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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Leaching Model of Radionuclides in Metal-Organic Framework Particles

Metal-organic frameworks (MOFs) have been used to sequester radionuclides and seal them inside of porous scaffolds using postsynthetic modification procedures. Experiments show that certain Zr-MOF with different capping linkers significantly affects the radionuclide release kinetics. In this work, we developed a leaching model of radionuclides in Zr-MOF particles. The model assumes that uranyl species occupy two energetically favored sites: the metal node and the MOF pores. For a given overall concentration of uranyl species, the partitions of uranyl species at the metal nodes and within the pores are determined by their chemical potentials. The model also considers the effect of particle surface and concentration on chemical potentials and diffusivity. The effects of spatial and structural dependent chemical potentials and diffusivity as well as particle sizes on leaching kinetics are investigated with the model. Predicted and measured uranyl leaching kinetics in Zr-MOF particles under batch experiments are compared. The results demonstrate the model’s capability for exploring the mechanisms of leaching and provide guidance for material design.

Metal-Organic Framework, Diffusion, uranyl, Leachi↗
DOE OSTI2017

Postsynthetic Tuning of Metal–Organic Frameworks for Targeted Applications

Metal–organic frameworks (MOFs) are periodic, hybrid, atomically well-defined porous materials that typically form by self-assembly and consist of inorganic nodes (metal ions or clusters) and multitopic organic linkers. MOFs as a whole offer many intriguing properties, including ultrahigh porosity, tunable chemical functionality, and low density. These properties point to numerous potential applications, including gas storage, chemical separations, catalysis, light harvesting, and chemical sensing, to name a few. Reticular chemistry, or the linking of molecular building blocks into predetermined network structures, has been employed to synthesize thousands of MOFs. Given the vast library of candidate nodes and linkers, the number of potentially synthetically accessible MOFs is enormous. Nevertheless, a powerful complementary approach to obtain specific structures with desired chemical functionality is to modify known MOFs after synthesis. This approach is particularly useful when incorporation of particular chemical functionalities via direct synthesis is challenging or impossible. Here, the challenges may stem from limited stability or solubility of precursors, unwanted secondary reactivity of precursors, or incompatibility of functional groups with the conditions needed for direct synthesis. MOFs can be postsynthetically modified by replacing the metal nodes and/or organic linkers or via functionalization of the metal nodes and/or organic linkers.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Zirconium-Based Metal–Organic Frameworks as Reusable Antibacterial Peroxide Carriers for Protective Textiles

Countries around the world have sought efficient protective coverings, including masks, gowns, and fabrics, for air purification to protect people against infectious diseases. However, the demand for significant quantities of disposable protective textiles poses a global challenge, especially when the production of protective gear is suspended due to COVID-19 outbreaks in factories and along supply lines. Therefore, the development of reusable, self-decontaminating protective masks and coverings loaded with disinfectants, such as antibacterial peroxide species, presents an attractive strategy to fight against bacteria risks. In this work, we incorporated persulfate ions, which serve as stable active peroxide precursors, into two porous zirconium-based metal–organic frameworks (Zr-MOFs), enabling these materials to act as regenerable reservoirs for the slow release of biocidal hydrogen peroxide upon hydrolysis by contact with humid air. Single-crystal X-ray diffraction studies reveal the two different coordination motifs for the persulfate ions, which can either bridge between two adjacent nodes or coordinate to a single node depending on both the node connectivity and the distances between open metal sites. The active peroxide precursors within the porous Zr-MOF carriers are stable during storage and easily regenerated once consumed. Importantly, these persulfate-loaded Zr-MOFs can be integrated onto textiles using a facile aqueous in-situ growth procedure, and these composites demonstrate potent and reusable biocidal activity against both Gram-negative bacteria and Gram-positive bacteria. Altogether, this approach presents a viable strategy to develop robust protective textiles capable of rapidly deactivating pathogens.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Toward Design Rules of Metal–Organic Frameworks for Adsorption Cooling: Effect of Topology on the Ethanol Working Capacity

