Hofmann-type Metal Organic Framework Research Articles

Fabrication of bimetallic Hofmann-type metal-organic Frameworks@Cellulose aerogels for efficient iodine capture

Abstract It is of great significance to capture radioiodine from nuclear-related activities. Herein, We fabricated two kinds of hybrid aerogels composed with bimetal Hofmann-type metal-organic frameworks (Co–Fe)II(pz)[NiII(CN)4] and cellulose aerogels by in-situ growth and doping method (named CoFe@CA-IS and CoFe@CA-D, respectively). The hybrid aerogels possessed excellent iodine adsorption performance. The addition of (Co–Fe)II(pz)[NiII(CN)4] increased the porosity of the hybrid aerogels. The porosities of CoFe@CA-IS and CoFe@CA-D were reached 86.7% and 87.8%, respectively, which are higher than pure cellulose aerogels. Furthermore, the doping method provide a significant improve of adsorption performance. The equilibrium adsorption capacity of CoFe@CA-D reached 457.99 mg g−1 and the equilibrium adsorption capacity of CoFe@CA-IS was 194.34 mg g−1. In addition, the hybrid aerogels showed excellent recycle ability, the equilibrium adsorption capacity of CoFe@CA-IS and CoFe@CA-D remained 81% and 91% after 5 cycles. The results suggested that this metal-organic framework@cellulose hybrid aerogel showed great potential in iodine treatment and could be applied in a wide field.

A Chemically Stable Hofmann-Type Metal-Organic Framework with Sandwich-Like Binding Sites for Benchmark Acetylene Capture.

The realization of porous materials for highly selective separation of acetylene (C2 H2 ) from various other gases (e.g., carbon dioxide and ethylene) by adsorption is of prime importance but challenging in the petrochemical industry. Herein, a chemically stable Hofmann-type metal-organic framework (MOF), Co(pyz)[Ni(CN)4 ] (termed as ZJU-74a), that features sandwich-like binding sites for benchmark C2 H2 capture and separation is reported. Gas sorption isotherms reveal that ZJU-74a exhibits by far the record C2 H2 capture capacity (49 cm3 g-1 at 0.01 bar and 296 K) and thus ultrahigh selectivity for C2 H2 /CO2 (36.5), C2 H2 /C2 H4 (24.2), and C2 H2 /CH4 (1312.9) separation at ambient conditions, respectively, of which the C2 H2 /CO2 selectivity is the highest among all the robust MOFs reported so far. Theoretical calculations indicate that the oppositely adjacent nickel(II) centers together with cyanide groups from different layers in ZJU-74a can construct a sandwich-type adsorption site to offer dually strong and cooperative interactions for the C2 H2 molecule, thus leading to its ultrahigh C2 H2 capture capacity and selectivities. The exceptional separation performance of ZJU-74a is confirmed by both simulated and experimental breakthrough curves for 50/50 (v/v) C2 H2 /CO2 , 1/99 C2 H2 /C2 H4 , and 50/50 C2 H2 /CH4 mixtures under ambient conditions.

Morphology regulation of metal–organic framework-derived nanostructures for efficient oxygen evolution electrocatalysis

A series of morphology-regulated oxygen-evolution electrocatalysts including nanosheets, nanoflowers, nanotubes and aggregations derived from Hofmann-type metal–organic frameworks have been developed and demonstrated efficient catalytic properties.

The substituent guest effect on four-step spin-crossover behavior

The fluoro substituent strategy on the guest in a three-dimensional Hofmann-type metal–organic framework is explored for four-step spin-crossover properties.

Asymmetric seven-/eight-step spin-crossover in a three-dimensional Hofmann-type metal–organic framework

An unprecedented hysteretic seven-/eight-step spin-crossover behavior is revealed. Most importantly, a molecular alloy based on a Hofmann-type framework is used as a strategy to explore multi-step spin-crossover materials for the first time.

Spin-Crossover Phenomenon in Microcrystals and Nanoparticles of a [Fe(2-mpz)2Ni(CN)4] Two-Dimensional Hofmann-Type Polymer: A Detailed Nano-Topographic Study.

The diamagnetic two-dimensional Hofmann-type metal-organic framework [ZnII(2-mpz)2Ni(CN)4] has been successfully synthesized along with its isostructural hysteretic spin-crossover FeII analogue in the form of both bulk microcrystalline powder and nanoparticles. Detailed atomic force microscopy topographic study revealed a nanogrowth relationship between the height and length of the nanoparticle.

Hierarchical bimetal embedded in carbon nanoflower electrocatalysts derived from metal-organic frameworks for efficient oxygen evolution reaction

Developing high-performance and cost-effective electrocatalysts for oxygen evolution reaction (OER) is crucial to renewable energy conversion and storage technologies. Herein, bimetallic N-doped carbon electrocatalysts with various morphologies are derived from Hofmann-type metal-organic frameworks by carbonization and oxidization. Notably, the flower-like nano-catalyst FeNi@OCNF exhibits core@shell structure, hierarchical pore network and large specific surface area (331.3 m2 g−1), leading to tunable electronic structure, efficient mass transfer as well as abundant exposed active sites. Moreover, the formative FeCx, NiO and FeNi bimetal mutually optimize electronic structure of graphitic layer, conducing to high property. FeNi@OCNF demonstrates an excellent OER performance with a low overpotential of 281 mV at 10 mA cm−2, signally outperforming the other catalyst CoNi@OCNP (373 mV) and commercial IrO2 (308 mV), and also owns long-term stability. The result may inspire more design of MOF-derived catalysts with multiscale structures and multi-components for various electrochemical energy conversion devices.

