Metal-organic frameworks for separations

Design and engineering of microenvironments of supported catalysts toward more efficient chemical synthesis

Catalytic species such as molecular catalysts and metal catalysts are commonly attached to varieties of supports to simplify their separation and recovery and accommodate various reaction conditions. The physicochemical microenvironments surrounding catalytic species play an important role in catalytic performance, and the rational design and engineering of microenvironments can achieve more efficient chemical synthesis, leading to greener and more sustainable catalysis. In this review, we highlight recent works addressing the topic of the design and engineering of microenvironments of supported catalysts, including supported molecular catalysts and supported metal catalysts. Six types of materials, including oxide nano/microparticle, mesoporous silica nanoparticle (MSN), polymer nanomaterial, reticular material, zeolite, and carbon-based nanomaterial, are widely used as supports for the immobilization of catalytic species. We summarize and discuss the synthesis and modification of supports and the positive effects of microenvironments on catalytic properties such as metal-support interaction, molecular recognition, pseudo-solvent effect, regulating mass transfer, steric effect, etc. These design principles and engineering strategies allow access to a better understanding of structure-property relationships and advance the development of more efficient catalytic processes.

Competitive Effect of Surface Hydrophobicity-Hydrophilicity and the Number of Accessible Protons on Water-Assisted Proton Conductivity in Metal-Organic Frameworks: Dielectric σ-Relaxation Triggered by Disordered Guest Ionic Migration and Its Mechanism

The rapid upsurge of metal-organic frameworks (MOFs) has sparked profound interest in their potential as proton conductors for proton exchange membrane fuel cells. However, proton-conducting behaviors of hydrophobic MOFs remain poorly understood compared with their hydrophilic counterparts, largely due to the absence of a microscopic phase separation structure akin to that found in Nafion membranes. Herein, we demonstrate a strategy for regulating the structures and proton conductivities of MOFs by separately incorporating hydrophobic -C(CF3)2- group alongside hydrophilic -O- and -SO2- groups into organic ligands as linkers. Three analogous MOFs, {[Zr6(obba)4(μ3-O)4(μ3-OH)4(OH)3(H2O)3(HCOO)]·3.5DMF·3CH3COCH3}n (Zr-obba, H2obba = 4,4'-oxybis(benzoic acid)), {[Zr6(sdba)4(μ3-O)4(μ3-OH)4(OH)2(H2O)2(HCOO)2]·2(CH3)2NH2+·2HCOO-·7(CH3)2NH·6.5H2O}n (Zr-sdba, H2sdba = 4,4'-sulfonyldibenzoic acid), and {[Zr6(hfipbba)4(μ3-O)4(μ3-OH)4(OH)4(H2O)4]·7.5(CH3)2NH2+·7.5HCOO-·3.5(CH3)2NH}n (Zr-hfipbba, H2hfipbba = 4,4'-(hexafluoroisopropylidene)bis(benzoic acid)), were prepared and characterized. Interestingly, we observed a trend in proton conductivity: Zr-obba > Zr-sdba > Zr-hfipbba, which can be attributed to the competitive effect of surface hydrophobicity-hydrophilicity and the availability of accessible protons. More importantly, we identified dielectric σ-relaxation in Zr-sdba and Zr-hfipbba, which is linked to the thermally activated migration of disordered guest ions within the MOFs, highlighting the significant relationship between proton conduction and dielectric relaxation. This finding contributes to a deeper understanding of the critical roles that hydrophobicity-hydrophilicity play in proton conduction and the dielectric σ-relaxation mechanism in crystalline MOFs.

Preparation of a 6FDA-DAM/ODA Mixed Matrix Membrane Doped with MOFs and Its Application in Gas Separation

Mixed matrix membranes (MMMs) can significantly improve gas separation performance, but the type and state of the filler in the membrane matrix are key indicators for the development of MMMs. Therefore, in this work, 6FDA-DAM/ODA (1:1), metal-organic frameworks (MOFs) with different particle sizes (UiO-66 and UiO-66-NH2) were synthesized, and then MOFs were doped into 6FDA-DAM/ODA to prepare MMMs. The effects of the dopant materials and their particle sizes on the gas separation performance of the membranes were investigated by testing the permeability of the MMMs to H2, CO2, CH4, and N2. When the dopant material was UIO-66, the permeability and selectivity of MMMs for each gas were significantly improved compared with that of the original membrane; when the dopant material was 300 nm UIO-66-NH2 with a loading of 10 wt %, the permeability performance and the CO2/CH4 selectivity increased from 44.1 to 57.2 compared with that of the original membrane. The permeation performance for CO2, N2, and H2 and the selectivity for CO2/N2, H2/N2, and H2/CH4 were also significantly improved. In terms of comprehensive separation performance, doping 300 nm UiO-66-NH2 was better than doping 70 and 400 nm UiO-66-NH2 and also showed excellent performance in 50:50 (vol/vol) CO2/CH4 binary mixed gas separation. This work provides an idea for the fabrication of MMMs for high-performance gas separation.

Observation of O2 Molecules Inserting into Fe-H Bonds in a Ferrous Metal-Organic Framework

Exploring the interactions between oxygen molecules and metal sites has been a significant topic. Most previous studies concentrated on enzyme-mimicking metal sites interacting with O2 to form M-OO species, leaving the development of new types of O2-activating metal sites and novel adsorption mechanisms largely overlooked. In this study, we reported an Fe(II)-doped metal-organic framework (MOF) [Fe3Zn2H4(bibtz)3] (MAF-203, H2bibtz = 1H,1'H-5,5'-bibenzo[d][1,2,3]triazole), featuring an unprecedented tetrahedral Fe(II)HN3 site. This MOF exhibits selective adsorption behavior for O2 from air, achieving an O2/N2 separation selectivity of up to 67.1. Breakthrough experiments confirmed that MAF-203 can effectively capture O2 from the air even under a high relative humidity of 60%. X-ray absorption spectroscopy, in situ diffuse reflectance infrared Fourier transform spectra, and ab initio molecular dynamics simulations were utilized to monitor the O2 loading process on the Fe(II)HN3 site. Interestingly, O2 molecules could insert into the Fe-H bonds of the tetrahedral FeIIHN3 sites, forming FeIII-OOH species (instead of the commonly observed Fe-OO species) with an ultrahigh adsorption enthalpy of -99.2 kJ mol-1. Consequently, the O2 capture behavior of MAF-203 enables efficient electrochemical 2e- oxygen reduction for the production of H2O2 with air as the feedstock. Specifically, in a solid-state electrolyte electrolyzer without any liquid electrolyte, MAF-203 achieved selective O2 capture and continuous production of medical-grade H2O2 (3.2 wt %) solution without salts for 70 h, with performance comparable to that under pure O2 conditions. The O2 adsorption and activation mechanisms inaugurate a fresh chapter in grasping the interaction between O2 molecules and metal sites.

Controlling the Mechanism of Nucleation and Growth Enables Synthesis of UiO-66 Metal-Organic Framework with Desired Macroscopic Properties

By combining in situ X-ray diffraction, Zr K-edge X-ray absorption spectroscopy and 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, we show that the properties of the final MOF are influenced by H2O and HCl via affecting the nucleation and crystal growth at the molecular level. The nucleation implies hydrolysis of monomeric zirconium chloride complexes into zirconium-oxo species, and this process is promoted by H2O and inhibited by HCl, allowing to control crystal size by adjusting H2O/Zr and HCl/Zr ratios. The rate-determining step of crystal growth is represented by the condensation of monomeric and oligomeric zirconium-oxo species into clusters, or nodes, with the structure identical to that in secondary building units (SBU) of UiO-66 framework. The rapid crystallization in the absence of HCl leads to formation of defective secondary building units with missing zirconium atoms, providing a pathway to control the number of defects in UiO-66 crystals. Remarkably, we have shown that assembling of the metal nodes and linkers into the UiO-66 structure is not the rate-limiting step, and the degree of deprotonation of the linker has no direct effect on the crystallization kinetics or crystal size of product.

