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Results for “two-dimensional metal-organic framework”

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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

A p -orbital honeycomb-Kagome lattice realized in a two-dimensional metal-organic framework

The experimental realization of p-orbital systems is desirable because p-orbital lattices have been proposed theoretically to host strongly correlated electrons that exhibit exotic quantum phases. Here, we synthesize a two-dimensional Fe-coordinated bimolecular metal-organic framework which constitutes a honeycomb lattice of 1,4,5,8,9,12-hexaazatriphenylene molecules and a Kagome lattice of 5,15-di(4-pyridyl)-10,20-diphenylporphyrin molecules on a Au(111) substrate. Density-functional theory calculations show that the framework features multiple well-separated spin-polarized Kagome bands, namely Dirac cone bands and Chern flat bands, near the Fermi level. Using tight-binding modelling, we reveal that these bands are originated from two effects: the low-lying molecular orbitals that exhibit p-orbital characteristics and the honeycomb-Kagome lattice. This study demonstrates that p-orbital Kagome bands can be realized in metal-organic frameworks by using molecules with molecular orbitals of p-orbital like symmetry.

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

Multifunctional two-dimensional metal-organic frameworks for radionuclide sequestration and detection

Two lanthanide containing porous coordination polymers, [Ln2(bpdc)6(phen)2] · nH2O (1) and [Ln2(bpdc)6(terpy)2] · 3H2O (2) (Ln = either Pr, Nd or Sm-Dy); bpdc: 2,2'-bipyridine-5,5'-dicarboxylic acid, phen: 1,10-phenanthroline, and terpy: 2,2':6',2''-terpyridine, have been hydrothermally synthesized and structurally characterized by powder and single crystal X-ray diffraction. The crystallographic analyses reveal compounds 1 and 2 feature Ln3+ containing dimeric nodes that form a porous two-dimensional (2D) and non-porous three-dimensional (3D) framework, respectively. Each material is stable in aqueous media between pH 3-10 and exhibits modest thermal stability to ~400ºC. Notably, a portion of the phen and bpdc ligands in 1 can be removed thermally, without compromising the crystal structure, causing the surface area and pore volume to increase. The optical properties of 1 and 2 with Gd3+, Sm3+, Tb3+, and Eu3+ were explored in the solid-state using absorbance, fluorescence, and lifetime spectroscopies. The analyses reveal a complex blend of metal and ligand emission in the materials containing Sm3+ and Tb3+, while those featuring Eu3+ are dominated by intense metal-based emission. Compound 1 with Eu3+ displayed promise for the capture and detection of the uranyl cation, (UO2)2+, from aqueous media. In short, uranyl capture was observed at pH 4 and the adsorption thereof was detectable via vibrational and fluorescence spectroscopies and colorimetrically as the off-white color of 1 turned yellow with uptake. Finally, both 1 and 2 with Eu3+ produce bright red emission upon irradiation with Cu ka X-ray radiation (8.04 keV) and are candidate materials for applications in solid-state scintillation.

Surbella, Robert G.↗
DOE OSTI2023

Magnetic order in the two-dimensional metal-organic framework manganese pyrazinecarboxylate with Mn-Mn dimers

The magnetic properties of [Mn(pyrazinecarboxylate) 2 ] n , empirical formula C 10 H 6 MnN 4 O 4 , are investigated through susceptibility, heat capacity, and neutron scattering measurements. The structure consists of Mn-Mn dimers linked on a distorted 2D hexagonal structure. The weak out-of-plane interactions create a quasi-2D magnetic material within the larger three-dimensional metal-organic framework structure. Here, we show that this material undergoes a two-stage magnetic transition, related to the low dimensionality of the Mn lattice. First, at 5 K, which is assigned to the initial development of short-range order in the 2D layers. This is followed by long-range order at 3.3 K. Applied field measurements reveal the potential to induce magnetic transitions in moderately small fields of ~2 T. Neutron powder diffraction enabled the determination of a unique magnetic space group P2 1 '/c (No. 14.77) at 1.5 K. This magnetic structure consists of antiferromagnetically coupled Mn-Mn dimers with spins principally along the out-of-plane $a$ axis.

