Chiral Layered Magnetoelectrics
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75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Engineering topics
Chen, Zhijie
Publications and source records attributed to Chen, Zhijie.
Rational design of stable functional metal–organic frameworks
Functional porous metal–organic frameworks (MOFs) have been explored for a number of potential applications in catalysis, chemical sensing, water capture, gas storage, and separation. MOFs are among the most promising candidates to address challenges facing our society related to energy and environment, but the successful implementation of functional porous MOF materials are contingent on their stability; therefore, the rational design of stable MOFs plays an important role towards the development of functional porous MOFs. In this Focus article, we summarize progress in the rational design and synthesis of stable MOFs with controllable pores and functionalities. The implementation of reticular chemistry allows for the rational top-down design of stable porous MOFs with targeted topological networks and pore structures from the pre-selected building blocks. We highlight the reticular synthesis and applications of stable MOFs: (1) MOFs based on high valent metal ions (e.g., Al 3+ , Cr 3+ , Fe 3+ , Ti 4+ and Zr 4+ ) and carboxylate ligands; (2) MOFs based on low valent metal ions (e.g., Ni 2+ , Cu 2+ , and Zn 2+ ) and azolate linkers. We envision that the synthetic strategies, including modulated synthesis and post-synthetic modification, can potentially be extended to other more complex systems like metal-phosphonate framework materials.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Structure and thermodynamics of water adsorption in NU-1500-Cr
Abstract Metal-organic frameworks (MOFs) are a class of materials with diverse chemical and structural properties, and have been shown to effectively adsorb various types of guest molecules. The mechanism of water adsorption in NU-1500-Cr, a high-performance atmospheric water harvesting MOF, is investigated using a combination of molecular dynamics simulations and infrared spectroscopy. Calculations of thermodynamic and dynamical properties of water as a function of relative humidity allow for following the adsorption process from the initial hydration stage to complete filling of the MOF pores. Initial hydration begins at the water molecules that saturate the open Cr 3+ sites of the framework, which is then followed by the formation of water chains that extend along the channels connecting the hexagonal pores of the framework. Water present in these channels gradually coalesces and fills the hexagonal pores sequentially after the channels are completely hydrated. The development of hydrogen-bond networks inside the MOF pores as a function of relative humidity is characterized at the molecular level using experimental and computational infrared spectroscopy. A detailed analysis of the OH-stretch vibrational band indicates that the low-frequency tail stems from strongly polarized hydrogen-bonded water molecules, suggesting the presence of some structural disorder in the experimental samples. Strategies for designing efficient water harvesting MOFs are also proposed based on the mechanism of water adsorption in NU-1500-Cr.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Above-Room-Temperature Ferromagnetism in Thin van der Waals Flakes of Cobalt-Substituted Fe 5 GeTe 2
Two-dimensional (2D) magnetic van der Waals materials provide a powerful platform for studying the fundamental physics of low-dimensional magnetism, engineering novel magnetic phases, and enabling thin and highly tunable spintronic devices. To realize high-quality and practical devices for such applications, there is a critical need for robust 2D magnets with ordering temperatures above room temperature that can be created via exfoliation. Here, in this paper, the study of exfoliated flakes of cobalt-substituted Fe 5 GeTe 2 (CFGT) exhibiting magnetism above room temperature is reported. Via quantum magnetic imaging with nitrogen-vacancy centers in diamond, ferromagnetism at room temperature was observed in CFGT flakes as thin as 16 nm corresponding to 16 layers. This result expands the portfolio of thin room-temperature 2D magnet flakes exfoliated from robust single crystals that reach a thickness regime relevant to practical spintronic applications. The Curie temperature T c of CFGT ranges from 310 K in the thinnest flake studied to 328 K in the bulk. To investigate the prospect of high-temperature monolayer ferromagnetism, Monte Carlo calculations were performed, which predicted a high value of T c of ~270 K in CFGT monolayers. Pathways toward further enhancing monolayer T c are discussed. These results support CFGT as a promising platform for realizing high-quality room-temperature 2D magnet devices.