Hysteretic four-step spin-crossover in a 3D Hofmann-type metal-organic framework with aromatic guest.

A new Hofmann-type metal-organic framework with bent pillar ligand, [Fe(dpoda){Ag(CN)2}2] (dpoda = 2,5-di-(pyridyl)-1,3,4-oxadiazole), was synthesized. Four-, two- and one-step spin-crossover (SCO) properties were obtained by using different sizes of aromatic guests. Most importantly, hysteretic four-step SCO behaviour with the sequence of LS ↔ HS0.25LS0.75↔ HS0.5LS0.5↔ HS0.67LS0.33↔ HS is observed for the first time.

Guest-Switchable Multi-Step Spin Transitions in an Amine-Functionalized Metal-Organic Framework.

Materials with hysteretic multi-step spin-crossover (SCO) have potential application in high-order data storage. Here, an unprecedented hysteretic four-step SCO behavior with the sequence of LS↔HS0.25 LS0.75 ↔HS0.5 LS0.5 ↔ HS0.75 LS0.25 ↔HS is found in a three-dimensional (3D) Hofmann-type metal-organic framework (MOF), which is evidenced by magnetic, differential scanning calorimetry, and crystal data. Further experiments involving guest exchange leads to the first reversible modulation of four-, two-, and one-stepped SCO behaviors, which provides a new strategy for developing multi-step SCO materials.

Guest Induced Strong Cooperative One- and Two-Step Spin Transitions in Highly Porous Iron(II) Hofmann-Type Metal-Organic Frameworks.

The synthesis, crystal structure, magnetic, calorimetric, and Mössbauer studies of a series of new Hofmann-type spin crossover (SCO) metal-organic frameworks (MOFs) is reported. The new SCO-MOFs arise from self-assembly of FeII, bis(4-pyridyl)butadiyne (bpb), and [Ag(CN)2]- or [MII(CN)4]2- (MII = Ni, Pd). Interpenetration of four identical 3D networks with α-Po topology are obtained for {Fe(bpb)[AgI(CN)2]2} due to the length of the rod-like bismonodentate bpb and [Ag(CN)2]- ligands. The four networks are tightly packed and organized in two subsets orthogonally interpenetrated, while the networks in each subset display parallel interpenetration. This nonporous material undergoes a very incomplete SCO, which is rationalized from its intricate structure. In contrast, the single network Hofmann-type MOFs {Fe(bpb)[MII(CN)4]}·nGuest (MII = Ni, Pd) feature enhanced porosity and display complete one-step or two-step cooperative SCO behaviors when the pores are filled with two molecules of nitrobenzene or naphthalene that interact strongly with the pyridyl and cyano moieties of the bpb ligands via π-π stacking. The lack of these guest molecules favors stabilization of the high-spin state in the whole range of temperatures. However, application of hydrostatic pressure induces one- and two-step SCO.

Exploring the geometric, magnetic and electronic properties of Hofmann MOFs for drug delivery.

The geometric, magnetic, and electronic properties and the drug capturing abilities of Hofmann-type metal organic frameworks (MOFs) were examined using theoretical calculations. The detailed theoretical calculations predicted that the Hofmann sheet can have two different conformations, planar and twisted. The Ni-Co sheet was the most stable among the systems studied, whereas the Ni-Fe sheet was the least stable. All of the sheets were magnetic spin semiconductors, having Dirac-like and dispersionless bands, which give rise to a major spatial separation between the charge carriers upon excitation. After treatment with bidentate ligands, such as pyrazine and bipyridine, these sheets produce a three dimensional cage-like structure, which is efficient for capturing small drug molecules, e.g., fluorouracil and niacin. This study shows that the magnetic metal atom and ligand structure have a significant effect on the drug capturing abilities of these systems. Therefore, these systems may be a tunable host system for drug delivery.

Binding energy of gas molecule with two pyrazine molecules as organic linker in metal–organic framework: its theoretical evaluation and understanding of determining factors

We explored the interactions of gas molecules such as H2, CH4, C2H4, C2H6, CO2, and CS2 sandwiched by two pyrazine (Pz) molecules, which were employed as a model of organic linker in the Hofmann-type metal–organic framework (MOF). The MP2.5/aug-cc-pVTZ method was employed here, because this method presents almost the same binding energy as that calculated by the CCSD(T)/aug-cc-pVDZ with MP2.5-evaluated basis set extension effects to aug-cc-pVTZ basis set. The binding energy of the gas molecule increases in the order H2 < CH4 < CO2 < C2H4 ≈ C2H6 < CS2. The energy decomposition analysis of the interaction energy indicates that the electrostatic term presents the largest contribution to the interaction energy at the Hartree–Fock level. However, the dispersion interaction provides dominant contribution to the total binding energy at correlated level. We newly found a linear correlation between the z-component of polarizability of gas molecules and dispersion energy, where the z-axis was taken to be perpendicular to two Pz rings. These results are useful for understanding and predicting the binding energy of the gas molecule with the organic linkers of MOF.