Transformation Of Metal-organic Frameworks Research Articles

Transformation of Metal-Organic Framework from Kinetic to Thermodynamic Product for Controlled Delivery of Vitamin C.

A biocompatible metal-organic framework (MOF), named HSTC-4, constructed using the flexible 4,4'-oxybis(benzoic acid) (OBA), was developed to enable efficient loading and controlled release of vitamin C (VC) through a combination of strategies involving ligand length, structure design, and metal selection. The kinetic product HSTC-4 demonstrates a propensity for transforming into the thermodynamically stable HSTC-5 under external stimuli, such as photoillumination and vacuum heating, as witnessed by single-crystal to single-crystal transformation. Density functional theory (DFT) calculations reveal that the VC guest molecules exhibit stronger binding affinity with HSTC-5 due to its narrower pores compared to HSTC-4, resulting in a slower release of VC from VC@HSTC-5. Furthermore, precise control over VC release can be achieved by introducing surface modifications involving SiO2 onto the structure of VC@HSCT-5, while simultaneously adjusting environmental factors such as pH and temperature conditions. Preliminary cell culture experiments and cytotoxicity assays highlight the biocompatibility of HSTC-5, suggesting that it is a promising platform for sustained drug delivery and diverse biomedical applications.

Universal Strategy for Metal-Organic Framework Growth: From Cascading-Functional Films to MOF-on-MOFs.

Transformation of metal-organic framework (MOF) particles into thin films is urgently needed for the persistent development of well-applicable devices, and recently emerging functional-integrated hybrid frameworks. Although some flexible polymers and exclusive modification approaches have been proposed, the additive-free and widely applicable strategy has not been reported, hampering the deep investigation of the structure-performance relationship. A universal strategy for the in situ growth of large-area and continuous MOF films with controllable microstructures is introduced, through the modification of multi-scale and multi-structure substrates with poly(4-vinylpyridine) as the anchor to capture metal ions via Coulomb attraction. Based on the clarified structure-adsorption-separation mechanisms, the customized devices fabricated by in situ growth can achieve highly selective adsorption and excellently synergetic separation of various industrially relevant isomers. In addition, this strategy is also feasible for the construction of MOF-on-MOFs with varied lattice parameters. This strategy is easy to implement and will be widely applicable to the surface growth of diverse MOFs on desired substrates, and provides a new concept for developing hybrid MOFs integrating with customized functionalities.

Single-Crystal-to-Single-Crystal Transformation of Two Copper(II) Metal-Organic Frameworks Modulated by Auxiliary Ligands.

The single-crystal-to-single-crystal (SCSC) transformations of metal-organic frameworks (MOFs) are fascinating because we can directly observe the change of the crystal structure during the transformation process. It also greatly helps to understand the delicate interaction between the guest molecules and the skeleton framework and therefore fosters a deep understanding of gas storage and separation within the frameworks. Herein, we report two novel MOFs, [Cu8(BCB)4(μ3-OH)2(μ3-O)(H2O)8(Py)5]·16DMF·52H2O (1) and [Cu3(BCB)2(Py)6]·DMF·11H2O (2) (Py = pyridine; DMF = N,N'-dimethylformamide), which were constructed through the self-assembly of Cu2+ and 4,4',4″-benzenetricarbonyltribenzoic acid (H3BCB) by a solvothermal reaction. Although the structure and coordination patterns of compound 1 are pretty different from those of 2, the two Cu-MOFs were prepared from identical ligands and similar reaction conditions. Interestingly, compound 1 will change to 2 wholly and gradually after the addition of a certain amount of Py with a small amount of dilute hydrochloric acid. This conversion represents a scarce example of SCSC transformation involving transition-metal-based MOFs. Moreover, with its microporous nature, compound 2 shows large carbon dioxide (CO2) uptake capability and good selectivity for CO2/N2 separation. Furthermore, both compounds 1 and 2 could be used as excellent heterogeneous catalysts toward the cyanosilylation reaction under solvent-free conditions.

Porous Oxyhydroxide Derived from Metal-Organic Frameworks as Efficient Triphosphatase-like Nanozyme for Chromium(III) Ion Colorimetric Sensing.

