Four novel 3D RE-MOFs based on maleic hydrazide: Syntheses, structural diversity, efficient electromagnetic wave absorption and antibacterial activity properties

Recent Progress and Prospect of Metal-Organic Framework-Based Nanozymes in Biomedical Application

A nanozyme is a nanoscale material having enzyme-like properties. It exhibits several superior properties, including low preparation cost, robust catalytic activity, and long-term storage at ambient temperatures. Moreover, high stability enables repetitive use in multiple catalytic reactions. Hence, it is considered a potential replacement for natural enzymes. Enormous research interest in nanozymes in the past two decades has made it imperative to look for better enzyme-mimicking materials for biomedical applications. Given this, research on metal-organic frameworks (MOFs) as a potential nanozyme material has gained momentum. MOFs are advanced hybrid materials made of inorganic metal ions and organic ligands. Their distinct composition, adaptable pore size, structural diversity, and ease in the tunability of physicochemical properties enable MOFs to mimic enzyme-like activities and act as promising nanozyme candidates. This review aims to discuss recent advances in the development of MOF-based nanozymes (MOF-NZs) and highlight their applications in the field of biomedicine. Firstly, different enzyme-mimetic activities exhibited by MOFs are discussed, and insights are given into various strategies to achieve them. Modification and functionalization strategies are deliberated to obtain MOF-NZs with enhanced catalytic activity. Subsequently, applications of MOF-NZs in the biosensing and therapeutics domain are discussed. Finally, the review is concluded by giving insights into the challenges encountered with MOF-NZs and possible directions to overcome them in the future. With this review, we aim to encourage consolidated efforts across enzyme engineering, nanotechnology, materials science, and biomedicine disciplines to inspire exciting innovations in this emerging yet promising field.

Texture Regulation of Metal-Organic Frameworks, Microwave Absorption Mechanism-Oriented Structural Optimization and Design Perspectives

Texture regulation of metal-organic frameworks (MOFs) is essential for controlling their electromagnetic wave (EMW) absorption properties. This review systematically summarizes the recent advancements in texture regulation strategies for MOFs, including etching and exchange of central ions, etching and exchange of ligands, chemically induced self-assembly, and MOF-on-MOF heterostructure design. Additionally, the EMW absorption mechanisms in approaches based on structure-function dependencies, including nano-micro topological engineering, defect engineering, interface engineering, and hybrid engineering, are comprehensively explored. Finally, current challenges and future research orientation are proposed. This review aims to provide new perspectives for designing MOF-derived EMW-absorption materials to achieve essential breakthroughs in mechanistic investigations in this promising field.

Metal organic framework-based antibacterial agents and their underlying mechanisms

Bacteria, as the most abundant living organisms, have always been a threat to human life until the development of antibiotics. However, with the wide use of antibiotics over a long time, bacteria have gradually gained tolerance to antibiotics, further aggravating threat to human beings and environmental safety significantly. In recent decades, new bacteria-killing methods based on metal ions, hyperthermia, free radicals, physical pricks, and the coordination of several multi-mechanisms have attracted increasing attention. Consequently, multiple types of new antibacterial agents have been developed. Among them, metal organic frameworks (MOFs) appear to play an increasingly important role. The unique characteristics of MOFs make them suitable multiple-functional platforms. By selecting the appropriate metastable coordination bonds, MOFs can act as reservoirs and release antibacterial metal ions or organic linkers; by constructing a porous structure, MOFs can act as carriers for multiple types of agents and achieve slow and sustained release; and by designing their composition and the pore structure precisely, MOFs can be endowed with properties to produce heat and free radicals under stimulation. Importantly, in combination with other materials, MOFs can act as a platform to kill bacteria effectively through the synergistic effect of multiple types of mechanisms. In this review, we focus on the recent development of MOF-based antibacterial agents, which are classified according to their antibacterial mechanisms.

