand the library of large-scale silsesquioxane precursors by demonstrating that photoluminescent nanocrystalline silicon that has been surface-capped with oligo­(triethoxysilylethylene), denoted as ncSi:(CH₂CH₂Si­(OEt)₃)_<i>n</i>H, can be self-assembled into a photoluminescent nanocrystalline silicon periodic mesoporous organosilica (ncSi-PMO). A comprehensive multianalytical characterization of the structural and optical properties of ncSi-PMO demonstrates that the material gainfully combines the photoluminescent properties of nanocrystalline silicon with the porous structure of the PMO. This integration of two functional components makes ncSi-PMO a promising multifunctional material for optoelectronic and biomedical applications