The dephosphorylation that involves the removal of a phosphate group from a substrate molecule plays a significant role in living organisms. An enzyme mimic (nanozyme) with phosphatase-like catalytic activity has recently received attention in terms of its capacity for dephosphorylation. In this study, three types of highly porous oxyhydroxide with remarkable triphosphatase-like catalytic activities, ZrOOH, GdOOH, and HfOOH, have been prepared through the transformation of metal-organic frameworks (MOFs) using a simple alkaline hydrolysis method. The triphosphatase mimetic activities of ZrOOH, GdOOH, and HfOOH were then thoroughly investigated and verified. In particular, an isotopic tracing experiment revealed that abundant surface hydroxyls could serve as nucleophilic agents to directly attack the electropositive phosphorus atom, causing the cleavage of the terminal phosphoester bonds of phosphoester substrate molecules. The kinetic analysis provided calculated values of Km of 105.7, 90.5, and 46.1 μM, while the Vmax values were 3.57, 4.76, and 2.74 × 10-8 M s-1 and Ea values were estimated to be 47.52, 41.15, and 52.79 kJ/mol for ZrOOH, GdOOH, and HfOOH, respectively. The chromium(III) ions acting as "poisoning" inhibitors efficiently downregulated the triphosphatase mimetic activity of GdOOH. On the basis of this effect, a colorimetric chromium(III) ion-sensing system was explored, which provided a relevant linear response range for the detection of chromium(III) ions of 5.0-200 μM and a low detection limit of 0.84 μM. This work not only shows the great potential of ZrOOH, GdOOH, and HfOOH as triphosphatase nanozymes but also deepens our understanding of the role of surface hydroxyls on phosphatase-mimicking nanozyme catalytic dephosphorization, which could be used in the rational design of phosphatase-mimicking nanozymes. Furthermore, the developed colorimetric sensing system could be applied to chromium(III) ion detection in biological systems.

A cationic thorium-organic framework with triple single-crystal-to-single-crystal transformation peculiarities for ultrasensitive anion recognition.

Single-crystal-to-single-crystal transformation of metal–organic frameworks has been met with great interest, as it allows for the creation of new materials in a stepwise manner and direct visualization of structural transitions when subjected to external stimuli. However, it remains a peculiarity among numerous metal–organic frameworks, particularly for the ones constructed from tetravalent metal cations. Herein, we present a cationic thorium–organic framework displaying unprecedented triple single-crystal-to-single-crystal transformations in organic solvents, water, and NaIO3 solution. Notably, both the interpenetration conversion and topological change driven by the SC–SC transformation have remained elusive for thorium–organic frameworks. Moreover, the single-crystal-to-single-crystal transition in NaIO3 solution can efficiently and selectively turn the ligand-based emission off, leading to the lowest limit of detection (0.107 μg kg−1) of iodate, one of the primary species of long-lived fission product 129I in aqueous medium, among all luminescent sensors.

Ru-zirconia catalyst derived from MIL140C for carbon dioxide conversion to methane

A novel material, designated Ru/ZrO2@C(MIL), was prepared by thermal transformation of metal organic framework (MOF), MIL-140C-10, in which 10 % of the conventional biphenyl-dicarboxylate linkers had been substituted with bipyridyl-dicarboxylate linkers, thereby providing sites for Ru coordination with the framework. This MOF precursor was compositionally and morphologically transformed when heated, at 500 °C, in a mixture of H2 and CO2 (3:1). The transformation afforded a high surface area product (114 m2/g) with exceptional stability and high Ru metal dispersion which was very effective as catalyst for the hydrogenation of CO2 to CH4, giving a CH4 production of 53 mol/g Ru/h (at 350 °C, 40 bar and WHSV 344 L/h/g cat.). TEM results show that the active form of the catalyst was a partially degraded (‘unzipped’) MOF structure where Ru° and ZrO2 nanoparticles (2−5 and 10−20 nm diameter, respectively) were dispersed upon carbonaceous ribbons.

