Semiconductor Metal-Organic Frameworks: Future Low-Bandgap Materials

Cooperative Coupling of Oxidative Organic Synthesis and Hydrogen Production over Semiconductor-Based Photocatalysts

Merging hydrogen (H₂) evolution with oxidative organic synthesis in a semiconductor-mediated photoredox reaction is extremely attractive because the clean H₂ fuel and high-value chemicals can be coproduced under mild conditions using light as the sole energy input. Following this dual-functional photocatalytic strategy, a dreamlike reaction pathway for constructing C-C/C-X (X = C, N, O, S) bonds from abundant and readily available X-H bond-containing compounds with concomitant release of H₂ can be readily fulfilled without the need of external chemical reagents, thus offering a green and fascinating organic synthetic strategy. In this review, we begin by presenting a concise overview on the general background of traditional photocatalytic H₂ production and then focus on the fundamental principles of cooperative photoredox coupling of selective organic synthesis and H₂ production by simultaneous utilization of photoexcited electrons and holes over semiconductor-based catalysts to meet the economic and sustainability goal. Thereafter, we put dedicated emphasis on recent key progress of cooperative photoredox coupling of H₂ production and various selective organic transformations, including selective alcohol oxidation, selective methane conversion, amines oxidative coupling, oxidative cross-coupling, cyclic alkanes dehydrogenation, reforming of lignocellulosic biomass, and so on. Finally, the remaining challenges and future perspectives in this flourishing area have been critically discussed. It is anticipated that this review will provide enlightening guidance on the rational design of such dual-functional photoredox reaction system, thereby stimulating the development of economical and environmentally benign solar fuel generation and organic synthesis of value-added fine chemicals.

When Conductive MOFs Meet MnO2: High Electrochemical Energy Storage Performance in an Aqueous Asymmetric Supercapacitor

Metal organic frameworks (MOFs) have been widely researched and applied in many fields. However, the poor electrical conductivity of many traditional MOFs greatly limits their application in electrochemistry, especially in energy storage. Benefited from the full charge delocalization in the atomical plane, conductive MOFs (c-MOFs) exhibit good electrochemical performance. Besides, unlike graphene, c-MOFs are provided with 1D cylindrical channels, which can facilitate the ion transport and enable high ion conductivity. Transition-metal oxides (TMOs) are promising materials with good electrochemical energy storage performance due to their excellent oxidation-reduction activity. When composited with TMOs, the c-MOFs can significantly improve the capacitance and rate performance. In this work, for the first time, we designed serial MnO₂@Ni-HHTP (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) nanoarrays with different lengths and explored how the lengths influence the electrochemical energy storage performance. By taking advantage of the high redox activity of MnO₂ and the excellent electron and ion conductivity in Ni-HHTP, when assembled as the positive electrode material in an aqueous asymmetric supercapacitor, the device displays high energy density, outstanding rate performance, and superior cycle stability. We believe that the results of this work would provide a good prospect for developing other c-MOF composites as a potential class of electrode materials in energy storage and conversion.

Templated interfacial synthesis of metal-organic framework (MOF) nano- and micro-structures with precisely controlled shapes and sizes

Metal-organic frameworks (MOF) are an emerging class of microporous materials with promising applications. MOF nanocrystals, and their assembled super-structures, can display unique properties and reactivities when compared with their bulk analogues. MOF nanostructures of 0-D, 2-D, and 3-D dimensions can be routinely obtained by controlling reaction conditions and ligand additives, while formation of 1-D MOF nanocrystals (nanowires and nanorods) and super-structures has been relatively rare. We report here a facile templated interfacial synthesis methodology for the preparation of a series of 1-D MOF nano- and micro-structures with precisely controlled shapes and sizes. Specifically, by applying track-etched polycarbonate (PCTE) membranes as the templates and at the oil/water interface, we rapidly and reproducibly synthesize zeolitic imidazolate framework-8 (ZIF-8) and ZIF-67 nano- and micro structures of sizes ranging from 10 nm to 20 μm. We also identify a size confinement effect on MOF crystal growth, which leads to single crystals under the most restricted conditions and inter-grown polycrystals at larger template pore sizes, as well as surface directing effects that influence the crystallographic preferred orientation. Our findings provide a potentially generalizable method for controlling the size, morphology, and crystal orientations of MOF nanomaterials, as well as offering fundamental understanding into MOF crystal growth mechanisms.

