Nuclear energy is among the most viable alternatives to our current fossil fuel-based energy economy. The mass deployment of nuclear energy as a low-emissions source requires the reprocessing of used ...nuclear fuel to recover fissile materials and mitigate radioactive waste. A major concern with reprocessing used nuclear fuel is the release of volatile radionuclides such as xenon and krypton that evolve into reprocessing facility off-gas in parts per million concentrations. The existing technology to remove these radioactive noble gases is a costly cryogenic distillation; alternatively, porous materials such as metal-organic frameworks have demonstrated the ability to selectively adsorb xenon and krypton at ambient conditions. Here we carry out a high-throughput computational screening of large databases of metal-organic frameworks and identify SBMOF-1 as the most selective for xenon. We affirm this prediction and report that SBMOF-1 exhibits by far the highest reported xenon adsorption capacity and a remarkable Xe/Kr selectivity under conditions pertinent to nuclear fuel reprocessing.
Used nuclear fuel reprocessing represents a unique challenge when dealing with radionuclides such as isotopes of 85Kr and 129I2 due to their volatility and long half-life. Efficient capture of 129I2 ...(t 1/2 = 15.7 × 106 years) from the nuclear waste stream can help reduce the risk of releasing I2 radionuclide into the environment and/or potential incorporation into the human thyroid. Metal organic frameworks have the reported potential to be I2 adsorbents but the effect of water vapor, generally present in the reprocessing off-gas stream, is rarely taken into account. Moisture-stable porous metal organic frameworks that can selectively adsorb I2 in the presence of water vapor are thus of great interest. Herein, we report on the I2 adsorption capacity of two microporous metal organic frameworks at both dry and humid conditions. Single-crystal X-ray diffraction and Raman spectroscopy reveal distinct sorption sites of molecular I2 within the pores in proximity to the phenyl- and phenol-based linkers stabilized by the I···π and I···O interactions, which allow selective uptake of iodine.
The use of s-block metal centers to construct coordination networks (CNs) is comparatively rare. The predominance of ionic forces and the absence of well-defined secondary building units make the ...rational construction of porous s-block CNs a challenging task. However, the nontoxic subset of these metals (Li, Na, K, Mg, Ca) based CNs, potentially useful for gas storage, separation, drug delivery, catalysis, and electrochemical applications, makes exploratory synthesis a worthwhile endeavor. In this review, we discuss the recent advances in the synthesis of s-block-CNs, produced using common carboxylic acid based linkers.
The influence of crystallite size on the adsorption reactivity of phosphate on 2-line to 6-line ferrihydrites was investigated by combining adsorption experiments, structure and surface analysis, and ...spectroscopic analysis. X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that the ferrihydrite samples possessed a similar fundamental structure with a crystallite size varying from 1.6 to 4.4 nm. N2 adsorption on freeze-dried samples revealed that the specific surface area (SSABET) decreased from 427 to 234 m2 g–1 with increasing crystallite size and micropore volume (V micro) from 0.137 to 0.079 cm3 g–1. Proton adsorption (Q H) at pH 4.5 and 0.01 M KCl ranged from 0.73 to 0.55 mmol g–1. Phosphate adsorption capacity at pH 4.5 and 0.01 M KCl for the ferrihydrites decreased from 1690 to 980 μmol g–1 as crystallite size increased, while the adsorption density normalized to SSABET was similar. Phosphate adsorption on the ferrihydrites exhibited similar behavior with respect to both kinetics and the adsorption mechanism. The kinetics could be divided into three successive first-order stages: relatively fast adsorption, slow adsorption, and a very slow stage. With decreasing crystallite size, ferrihydrites exhibited increasing rate constants per mass for all stages. Analysis of OH– release and attenuated total reflectance infrared spectroscopy (ATR-IR) and differential pair distribution function (d-PDF) results indicated that initially phosphate preferentially bound to two Fe–OH2 1/2+ groups to form a binuclear bidentate surface complex without OH– release, with smaller size ferrihydrites exchanging more Fe–OH2 1/2+ per mass. Subsequently, phosphate exchanged with both Fe–OH2 1/2+ and Fe–OH1/2– with a constant amount of OH– released per phosphate adsorbed. Also in this stage binuclear bidentate surface complexes were formed with a P–Fe atomic pair distance of ∼3.25 Å.
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.
Correction procedures for obtaining accurate X-ray structure factors from large area detectors are considered, including subpanel effects, over excited pixels and careful intensity corrections. ...Problems associated with data normalization, the use of a pixel response correction from a glass standard and minimization of systematic errors are also discussed. Data from glassy GeSe
2 and liquid water measured with a Perkin Elmer amorphous-Silicon detector are used to demonstrate the effectiveness of these correction procedures. This requires reduction of systematic errors in the measured intensity to around the 0.1% level.
Structure of Ferrihydrite, a Nanocrystalline Material Michel, F. Marc; Ehm, Lars; Antao, Sytle M ...
Science (American Association for the Advancement of Science),
06/2007, Volume:
316, Issue:
5832
Journal Article
Peer reviewed
Despite the ubiquity of ferrihydrite in natural sediments and its importance as an industrial sorbent, the nanocrystallinity of this iron oxyhydroxide has hampered accurate structure determination by ...traditional methods that rely on long-range order. We uncovered the atomic arrangement by real-space modeling of the pair distribution function (PDF) derived from direct Fourier transformation of the total x-ray scattering. The PDF for ferrihydrite synthesized with the use of different routes is consistent with a single phase (hexagonal space group P6₃mc; a = ~5.95 angstroms, c = ~9.06 angstroms). In its ideal form, this structure contains 20% tetrahedrally and 80% octahedrally coordinated iron and has a basic structural motif closely related to the Baker-Figgis δ-Keggin cluster. Real-space fitting indicates structural relaxation with decreasing particle size and also suggests that second-order effects such as internal strain, stacking faults, and particle shape contribute to the PDFs.
Open and close: Inspired by close‐packing of spheres, to strengthen the framework–H2 interaction in MOFs (metal‐organic frameworks), a strategy is devised to increase the number of nearest ...neighboring open metal sites of each H2‐hosting cage, and to align the open metal sites toward the H2 molecules. Two MOF polymorphs were made, one exhibiting a record high hydrogen uptake of 3.0 wt % at 1 bar and 77 K.
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