36 MATERIALS SCIENCE↗
DOE OSTI2022

In situ anodic electrodeposition of two-dimensional conductive metal-organic framework@nickel foam for high-performance flexible supercapacitor

Owing to their large specific surface area and well-defined porosity, metal-organic frameworks (MOFs) have long been considered as promising materials for energy storage. Unfortunately, their straightforward utilization in supercapacitors was hindered for years due to poor conductivity until the emergence of 2D conductive MOF materials. To date, several 2D conductive MOF-based supercapacitors have been reported. Nevertheless, almost all these supercapacitors were fabricated from MOF powders through a slurry coating method or dense packing method, which negatively affected their capacitor performance. Herein, we have developed an anodic electrodeposition (AED) approach to fabricate a uniformly deposited 2D conducting MOF on nickel foam and use it directly as electrodes for supercapacitors without any additives. Finally, the superior performance of the 2D conducting MOF on nickel foam in both aqueous and organic electrolytes was then disclosed by a series of electrochemical measurements, demonstrating the significant advantages of the AED approach over traditional methods.

2D conductive metal-organic frameworks↗
DOE OSTI2026

A Quinoidal Two‐Dimensional Metal–Organic Framework for High‐Performance Micro‐Supercapacitors and Solid‐State Lithium Batteries

Two-dimensional (2D) metal-organic frameworks (MOFs) integrating redox-active linkers enable dense charge sites and open ion pathways for microscale energy storage. We report a quinoidal dicarboxylate ligand, AQM-H2L, derived from p-azaquinodimethane, forming crystalline frameworks with Cu2+ and Zn2+ nodes. The Cu-based MOF (AQM-AQM-H2L-Cu) exhibits layered sheets (>14 Å spacing) constructed from dinuclear Cu-carboxylate units and conjugated AQM linkers, which narrow the bandgap and introduce Cu2+/Cu+ pseudocapacitance. Exfoliated nanosheets (∼5 nm) retain crystallinity and excellent processability. Integrated into graphene films, they deliver areal and volumetric capacitances of 29.6 mF cm-2 and 18.1 F cm-3, achieving 2.6 mWh cm-3 energy density at 160 mW cm-3. As ionic fillers (1 wt%) in PEO solid polymer electrolytes, the nanosheets markedly enhance LiFePO4 cell performance, affording 169.8 mAh g-1 at 0.2 C and 93% retention after 400 cycles. This work establishes quinoidal linkers as a compact and robust design motif for ionically active 2D frameworks toward high-performance miniature and solid-state energy devices.

Chen, Ziman↗
DOE OSTI2023

Haldane topological spin-1 chains in a planar metal-organic framework

Haldane topological materials contain unique antiferromagnetic chains with symmetry-protected energy gaps. Such materials have potential applications in spintronics and future quantum computers. Haldane topological solids typically consist of spin-1 chains embedded in extended three-dimensional (3D) crystal structures. Here, we demonstrate that [Ni(μ-4,4'-bipyridine)(μ-oxalate)] n (NiBO) instead adopts a two-dimensional (2D) metal-organic framework (MOF) structure of Ni 2+ spin-1 chains weakly linked by 4,4'-bipyridine. NiBO exhibits Haldane topological properties with a gap between the singlet ground state and the triplet excited state. The latter is split by weak axial and rhombic anisotropies. Several experimental probes, including single-crystal X-ray diffraction, variable-temperature powder neutron diffraction (VT-PND), VT inelastic neutron scattering (VT-INS), DC susceptibility and specific heat measurements, high-field electron spin resonance, and unbiased quantum Monte Carlo simulations, provide a detailed, comprehensive characterization of NiBO. Vibrational (also known as phonon) properties of NiBO have been probed by INS and density-functional theory (DFT) calculations, indicating the absence of phonons near magnetic excitations in NiBO, suppressing spin-phonon coupling. The work here demonstrates that NiBO is indeed a rare 2D-MOF Haldane topological material.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Tuning Interface Electronic Properties via Chiral Two‐Dimensional Metal‐Organic Frameworks