Crystalline Porous Materials for Nonlinear Optics

Crystalline porous materials have been extensively explored for wide applications in many fields including nonlinear optics (NLO) for frequency doubling, two-photon absorption/emission, optical limiting effect, photoelectric conversion, and biological imaging. The structural diversity and flexibility of the crystalline porous materials such as the metal-organic frameworks, covalent organic frameworks, and polyoxometalates provide numerous opportunities to orderly organize the dipolar chromophores and to systemically modify the type and concentration of these dipolar chromophores in the confined spaces, which are highly desirable for NLO. Here, the recent advances in the crystalline porous NLO materials are discussed. The second-order NLO of crystalline porous materials have been mainly devoted to the chiral and achiral structures, while the third-order NLO crystalline porous materials have been categorized into pure organic and hybrid organic/inorganic materials. Some representative properties and applications of these crystalline porous materials in the NLO regime are highlighted. The future perspective of challenges as well as the potential research directions of crystalline porous materials have been also proposed.

Carbon Dioxide Enrichment PEBAX/MOF Composite Membrane for CO2 Separation

Zeolitic imidazole framework (ZIF-8) was incorporated into poly(ether-block-amide) (Pebax-1657) in differing ratios to prepare mixed matrix membranes (MMMs) for gas separation. As ZIF-8 loading is increased, gas separation selectivity also gradually increases. For economic considerations, the proportion of the increase in selectivity to the amount of MOF loaded per unit was calculated. The results show that mixing 5% MOF gives the best unit performance. With this, a variety of MOFs (UiO-66, UiO-66-NH₂, A520, MIL-68(Al) and MIL-100(Fe)) were mixed with PEBAX at 5 loading to prepare MMMs. In this work, metal-organic frameworks (MOFs) were processed using the dry-free method, where in the synthesized MOF was not dried prior to incorporation. The gas separation performance test carried out shows the highest separation performance was exhibited by P-UiO-66, wherein the CO₂/N₂ gas selectivity was 85.94, and the permeability was 189.77 (Barrer), which was higher than Robeson’s Upper bound in 2008, and obtained a high permeability and selectivity among mixed matrix membranes. In the preparation of high quality MMMs for gas separation, details regarding the interface phenomenon were assessed.

What Lies beneath a Metal-Organic Framework Crystal Structure? New Design Principles from Unexpected Behaviors

The rational design principles established for metal-organic frameworks (MOFs) allow clear structure-property relationships, fueling expansive growth for energy storage and conversion, catalysis, and beyond. However, these design principles are based on the assumption of compositional and structural rigidity, as measured crystallographically. Such idealization of MOF structures overlooks subtle chemical aspects that can lead to departures from structure-based chemical intuition. In this Perspective, we identify unexpected behavior of MOFs through literature examples. Based on this analysis, we conclude that departures from ideality are not uncommon. Whereas linker topology and metal coordination geometry are useful starting points for understanding MOF properties, we anticipate that deviations from the idealized crystal representation will be necessary to explain important and unexpected behaviors. Although this realization reinforces the notion that MOFs are highly complex materials, it should also stimulate a broader reexamination of the literature to identify corollaries to existing design rules and reveal new structure-property relationships.

Water-assisted spin-flop antiferromagnetic behaviour of hydrophobic Cu-based metal-organic frameworks

Solvent-dependent magnetism in Cu-based metal-organic frameworks (MOFs) is reported. Spin-flop magnetic behaviour occurs at different dehydrated states of MOFs. The oxygens of guest and coordinated water molecules are responsible as water removal tunes the coordination geometry around the Cu centre and the electronic structure of the framework.

