Publications

Abstract not provided.

Here, we apply density functional theory (DFT) to investigate rare-earth metal organic frameworks (RE-MOFs), RE12(μ3-OH)16(C8O6H4)8(C8O6H5)4 (RE = Y, Eu, Tb, Yb), and characterize the level of theory needed to accurately predict structural and electronic properties in MOF materials with 4f-electrons. A two-step calculation approach of geometry optimization with spin-restricted DFT and large core potential (LCPs), and detailed electronic structures with spin-unrestricted DFT with a full valence potential + Hubbard U correction is investigated. Spin-restricted DFT with LCPs resulted in good agreement between experimental lattice parameters and optimized geometries, while a full valence potential is necessary for accurate representation of the electronic structure. The electronic structure of Eu-DOBDC MOF indicated a strong dependence on the treatment of highly localized 4f-electrons and spin polarization, as well as variation within a range of Hubbard corrections (U = 1-9 eV). For Hubbard corrected spin-unrestricted calculations, a U value of 1-4 eV maintains the non-metallic character of the band gap with slight deviations in f-orbital energetics. When compared with experimentally reported results, the importance of the full valence calculation and the Hubbard correction in correctly predicting the electronic structure is highlighted.

The degradation of a chemical warfare agent simulant using a catalytically active Zr-based metal-organic framework (MOF) as a function of different solvent systems was investigated. Complementary molecular modelling studies indicate that the differences in the degradation rates are related to the increasing size in the nucleophile, which hinders the rotation of the product molecule during degradation. Methanol was identified as an appropriate solvent for non-Aqueous degradation applications and demonstrated to support the MOF-based destruction of both sarin and soman.

The adsorption of chemical warfare agents and their simulants by Zr (UiO-66) and rare-earth (Y, UiO-66-DOBDC analog)-based metal-organic frameworks (MOFs) is explored here using density functional theory. In particular, we investigate the role of linker functional group (OH, H) and metal atom identity on the binding energies of organophosphorous compounds. Commonly used cluster approximations for MOF secondary building units and various optimization constraints are compared with three-dimensional periodic results. An in-depth scan of potential binding sites and orientations reveals little effect due to metal identity, whereas the effect of linker functionalization depends on the substrate. This finding strongly suggests that full linkers and functional groups should be included in cluster models. Importantly, defect sites show considerably improved binding of organophosphorous compounds as compared to ideal clusters. Favorable binding is also demonstrated at two additional adsorption sites, ZrOH and μ3-OH, that likely play a role in the initial adsorption process. The results presented here portray the importance of including full three-dimensional pore structures in the adsorption process of organophosphorous compounds in MOFs; a critical first step in the degradation of these harmful chemicals.

Nanoporous materials such as metal-organic frameworks (MOFs) have attractive properties for selective capture of chemical warfare agents (CWAs). For obvious reasons, most research on adsorption of CWAs is performed with simulant molecules rather than real agents. This paper examines how effectively common CWA simulants mimic the adsorption properties of sarin and soman. To this end, we perform molecular simulations in the dilute adsorption limit for four simulants [dimethyl methylphosphonate (DMMP), diethyl chlorophosphate (DCP), diisopropyl fluorophosphate, and dimethyl p-nitrophenyl phosphate (DMNP)] and sarin and soman in a set of 2969 MOFs with experimentally known crystal structures. To establish the robustness of the conclusions with respect to the force field used in these simulations, each system was examined with two independent force fields, a "generic" force field and a density functional theory (DFT)-derived force field we established based on extensive dispersion-corrected DFT calculations of adsorption in the well-known MOF UiO-66. Our results show that when judging the performance of adsorbents using the heat of adsorption, DCP and DMMP are the best simulants for the adsorption of sarin, while DMNP is the best simulant for soman. The adsorption properties of DCP or DMMP show a strong correlation with sarin over a range of MOFs, but the correlation between DMNP and soman is considerably weaker. Comparisons of results with both force fields indicate that our main conclusions are robust with respect to the force field used to define adsorbate-MOF interactions.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

UiO-66 is a highly stable metal-organic framework (MOF) that has garnered interest for many adsorption applications. For small, nonpolar adsorbates, physisorption is dominated by weak Van der Waals interactions limiting the adsorption capacity. A common strategy to enhance the adsorption properties of isoreticular MOFs, such as UiO-66, is to add functional groups to the organic linker. Low and high pressure O2 isotherms were measured on UiO-66 MOFs functionalized with electron donating and withdrawing groups. It was found that the electron donating effects of -NH2, -OH, and -OCF3 groups enhance the uptake of O2. Interestingly, a significant enhancement in both the binding energy and adsorption capacity of O2 was observed for UiO-66-(OH)2-p, which has two -OH groups para from one another. Density functional theory (DFT) simulations were used to calculate the binding energy of oxygen to each MOF, which trended with the adsorption capacity and agreed well with the heats of adsorption calculated from the Toth model fit to multi-temperature isotherms. DFT simulations also determined the highest energy binding site to be on top of the electron π-cloud of the aromatic ring of the ligand, with a direct trend of the binding energy with low pressure adsorption capacity. Uniquely, DFT found that oxygen molecules adsorbed to UiO-66-(OH)2-p prefer to align parallel to the -OH groups on the aromatic ring. Similar effects for the electron donation of the functional groups were observed for the low pressure adsorption of N2, CH4, and CO2.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

Abstract not provided.

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). 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.