Using combined experimental and computational approaches, we studied the adsorption behavior of ethanol in a series of metal-organic frameworks (MOFs) with similar building blocks but different topologies and tested their performance as adsorption coolers. Here, we analyzed the relationship between the MOF structures and their ethanol working capacities under different working conditions. Molecular-level insights into the microscopic adsorption behavior were also gained from atomistic simulations. Based on the structure-property relationships that we found, we selected another MOF (MOF-525) for study, and our experiments and simulations both showed superior ethanol working capacity for this MOF, which verified our design rules.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Controlled Demolition and Reconstruction of Imidazolate and Carboxylate Metal–Organic Frameworks by Acid Gas Exposure and Linker Treatment

The metal-linker coordination bond in metal–organic frameworks (MOFs) can be unstable in humid and acid gas environments, leading to loss of crystallinity and porosity. This degradation is not necessarily irreversible; solvent-assisted crystal redemption (“SACRed”) has been shown to recover the physical and chemical properties of ZIF-8 exposed to humid SO 2 . This approach can also be useful in creating mixed-linker materials that might be challenging to produce via de novo synthesis. Here, we expand more generally the concept of controlled degradation of a MOF with acid gas, followed by treatment with a fresh linker solution, to the use of different template MOFs (ZIFs, UiO-66, and UiO-67) and acid gases (SO 2 and NO 2 in dry and humid conditions). Significant losses in porosity and crystallinity along with structural changes (acid gas-linker complexes and linker functionalizations) are observed in the acid gas-exposed MOF templates, and SACRed is shown to reconstruct these partially demolished MOFs with a high degree of structural recovery. Detailed structural and spectroscopic characterizations of the controlled degradation and subsequent recovery are presented and analyzed. Furthermore, these findings indicate the generality of controlled degradation and reconstruction as a means for linker replacement in a wider variety of MOFs and also create the potential for linker substitutions (with non-native linkers) to obtain new hybrid MOFs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Iodosylbenzene Coordination Chemistry Relevant to Metal–Organic Framework Catalysis

Hypervalent iodine compounds formally feature expanded valence shells at iodine. These reagents are broadly used in synthetic chemistry due to the ability to participate in well-defined oxidation-reduction processes and because the ligand-exchange chemistry intrinsic to the hypervalent center allows hypervalent iodine compounds to be applied to a broad array of oxidative substrate functionalization reactions. We have recently developed methods to generate these compounds from O 2 that are predicated on diverting reactive intermediates of aldehyde autoxidation towards the oxidation of aryl iodides. Coupling the aerobic oxidation of aryliodides with catalysts that effect C–H bond oxidation would provide a strategy to achieve aerobic C–H oxidation chemistry. In this Forum article we discuss the aspects of hypervalent iodine chemistry and bonding that render this class of reagents attractive lynchpins for aerobic oxidation chemistry. We then discuss the oxidation processes relevant to the aerobic preparation of 2-(tertbutylsulfonyl) iodosylbenzene, which is a popular hypervalent iodine reagent for use with porous metal-organic framework-based catalysts because it displays significantly enhanced solubility as compared with unsubstituted iodosylbenzene. We demonstrate that popular synthetic methods to this reagent often provide material that displays unpredictable disproportionation behavior due to the presence of trace impurities. We provide a revised synthetic route that avoids impurities common in the reported methods and provides access to material that displays predictable stability. Lastly, we describe the coordination chemistry of hypervalent iodine compounds with metal clusters relevant to MOF chemistry and discuss the potential implications of this coordination chemistry to catalysis in MOF scaffolds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Screening Diffusion of Small Molecules in Flexible Zeolitic Imidazolate Frameworks Using a DFT-Parameterized Force Field