Control over structural symmetries in nanomaterials offers a powerful approach to engineer electronic properties. For instance, breaking of mirror symmetries in two-dimensional (2D) materials with a hexagonal lattice can lead to nontrivial electronic topologies and correlated-electron phenomena. Yet, the impact of structural chirality on the electronic properties of 2D materials and interfaces remains underexplored. Here, how chiral phases of a 2D metal-organic framework (MOF) with a hexagonal lattice—consisting of hexaazatriphenylene molecules coordinated to Cu atoms—scatter, confine, and perturb the Shockley surface state (SS) electrons of an underlying Ag(111) substrate is investigated. Via low-temperature scanning tunneling microscopy and spectroscopy, noncontact atomic force microscopy, and numerical calculations based on an electronic plane-wave expansion method, modifications of the Ag(111) SS band structure are shown and quantified, including gap openings and lifts of band degeneracies, driven exclusively by the structural chirality of the 2D MOF phases. These findings highlight how structural symmetries, in particular chirality, affect electronic states at material interfaces, expanding on the toolkit for designing 2D materials with tailored electronic properties.

band structure engineering↗
DOE OSTI2022

Flexible 2D Boron Imidazolate Framework for Polysulfide Adsorption in Lithium–Sulfur Batteries

We report the "polysulfide shuttle," a process initiated by the dissolution of polysulfides, is recognized to be one of the major failure mechanisms of lithium-sulfur (Li-S) batteries. Much research effort has been dedicated toward efficient cathode additives and host materials to suppress the leaching of polysulfide species. Herein, we report a new 2D metal-organic framework constituted by a tritopic ligand, boron imidazolate ([BH(Im) 3 ] - , Im = imidazole), and Co 2+ ions for lithium polysulfide adsorption. The cobalt imidazolate framework (CoN 6 -BIF) contains octahedrally coordinated Co centers that form two-dimensional layers in the a,b plane. Composite cathodes containing CoN 6 -BIF exhibited high sulfur utilization and capacity retention, resulting in improved specific capacity and cycle life compared to sulfur/carbon controls. Density functional theory (DFT) calculations suggest that CoN 6 -BIF linkers are rotationally flexible, allowing the framework to accommodate polysulfide in the expanded pores. This unusual property of BIFs opens up new avenues for exploring flexible metal-organic frameworks (MOFs) and their applications to energy storage.

25 ENERGY STORAGE↗
DOE OSTI2020

Structural and electronic switching of a single crystal 2D metal-organic framework prepared by chemical vapor deposition

The incorporation of metal-organic frameworks into advanced devices remains a desirable goal, but progress is hindered by difficulties in preparing large crystalline metal-organic framework films with suitable electronic performance. We demonstrate the direct growth of large-area, high quality, and phase pure single metal-organic framework crystals through chemical vapor deposition of a dimolybdenum paddlewheel precursor, Mo 2 (INA) 4 . These exceptionally uniform, high quality crystals cover areas up to 8600 µm 2 and can be grown down to thicknesses of 30 nm. Moreover, scanning tunneling microscopy indicates that the Mo 2 (INA) 4 clusters assemble into a two-dimensional, single-layer framework. Devices are readily fabricated from single vapor-phase grown crystals and exhibit reversible 8-fold changes in conductivity upon illumination at modest powers. Moreover, we identify vapor-induced single crystal transitions that are reversible and responsible for 30-fold changes in conductivity of the metal-organic framework as monitored by in situ device measurements. Gas-phase methods, including chemical vapor deposition, show broader promise for the preparation of high-quality molecular frameworks, and may enable their integration into devices, including detectors and actuators.

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

Chemical Tuning Meets 2D Molecular Magnets

Two-dimensional (2D) magnets provoke a surge of interest in large anisotropy in reduced dimensions and are promising for next-generation information technology where dynamic magnetic tuning is essential. Until recently, the crucial metal-organic magnet Cr(pyz) 2 ∙xLiCl∙yTHF with considerable high coercivity and high-temperature magnetic order opens up a new platform to control magnetism in metal-organic materials at room temperature. Here we report an in-situ chemical tuning route to realize the controllable transformation of low-temperature magnetic order into room-temperature hard magnetism in Cr(pyz) 2 ∙xLiCl∙yTHF. The chemical tuning via electrochemical lithiation and solvation/desolvation exhibits continuously variable magnetic features from cryogenic magnetism to the room-temperature optimum performance of coercivity (H c ) of 8500 Oe and energy product of 0.6 MGOe. Such chemically flexible tunability of room-temperature magnetism is ascribed to the different degrees of lithiation and solvation that modify the stoichiometry and Cr-pyrazine coordination framework. Furthermore, the additively manufactured hybrid magnets show air stability and electromagnetic induction, providing potential applications. Our findings here suggest chemical tuning as a universal approach to control the anisotropy and magnetism of 2D hybrid magnets at room temperature, promising for data storage, magnetic refrigeration, and spintronics.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Raman scattering spectra of boron imidazolate frameworks containing different magnetic ions