2D magnetism↗
Probing antiferromagnetic coupling in magnetic insulator/metal heterostructures
Using depth- and element-resolved characterization, we report insights into antiferromagnetic coupling in Y 3 Fe 5 O 12 /permalloy (YIG/Py) and Y 3 Fe 5 O 12 /Co (YIG/Co) thin-film heterostructures grown on Si/SiO 2 and Gd 3 Ga 5 O 12 substrates. We build on recent work demonstrating antiferromagnetic coupling in polycrystalline YIG/metallic-ferromagnetic systems by characterizing differences in the structural and magnetic properties which depend on the choice of ferromagnet (Py vs Co), seed layer (with and without Pt), and substrate (Si/SiO 2 vs Gd 3 Ga 5 O 12 ). These differences in the sample structure manifest as notable changes in interface coupling sign, magnetic reversal mechanisms, magnetic depth profiles, and domain structure. Through a combination of magnetometry, polarized neutron reflectometry, and x-ray photoemission electron microscopy, a comprehensive picture of the magnetic interactions is realized, with lateral- and depth resolution at submicrometer and nanometer scales, respectively. These results confirm that both Co and Py share a preference to align antiparallel to polycrystalline YIG grown on some substrates (Si/SiO 2 and Si/SiO 2 /Pt), while coupling ferromagnetically with highly oriented YIG on (111) Gd 3 Ga 5 O 12 and (110) Gd 3 Ga 5 O 12 /Pt substrates. The complex interplay among magnetic interactions at the YIG/ferromagnetic interface has important implications for spintronic and magnonic devices based on this platform.
Exchange interaction↗
Large magnetoelectric resistance in the topological Dirac semimetal α-Sn
The spin-momentum locking of surface states in topological materials can produce a resistance that scales linearly with magnetic and electric fields. Such a bilinear magnetoelectric resistance (BMER) effect offers a new approach for information reading and field sensing applications, but the effects demonstrated so far are too weak or for low temperatures. This article reports the first observation of BMER effects in topological Dirac semimetals; the BMER responses were measured at room temperature and were substantially stronger than those reported previously. The experiments used topological Dirac semimetal α-Sn thin films grown on silicon substrates. The films showed BMER responses that are 10 6 times larger than previously measured at room temperature and are also larger than those previously obtained at low temperatures. These results represent a major advance toward realistic BMER applications. Significantly, the data also yield the first characterization of three-dimensional Fermi-level spin texture of topological surface states in α-Sn.
36 MATERIALS SCIENCE↗
Heteroatom-Doped Porous Carbons as Effective Adsorbers for Toxic Industrial Gasses
Not provided.
Materials Science↗
Leveraging Nitrogen Linkages in the Formation of a Porous Thorium–Organic Nanotube Suitable for Iodine Capture
We report the synthesis, characterization, and iodine capture application of a novel thorium–organic nanotube, TSN-626, [Th 6 O 4 (OH) 4 (C 6 H 4 NO 2 ) 7 (CHO 2 ) 5 (H 2 O) 3 ]·3H 2 O. The classification as a metal–organic nanotube (MONT) distinguishes it as a rare and reduced dimensionality subset of metal–organic frameworks (MOFs); the structure is additionally hallmarked by low node connectivity. TSN-626 is composed of hexameric thorium secondary building units and mixed O/N-donor isonicotinate ligands that demonstrate selective ditopicity, yielding both terminating and bridging moieties. Because hard Lewis acid tetravalent metals have a propensity to bind with electron donors of rival hardness (e.g., carboxylate groups), such Th–N coordination in a MOF is uncommon. However, the formation of key structural Th–N bonds in TSN-626 cap some of the square antiprismatic metal centers, a position usually occupied by terminal water ligands. TSN-626 was characterized by using complementary analytical and computational techniques: X-ray diffraction, vibrational spectroscopy, N 2 physisorption isotherms, and density functional theory. TSN-626 satisfies design aspects for the chemisorption of iodine. The synergy between accessibility through pores, vacancies at the metal–oxo nodes, and pendent N-donor sites allowed a saturated iodine loading of 955 mg g –1 by vapor methods. Furthermore, the crystallization of TSN-626 diversifies actinide–MOF linker selection to include soft electron donors, and these Th–N linkages can be leveraged for the investigation of metal-to-ligand bonding and unconventional topological expressions.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
A Van der Waals Interface Hosting Two Groups of Magnetic Skyrmions
