Hybrid Porous Crystalline Materials from Metal Organic Frameworks and Covalent Organic Frameworks

Structure-Controlled Interpenetrated MOF@COF via C-C Linkage for Enhanced Photocatalysis

Diversifying the connecting junctions will be feasible for the controllable collaboration of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) to rationally design multifunction-integrated heterostructures with enhanced performance, yet it is in the nascent stage. Herein, by intelligently exploiting the polymerization of vinyl group, C-C bond is innovatively introduced to construct the core-shell MOF@COF heterostructures with adjustable shell thickness and rare interpenetrated structure. The unique structure endows prepared C-C-linked MIL-68@COF-Vs with more superior visible-light harvesting and photogenerated carrier separation capability, leading to significantly higher photocatalytic activity and faster degradation rate than pristine MIL-68-C=Cs, COF-V, and imine-linked MIL-68-NH2@COF-V. Further, the customized MIL-68@COF-V is in situ grown as reusable films with dramatically boosted performance under ambient conditions, which realize the highly efficient degradation of tetracycline within 15 min (96.5 %), rhodamine 6G within 25 min (97.6 %), and phenol within 40 min (95.3 %) by solar drive. This work exhibits the distinctive advantages of C-C junction in the MOF@COF construction, and highlights the application prospect of rational-designed heterostructure in the treatment of persistent organic pollutants.

Covalent Organic Framework-Involved Sensors for Efficient Enrichment and Monitoring of Food Hazards: A Systematic Review

The food safety issues caused by environmental pollution have posed great risks to human health that cannot be ignored. Hence, the precise monitoring of hazard factors in food has emerged as a critical concern for the food safety sector. As a novel porous material, covalent organic frameworks (COFs) have garnered significant attention due to their large specific surface area, excellent thermal and chemical stability, modifiability, and abundant recognition sites. This makes it a potential solution for food safety issues. In this research, the synthesis and regulation strategies of COFs were reviewed. The roles of COFs in enriching and detecting food hazards were discussed comprehensively and extensively. Taking representative hazard factors in food as the research object, the expression forms and participation approaches of COFs were explored, along with the effectiveness of corresponding detection methods. Finally, the development directions of COFs in the future as well as the problems existing in practical applications were discussed, which was beneficial to promote the application of COFs in food safety and beyond.

Diagnosis and therapy of Alzheimer's disease: Light-driven heterogeneous redox processes

Light-driven heterogeneous processes are promising approaches for diagnosing and treating Alzheimer's disease (AD) by regulating its relevant biomolecules. The molecular understanding of the heterogeneous interface environment and its interaction with target biomolecules is important. This review critically appraises the advances in AD early diagnosis and therapy employing heterogeneous light-driven redox processes, encompassing photoelectrochemical (PEC) biosensing, photodynamic therapy, photothermal therapy, PEC therapy, and photoacoustic therapy. The design strategies for heterogeneous interfaces based on target biomolecules and applications are also compiled. Finally, the remaining challenges and future perspectives are discussed. The present review may promote the fundamental understanding of AD diagnosis and therapy and facilitate interdisciplinary studies at the junction of nanotechnology and bioscience.

Interconversion and functional composites of metal-organic frameworks and hydrogen-bonded organic frameworks

Metal-organic frameworks (MOFs), an emerging class of highly ordered crystalline porous materials, possess structural tunability, high specific surface area, well-defined pores, and diverse pore environments and morphologies, making them suitable for various potential applications. Moreover, hydrogen-bonded organic frameworks (HOFs), constructed from organic molecules with complementary hydrogen-bonding patterns, are rapidly evolving into a novel category of porous materials due to their facile mild preparation conditions, solution processability, easy regeneration capability, and excellent biocompatibility. These distinctive advantages have garnered significant attention across diverse fields. Considering the inherent binding affinity between MOFs and HOFs along with the fact that many MOF linkers can serve as building blocks for constructing HOFs, their combination holds promise in creating functional materials with enhanced performance. This feature paper provides an introduction to the interconversion between MOFs and HOFs followed by highlighting the emerging applications of MOF-HOF composites. Finally, we briefly discuss the current challenges associated with future perspectives on MOF-HOF composites.

Synthesis of Calix[4]arene-Based Porous Organic Cages and Their Gas Adsorption

Two crystalline large-sized porous organic cages (POCs) based on conical calix[4]arene (C4A) were designed and synthesized. The four-jaw C4A unit tends to follow the face-directed self-assembly law with the planar triangular building blocks such as tris(4-aminophenyl)amine (TAPA) or 1,3,5-tris(4-aminophenyl)benzene (TAPB) to generate a predictable cage with a stoichiometry of [6+8]. The formation of the large cages is confirmed through their relative molecular mass measured using MALDI-TOF/TOF spectra. The protonated molecular ion peaks of C4A-TAPA and C4A-TAPB were observed at m/z 5109.0 (calculated for C336H240O24N32: m/z 5109.7) and m/z 5594.2 (calculated for C384H264O24N24: m/z 5598.4). C4A-POCs exhibit I-type N2 adsorption-desorption isotherms with the BET surface areas of 1444.9 m2 ⋅ g-1 and 1014.6 m2 ⋅ g-1. The CO2 uptakes at 273 K are 62.1 cm3 ⋅ g-1 and 52.4 cm3 ⋅ g-1 at a pressure of 100 KPa. The saturated iodine vapor static uptakes at 348 K are 3.9 g ⋅ g-1 and 3.5 g ⋅ g-1. The adsorption capacity of C4A-TAPA for SO2 reaches to 124.4 cm3 ⋅ g-1 at 298 K and 1.3 bar. Additionally, the adsorption capacities of C4A-TAPA for C2H2, C2H4, and C2H6 were evaluated.