We present a Raman scattering spectroscopic study of boron imidazolate metal-organic frameworks (BIFs) with three different magnetic metal ions and one non-magnetic in a wide frequency range from 25 to 1700 cm−1, which covers local vibrations of the imidazolate linkers as well as collective lattice vibrations. We show that the spectral region above 800 cm−1 belongs to the local vibrations of the linkers, which have the same frequencies for the studied BIFs without any dependence on the structure of the BIFs and are easily interpreted based on the spectra of imidazolate linkers. In contrast, collective lattice vibrations, observed below 100 cm−1, show a distinction between cage and two-dimensional BIFs structures, with a weak dependence on the metal node. We identify the range of vibrations around 200 cm−1, which are distinct for each metal-organic framework, depending on a metal node. Our work demonstrates the energy hierarchy in the vibrational response of BIFs.

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

Mixed matrix membranes for post-combustion carbon capture: From materials design to membrane engineering

Mixed matrix materials (MMMs) containing nanofillers dispersed in continuous polymer matrices have emerged as an exciting and versatile platform to develop membranes with superior CO 2 /N 2 separation performance for post-combustion carbon capture. Both polymers and nanofillers can be vertically designed and engineered to combine the advantages of excellent processability (derived from polymers) and strong size-sieving ability or/and significant permanent porosity (originated from nanofillers). However, the MMMs face major challenges, such as interfacial incompatibility, particle agglomeration, and poor thin-film formability. This report provides a comprehensive yet critical review of various polymers and nanofillers (such as metal-organic frameworks, covalent organic frameworks, and two-dimensional materials) with promising CO 2 /N 2 separation properties. We exhaustively describe strategies to improve interfacial compatibility, such as in situ syntheses of polymers and nanofillers and functionalization of both components to improve adhesion. Moreover, we highlight various approaches to engineer the MMMs into thin-film composite (TFC) membranes. The review reveals the structure/property relationship in these MMMs and outlines the challenges and opportunities to realize their potential for practical applications.

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

From n- to p-type material: Effect of Metal Ion on Charge Transport in Metal-Organic Materials

An intriguing new class of two-dimensional (2D) materials based on metal–organic frameworks (MOFs) has recently been developed that displays electrical conductivity, a rarity among these nanoporous materials. The emergence of conducting MOFs raises questions about their fundamental electronic properties, but few studies exist in this regard. Here, we present an integrated theory and experimental investigation to probe the effects of metal substitution on the charge transport properties of M-HITP, where M = Ni or Pt and HITP = 2,3,6,7,10,11-hexaiminotriphenylene. The results show that the identity of the M-HITP majority charge carrier can be changed without intentional introduction of electronically active dopants. We observe that the selection of the metal ion substantially affects charge transport. Using the known structure, Ni-HITP, we synthesized a new amorphous material, a-Pt-HITP, which although amorphous is nevertheless found to be porous upon desolvation. Importantly, this new material exhibits p-type charge transport behavior, unlike Ni-HITP, which displays n-type charge transport. These results demonstrate that both p- and n-type materials can be achieved within the same MOF topology through appropriate choice of the metal ion.

