Recent Progress in Preparations and Multifunctional Applications Towards MOF/GDY Composites and Their Derivative Materials

This paper reviews the application of deep eutectic solvents (DESs) in the synthesis of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) as well as their prospects in the field of solid-phase extraction (SPE). Porous organic frameworks (POFs) have unique properties such as a large specific surface area, high porosity, and easy modification. Thus, these materials are widely applied in the fields of catalysis, adsorption, drug delivery, gas storage, and separation. POFs include MOFs, COFs, conjugated microporous polymers (CMPs), porous aromatic frameworks (PAFs), and covalent triazine frameworks (CTFs). MOFs are constructed from metal ions/clusters and organic ligands through coordination bonds and can be extended in two or three dimensions by repeated coordination with potential voids. COFs are formed from two monomers containing light elements (such as carbon, hydrogen, oxygen, nitrogen, boron, and other elements) via coordination bonds and have large two- or three-dimensional structures. However, conventional POF synthesis methods generally suffer from disadvantages such as long synthesis times, high temperature and pressure requirements, and the use of toxic and hazardous reaction solvents. DES consists of a hydrogen bond acceptor (HBA) and a hydrogen bond donor (HBD) bound by hydrogen-bonding interactions. It is a promising green solvent for material synthesis owing to its low vapor pressure, high stability, and ease of preparation. DES can be used to prepare MOFs and COFs and, in specific cases, acts as a structure-directing agent, which has an important impact on the structure and properties of the resulting frameworks. Using appropriate DES formulations, researchers can modulate the crystal structures, pore sizes, and surface properties of MOFs and COFs, resulting in materials with excellent characteristics. SPE is an analytical technique in which a sample solution is added to an SPE column; the sample solution is forced through the stationary phase, and the target compounds are collected for analysis by elution with an organic solvent. Therefore, suitable stationary-phase materials are critical for SPE. Owing to their large specific surface areas and abundant active sites, MOFs and COFs exhibit outstanding adsorption capacity and selectivity in SPE and can effectively enrich target analytes from complex samples. DES-based MOFs and COFs have shown potential use in a wide range of applications, such as in environmental analysis, food testing, and biological sample analysis. Although DES-based MOFs and COFs for SPE are still in the early stages of development, their properties such as efficient enrichment and high selectivity offer good prospects for practical applications. Future research should continue to explore DES-based synthesis methods in depth to prepare other MOFs and COFs with the desired properties and investigate their potential applications in various fields. These efforts are expected to apply these novel materials in commercialized solid-phase extraction methods, bringing new development opportunities in the field of analytical chemistry.

Graphdiyne (GDY) is a two-dimensional (2D) carbon allotrope consisting of sp2- and sp-hybridized carbon atoms. It and GDY-based materials have tremendous application potentials in the fields of catalysis, energy, sensor, electronics and optoelectronics because of their excellent chemical and physical properties. Thus, the explorations to synthesize high-quality GDY and GDY-based materials and to reveal the relationship between their structures and properties are of significance, in which their structural characterization and identification are a crucial step. In this review, we focus on advanced structural characterization techniques and results on GDY, GDY derivatives, GDY composites and doped GDY, including scanning electron microscope (SEM), transmission electron microscope (TEM), atomic force microscope (AFM), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV-vis) spectroscopy, nuclear magnetic resonance (NMR) spectroscopy, X-ray absorption spectroscopy (XAS), electron energy loss spectroscopy (EELS), and energy-dispersive X-ray spectroscopy (EDS). This review can provide a systemic understanding of the structural characterization and identification of GDY and GDY-based materials and help their development for high-performance applications.

Nanozymes, a class of synthetic nanomaterials possessing enzymatic catalytic properties, exhibit distinct advantages such as exceptional stability and cost-effectiveness. Among them, metal-organic framework (MOF)-based nanozymes have garnered significant attention due to their large specific surface area, tunable pore size and uniform structure. MOFs are porous crystalline materials bridged by inorganic metal ions/clusters and organic ligands, which hold immense potential in the fields of catalysis, sensors and drug carriers. The combination of MOFs with diverse nanomaterials gives rise to various types of MOF-based nanozyme, encompassing original MOFs, MOF-based nanozymes with chemical modifications, MOF-based composites and MOF derivatives. It is worth mentioning that the metal ions and organic ligands in MOFs are perfectly suited for designing oxidoreductase-like nanozymes. In this review, we intend to provide an overview of recent trends and progress in MOF-based nanozymes with oxidoreductase-like activity. Furthermore, the current obstacles and prospective outlook of MOF-based nanozymes are proposed and briefly discussed. This comprehensive analysis aims to facilitate progress in the development of novel MOF-based nanozymes with oxidoreductase-like activity while serving as a valuable reference for scientists engaged in related disciplines.