Fabrication of binary metal-organic frameworks of Ni-Mn@ZIFs(Cox·Zn1-xO) decorated on CF/CuO nanowire for high-performance electrochemical pseudocapacitors

Herein, metal-organic frameworks (MOFs) derived nanoflower-like based binary transition metal (Ni-Mn) are successfully fabricated by a simple synthesis method. The fabricated nanoflower-like structure displays a unique nanoflower-like architecture and internal porous channels constructed by MOF coated on CuO/CF/ZIFs (Cox·Zn1-xO) substrate, which is beneficial for the penetration of electrolyte and electron/ion transportation. The as-prepared CF/CuO/ZIFs (Cox·Zn1-xO)@BMOF(Ni-Mn) electrode materials present significant synergy among transition metal ions, contributing to enhanced electrochemical performances. The as-prepared CF/CuO/ZIFs (Cox·Zn1-xO)@BMOF(Ni-Mn) hybrid nanoflower-like display a high specific capacity of 1249.99 C g-1 at 1 A g-1 and the specific capacitance retention is about 91.74% after 5000 cycles. In addition, the as-assembled CF/CuO/ZIFs (Cox·Zn1-xO)@BMOF(Ni-Mn)//AC asymmetric supercapacitor (ASC) device exhibited a maximum energy density of 21.77 Wh·kg-1 at a power density of 799 W kg-1, and the capacity retention rate after 5000 charge and discharge cycles was 88.52%.

Boosted Enzyme Activity via Encapsulation within Metal-Organic Frameworks with Pores Matching Enzyme Size and Shape

A novel and versatile approach called "physical imprinting" is introduced to modulate enzyme conformation using mesoporous materials, addressing challenges in achieving improved enzyme activity and stability. Metal-organic frameworks with tailored mesopores, precisely matching enzyme size and shape, are synthesized. Remarkably, enzymes encapsulated within these customized mesopores exhibit over 1670% relative activity compared to free enzymes, maintaining outstanding efficiency even under harsh conditions such as heat, exposure to organic solvents, wide-ranging pH extremes from acidic to alkaline, and exposure to a digestion cocktail. After 18 consecutive cycles of use, the immobilized enzymes retain 80% of their initial activity. Additionally, the encapsulated enzymes exhibit a substantial increase in catalytic efficiency, with a 14.1-fold enhancement in kcat/KM compared to native enzymes. This enhancement is among the highest reported for immobilized enzymes. The improved enzyme activity and stability are corroborated by solid-state UV-vis, electron paramagnetic resonance, Fourier-transform infrared spectroscopy, and solid-state NMR spectroscopy. The findings not only offer valuable insights into the crucial role of size and shape complementarity within confined microenvironments but also establish a new pathway for developing solid carriers capable of enhancing enzyme activity and stability.

Research Progress on the Preparation Methods for and Flame Retardant Mechanism of Black Phosphorus and Black Phosphorus Nanosheets

Black phosphorus and black phosphorus nanosheets are widely used in the flame retardant field because of their excellent properties, but the immature preparation methods have resulted in extremely high preparation cost, which greatly limits their development and application. In this paper, various preparation methods of black phosphorus and black phosphorus nanosheets are described in detail, the advantages and disadvantages of each method are analyzed in depth, the flame-retardant mechanism and application of black phosphorus and black phosphorus nanosheets in flame retardants are discussed, and the subsequent development direction of black phosphorus and black phosphorus nanosheets is proposed.

UiO-66/AgNPs Coating for Dental Implants in Preventing Bacterial Infections

Titanium (Ti)-based biomaterials lack inherent antimicrobial activities, and the dental plaque formed on the implant surface is one of the main risk factors for implant infections. Construction of an antibacterial surface can effectively prevent implant infections and enhance implant success. Silver nanoparticles (AgNPs) exhibit broad antibacterial activity and a low tendency to induce drug resistance, but AgNPs easily self-aggregate in the aqueous environment, which significantly impairs their antibacterial activity. In this study, UiO-66/AgNP (U/A) nanocomposite was prepared, where zirconium metal-organic frameworks (UiO-66) were employed as the confinement matrix to control the particle size and prevent aggregation of AgNPs. The bactericidal activity of U/A against methicillin-resistant Staphylococcus aureus and Escherichia coli increased nearly 75.51 and 484.50 times compared with individually synthesized Ag. The antibacterial mechanism can be attributed to the enhanced membrane rupture caused by the ultrafine AgNPs on UiO-66, leading to protein leakage and generation of intracellular reactive oxygen species. Then, U/A was loaded onto Ti substrates (Ti-U/A) by using self-assembly deposition methods to construct an antibacterial surface coating. Ti-U/A exhibited excellent antibacterial activities and desired biocompatibility both in vitro and in vivo. The U/A nanocomposite coating technique is thus expected to be used as a promising surface modification strategy for Ti-based dental implants for preventing dental implant infections.

Enhanced photocatalysis of metal/covalent organic frameworks by plasmonic nanoparticles and homo/hetero-junctions

Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have garnered attention in photocatalysis due to their unique features including extensive surface area, adjustable pores, and the ability to incorporate various functional groups. However, challenges such as limited visible light absorption and rapid electron-hole recombination often hinder their photocatalytic efficiency. Recent developments have introduced plasmonic nanoparticles (NPs) and junctions to enhance the photocatalytic performance of MOFs/COFs. This paper provides a comprehensive review of recent advancements in MOF/COF-based photocatalysts improved by integration of plasmonic NPs and junctions. We begin by examining the utilization of plasmonic NPs, known for absorbing longer-wavelength light compared to typical MOFs/COFs. These NPs exhibit localized surface plasmon resonance (LSPR) when excited, effectively enhancing the photocatalytic performance of MOFs/COFs. Moreover, we discuss the role of homo/hetero-junctions in facilitating charge separation, further boosting the photocatalytic performance of MOFs/COFs. The mechanisms behind the improved photocatalytic performance of these composites are discussed, along with an assessment of challenges and opportunities in the field, guiding future research directions.

