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Control of the Structural Charge Distribution and Hydration State upon Intercalation of CO 2 into Expansive Clay Interlayers
Numerous experimental investigations indicated that expansive clays such as montmorillonite can intercalate CO 2 preferentially into their interlayers and therefore potentially act as a material for CO 2 separation, capture, and storage. However, an understanding of the energy–structure relationship during the intercalation of CO 2 into clay interlayers remains elusive. Here, in this study, we use metadynamics molecular dynamics simulations to elucidate the energy landscape associated with CO 2 intercalation. Our free energy calculations indicate that CO 2 favorably partitions into nanoconfined water in clay interlayers from a gas phase, leading to an increase in the CO 2 /H 2 O ratio in clay interlayers as compared to that in bulk water. CO 2 molecules prefer to be located at the centers of charge-neutral hydrophobic siloxane rings, whereas interlayer spaces close to structural charges tend to avoid CO 2 intercalation. The structural charge distribution significantly affects the amount of CO 2 intercalated in the interlayers. These results provide a mechanistic understanding of CO 2 intercalation in clays for CO 2 separation, capture, and storage.
A Combined Wave Function and Density Functional Approach for K-Edge X-ray Absorption Near-Edge Spectroscopy: A Case Study of Hydrated First-Row Transition Metal Ions
The prediction of X-ray absorption spectra (XAS) of transition metal complexes has important and broad application areas in chemistry and biology. In this letter, we have investigated the predictive ability of multiconfiguration pair-density functional theory (MC-PDFT) for X-ray absorption spectra by calculating the metal K pre-edge features of aquated 3d transition metal ions in common oxidation states. MC-PDFT results were compared with experimentally measured spectra as well as analyzed against results from restricted active-space second-order perturbation theory (RASPT2) and time-dependent density functional theory (TDDFT). As expected, TDDFT performs well for excited states that can be accurately represented by singly excited configurations but fails for excited states where higher order excitations become important. On the other hand, both RASPT2 and MC-PDFT provide quantitatively accurate results for all excited states irrespective of their character. While core-level spectroscopy with RASPT2 is accurate, it is computationally expensive. Finally, our results show that MC-PDFT performs equally well with significantly lower computational cost and is an encouraging alternate approach for X-ray spectroscopies.
The Back Door to the Surface Hydrated Electron
We use a Mg + metal to extend the size regime of water clusters to extrapolate to the bulk limit of the Vertical Detachment Energy (VDE) of the solvated electron to >3,200, a value between one to over two orders of magnitude for clusters previously measured experimentally or computed theoretically. We relate the VDE to the energy difference between the Mg + (H 2 O) $n$ and Mg 2+ (H 2 O) $n$ systems and the metal’s second ionization potential. The extrapolated bulk VDEs of the localized surface electron, which moves away from the metal as n increases, are 1.89 ± 0.01 eV for semiempirical ($n$ ~ 3,200; PM6-D 3 H 4 ) and 1.73 ± 0.03 eV ($n$ ~ 150; HF), 1.83 ± 0.02 eV ($n$ ~ 150; MP2) for ab-initio, in excellent agreement with the 1.6 – 1.8 eV range of experimental results. In conclusion, the VDEs converge from above (larger values) to the bulk limit, in a manner qualitatively different than previous studies and experiments, a fact justifying the “back door” approach to the solvated electron.
How to Probe Hydrated Dielectrons Experimentally: Ab Initio Simulations of the Absorption Spectra of Aqueous Dielectrons, Electron Pairs, and Hydride
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Optically Triggered Nucleation Eliminates Hydration Hysteresis in Swelling Minerals
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Surface Reconstruction in Hydrated Amphiphilic Block Copolymer Thin Films Probed by Fluid Cell Atomic Force Microscopy
In many thin film materials, nuanced interplays of interfacial energies control the surface morphology and rearrangement. This work evaluates polymer−solvent interactions and solvent-driven surface reconstructions via ex situ and in situ fluid cell Atomic Force Microscopy (fc-AFM) analysis of amphiphilic block copolymer (BCP) thin films upon exposure to deionized (DI) water. We examine the differences in surface morphology, whole-film swelling, and force response in thin films of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) and polystyrene- block-poly[(allyl glycidyl ether)-co-(ethylene oxide)] (PS-b- P[AGE-co-EO]) processed into standing-up cylinder morphologies perpendicular to a silicon substrate (⊥C). Using Amplitude Modulation AFM (AM-AFM) and Amplitude-Phase Distance (APD) force spectroscopy, this work probes the mechanoresponsive nature of the dynamic surface layers of these films, unveiling surface layer stratification and surface chain rearrangement via minimal tip−sample stimulation. To help rationalize the observed reconfigurations, the energetic driving forces were estimated using the harmonic mean approximations of interfacial energies. Given the nonionizable nature of the minority P(AGE-co-EO) block and the energetic driving forces for chain mobility, this work shows how the elimination of unfavorable PS−water interfaces drives chain rearrangement and coverage of the PS surface by chains of the hydrophilic block. This work highlights considerations for increasing the heterogeneity and complexity of BCP thin films via random blocks and how those changes to local interfacial energies may drive larger scale film morphology reconstructions, with broader implications for tuning interface hydrophilicity.
Printing Composites with Salt Hydrate Phase Change Materials for Thermal Energy Storage
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Hybrid Polymer Salogels for Reversible Entrapment of Salt-Hydrate-Based Thermal Energy Storage Materials
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Effect of Temperature on Local Hydration of Zn in Hematite
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Post-translational Succinylation of Mycobacterium tuberculosis Enoyl-CoA Hydratase EchA19 Slows Catalytic Hydration of Cholesterol Catabolite 3-Oxo-chol-4,22-diene-24-oyl-CoA
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Nanoscale Prediction of the Thermal, Mechanical, and Transport Properties of Hydrated Clay on 10 6 - and 10 15 -Fold Larger Length and Time Scales
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Effect of Hydration on the Molecular Dynamics of Hydroxychloroquine Sulfate
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Resolving the Structural Debate for the Hydrated Excess Proton in Water
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Heat Flow on the U.S. Beaufort Margin, Arctic Ocean: Implications for Ocean Warming, Methane Hydrate Stability, and Regional Tectonics
The Arctic Ocean represents one of the last geological frontiers on Earth. The formation of the Arctic Ocean remains unclear, and although it is well understood that the Arctic surface temperature is warming at a rate approximately twice as fast as the rest of the Earth, it is unclear how deep Arctic Ocean temperatures are changing. Understanding whether deep Arctic Ocean water is warming is important, since it can lead to the breakdown and release of huge quantities of frozen methane molecules trapped below the Arctic seafloor, which can increase ocean acidity and destabilize the seafloor. To understand both Arctic Ocean temperature change and geologic evolution, we collected temperature measurements at 103 sites. These measurements tell us how temperature increases with depth below the seafloor and can be used to understand both ocean temperature change and regional geology. Analysis of our data shows that at depths of 300–900 m below sea level, the Arctic Ocean has been warming steadily for perhaps several decades—nearly twice as deep as previous studies suggest. At ocean depths greater than 1,000 m, our analysis also reveals surprisingly high temperature increases with depth in the seafloor. The cause of these significant increases is unclear.