Graphdiyne for Electrochemical Energy Storage Devices

Metal–organic frameworks (MOFs), as a new type of nanomaterial, have been rapidly developed and widely applied in the environmental area. However, the algae removal efficiency of MOFs, the effect of metal ions and organic ligands contained in MOFs and the stability of MOFs in water need further study. Based on the characteristics of algae, five types of MOFs, which were Cu-MOF-74, Zn-MOF-74, ZIF-8, Ag/AgCl@ZIF-8 and MIL-125(Ti) were synthesized and characterized by X-ray diffractometer (XRD), field emission scanning electron microscope (FESEM), and X-ray photoelectron spectroscopy (XPS). The effect of MOFs on the growth of Microcystis aeruginosa was comparatively studied, and the inhibition mechanism of MOFs on algae as well as the stability of MOFs was explored. Results showed that all of the as-synthetic MOFs had superior stability in water, and the order of stability of MOFs followed the order MIL-125(Ti) > Cu-MOF-74 > Ag/AgCl@ZIF-8 > ZIF-8 > Zn-MOF-74. The types of metal ions and organic ligands doped in MOFs have grade affected the inhibitory efficiency on the algae: containing Cu2+ and Ag+ ions, MOFs had more significant inhibitory capacity to algae than those containing Zn2+ ions; meanwhile, compared with MOFs which are assembled with 2,5-dihydroxyterephthalic acid (DHTA) organic ligands, MOFs containing 2-methylimidazole (GC) organic contributed to the removal of algae significantly. The order of inhibitory effects of algae by five MOFs follows the order Cu-MOF-74 > Ag/AgCl@ZIF-8 > ZIF-8 > Zn-MOF-74 > MIL-125(Ti). The physiological characteristics of algal cells were changed after being treated with different concentrations of Cu-MOF-74. Once the concentration of Cu-MOF-74 reached 1 mg L−1, the algal cells began to be inhibited, the relative inhibition rate of algal cells at 120 h was over 400%, and the inhibition process fitted pseudo-second-order kinetic model well. The Cu2+ released by Cu-MOF-74 that the concentration higher than 1 mg L−1 would lead to the destruction of algae cell morphology and the loss of cell integrity, causing cell contents to be partially released into the water, promoting the accumulation and precipitation of algal cells which were destabilizing already to achieve the purpose of inhibition of algae. In summary, MOFs can be used to inhibit the growth of cyanobacteria and have a promising application prospect.

Metal-organic frameworks (MOFs) are formed by self-assembly of metal ions or clusters with organic ligands, and are widely used in the fields of catalysis, sensing, energy and biomedicine. Recently, biological composites based on MOFs have attracted increasing attention. MOFs can be used as a platform for encapsulating bioactive substances due to the advantages such as large pore capacity, large specific surface area and diverse structure composition. These features can protect bioactive substances from adverse conditions, e.g. high temperature, high pressure, and organic solvents, thus improving the anti-adversity of bioactive substances. This review summarizes the advances of using MOFs as protective coatings to improve the anti-adversity of different bioactive substances, and introduces the synthesis strategy of MOFs-based biological composites, with the aim to promote the practical application of MOFs-based biological composites.