Fabrication of well-aligned Co-MOF arrays through a controlled and moderate process for the development of a flexible tetrabromobisphenol A sensor

Tetrabromobisphenol A (TBBPA) has attracted a great deal of attention due to its side effects and potential bioaccumulation properties. It is of great importance to construct and develop novel electrochemical sensors for the sensitive and selective detection of TBBPA. In the present study, cobalt (Co) based metal-organic frameworks (MOFs) were synthesized on carbon cloth (CC) by using cobalt nitrate hexahydrate and 2-methylimidazole. The morphological characterization was carried out by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The results showed that Co-MOFs/CC have a leaf-like structure and abundant surface functional groups. The electrochemical properties of the sensor were investigated by differential pulse voltammetry (DPV). The effects of different ratios of metal ions to organic ligands, reaction temperature, time, concentration, pH value of the electrolyte, and incubation time on the oxidation peak current of TBBPA were studied. Under the optimal conditions, the linear range of the designed sensor was 0.1 μM-100 μM, and the limit of detection was 40 nM. The proposed sensor is simple, of low cost and efficient, which can greatly facilitate the detection tasks of environmental monitoring workers.

Bioinspired 2D nanofluidic membranes for energy applications

Bioinspired two-dimensional (2D) nanofluidic membranes have been explored for the creation of high-performance ion transport systems that can mimic the delicate transport functions of living organisms. Advanced energy devices made from these membranes show excellent energy storage and conversion capabilities. Further research and development in this area are essential to unlock the full potential of energy devices and facilitate the development of high-performance equipment toward real-world applications and a sustainable future. However, there has been minimal review and summarization of 2D nanofluidic membranes in recent years. Thus, it is necessary to carry out an extensive review to provide a survey library for researchers in related fields. In this review, the classification and the raw materials that are used to construct 2D nanofluidic membranes are first presented. Second, the top-down and bottom-up methods for constructing 2D membranes are introduced. Next, the applications of bioinspired 2D membranes in osmotic energy, hydraulic energy, mechanical energy, photoelectric conversion, lithium batteries, and flow batteries are discussed in detail. Finally, the opportunities and challenges that 2D nanofluidic membranes are likely to face in the future are envisioned. This review aims to provide a broad knowledge base for constructing high-performance bioinspired 2D nanofluidic membranes for advanced energy applications.

Constructing green superhydrophilic and superoleophobic COFs-MOFs hybrid-based membrane for efficiently emulsion separation and synchronous removal of microplastics, dyes, and pesticides

Oil spills and micropollutants have become thorny environmental issues, posing serious threat to ecosystem and human health. To settle such dilemma, this study successfully constructed a robust and environmentally-friendly MOFs-COFs hybrid-based membrane (FS-50/COF(MATPA)-MOF(Zr)/PDA@PVDF) for the first time through solution synthesis and solvothermal method, combined with surface modification of FS-50 molecule. Importantly, we employed a simple two-step strategy to obtain the high-aspect-ratio MOFs fibers: (1) solvent regulation to generate smaller needle-like whiskers during the in-situ growth of MOFs on COFs; (2) high pressure induced directional crystallization in filtration process. The introduction of polydopamine (PDA) greatly improved the adhesion between coating and PVDF membrane. The in-situ growth of high length-diameter ratio MOFs fibers on blocky COFs greatly enhanced the specific surface area of MOFs-COFs hybrid, thus provided sufficient absorption sites. The functional groups of FS-50 endowed the hybrid membrane with superhydrophilicity and superoleophobicity, which facilitated to selectively penetrate water molecules and repel non-polar pollutants. The separation efficiency and decontamination mechanism of hybrid membrane to the simulated oily wastewater (containing various MPs, dyes, and pesticides) were investigated through experiments and theoretical calculations. The hybrid membrane could selectively and synchronously adsorb various dyes (20 mg/L-120 mg/L, almost 100% removal) and pesticides (10 mg/L for DIF and TET, adsorption rates 93.2% and 90.9%, respectively) from oil-water emulsion (50 mL). The large-scale coated sponge (6 cm × 4.5 cm × 3 cm) could quickly achieve separation of oil-water mixture (almost 100%) with a water permeability of more than 162 L m-2·h-1·bar-1, and simultaneously remove various MPs (PP-2000, PP-100, PE-2000, PS-100, 0.2 g/300 mL for each), Sudan Ⅲ (C0 = 200 mg/L), and DIF (C0 = 10 mg/L) from a simulant oily wastewater (300 mL), with the removal rates of almost 100% for MPs, 99.7% for Sudan Ⅲ, and 95.8% for DIF. Furthermore, we elucidated the removal mechanism of pesticide and dyes through simulating the theoretical adsorption energy and potential adsorption sites. The hybrid membrane not only provides a promising candidate for the removal of multiple pollutants from oil-water emulsion, but also opens a new strategy for achieving efficient and clean aquatic environment restoration.

Hybrid organic frameworks: Synthesis strategies and applications in photocatalytic wastewater treatment - A review

Hybrid organic framework materials are a class of hierarchical porous crystalline materials that have emerged in recent years, composed of three types of porous crystal materials, namely metal-organic frameworks (MOFs), covalent organic frameworks (COFs), and hydrogen-bonded organic frameworks (HOFs). The combination of various organic framework properties in hybrid organic frameworks generates synergistic effects, which has attracted widespread attention from researchers. The synthesis methods of hybrid organic frameworks are also an intriguing topic, enabling the formation of core-shell heterostructures through epitaxial growth, template conversion, medium growth, or direct combination. These hybrid organic framework materials have demonstrated remarkable performance in the application of photocatalytic wastewater purification and have developed various forms of applications. This article reviews the preparation principles and methods of various hybrid organic frameworks and provides a detailed overview of the research progress of photocatalytic water purification hybrid organic frameworks. Finally, the challenges and development prospects of hybrid organic framework synthesis and their application in water purification are briefly discussed.