Harnessing Large Language Models to Collect and Analyze Metal-Organic Framework Property Data Set

This research focused on the efficient collection of experimental metal-organic framework (MOF) data from scientific literature to address the challenges of accessing hard-to-find data and improving the quality of information available for machine learning studies in materials science. Utilizing a chain of advanced large language models (LLMs), we developed a systematic approach to extract and organize MOF data into a structured format. Our methodology successfully compiled information from more than 40,000 research articles, creating a comprehensive and ready-to-use data set. Specifically, data regarding MOF synthesis conditions and properties were extracted from both tables and text and then analyzed. Subsequently, we utilized the curated database to analyze the relationships between synthesis conditions, properties, and structure. Through machine learning, we identified the existence of a gap between simulation data and experimental data, and further analysis revealed the factors contributing to this discrepancy. Additionally, we leveraged the extracted synthesis condition data to develop a synthesis condition recommender system. This system suggests optimal synthesis conditions based on the provided precursors, offering a practical tool to refine synthesis strategies. This underscores the importance of experimental datasets in advancing MOF research.

Insights into the MOF-Based Classic Configuration for the Differences in Effective Dye Adsorption, Magnetic Properties, and Computational Analyses

Two 3D/2D anionic metal-organic frameworks (MOFs), [Cu(HL)]n (1) and [Mn3(L)2(DMF)4]n (2) (DMF = N,N-dimethylformamide), were synthesized by the solvothermal reaction of metal salts and 5'-(4-carboxyphenyl)-2',4',6'-triethyl-[1,1':3',1″-terphenyl]-4,4″-dicarboxylic acid (H3L). Single-crystal X-ray diffraction analyses revealed that complex 1 shows three-dimensional (3D) frameworks with a (3,6)-connected 3-fold interpenetrated topology with the Schläfli symbols of {4.62}2{42.610.83}, whereas the topology of the two-dimensional (2D) architecture can be defined as 2-fold stacked layers with the Schläfli symbols of {43}2{46.66.83} for complex 2. In addition, density functional theory calculations, together with UV-vis adsorption spectroscopy, zeta potential, effective aperture size analysis, TEM, and SEM, were also performed to determine the accurate adsorption sites and significant differences in dye adsorption for complexes 1 and 2. Interestingly, UV-vis studies confirm that Mn-MOF displays remarkable adsorption efficiency for cationic rhodamine B, methylene blue, malachite green, and methyl green, and the removal rate reached 95.2, 95.0, 87.0, and 78.0%, respectively, while almost no adsorption capacity was detected for anionic cresol red and methyl orange. However, Cu-MOF failed to efficiently adsorb any selected dyes. Moreover, the magnetic properties were also investigated through experimental and theoretical calculations in detail, which revealed the weak and stronger antiferromagnetic interactions that occurred between Cu(II) and Mn(II) centers, respectively. Finally, this work provides the profound mechanisms for magnetism and dye adsorption.

Guest Diffusion Versus Recrystallization in A Single Crystal: Two Growing Mechanisms for Griseofulvin Clathrates

Griseofulvin represents a rare case of a close-packed organic apohost that can clathrate selected volatile guests in a solid-gas fashion. Inclusion mechanisms and solvent exchange were investigated by a combination of single crystal and powder X-ray diffraction, coupled to optical microscopy and thermal analyses. In particular, gas diffusion and dissolution/recrystallization are alternatively observed, depending on the host polymorph, as well as the chemical nature of the guest and its physical state.

Unveiling the Origin of the Scale-Dependent Conductivity of Ni3(HITP)2 Metal-Organic Framework Thin Films

Conductive metal-organic frameworks (MOFs) are crystalline, intrinsically porous materials that combine remarkable electrical conductivity with exceptional structural and chemical versatility. This rare combination makes these materials highly suitable for a wide range of energy-related applications. However, the electrical conductivity in MOF-based devices is often limited by the presence of different types of structural disorder. Here, the electrical transport characteristics of high quality Ni3(HITP)2 nanometer-thin films are reported. These findings reveal a tenfold difference in conductivity between the micro- and nano-scale, attributed to poor electrical connection among a limited number of crystalline grains. Average in-plane conductivity values at the micro- (σIP,micro = 0.7 ± 0.3 S cm-1) and nano- (σIP,nano = 6 ± 3 S cm-1) scales is determined, and the value of the inter-grain resistance, Rinter-grain = 40 kΩ is found. Using a 2D resistor network model with a 40 kΩ base resistance and scattered higher resistances, surface potential maps of in-operando MOF-based electrical devices are successfully reproduced. Additionally, a structure-property relationship that links the density and spatial distribution of electrical failures in inter-grain connections to the observed micro-scale conductivity in MOF thin films is established.

Equipartitioning of Molecular Degrees of Freedom in MD Simulations of Gaseous Systems via an Advanced Thermostatization Strategy

This work introduces a dedicated thermostatization strategy for molecular dynamics simulations of gaseous systems. The proposed thermostat is based on the stochastic canonical velocity rescaling approach by Bussi and co-workers and is capable of ensuring an equal distribution of the kinetic energy among the translational, rotational, and vibrational degrees of freedom. The outlined framework ensures the correct treatment of the kinetic energy in gaseous systems, which is typically not the case in standard approaches due to the limited number of collisions between particles associated with a large free mean path. Additionally, an efficient strategy to effectively correct for intramolecular contributions to the virial in quantum mechanical simulations is presented. The equipartitioning thermostat was successfully tested by the determination of pV diagrams for carbon dioxide and methane at the density functional tight binding level of theory. The results unequivocally demonstrate that the equipartitioning thermostat can effectively achieve an equal distribution of the kinetic energy among the different degrees of freedom, thereby ensuring correct pressure in gaseous systems. Furthermore, RDF calculations show the capability of the proposed method to accurately depict the structure of gaseous systems, as well as enable an adequate treatment of gas molecules under confinement, as exemplified by an MD simulation of (CO2)50@MOF-5.

Influence of Deposition Temperature on Cu-BDC Surface-Anchored Metal-Organic Framework Formation

Surface-anchored metal-organic frameworks (surMOFs) are crystalline, nanoporous, supramolecular materials mounted to substrates that have the potential for integration within device architectures relevant for a variety of electronic, photonic, sensing, and gas storage applications. This research investigates the thin film formation of the Cu-BDC (copper benzene-1,4-dicarboxylate) MOF system on a carboxylic acid-terminated self-assembled monolayer by alternating deposition of solution-phase inorganic and organic precursors. X-ray diffraction (XRD) and atomic force microscopy (AFM) characterization demonstrate that crystalline Cu-BDC thin films are formed via Volmer-Weber growth. Changes in film morphology as the deposition temperature increases are seen by AFM with more isolated nanorod-like crystallites observed at lower temperatures, while vertical nanoplatelet-like structures form at higher temperatures. At 45 °C, the nanoplatelets are observed to be composed of fused nanorod segments aligned in one direction. Ellipsometry confirms that both increasing temperature and number of deposition cycles yield more film deposition in agreement with infrared reflectance-absorbance spectroscopy (IRRAS) that was further used to characterize the chemical binding and orientation in the surface-bound Cu-BDC nanostructures. In addition to observing strong preferred orientation of the nanostructures from the enhancement of the symmetric carboxylate stretch and absence of the antisymmetric stretch, IRRAS results show the emergence of a new binding motif associated with segmented nanoplatelet formation at a higher deposition temperature as well as at high surface coverage after 12 deposition cycles. From the appearance of this higher frequency symmetric carboxylate peak alongside peak splitting in BDC deformation modes, IRRAS data support the presence of a strained configuration that accompanies the appearance of Cu-BDC segmented nanoplatelets observed by AFM.

