Improved optical quality of heteroepitaxially grown metal-organic framework thin films by modulating the crystal growth

Fabricating high-quality thin films of metal-organic frameworks (MOFs) is important for integrating MOFs in various applications. Specifically, optical/electrical devices require MOF thin films that are crystallographically oriented, with closely packed crystals and smooth surfaces. Although the heteroepitaxial growth approach of MOFs on metal hydroxides has been demonstrated to control the orientation of the three crystallographic axes, the fabrication of MOF thin films with both three-dimensional crystallographic orientation and smooth surfaces remains a challenge. In this study, we report the fabrication of high-quality thin films of MOFs with closely packed MOF crystals, smooth surfaces, optical transparency, and crystal alignment by modulating the crystal growth of MOFs using the heteroepitaxial growth approach. High-quality thin films of Cu-paddlewheel-based pillar-layered MOFs are fabricated on oriented Cu(OH)2 thin films via epitaxial growth using acetate ions as modulators to control the crystal morphology. Increasing the modulator concentration results in a uniform crystal shape with a relatively long one-dimensional pore direction and uniform heterogeneous nucleation over the entire film. The MOF thin films fabricated using the modulator exhibit high optical transparency. High-quality MOF thin films with dense and flat surfaces will pave the way for integrating MOFs into sophisticated optical and electrical devices.

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.

Direct Optical Patterning of Metal-Organic Frameworks via Photoacid-Induced Etching

Metal-organic frameworks (MOFs) are a class of porous materials constructed from organic linkers and inorganic building blocks. Coordinative competition labilizes some MOFs under harsh chemical conditions because of their weak bonding. However, instability is not always a negative property of a material. In this study, we demonstrated the use of the acidic lability of MOFs for direct optical patterning. The controllable acid release from the photoacid generator at the exposed area causes bond cleavage between the linkers and metal ions/clusters, leading to solubility changes and pattern formation after development. This process avoids redundant steps and possible contamination in traditional photolithography, while maintaining the original properties of patterned MOFs. The preserved porosity and crystallinity promoted the development of MOFs for gas sensors and solid displays.

Classification and Identification of Perfume Scents by an Enantioselective Colorimetric Sensor Array of Chiral Metal-Organic-Framework-Based Fabry-Pérot Films

Many odors, like perfumes, are complex mixtures of chiral and achiral molecules where the cost-efficient (enantio-)selective sensing represents a major technical challenge. Here, we present a colorimetric sensor array of surface-mounted metal-organic-framework (SURMOF) films in Fabry-Pérot (FP) cavities. The optical properties of the FP-SURMOF films with different chiral and achiral structures are affected by the (enantio-)selective adsorption of the analytes in the SURMOF pores, resulting in different responses to the analyte molecules. The read-out of the sensor array is performed by the digital camera of a common smartphone, where the RGB values are determined. By analyzing the sensor array data with simple machine learning algorithms, the analytes are discriminated. After demonstrating the enantioselective response for a pair of pure chiral odor molecules, we apply the sensor array to detect and discriminate a large number (16) of common commercial perfumes and eau de toilettes. While our untrained human nose is not able to discriminate all perfumes, the presented colorimetric sensor array can classify all perfumes with great classification accuracy. Moreover, the sensor array was used to identify unlabeled samples correctly. We foresee such an FP-chiral-SURMOF-based sensor array as a powerful approach toward inexpensive selective odors sensing applications.

Chemical Bonding and Crystal Structure Schemes in Atomic/Molecular Layer Deposited Fe-Terephthalate Thin Films

Advanced deposition routes are vital for the growth of functional metal-organic thin films. The gas-phase atomic/molecular layer deposition (ALD/MLD) technique provides solvent-free and uniform nanoscale thin films with unprecedented thickness control and allows straightforward device integration. Most excitingly, the ALD/MLD technique can enable the in situ growth of novel crystalline metal-organic materials. An exquisite example is iron-terephthalate (Fe-BDC), which is one of the most appealing metal-organic framework (MOF) type materials and thus widely studied in bulk form owing to its attractive potential in photocatalysis, biomedicine, and beyond. Resolving the chemistry and structural features of new thin film materials requires an extended selection of characterization and modeling techniques. Here we demonstrate how the unique features of the ALD/MLD grown in situ crystalline Fe-BDC thin films, different from the bulk Fe-BDC MOFs, can be resolved through techniques such as synchrotron grazing-incidence X-ray diffraction (GIXRD), Mössbauer spectroscopy, and resonant inelastic X-ray scattering (RIXS) and crystal structure predictions. The investigations of the Fe-BDC thin films, containing both trivalent and divalent iron, converge toward a novel crystalline Fe(III)-BDC monoclinic phase with space group C2/c and an amorphous Fe(II)-BDC phase. Finally, we demonstrate the excellent thermal stability of our Fe-BDC thin films.

Immobilization of europium and terbium ions with tunable ratios on a dispersible two-dimensional metal-organic framework for ratiometric photoluminescence detection of D2O

A two-dimensional zirconium-based metal-organic framework (2D Zr-MOF), ZrBTB (BTB = 1,3,5-tri(4-carboxyphenyl)benzene), is used as a platform to simultaneously immobilize terbium ions and europium ions with tunable ratios on its hexa-zirconium nodes by a post-synthetic modification. The crystallinity, morphology, porosity and photoluminescence (PL) properties of the obtained 2D Zr-MOFs with various europium-to-terbium ratios are investigated. With the energy transfer from the excited BTB linker to the installed terbium ions and the energy transfer from terbium ions to europium ions, a low loading of immobilized europium ions and a high loading of surrounding terbium ions in the 2D Zr-MOF result in the optimal PL emission intensities of europium; this phenomenon is not observable for the physical mixture of both terbium-installed ZrBTB and europium-installed ZrBTB. The role of installed terbium ions as efficient mediators for the energy transfer from the excited BTB linker to the installed europium ion is confirmed by quantifying PL quantum yields. As a demonstration, these materials with modulable PL characteristics are applied for the ratiometric detection of D2O in water, with the use of the stable emission from the BTB linker as the reference. With the strong emission of immobilized europium ions and the good dispersity in aqueous solutions, the optimal bimetal-installed ZrBTB, Eu-Tb-ZrBTB(1 : 10), can achieve the sensing performance outperforming those of the terbium-installed ZrBTB, europium-installed ZrBTB and the physical mixture of both.

Semiconducting 2D Copper(I) Iodide Coordination Polymer as a Potential Chemiresistive Sensor for Methanol

The development of a cost-effective, ultra-selective, and room temperature gas sensor is the need of an hour, owing to the rapid industrialization. Here, a new 2D semiconducting Cu(I) coordination polymer (CP) with 1,4-di(1H-1,2,4-triazol-1-yl)benzene (1,4-TzB) ligand is reported. The CP1 consists of a Cu2I2 secondary building unit bridged by 1,4-TzB, and has high stability as well as semiconducting properties. The chemiresistive sensor, developed by a facile drop-casting method derived from CP1, demonstrates a response value of 66.7 at 100 ppm on methanol exposure, accompanied by swift transient (response and recovery time 17.5 and 34.2 s, respectively) behavior. In addition, the developed sensor displays ultra-high selectivity toward methanol over other volatile organic compounds , boasting LOD and LOQ values of 1.22 and 4.02 ppb, respectively. The CP is found to be a state-of-the-art chemiresistive sensor with ultra-high sensitivity and selectivity toward methanol at room temperature.