Recent progress in the synthesis and applications of covalent organic framework-based composites

Covalent organic frameworks (COFs) have historically been of interest to researchers in different areas due to their distinctive characteristics, including well-ordered pores, large specific surface area, and structural tunability. In the past few years, as COF synthesis techniques developed, COF-based composites fabricated by integrating COFs and other functional materials including various kinds of metal or metal oxide nanoparticles, ionic liquids, metal-organic frameworks, silica, polymers, enzymes and carbon nanomaterials have emerged as a novel kind of porous hybrid material. Herein, we first provide a thorough summary of advanced strategies for preparing COF-based composites; then, the emerging applications of COF-based composites in diverse fields due to their synergistic effects are systematically highlighted, including analytical chemistry (sensing, extraction, membrane separation, and chromatographic separation) and catalysis. Finally, the current challenges associated with future perspectives of COF-based composites are also briefly discussed to inspire the advancement of more COF-based composites with excellent properties.

Introducing a Pyrazinoquinoxaline Derivative into a Metal-Organic Framework: Achieving Fluorescence-Enhanced Detection for Cs+ and Enhancing Photocatalytic Activity

Conventional photoresponsive materials have low photon utilization due to irregular distribution of photoactive groups, which severely limits the related real applications. Metal-organic frameworks (MOFs) can modulate the regular arrangement of functional groups to improve the electron transport paths and enhance the photon utilization, which provides strong support for the development of photoactive materials with excellent performance. In this work, one effective strategy for constructing a photoactive MOF had been developed via the utilization of Cd2+ and pyrazinoquinoxaline tetracarboxylic acid. The structural advantages of the Cd-MOF, such as a porous structure, abundant subject-object interaction sites, and a stable framework, ensure the prerequisite for various applications, while the better synergistic effect of Cd3 clusters and the pyrazinoquinoxaline derivative ensures efficient electron transfer efficiency. Therefore, by virtue of these structural advantages, the Cd-MOF can achieve fluorescence quenching detection for a variety of substrates, such as Fe3+, Cr2O72-, MnO4-, nitrofuran antibiotics, and TNP explosives, while fluorescence enhancement detection can be achieved for halogen ions, Cs+, Pb2+, and NO2-. In addition, the Cd-MOF can be used as a photocatalyst to successfully achieve the photocatalytic conversion of benzylamine to N-benzylbenzimidate under mild conditions. Thus, the Cd-MOF as a whole shows the possibility of application as a diverse fluorescence detection and photocatalyst and also illustrates the feasibility of preparing high-performance photoactive materials using the pyrazinoquinoxaline derivative.

Fluorinated-Squaramide Covalent Organic Frameworks for High-Performance and Interference-Free Extraction of Synthetic Cannabinoids

Synthetic cannabinoids (SCs), one of the largest groups of new psychoactive substances (NPSs), have emerged as a significant public health threat in different regions worldwide. Analyzing SCs in water samples is critical to estimate their consumption and control. However, due to their low background concentration and the coexistence of complex matrix, the selective and effective enrichment of SCs is still challenging. In this study, a series of fluorinated-squaramide-based covalent organic frameworks (COF: FSQ-2, FSQ-3, and FSQ-4) are synthesized, and the as-prepared FSQ-4 exhibits strong affinity to different SCs. The proper pore size (1.4 nm) and pre-located functional groups (hydrogen-bond donors, hydrogen-bond acceptors, and fluorophilic segments) work synergistically for efficient SCs capture. Remarkably, when coupled FSQ-4 with solid-phase microextraction (SPME), trace-level (part per trillion, 10-9 ) determination of 13 SCs can be easily achieved, representing one of the best results among NPS analyses, and the excellent extraction performance can be maintained under various interfering conditions.

Covalent organic frameworks: linkage types, synthetic methods and bio-related applications

Covalent organic frameworks (COFs) are composed of small organic molecules linked via covalent bonds, which have tunable mesoporous structure, good biocompatibility and functional diversities. These excellent properties make COFs a promising candidate for constructing biomedical nanoplatforms and provide ample opportunities for nanomedicine development. A systematic review of the linkage types and synthesis methods of COFs is of indispensable value for their biomedical applications. In this review, we first summarize the types of various linkages of COFs and their corresponding properties. Then, we highlight the reaction temperature, solvent and reaction time required by different synthesis methods and show the most suitable synthesis method by comparing the merits and demerits of various methods. To appreciate the cutting-edge research on COFs in bioscience technology, we also summarize the bio-related applications of COFs, including drug delivery, tumor therapy, bioimaging, biosensing and antimicrobial applications. We hope to provide insight into the interdisciplinary research on COFs and promote the development of COF nanomaterials for biomedical applications and their future clinical translations.

Taming Multiscale Structural Complexity in Porous Skeletons: From Open Framework Materials to Micro/Nanoscaffold Architectures

Recent developments in the design and synthesis of more and more sophisticated organic building blocks with controlled structures and physical properties, combined with the emergence of novel assembly modes and nanofabrication methods, make it possible to tailor unprecedented structurally complex porous systems with precise multiscale control over their architectures and functions. By tuning their porosity from the nanoscale to microscale, a wide range of functional materials can be assembled, including open frameworks and micro/nanoscaffold architectures. During the last two decades, significant progress is made on the generation and optimization of advanced porous systems, resulting in high-performance multifunctional scaffold materials and novel device configurations. In this perspective, a critical analysis is provided of the most effective methods for imparting controlled physical and chemical properties to multifunctional porous skeletons. The future research directions that underscore the role of skeleton structures with varying physical dimensions, from molecular-level open frameworks (<10 nm) to supramolecular scaffolds (10-100 nm) and micro/nano scaffolds (>100 nm), are discussed. The limitations, challenges, and opportunities for potential applications of these multifunctional and multidimensional material systems are also evaluated in particular by addressing the greatest challenges that the society has to face.