Multiple magnetic skyrmion phases add an additional degree of freedom for skyrmion-based ultrahigh-density spin memory devices. Extending the field to 2D van der Waals magnets is a rewarding challenge, where the realizable degree of freedoms (e.g., thickness, twist angle, and electrical gating) and high skyrmion density result in intriguing new properties and enhanced functionality. In this work, a van der Waals interface, formed by two 2D ferromagnets Cr 2 Ge 2 Te 6 and Fe 3 GeTe 2 with a Curie temperature of ≈65 and ≈205 K, respectively, hosting two groups of magnetic skyrmions, is reported. Two sets of topological Hall effect signals are observed below 6s0 K when Cr 2 Ge 2 Te 6 is magnetically ordered. These two groups of skyrmions are directly imaged using magnetic force microscopy, and supported by micromagnetic simulations. Interestingly, the magnetic skyrmions persist in the heterostructure with zero applied magnetic field. The results are promising for the realization of skyrmionic devices based on van der Waals heterostructures hosting multiple skyrmion phases.
2D magnetism↗
Porous materials for hydrogen storage
Hydrogen is a clean energy carrier and a promising candidate to realize carbon-neutral systems for a sustainable future because the combustion of hydrogen produces only water. The large-scale implementation of hydrogen, particularly in zero-emission hydrogen-powered fuel-cell automobiles, requires efficient hydrogen storage systems; however, the current on-board hydrogen storage technologies mainly rely on costly and potentially unsafe high-pressure compression strategies that reach pressures of up to 700 bar. Recently, solid-state porous materials, such as metal-organic frameworks, have emerged as sorbents that can conceivably store comparable amounts of hydrogen in a safer and more efficient manner relative to the current high-pressure storage technologies. Here this review summarizes the current progress on the development of state-of-the-art porous materials and their composites for hydrogen storage. We hope this work will inspire efforts toward creating next-generation hydrogen storage materials.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Reticular Chemistry for Highly Porous Metal–Organic Frameworks: The Chemistry and Applications
Current global crises related to clean energy and the environment entail the development of materials that are capable of addressing these challenges. Metal–organic frameworks (MOFs), a class of functional materials assembled from metal-containing nodes and organic ligands via coordination bonds, have been successfully developed for various applications, including catalysis, toxic chemical removal, and gas storage and separation, as a result of their highly tailorable nature and precisely engineered pore structures. In particular, the exceptionally high surface areas and porosities of MOFs are two of their most attractive characteristics and place them among the best porous materials for the storage of clean energy gases, such as hydrogen and methane. Reticular chemistry stands out as a prominent approach to the design of MOFs as this strategy allows for the rational top-down design of frameworks guided by topological nets to afford extended framework structures with precise architectural arrangements at the molecular level. Furthermore, bridging the gap between reticular chemistry design strategies and highly porous MOFs can facilitate the development of next-generation high-performance materials through state-of-the-art chemical design.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Investigating the Influence of Hexanuclear Clusters in Isostructural Metal–Organic Frameworks on Toxic Gas Adsorption
The efficient capture of toxic gases, such as ammonia (NH 3 ) and sulfur dioxide (SO 2 ), can protect the general population and mitigate widespread air pollution. Metal–organic frameworks (MOFs) comprise a tunable class of adsorbents with high surface areas that can meet this challenge by selectively capturing these gases at low concentrations. In this work, we explored how modifying the metal ions in the node of an isostructural MOF series from a transition metal to a lanthanide or actinide influences the electronic environment of the node-based active site. Next, we investigated the adsorption properties of each MOF toward the relatively basic NH 3 and relatively acidic SO 2 gases. Within the NU-907 family of MOFs, we found that Zr 6 -NU-907 exhibits the best uptake toward NH 3 at low pressures, while Th 6 -NU-907 demonstrates the best low-pressure performance for SO 2 adsorption. Here, tracking the infrared (IR) stretching frequency of the node-based μ 3 -OH groups provides insights into the electronegativity of the metal ion and suggests that the most electronegative metal ion (Zr) affords the node with the best NH 3 uptake at low pressures. In contrast, the Th 6 node contains additional coordinated water groups relative to the other M 6 nodes, which appears to yield the MOF with the greatest affinity for SO 2 uptake that occurs predominately through reversible physisorption interactions. Finally, in situ NH3 IR spectroscopic studies indicate that both NH 4 + and Lewis-bound NH 3 species form during adsorption. Combined, these results suggest that tuning the electronic properties and structure of the node-based active site in an MOF presents a viable strategy to change the affinity of an MOF toward toxic gases.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Are you using the right probe molecules for assessing the textural properties of metal–organic frameworks?