Exploring affinity between organic probes and Prussian Blue Analogues via inverse gas chromatography

Prussian Blue Analogues (PBAs), which are characterized by their open structure, high stability, and non-toxic properties, have recently been the subject of research for various applications, including their use as electrode precursors for capacitive deionization, gas storage, and environmental purification. These materials can be readily tailored to enhance their affinity towards gases for integration with sensing devices. An improved understanding of PBA-gas interactions is expected to enhance material development and existing sensor deposition schemes greatly. The use of inverse gas chromatography (IGC) is a robust approach for examining the relationship between porous materials and gases. In this study, the adsorption properties of (functionalized) hydrocarbons, i.e., probe molecules, on the copper hexacyanoferrate (CuHCF) lattice were studied via IGC, demonstrating that alkylbenzenes have a higher affinity for this material than n-alkanes. This difference was rationalized by steric hindrance, π-π interactions, and vapour pressure effects. Along the same line, the five isomers of hexane showed decreasing selectivity upon increased steric hindrance. Enthalpy values for n-pentane, n-hexane and n-heptane were lower than that of toluene. The introduction of increased probe masses resulted in a surface coverage of 46% for toluene. For all n-alkane probe molecules this percentage was lower. However, the isotherms of these probes did not show saturation points and the observed linear regime proves beneficial for gas sensing. Our work demonstrates the versatility of CuHCF for gas sensing purposes and the potential of IGC to characterize the adsorption characteristics of such a porous nanomaterial.

Defect-enabling zirconium-based metal-organic frameworks for energy and environmental remediation applications

This comprehensive review explores the diverse applications of defective zirconium-based metal-organic frameworks (Zr-MOFs) in energy and environmental remediation. Zr-MOFs have gained significant attention due to their unique properties, and deliberate introduction of defects further enhances their functionality. The review encompasses several areas where defective Zr-MOFs exhibit promise, including environmental remediation, detoxification of chemical warfare agents, photocatalytic energy conversions, and electrochemical applications. Defects play a pivotal role by creating open sites within the framework, facilitating effective adsorption and remediation of pollutants. They also contribute to the catalytic activity of Zr-MOFs, enabling efficient energy conversion processes such as hydrogen production and CO2 reduction. The review underscores the importance of defect manipulation, including control over their distribution and type, to optimize the performance of Zr-MOFs. Through tailored defect engineering and precise selection of functional groups, researchers can enhance the selectivity and efficiency of Zr-MOFs for specific applications. Additionally, pore size manipulation influences the adsorption capacity and transport properties of Zr-MOFs, further expanding their potential in environmental remediation and energy conversion. Defective Zr-MOFs exhibit remarkable stability and synthetic versatility, making them suitable for diverse environmental conditions and allowing for the introduction of missing linkers, cluster defects, or post-synthetic modifications to precisely tailor their properties. Overall, this review highlights the promising prospects of defective Zr-MOFs in addressing energy and environmental challenges, positioning them as versatile tools for sustainable solutions and paving the way for advancements in various sectors toward a cleaner and more sustainable future.

Metal-Organic Frameworks in Surface Enhanced Raman Spectroscopy-Based Analysis of Volatile Organic Compounds

Volatile Organic Compounds (VOC) are a major class of environmental pollutants hazardous to human health, but also highly relevant in other fields including early disease diagnostics and organoleptic perception of aliments. Therefore, accurate analysis of VOC is essential, and a need for new analytical methods is witnessed for rapid on-site detection without complex sample preparation. Surface-Enhanced Raman Spectroscopy (SERS) offers a rapidly developing versatile analytical platform for the portable detection of chemical species. Nonetheless, the need for efficient docking of target analytes at the metallic surface significantly narrows the applicability of SERS. This limitation can be circumvented by interfacing the sensor surface with Metal-Organic Frameworks (MOF). These materials featuring chemical and structural versatility can efficiently pre-concentrate low molecular weight species such as VOC through their ordered porous structure. This review presents recent trends in the development of MOF-based SERS substrates with a focus on elucidating respective design rules for maximizing analytical performance. An overview of the status of the detection of harmful VOC is discussed in the context of industrial and environmental monitoring. In addition, a survey of the analysis of VOC biomarkers for medical diagnosis and emerging applications in aroma and flavor profiling is included.

Metal-organic frameworks for biomedical applications: A review

Metal-organic frameworks (MOFs) are emergent materials in diverse prospective biomedical uses, owing to their inherent features such as adjustable pore dimension and volume, well-defined active sites, high surface area, and hybrid structures. The multifunctionality and unique chemical and biological characteristics of MOFs allow them as ideal platforms for sensing numerous emergent biomolecules with real-time monitoring towards the point-of-care applications. This review objects to deliver key insights on the topical developments of MOFs for biomedical applications. The rational design, preparation of stable MOF architectures, chemical and biological properties, biocompatibility, enzyme-mimicking materials, fabrication of biosensor platforms, and the exploration in diagnostic and therapeutic systems are compiled. The state-of-the-art, major challenges, and the imminent perspectives to improve the progressions convoluted outside the proof-of-concept, especially for biosensor platforms, imaging, and photodynamic therapy in biomedical research are also described. The present review may excite the interdisciplinary studies at the juncture of MOFs and biomedicine.

A three-modal fluorescent sensor harnessing diverse luminescent mechanisms for the purpose of segmented Baijiu identification

The classification and verification of segmented Baijiu hold significant importance as they profoundly influence the blending and overall quality of the Baijiu. Our scholarly investigation yielded a fluorescent sensor with three luminescent modes by integrating Tb3+ and RHB into UiO-66. The interplay between carboxyl-containing compounds and RHB/Tb@TLU-2 orchestrates a harmonious molecular association, where the convergence of carboxyl groups with Tb3+ yields a resonating impact on the antenna effect of BDC-SO3-. Furthermore, the acidity and alkalinity of reactants induced a charge transfer interaction between BDC-NH2 and Zr4+ and led to structural changes in RHB/Tb@TLU-2, resulting in observable fluorescence signal variations across the three emission centers. The sensor array successfully identified eight organic acids, achieving an impressive 97.5 % accuracy in discerning segmented Baijiu samples from four Baijiu pits. This meticulous methodology prioritizes simplicity, swiftness, and effectiveness, paving the path for comprehensive segmented Baijiu analysis in the esteemed realm of Brewing production.

A Robust Pyrazolate Metal-Organic Framework for Efficient Catalysis of Dehydrogenative C-O Cross Coupling Reaction

Construction of robust heterogeneous catalysts with atomic precision is a long-sought pursuit in the catalysis field due to its fundamental significance in taming chemical transformations. Herein, we present the synthesis of a single-crystalline pyrazolate metal-organic framework (MOF) named PCN-300, bearing a lamellar structure with two distinct Cu centers and one-dimensional (1D) open channels when stacked. PCN-300 exhibits exceptional stability in aqueous solutions across a broad pH range from 1 to 14. In contrast, its monomeric counterpart assembled through hydrogen bonding displays limited stability, emphasizing the role of Cu-pyrazolate coordination bonds in framework robustness. Remarkably, the synergy of the 1D open channels, excellent stability, and the active Cu-porphyrin sites endows PCN-300 with outstanding catalytic activity in the cross dehydrogenative coupling reaction to form the C-O bond without the "compulsory" ortho-position directing groups (yields up to 96%), outperforming homogeneous Cu-porphyrin catalysts. Moreover, PCN-300 exhibits superior recyclability and compatibility with various phenol substrates. Control experiments reveal the synergy between the Cu-porphyrin center and framework in PCN-300 and computations unveil the free radical pathway of the reaction. This study highlights the power of robust pyrazolate MOFs in directly activating C-H bonds and catalyzing challenging chemical transformations in an environmentally friendly manner.

