Implementing Mesoporosity in Zeolitic Imidazolate Frameworks through Clip-Off Chemistry in Heterometallic Iron-Zinc ZIF-8

Stable Compressible Liquids Made of Hierarchical MOF Nanocrystals

Compressible liquids can be produced by dispersing nanoparticles containing hydrophobic pores as colloidal suspensions in water. Due to the water intrusion into the hydrophobic nanopores under pressure, these compressible liquids exhibit significantly greater compressibility than traditional liquids, lending them to energy storage and absorption applications. Metal-organic frameworks (MOFs) such as ZIF-8 have been proposed for this application due to their large porosity, but their physical and chemical stability in aqueous environments presents challenges, prone to hydrolysis or separation from the liquid phase. In this work, the stability concerns of ZIF-8 used for compressible liquids have been circumvented by producing nanoparticles of mesoporous ZIF-8 by a template-directed synthesis. The stability, compressibility, and intrusion kinetics were compared between ZIF-8 with and without mesopores. The mesoporous ZIF-8, uniquely containing hydrophobic micropores and hydrophilic mesopores, presents compressibility comparable to that of conventional ZIF-8 due to the hydrophobic micropores but has the added benefit of significantly increased physical and chemical stability due to the hydrophilic mesopores. The presence of mesopores slightly reduces the water intrusion pressure and accelerates the kinetics that can benefit the cyclic compressibility for vibrations or repeated impact applications as water molecules reversibly intrude and extrude the micropores. This work can inspire future endeavors on understanding and developing compressible and porous liquids with sufficient stability for practical uses.

Solvent-free approach for the synthesis of heterometallic Fe-Zn-ZIF glass via a melt-quenched process

We report the solvent-free synthesis of a crystalline heterometallic imidazolate derivative with formula [Fe1Zn2(im)6(Him)2], designated MUV-25, incorporating both iron and zinc. The structure imposes strict positional constraints on the metal centres due to the lattice containing distinct geometric coordination sites, tetrahedral and octahedral. As a consequence, each metal is exclusively directed to its specific coordination site, ensuring precise spatial organization within the lattice. Atom locations were meticulously monitored utilizing X-ray diffraction (single crystal and total scattering) and XAS techniques, demonstrating that the tetrahedral sites are occupied exclusively by zinc, and the octahedral sites are occupied by iron. This combination of metal centres results, upon heating, in a structural phase transformation to the zni topology at a very low temperature. Further heating causes the melting of the solid, yielding a heterometallic MOF-derived glass. The methodology lays the groundwork for tailoring crystalline structures to advance the development of novel materials capable of melting and forming glasses upon cooling.

Plasma-induced Fe-doped zeolitic imidazolate framework-8 derived P-Fe-N3C for enhanced phenol degradation

Plasma-synergistic catalysis is considered an effective method for degrading aromatic organic pollutants in water. However, the underlying synergistic catalytic mechanism between plasma and catalysts remains poorly understood. Here, we propose a plasma-metal organic frameworks (MOFs) synergistic strategy to investigate the mechanism of plasma-synergistic catalysts for phenol degradation. The results show that Fe-doped Zeolitic Imidazolate Framework-8 (Fex-ZIF8, x = 0, 0.1, 0.2, 0.4) undergoes the plasma-induced transformation into an Fe-N3C structure (P-Fe-N3C), leading to a 4.5-fold enhancement in the phenol degradation rate compared to only plasma discharge. Density functional theory (DFT) calculations indicate that the plasma-induced structural transformation of Fex-ZIF8 promotes the redistribution of point charges and space charges around the Fe center, thereby lowering the activation energy barrier in the rate-determining step (*C6H4(OH)2). These findings not only provide theoretical support for the degradation of water pollutants via plasma-synergistic catalysts but also offer a novel strategy for constructing MOFs-derived materials.

Intra-Mesopore Immunoassay Based on Core-Shell Structured Magnetic Hierarchically Porous ZIFs