Architecting Ultra-Robust Zr(IV) Metal-Organic Framework for Energy-Efficient Desiccant Air Conditioning

Air-conditioning systems, composed mainly of humidity control and heat reallocation units, play a pivotal role in upholding superior air quality and human well-being across diverse environments ranging from international space stations and pharmacies to granaries and cultural relic preservation sites, and to commercial and residential buildings. The adoption of sorbent water as the working pair and low-grade renewable or waste heat in adsorption-driven air-conditioning presents a state-of-the-art solution, notably for its energy efficiency and eco-friendliness vis-à-vis conventional electricity-driven vapor compression cycles. Here, we introduce a rational π-extension strategy to engineer an ultrarobust and highly porous zirconium metal-organic framework (Zr-MOF). This MOF sorbent showcases hysteresis-free S-shaped water sorption isotherms, characterized by a rapid ascent within the 40-60% relative humidity range with a working capacity of 0.63 g g-1, thus facilitating intelligent indoor humidity regulation. Moreover, we demonstrate, for the first time, that this material with such distinctive isotherms can yield a 10 °C temperature lift between ambient and chiller output with a high cooling capacity of 336 kW h m-3 per cycle, even at exceptionally low driving temperatures (below 50 °C), while also delivering a substantial coefficient of performance of 0.96. This material is amenable to scale-up and is chemically ultrastable that can endure strong acids and be cycled for at least 200 runs without compromising any of its capacity. These exceptional attributes signify the viability of this material as a pragmatic alternative for deployment in energy-efficient desiccant air-conditioning systems, particularly in hot and humid climatic regions.

Water sorption performance of the zeolitic metal azolate framework MAF-7

Water sorption isotherms of [Zn(mtz)2]n (MAF-7) were collected over a wide temperature range (15-45 °C) and its water sorption performance was assessed in terms of water uptake, sorption kinetics, recyclability, and regeneration temperature. Additionally, molecular simulations were conducted to elucidate the locations of water molecules within the pore cavity of MAF-7.

Construction of a Fluorinated-Anion Pillared Metal-Organic Framework Exhibiting Dual-Pore Architecture for Simultaneous Enhancement of C2H2 Adsorption Capacity and Selectivity

Physisorption-based separation processes represents a promising alternative to the conventional thermally driven methods, such as cryogenic separation. However, a significant challenge lies in balancing the trade-off between adsorption capacity and selectivity of adsorbents. In this study, we introduce a novel fluorinated-anion pillared metal-organic frameworks (APMOFs) featuring a dual-pore architecture, constructed using a pyridine-oxazole bifunctional ligand. The inherent low symmetry of the ligand leads to significant distortion of the fluorinated-anion pillars, resulting in a distinctive type of APMOFs characterized by dual-pore architecture. On pore structure with constrict pore width is enriched with a high density of anion fluorinated pillars, offering numerous active sites advantageous for enhancing separation selectivity. Concurrently, the other pore structure exhibits larger dimensions, facilitating increased gas molecule accommodation and thereby augmenting adsorption capacity. Gas sorption studies reveal a substantial C2H2 adsorption capacity and a high C2H2/CO2 separation selectivity. Breakthrough experiments confirm its exceptional separation performance, while theoretical investigations elucidate a sequential adsorption process within these APMOFs, underscoring the efficacy of this strategy in overcoming trade-off limits in adsorbents.

Unravelling nonclassical beam damage mechanisms in metal-organic frameworks by low-dose electron microscopy

Recent advances in direct electron detectors and low-dose imaging techniques have opened up captivating possibilities for real-space visualization of radiation-induced structural dynamics. This has significantly contributed to our understanding of electron-beam radiation damage in materials, serving as the foundation for modern electron microscopy. In light of these developments, the exploration of more precise and specific beam damage mechanisms, along with the development of associated descriptive models, has expanded the theoretical framework of radiation damage beyond classical mechanisms. We unravel, in this work, the nonclassical beam damage mechanisms of an open-framework material, i.e. UiO-66(Hf) metal-organic framework, by integrating low-dose electron microscopy and ab initio simulations of radiation induced structural dynamics. The physical origins of radiation damage phenomena, spanning across multiple scales including morphological, lattice, and molecular levels, have been unequivocally unveiled. Based on these observations, potential alternative mechanisms including reversible radiolysis and radiolysis-enhanced knock-on displacement are proposed, which account for their respective dynamic crystalline-to-amorphous interconversion and site-specific ligand knockout events occurring during continuous beam radiation. The current study propels the fundamental understanding of beam damage mechanisms from dynamic and correlated perspectives. Moreover, it fuels technical innovations, such as low-dose ultrafast electron microscopy, enabling imaging of beam-sensitive materials with uncompromised spatial resolution.

Integration of metal-organic frameworks and clay toward functional composite materials

Metal-organic frameworks (MOFs) have become increasingly important as a class of porous crystalline materials because of their diverse applications. At the same time, significant progress has been achieved in the field of MOF-based composite materials toward novel applications based on the synergistic effect of two or more different components. Clay materials have been explored recently in MOF chemistry for the synthesis of MOF-clay composites, which are a new class of functional materials synthesized by a cooperative combination of MOFs with clay. Such composites have evolved only in the recent past with important functions and applications, such as enhanced gas storage and separation, CO2 capture and conversion, catalysis, drug delivery, and water harvesting. Notably, the typical shortcomings of MOFs, such as moisture sensitivity, poor water dispersibility, poor thermal and chemical stability, and poor processability, could be overcome by developing novel MOF-clay composites. This article provides a concise overview of MOF-clay composites and their applications in various fields that will drive the interest of researchers to explore the emerging field of MOF-clay chemistry. In the initial sections, we classify the clays that have been used in MOF chemistry and briefly discuss their structures and chemistry. We also present the advantages of MOF-clay composites and discuss their synthetic methodologies. In the later sections, we classify different MOF-clay composites based on the clay and present some representative examples of such composites that show unique properties and applications. Finally, the development in this field is summarized, and the future scope of such composites is discussed.

Ultra-sensitive detection of 4-chloro-2-methylphenoxyacetic acid herbicide using a porous Co-1,4-benzenedicarboxylate /montmorillonite nanocomposite sensor

The detection of 4-chloro-2-methylphenoxyacetic acid (CMPA) herbicide is crucial due to the potential health risks linked to exposure through drinking water, air, and food, which may adversely affect liver and kidney functions. To address this environmental concern and promote sustainable agriculture, a sensitive carbon paste sensor incorporating a composite material was developed. The composite sensor is based on porous cobalt-1,4-benzenedicarboxylate metal-organic framework and exfoliated montmorillonite nanolayers (Co-OF/MMt). This sensor enables the voltammetric detection of CMPA in real soil samples using linear sweep adsorptive anodic stripping voltammetry (LS-AdASV), facilitating early and accurate monitoring of herbicide levels. The Co-OF/MMt nanocomposite was synthesized via a hydrothermal method involving the precipitation of Co-OF in the presence of MMt. Comprehensive characterization of the synthesized materials was carried out using Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), SEM-Energy dispersive X-ray spectroscopy (SEM-EDX) and surface area analysis (BET). The resulting modified carbon paste sensor, utilizing 1.0% Co-OF/MMt nanocomposite, exhibited superior electrochemical properties compared with the bare carbon paste sensor, possessing an electroactive surface area of 1004.1 m2/g with a minimal resistivity (Rct) of 330 Ω. Under standard operating conditions, the developed sensor demonstrated detection limits of 0.03 nM and 0.1 nM across two broad linear ranges (0.03 to 0.10 nM - 0.10 to 1.0 nM) and (0.1 to 1.0 nM - 1.0 to 7.0 nM), respectively, for CMPA determination in both bulk and soil samples. These results pointed out the promising electrochemical modified sensor for the direct and simple detection of certain herbicides in environmental matrices, without the need for sample pretreatment steps. This capability supports sustainable development goals by enhancing effective environmental monitoring.

Highly Porous Scandium(III) Tetrafluoroisophthalate Framework for Adsorptive Separation of Light Alkanes

The separation of light alkanes is one of the most important tasks for modern industry due to the widespread use of ethane and propane as chemical feedstocks. Their extraction from natural gas is a challenging task and is now carried out by cryogenic distillation at a limited number of plants around the world. The development of new materials for adsorption separation is therefore important. Among the different types of adsorbents, metal-organic frameworks (MOFs) are one of the most interesting due to their infinite design possibilities. Here we present a highly porous perfluorinated MOF [Sc(OH)(1,3-tFbdc)] (1,1,3-tFbdc2-─1,3-C6F4(COO)22- tetrafluoroisophthalate linker) with a BET surface area greater than 1000 m·g-1 and its ability to separate light alkanes was investigated. The ability of 1 to separate light hydrocarbons at 0 and 25 °C is demonstrated by IAST calculation of selectivity factors as well as by dynamic breakthrough experiments. The role of fluorine substituents within the organic linker of MOF 1 in gas adsorption is revealed by quantum chemical calculations.