Hydrophobic Metal-Organic Frameworks and Derived Composites for Microelectronics Applications

The extraordinary characteristic features of metal-organic frameworks (MOFs) make them applicable for use in a variety of fields but their conductivity in microelectronics over a wide relative humidity (RH) range has not been extensively explored. To achieve good performance, MOFs must be stable in water, i. e., under humid conditions. However, the design of ultrastable hydrophobic MOFs with high conductivity for use in microelectronics as conducting and dielectric materials remains a challenge. In this Review, we discuss applications of an emerging class of hydrophobic MOFs with respect to their use as active sensor coatings, tunable low-κ dielectrics and conductivity, which provide high-level roadmap for stimulating the next steps toward the development and implementation of hydrophobic MOFs for use in microelectronic devices. Several methodologies including the incorporation of long alkyl chain and fluorinated linkers, doping of redox-active 7,7,8,8-tetracyanoquinodimethane (TCNQ), the use of guest molecules, and conducting polymers or carbon materials in the pores or surface of MOFs have been utilized to produce hydrophobic MOFs. The contact angle of a water droplet and a coating can be used to evaluate the degree of hydrophobicity of the surface of a MOF. These unique advantages enable hydrophobic MOFs to be used as a highly versatile platform for exploring multifunctional porous materials. Classic representative examples of each category are discussed in terms of coordination structures, types of hydrophobic design, and potential microelectronic applications. Lastly, a summary and outlook as concluding remarks in this field are presented. We envision that future research in the area of hydrophobic MOFs promise to provide important breakthroughs in microelectronics applications.

Photoconductive Coordination Polymer with a Lead-Sulfur Two-Dimensional Coordination Sheet Structure

Coordination polymers with metal-sulfur (M-S) bonds in their nodes have interesting optical properties and can be used as photocatalysts for water splitting. A wide range of inorganic-organic hybrid materials with M-S bonds have been prepared in recent years. However, there is a dearth of structural information because of their low crystallinity, which has hampered the understanding of their underlying chemistry and physics. Thus, we conducted a structural study of a novel, highly crystalline coordination polymer with M-S bonds. Theoretical calculations were performed to elucidate its photoconductivity mechanism. The photoconductive, three-dimensional coordination polymer [Pb(tadt)]n (denoted as KGF-9; tadt = 1,3,4-thiadiazole-2,5-dithiolate) was synthesized and confirmed to have a three-dimensional structure containing a two-dimensional Pb-S framework by single-crystal X-ray diffraction. We also performed diffuse-reflectance ultraviolet-visible-near-infrared spectroscopy, time-resolved microwave conductivity, and photoelectron yield spectroscopy measurements on the bulk powder samples, as well as first-principles calculations. Additionally, direct-current photoconductivity measurements were conducted on a single-crystal sample.

Effects of ligand functionalization on the band gaps and luminescent properties of a Zr12 oxo-cluster based metal–organic framework

Herein, effective optical band gap engineering of a robust Zr₁₂ oxo-based hcp UiO-66 has been realized through linker functionalization.

Direct X-ray and electron-beam lithography of halogenated zeolitic imidazolate frameworks

Metal-organic frameworks (MOFs) offer disruptive potential in micro- and optoelectronics because of the unique properties of these microporous materials. Nanoscale patterning is a fundamental step in the implementation of MOFs in miniaturized solid-state devices. Conventional MOF patterning methods suffer from low resolution and poorly defined pattern edges. Here, we demonstrate the resist-free, direct X-ray and electron-beam lithography of MOFs. This process avoids etching damage and contamination and leaves the porosity and crystallinity of the patterned MOFs intact. The resulting high-quality patterns have excellent sub-50-nm resolution, and approach the mesopore regime. The compatibility of X-ray and electron-beam lithography with existing micro- and nanofabrication processes will facilitate the integration of MOFs in miniaturized devices.