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

High-Resolution Imaging of Unstained Polymer Materials

Electron microscopy has played an important role in polymer characterization. Traditionally, electron diffraction is used to study crystalline polymers while transmission electron microscopy is used to study microphase separation in stained block copolymers and other multiphase systems. We describe developments that eliminate the barrier between these two approaches - it is now possible to image polymer crystals with atomic resolution. The focus of this Review is on high-resolution imaging (30 Å and smaller) of unstained polymers. Recent advances in hardware allow for capturing numerous (as many as 105) low-dose images from an unperturbed specimen; beam damage is a significant barrier to high-resolution electron microscopy of polymers. Machine-learning-based software is then used to sort and average the images to retrieve pristine structural information from a collection of noisy images. Acknowledging the heterogeneity in polymer samples prior to averaging is essential. Molecular conformations in a wide range of amphiphilic block copolymers, polymerized ionic liquids, and conjugated polymers can be gleaned from two-dimensional projections (2D), three-dimensional (3D) tomograms, and four-dimensional (4D) scanning transmission electron microscopy (STEM) data sets where 2D diffraction patterns are taken as a function of position. Some methods such as phase contrast STEM have been used to image closely related materials such as metal-organic frameworks but not polymers. With improvements in hardware and software, such methods may soon be applied to polymers. Our goal is to provide a comprehensive understanding of the strategies toward the high-resolution imaging of radiation sensitive polymer materials at different length scales.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Synthetic Access to a Framework-Stabilized and Fully Sulfided Analogue of an Anderson Polyoxometalate that is Catalytically Competent for Reduction Reactions

Polyoxometalates (POMs) featuring 7, 12, 18, or more redox-accessible transition metal ions are ubiquitous as selective catalysts, especially for oxidation reactions. The corresponding synthetic and catalytic chemistry of stable, discrete, capping-ligand-free polythiometalates (PTMs), which could be especially attractive for reduction reactions, is much less well developed. Among the challenges are the propensity of PTMs to agglomerate and the tendency for agglomeration to block reactant access of catalyst active sites. Nevertheless, the pervasive presence of transition metal sulfur clusters metalloenzymes or cofactors that catalyze reduction reactions and the justifiable proliferation of studies of two-dimensional (2D) metal-chalcogenides as reduction catalysts point to the promise of well-defined and controllable PTMs as reduction catalysts. Here, we report the fabrication of agglomeration-immune, reactant-accessible, capping-ligand-free Co II Mo 6 IV S 24 n– clusters as periodic arrays in a water-stable, hierarchically porous Zr-metal–organic framework (MOF; NU1K) by first installing a disk-like Anderson polyoxometalate, Co III Mo 6 VI O 24 m– , in size-matched micropores where the siting is established via difference electron density (DED) X-ray diffraction (XRD) experiments. Flowing H 2 S, while heating, reduces molybdenum(VI) ions to Mo(IV) and quantitatively replaces oxygen anions with sulfur anions (S 2– , HS – , S 2 2– ). DED maps show that MOF-templated POM-to-PTM conversion leaves clusters individually isolated in open-channel-connected micropores. Importantly, the structure of the immobilized cluster as determined, in part, by X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS) analysis, and pair distribution function (PDF) analysis of total X-ray scattering agrees well with the theoretically simulated structure. PTM@MOF displays both electrocatalytic and photocatalytic competency for hydrogen evolution. Nevertheless, the initially installed PTM appears to be a precatalyst, gaining competency only after the loss of ~3 to 6 sulfurs and exposure to hydride-forming metal ions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Tuning Two-Dimensional Phthalocyanine Dual Site Metal–Organic Framework Catalysts for the Oxygen Reduction Reaction

Metal-organic frameworks (MOFs) offer an interesting opportunity for catalysis, particularly for metal-nitrogen-carbon (M-N-C) motifs by providing an organized porous structural pattern and well-defined active sites for the oxygen reduction reaction (ORR), a key need for hydrogen fuel cells and related sustainable energy technologies. Here, in this work, we leverage electrochemical testing with computational models to study the electronic and structural properties in these systems and their relationship to ORR activity and stability based on dual transitional metal centers. These consists of two M1 metals with amine nodes coordinated to a single M2 metal with a phthalocyanine linker, where M1/M2 = Co, Ni, or Cu. Co-based metal centers, in particular Ni-Co, demonstrate the highest overall activity of all nine tested MOFs. Computationally, we identify the dominance of Co-sites, relative higher importance of the M2 site, and the role of layer M1 interactions on the ORR activity. Selectivity measurements indicate that M1 sites of MOFs, particularly Co, exhibits lowest (< 4%), and Ni demonstrates highest (>46%) two-electron selectivity, in good agreement with computational studies. Direct in-situ stability characterization, measuring dissolved metal ions, and calculations, using an alkaline stability metric, confirm that Co is the most stable metal in the MOF, while Cu exhibits notable instability at the M1. Overall, this study reveals how atomistic coupling of electronic and structural properties affects the ORR performance of dual site MOF catalysts and opens new avenues for tunable design and future development of these systems for practical electrochemical applications.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