Dimensionally Extending from 1D MX-Chain to Ladder and Nanotube Systems: Structural and Electronic Properties

Molecular one-dimensional (1D) electron systems have attracted much attention due to their unique electronic state, physical and chemical properties derived from high-aspect-ratio structures. Among 1D materials, mixed-valence halogen-bridged transition-metal chain complexes (MX-chains) based on coordination assemblies are currently of particular interest because their electronic properties, such as mixed-valence state and band gap, can be controlled by substituting components and varying configurations. In particular, chemistry has recently noted that dimensionally extending MX-chains through organic rung ligands can introduce and modulate electronic coupling of metal atoms between chains, i. e., interchain interactions. In this review, for the first time, we highlight the recent progress on MX systems from the viewpoint of dimensionally extending from 1D chain to ladder and nanotube, mainly involving structural design and electronic properties. Overall, dimensional extension can not only tune the electronic properties of MX-chain, but also build the unique platform for studying transport dynamics in confined space, such as proton conduction. Based on these features, we envision that the MX-chain systems provide valuable insights into deep understanding of 1D electron systems, as well as the potential applications such as nanoelectronics.

Thermodynamics of Polyethylene Glycol Intrusion in Microporous Water

Polymers can be used to augment the properties of microporous materials, affording enhanced processability, stability, and compatibility. Manipulating polymers to target specific properties, however, requires detailed knowledge of how different polymers and microporous materials interact. Here, we report a study of the thermodynamics of polyethylene glycol (PEG) intrusion into a representative hydrophobic zeolite (silicalite-1) and metal-organic framework [ZIF-67; Co(2-methylimidazolate)2] in water, both of which can be formed into colloidally stable aqueous dispersions─termed "microporous water"─with dry, guest-accessible pore networks. Through a combination of O2 capacity measurements and isothermal titration calorimetry (ITC), we establish relationships between PEG intrusion behavior, polymer length, polymer end groups, and the structure of the microporous framework. In particular, we find that PEG intrusion is exothermic for silicalite-1 but endothermic for ZIF-67. Our results provide fundamental insights into polymer intrusion in microporous materials that should inform efforts to design composite solids and fluids with enhanced functionality.

Antimicrobial zeolites and metal-organic frameworks

The current surge in antibiotic resistance and the emergence of pandemics have created an urgent need for novel antimicrobial strategies. The controlled release of antimicrobial active principles remains the most viable strategy to date, and transition metal ions currently represent the main alternative to antibiotics. In this review, we explore the potential of two types of materials, zeolites and metal-organic frameworks (MOFs), for the controlled release of antimicrobial active principles, notably transition metal ions. These materials have unique crystalline microporous structures that act as reservoirs, enabling sustained bactericidal effects in various applications such as coatings, packaging, and medical devices. However, there are currently no convenient and standardised methods for evaluating their metal ion release and antimicrobial efficacy. This work discusses analytical techniques and the proposed mechanisms of action while highlighting recent advances in film, membrane, and coating technologies. By addressing the current limitations, microporous materials can revolutionise antimicrobial approaches, offering enhanced effectiveness and long-term sustainability.

MnO2 nanoparticles enhance the activity of the Zr-MOF matrix electrochemical sensor for efficiently identifying ultra-trace tetracycline residues in food

A novel nanobiosensor was constructed by in situ locating nanometer MnO2 particles with controllable size and morphology in a Zr-MOF substrate to serve as an electrochemical probe. The synergistic effect of the two components, Zr-MOFs with high specific surface area and compatibility as a carrier for MnO2, resulted in improved electrochemical activity and excellent electrochemical identification performance for the MnO2@Zr-MOF/GCE biosensor. Under optimized experimental conditions and using CV and DPV technology, the biosensor showed a wide linear detection range (2-200 μM), a low detection limit (2.577 × 10-8 M), a recovery range (106.26-115.01%), and maximum relative standard deviation (5.155) for tetracycline (TC) identification. The recognition mechanism of the sensor was investigated adopting Laviron adsorption theory. The applicability of the sensor was verified through practical measurements. Overall, the MnO2 @Zr-MOF/GCE sensor possesses the advantages of fast analysis speed, high sensitivity, high selectivity, and simple operation, making it suitable for detecting trace amounts of TC in food.

TCNQ and Its Derivatives as Electrode Materials in Electrochemical Investigations-Achievement and Prospects: A Review

7,7',8,8'-tetracyanoquinodimethane (TCNQ) is one of the most widely used effective surface electron acceptors in organic electronics and sensors, which opens up a very interesting field in electrochemical applications. In this review article, we outline the historical context of electrochemically stable selective electrode materials based on TCNQ and its derivatives and their development, their electrochemical characteristics, and the experimental aspects of their electrochemical applications. TCNQ-modified electrodes are characterized by long-term stability, reproducibility, and a low detection limit compared to other sensors; thus, their use can increase determination speed and flexibility and reduce investigation costs. TCNQ and its derivatives can also be successfully combined with other detector materials for cancer-related clinical diagnostic testing. Examples of simple, rapid, and sensitive detection procedures for various analytes are provided. Applications of new electrochemically stable TCNQ-based metal/covalent-organic hybrid frameworks, with exceptionally large surface areas, tunable pore sizes, diverse functionality, and high electrical conductivity, are also presented. As a result, they also offer enormous potential as revolutionary catalysts, drug carrier systems, and smart materials, as well as for use in gas storage. The use of TCNQ compounds as promising active electrode materials in high-power organic batteries/energy storage devices is discussed. We hope that the information featured in this review will provide readers with a good understanding of the chemistry of TCNQ and, more importantly, help to find good ways to prepare new micro-/nanoelectrode materials for rational sensor design.

Three in one: engineering MOF channels via coordinated water arrays for regulated separation of alkanes and alkenes

Purifying alkenes (mainly ethylene and propylene) by removing their corresponding alkanes is crucial yet challenging in the chemical industry. Selective physisorption shows promise for effective separation but demands precise pore dimensions and/or pore chemistry of adsorbents. We report an yttrium-based metal-organic framework, Y2(TCHB)(OH)2·2H2O (HIAM-317, TCHB = 3,3',5,5'-tetrakis(4-carboxyphenyl)-2,2',4,4',6,6'-hexamethyl-1,1'-biphenyl), that can separate ethylene/ethane and propylene/propane via mechanisms regulated by coordinated water arrays. In the presence of coordinated water arrays, HIAM-317 sieves alkanes from alkenes. When fully activated by removing coordinated water arrays, it selectively adsorbs ethane over ethylene and propylene over propane. This separation ability has been experimentally verified, and the underlying mechanism was uncovered through theoretical calculations and modeling.

Single Crystalline, Non-Stoichiometric Hydrogen-Bonded Organic Frameworks Showing Versatile Fluorescence Depending on Composition Ratios and Distributions

Hydrogen-bonded organic frameworks (HOFs) composed of multicomponent molecules in a non-stoichiometric composition have drawn great interest due to their tunable properties. However, the photobehavior of the single crystals of such mixed HOFs has not been explored. Here, we report on the synthesis, characterization and photobehavior of single crystalline non-stoichiometric HOFs (NS-HOFs). NS-HOFs (BTNT-1) with various composition ratios were successfully obtained as single crystals from two analogue tetratopic carboxylic acids, possessing naphthalene and benzothiadiazole cores (NTTA and BTTA, respectively). The heterogeneous distribution of the components was thoroughly confirmed by time-resolved fluorescence microscopy and local crystallographic analysis using focused synchrotron X-ray radiation. The versatile fluorescence of BTNT-1 behavior depends on the composition ratio and distribution of the component in the single crystals. We observed not only fluorescence bands with various colors such as purple, blue, green and white, depending on the composition ratios, but also different emission bands from a single crystal. We provide details on their emission lifetimes following the composition, emission color and targeted region on the crystal. This work is the first example of single crystal studies applied to organic porous co-crystals and demonstrates unique and versatile optical properties of carboxylic acid-based NS-HOFs. The results provide a concept of creating functional mixed porous materials capable of different and tunable optical properties.