A data-driven perspective on the colours of metal-organic frameworks

Colour is at the core of chemistry and has been fascinating humans since ancient times. It is also a key descriptor of optoelectronic properties of materials and is often used to assess the success of a synthesis. However, predicting the colour of a material based on its structure is challenging. In this work, we leverage subjective and categorical human assignments of colours to build a model that can predict the colour of compounds on a continuous scale. In the process of developing the model, we also uncover inadequacies in current reporting mechanisms. For example, we show that the majority of colour assignments are subject to perceptive spread that would not comply with common printing standards. To remedy this, we suggest and implement an alternative way of reporting colour—and chemical data in general. All data is captured in an objective, and standardised, form in an electronic lab notebook and subsequently automatically exported to a repository in open formats, from where it can be interactively explored by other researchers. We envision this to be key for a data-driven approach to chemical research.

Colour is at the core of chemistry and has been fascinating humans since ancient times.

An Ideal Spin Filter: Long-Range, High-Spin Selectivity in Chiral Helicoidal 3-Dimensional Metal Organic Frameworks

An enantiopure, conductive, and paramagnetic crystalline 3-D metal-organic framework (MOF), based on Dy(III) and the l-tartrate chiral ligand, is proved to behave as an almost ideal electron spin filtering material at room temperature, transmitting one spin component only, leading to a spin polarization (SP) power close to 100% in the ±2 V range, which is conserved over a long spatial range, larger than 1 μm in some cases. This impressive spin polarization capacity of this class of nanostructured materials is measured by means of magnetically polarized conductive atomic force microscopy and is attributed to the Chirality-Induced Spin Selectivity (CISS) effect of the material arising from a multidimensional helicity pattern, the inherited chirality of the organic motive, and the enhancing influence of Dy(III) ions on the CISS effect, with large spin-orbit coupling values. Our results represent the first example of a MOF-based and CISS-effect-mediated spin filtering material that shows a nearly perfect SP. These striking results obtained with our robust and easy-to-synthesize chiral MOFs constitute an important step forward in to improve the performance of spin filtering materials for spintronic device fabrication.

Current Progress and Future Directions in Gas-Phase Metal-Organic Framework Thin-Film Growth

Deposition of materials as a thin film is important for various applications, such as sensors, microelectronic devices, and membranes. There have been breakthroughs in gas-phase metal-organic framework (MOF) thin-film growth, which is more applicable to micro- and nanofabrication processes and also less harmful to the environment than solvent-based methods. Three different types of gas-phase MOF thin film deposition methods have been developed using chemical vapor deposition (CVD), atomic layer deposition (ALD), and physical vapor deposition (PVD)-CVD combined techniques. The CVD-based method basically converts metal oxide layers into MOF thin films by exposing the surface to ligand vapor. The ALD-based method allows growing MOF thin films following layer-by-layer (LBL) growth by sequentially exposing gas-phase metal and ligand precursors. The PVD-CVD method uses PVD for metal deposition and CVD for ligand deposition, which is similar to LBL growth. These gas-phase growth methods can broaden the use of MOFs in diverse areas. Herein, the current progress of gas-phase MOF thin film growth is discussed and future directions suggested.

Iontronics Using V2CTx MXene-Derived Metal-Organic Framework Solid Electrolytes

Electronic applications of porous metal-organic frameworks (MOFs) have recently emerged as an important research area. However, there is still no report on using MOF solid electrolytes in iontronics, which could take advantage of the porous feature of MOFs in the ionic transport. In this article, MXene-derived two-dimensional porphyrinic MOF (MX-MOF) films are demonstrated as an electronic-grade proton-conducting electrolyte. Meanwhile, the MX-MOF film shows high quality, chemical stability, and capability of standard device patterning processes (e.g., dry etching and optical and electron beam lithography). Using the commercialized nanofabrication processes, an electric double-layer (EDL) transistor is demonstrated using the MX-MOF film (derived from V₂CT_x MXene) as an ionic gate and MoS₂ film as a semiconducting channel layer. The EDL transistor, operated by applying an electric field to control the interaction between ions and electrons, is the core device platform in the emerging iontronics field. Therefore, The MX-MOF, confirmed as a solid electrolyte for EDL transistor devices, could have a significant impact on iontronics research and development.

