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  1. Free, publicly-accessible full text available August 16, 2024
  2. The stability of metal–organic frameworks (MOFs) in water affects their ability to function as chemical catalysts, their capacity as adsorbents for separations in water vapor presence, and their usefulness as recyclable water harvesters. Here, we have examined water stability of four node-modified variants of the mesoporous MOF, NU-1000, namely formate-, Acac-, TFacac-, and Facac-NU-1000, comparing these with node-accessible NU-1000. These NU-1000 variants present ligands grafted to NU-1000's hexa-Zr( iv )-oxy nodes by displacing terminal aqua and hydroxo ligands. Facac-NU-1000, containing the most hydrophobic ligands, showed the greatest water stability, being able to undergo at least 20 water adsorption/desorption cycles without loss of water uptake capacity. Computational studies revealed dual salutary functions of installed Facac ligands: (1) enhancement of framework mechanical stability due to electrostatic interactions; and (2) transformation and shielding of the otherwise highly hydrophilic nodes from H-bonding interactions with free water, presumably leading to weaker channel-stressing capillary forces during water evacuation – consistent with trends in free energies of dehydration across the NU-1000 variants. Water harvesting and hydrolysis of chemical warfare agent simulants were examined to gauge the functional consequences of modification and mechanical stabilization of NU-1000 by Facac ligands. The studies revealed a harvesting capacity of ∼1.1 L of water vapor per gram of Facac-NU-1000 per sorption cycle. They also revealed retention of catalytic MOF activity following 20 water uptake and release cycles. This study provides insights into the basis for node-ligand-engendered stabilization of wide-channel MOFs against collapse during water removal. 
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    A huge challenge facing scientists is the development of adsorbent materials that exhibit ultrahigh porosity but maintain balance between gravimetric and volumetric surface areas for the onboard storage of hydrogen and methane gas—alternatives to conventional fossil fuels. Here we report the simulation-motivated synthesis of ultraporous metal–organic frameworks (MOFs) based on metal trinuclear clusters, namely, NU-1501-M (M = Al or Fe). Relative to other ultraporous MOFs, NU-1501-Al exhibits concurrently a high gravimetric Brunauer−Emmett−Teller (BET) area of 7310 m 2 g −1 and a volumetric BET area of 2060 m 2 cm −3 while satisfying the four BET consistency criteria. The high porosity and surface area of this MOF yielded impressive gravimetric and volumetric storage performances for hydrogen and methane: NU-1501-Al surpasses the gravimetric methane storage U.S. Department of Energy target (0.5 g g −1 ) with an uptake of 0.66 g g −1 [262 cm 3 (standard temperature and pressure, STP) cm −3 ] at 100 bar/270 K and a 5- to 100-bar working capacity of 0.60 g g −1 [238 cm 3 (STP) cm −3 ] at 270 K; it also shows one of the best deliverable hydrogen capacities (14.0 weight %, 46.2 g liter −1 ) under a combined temperature and pressure swing (77 K/100 bar → 160 K/5 bar). 
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  5. MOF-encapsulated nanoparticles (NP@MOFs) are hybrid, heterogeneous catalysts, where the MOF could boost the activity and selectivity of the encapsulated NP for the reaction of choice by controlling reactant orientation. However, due to overwhelming combinatorics, methods to rapidly identify promising NP + MOF combinations for a given application are needed. Earlier work used a “surrogate” inert pore on top of NP-representative surfaces to generically capture MOF steric effects, hence enabling computational screening to focus on NP composition. However, the surrogate pore method neglects electronic effects of the MOF on the NP. Here, we use density functional theory to study how paradigmatic MOF linkers (imidazolate, carboxylate, and thiolate) impact the electronic structure of representative metal surfaces, and in turn the binding of small species, whose formation energies are commonly used in descriptor-based catalyst screening. We find that the coordinating moiety and functionalization of the linker modulates the shift in the metal d-band center and the electron transfer, which is correlated to experimentally measurable quantities such as C–O vibration frequencies. However, in the majority of cases, the effect of the linker on binding energies (for C*, O*, N*, H*, OH*, CH 3 * and CO*) was less than 10 kJ mol −1 . Furthermore, scaling relationships between binding energies were only slightly affected by linker-originated electronic effects. Therefore, activity/selectivity “heat maps” derived from calculations under “generic” steric constrains could remain useful to screen the optimal NP composition of an NP@MOF catalyst. On the other hand, the placement of a given NP composition on the aforementioned heat maps is affected by the MOF. For an n -butane oxidation case study, we estimated that Ag 3 Pd—a promising NP composition for selective 1-butanol formation according to previous screenings using the surrogate pore method—has a ∼85% probability of retaining a selectivity for 1-butanol above 75% when encapsulated in a carboxylic MOF of suitable pore size. 
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