Close-packing effect of water clusters within metal-organic framework pores on proton conductivity: a dielectric relaxation phenomenon in loose space and colossal dielectric permittivity

Proton-conducting metal-organic frameworks (MOFs) have attracted tremendous attention for their promising application in proton-exchange membrane fuel cells. Water clusters play an extremely important role in the proton-conduction process and affect the proton conductivity of host materials. To date, the close-packing effect of water clusters within pores on proton conductivity due to the amorphous structure of commercial proton-exchange membranes is unclear. Herein, we prepared two crystalline MOFs containing different water clusters, namely, [Sm2(fum)3(H2O)4]·3H2O (Sm-fum-7H2O) and [Er2(fum)3(H2O)4]·8H2O (Er-fum-12H2O) (H2fum = fumaric acid), and regulated their proton conductivities by changing the water clusters. As expected, Sm-fum-7H2O showed a high proton conductivity of 6.89 × 10-4 S cm-1 at 333 K and ∼97% RH because of the close packing of the water clusters within the pores triggered by a lanthanide contraction effect, outperforming that of Er-fum-12H2O and some previously reported MOFs. Additionally, Sm-fum-7H2O and Er-fum-12H2O demonstrated high dielectric functions, reaching 2.22 × 103 and 1.42 × 105 at 102.5 Hz, respectively, making Er-fum-12H2O a highly dielectric material. More importantly, broadband dielectric spectroscopy measurements indicated that there was a dielectric relaxation process in Er-fum-12H2O with an activation energy of 0.59 eV. The present findings provide a better understanding of the crucial role of confined water clusters in proton conductivity and the novel phenomenon of the coexistence of proton conduction and dielectric relaxation in crystalline MOF materials.

2D Nitrogen-Doped Graphene Materials for Noble Gas Separation

Noble gases, notably xenon, play a pivotal role in diverse high-tech applications. However, manufacturing xenon is an inherently challenging task, due to its unique properties and trace abundance in the Earth's atmosphere. Consequently, there is a pressing need for the development of efficient methods for the separation of noble gases. Using mild fluorographene chemistry, nitrogen-doped graphene (GNs) materials are synthesized with abundant aromatic regions and extensive nitrogen doping within the vacancies and holes of the aromatic lattice. Due to the organized interlayer "nanochannels", nitrogen functional groups, and defects within the two-dimensional (2D) structures, GNs exhibits effective selectivity for Xe over Kr at low pressure. This enhanced selectivity is attributed to the stronger binding affinity of Xe to GN compared to Kr. The adsorption is governed by London dispersion forces, as revealed by theoretical calculations using symmetry-adapted perturbation theory (SAPT). Investigation of other GNs differing in nitrogen content, surface area, and pore sizes underscores the significance of nitrogen functional groups, defects, and interlayer nanochannels over the surface area in achieving superior selectivity. This work offers a new perspective on the design and fabrication of functionalized graphene derivatives, exhibiting superior noble gas storage and separation activity exploitable in gas production technologies.

Integrating Biocatalysts into Metal-Organic Frameworks: Disentangling the Roles of Affinity, Molecular Weight, and Size

The integration of biocatalysts within metal-organic frameworks (MOFs) is attracting growing interest due to its potential to both enhance biocatalyst stability and sustain biocatalyst activity in organic solvents. However, the factors that facilitate the post-synthetic infiltration of such large molecules into MOF pores remain unclear. This systematic study enabled the identification of the influence of biocatalyst molecular size, molecular weight and affinity on the uptake by an archetypal MOF, NU-1000. We analyzed a range of six biocatalysts with molecular weights from 1.9 kDa to 44.4 kDa, respectively. By employing a combination of fluorescence tagging and 3D-STED confocal laser scanning microscopy, we distinguished between biocatalysts that were internalized within the MOF pores and those sterically excluded. The catalytic functions of the biocatalysts hosted within the MOF were investigated and found to show strong variations relative to the solvated case, ranging from a two-fold increase to a strong decrease.

Dual Signature of Chirality Induced Spin Selectivity through Spontaneous Resolution of 2D Metal-Organic Frameworks

The Chiral-Induced Spin Selectivity (CISS) effect has emerged as a fascinating phenomenon within the realm of electron's spin manipulation, showcasing a unique interplay between electron's spin and molecular chirality. Subsequent to its discovery, researchers have been actively involved in exploring the new chiral molecules as effective spin filters. In the realm of observing the CISS effect, the conventional approach has mandated the utilization of two distinct enantiomers of chiral molecules. However, this present study represents a significant advancement by demonstrating the ability to control both spin states of electrons in a single system. In this work, we have demonstrated the preparation of chiral metal-organic frameworks (MOFs) via a "spontaneous resolution" process, obviating the requirement for chiral sources. This resulted in the production of chiral crystals exhibiting opposite handedness (1P and 1M) and these crystals were subsequently employed as a new class of spin filters based on CISS effect. Remarkably, this work signifies the first instance of achieving dual signature of spin selectivity from a single and exclusively achiral system through a spontaneous resolution process. This holds immense potential as it facilitates the production of two distinct spin-filtering materials from a unified system. Furthermore, we investigated the contact potential differences (CPD) of these chiral crystals and, for the first time, associated it with the preferential spin transport properties. Our findings revealed a correlation between the CPD and the chirality of the crystals, as well as the magnetization orientations of the ferromagnetic substrate, which can be elucidated by the CISS effect. In overall, the significant findings achieved using these robust and easily synthesized MOF crystals without the requirement for chiral medium represent a crucial advancement in enhancing the effectiveness of spin filtering materials to produce spintronic devices.

Energetic coordination polymers (ECPs) based on tetrazole N-oxides: green nitrogen-rich energetic complexes of variable dimensions

In recent years, it has been demonstrated that the energetic properties of many tetrazole-containing compounds can be enhanced through the formation of the corresponding N-oxides. The introduction of N-O groups increases the oxygen balance of tetrazole compounds, while providing additional coordination sites and enriching the coordination modes between tetrazole compounds and metal ions. The introduction of O atoms alters the polarity of the substance from N to N-O, the packing and density increase and therefore the detonation velocity (VD) and pressure (P) also increase. Based on this, energetic coordination polymers (ECPs) with tetrazole N-oxides serving as ligands possess extremely high research value. In this paper, we aim to summarize the existing ECPs based on tetrazole N-oxides briefly and discuss their advantages, emphasizing their excellent stability and application prospects.

Structural Comparisons, Fluorescence Properties, and Glass-to-Crystal Transformations of Heat-Cooled and Melt-Quenched Zeolitic Imidazolate Framework Glass

As a representative of zeolitic imidazolate framework glass, agZIF-62 has been reported to be synthesized using a melt-quenching method in which the ZIF-62 crystal is heated to a temperature above the melting point. Interestingly, we unexpectedly found that agZIF-62 can also be synthesized by simple heating at temperatures lower than the melting point, which may be assisted by the release of encapsulated solvent molecules. The structural differences between melt-quenched agZIF-62 (MQ-agZIF-62) and heat-cooled agZIF-62 (HC-agZIF-62) were investigated. The results indicated that MQ-agZIF-62 is closer to the liquid state, while HC-agZIF-62 is closer to the crystal state. Interestingly, their luminescent emissions exhibit significant differences. Compared with the ZIF-62 crystal, MQ-agZIF-62 showed a blue-shift of 14 nm, whereas HC-agZIF-62 showed a red-shift of 9 nm. The emission intensity of agZIF-62 is also significantly stronger than that of ZIF-62; thus, rapid semiquantitative detection of the content of the MOF glass in glass and crystal mixtures can be achieved. In addition, HC-agZIF-62 and MQ-agZIF-62 can transform into ZIF-62 crystals via a solvent-media mechanism. This study provides new insights into ZIF-62 glass.