Textural properties—such as the surface area, pore size distribution, and pore volume—are at the forefront of characterization for porous materials. Therefore, it is essential to accurately and reproducibly report a material's textural properties as they could ultimately dictate its applicability. This work aims to provide insightful and comprehensive studies of textural properties for a set of metal–organic frameworks (MOFs), a class of porous materials, using various gases to equip researchers in the field with a helpful guide and reference. Here, we selected a series of nine MOFs with different surface areas, pore sizes, shapes, and chemical environments to represent a wide range of materials. We probed the textural properties of these MOFs using traditional and distinctive gases: N 2 , Kr and O 2 at 77 K, Ar at 87 K, and CO 2 at 195 and 273 K. With regard to surface area, we discuss the validity and challenges associated with the current BET method, the importance of utilizing the Rouquerol et al. consistency criteria to ensure accuracy and reproducibility, and the recommended gas probes for certain materials. For pore size distribution, we discuss the efficacy of each probe for determining the pore sizes within a porous material relative to the calculated distribution from its crystal structure, the limitations of current computational kernels used to calculate pore size distributions, and the need for advanced kernels to envelope the diversity of porous materials. Finally, for pore volume, we discuss the use of the Gurvich rule to obtain the total pore volume in comparison with calculated values from crystal structures and its consistency as a metric for porous materials. Ultimately, we hope that this article will aid researchers in characterizing the textural properties of porous materials and encourage the development of new kernels capable of encompassing the complexity of MOFs and other porous materials.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Active mechanisorption driven by pumping cassettes
Pumping macrocycles onto surfaces Numerous chemical processes, ranging from water purification to catalysis, involve sorption of small molecules onto surfaces. Typically, spontaneous attractive interactions favor the binding event. Feng et al . report a mechanisorption process that requires redox manipulations to pump macrocycles from bulk solution onto axles immobilized on a metal-organic framework. The resulting rotaxanes store energy through nonequilibrium charge concentration in their mechanical bonds. Ultimately, the technique could also prove useful for actively partitioning compounds with particular functionality between surface and bulk environments. —JSY
Science & Technology - Other Topics↗
The Molecular Path Approaching the Active Site in Catalytic Metal–Organic Frameworks
How molecules approach, bind at, and release from catalytic sites is key to heterogeneous catalysis, including for emerging metal-organic framework (MOF)-based catalysts. Here, we use in situ synchrotron X-ray scattering analysis to evaluate the dominant binding sites for reagent and product molecules in the vicinity of catalytic Ni-oxo clusters in NU-1000 with different surface functionalization under conditions approaching those used in catalysis. The locations of the reagent and product molecules within the pores can be linked to the activity for ethylene hydrogenation. For the most active catalyst, ethylene reagent molecules bind close to the catalytic clusters, but only at temperatures approaching experimentally observed onset of catalysis. The ethane product molecules favor a different binding location suggesting that the product is readily released from the active site. An unusual guest-dependence of the framework negative thermal expansion is documented. We hypothesize that reagent and product binding sites reflect the pathway through the MOF to the active site and can be used to identify key factors that impact the catalytic activity.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