Electronic Structure Modeling of Metal-Organic Frameworks

Owing to their molecular building blocks, yet highly crystalline nature, metal-organic frameworks (MOFs) sit at the interface between molecule and material. Their diverse structures and compositions enable them to be useful materials as catalysts in heterogeneous reactions, electrical conductors in energy storage and transfer applications, chromophores in photoenabled chemical transformations, and beyond. In all cases, density functional theory (DFT) and higher-level methods for electronic structure determination provide valuable quantitative information about the electronic properties that underpin the functions of these frameworks. However, there are only two general modeling approaches in conventional electronic structure software packages: those that treat materials as extended, periodic solids, and those that treat materials as discrete molecules. Each approach has features and benefits; both have been widely employed to understand the emergent chemistry that arises from the formation of the metal-organic interface. This Review canvases these approaches to date, with emphasis placed on the application of electronic structure theory to explore reactivity and electron transfer using periodic, molecular, and embedded models. This includes (i) computational chemistry considerations such as how functional, k-grid, and other model variables are selected to enable insights into MOF properties, (ii) extended solid models that treat MOFs as materials rather than molecules, (iii) the mechanics of cluster extraction and subsequent chemistry enabled by these molecular models, (iv) catalytic studies using both solids and clusters thereof, and (v) embedded, mixed-method approaches, which simulate a fraction of the material using one level of theory and the remainder of the material using another dissimilar theoretical implementation.

Advances in metal-organic framework coatings: versatile synthesis and broad applications

Metal-organic frameworks (MOFs) as a new kind of porous crystalline materials have attracted much interest in many applications due to their high porosity, diverse structures, and controllable chemical structures. However, the specific geometrical morphologies, limited functions and unsatisfactory performances of pure MOFs hinder their further applications. In recent years, an efficient approach to synthesize new composites to overcome the above issues has been achieved, by integrating MOF coatings with other functional materials, which have synergistic advantages in many potential applications, including batteries, supercapacitors, catalysis, gas storage and separation, sensors, drug delivery/cytoprotection and so on. Nevertheless, the systemic synthesis strategies and the relationships between their structures and application performances have not been reviewed comprehensively yet. This review emphasizes the recent advances in versatile synthesis strategies and broad applications of MOF coatings. A comprehensive discussion of the fundamental chemistry, classifications and functions of MOF coatings is provided first. Next, by modulating the different states (e.g. solid, liquid, and gas) of metal ion sources and organic ligands, the synthesis methods for MOF coatings on functional materials are systematically summarized. Then, many potential applications of MOF coatings are highlighted and their structure-property correlations are discussed. Finally, the opportunities and challenges for the future research of MOF coatings are proposed. This review on the deep understanding of MOF coatings will bring better directions into the rational design of high-performance MOF-based materials and open up new opportunities for MOF applications.

A review of functional sorbents for adsorptive removal of arsenic ions in aqueous systems

The presence of arsenic in the water system has been a universal problem over the past several decades. Inorganic arsenic ions mainly occur in two oxidation states, As(V) and As(III), in the natural environment. These two oxidation states of arsenic ions are ubiquitous in natural waters and pose significant health hazards to humans when present at or above the allowable limits. Therefore, treatment of arsenic ions has become more stringent based on various techniques (e.g., membrane filtration, adsorption, and ion exchange). This paper aims to review the current knowledge on various functional adsorbents through comparison of removal potential for As on the basis of key performance metrics, especially the partition coefficient (PC). As a whole, novel materials exhibited far better removal performance for As(V) and As(III) than conventional materials. Of the materials reviewed, the advanced sorbent like ZrO(OH)₂/CNTs showcased superior performances such as partition coefficient values of 584.6 (As(V) and 143.8 mol kg^-1 M^-1 (As(III) with excellent regenerability (>90 % of desorption efficiency after three sorption cycles). The results of this review are expected to help researchers to establish a powerful strategy for abatement of arsenic ions in wastewater.

