Publications

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Herein, we describe a novel multifunctional metal–organic framework (MOF) materials platform that displays both porosity and tunable emission properties as a function of the metal identity (Eu, Nd, and tuned compositions of Nd/Yb). Their emission collectively spans the deep red to near-infrared (NIR) spectral region (~614–1350 nm), which is highly relevant for in vivo bioimaging. These new materials meet important prerequisites as relevant to biological processes: they are minimally toxic to living cells and retain structural integrity in water and phosphate-buffered saline. To assess their viability as optical bioimaging agents, we successfully synthesized the nanoscale Eu analog as a proof-of-concept system in this series. In vitro studies show that it is cell-permeable in individual RAW 264.7 mouse macrophage and HeLa human cervical cancer tissue culture cells. The efficient discrimination between the Eu emission and cell autofluorescence was achieved with hyperspectral confocal fluorescence microscopy, used here for the first time to characterize MOF materials. Importantly, this is the first report that documents the long-term conservation of the intrinsic emission in live cells of a fluorophore-based MOF to date (up to 48 h). As a result this finding, in conjunction with the materials’ very low toxicity, validates the biocompatibility in these systems and qualifies them as promising for use in long-term tracking and biodistribution studies.

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Here we report for the first time the feasibility of using metal-organic frameworks (MOFs) as electrodes for aqueous Na-ion batteries. We show that Fe-MIL-100, a known redox-active MOF, is electrochemically active in a Na aqueous electrolyte, under various compositions. Emphasis was placed on investigating the electrode-electrolyte interface, with a focus on identifying the relationship between additives in the composition of the working electrode, particle size and overall performance. We found that the energy storage capacity is primarily dependent on the binder additive in the composite; the best activity for this MOF is obtained with Nafion as a binder, owing to its hydrophilic and ion conducting nature. Kynar-bound electrodes are clearly less effective, due to their hydrophobic character, which impedes wetting of the electrode. The binder-free systems show the poorest electrochemical activity. There is little difference in the overall performance as function of particle size (micro vs. nano), implying the storage capacities in this study are not limited by ionic and/or electronic conductivity. Excellent reversibility and high coulombic efficiency are achieved at higher potential ranges, observed after cycle 20. That is despite progressive capacity decay observed in the initial cycles. Importantly, structural analyses of cycled working electrodes confirm that the long range crystallinity remains mainly unaltered with cycling. These findings suggest that limited reversibility of the intercalated Na ions in the lower potential range, together with the gradual lack of available active sites in subsequent cycles is responsible for the rapid decay in capacity retention.

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We report here the synthesis of a neutral viologen derivative, C₂₄H₁₆N₂O₄·2H₂O. The non-solvent portion of the structure (Z-Lig) is a zwitterion, consisting of two positively charged pyridinium cations and two negatively charged carboxylate anions. The carboxylate group is almost coplanar [dihedral angle = 2.04 (11)°] with the benzene ring, whereas the dihedral angle between pyridine and benzene rings is 46.28 (5)°. TheZ-Lig molecule is positioned on a center of inversion (Fig. 1). The presence of the twofold axis perpendicular to thec-glide plane in space groupC2/c generates a screw-axis parallel to thebaxis that is shifted from the origin by 1/4 in theaandcdirections. This screw-axis replicates the molecule (and solvent water molecules) through space. TheZ-Lig molecule links to adjacent moleculesviaO—H...O hydrogen bonds involving solvent water molecules as well as intermolecular C—H...O interactions. There are also π–π interactions between benzene rings on adjacent molecules.

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An open pored metal-organic framework (MOF) with oxygen selectivity at exceptionally high temperatures is confirmed by synthesis, sorption, and synchrotron structural analyses. The large-pore MIL-100 framework with access to the metal center (e.g., Sc and Fe) resulted in preferential O2 over N2 gas uptake at temperatures ranging from 77 K to ambient temperatures (258, 298, and 313 K). Most notably, Sc-MIL-100 shows exceptional O2 sorption; pair distribution function analyses indicate that this is due to distortions in the framework owing to the size of Sc atoms, in particular in the trimer metal cluster. Experimental studies also correlate very well with GCMC simulations, confirming more favorable O2-framework interactions at pressures up to 1 bar, due to the close proximity of O2 to the high density of metal centers in the small tetrahedral cages. Both materials maintain their crystallinity upon gas adsorption cycling, are regenerable, and show exceptional promise for use in energy efficient oxygen purification processes, such as Pressure Swing Adsorption.

The separation of oxygen from nitrogen using metal-organic frameworks (MOFs) is of great interest for potential pressure-swing adsorption processes for the generation of purified O2 on industrial scales. This study uses ab initio molecular dynamics (AIMD) simulations to examine for the first time the pure-gas and competitive gas adsorption of O2 and N2 in the M2(dobdc) (M = Cr, Mn, Fe) MOF series with coordinatively unsaturated metal centers. Effects of metal, temperature, and gas composition are explored. This unique application of AIMD allows us to study in detail the adsorption/desorption processes and to visualize the process of multiple guests competitively binding to coordinatively unsaturated metal sites of a MOF.

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We study nanoporous-carbon (NPC) grown via pulsed laser deposition (PLD) as an electrically conductive anode host material for Mg2+ intercalation. NPC has high surface area, and an open, accessible pore structure tunable via mass density that can improve diffusion. We fabricate 2032 coin cells using NPC coated stainless-steel disk anodes, metallic Mg cathodes, and a Grignardbased electrolyte. NPC mass density is controlled during growth, ranging from 0.06-1.3 g/cm3. The specific surface area of NPC increases linearly from 1,000 to 1,700 m2/g as mass density decreases from 1.3 to 0.26 g/cm3, however, the surface area falls off dramatically at lowermass densities, implying a lack of mechanical integrity in such nanostructures. These structural characterizations correlate directly with coin cell electrochemical measurements. In particular, cyclic voltammetry (CV) scans for NPC with density ∼0.5 g/cm3 and BET surface area ∼1500 m2/g infer the possibility of reversible Mg-ion intercalation. Higher density NPC yields capacitive behavior, most likely resulting from the smaller interplanar spacings between graphene sheet fragments and tighter domain boundaries; lower density NPC results in asymmetrical CV scans, consistent with the likely structural degradation resulting from mass transport through soft, low-density carbon materials.

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Oxy-fuel combustion is a well-known approach to improve the heat transfer associated with stationary energy processes. Its overall penetration into industrial and power markets is constrained by the high cost of existing air separation technologies for generating oxygen. Cryogenic air separation is the most widely used technology for generating oxygen but is complex and expensive. Pressure swing adsorption is a competing technology that uses activated carbon, zeolites and polymer membranes for gas separations. However, it is expensive and limited to moderate purity O₂ . MOFs are cutting edge materials for gas separations at ambient pressure and room temperature, potentially revolutionizing the PSA process and providing dramatic process efficiency improvements through oxy-fuel combustion. This LDRD combined (1) MOF synthesis, (2) gas sorption testing, (3) MD simulations and crystallography of gas siting in pores for structure-property relationship, (4) combustion testing and (5) technoeconomic analysis to aid in real-world implementation.

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