Flexible metal–organic frameworks (MOFs) hold great promise as smart materials for specific applications such as gas separation. These materials undergo interesting structural changes in response to ...guest molecules, which is often associated with unique adsorption behavior not possible for rigid MOFs. Understanding the dynamic behavior of flexible MOFs is crucial yet challenging as it involves weak host–guest interactions and subtle structural transformation not only at the atomic/molecular level but also in a nonsteady state. We report here an in-depth study on the adsorbate- and temperature-dependent adsorption in a flexible MOF by crystallizing atomic gases into its pores. Mn(ina)2 shows an interesting temperature-dependent response toward noble gases. Its nonmonotonic, temperature-dependent adsorption profile results in an uptake maximum at a temperature threshold, a phenomenon that is unusual. Full characterization of Xe-loaded MOF structures is performed by in situ single-crystal and synchrotron X-ray diffraction, IR spectroscopy, and molecular modeling. The X-ray diffraction analysis offers a detailed explanation into the dynamic structural transformation and provides a convincing rationalization of the unique adsorption behavior at the molecular scale. The guest and temperature dependence of the structural breathing gives rise to an intriguing reverse of Xe/Kr adsorption selectivity as a function of temperature. The presented work may provide further understanding of the adsorption behavior of noble gases in flexible MOF structures.
A comprehensive understanding of the solid-electrolyte interphase (SEI) composition is crucial to developing high-energy batteries based on lithium metal anodes. A particularly contentious issue ...concerns the presence of LiH in the SEI. Here we report on the use of synchrotron-based X-ray diffraction and pair distribution function analysis to identify and differentiate two elusive components, LiH and LiF, in the SEI of lithium metal anodes. LiH is identified as a component of the SEI in high abundance, and the possibility of its misidentification as LiF in the literature is discussed. LiF in the SEI is found to have different structural features from LiF in the bulk phase, including a larger lattice parameter and a smaller grain size (<3 nm). These characteristics favour Li
transport and explain why an ionic insulator, like LiF, has been found to be a favoured component for the SEI. Finally, pair distribution function analysis reveals key amorphous components in the SEI.
A library of thio- and selenourea derivatives is used to adjust the kinetics of PbE (E = S, Se) nanocrystal formation across a 1000-fold range (
= 10
to 10
s
), at several temperatures (80-120 °C), ...under a standard set of conditions (Pb : E = 1.2 : 1, Pb(oleate)
= 10.8 mM, chalcogenourea = 9.0 mM). An induction delay (
) is observed prior to the onset of nanocrystal absorption during which PbE solute is observed using
X-ray total scattering. Density functional theory models fit to the X-ray pair distribution function (PDF) support a Pb
(μ
-S)
(Pb(O
CR)
)
structure. Absorption spectra of aliquots reveal a continuous increase in the number of nanocrystals over more than half of the total reaction time at low temperatures. A strong correlation between the width of the nucleation phase and reaction temperature is observed that does not correlate with the polydispersity. These findings are antithetical to the critical concentration dependence of nucleation that underpins the La Mer hypothesis and demonstrates that the duration of the nucleation period has a minor influence on the size distribution. The results can be explained by growth kinetics that are size dependent, more rapid at high temperature, and self limiting at low temperatures.
The cryogenic separation of noble gases is energy-intensive and expensive, especially when low concentrations are involved. Metal–organic frameworks (MOFs) containing polarizing groups within their ...pore spaces are predicted to be efficient Xe/Kr solid-state adsorbents, but no experimental insights into the nature of the Xe–network interaction are available to date. Here we report a new microporous MOF (designated SBMOF-2) that is selective toward Xe over Kr under ambient conditions, with a Xe/Kr selectivity of about 10 and a Xe capacity of 27.07 wt % at 298 K. Single-crystal diffraction results show that the Xe selectivity may be attributed to the specific geometry of the pores, forming cages built with phenyl rings and enriched with polar −OH groups, both of which serve as strong adsorption sites for polarizable Xe gas. The Xe/Kr separation in SBMOF-2 was investigated with experimental and computational breakthrough methods. These experiments showed that Kr broke through the column first, followed by Xe, which confirmed that SBMOF-2 has a real practical potential for separating Xe from Kr. Calculations showed that the capacity and adsorption selectivity of SBMOF-2 are comparable to those of the best-performing unmodified MOFs such as NiMOF-74 or Co formate.
In situ X‐ray scattering measurements of CsPbX3 (X = Cl, Br, I) nanocrystal formation and halide exchange at NSLS‐II beamlines were performed in an automated flow reactor. Total scattering ...measurements were performed at the 28‐ID‐2 (XPD) beamline and small‐angle X‐ray scattering at the 16‐ID (LiX) beamline. Nanocrystal structural parameters of interest, including size, size distribution and atomic structure, were extracted from modeling the total scattering data. The results highlight the potential of these beamlines and the measurement protocols described in this study for studying dynamic processes of colloidal nanocrystal synthesis in solution with timescales on the order of seconds.