Functional metal-organic liquids

For decades, the study of coordination polymers (CPs) and metal-organic frameworks (MOFs) has been limited primarily to their behavior as crystalline solids. In recent years, there has been increasing evidence that they can undergo reversible crystal-to-liquid transitions. However, their "liquid" states have primarily been considered intermediate states, and their diverse properties and applications of the liquid itself have been overlooked. As we learn from organic polymers, ceramics, and metals, understanding the structures and properties of liquid states is essential for exploring new properties and functions that are not achievable in their crystalline state. This review presents state-of-the-art research on the liquid states of CPs and MOFs while discussing the fundamental concepts involved in controlling them. We consider the different types of crystal-to-liquid transitions found in CPs and MOFs while extending the interpretation toward other functional metal-organic liquids, such as metal-containing ionic liquids and porous liquids, and try to suggest the unique features of CP/MOF liquids. We highlight their potential applications and present an outlook for future opportunities.

Amyloid detection in neurodegenerative diseases using MOFs

Neurodegenerative diseases (amyloid diseases such as Alzheimer's and Parkinson's), stemming from protein misfolding and aggregation, encompass a spectrum of disorders with severe systemic implications. Timely detection is pivotal in managing these diseases owing to their significant impact on organ function and high mortality rates. The diverse array of amyloid disorders, spanning localized and systemic manifestations, underscores the complexity of these conditions and highlights the need for advanced detection methods. Traditional approaches have focused on identifying biomarkers using imaging techniques (PET and MRI) or invasive procedures. However, recent efforts have focused on the use of metal-organic frameworks (MOFs), a versatile class of materials known for their unique properties, in revolutionizing amyloid disease detection. The high porosity, customizable structures, and biocompatibility of MOFs enable their integration with biomolecules, laying the groundwork for highly sensitive and specific biosensors. These sensors have been employed using electrochemical and photophysical techniques that target amyloid species under neurodegenerative conditions. The adaptability of MOFs allows for the precise detection and quantification of amyloid proteins, offering potential advancements in early diagnosis and disease management. This review article delves into how MOFs contribute to detecting amyloid diseases by categorizing their uses based on different sensing methods, such as electrochemical (EC), electrochemiluminescence (ECL), fluorescence, Förster resonance energy transfer (FRET), up-conversion luminescence resonance energy transfer (ULRET), and photoelectrochemical (PEC) sensing. The drawbacks of MOF biosensors and the challenges encountered in the field are also briefly explored from our perspective.

Dielectric response of metal-organic frameworks as a function of confined guest species investigated by molecular dynamics simulations

When using metal-organic frameworks (MOFs) as electric field-dependent sensor devices, understanding their dielectric response is crucial as the orientation of polar groups is largely affected by confinement. To shed light on this at the molecular level, the response to a static field was computationally investigated for two structurally related MOFs, depending on their loading with guest molecules. The pillared-layer MOFs differ in their pillar moiety, with one bearing a rotatable permanent dipole moment and the other being non-polar. Two guest molecules with and without polarity, namely, methanol and methane, were considered. A comprehensive picture of the response of the guest molecules could be achieved with respect to both the amount and polarity of the confined species. For both MOFs, the dielectric response is very sensitive to the introduction of methanol, showing an anisotropic and non-linear increase in the system's relative permittivity expressed by a strongly increasing polarization response to external electric fields scaling with the number of confined methanol molecules. As expected, the effect of methane in the non-dipolar MOF is negligible, whereas subtle differences can be observed for the dipolar response of the MOF with rotatable dipolar linker groups. Taking advantage of these anisotropic and guest-molecule-specific confinement effects may open pathways for future sensing applications. Finally, methanol-induced global framework dynamics were observed in both MOFs.

Facile Tailoring of Metal-Organic Frameworks for Förster Resonance Energy Transfer-Driven Enhancement in Perovskite Photovoltaics

Förster resonance energy transfer (FRET) has demonstrated its potential to enhance the light energy utilization ratio of perovskite solar cells by interacting with metal-organic frameworks (MOFs) and perovskite layers. However, comprehensive investigations into how MOF design and synthesis impact FRET in perovskite systems are scarce. In this work, nanoscale HIAM-type Zr-MOF (HIAM-4023, HIAM-4024, and HIAM-4025) is meticulously tailored to evaluate FRET's existence and its influence on the perovskite photoactive layer. Through precise adjustments of amino groups and acceptor units in the organic linker, HIAM-MOFs are synthesized with the same topology, but distinct photoluminescence (PL) emission properties. Significant FRET is observed between HIAM-4023/HIAM-4024 and the perovskite, confirmed by spectral overlap, fluorescence lifetime decay, and calculated distances between HIAM-4023/HIAM-4024 and the perovskite. Conversely, the spectral overlap between the PL emission of HIAM-4025 and the perovskite's absorption spectrum is relatively minimal, impeding the energy transfer from HIAM-4025 to the perovskite. Therefore, the HIAM-4023/HIAM-4024-assisted perovskite devices exhibit enhanced EQE via FRET processes, whereas the HIAM-4025 demonstrates comparable EQE to the pristine. Ultimately, the HIAM-4023-assisted perovskite device achieves an enhanced power conversion efficiency (PCE) of 24.22% compared with pristine devices (PCE of 22.06%) and remarkable long-term stability under ambient conditions and continuous light illumination.

Powders to Thin Films: Advances in Conjugated Microporous Polymer Chemical Sensors

Chemical sensing of harmful species released either from natural or anthropogenic activities is critical to ensuring human safety and health. Over the last decade, conjugated microporous polymers (CMPs) have been proven to be potential sensor materials with the possibility of realizing sensing devices for practical applications. CMPs found to be unique among other porous materials such as metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) due to their high chemical/thermal stability, high surface area, microporosity, efficient host-guest interactions with the analyte, efficient exciton migration along the π-conjugated chains, and tailorable structure to target specific analytes. Several CMP-based optical, electrochemical, colorimetric, and ratiometric sensors with excellent selectivity and sensing performance were reported. This review comprehensively discusses the advances in CMP chemical sensors (powders and thin films) in the detection of nitroaromatic explosives, chemical warfare agents, anions, metal ions, biomolecules, iodine, and volatile organic compounds (VOCs), with simultaneous delineation of design strategy principles guiding the selectivity and sensitivity of CMP. Preceding this, various photophysical mechanisms responsible for chemical sensing are discussed in detail for convenience. Finally, future challenges to be addressed in the field of CMP chemical sensors are discussed.