UiO-67 metal-organic gel material deposited on photonic crystal matrix for photoelectrocatalytic hydrogen production

Robust UiO-67 metal-organic framework nanoparticles have been precisely and uniformly anchored on the surface of a photonic crystal via metal-organic gelation, resulting in a nanoscale UiO-67 composite. Mott-Schottky measurements indicate that UiO-67/B is an n-type semiconductor with electron conduction, and the band gap significantly decreases with the assistance of the photonic crystal matrix with a band gap of 0.75 eV. Benefiting from the abundant photoelectrons trapped from the photonic crystal, good hydrogen evolution reaction performance is achieved under light irradiation. The current density increases from 3.2 to 7.0 mA cm-2 at -0.6 V (vs. RHE) for UiO-67/B. The optimized carrier density obtained from UiO-67/B is apparently increased 2.15 times under light irradiation for 30 min. This work provides a rational strategy to address the photo-capture and energy transfer issues of metal-organic frameworks under visible light irradiation for H2 production in artificial photosynthesis.

A Semiconducting Bi2O2(C4O4) Coordination Polymer Showing a Photoelectric Response

Inorganic semiconductors are extensively considered to be among the most promising materials to convert solar light into electricity or chemical energy owing to their efficiency in the separation of photoinduced electron/hole. Bismuth oxides, and, in particular, those built up of [Bi₂O₂]²⁺ layers, show an efficient charge separation and, thus, high photocatalytic activities. To explore a possible synergetic effect of bismuth metallic nodes combined with the electron-rich linker squarate, Bi₂O₂(C₄O₄) or IEF-3 (an IMDEA Energy framework) was hydrothermally prepared and adequately characterized. As determined from the X-ray structure, [Bi₂O₂]²⁺ layers are interconnected by squarate ligands, having a pronounced effect of the 6s² lone pair on the bismuth local environment. IEF-3 shows high thermal and chemical robustness at industrially relevant model aggressive media. A large panel of physicochemical methods were applied to recognize IEF-3 as an UV-absorbing n-type semiconductor, showing a photocurrent response comparable to that of α-Bi₂O₃, offering further possibilities for tuning its electrochemical properties by modifying the ligand. In this way, the well-known compositional and structural versatility of coordination polymers may be applied in the future to fine-tune metal-organic semiconductor systems.

Deterministic control of surface mounted metal–organic framework growth orientation on metallic and insulating surfaces

Surface-Mounted Metal–Organic Frameworks (SURMOFs) growth orientation in [100] or [111] can be deterministically controlled by the SAM chain length, regardless of the surface nature (metallic or insulating).

Electrical conductivity and magnetic bistability in metal–organic frameworks and coordination polymers: charge transport and spin crossover at the nanoscale

This review aims to reassess the progress, issues and opportunities in the path towards integrating conductive and magnetically bistable coordination polymers and metal–organic frameworks as active components in electronic devices.

Enhanced d–d transitions in HKUST/Bi2WO6 nanocomposite mediated visible-light driven selective conversion of benzyl alcohol to benzaldehyde

Graphical representation of the involvement of the d–d transition in the photocatalytic conversion of benzyl alcohol to benzaldehyde.

Achieving current rectification ratios ≥ 105 across thin films of coordination polymer

A record value of the current rectification ratio (RR ≥ 10⁵) across molecularly doped thin films of a Cu(ii)-coordination polymer is achieved.