Quantitatively modeling adsorbate diffusion through zeolitic imidazolate frameworks (ZIFs) must account for the inherent flexibility of these materials. Here, the lack of a transferable intramolecular ZIF force field (FF) for use in classical simulations has previously made an accurate simulation of adsorbate diffusion in many ZIFs impossible. We resolve this problem by introducing a density functional theory parameterized force field (FF) for ZIFs named the intraZIF-FF, which includes perturbations to the class I force fields previously used to model ZIFs. This FF outperforms ad hoc force fields at predicting ab initio relative energies and atomic forces taken from fully periodic ab initio molecular dynamics simulations of SALEM-2, ZIF-7, ZIF-8, and ZIF-90. We use the intraZIF-FF to predict the infinite dilution self-diffusion coefficients of 30 adsorbates with molecular diameters ranging from 2.66 to 7.0 Å in these 4 ZIFs. These results greatly increase the number of adsorbates for which accurate information about molecular diffusion in ZIFs is available.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Predicted Efficient Visible-Light Driven Water Splitting and Carbon Dioxide Reduction Using Photoredox-Active UiO-NDI Metal Organic Framework

The structural and electronic properties of metal–organic frameworks (MOFs) constructed from stable Zr(IV) oxide-based nodes and naphthalenediimide-based linkers (UiO(Zr)-NDI) can be tuned to make them useful for specific photoredox processes. The NDI linker presents outside, inside, and core positions where functionalization can influence its optical properties, and such substitution in combination with suitable optical band gaps and band edge positions in UiO(Zr)-NDI offers a platform for the design of efficient MOF-based photocatalysts for water splitting and CO 2 reduction. Here, the band gaps and edge positions remain similar for UiO nodes when Zr is substituted with Ti, Th, or Ce. However, in contrast to the case for Zr-, Ti-, and Th-based UiO-NDIs, where photoexcitation remains localized on the NDI linkers owing to the very high energies of unoccupied node-based bands, for UiO(Ce)-NDI, the availability of low-lying empty f orbitals in the metal node offers the potential for energy transfer and exciton migration, which could further boost photocatalytic performance by extending exciton lifetimes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Bimetallic Metal–Organic Framework Fe/Co-MIL-88(NH 2 ) Exhibiting High Peroxidase-like Activity and Its Application in Detection of Extracellular Vesicles

Metal–organic frameworks (MOFs) have many attractive features, including tunable composition, rigid structure, controllable pore size, and large specific surface area, and thus are highly applicable in molecular analysis. Depending on the MOF structure, a high number of un-saturated metal sites can be exposed to catalyze chemical reactions. In the present work, we report that by using both Co(II) and Fe(III) to prepare the MIL-88(NH 2 ) MOF, we can produce the bimetallic MOF that can catalyze the conversion of 3,3', 5,5"-tetramethylbenzidine (TMB) to a color product through reaction with H 2 O 2 at a higher reaction rate than the monometallic Fe-MIL-88(NH 2 ). The Michaelis constants (K m ) of the catalytic reaction for TMB and H 2 O 2 are 3-5 times smaller, and the catalytic constants (k cat ) are 5-10 times higher than those of the horse-radish peroxidase (HRP), supporting ultrahigh peroxidase-like activity. These values are also much more superior to those of the HRP-mimicking MOFs reported previously. Interestingly, the bimetallic MOF can be coupled with glucose oxidase (GOx) to trigger the cascade enzymatic reaction for highly sensitive detection of extracellular vesicles (EVs), a family of important biomarkers. Through conjugation to the aptamer that recognizes the marker protein on EV surface, the MOF can help isolate the EVs from biological matrices, which are subsequently labeled by GOx via antibody recognition. The cascade enzymatic reaction between MOF and GOx enables detection of EVs at a concentration as low as 7.8 × 10 4 particles/ml. Further, the assay can be applied to monitor EV secretion by cultured cells, and also can successfully detect the different EV quantities in the sera samples collected from cancer patients and healthy controls. Overall, we prove that the bimetallic Fe/Co-MIL-88(NH 2 ) MOF, with its high peroxidase-activity and high biocompatibility, is a valuable tool deployable in clinical assays to facility disease diagnosis and prognosis.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Catalytic Zirconium/Hafnium-Based Metal–Organic Frameworks