On-Demand Tunable Electrical Conductance Anisotropy in a MOF-Polymer Composite

Property optimization through orientation control of metal-organic framework (MOF) crystals that exhibit anisotropic crystal structures continues to garner tremendous interest. Herein, an electric field is utilized to post-synthetically control the orientation of conductive layered Cu3(HHTP)2 (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) crystals dispersed in an electronically insulating poly(ethylene glycol) diacrylate (PEGDA) oligomer matrix. Optical and electrical measurements are performed to investigate the impact of the electric field on the alignment of Cu3(HHTP)2 crystals and the formation of aggregated microstructures, which leads to an ≈5000-fold increase in the conductivity of the composite. Notably, the composite thin-films containing aligned Cu3(HHTP)2 crystals exhibit significant conductivity of ≈10-3 S cm-1 despite the low concentration (≈1 wt.%) of conductive Cu3(HHTP)2. The use of an electric field to align Cu3(HHTP)2 crystals can rapidly generate various desired patterns that exhibit on-demand tunable collective charge transport anisotropy. The findings provide valuable insights toward the manipulation and utilization of conductive MOFs with anisotropic crystal structures for various applications such as adhesive electrical interconnects and microelectronics.

Inorganic-organic hybrid Cu-dipyridyl semiconducting polymers based on the redox-active cluster [SFe3(CO)9]2-: filling the gap in iron carbonyl chalcogenide polymers

The construction of sulfur-incorporated cluster-based coordination polymers was limited and underexplored due to the lack of efficient synthetic routes. Herein, we report facile mechanochemical ways toward a new series of SFe3(CO)9-based dipyridyl-Cu polymers by three-component reactions of [Et4N]2[SFe3(CO)9] ([Et4N]2[1]) and [Cu(MeCN)4][BF4] with conjugated or conjugation-interrupted dipyridyl ligands, 1,2-bis(4-pyridyl)ethylene (bpee), 1,2-bis(4-pyridyl)ethane (bpea), 4,4'-dipyridyl (dpy), or 1,3-bis(4-pyridyl)propane (bpp), respectively. X-ray analysis showed that bpee-containing 2D polymers demonstrated unique SFe3(CO)9 cluster-armed and cluster-one-armed coordination modes via the hypervalent μ5-S atom. These S-Fe-Cu polymers could undergo flexible structural transformations with the change of cluster bonding modes by grinding with stoichiometric amounts of dipyridyls or 1/[Cu(MeCN)4]+. They exhibited semiconducting behaviors with low energy gaps of 1.55-1.79 eV and good electrical conductivities of 3.26 × 10-8-1.48 × 10-6 S cm-1, tuned by the SFe3(CO)9 cluster bonding modes accompanied by secondary interactions in the solid state. The electron transport efficiency of these polymers was further elucidated by solid-state packing, X-ray photoelectron spectroscopy (XPS), X-ray absorption near-edge spectroscopy (XANES), density of states (DOS), and crystal orbital Hamilton population (COHP) analysis. Finally, the solid-state electrochemistry of these polymers demonstrated redox-active behaviors with cathodically-shifted patterns compared to that of [Et4N]2[1], showing that their efficient electron communication was effectively enhanced by introducing 1 and dipyridyls as hybrid ligands into Cu+-containing networks.

High-Performance Ni3(HHTP)2 Film-Based Flexible Field-Effect Transistor Gas Sensors

Conductive metal-organic frameworks (MOFs) have received increasing attention in recent years and present high application potential as sensing elements in electronic sensors. In this study, flexible field-effect transistor (FET) sensors based on conductive MOF, i.e., Ni3(HHTP)2, have been constructed. This Ni3(HHTP)2 sensor has high sensitivity (detection limit of 56 ppb) as well as superior selectivity for NO2 detection at room temperature, which is demonstrated by accurate gas detection in a mixed gas atmosphere. Moreover, by employing six flexible substrates, i.e., polyimide (PI), tape (PET), facemask, paper cup, tablecloth, and take-out bag (textile), we successfully demonstrate the universality of the flexible sensor construction with conductive MOF as sensing film on various substrates. This study of conductive MOF-based flexible electronic sensors offers a new opportunity for a wide range of sensing applications with wearable and portable electronic devices.

Crosslinking-induced patterning of MOFs by direct photo- and electron-beam lithography

Metal-organic frameworks (MOFs) with diverse chemistry, structures, and properties have emerged as appealing materials for miniaturized solid-state devices. The incorporation of MOF films in these devices, such as the integrated microelectronics and nanophotonics, requires robust patterning methods. However, existing MOF patterning methods suffer from some combinations of limited material adaptability, compromised patterning resolution and scalability, and degraded properties. Here we report a universal, crosslinking-induced patterning approach for various MOFs, termed as CLIP-MOF. Via resist-free, direct photo- and electron-beam (e-beam) lithography, the ligand crosslinking chemistry leads to drastically reduced solubility of colloidal MOFs, permitting selective removal of unexposed MOF films with developer solvents. This enables scalable, micro-/nanoscale (≈70 nm resolution), and multimaterial patterning of MOFs on large-area, rigid or flexible substrates. Patterned MOF films preserve their crystallinity, porosity, and other properties tailored for targeted applications, such as diffractive gas sensors and electrochromic pixels. The combined features of CLIP-MOF create more possibilities in the system-level integration of MOFs in various electronic, photonic, and biomedical devices.

Detection and treatment of mono and polycyclic aromatic hydrocarbon pollutants in aqueous environments based on electrochemical technology: recent advances

Mono and polycyclic aromatic hydrocarbons are widely distributed and severely pollute the aqueous environment due to natural and human activities, particularly human activity. It is crucial to identify and address them in order to reduce the dangers and threats they pose to biological processes and ecosystems. In the fields of sensor detection and water treatment, electrochemistry plays a crucial role as a trustworthy and environmentally friendly technology. In order to accomplish trace detection while enhancing detection accuracy and precision, researchers have created and studied sensors using a range of materials based on electrochemical processes, and their results have demonstrated good performance. One cannot overlook the challenges associated with treating aromatic pollutants, including mono and polycyclic. Much work has been done and good progress has been achieved in order to address these challenges. This study discusses the mono and polycyclic aromatic hydrocarbon sensor detection and electrochemical treatment technologies for contaminants in the aqueous environment. Additionally mentioned are the sources, distribution, risks, hazards, and problems in the removal of pollutants. The obstacles to be overcome and the future development plans of the field are then suggested by summarizing and assessing the research findings of the researchers.

Strategies to Improve Electrical Conductivity in Metal-Organic Frameworks: A Comparative Study

Metal-organic frameworks (MOFs), formed by the combination of both inorganic and organic components, have attracted special attention for their tunable porous structures, chemical and functional diversities, and enormous applications in gas storage, catalysis, sensing, etc. Recently, electronic applications of MOFs like electrocatalysis, supercapacitors, batteries, electrochemical sensing, etc., have become a major research topic in MOF chemistry. However, the low electrical conductivity of most MOFs represents a major handicap in the development of these emerging applications. To overcome these limitations, different strategies have been developed to enhance electrical conductivity of MOFs for their implementation in electronic devices. In this review, we outline all these strategies employed to increase the electronic conduction in both intrinsically (framework-modulated) and extrinsically (guests-modulated) conducting MOFs.

A redox active rod coordination polymer from tetrakis(4-carboxylic acid biphenyl)tetrathiafulvalene

An enlarged version of the ubiquitous tetrathiafulvalene-tetrabenzoic acid is described, with 4,4'-biphenyl moieties as spacers between the coordination moieties and the electroactive core. The obtained rectangular ligand has a 14 × 22 Å2 size and is combined with Zn(II) under solvothermal conditions to yield a coordination polymer endowed with large cavities of ca. 15 × 11 Å2/10 × 10 Å2. The topology of the material is discussed in detail using the Points of Extension and Metals (PE&M) or the Straight-rod (STR) representation, and the sqc1121 or tfo topological type of the structure is observed, respectively. Its stability towards solvent removal and electrical properties are discussed. The material does not present any permanent porosity upon desolvation according to nitrogen sorption measurements at 77 K. Nevertheless, a significant increase in conductivity is observed on compressed pellets of the material upon post-synthetic oxidation with iodine. Raman spectroscopy combined with density functional theory (DFT) calculations has been used to characterize the oxidation state of tetrakis(4-carboxylic acid biphenyl)tetrathiafulvalene for coordination polymers.