Covalent connections between metal-organic frameworks and polymers including covalent organic frameworks

Hybrid composite materials combining metal-organic frameworks (MOFs) and polymers have emerged as a versatile platform for a broad range of applications. The crystalline, porous nature of MOFs and the flexibility and processability of polymers are synergistically integrated in MOF-polymer composite materials. Covalent bonds, which form between two distinct materials, have been extensively studied as a means of creating strong molecular connections to facilitate the dispersion of "hard" MOF particles in "soft" polymers. Numerous organic transformations have been applied to post-synthetically connect MOFs with polymeric species, resulting in a variety of covalently connected MOF-polymer systems with unique properties that are dependent on the characteristics of the MOFs, polymers, and connection modes. In this review, we provide a comprehensive overview of the development and strategies involved in preparing covalently connected MOFs and polymers, including recently developed MOF-covalent organic framework composites. The covalent bonds, grafting strategies, types of MOFs, and polymer backbones are summarized and categorized, along with their respective applications. We highlight how this knowledge can serve as a basis for preparing macromolecular composites with advanced functionality.

A simple and portable vacuum assisted headspace solid phase microextraction device coupled to gas chromatography based on covalent organic framework/metal organic framework hybrid for simultaneous analysis of volatile and semi-volatile compounds in soil

Various microextraction methods have demonstrated a positive effect when assisted by vacuum. However, working with such systems is often laborious, they often require expensive and non-portable vacuum pumps, and may even suck off some sample vapor or solid particles during the evacuation process. To address these issues, a simple, and affordable vacuum-assisted headspace solid-phase microextraction (HS-SPME) device was developed in this study. The device, named In Syringe Vacuum-assisted HS-SPME (ISV-HS-SPME), utilizes an adjustable 40 mL glass syringe as a vacuum provider and sampling vessel. A new fiber coating, made from a hybrid of covalent triazine-based frameworks and metal-organic frameworks (COF/MOF), was prepared and characterized by Fourier transform infrared spectrometry, field emission scanning electron microscopy, energy dispersive X-ray, X-ray diffraction, thermogravimetric analysis, and Brunauer-Emmett-Teller techniques for use in the ISV-HS-SPME. By optimizing parameters such as extraction temperature, extraction time, desorption temperature, desorption time, and, humidity using a simplex method, the ISV system was found to increase the extraction efficiency of polycyclic aromatic hydrocarbons (PAHs) and benzene, toluene, ethylbenzene, and xylenes (BTEX) in solid samples by up to 175%. The determinations were followed by GC-FID measurements. Compared to three commercially available fibers, the ISV-HS-SPME device with the COF/MOF (2DTP/MIL-101-Cr) fiber exhibited significantly higher peak areas for PAHs and BTEX. The linear dynamic ranges for BTEX and PAHs were 7.1-9000 ng g-1 and 0.23-9000 ng g-1, respectively, with limits of detection ranging from 2.1-5 ng g-1 for BTEX and 0.07-1.6 ng g-1 for PAHs. The relative standard deviation of the method was 2.6-7.8% for BTEX and 1.6-6.7% for PAHs. The ISV-HS-SPME was successfully used to simultaneously determine PAHs and BTEX in polluted soil samples with recoveries ranging from 80.4 to 108%.

Interfacial chemistries in metal-organic framework (MOF)/covalent-organic framework (COF) hybrids

Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) have been attracting tremendous attention in various applications due to their unique structural properties. Recent interest has been focused on their combination as hybrids to enable the engineering of new classes of frameworks with complementary properties. This review gives a comprehensive summary on the interfacial chemistries in MOF/COF hybrids, which play critical roles in their hybridization. The challenges and perspectives in the field of MOF/COF hybrids are also provided to inspire more efforts in diversifying this hybrid family and their cross-disciplinary applications.

Metal-organic frameworks (MOFs) based luminescent and electrochemical sensors for food contaminant detection

With the increasing population, food toxicity has become a prevalent concern due to the growing contaminants of food products. Therefore, the need for new materials for toxicant detection and food quality monitoring will always be in demand. Metal-organic frameworks (MOFs) based on luminescence and electrochemical sensors with tunable porosity and active surface area are promising materials for food contaminants monitoring. This review summarizes and studies the most recent progress on MOF sensors for detecting food contaminants such as pesticides, antibiotics, toxins, biomolecules, and ionic species. First, with the introduction of MOFs, food contaminants and materials for toxicants detection are discussed. Then the insights into the MOFs as emerging materials for sensing applications with luminescent and electrochemical properties, signal changes, and sensing mechanisms are discussed. Next, recent advances in luminescent and electrochemical MOFs food sensors and their sensitivity, selectivity, and capacities for common food toxicants are summarized. Further, the challenges and outlooks are discussed for providing a new pathway for MOF food contaminant detection tools. Overall, a timely source of information on advanced MOF materials provides materials for next-generation food sensors.

3D Lanthanide Neodymium Porphyrin Metal-Organic Framework for Photocatalytic Oxidation of Styrene

A novel three-dimensional lanthanide porphyrin-based MOF (Nd-PMOFs) was synthesized by using tetracarboxyphenyl porphyrin as the ligand and the lanthanide Nd as the coordination metal. Its specific crystal structure information was obtained by single-crystal diffraction with the space group C2/c and the empirical formula C₇₂H₄₅N₆Nd₂O_15.25. This new Nd porphyrin-based MOF with an organic framework formed by a unique coordination method enables the effective separation of photogenerated electrons and holes under photoluminescence, giving it excellent photocatalytic property which could be verified by the characterization data. The photocatalytic performance was examined by taking tert-butyl hydroperoxide as the oxidant and Nd-PMOFs as the catalyst for photocatalytic oxidation of styrene to benzaldehyde with 91.4% conversion and 81.2% benzaldehyde selectivity under optimal reactions, which surpasses most of the results reported in the literature. Several styrenes with other substituents were screened to explore the general applicability of Nd-PMOF for photocatalysis of styrene, among which Nd-PMOFs also exhibited excellent photocatalytic performance. This work offers the possibility to apply lanthanide organometallic frameworks, which are widely used in fluorescent materials, to photocatalysis. In addition, it also provides a new method for the catalytic generation of benzaldehyde from styrene that is consistent with the needs of modern green development.

