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Query: UMLS:C0027960 (
mole
)
21,279
document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)
We use first-principles density functional theory total energy and linear response phonon calculations to compute the Helmholtz and Gibbs free energy as a function of temperature, pressure, and cell volume in the flexible metal-organic framework material
MIL
-53(Cr) within the quasiharmonic approximation. GGA and metaGGA calculations were performed, each including empirical van der Waals (vdW) forces under the D2, D3, or D3(BJ) parameterizations. At all temperatures up to 500 K and pressures from -30 MPa to 30 MPa, two minima in the free energy versus volume are found, corresponding to the narrow pore (
np
) and large pore (
lp
) structures. Critical positive and negative pressures are identified, beyond which there is only one free energy minimum. While all results overestimated the stability of the
np
phase relative to the
lp
phase, the best overall agreement with experiment is found for the metaGGA PBEsol+RTPSS+U+J approach with D3 or D3(BJ) vdW forces. For these parameterizations, the calculated free energy barrier for the
np
-
lp
transition is only 3 to 6 kJ per
mole
of Cr
4
(OH)
4
(C
8
H
4
O
4
)
4
.
...
PMID:Thermodynamics of the Flexible Metal-Organic Framework Material MIL-53(Cr) From First Principles. 2869 Jul 13
A comparative study of the intermolecular dynamics of CS
2
in monocationic and dicationic ionic liquids (ILs) was performed using optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). The reduced spectral densities (RSDs) of mixtures of CS
2
in 1-alkyl-3-methylimidazolium bis[(trifluoromethane)sulfonyl]amide ([C
n
C
1
im][NTf
2
] for n = 3-5) and 1,2n-bis(3-methylimidazolium-1-yl) alkane bis[(trifluoromethane)sulfonyl]amide ([(C
1
im)
2
C
2n
][NTf
2
]
2
for n = 3-5) were investigated as a function of concentration at 295 K. An additivity model was used to obtain the CS
2
contribution to the RSD of a mixture in the 0-200 cm
-1
region. One of the aims of this study is to show how CS
2
can be used as a probe of intermolecular/interionic interactions in ILs. The concentrations were chosen such that the CS
2
-to-imidazolium ring
mole
fraction of a mixture with [(C
1
im)
2
C
2n
][NTf
2
]
2
(DIL(2n)) is the same as that of a mixture with [C
n
C
1
im][NTf
2
] (
MIL
(n)). As found previously for CS
2
in monocationic ILs, the intermolecular spectrum of CS
2
in dicationic ILs is lower in frequency and narrower than that of neat CS
2
. The new result is that the intermolecular spectrum of CS
2
is higher in frequency in DIL(2n) than in the corresponding
MIL
(n), indicating that CS
2
molecules experience a stiffer potential in dicationic ILs than in monocationic ILs. The intermolecular dynamics of CS
2
being higher in frequency in DIL(2n) than in
MIL
(n) is consistent with recent molecular dynamics simulations (Lynden-Bell and Quitevis, J. Chem. Phys., 2018, 148, 193844) that show the stiffer potential is the result of greater confinement of CS
2
in DIL(2n) than in
MIL
(n). We also show in this study how effects due to dilution and the intermolecular potential seen by a solute molecule in solution are unraveled.
...
PMID:Optical Kerr effect spectroscopy of CS
2
in monocationic and dicationic ionic liquids: insights into the intermolecular interactions in ionic liquids. 3030 95
Herein, we report a novel composite material of Nb
2
O
5
@MIL-125 that exhibited enhanced photoreduction of hexavalent chromium. The composite material was fabricated through an impregnation approach, which comprised of a two-step hydrothermal synthesis. As-prepared Nb
2
O
5
nanospheres exhibited very poor charge separation;
MIL
-125 (Ti) which is a Ti-based metal-organic framework was introduced into the lattice of the spheres to improve charge recombination rate. The synthesized material's phase, crystallinity, textural and morphological studies were investigated utilizing XRD, Raman, TEM, SEM, and EDS, respectively. While the optical and photoelectrochemical behavior of the samples were obtained from UV-vis-DRS, PL, and EIS data. This data combined, illustrated the successful formation of a functional and effective heterointerface between Nb
2
O
5
and
MIL
-125 (Ti). Ti introduced as the MOF in the lattice of Nb
2
O
5
had an essential synergetic effect as the composite bearing the highest
mole
ratio of Ti showed higher effective photoreduction of hexavalent chromium. This was further complemented the PL and XPS data which highlighted the Nb-
MIL
-125 (2-3) composite to have excellent charge separation and rapid photoreduction of chromium.
...
PMID:Photoreduction of chromium (VI) by a composite of niobium (V) oxide impregnated with a Ti-based MOF. 3240 Feb 76
