Incorporating open metal sites (OMS) into metal–organic frameworks allows design of well-defined binding sites for selective molecular adsorption, which has a profound impact on catalysis and separations. We demonstrate that Cu­(I) sites incorporated into MFU-4l preferentially adsorb olefins over paraffins. Density functional theory (DFT) calculations show that the OMS are independent, with no dependence of binding energy on olefin loading up to one olefin per Cu­(I). Experimentally, increasing Cu­(I) loading increased olefin uptake without affecting the binding energy, as predicted by DFT and confirmed by temperature-programmed desorption. The potential of this material for olefin/paraffin separation under ambient conditions was investigated by gas adsorption and column breakthrough experiments for an equimolar ratio of olefin/paraffin. High-grade propylene and ethylene (>99.999%) can be generated using temperature–concentration swing recycling from a Cu­(I)-MFU-4l packed column with no measurable paraffin breakthrough.

Highly porous zirconium-based metal−organic frameworks (MOFs) have been widely studied as materials for sorption and destruction of chemical warfare agents (CWAs). It is important to understand the diffusion of CWAs, their reaction products, and environmental molecules through MOFs to utilize these materials for protection against CWA threats. As a first step toward this goal, we study adsorption and diffusion of acetone in pristine UiO-66. We have chosen to study UiO-66 because it has been demonstrated to be effective for destruction of CWAs and simulants; we use acetone because it is a prototypical polar organic molecule small enough to be expected to diffuse fairly rapidly through nondefective UiO-66. We specifically examine the impact of framework flexibility and hydrogen bonding between acetone and the OH groups on the nodes of the framework on the diffusivity of acetone. We find that inclusion of flexibility is essential for meaningful predictions of diffusion of acetone. We have identified the dynamics of the three linkers making up the triangular window between adjacent pores as the critical factor in controlling diffusion of acetone. We demonstrate from experiments and first-principles calculations that acetone readily hydrogen bonds to UiO-66 framework OH groups. We have modified the classical potential for UiO-66 to accurately model the framework−acetone hydrogen bonds, which are not accounted for in many MOF potentials. We find that hydrogen bonding decreases the diffusivity by about 1 order of magnitude at low loading and about a factor of 3 at high loading. Thus, proper accounting of hydrogen bonding and framework flexibility are both critical for obtaining physically realistic values of diffusivities for acetone and similar-sized polar molecules in UiO-66.

Metal−organic frameworks (MOFs) and specifically the UiO family of MOFs have been extensively studied for the adsorption and degradation of chemical warfare agents (CWAs) and their simulants. We present a combined experimental and computational study of the adsorption of dimethyl methylphosphonate (DMMP), a CWA adsorption simulant, in functionalized UiO-67. We have used density functional theory (DFT) to design functionalized MOFs having a range of binding energies for DMMP. We have selected three different functionalized MOFs for experimental synthesis and characterization from a total of eight studied with DFT. These three MOFs were identified as having the weakest, intermediate, and strongest binding energies for DMMP of the set, as predicted by our DFT calculations. We find that the order of predicted binding energies agrees with data from temperature-programmed desorption experiments. Moreover, the values of the binding energies are also in good agreement. This serves as a proof of concept that ab initio calculations can guide experiments in designing MOFs that exhibit a higher affinity for CWAs and their simulants. One surprising outcome of this work is that reactions between DMMP and the three functionalized UiO-67 MOFs were not observed under ultrahigh-vacuum conditions for the exposure of DMMP of up to 9000 L. This lack of reactivity is attributed to the low levels of defects in the materials used.

Thermodynamic and kinetic properties of molecular adsorption and transport in metal–organic frameworks (MOFs) are crucially important for many applications, including gas adsorption, filtration, and remediation of harmful chemicals. Using the in situ 1H nuclear magnetic resonance (NMR) isotherm technique, we measured macroscopic thermodynamic and kinetic properties such as isotherms and rates of mass transfer while simultaneously obtaining microscopic information revealed by adsorbed molecules via NMR. Upon investigating isopropyl alcohol adsorption in MOF UiO-66 by in situ NMR, we obtained separate isotherms for molecules adsorbed at distinct environments exhibiting distinct NMR characteristics. A mechanistic view of the adsorption process is obtained by correlating such resolved isotherms with the cage structure effect on the nucleus-independent chemical shift, molecular dynamics such as the crowding effect at high loading levels, and the loading level dependence of the mass transfer rate as measured by NMR and elucidated by classical Monte Carlo simulations.