Biosensor Based on ZIF-67-HRP and MWCNTs Nanocomposite Modified Glass Carbon Electrode for the Detection of Luteolin in Vegetables

Luteolin has various pharmacological properties, including anti-inflammatory, antioxidant, and antitumor characteristics. Due to its potential value in drugs and functional foods, it is important to develop an efficient method for detecting luteolin. In this work, the poor selectivity of existing luteolin nonenzymatic sensors was solved by translating the enzyme-catalyzed reaction from bulk solution to the surface of a horseradish peroxidase (HRP) modified electrode through an electrocatalytic oxidation process. Here, we modified the surface of a glassy carbon electrode (GCE) with metal-organic frameworks (MOFs; ZIF-67 here, abbreviated as ZIF), functional nanomaterials, and HRP and finally covered it with Nafion (NF). In this case, luteolin acts as a hydrogen donor, and the electrode acts as a hydrogen acceptor; the oxidation reaction occurs on the electrode surface. The use of ZIF-67 ensured the conformational stability of HRP to ensure the selectivity and anti-interference property, and SDS-dispersed multiwalled carbon nanotubes (MWCNTs) enhanced the electrode conductivity. The use of NF avoids shedding of the electrode material during the testing process. A UV-vis spectrophotometer was used to study the selectivity of luteolin by HRP and the compatibility between HRP and ZIF. The materials were characterized and analyzed by scanning electron microscopy and transmission electron microscopy. Due to the synergistic effect of these nanomaterials, the linear range of NF/ZIF-HRP/MWCNTs-SDS/GCE was 1.0 × 10-2 to 6.0 μM, with detection limits of 25.3 nM (S/N = 3). The biosensor showed long-term stability and reproducibility, with a relative standard deviation of 4.2% for the peak current (n = 5). Finally, the biosensor was successfully used to detect luteolin in carrots, celery, and cauliflower.

Revolutionizing Tetracycline Hydrochloride Remediation: 3D Motile Light-Driven MOFs Based Micromotors in Harsh Saline Environments

Traditional light-driven metal-organic-frameworks (MOFs)-based micromotors (MOFtors) are typically constrained to two-dimensional (2D) motion under ultraviolet or near-infrared light and often demonstrate instability and susceptibility to ions in high-saline environments. This limitation is particularly relevant to employing micromotors in water purification, as real wastewater is frequently coupled with high salinity. In response to these challenges, ultrastable MOFtors capable of three-dimensional (3D) motion under a broad spectrum of light through thermophoresis and electrophoresis are successfully synthesized. The MOFtors integrated photocatalytic porphyrin MOFs (PCN-224) with a photothermal component made of polypyrrole (PPy) by three distinct methodologies, resulting in micromotors with different motion behavior and catalytic performance. Impressively, the optimized MOFtors display exceptional maximum velocity of 1305 ± 327 µm s-1 under blue light and 2357 ± 453 µm s-1 under UV light. In harsh saline environments, these MOFtors are not only maintain high motility but also exhibit superior tetracycline hydrochloride (TCH) removal efficiency of 3578 ± 510 mg g-1, coupling with sulfate radical-based advanced oxidation processes and peroxymonosulfate. This research underscores the significant potential of highly efficient MOFtors with robust photocatalytic activity in effectively removing TCH in challenging saline conditions, representing a substantial advancement in applying MOFtors within real-world water treatment technologies.

An ultrasound assisted dispersive micro solid-phase extraction and a composite ionic liquid-metal organic framework for sixteen polycyclic aromatic hydrocarbons analysis in fruit juice and environmental water samples

Aluminum-based metal organic framework composite containing ionic liquid was prepared and used as sorbent for extraction of sixteen polycyclic aromatic hydrocarbons in list of priority pollutants of United States Environmental Protection Agency before their analysis by gas chromatography/mass spectrometry. The dispersive micro solid-phase extraction method, known as a simple and fast method, was preferred as the extraction method. The optimized parameter conditions were 5 mL of sample solution, 10 min sonication by ultrasonic bath, 30 mg of sorbent, 30 °C extraction temperature, 0.1 mL of hexane as elution solvent with 5 min elution time. The suggested method presented that limit of detection and limit of quantification were in the range of 0.01-0.10 μg l-1, and 0.04-0.33 μg L-1, respectively. The intra-day and inter-day repeatability were within the ranges of 1.18-4.88 % and 1.02-5.06 %, respectively. The recoveries for polycyclic aromatic hydrocarbons in peach juice, cherry juice, tap water and rain water samples were obtained in the range of 84.9-99.9 % for spiked 5, 50 and 100 μg l-1 standard polycyclic aromatic hydrocarbons solution.

Designing antibacterial materials through simulation and theory

Antibacterial materials have a wide range of potential applications in bio-antimicrobial, environmental antimicrobial, and food antimicrobial fields due to their intrinsic antimicrobial properties, which can circumvent the development of drug resistance in bacteria. Understanding the intricate mechanisms and intrinsic nature of diverse antibacterial materials is significant for the formulation of guidelines for the design of materials with rapid and efficacious antimicrobial action and a high degree of biomedical material safety. Herein, this review highlights the recent advances in investigating antimicrobial mechanisms of different antibacterial materials with a particular focus on tailored computer simulations and theoretical analysis. From the view of structure and function, we summarize the characteristics and mechanisms of different antibacterial materials, introduce the latest advances of new antibacterial materials, and discuss the design concept and development direction of new materials. In addition, we underscore the significance of employing simulation and theoretical methodologies to elucidate the intrinsic antimicrobial mechanisms, which is crucial for a comprehensive comprehension of the control strategies, safer biomedical applications, and the management of health and environmental concerns associated with antibacterial materials. This review could potentially stimulate further endeavors in fundamental research and facilitate the extensive utilization of computational and theoretical approaches in the design of novel functional nanomaterials.

Understanding the Adsorption and Diffusion Behaviors of PBUT in Biocompatible MOFs

With the increasing incidence of chronic kidney disease, the effective control of protein-bound uremic toxins (PBUTs), which are difficult to remove through dialysis, has become a priority. In this study, the adsorption and diffusion behaviors of several metal-organic frameworks (MOFs) for PBUTs (indoxyl sulfate and p-cresyl sulfate) were studied by molecular dynamics (MD) simulations and umbrella sampling. For the NU series of MOFs, good correlations between the Gibbs free energy (ΔG) and the experimental clearance rates of PBUTs are found. For the adsorption behaviors, in terms of ΔG, DAJWET exhibits the best adsorption effect for indoxyl sulfate (IS), whereas NU-1000 shows the best effect for p-cresyl sulfate (pCS). Similar trends observed in the radial distribution function and mean square displacement results suggest that the π-π stacking interactions play a crucial role in the adsorption and diffusion of PBUTs by MOFs. Furthermore, it can be concluded that MOFs with highly conjugated groups (porphyrin rings and pyrene groups) tend to generate more PBUT attraction, and provide design principles for potential MOF candidates in the removal of PBUTs.

From Nanozymes to Multi-Purpose Nanomaterials: The Potential of Metal-Organic Frameworks for Proteomics Applications

Metal-organic frameworks (MOFs) have the potential to revolutionize the biotechnological and medical landscapes due to their easily tunable crystalline porous structure. Herein, the study presents MOFs' potential impact on proteomics, unveiling the diverse roles MOFs can play to boost it. Although MOFs are excellent catalysts in other scientific disciplines, their role as catalysts in proteomics applications remains largely underexplored, despite protein cleavage being of crucial importance in proteomics protocols. Additionally, the study discusses evolving MOF materials that are tailored for proteomics, showcasing their structural diversity and functional advantages compared to other types of materials used for similar applications. MOFs can be developed to seamlessly integrate into proteomics workflows due to their tunable features, contributing to protein separation, peptide enrichment, and ionization for mass spectrometry. This review is meant as a guide to help bridge the gap between material scientists, engineers, and MOF chemists and on the other side researchers in biology or bioinformatics working in proteomics.