A Review on Metal-Organic Framework-Derived Porous Carbon-Based Novel Microwave Absorption Materials

The development of microwave absorption materials (MAMs) is a considerable important topic because our living space is crowed with electromagnetic wave which threatens human's health. And MAMs are also used in radar stealth for protecting the weapons from being detected. Many nanomaterials were studied as MAMs, but not all of them have the satisfactory performance. Recently, metal-organic frameworks (MOFs) have attracted tremendous attention owing to their tunable chemical structures, diverse properties, large specific surface area and uniform pore distribution. MOF can transform to porous carbon (PC) which is decorated with metal species at appropriate pyrolysis temperature. However, the loss mechanism of pure MOF-derived PC is often relatively simple. In order to further improve the MA performance, the MOFs coupled with other loss materials are a widely studied method. In this review, we summarize the theories of MA, the progress of different MOF-derived PC‑based MAMs, tunable chemical structures incorporated with dielectric loss or magnetic loss materials. The different MA performance and mechanisms are discussed in detail. Finally, the shortcomings, challenges and perspectives of MOF-derived PC‑based MAMs are also presented. We hope this review could provide a new insight to design and fabricate MOF-derived PC-based MAMs with better fundamental understanding and practical application.

Recent progress of MOF-derived porous carbon materials for microwave absorption

Microwave absorbing materials (MAM) have attracted considerable attention over the years in stealth and information technologies. Metal–organic framework (MOF) with a unique microstructure and electronic state has become an attractive focus as self-sacrificing precursors of microwave absorbers. The MOF-derived porous carbon (PC) materials exhibit a high absorbing performance due to the stable three-dimensional structure and homogeneous distribution of metal particles. MOF-derived PC materials are promising for ideal MAM via tuning of the structure and composition, resulting in appropriate impedance matching and the synergistic effect between magnetic and dielectric loss. In this review, the MOF-derived PC materials and their basic absorption mechanisms (dielectric loss, magnetic loss and impedance matching) are introduced, as well as the characters of various MOF-derived PC materials. In addition, this review provides a comprehensive introduction and tabulates the recent progress based on the classification of the MOF-derived metallic state, such as pure PC (without reduced metals), mono-metal/PC, multi-metal/PC, metal oxides/PC and other derived PC composites. Finally, the challenges faced by MOF-derived PC materials are overviewed, and their further development is mentioned.

MOF-derived PC materials with unique characteristic have been widely concerned as microwave absorbers over the years.

Enhanced Microwave Absorption and Electromagnetic Properties of Si-Modified rGO@Fe3O4/PVDF-co-HFP Composites

Graphene has been regarded as one of the most promising two-dimensional nanomaterials. Even so, graphene was still faced with several key issues such as impedance mismatching and narrow bandwidth, which have hindered the practical applications of graphene-based nanocomposites in the field of microwave absorption materials. Herein, a series of Si-modified rGO@Fe3O4 composites were investigated and fabricated by a simple method. On one hand, the degree of defects in graphene carbon could be tuned by different silane coupling reagents, which were beneficial to enhancing the dielectric loss. On the other hand, the spherical Fe3O4 nanoparticles provided the magnetic loss resonance, which contributed to controlling the impedance matching. Subsequently, the electromagnetic absorption (EMA) properties of Si-modified rGO@Fe3O4 composites with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) were investigated in this work. As a result, the Si(2)-rGO@Fe3O4/PVDF-co-HFP composite exhibited the excellent EMA performance in the range of 2-18 GHz. The maximum reflection loss (RLmax) reached -32.1 dB at 3.68 GHz at the thickness of 7 mm and the effective absorption frequency bandwidth for reflection loss (RL) below -10 dB was 4.8 GHz at the thickness of 2 mm. Furthermore, the enhanced absorption mechanism revealed that the high-efficiency absorption performance of Si(2)-rGO@Fe3O4/PVDF-co-HFP composite was attributed to the interference absorption (quarter-wave matching model) and the synergistic effects between Si(2)-rGO@Fe3O4 and PVDF-co-HFP. This work provides a potential strategy for the fabrication of the high-performance EMA materials.