Metal organic frameworks (MOFs) are attracting increasing attention in the field of pollution control due to their inherent characteristics, such as high porosity, large specific surface areas, and tunable structure and composition. Though more than 20000 kinds of MOFs structures have been reported so far, the majority of them are regular and composed of different kinds of building units. Defect engineering in MOFs is an exciting concept for tailoring material properties, which opens up novel opportunities in practical application. Defects are usually present in MOFs, which would alter the performance of MOFs by changing surface properties, pore structure, and the number of active sites. Since defects can enhance the performance of MOFs in adsorption and catalytic degradation of pollutants, various methods for designing and generating defects have been employed. Based on selected reports spanning the last decades, this review focuses on the most recent and significant developments in the classification of defects in MOFs and methods of introducing defects into MOFs. According to the composition of MOFs, defects can be divided into missing-linkers defect and missing-clusters defect. The main methods of introducing defects into MOFs include de novo synthesis and post-synthetic treatment. De novo synthesis method includes mixed linker approach, modulation approach and fast crystal growth approach. Post-synthetic treatment method involves acid/base treatment approach, harsh activation approach, solvent-assisted linker exchange and mechanical treatment approach. The use of defective MOFs as adsorbent and catalyst in pollutant removal is also highlighted. Because single physical-chemical characterization has its limitations, researchers adopt various techniques to characterize the existence and concentration of defects, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), etc. Reasonable defects could be controlled by adjusting the synthesis conditions in an attempt to obtain MOFs with excellent performance in adsorption and catalysis. At the hand of adsorption, the adsorption of pollutants in water and gases onto defective MOFs is mainly affected by pore distribution, specific surface area and surface charge. The introduction of missing-linkers defect or missing-clusters defect would make the regular pore structure into locally disordered structure, and create new micropores, mesopores even macropores. Thereby, the pore volume and specific surface area of MOFs are increased, and then enhancing the adsorption performance. In view of photocatalysis, introducing defects into photo-responsive MOFs can not only promote the transfer of photo-generated electrons, but also inhibit electron-hole recombination, and even optimize the energy band structure, which synergistically results in the improvement of photocatalytic performance. From the perspective of chemical catalysis, the pores formed by missing-linkers defect or missing-clusters defect in MOFs would expose the interior surface, which creates additional catalytic sites for pollutants reaching, and then enhances the catalysis performance of MOFs. In short, defective MOFs have a wide range of applications in the fields of adsorption and catalysis. After summarizing the recent progress of the field, the advantages and shortcomings of present defective MOFs in pollution control are presented. On the basis of this, it is apparent that further deepening the basic theoretical study of defective MOFs will be helpful for its wide applications. The defect engineering of MOFs is beneficial for further industrialization. Finally, some potential research topics in construction of defects in MOFs for environmental application have also been proposed in the review.

Hierarchical Pore Structures as Highways for Enzymes and Substrates

Metal-Organic Frameworks (MOFs), a novel class of porous extended crystalline structures, are favored in different fields of heterogeneous catalysis, CO2 separation and conversion, and energy storage (supercapacitors) due to their convenience of synthesis, structural tailor-ability, tunable pore size, high porosity, large specific surface area, devisable structures, and adjustable compositions. Nickel (Ni) is a ubiquitous element extensively applied in various fields of catalysis and energy storage due to its low cost, high abundance, thermal and chemical stability, and environmentally benign nature. Ni-based MOFs and their derivatives provide us with the opportunity to modify different properties of the Ni center to improve their potential as heterogeneous catalysts or energy storage materials. The recent achievements of Ni-MOFs and their derivatives as catalysts, membrane materials for CO2 separation and conversion, electrode materials and their respective performance have been discussed in this review.

Graphdiyne (GDY), a rising star of carbon allotropes, features a two-dimensional all-carbon network with the cohybridization of sp and sp2 carbon atoms and represents a trend and research direction in the development of carbon materials. The sp/sp2-hybridized structure of GDY endows it with numerous advantages and advancements in controlled growth, assembly, and performance tuning, and many studies have shown that GDY has been a key material for innovation and development in the fields of catalysis, energy, photoelectric conversion, mode conversion and transformation of electronic devices, detectors, life sciences, etc. In the past ten years, the fundamental scientific issues related to GDY have been understood, showing differences from traditional carbon materials in controlled growth, chemical and physical properties and mechanisms, and attracting extensive attention from many scientists. GDY has gradually developed into one of the frontiers of chemistry and materials science, and has entered the rapid development period, producing large numbers of fundamental and applied research achievements in the fundamental and applied research of carbon materials. For the exploration of frontier scientific concepts and phenomena in carbon science research, there is great potential to promote progress in the fields of energy, catalysis, intelligent information, optoelectronics, and life sciences. In this review, the growth, self-assembly method, aggregation structure, chemical modification, and doping of GDY are shown, and the theoretical calculation and simulation and fundamental properties of GDY are also fully introduced. In particular, the applications of GDY and its formed aggregates in catalysis, energy storage, photoelectronic, biomedicine, environmental science, life science, detectors, and material separation are introduced.