Single-Crystal Structural Analysis of 2D Metal-Organic Frameworks and Covalent Organic Frameworks by Three-Dimensional Electron Diffraction

ConspectusIn the development of 2D metal-organic frameworks (MOFs) and 2D covalent organic frameworks (COFs), obtaining structural details at the atomic level is crucial to understanding their properties and related mechanisms in potential applications. However, since 2D-MOFs and COFs are composed of layered structures and often exhibit sheet-like morphologies, it is challenging to grow large crystals suitable for single-crystal X-ray diffraction (SCXRD). Therefore, ab initio structure determination, which refers to solving the structure directly from experimental data without using any prior knowledge or computational input, is extremely rare for 2D-MOFs and COFs. In contrast to SCXRD, three-dimensional electron diffraction (3DED) only requires crystals sized in tens or hundreds of nanometers, making it an ideal method for single-crystal analysis of 2D-MOFs and COFs and obtaining their fine structural details.In this Account, we describe our recent development of the 3DED method and its application in structure determination and property studies of 2D-MOFs and COFs. A key development is the establishment of a continuous 3DED data collection protocol. By collecting electron diffraction (ED) patterns continuously while performing crystal tilting, the electron dose applied to the target nanocrystal is greatly reduced. This allows the acquisition of high-resolution 3DED data from 2D-MOFs and COFs by minimizing their damage under the electron beam. We have also developed an approach to couple 3DED with real-space structure solution methods, i.e., simulated annealing (SA), for single-crystal structural analysis of materials that do not have high crystallinity. We successfully determined two 2D-COF structures by combining 3DED with SA.We provide several examples demonstrating the application of 3DED for the ab initio structure determination of 2D-MOFs and COFs, revealing not only their in-plane structures but also their stacking modes at the atomic level. Notably, the obtained structural details serve as the foundation for further understanding the properties of 2D-MOFs and COFs, such as their electronic band structures, charge mobilities, etc. Beyond structure determination, we describe our work on using 3DED as a high-throughput method for the discovery of new materials. Using this approach, we discovered a novel MOF that was present only in trace amounts within a multiphasic mixture. Through this discovery, we were able to tune the synthesis conditions to obtain its pure phase.We detail how 3DED can be used to probe different levels of molecular motions in MOFs through the analysis of anisotropic displacement parameters (ADPs). Additionally, we show that 3DED can provide accurate information about intermolecular weak interactions such as hydrogen bonding and van der Waals (vdW) interactions. Our studies demonstrate that 3DED is a valuable method for the structural analysis of 2D-MOFs and COFs. We envision that 3DED can accelerate research in these fields by providing unambiguous structural models at the atomic level.

A chemical perspective on the chiral induced spin selectivity effect

This review discusses opportunities in chemistry that are enabled by the chiral induced spin selectivity (CISS) effect. First, the review begins with a brief overview of the seminal studies on CISS. Next, we discuss different chiral material systems whose properties can be tailored through chemical means, with a special emphasis on hybrid organic-inorganic layered materials that exhibit some of the largest spin filtering properties to date. Then, we discuss the promise of CISS for chemical reactions and enantioseparation before concluding.

In-situ imaging of heat-induced phase transition in a two-dimensional conjugated metal-organic framework

Atomically-resolved in-situ high-resolution transmission electron microscopy (HRTEM) imaging of the structural dynamics in organic materials remains a major challenge. This difficulty persists even with aberration-corrected instruments, as HRTEM images necessitate a high electron dose that is generally intolerable for organic materials. In this study, we report the in-situ HRTEM imaging of heat-induced structural dynamics in a benzenehexathiol-based two-dimensional conjugated metal-organic framework (2D c-MOF, i.e., Cu3(BHT)). Leveraging its hydrogen-free structure and high electrical conductivity, Cu3(BHT) exhibits high electron beam resistance. We demonstrate atomic resolution imaging at an 80 kV electron accelerating voltage using our Cc/Cs-corrected SALVE instrument. However, continuous electron irradiation eventually leads to its amorphization. Intriguingly, under heating in a MEMS holder, the Cu3(BHT) undergoes a phase transition to a new crystalline phase and its phase transition, occurring within the temperature range of 480 °C to 620 °C in dependence on the electron beam illumination. Using HRTEM and energy-dispersive X-ray mapping, we identify this new phase as CuS. Our findings provide insights into the mechanisms governing structural transitions in purposefully engineered structures, potentially pivotal for future endeavours involving the production of metal oxide/sulfide nanoparticles from MOF precursors.

Time-resolved serial femtosecond crystallography for investigating structural dynamics of chemical systems

Time-resolved serial femtosecond crystallography (TR-SFX) has emerged as a crucial tool for studying the structural dynamics of proteins. In principle, TR-SFX has the potential to be a powerful tool not only for studying proteins but also for investigating chemical reactions. However, non-protein systems generally face challenges in indexing due to sparse Bragg spots and encounter difficulties in effectively exciting target molecules. Nevertheless, successful TR-SFX studies on chemical systems have been recently reported in a few instances, boding well for the application of TR-SFX to study chemical reactions in the future. In this context, we review the static SFX and TR-SFX studies conducted on chemical systems reported to date and suggest prospects for future research directions.

Recent advances in photonic crystal-based chemical sensors

The increasing attention towards environmental quality, food safety, public security and medical diagnosis demands high requirements and standards for chemical sensors with merits of rapid response, high precision, long-term stability and reusability. In this case, a prominent innovation in sensory materials holds potential to realize new generations of chemical sensor technologies. Specifically, photonic crystals (PCs) as structured dielectric materials with spatially periodic ordered arrangements offer unique advantages in improving the sensing performance of chemical sensors. Consequently, the promising properties of PCs promote research on their implementation as an integral part of chemical sensors. This review highlights the integration of PCs into chemical sensors including a range of building blocks for the construction of PCs with versatile opal or opal inverse structural architectures and a delicate choice of surface functionality with associated sensing interfaces for target recognition and signal transduction. Subsequently, based on their synthesis and functionality, we focus on introducing the sensing principles of recent advances in PC-based chemical sensors, such as reflection spectra-based sensing, visual colorimetric sensing, fluorescence sensing, surface-enhanced Raman spectroscopy (SERS)-based sensing and other integrated sensing. Finally, the future prospects and challenges are discussed for the further improvement of PC-based chemical sensors.

Room-temperature synthesis of a Zr-UiO-66 metal-organic framework via mechanochemical pretreatment for the rapid removal of EDTA-chelated copper from water

Treatment of heavy metal pollution in complexed states within water bodies presents significant challenges in the current water treatment field. Adsorption as a means for the removal of heavy metals is characterized by its simplicity of operation, stable effluent, and minimal equipment requirements. Metal-organic frameworks (MOFs) as adsorbents hold significant interest for applications in water treatment. In this study, we investigated a green synthesis approach for the ball-milling pretreated synthesis of UiO-66(Zr) at room temperature, abbreviated as UiO-66(Zr)-rm. Besides having the same thermal stability and crystal structure as the product from microwave-assisted synthesis (UiO-66(Zr)-mw), the resulting UiO-66(Zr)-rm features smaller particle size and superior mesoporous structure. The adsorption efficiency and mechanism for removing EDTA-chelated copper (EDTA-CuII), a complexed heavy metal in water, were extensively analyzed. UiO-66(Zr)-rm presented a maximum adsorption capacity over EDTA-CuII of 43 mg g-1 and a much higher adsorption rate (0.16 g (mg h)-1) than UiO-66(Zr)-mw (0.06 g (mg h)-1). Hierarchically mesostructured defects allow the sorbate to have more effective diffusion in a shorter time to achieve faster adsorption kinetics. Benefiting from the mild synthesis conditions and nontoxic solvents, UiO-66(Zr) has the potential to be produced at a scaled-up level, thereby exhibiting excellent adsorption performance for the removal of complexed heavy metals in the future.