Metal–organic frameworks (MOFs) are highly versatile materials that find applications in several fields. Highly stable zirconium/hafnium-based MOFs were recently introduced and nowadays represent a rapidly growing family. Their unique and intriguing properties make them privileged materials and outstanding candidates in heterogeneous catalysis, finding use either as catalysts or catalyst supports. Various techniques have been developed to incorporate active species into Zr-MOFs, giving rise to catalysts that often demonstrate higher performances or unusual activity when compared with their homogeneous analogues. Catalytic functions are commonly incorporated at the zirconium-oxide node, at the linker, or encapsulated in the pores. Representative examples are discussed, and advantages in adopting Zr- and Hf-MOFs in catalytic applications are highlighted.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Energy Efficient Formaldehyde Synthesis by Direct Hydrogenation of Carbon Monoxide in Functionalized Metal–Organic Frameworks

Formaldehyde (CH 2 O) 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 CH 2 O followed by condensation of CH 2 O from a mixture of CO and H 2 , which are non-condensable 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. Here, we predict that the thermodynamics of CH 2 O 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 CH 2 O synthesis.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Phase Transitions in Metal–Organic Frameworks Directly Monitored through In Situ Variable Temperature Liquid-Cell Transmission Electron Microscopy and In Situ X-ray Diffraction

Zr 6 -based metal–organic frameworks (MOFs) with tetratopic organic linkers have been extensively investigated owing to their versatile structural tunability. While diverse topologies and polymorphism in the resulting MOFs are often encountered with tetratopic linkers and Zr 6 nodes, reports on phase transitions within these systems are rare. Thus, we have a limited understanding of polymorph transformations, hindering the rational development of pure phase materials. In this study, a phase transition from a microporous MOF, scu-NU-906, to a mesoporous MOF, csq-NU-1008, was discovered and monitored through in situ variable temperature liquid-cell transmission electron microscopy (VT-LCTEM), high-resolution transmission electron microscopy (HRTEM), and in situ variable temperature powder X-ray diffraction (VT-PXRD). Furthermore, it was found that the microporous- to-mesoporous transformation in the presence of formic acid occurs via a concomitant dissolution–reprecipitation process.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Origins of Acid-Gas Stability Behavior in Zeolitic Imidazolate Frameworks: The Unique High Stability of ZIF-71

Zeolitic imidazolate frameworks (ZIFs) are promising materials for industrial process separations, but recent literature reports have highlighted their vulnerability to acid gases (e.g., SO 2 , CO 2 , NO 2 , H 2 S), often present in practical applications. While previous work has documented the widely varying stability behavior of many ZIFs under varying (humid and dry) acid gas environments, efforts to explain or correlate these experimental observations via empirical descriptors have not succeeded. A key observation is that ZIF-71 (RHO topology) is an extraordinarily stable ZIF material, retaining both structure and porosity under prolonged humid SO 2 exposure whereas many other well-known ZIFs with different linkers and topologies (such as ZIF-8) were shown to degrade. Through a combination of hybrid quantum mechanics/molecular mechanics (QM/MM) based methods and statistical mechanical models, we successfully explain this important experimental observation via atomistic investigations of the reaction mechanism. Our holistic approach reveals an ~9 times lower average defect formation rate in ZIF-71 RHO compared to ZIF-8 SOD, leading to the conclusion that the observed experimental stability of this material rises from kinetic effects. Moreover, our analysis reveals that differing stability of the two materials is determined by the distributions of acid gas molecules, which is difficult to capture using empirical descriptors. Furthermore, our results suggest wider applicability of the present approach, toward identifying tuned functional groups and topologies that move the acid gas distributions away from more reactive sites and thus allow enhanced kinetic stability.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