Sulfur-Bridged Co(II)-Thiacalix[4]arene Metal-Organic Framework as an Electrochemical Sensor for the Determination of Toxic Heavy Metals

A novel sulfur-bridged metal-organic framework (MOF) [Co(TIC4R-I)_0.25Cl₂]·3CH₃OH (Co-TIC4R-I) based on thiacalix[4]arene derivatives was successfully obtained using a solvothermal method. Remarkably, adjacent TIC4R-I ligands were linked via Co(II) cations to form a three-dimensional (3D) microporous architecture. Subsequently, Co-TIC4R-I was modified on a glassy carbon electrode (Co-TIC4R-I/GCE) to produce an electrochemical sensor for the detection of heavy-metal ions (HMIs), namely, Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺, in aqueous solutions. It was found that Co-TIC4R-I/GCE exhibited wide linear detection ranges of 0.10-17.00, 0.05-16.00, 0.05-10.00, and 0.80-15.00 μM for Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺, respectively, in addition to low limit of detection (LOD) values of 0.017, 0.008, 0.016, and 0.007 μM. Moreover, the fabricated sensor employed for the simultaneous detection of these metals has achieved LOD values of 0.0067, 0.0027, 0.0064, and 0.0037 μM for Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺, respectively. The sensor also exhibited satisfactory selectivity, reproducibility, and stability. Furthermore, the relative standard deviation (RSD) values of Cd²⁺, Pb²⁺, Cu²⁺, and Hg²⁺ were 3.29, 3.73, 3.11, and 1.97%, respectively. Moreover, the fabricated sensor could sensitively detect HMIs in various environmental samples. The high performance of the sensor was attributed to its sulfur adsorption sites and abundant phenyl rings. Overall, the sensor described herein provides an efficient method for the determination of extremely low concentrations of HMIs in aqueous samples.

Designed Synthesis of Three-Dimensional Covalent Organic Frameworks: A Mini Review

Covalent organic frameworks are porous crystals of polymers with two categories based on their covalent linkages: layered structures with two dimensions and networks with three-dimensional structures. Three-dimensional covalent organic frameworks are porous, have large surface areas, and have highly ordered structures. Since covalent bonds are responsible for the formation of three-dimensional covalent organic frameworks, their synthesis has been a challenge and different structures are generated during the synthesis. Moreover, initially, their topologies have been limited to dia, ctn, and bor which are formed by the condensation of triangular or linear units with tetrahedral units. There are very few building units available for their synthesis. Finally, the future perspective of 3D COFs has been designated for the future development of three-dimensional covalent organic frameworks.

Engineering Polymeric Nanofluidic Membranes for Efficient Ionic Transport: Biomimetic Design, Material Construction, and Advanced Functionalities

Design elements extracted from biological ion channels guide the engineering of artificial nanofluidic membranes for efficient ionic transport and spawn biomimetic devices with great potential in many cutting-edge areas. In this context, polymeric nanofluidic membranes can be especially attractive because of their inherent flexibility and benign processability, which facilitate massive fabrication and facile device integration for large-scale applications. Herein, the state-of-the-art achievements of polymeric nanofluidic membranes are systematically summarized. Theoretical fundamentals underlying both biological and synthetic ion channels are introduced. The advances of engineering polymeric nanofluidic membranes are then detailed from aspects of structural design, material construction, and chemical functionalization, emphasizing their broad chemical and reticular/topological variety as well as considerable property tunability. After that, this Review expands on examples of evolving these polymeric membranes into macroscopic devices and their potentials in addressing compelling issues in energy conversion and storage systems where efficient ion transport is highly desirable. Finally, a brief outlook on possible future developments in this field is provided.

MOF/COF hybrids as next generation materials for energy and biomedical applications

The rapid increase in the number and variety of metal organic frameworks (MOFs) and covalent organic frameworks (COFs) has led to groundbreaking applications in the field of materials science and engineering. New MOF/COF hybrids combine the outstanding features of MOF and COF structures, such as high crystallinities, large surface areas, high porosities, the ability to decorate the structures with functional groups, and improved chemical and mechanical stabilities. These new hybrid materials offer promising performances for a wide range of applications including catalysis, energy storage, gas separation, and nanomedicine. In this highlight, we discuss the recent advancements of MOF/COF hybrids as next generation materials for energy and biomedical applications with a special focus on the use of computational tools to address the opportunities and challenges of using MOF/COF hybrids for various applications.

Tale of COF-on-MOF Composites with Structural Regulation and Stepwise Luminescence Enhancement

Integrating metal-organic framework (MOF)-covalent organic framework (COF) allows versatile engineering of hybrid materials with properties superior to pristine components, especially COFs suffered from aggregation-caused quenching (ACQ), unlocking more possibilities to improve the luminescence of COFs. In this work, we prepared various MOF@COF composites with different COF layer thicknesses, in which stable UiO-66-NH₂ served as the inner substrate and 1,3,5-benzenetricarboxaldehyde (BT), and 3,3'-dihydroxybenzidine (DH) were used to construct a COF layer. In addition to the conventional preparation method, we increased the ratio of BT and DH to be 1:2.5, and impressively, the morphologies of acquired UC (1:2.5) materials were quite different from the previous reticular structure and gradually extended from the spherical structure to the prickly structure with the increase of COF monomers. Remarkably, all of the UC materials possessed better luminescence properties than individual COF due to the limited COF layers. Meanwhile, UC-1 materials with an optimal COF layer displayed the strongest emission. In comparison with a single COF, the quantum yields of UC-1 and UC-1 (1:2.5) were increased nearly 7 times and 5 times, respectively. Moreover, the fluorescence of UC-1 materials was progressively enhanced via selective F^- sensing. This work is expected to shed light on the potential hybridization of MOF-COF with structural adjustment, morphological design, and luminescence enhancement.