A straightforward strategy to synthesize supramolecular amorphous zirconium metal-organic gel for efficient Pb(II) removal

The transformation of metal-organic frameworks (MOFs) to metal-organic gels (MOGs) is an attractive but challenging issue because they are generally regarded as the opposite, with the former being hard and the latter soft. Herein, a straightforward strategy was developed to synthesize amorphous Zr-MOG-12 by gelatinization of UiO-66-NH2 (i.e. Zr-MOF) via a facile standing time-controlled crystallization method. The precursor ZrCl4 obtains oxide and hydroxide bridges after standing at room temperature, which promotes the formation of [Zr6O4(OH)4]12+ clusters and induces rapid and excessive nucleation rate, and further leads to the coordination perturbation of UiO-66-NH2 nanoparticles to achieve Zr-MOG-12. The as-prepared Zr-MOG-12 integrates the more hierarchical porous structure of gel-based soft materials and the amorphous structure of lower-coordinated active sites, which exhibits superb adsorption capacity for Pb(II) with excellent selectivity and reusability, indicating that Zr-MOG-12 is more promising to removal Pb(II) in practical water treatment. In addition, the transformation of amorphous Zr-MOG-12 to highly crystaline Zr-MOF’ has been achieved by the solvothermal reorganization using glacial acetic acid as the crystallization promoter. The novel methods proposed in this study successfully link crystalline MOF with amorphous MOG, providing new opportunities for facile preparation and transformation of MOFs and MOGs.

Electrochemical Transformation of Metal Organic Framework into Ultrathin Metal Hydroxide-(oxy)hydroxide Nanosheets for Alkaline Water Oxidation

Electrochemical water oxidation requires highly active electrocatalyst system with improved catalytic activity, high mechanical stability and strong catalyst-support interaction. In this respect, a...

Highly efficient multi-metal catalysts for carbon dioxide reduction prepared from atomically sequenced metal organic frameworks

The precise control on the combination of multiple metal atoms in the structure of metal-organic frameworks (MOFs) endowed by reticular chemistry, allows the obtaining of materials with compositions that are programmed for achieving enhanced reactivity. The present work illustrates how through the transformation of MOFs with desired arrangements of metal cations, multi-metal spinel oxides with precise compositions can be obtained, and used as catalyst precursor for the reverse water-gas shift reaction. The differences in the spinel initial composition and structure, determined by neutron powder diffraction, influence the overall catalytic activity with changes in the process of in situ formation of active, metal-oxide supported metal nanoparticles, which have been monitored and characterized with in situ X-ray diffraction and photoelectron spectroscopy studies.

Microwave induced transformation of metal organic frameworks into defect rich carbon nanofibers

We report a fast and facile microwave synthesis of defect rich, nitrogen doped carbon nanofibers from novel MOF precursors.

Transformation of Metal-Organic Frameworks into Stable Organic Frameworks with Inherited Skeletons and Catalytic Properties.

Metal-organic frameworks (MOFs) are an emerging class of porous materials with attractive properties, however, their practical applications are heavily hindered by their fragile nature. We report herein an effective strategy to transform fragile coordination bonds in MOFs into stable covalent organic bonds under mild annealing decarboxylative coupling reaction conditions, which results in highly stable organic framework materials. This strategy successfully endows intrinsic framework skeletons, porosity and properties of the parent MOFs in the daughter organic framework materials, which exhibit excellent chemical stability under harsh catalytic conditions. Therefore, this work opens a new avenue to synthesize stable organic framework materials derived from MOFs for applications in different fields.

Influence of temperature on metal-organic frameworks

Abstract Reaction temperature is one of the key parameters in the synthesis of metal-organic frameworks (MOFs). Though there is no convergence with regard to the various experimental parameters, reaction temperature has been found to have remarkable influence on the formation and structure of MOFs, especially toward the control of topology and dimensionality of the MOF structures. Theoretically, the reaction temperature affects directly the reaction energy barrier in reaction thermodynamics and the reaction rate in the reaction kinetics. This review aims to show the influence of reaction temperature on crystal growth/assembly, structural modulation and transformation of MOFs, and to provide primary information and insights into the design and assembly of desired MOFs.