Advanced Hybrid materials in electrochemical sensors: Combining MOFs and conducting polymers for environmental monitoring

The integration of conducting polymers (CPs) with metal-organic frameworks (MOFs) has arisen as a dynamic and innovative approach to overcome some intrinsic limitations of both materials, representing a transformative method to address the pressing need for high-performance environmental monitoring tools. MOFs, with their intricate structures and versatile functional groups, provide tuneable porosity and an extensive surface area, facilitating the selective adsorption of target analytes. Conversely, CPs, characterized by their exceptional electrical conductivity and redox properties, serve as proficient signal transducers. By combining these two materials, a novel class of hybrid materials emerges, capitalizing on the unique attributes of both components. These MOF/CP hybrids exhibit heightened sensitivity, selectivity, and adaptability, making them primordial in detecting and quantifying environmental contaminants. This review examines the synergy between MOFs and CPs, highlighting recent advancements, challenges, and prospects, thus offering a promising solution for developing advanced functional materials with tailored properties and multifunctionality to be applied in electrochemical sensors for environmental monitoring.

Polymorphism and orientation control of copper-dicarboxylate metal-organic framework thin films through vapour- and liquid-phase growth

Precise control over the crystalline phase and crystallographic orientation within thin films of metal-organic frameworks (MOFs) is highly desirable. Here, we report a comparison of the liquid- and vapour-phase film deposition of two copper-dicarboxylate MOFs starting from an oriented metal hydroxide precursor. X-ray diffraction revealed that the vapour- or liquid-phase reaction of the linker with this precursor results in different crystalline phases, morphologies, and orientations. Pole figure analysis showed that solution-based growth of the MOFs follows the axial texture of the metal hydroxide precursor, resulting in heteroepitaxy. In contrast, the vapour-phase method results in non-epitaxial growth with uniplanar texture only.

Synthesis of novel Cu/Fe based benzene Dicarboxylate (BDC) metal organic frameworks and investigations into their optical and electrochemical properties

In the recent past Metal-organic frameworks (MOFs) based thin films have demonstrated superior performance in various technological applications such as optical and optoelectronic devices, electrochemical energy storage, catalysis, and sensing. Herein we report tuning the optical performance of stable complexes using Cu and Fe metal ions with carboxylate benzene dicarboxylic (BDC), leading toward the formation of novel MOF structures. The formation of Cu-BDC and Fe-BDC were confirmed by XRD and SEM studies. The thermal stability of two MOFs was investigated, indicating that, the Cu-BDC is more stable than Fe-BDC. Further, the optical properties were investigated in the wavelength range 325-1100 nm, and the Fe-BDC exhibited greater optical transmission properties than Cu-BDC by 33 %, as investigated by Wemple-DiDomenico and Tauc models. The dispersion parameters related to optical studies for Cu-BDC were better in comparison to Fe-BDC, which could be attributed to the increase in Cu valence electrons due to an increase in the number of cations. The electrochemical behavior in terms of CV measurements shows the presence of pseudo capacitance in both Fe-BDC and Cu-BDC MOFs. The improved CV performance of Cu-BDC MOF suggests that it could be used as a storage material. This work successfully demonstrates the tailoring of optical properties related to MOF thin films through the formation of stable complexes using BDC as a potential material for the fabrication of OLED's and Solar cells. The improved CV performance suggests that these MOF based materials could be used as anodes in fabrication of batteries or supercapacitors.

Hydrocarbon Sorption in Flexible MOFs-Part III: Modulation of Gas Separation Mechanisms

Single gas sorption experiments with the C4-hydrocarbons n-butane, iso-butane, 1-butene and iso-butene on the flexible MOFs Cu-IHMe-pw and Cu-IHEt-pw were carried out with both thermodynamic equilibrium and overall sorption kinetics. Subsequent static binary gas mixture experiments of n-butane and iso-butane unveil a complex dependence of the overall selectivity on sorption enthalpy, rate of structural transition as well as steric effects. A thermodynamic separation favoring iso-butane as well as kinetic separation favoring n-butane are possible within Cu-IHMe-pw while complete size exclusion of iso-butane is achieved in Cu-IHEt-pw. This proof-of-concept study shows that the structural flexibility offers additional levers for the precise modulation of the separation mechanisms for complex mixtures with similar chemical and physical properties with real selectivities of >10.

Laser-Driven Rapid Synthesis of Metal-Organic Frameworks and Investigation of UV-NIR Optical Absorption, Luminescence, Photocatalytic Degradation, and Gas and Ion Adsorption Properties

In this study, we designed a platform based on a laser-driven approach for fast, efficient, and controllable MOF synthesis. The laser irradiation method was performed for the first time to synthesize Zn-based MOFs in record production time (approximately one hour) compared to all known MOF production methods with comparable morphology. In addition to well-known structural properties, we revealed that the obtained ZnMOFs have a novel optical response, including photoluminescence behavior in the visible range with nanosecond relaxation time, which is also supported by first-principles calculations. Additionally, photocatalytic degradation of methylene blue with ZnMOF was achieved, degrading the 10 ppm methylene blue (MB) solution 83% during 1 min of irradiation time. The application of laser technology can inspire the development of a novel and competent platform for a fast MOF fabrication process and extend the possible applications of MOFs to miniaturized optoelectronic and photonic devices.

Enhanced Direct Exchange Interaction and Hybridization by Single-Atom Linkers for High Curie Temperature and Superior Visible-Light Harvesting in Cr3(CN3)2

Designing two-dimensional (2D) ferromagnetic (FM) semiconductors with elevated Curie temperature, high carrier mobility, and strong light harvesting is challenging but crucial to the development of spintronics with multifunctionalities. Herein, we show first-principles computation evidence of the 2D metal-organic framework Kagome ferromagnet Cr3(CN3)2. Monolayer Cr3(CN3)2 is predicted to be an FM semiconductor with a record-high Curie temperature of 943 K owing to the use of a single-atom linker (N), which results in strong direct d-p exchange interaction and hybridization between dyz/xz and pz of Cr and N, as well as excellent matching characteristics in energy and symmetry. The single-atom linker structural feature also leads to notable band dispersion and a relatively high carrier mobility of 420 cm2 V-1 s-1. Moreover, under the in-plane strain, 2D Cr3(CN3)2 can be tuned to possess a strong visible-light-harvesting functionality. These novel properties render monolayer Cr3(CN3)2 a distinct 2D ferromagnet with high potential for the development of multifunctional spintronics.