Progress in Hybridization of Covalent Organic Frameworks and Metal-Organic Frameworks

Metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) hybrid materials are a class of porous crystalline materials that integrate MOFs and COFs with hierarchical pore structures. As an emerging porous frame material platform, MOF/COF hybrid materials have attracted tremendous attention, and the field is advancing rapidly and extending into more diverse fields. Extensive studies have shown that a broad variety of MOF/COF hybrid materials with different structures and specific properties can be synthesized from diverse building blocks via different chemical reactions, driving the rapid growth of the field. The allowed complementary utilization of π-conjugated skeletons and nanopores for functional exploration has endowed these hybrid materials with great potential in challenging energy and environmental issues. It is necessary to prepare a "family tree" to accurately trace the developments in the study of MOF/COF hybrid materials. This review comprehensively summarizes the latest achievements and advancements in the design and synthesis of MOF/COF hybrid materials, including COFs covalently bonded to the surface functional groups of MOFs (MOF@COF), MOFs grown on the surface of COFs (COF@MOF), bridge reaction between COF and MOF (MOF+COF), and their various applications in catalysis, energy storage, pollutant adsorption, gas separation, chemical sensing, and biomedicine. It concludes with remarks concerning the trend from the structural design to functional exploration and potential applications of MOF/COF hybrid materials.

Trap Inlaid Cationic Hybrid Composite Material for Efficient Segregation of Toxic Chemicals from Water

Metal-based oxoanions are potentially toxic pollutants that can cause serious water pollution. Therefore, the segregation of such species has recently received significant research attention. Even though several adsorbents have been employed for effective management of chemicals, their limited microporous nature along with non-monolithic applicability has thwarted their large-scale real-time application. Herein, we developed a unique anion exchangeable hybrid composite aerogel material (IPcomp-6), integrating a stable cationic metal-organic polyhedron with a hierarchically porous metal-organic gel. The composite scavenger demonstrated a highly selective and very fast segregation efficiency for various hazardous oxoanions such as, HAsO₄ ^2- , SeO₄ ^2- , ReO₄ ^- , CrO₄ ^2- , MnO₄ ^- , in water, in the presence of 100-fold excess of other coexisting anions. The material was able to selectively eliminate trace HAsO₄ ^2- even at low concentration to well below the As^V limit in drinking water defined by WHO.

Emerging single atom catalysts in gas sensors

Single atom catalysts (SACs) offer unprecedented opportunities for high-efficiency reactions taking place in many important fields of catalytic processes, electrochemistry, and photoreactions. Due to their maximized atomic utilization and unique electronic and chemical properties, SACs can provide high activity and excellent selectivity for gas adsorption and electron transport, leveraging SACs that enhance the detection sensitivity and selectivity to target gases. In the past few years, SACs including both noble (Pt, Pd, Au, etc.) and non-noble (Mn, Ni, Zn etc.) metals have been demonstrated to be very useful in optimizing sensing performances. However, a comprehensive review on this topic is still missing. Herein, we summarize the synthesis technologies of SACs that are applicable to gas sensors. The electronic and chemical interactions between SACs and host sensing materials, which are crucial to sensor functions, are discussed. Then, we highlight the application progress of various SACs in gas sensors. Prospects in the creation of new sensing materials with emerging SACs and versatile supports are also present. Finally, the challenges and prospects of SACs in the future development of sensors are analyzed.

COF-5/CoAl-LDH Nanocomposite Heterojunction for Enhanced Visible-Light-Driven CO2 Reduction

Photocatalytic conversion of CO₂ into value-added chemical fuels is an attractive route to mitigate global warming and the energy crisis. Reasonable design of optical properties and electronic behavior of the photocatalyst are essential to improve their catalytic activity. Herein, the 1D/2D heterojunction by direct in-situ synthesis of the covalent organic framework (COF)-5 colloid on the surface of CoAl layered double hydroxide (LDH) was used as the prospective photocatalyst for CO₂ reduction. COF-5/CoAl-LDH nanocomposite achieved 265.4 μmol g^-1 of CO with 94.6 % selectivity over CH₄ evolution in 5 h under visible light irradiation, which was 4.8 and 2.3 times higher than those of COF-5 colloid and CoAl-LDH, respectively. The enhanced catalytic activity was derived from the increased visible-light activity and the construction of type II-2 heterojunction, which greatly optimized visible light harvesting and accelerated the efficient separation of the photoinduced holes and electrons. This work paves the way for rational design of heterojunction catalysts in photocatalytic CO₂ reduction.

Magnetic UiO-66 functionalized with 4,4'-diamino-2,2'-stilbenedisulfonic as a highly recoverable acid catalyst for the synthesis of 4H-chromenes in green solvent

According to 4H-chromenes importance, we synthesized a novel magnetic UiO-66 functionalized with 4,4′-diamino-2,2′-stilbenedisulfonic as an efficient and reusable solid acid catalyst for synthesizing 4H-chromene skeletons via a one-pot three components reaction in a green solvent. The structure of the synthesized catalyst was confirmed by various techniques including FT-IR, XRD, BET, TGA, TEM, EDX, and SEM, and also the product yields were obtained in 83–96% of yields for all the reactions and under mild conditions. The reported procedure presents an environmentally friendly approach for synthesizing a significant number of 4H-chromene derivatives. Correspondingly, MOF-based catalyst makes it easy to separate from reaction media and reuse in the next runs.

Synthesis, Structural Characterization, and Biological Activities of Organically Templated Cobalt Phosphite (H2DAB)[Co(H2PO3)4]·2H2O

A novel hybrid cobalt phosphite, (H2DAB)[Co(H2PO3)4] 2H2O, was synthesized by using a slow evaporation method in the presence of cobalt nitrate, phosphorous acid, and 1,4-diaminobutane (DAB = 1,4-diaminobutane) as a structure-directing agent. Single-crystal X-ray diffraction analysis showed that the compound crystallizes in the triclinic system (space group P-1(n.2)) with the following unit cell parameters (Å, °) a = 5.4814 (3), b = 7.5515 (4), c = 10.8548 (6), α = 88.001 (4), β = 88.707 (5), γ = 85.126 (5), and V = 447.33 (4) Å3. The crystal structure is built up from corner-sharing [CoO6] octahedra, forming chains parallel to [001], which are interconnected by H2PO3− pseudo-tetrahedral units. The diprotonated cations, residing between the parallel chains, interact with the inorganic moiety via hydrogen bonds, thus leading to the formation of the 3D crystal structure. The Fourier transform infrared spectrum showed characteristic bands corresponding to the phosphite group and the organic amine. The thermal behavior of the compound mainly consisted of the loss of its organic moiety and the water molecules. The biological tests exhibited significant activity against Candida albicans and Escherichia coli strains at different concentrations, while less inhibitory activity was pronounced against Staphylococcus epidermidis and Saccharomyces cerevisiae, and in the case of multi-cellular organisms, no activity against the nematode model Steinernema feltiae was detected.