In‐situ flash experiments on rutile TiO2 were performed at the synchrotron at the Brookhaven National Laboratory. Pair distribution function analysis of total X‐ray scattering measurements yielded ...mean‐square atomic displacements of oxygen and titanium atoms during the progression of the 3 stages of flash. The displacements are measured to be far greater for oxygen atoms than for titanium atoms. These large displacements may signal an “elastic softening” of the lattice, which, recently, has been predicted as a precursor to the onset of flash.
In situ X-ray scattering measurements of CsPbX
(X = Cl, Br, I) nanocrystal formation and halide exchange at NSLS-II beamlines were performed in an automated flow reactor. Total scattering ...measurements were performed at the 28-ID-2 (XPD) beamline and small-angle X-ray scattering at the 16-ID (LiX) beamline. Nanocrystal structural parameters of interest, including size, size distribution and atomic structure, were extracted from modeling the total scattering data. The results highlight the potential of these beamlines and the measurement protocols described in this study for studying dynamic processes of colloidal nanocrystal synthesis in solution with timescales on the order of seconds.
Reactive flash sintering (RFS) enables the simultaneous synthesis and sintering of ceramics and has been shown to affect the reaction pathway of different materials. Herein, in situ synchrotron X‐ray ...diffraction (XRD) is used to investigate the (Mg,Ni,Co,Cu,Zn)O entropy‐stabilized oxide formation during: (i) conventional heating and (ii) RFS under current rate‐controlled mode. The same reaction pathway is verified in both instances: the starting rock‐salt (RS), spinel (Co3O4), tenorite (CuO), and wurtzite (ZnO) phases transform into a single RS phase with a (1 1 1) to (2 0 0) intensity ratio of 0.67, consistent with a random distribution of the cations into the structure. Pt lattice peak shift from the XRD patterns is used as standard to monitor the sample surface temperature, revealing a strong endothermic reaction during the RS single‐phase formation (Pt peaks shift toward higher angles while increasing sample temperature/current density). In RFS, the single‐phase RS structure is formed in just 60 s at a furnace temperature of 600°C and a current rate of 220 mA mm−2/min. Therefore, RFS greatly accelerates the synthesis of (Mg,Ni,Co,Cu,Zn)O, however, it does not play a role in the reaction pathway for this material formation.
Li metal batteries using Li metal as negative electrode and LiNi
Mn
Co
O
as positive electrode represent the next generation high-energy batteries. A major challenge facing these batteries is finding ...electrolytes capable of forming good interphases. Conventionally, electrolyte is fluorinated to generate anion-derived LiF-rich interphases. However, their low ionic conductivities forbid fast-charging. Here, we use CsNO
as a dual-functional additive to form stable interphases on both electrodes. Such strategy allows the use of 1,2-dimethoxyethane as the single solvent, promising superior ion transport and fast charging. LiNi
Mn
Co
O
is protected by the nitrate-derived species. On the Li metal side, large Cs
has weak interactions with the solvent, leading to presence of anions in the solvation sheath and an anion-derived interphase. The interphase is surprisingly dominated by cesium bis(fluorosulfonyl)imide, a component not reported before. Its presence suggests that Cs
is doing more than just electrostatic shielding as commonly believed. The interphase is free of LiF but still promises high performance as cells with high LiNi
Mn
Co
O
loading (21 mg/cm
) and low N/P ratio (~2) can be cycled at 2C (~8 mA/cm
) with above 80% capacity retention after 200 cycles. These results suggest the role of LiF and Cs-containing additives need to be revisited.
Iodine in Metal–Organic Frameworks at High Pressure Lobanov, Sergey S; Daly, John A; Goncharov, Alexander F ...
The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory,
07/2018, Letnik:
122, Številka:
29
Journal Article
Recenzirano
Odprti dostop
Capture of highly volatile radioactive iodine is a promising application of metal–organic frameworks (MOFs), thanks to their high porosity with flexible chemical architecture. Specifically, strong ...charge-transfer binding of iodine to the framework enables efficient and selective iodine uptake as well as its long-term storage. As such, precise knowledge of the electronic structure of iodine is essential for a detailed modeling of the iodine sorption process, which will allow for rational design of iodophilic MOFs in the future. Here we probe the electronic structure of iodine in MOFs at variable iodine···framework interaction by Raman and optical absorption spectroscopy at high pressure (P). The electronic structure of iodine in the straight channels of SBMOF-1 (Ca-sdb, sdb = 4,4′-sulfonyldibenzoate) is modified irreversibly at P > 3.4 GPa by charge transfer, marking a polymerization of iodine molecules into a 1D polyiodide chain. In contrast, iodine in the sinusoidal channels of SBMOF-3 (Cd-sdb) retains its molecular (I2) character up to at least 8.4 GPa. Such divergent high-pressure behavior of iodine in the MOFs with similar port size and chemistry illustrates adaptations of the electronic structure of iodine to channel topology and strength of the iodine···framework interaction, which can be used to tailor iodine-immobilizing MOFs.
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