It is crucial yet challenging to sensitively quantify low-abundance biomarkers in blood for early screening and diagnosis of various diseases. Herein, an analytical model of intra-mesopore immunoassay (IMIA) was proposed, which was competent to examine various biomarkers at the femtomolar level. The success is rooted in the design of an innovative superparamagnetic core-shell structure with Fe3O4 nanoparticles (NPs) at the core and hierarchically porous zeolitic imidazolate frameworks as a shell (Fe3O4@HPZIF-8), achieved through a soft-template directed self-assembly coupled with confinement growth mechanism. Such a unique configuration conceptualized IMIA where the HPZIF-8 shell served as a solid carrier to cover capture antibodies while the Fe3O4 core assisted its rapid separation. The large pore channels not only provided a stable microenvironment to maintain the recognition ability of captured antibodies but also enhanced their coating density, thus promoting the probability of capturing and binding target antigens, significantly improving immunoassay (IA) sensitivity. The practical clinic IA for cTnI (Cardiac Troponin I, biomarker of acute myocardial infarction (AMI)) in human serums was exemplified. The developed IMIA could accurately quantify slight fluctuations in cTnI concentrations in the serums of AMI patients at different stages after symptom onset with more than 100-fold enhancement of limit of detection (LOD) in comparison to conventional plate-based enzyme-linked immunosorbent assay (ELISA). Such high sensitivity of IMIA makes it a powerful tool for the accurate diagnosis of different diseases by altering the type of primary capture antibody.

Supramolecular Chemistry in Metal-Organic Framework Materials

Far from being simply rigid, benign architectures, metal-organic frameworks (MOFs) exhibit diverse interactions with their interior environment. From developing crystal sponges to studying reactions in framework materials, the role of both supramolecular chemistry and framework structure is evident. We explore the role of supramolecular chemistry in determining framework…guest interactions and attempts to understand the dynamic behavior in MOFs, including attempts to control pore behavior through the incorporation of mechanically-interlocked molecules. Appreciating and understanding the role of supramolecular interactions and dynamic behavior in metal-organic frameworks emerge as important directions for the field.

Hierarchically Micro- and Mesoporous Zeolitic Imidazolate Frameworks Through Selective Ligand Removal

A new method to engineer hierarchically porous zeolitic imidazolate frameworks (ZIFs) through selective ligand removal (SeLiRe) is presented. This innovative approach involves crafting mixed-ligand ZIFs (ML-ZIFs) with varying proportions of 2-aminobenzimidazole (NH2-bIm) and 2-methylimidazole (2-mIm), followed by controlled thermal treatments. This process creates a dual-pore system, incorporating both micropores and additional mesopores, suggesting selective cleavage of metal-ligand coordination bonds. Achieving this delicate balance requires adjustment of heating conditions for each mixed-ligand ratio, enabling the targeted removal of NH2-bIm from a variety of ML-ZIFs while preserving their inherent microporous framework. Furthermore, the distribution of the initial thermolabile ligand plays a pivotal role in determining the resulting mesopore architecture. The efficacy of this methodology is aptly demonstrated through the assessment of hierarchically porous ZIFs for their potential in adsorbing diverse organic dyes in aqueous environments. Particularly striking is the performance of the 10%NH2-ZIF-2 h, which showcases an astonishing 40-fold increase in methylene blue adsorption capacity compared to ZIF-8, attributed to larger pore volumes that accelerate the diffusion of dye molecules to adsorption sites. This versatile technique opens new avenues for designing micro/mesoporous ZIFs, particularly suited for liquid media scenarios necessitating efficient active site access and optimal diffusion kinetics, such as purification, catalysis, and sensing.

Lewis acidic Fe3+-driven catalytic active Ni3+ formation in Fe-free metal-organic framework for enhanced electrochemical glucose sensing

Manipulating metal valence states and porosity in the metal-organic framework (MOF) by alloying has been a unique tool for creating high-valent metal sites and pore environments in a structure that are inaccessible by other methods, favorable for accelerating the catalytic activity towards sensing applications. Herein, we report Fe3+-driven formation of catalytic active Ni3+ species in the amine-crafted benzene-dicarboxylate (BDC-NH2)-based MOF as a high-performance electrocatalyst for glucose sensing. This work took the benefit of different bonding stability between BDC-NH2 ligand, and Fe3+ and Ni2+ metal precursor ions in the heterometallic NixFe(1-x)-BDC-NH2 MOF. The FeCl3 that interacts weakly with ligand, oxidizes the Ni2+ precursor to Ni3+-based MOF owing to its Lewis acidic behavior and was subsequently removed from the structure supported by Ni atoms, during solvothermal synthesis. This enables to create mesopores within a highly stable Ni-MOF structure with optimal feed composition of Ni0.7Fe0.3-BDC-NH2. The Ni3+-based Ni0.7Fe0.3-BDC-NH2 demonstrates superior catalytic properties towards glucose sensing with a high sensitivity of 13,435 µA mM-1 cm-2 compared to the parent Ni2+-based Ni-BDC-NH2 (10897 μA mM-1cm-2), along with low detection limit (0.9 μM), short response time (≤5 s), excellent selectivity, and higher stability. This presented approach for fabricating high-valent nickel species, with a controlled quantity of Fe3+ integrated into the structure allowing pore engineering of MOFs, opens new avenues for designing high-performing MOF catalysts with porous framework for sensing applications.