Process of metal-organic framework (MOF)/covalent-organic framework (COF) hybrids-based derivatives and their applications on energy transfer and storage

The fossil-fuel shortage and severe environmental issues have posed ever-increasing demands on clean and renewable energy sources, for which the exploration of electrocatalysts has been a big challenge toward energy transfer and storage. Some indispensable features of electrocatalysts, such as large surface area, controlled structure, high porosity, and effective functionalization, have been proved to be critical for the improvement of electrocatalytic activities. Recently, the rapid expansion of metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and porous-organic polymers has provided extensive opportunities for the development of various electrocatalysts. Moreover, combining diverse descriptions of porous-organic frameworks (such as MOFs and COFs) can generate amazing and fantastic properties, affording the formed MOF/COF (including core-shell MOF@MOF and MOF@COF and layer-on-layer MOF-on-MOF or COF-on-MOF) heterostructures wide applications in diverse fields, especially in clean energy and energy transfer. To further boosts electronic conductivity, catalytic performances, and energy storage abilities, these MOF/COF hybrid materials have been widely utilized as versatile precursors for the manufacture of transition metal catalysts embedded within mesoporous carbon nitrides (M@CN_x) and porous carbon nitride frameworks (CN_x) via a facile pyrolysis process. Given that these M@CN_x and CN_x hybrids are composed of abundant catalytic centers, rich functionalities, and large specific surface areas, vast applications in energy transfer and energy storage fields can be realized. In this mini-review, we summarize the preparation strategies of MOF/COF-based hybrids, as well as their derivatives, nanostructure formation mechanism of M@CN_x and CN_x hybrids from MOF/COF-based hybrid materials, and their applications as catalysts for driving diverse reactions and electrode materials for energy storage. Further, current challenges and future prospects of applying these derivatives into energy conversion and storage devices are also discussed.

Recent Progress in the Synthesis and Applications of Composite Photocatalysts: A Critical Review

Photocatalysis is an advanced technique that transforms solar energy into sustainable fuels and oxidizes pollutants via the aid of semiconductor photocatalysts. The main scientific and technological challenges for effective photocatalysis are the stability, robustness, and efficiency of semiconductor photocatalysts. For practical applications, researchers are trying to develop highly efficient and stable photocatalysts. Since the literature is highly scattered, it is urgent to write a critical review that summarizes the state-of-the-art progress in the design of a variety of semiconductor composite photocatalysts for energy and environmental applications. Herein, a comprehensive review is presented that summarizes an overview, history, mechanism, advantages, and challenges of semiconductor photocatalysis. Further, the recent advancements in the design of heterostructure photocatalysts including alloy quantum dots based composites, carbon based composites including carbon nanotubes, carbon quantum dots, graphitic carbon nitride, and graphene, covalent-organic frameworks based composites, metal based composites including metal carbides, metal halide perovskites, metal nitrides, metal oxides, metal phosphides, and metal sulfides, metal-organic frameworks based composites, plasmonic materials based composites and single atom based composites for CO₂ conversion, H₂ evolution, and pollutants oxidation are discussed elaborately. Finally, perspectives for further improvement in the design of composite materials for efficient photocatalysis are provided.

Recent advances in the fabrication of 2D metal oxides

Atomically thin two-dimensional (2D) metal oxides exhibit unique optical, electrical, magnetic, and chemical properties, rendering them a bright application prospect in high-performance smart devices. Given the large variety of both layered and non-layered 2D metal oxides, the controllable synthesis is the critical prerequisite for enabling the exploration of their great potentials. In this review, recent progress in the synthesis of 2D metal oxides is summarized and categorized. Particularly, a brief overview of categories and crystal structures of 2D metal oxides is firstly introduced, followed by a critical discussion of various synthesis methods regarding the growth mechanisms, advantages, and limitations. Finally, the existing challenges are presented to provide possible future research directions regarding the synthesis of 2D metal oxides. This work can provide useful guidance on developing innovative approaches for producing both 2D layered and non-layered nanostructures and assist with the acceleration of the research of 2D metal oxides.

Zinc-Based Metal-Organic Frameworks in Drug Delivery, Cell Imaging, and Sensing

The design and structural frameworks for targeted drug delivery of medicinal compounds and improved cell imaging have been developed with several advantages. However, metal-organic frameworks (MOFs) are supplemented tremendously for medical uses with efficient efficacy. These MOFs are considered as an absolutely new class of porous materials, extensively used in drug delivery systems, cell imaging, and detecting the analytes, especially for cancer biomarkers, due to their excellent biocompatibility, easy functionalization, high storage capacity, and excellent biodegradability. While Zn-metal centers in MOFs have been found by enhanced efficient detection and improved drug delivery, these Zn-based MOFs have appeared to be safe as elucidated by different cytotoxicity assays for targeted drug delivery. On the other hand, the MOF-based heterogeneous catalyst is durable and can regenerate multiple times without losing activity. Therefore, as functional carriers for drug delivery, cell imaging, and chemosensory, MOFs' chemical composition and flexible porous structure allowed engineering to improve their medical formulation and functionality. This review summarizes the methodology for fabricating ultrasensitive and selective Zn-MOF-based sensors, as well as their application in early cancer diagnosis and therapy. This review also offers a systematic approach to understanding the development of MOFs as efficient drug carriers and provides new insights on their applications and limitations in utility with possible solutions.