Implementation of Thermal-Triggered Binary-Ternary Switchable Memory Performance in Zn/polysulfide/organic Complex-Based Memorizers by Finely Modulating the S62- Relaxation

Polysulfide-based multilevel memorizers are promising as novel memorizers, in which the occurrence of Sn2- relaxation is key for their multilevel memory. However, the effects of crystal packing and the side group of organic ligands on Sn2- relaxation are still ambiguous. In this work, ionic [Zn(S6)2·Zn2(Bipy)2SO4 (1), Zn(S6)2·Zn(Pmbipy)3 (2)] and neutral [ZnS6(Ombipy) (3), ZnS6(Phen)2 (4)] Zn/polysulfide/organic complexes with different packing modes and structures of organic ligands have been synthesized and were fabricated as memory devices. In both ionic and neutral Zn complexes, the S62- relaxation will be blocked by steric hindrances due to the packing of counter-cations and hydrogen-bond restrictions. Consequently, only the binary memory performances can be seen in FTO/1/Ag, FTO/2/Ag, and FTO/4/Ag, which originate from the more condensed packing of conjugated ligands upon electrical stimulus. Interestingly, FTO/3/Ag illustrates the unique thermally triggered reversible binary-ternary switchable memory performance. In detail, after introducing a methyl group on the 6'-position of bipyridine in ZnS6(Ombipy) (3), the ring-to-chain relaxation of S62- anions at room temperature will be inhibited, but it can happen at a higher temperature of 120 °C, which has been verified by elongated S-S lengths and the strengthened C-H···S hydrogen bond upon heating. The rules drawn in this work will provide a useful guide for the design of stimulus-responsive memorizers that can be applied in special industries such as automobile, oil, and gas industries.

Fabrication of Oriented Polycrystalline MOF Superstructures

The field of metal-organic frameworks (MOFs) has progressed beyond the design and exploration of powdery and single-crystalline materials. A current challenge is the fabrication of organized superstructures that can harness the directional properties of the individual constituent MOF crystals. To date, the progress in the fabrication methods of polycrystalline MOF superstructures has led to close-packed structures with defined crystalline orientation. By controlling the crystalline orientation, the MOF pore channels of the constituent crystals can be aligned along specific directions: these systems possess anisotropic properties including enhanced diffusion along specific directions, preferential orientation of guest species, and protection of functional guests. In this perspective, we discuss the current status of MOF research in the fabrication of oriented polycrystalline superstructures focusing on the specific crystalline directions of orientation. Three methods are examined in detail: the assembly from colloidal MOF solutions, the use of external fields for the alignment of MOF particles, and the heteroepitaxial ceramic-to-MOF growth. This perspective aims at promoting the progress of this field of research and inspiring the development of new protocols for the preparation of MOF systems with oriented pore channels, to enable advanced MOF-based devices with anisotropic properties.

Ligand-Oxidation-Based Anodic Synthesis of Oriented Films of Conductive M-Catecholate Metal-Organic Frameworks with Controllable Thickness

Effective control over the crystallization of metal-organic framework (MOF) films is of great importance not only for the performance study and optimization in related applications but also for the fundamental understanding of the involved reticular chemistry. Featuring many technological advantages, electrochemical synthesis has been extensively reported for many MOF materials but is still challenged by the production of dense oriented films with a large-range tuning of thickness. Here, we report a ligand-oxidation-based anodic strategy capable of synthesizing oriented films of two-dimensional (2D) and three-dimensional (3D) conductive M-catecholate MOFs (2D Cu3(HHTP)2, 2D Zn3(HHTP)2, 2D Co3(HHTP)2, 3D YbHHTP, and 2D Cu2TBA) with tunable thicknesses up to tens of micrometers on commonly used electrodes. This anodic strategy relies on the oxidation of redox-active catechol ligands and follows a stepwise electrochemical-chemical reaction mechanism to achieve effective control over crystallizing M-catecholate MOFs into films oriented in the [001] direction. Benefiting from the electrically conductive nature, Cu3(HHTP)2 films could be thickened at a steady rate (17.4 nm·min-1) from ∼90 nm to 10.7 μm via a growth mechanism differing from those adopted in previous electrochemical synthesis of dense MOF films with limited thickness due to the self-inhibition effect. This anodic synthesis could be further combined with a templating strategy to fabricate not only films with well-defined 2D features in sizes from micrometers to millimeters but also high aspect ratio mesostructures, such as nanorods, of Cu3(HHTP)2.

Densely Packed CO2 Aids Charge, Spin, and Lattice Ordering Partially Fluctuated in a Porous Metal-Organic Framework Magnet

Partial charge fluctuations in the charge-ordered state of a material, often triggered by structural disorders and/or defects, can significantly alter its physical characteristics, such as magnetic long-range ordering. However, it is difficult to post-chemically fix such accidental partial fluctuations to reconstruct a uniform charge-ordered state. Herein, we report CO2 -aided charge ordering demonstrated in a CO2 -post-captured layered magnet, [{Ru2 (o-ClPhCO2 )4 }2 {TCNQ(OMe)2 }] ⋅ CO2 (1⊃CO2 ; o-ClPhCO2 - =ortho-chlorobenzoate; TNCQ(OMe)2 =2,5-dimethoxy-7,7,8,8-tetracyanoquinodimethane). Pristine porous layered magnet 1 had a partially charge-fluctuated ordered state, which provided ferrimagnetic ordering at TC =65 K. Upon loading CO2 , 1 adsorbed one mole of CO2 , forming 1⊃CO2 , and raising TC to 100 K. This was because of the vanishing charge fluctuations without significantly changing the framework structure. This research illustrates the post-accessible host-guest chemistry delicately combined with charge, spin, and lattice ordering in a spongy magnet. Furthermore, it highlights how this innovative approach opens up new possibilities for technology and nanoscale magnetism manipulation.

Interfacing metal organic frameworks with polymers or carbon-based materials: from simple to hierarchical porous and nanostructured composites

In the past few years, metal organic frameworks (MOFs) have been assembled with (bio)polymers and a series of carbon-based materials (graphene, graphene oxide, carbon nanotubes, carbon quantum dots, etc.) leading to a wide range of composites differing in their chemical composition, pore structure and functionality. The objective was mainly to overcome the limitations of MOFs in terms of mechanical properties, chemical stability and processability while imparting novel functionality (electron conductivity, (photo)catalytic activity, etc.) and hierarchical porosity. These composites were considered for numerous applications including gas/liquid adsorption and separation, (photo)catalysis, biomedicine, energy storage, conversion and so on. The performance of such composites depends strongly on their microstructural and physico-chemical properties which are mainly driven by the chemical strategies used to design and process such composites. In this perspective article, we propose to cover this topic and provide a useful survey of recent progress in the synthesis and design of MOFs-carbon material composites. This article will describe the development of composites with increasing complexity in terms of porous architecture, spatial structuration and organisation, and functionality.