Engineering Insights into Tailored Metal-Organic Frameworks for CO2 Capture in Industrial Processes

Despite the known impacts on climate change of carbon dioxide emissions, the continued use of fossil fuels for energy generation leading to the emission of carbon dioxide (CO2) into the atmosphere is evident. Therefore, innovation to address and reduce CO2 emissions from industrial operations remains an urgent and crucial priority. A viable strategy in the area is postcombustion capture mainly through absorption by aqueous alkanolamines, which focuses on the separation of CO2 from flue gas, despite its limitations. Within this context, porous materials, particularly metal-organic frameworks (MOFs), have arisen as favorable alternatives owing to their significant adsorption capacity, selectivity, and reduced regeneration energy demands. This research evaluates the engineering insights into tailored MOFs for enhanced CO2 capture, focusing on three series of MOFs (ZIF, UiO-66, and BTC) to investigate the effects of organic ligands, functional groups, and metal ions. The evaluation encompassed a range of aspects including adsorption isotherms of pure gases [CO2 and nitrogen (N2)] and mixed gas mixture (CO2 and N2 with 15:85% ratio), along with utilization of the ideal adsorbed solution theory (IAST) to simulate multicomponent gas adsorption isotherms. Moreover, the reliability of IAST for mixed gas adsorption prediction has been investigated in detail. The research offers valuable insights into the correlation between the characteristics of MOFs and their effectiveness in gas separation and how these characteristics contribute to the differences between IAST predictions and experimental results. The findings enhance the understanding of how to enhance MOF characteristics in order to reduce CO2 emissions and also highlight the need for advanced models that consider thermodynamic nonidealities to accurately predict the behavior of mixed gas adsorption in MOFs. As a result, the incorporation of MOFs with enhanced predictability and reliability into CO2 capture industrial processes is facilitated.

An Overview of Various Applications of Cadmium Carboxylate Coordination Polymers

This review highlights the most recent applications of Cd(II)-carboxylate-based coordination polymers (Cd(II)-CBCPs), such as sensors, catalysts, and storage materials, in comparison with those of Zn(II) counterparts. A wide range of species with luminescence properties were designed by using proper organic fluorophores, especially a carboxylate bridging ligand combined with an ancillary N-donor species, both with a rigid structure. These characteristics, combined with the arrangement in Cd(II)-CBCPs' structure and the intermolecular interaction, enable the sensing behavior of a plethora of various inorganic and organic pollutants. In addition, the Lewis acid behavior of Cd(II) was investigated either in developing valuable heterogeneous catalysts in acetalization, cyanosilylation, Henry or Strecker reactions, Knoevenagel condensation, or dyes or drug elimination from wastewater through photocatalysis. Furthermore, the pores structure of such derivatives induced the ability of some species to store gases or toxic dyes. Applications such as in herbicides, antibacterials, and electronic devices are also described together with their ability to generate nano-CdO species.

Supramolecular Assembly Frameworks (SAFs): Shaping the Future of Functional Materials

Supramolecular assembly frameworks (SAFs) represent a new category of porous materials, utilizing non-covalent interactions, setting them apart from metal-organic frameworks (MOFs) and covalent organic frameworks (COFs). This category includes but is not restricted to hydrogen-bonded organic frameworks and supramolecular organic frameworks. SAFs stand out for their outstanding porosity, crystallinity, and stability, alongside unique dissolution-recrystallization dynamics that enable significant structural and functional modifications. Crucially, their non-covalent assembly strategies allow for a balanced manipulation of porosity, symmetry, crystallinity, and dimensions, facilitating the creation of advanced crystalline porous materials unattainable through conventional covalent or coordination bond synthesis. Despite their considerable promise in overcoming several limitations inherent to MOFs and COFs, particularly in terms of solution-processability, SAFs have received relatively little attention in recent literature. This Minireview aims to shed light on standout SAFs, exploring their design principles, synthesis strategies, and characterization methods. It emphasizes their distinctive features and the broad spectrum of potential applications across various domains, aiming to catalyze further development and practical application within the scientific community.

Green synthesis of MIL53(Al)-modified paper-based analytical device for efficient extraction of neonicotinoid insecticides from environmental water samples

BACKGROUND

There is a need to develop low-cost, reliable and portable devices to enhance the efficiency of microextraction techniques in complex samples. Metal-organic frameworks (MOFs) have proven to be promising sorbents due to their well-documented properties. However, their green preparation and combination with paper-based substrates have not been satisfactorily explored to fabricate sustainable sorptive phases.

RESULTS

In this work, the hybridization of a paper substrate (as a sustainable support) with MOFs (as a sorptive phase) was carried out by one-pot approach. Concretely, the selected MOF, MIL-53(Al), was in-situ growth onto the paper surface in aqueous solution without the need for high temperature or pressure, thereby aligning with the Green Analytical Chemistry principles. The optimized composite (MIL-53(Al)@cellulose paper) was characterized and evaluated as extraction sorbent for five neonicotinoids (NEOs) (thiamethoxam, clothianidin, imidacloprid, acetamiprid, and thiacloprid). Furthermore, its feasibility was demonstrated by isolating these pollutants from environmental water samples, followed their determination by HPLC coupled to diode array detection. The whole method showed satisfactory analytical performance with recoveries between 86 and 114 %, suitable precision (with RSD lower than 14 %), and limits of detection ranged from 1.0 to 1.6 μg L-1. Besides, the greenness of the method was assessed by application of different existing metrics. The developed extraction device was affordable (<0.08 €/device) and mechanical and chemically stable, being possible its reuse more than 11 cycles, thus demonstrating its suitability for rapid screening of pesticides in environmental samples.

SIGNIFICANCE

This report presents, for the first time, the green synthesis of MIL-53(Al)cellulose paper composite and its application as a sorptive phase for the extraction of NEOs from environmental water samples. We believe that the proposed strategy for fabricating these sustainable paper-based sorptive phases paves the way for further hybridizations with other MOFs or materials. Additionally, it opens up large possibilities for their application in extraction of pollutants or other hazardous compounds in aquatic environments.

Two-Dimensional Metal-Organic Frameworks/Epoxy Composite Coatings with Superior O2/H2O Resistance for Anticorrosion Applications

Corrosion protection technology plays a crucial role in preserving infrastructure, ensuring safety and reliability, and promoting long-term sustainability. In this study, we combined experiments and various analyses to investigate the mechanism of corrosion occurring on the epoxy-based anticorrosive coating containing the additive of two-dimensional (2D) and water-stable zirconium-based metal-organic frameworks (Zr-MOFs). By using benzoic acid as the modulator for the growth of the MOF, a 2D MOF constructed from hexazirconium clusters and BTB linkers (BTB = 1,3,5-tri(4-carboxyphenyl)benzene) with coordinated benzoate (BA-ZrBTB) can be synthesized. By coating the BA-ZrBTB/epoxy composite film (BA-ZrBTB/EP) on the surface of cold-rolled steel (CRS), we found the lowest coating roughness (RMS) of BA-ZrBTB/EP is 2.83 nm with the highest water contact angle as 99.8°, which represents the hydrophobic coating surface. Notably, the corrosion rate of the BA-ZrBTB/EP coating is 2.28 × 10-3 mpy, which is 4 orders of magnitude lower than that of the CRS substrate. Moreover, the energy barrier for oxygen diffusion through BA-ZrBTB/EP coating is larger than that for epoxy coating (EP), indicating improved oxygen resistance for adding 2D Zr-MOFs as the additive. These results underscore the high efficiency and potential of BA-ZrBTB as a highly promising agent for corrosion prevention in various commercial applications. Furthermore, this study represents the first instance of applying 2D Zr-MOF materials in anticorrosion applications, opening up new possibilities for advanced corrosion-resistant coatings.

Zirconium-based metal-organic frameworks and their roles in electrocatalysis

Due to their exceptional chemical stability in water and high structural tunability, zirconium(IV)-based MOFs (Zr-MOFs) have been considered attractive materials in the broad fields of electrocatalysis. Numerous studies published since 2015 have attempted to utilise Zr-MOFs in electrocatalysis, with the porous framework serving as either the active electrocatalyst or the scaffold or surface coating to further enhance the performance of the actual electrocatalyst. Herein, the roles of Zr-MOFs in electrocatalytic processes are discussed, and some selected examples reporting the applications of Zr-MOFs in various electrocatalytic reactions, including several studies from our group, are overviewed. Challenges, limitations and opportunities in using Zr-MOFs in electrocatalysis in future studies are discussed.