Solar energy, a clean and sustainable energy source, can be harvested and converted to solar fuel to meet the ever‐increasing energy demand. Integrating the photosensitizers and active catalytic sites into a single solid, metal–organic framework (MOF) with high void architectures and tunable chemical structures, is proposed as a promising platform for photocatalysis. However, compared with the traditional inorganic photocatalysts, the photocatalytic applications of MOFs are greatly hindered by its instability, especially the chemical instability. In this review, the background related to solar fuel production and MOFs are first discussed. Then, several strategies for designing stable MOFs are presented. Third, newly developed approaches for synthesizing highly efficient solar fuel production MOFs are summarized. Finally, the challenges and future perspectives using MOFs for solar fuel production are discussed. This review is expected to provide a deeper understanding of highly stable MOF design and new insights for the application of stable MOFs for solar fuel production.

Reticular chemistry for the rational design of mechanically robust mesoporous merged-net metal-organic frameworks

Metal-organic frameworks (MOFs) have been attracting tremendous attention owing to their great structural diversity and functional tunability. Despite numerous inherent merits and big progress in the fundamental research (synthesizing new compounds, discovering new structures, testing associated properties, etc.), poor chemical stability of most MOFs severely hinders their involvement in practical applications, which is the final goal for developing new materials. Therefore, constructing new stable MOFs or stabilizing extant labile MOFs is quite important. As with them, some "potential" applications would come true and a lot of new applications under harsh conditions can be explored. Efficient strategies are being pursued to solve the stability problem of MOFs and thereby achieve and expand their applications.In this Account, we summarize the research advance in the design and synthesis of chemically stable MOFs, particularly those stable in acidic, basic, and aqueous systems, as well as in the exploration of their applications in several expanding fields of environment, energy, and food safety, which have been dedicated in our lab over the past decade. The strategies for accessing stable MOFs can be classified into: (a) assembling high-valent metals (hard acid, such as Zr4+, Al3+) with carboxylate ligands (hard base) for acid-stable MOFs; (b) combining low-valent metals (soft acid, such as Co2+, Ni2+) and azolate ligands (soft base, such as pyrazolate) for alkali-resistant MOFs; (c) enhancing the connectivity of the building unit; (d) contracting or rigidifying the ligand; (e) increasing the hydrophobicity of the framework; and (f) substituting liable building units with stable ones (such as metal metathesis) to obtain robust MOFs. In addition, other factors, including the geometry and symmetry of building units, framework-framework interaction, and so forth, have also been taken into account in the design and synthesis of stable MOFs. On the basis of these approaches, the stability of resulting MOFs under corresponding conditions has been remarkably enhanced.With high chemical stability achieved, the MOFs have found many new and significant applications, aiming at addressing global challenges related to environmental pollution, energy shortage, and food safety.A series of stable MOFs have been constructed for detecting and eliminating contaminations. Various fluorescent MOFs were rationally customized to be powerful platforms for sensing hazardous targets in food and water, such as dioxins, antibiotics, veterinary drugs, and heavy metal ions. Some hydrophobic MOFs even showed effective and specific capture of low-concentration volatile organic compounds.Novel MOFs with record-breaking acid/base/nucleophilic regent resistance have expanded their application scope under harsh conditions. BUT-8(Cr)A, as the most acid-stable MOF yet, showed reserved structural integrity in concentrated H2SO4 and recorded high proton conductivity; the most alkali-resistant MOF, PCN-601, retained crystallinity even in boiling saturated NaOH aqueous solution, and such base-stable MOFs composed of non-noble metal clusters and poly pyrazolate ligands also demonstrated great potential in heterogeneous catalysis in alkaline/nucleophilic systems for the first time.It is believed that this Account will provide valuable references on stable MOFs' construction as well as application expansion toward harsh conditions, thereby being helpful to promote MOF materials to step from fundamental research to practical applications.

Coupling the Individual Motions of the Machine-like Components of Zirconium(IV) Organic Frameworks

Controlled Growth Interface of Charge Transfer Salts of Nickel-7,7,8,8-Tetracyanoquinodimethane on Surface of Graphdiyne