From a Collapse-Prone, Insulating Ni-MOF-74 Analogue to Crystalline, Porous, and Electrically Conducting PEDOT@MOF Composites

Electrically conductive porous metal-organic frameworks (MOFs) show great promise in helping advance electronics and clean energy technologies. However, large porosity usually hinders long-range charge transport, an essential criterion of electrical conductivity, underscoring the need for new strategies to combine these two opposing features and realize their diverse potentials. All previous strategies to boost the conductivity of porous MOFs by introducing redox-complementary guest molecules, conducting polymers, and metal nanoparticles have led to a significant loss of frameworks' porosity and surface areas, which could be otherwise exploited to capture additional guests in electrocatalysis and chemiresistive sensing applications. Herein, we demonstrate for the first time that the in situ oxidative polymerization of preloaded 3,4-ethylenedioxythiophene (EDOT) monomers into the polyethylenedioxythiophene (PEDOT) polymer inside the hexagonal cavities of an intrinsically insulating Ni2(NDISA) MOF-74 analogue (NDISA = naphthalenediimide N,N-disalicylate), which easily collapses and becomes amorphous upon drying, simultaneously enhanced the crystallinity, porosity, and electrical conductivity of the resulting PEDOT@Ni2(NDISA) composites. At lower PEDOT loading (∼22 wt %), not only did the Brunauer-Emmett-Teller surface area of the PEDOT@Ni2(NDISA) composite (926 m2/g) more than double from that of evacuated pristine Ni2(NDISA) (387 m2/g), but also its electrical conductivity (1.1 × 10-5 S/cm) soared 105 times from that of the pristine MOF, demonstrating unprecedented dual benefits of our strategy. At higher PEDOT loading (≥33 wt %), the electrical conductivity of Ni2(NDISA)⊃PEDOT composites further increased modestly (10-4 S/cm), but their porosity dropped precipitously as large amounts of PEDOT filled up the hexagonal MOF channels. Thus, our work presents a simple new strategy to simultaneously boost the structural stability, porosity, and electrical conductivity of intrinsically insulating and collapse-prone MOFs by introducing small amounts of conducting polymers that can not only reinforce the MOF scaffolds and prevent them from collapsing but also help create a much coveted non-native property by providing charge carriers and charge transport pathways.

Surface-Degenerate Semiconductor Photocatalysis for Efficient Water Splitting without Sacrificial Agents via a Reticular Chemistry Approach

The production of green hydrogen through photocatalytic water splitting is crucial for a sustainable hydrogen economy and chemical manufacturing. However, current approaches suffer from slow hydrogen production (<70 μmol ⋅ gcat -1  ⋅ h-1 ) due to the sluggish four-electrons oxygen evolution reaction (OER) and limited catalyst activity. Herein, we achieve efficient photocatalytic water splitting by exploiting a multifunctional interface between a nano-photocatalyst and metal-organic framework (MOF) layer. The functional interface plays two critical roles: (1) enriching electron density directly on photocatalyst surface to promote catalytic activity, and (2) delocalizing photogenerated holes into MOF to enhance OER. Our photocatalytic ensemble boosts hydrogen evolution by ≈100-fold over pristine photocatalyst and concurrently produces oxygen at ideal stoichiometric ratio, even without using sacrificial agents. Notably, this unique design attains superior hydrogen production (519 μmol ⋅ gcat -1  ⋅ h-1 ) and apparent quantum efficiency up to 13-fold and 8-fold better than emerging photocatalytic designs utilizing hole scavengers. Comprehensive investigations underscore the vital role of the interfacial design in generating high-energy photoelectrons on surface-degenerate photocatalyst to thermodynamically drive hydrogen evolution, while leveraging the nanoporous MOF scaffold as an effective photohole sink to enhance OER. Our interfacial approach creates vast opportunities for designing next-generation, multifunctional photocatalytic ensembles using reticular chemistry with diverse energy and environmental applications.

Transmission Porosimetry Study on High-quality Zr-fum-MOF Thin Films

Crystalline Zr-fum-MOF (MOF-801) thin films of high quality are prepared on glass and silicon substrates by direct growth under solvothermal conditions. The synthesis is described in detail and the influence of different synthesis parameters such as temperature, precursor concentration, and the substrate type on the quality of the coatings is illustrated. Zr-fum-MOF thin films are characterized in terms of crystallinity, porosity, and homogeneity. Dense films of optical quality are obtained. The sorption behavior of the thin films is studied with various adsorptives. It can be easily monitored by measuring the transmission of the films in gas flows of different compositions. This simple transmission measurement at only one wavelength allows a very fast evaluation of the adsorption properties of thin films as compared to traditional sorption methods. The sorption behavior of the thin films is compared with the sorption properties of Zr-fum-MOF powder samples.

Directing the Selectivity of Oxygen Reduction to Water by Confining a Cu Catalyst in a Metal Organic Framework

Electrocatalysis is to play a key role in the transition towards a sustainable chemical and energy industry and active, stable and selective redox catalysts are much needed. Porous structures such as metal organic frameworks (MOFs) are interesting materials as these may influence selectivity of chemical reactions through confinement effects. In this work, the oxygen reduction catalyst Cu-tmpa was incorporated into the NU1000 MOF. Confinement of the catalyst within NU1000 steers the selectivity of the oxygen reduction reaction (ORR) towards water rather than peroxide. This is attributed to retention of the obligatory H2 O2 intermediate in close proximity to the catalytic center. Moreover, the resulting NU1000|Cu-tmpa MOF shows an excellent activity and stability in prolonged electrochemical studies, illustrating the potential of this approach.

Metal-Organic Framework-Derived Ni-S/C Catalysts for Selective Alkyne Hydrogenation

A carbon matrix-supported Ni catalyst with surface/subsurface S species is prepared using a sacrificial metal-organic framework synthesis strategy. The resulting highly dispersed Ni-S/C catalyst contains surface discontinuous and electron-deficient Niδ+ sites modified by p-block S elements. This catalyst proved to be extremely active and selective for alkyne hydrogenation. Specifically, high intrinsic activity (TOF = 0.0351 s-1) and superior selectivity (>90%) at complete conversion were achieved, whereas an analogous S-free sample prepared by the same synthetic route performed poorly. That is, the incorporation of S in Ni particles and the carbon matrix exerts a remarkable positive effect on catalytic behavior for alkyne hydrogenation, breaking the activity-selectivity trade-off. Through comprehensive experimental studies, enhanced performance of Ni-S/C was ascribed to the presence of discontinuous Ni ensembles, which promote desorption of weakly π-bonded ethylene and an optimized electronic structure modified via obvious p-d orbital hybridization.

Porous crystalline materials for memories and neuromorphic computing systems

Porous crystalline materials usually include metal-organic frameworks (MOFs), covalent organic frameworks (COFs), hydrogen-bonded organic frameworks (HOFs) and zeolites, which exhibit exceptional porosity and structural/composition designability, promoting the increasing attention in memory and neuromorphic computing systems in the last decade. From both the perspective of materials and devices, it is crucial to provide a comprehensive and timely summary of the applications of porous crystalline materials in memory and neuromorphic computing systems to guide future research endeavors. Moreover, the utilization of porous crystalline materials in electronics necessitates a shift from powder synthesis to high-quality film preparation to ensure high device performance. This review highlights the strategies for preparing porous crystalline materials films and discusses their advancements in memory and neuromorphic electronics. It also provides a detailed comparative analysis and presents the existing challenges and future research directions, which can attract the experts from various fields (e.g., materials scientists, chemists, and engineers) with the aim of promoting the applications of porous crystalline materials in memory and neuromorphic computing systems.

Postsynthetic Photochemical Modification and 2D Structuring of Zr-MOF Thin Films Containing Benzophenone Linker Molecules

For the fabrication of next-generation MOF-based devices the availability of highly adaptable materials in suitable shapes is crucial. Here, we present thin films of a metal-organic framework (MOF) containing photoreactive benzophenone units. Crystalline, oriented and porous films of the zirconium-based bzpdc-MOF (bzpdc=benzophenone-4-4'-dicarboxylate) are prepared by direct growth on silicon or glass substrates. Via a subsequent photochemical modification of the Zr-bzpdc-MOF films, various properties can be tuned postsynthetically by covalent attachment of modifying agents. Apart from the modification with small molecules, also grafting-from polymerization reactions are possible. In a further extension, 2D structuring and photo-writing of defined structures is also possible, for example by using a photolithographic approach, paving the way towards micro-patterned MOF surfaces.