Formaldehyde (CH2O) is a highly versatile platform chemical with an annual production of over 30 megatons. The current most widely used industrial method for formaldehyde synthesis is very energy intensive and plagued with significant exergy losses. We propose a highly efficient heterogeneous nanoporous catalyst capable of direct hydrogenation of CO to CH2O followed by condensation of CH2O from a mixture of CO and H2, which are noncondensable gases. The key to this synthesis is a Lewis pair (LP) functionalized metal–organic framework (MOF) heterogeneous porous catalyst. We have computed reaction pathways, barriers, and uncertainties for CO hydrogenation on a LP functionalized MOF using various density functional theory (DFT) methods and high-level ab initio methods. We have assessed the uncertainties in the energetics inherent in the DFT functionals. We predict that the thermodynamics of CH2O synthesis will be enhanced relative to gas phase synthesis and more importantly, will not be equilibrium limited because the barrier to product desorption from the MOF is much lower than the barrier for the reverse reaction. Hence, the product will be continuously removed from the process, facilitating very high overall conversion rates. Our proposed process will dramatically improve the sustainability of CH2O synthesis.

Ammonia is a widely used toxic industrial chemical that can cause severe respiratory ailments. Therefore, understanding and developing materials for its efficient capture and controlled release is necessary. One such class of materials is 3D porous metal-organic frameworks (MOFs) with exceptional surface areas and robust structures, ideal for gas storage/transport applications. Herein, interactions between ammonia and UiO-67-X (X: H, NH 2 , CH 3 ) zirconium MOFs were studied under cryogenic, ultrahigh vacuum (UHV) conditions using temperature-programmed desorption mass spectrometry (TPD-MS) and in-situ temperature-programmed infrared (TP-IR) spectroscopy. Ammonia was observed to interact with μ 3 À OH groups present on the secondary building unit of UiO-67-X MOFs via hydrogen bonding. TP-IR studies revealed that under cryogenic UHV conditions, UiO-67-X MOFs are stable towards ammonia sorption. Interestingly, an increase in the intensity of the CÀ H stretching mode of the MOF linkers was detected upon ammonia exposure, attributed to NHÀ π interactions with linkers. These same binding interactions were observed in grand canonical Monte Carlo simulations. Based on TPD-MS, binding strength of ammonia to three MOFs was determined to be approximately 60 kJ mol À 1 , suggesting physisorption of ammonia to UiO-67-X. In addition, missing linker defect sites, consisting of H 2 O coordinated to Zr 4 + sites, were detected through the formation of nNH 3 •H 2 O clusters, characterized through in-situ IR spectroscopy. Structures consistent with these assignments were identified through density functional theory calculations. Tracking these bands through adsorption on thermally activated MOFs gave insight into the dehydroxylation process of UiO-67 MOFs. This highlights an advantage of using NH 3 for the structural analysis of MOFs and developing an understanding of interactions between ammonia and UiO-67-X zirconium MOFs, while also providing directions for the development of stable materials for efficient toxic gas sorption.

Metal organic frameworks (MOFs) containing zirconium secondary building units (SBUs) in UiO-67 and related MOFs, are highly active for neutralizing both the chemical warfare agents and simulants, such as dimethyl methylphosphonate (DMMP). However, two recent publications gave conflicting reports of DMMP reaction with UiO-67 under ultra high vacuum (UHV) conditions, with one reporting chemisorption and reaction (Wang et al.,

Copper selenide (Cu 2−x Se) is a promising material for plasmonic nanoparticle applications. Cu 2−x Se becomes plasmonically active in the oxidized state (x > 0), where free carrier density increases with increasing oxidation. It also has considerable cation (Cu) disorder. To date, there has not been a theoretical study of the impact of the degree of oxidation and cation disorder on the electronic and optical properties of Cu 2−x Se. We used density functional theory (DFT) to investigate the effects of the concentration of Cu vacancies and disorder on the properties of Cu 2−x Se. We used both generalized gradient approximation (GGA) and hybrid-GGA functionals to compute the structural, electronic, and optical properties of the cubic phase of Cu 2−x Se for x = 0, 0.25, 0.5, and 0.75. We performed ab initio molecular dynamics simulations at 300 K to simulate disorder, taking snapshots sampled from simulations of periodic supercells with different levels and arrangements of defects. The HSE06+U hybrid-GGA functional was used to calculate the electronic properties, including the optical band gaps, for a total of 400 different configurations. We found that the average optical band gap increases with increasing oxidation. We also found that only the stoichiometric, x = 0, materials are semiconductors, and the electronic band gap generally increases, increasing disorder.