CO2 Reduction to Methane and Ethylene on a Single-Atom Catalyst: A Grand Canonical Quantum Mechanics Study

In recent years, two-dimensional metal-organic frameworks (2D MOF) have attracted great interest for their ease of synthesis and for their catalytic activities and semiconducting properties. The appeal of these materials is that they are layered and easily exfoliated to obtain a monolayer (or few layer) material with interesting optoelectronic properties. Moreover, they have great potential for CO2 reduction to obtain solar fuels with more than one carbon atom, such as ethylene and ethanol, in addition to methane and methanol. In this paper, we explore how a particular class of 2D MOF based on a phthalocyanine core provides the reactive center for the production of ethylene and ethanol. We examine the reaction mechanism using the new grand canonical potential kinetics (GCP-K) or grand canonical quantum mechanics (GC-QM) computational methodology, which obtains reaction rates at constant applied potential to compare directly with experimental results (rather than at constant electrons as in standard QM). We explain the reaction mechanism underlying the formation of methane and ethylene. Here, the key reaction step is direct coupling of CO into CHO, without the usual rate-determining CO-CO dimerization step observed on Cu metal surfaces. Indeed, the 2D MOF behaves like a single-atom catalyst.

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.

A promising sensing platform for explosive markers: Zeolite-like metal-organic framework based monolithic composite as a case study

Preconcentration for on-site detection or subsequent determination is a promising technique for selective sensing explosive markers at low concentrations. Here, we report divinylbenzene monolithic polymer in its blank form (neat-DVB) and as a composite incorporated with sodalite topology zeolite-like metal-organic frameworks (3-ZMOF@DVB), as a sensitive, selective, and cost-effective porous preconcentrator for aliphatic nitroalkanes in the vapor phase as explosive markers at infinite dilution. The developed materials were fabricated as 18 cm gas chromatography (GC) monolithic capillary columns to study their separation performance of nitroalkane mixture and the subsequent physicochemical study of adsorption using the inverse gas chromatography (IGC) technique. A strong preconcentration effect was indicated by a specific retention volume adsorption/desorption ratio equal to 3 for nitromethane on the neat-DVB monolith host-guest interaction, and a 14% higher ratio was observed using the 3-ZMOF@DVB monolithic composite despite the low percentage of 0.7 wt.% of sod-ZMOF added. Furthermore, Incorporating ZMOF resulted in a higher percentage of micropores, increasing the degree of freedom more than bringing stronger adsorption and entropic-driven interaction more than enthalpic. The specific free energy of adsorption (ΔGS) values increased for polar probes and nitroalkanes, denoting that adding ZMOFs earned the DVB monolithic matrix a more specific character. Afterward, Lewis acid-base properties were calculated, estimating the electron acceptor (KA) and electron donor (KB) constants. The neat-DVB was found to have a Lewis basic character with KB/KA = 7.71, and the 3-ZMOF@DVB had a less Lewis basic character with KB/KA = 3.82. An increased electron-accepting nature can be directly related to incorporating sod-ZMOF into the DVB monolithic matrix. This work considers the initial step in presenting a portable explosives detector or preconcentrating explosive markers trace prior to more sophisticated analysis. Additionally, the IGC technique allows for understanding the factors that led to the superior adsorption of nitroalkanes for the developed materials.

Synthesis and photochemical modification of monolayer thin MOF flakes for incorporation in defect free polymer composites

Metal-organic frameworks (MOFs) with benzophenone linker molecules are characterized by their ability to undergo photochemical postsynthetic modification. While this approach opens up almost unlimited possibilities for tailoring materials to specific applications, the processability of the large particles is still lacking. In this work, we present a new approach to fabricate micro flakes of the stable Zr-bzpdc-MOF (bzpdc = benzophenone-4-4'-dicarboxylate) with a thickness of only a few monolayers. The crystalline and nanoporous flakes form dispersions in acetone that are stable for months. Embedding the flakes in polymer composites was investigated as one of many possible applications. Zr-bzpdc-MOF micro flakes were decorated with poly(dimethylsiloxane) (PDMS) via a photochemical postsynthetic modification and incorporated into silicon elastomers. The PDMS functionalization allows covalent cross-linking between the MOF and the polymer while maintaining the porosity of the MOF. The resulting hybrid materials provide defect-free interfaces and show preferential adsorption of CO2 over CH4, making them attractive for gas separation or sensing applications. The work should serve as a basis for bringing bzpdc-MOFs into real-world applications - in polymeric membranes, but also beyond.

Reticular Chemistry for Optical Sensing of Anions

In the last few decades, reticular chemistry has grown significantly as a field of porous crystalline molecular materials. Scientists have attempted to create the ideal platform for analyzing distinct anions based on optical sensing techniques (chromogenic and fluorogenic) by assembling different metal-containing units with suitable organic linking molecules and different organic molecules to produce crystalline porous materials. This study presents novel platforms for anion recognition based on reticular chemistry with high selectivity, sensitivity, electronic tunability, structural recognition, strong emission, and thermal and chemical stability. The key materials for reticular chemistry, Metal-Organic Frameworks (MOFs), Zeolitic Imidazolate Frameworks (ZIFs), and Covalent-Organic Frameworks (COFs), and the pre- and post-synthetic modification of the linkers and the metal oxide clusters for the selective detection of the anions, have been discussed. The mechanisms involved in sensing are also discussed.

Influence laws of air gap structure manipulation of covalent organic frameworks on dielectric properties and exciton effects for photopolymerization

Boosting the dissociation of excitons is essential to enhance the photocatalytic efficiency. However, the relationship between the structure of the catalyst and the exciton effect on the photocatalytic activity is still unclear as the main problem. Here, it is proposed that as a descriptive factor, an experimentally measurable dielectric constant (εr) is available to quantitatively describe its relationship with exciton binding energy (Eb) and photocatalytic activity. With tuning the linker of covalent organic frameworks (COFs), the "air gap" structure is oriented to shrink, leading to an increased εr of COFs and a lower Eb to facilitate exciton dissociation. Meanwhile, taking "water-/oxygen-fueled" photo-induced electron transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization as a demonstration platform, it can be seen that COFs with a small "air gap" structure have relatively superior photocatalytic activity. This provides important implications for the evolution of efficient photocatalysts.

Novel UiO-NH2-like Zr-Based MOF (Basu-DPU) as an Excellent Catalyst for Preparation of New 6H-Chromeno[4,3-b]quinolin-6-ones

A new two-fold interpenetrated pillar-layered metal-organic framework (MOF) was designed and synthesized based on zirconium cations, an amine-functionalized ligand, and a linear exo-bidentate bis-pyridine ligand. The structure of the prepared framework was evaluated using various techniques, such as Fourier transform infrared (FTIR), ¹³C NMR, energy-dispersive X-ray (EDX), elemental mapping analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis/differential thermal analysis (TGA/DTA), and Brunauer-Emmett-Teller (BET). Then, catalytic application of the prepared zirconium-based MOF was successfully explored in the synthesis of novel 6H-chromeno[4,3-b]quinolin-6-ones 4(a-l) through a one-pot three-component condensation reaction of 4-hydroxycumarine, 1-naphthylamine, and aromatic aldehydes under solvent-free conditions at 110 °C. The pure products were obtained with high atom efficiency (AE) and short reaction times and characterized by FTIR, NMR, and mass spectrometry techniques.