Downsizing coordination polymers (CPs) to thin film configurations is a prerequisite for device applications. However, fabrication of thin films of CPs including metal–organic frameworks (MOFs) with reasonable electrical conductivity is challenging. Herein, thin film fabrication of a Cu(ii)-CP employing a layer-by-layer method is demonstrated whereby a self-assembled monolayer on Au was used as the functionalized substrate. Growth of the Cu(ii)-CP at the solid–liquid interface generated open-metal Cu(ii) sites in the thin film which were susceptible to activation by molecular dopant molecules. A significant enhancement in in-plane electrical conductivity and an unheralded cross-plane current rectification ratio (exceeding 10⁵ both at room-temperature and at an elevated temperature) were achieved. Such a remarkable rectification ratio was realized, similar to those of commercial Si rectifier diodes. This phenomenon is attributed to the formation of an electronic heterostructure in the molecularly doped thin film. Molecular doping additionally transformed the interfacial properties of thin films from hydrophilic to highly hydrophobic.

A highly crystalline anthracene-based MOF-74 series featuring electrical conductivity and luminescence

Recently, a small group of metal-organic frameworks (MOFs) has been discovered featuring substantial charge transport properties and electrical conductivity, hence promising to broaden the scope of potential MOF applications in fields such as batteries, fuel cells and supercapacitors. In combination with light emission, electroactive MOFs are intriguing candidates for chemical sensing and optoelectronic applications. Here, we incorporated anthracene-based building blocks into the MOF-74 topology with five different divalent metal ions, that is, Zn²⁺, Mg²⁺, Ni²⁺, Co²⁺ and Mn²⁺, resulting in a series of highly crystalline MOFs, coined ANMOF-74(M). This series of MOFs features substantial photoluminescence, with ANMOF-74(Zn) emitting across the whole visible spectrum. The materials moreover combine this photoluminescence with high surface areas and electrical conductivity. Compared to the original MOF-74 materials constructed from 2,5-dihydroxy terephthalic acid and the same metal ions Zn²⁺, Mg²⁺, Ni²⁺, Co²⁺ and Mn²⁺, we observed a conductivity enhancement of up to six orders of magnitude. Our results point towards the importance of building block design and the careful choice of the embedded MOF topology for obtaining materials with desired properties such as photoluminescence and electrical conductivity.

A Highly Conductive MOF of Graphene Analogue Ni3 (HITP)2 as a Sulfur Host for High-Performance Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries have been considered as one of the most promising energy storage systems owing to their high theoretical capacity and energy density. However, their commercial applications are obstructed by sluggish reaction kinetics and rapid capacity degradation mainly caused by polysulfide shuttling. Herein, the first attempt to utilize a highly conductive metal-organic framework (MOF) of Ni₃ (HITP)₂ graphene analogue as the sulfur host material to trap and transform polysulfides for high-performance Li-S batteries is made. Besides, the traditional conductive additive acetylene black is replaced by carbon nanotubes to construct matrix conduction networks for triggering the rate and cycling performance of the active cathode. As a result, the S@Ni₃ (HITP)₂ with sulfur content of 65.5 wt% shows excellent sulfur utilization, rate performance, and cyclic durability. It delivers a high initial capacity of 1302.9 mAh g^-1 and good capacity retention of 848.9 mAh g^-1 after 100 cycles at 0.2 C. Highly reversible discharge capacities of 807.4 and 629.6 mAh g^-1 are obtained at 0.5 and 1 C for 150 and 300 cycles, respectively. Such kinds of pristine MOFs with high conductivity and abundant polar sites reveal broad promising prospect for application in the field of high-performance Li-S batteries.

Metal-Organic Frameworks in Modern Physics: Highlights and Perspectives

Owing to the synergistic combination of a hybrid organic-inorganic nature and a chemically active porous structure, metal-organic frameworks have emerged as a new class of crystalline materials. The current trend in the chemical industry is to utilize such crystals as flexible hosting elements for applications as diverse as gas and energy storage, filtration, catalysis, and sensing. From the physical point of view, metal-organic frameworks are considered molecular crystals with hierarchical structures providing the structure-related physical properties crucial for future applications of energy transfer, data processing and storage, high-energy physics, and light manipulation. Here, the perspectives of metal-organic frameworks as a new family of functional materials in modern physics are discussed: from porous metals and superconductors, topological insulators, and classical and quantum memory elements, to optical superstructures, materials for particle physics, and even molecular scale mechanical metamaterials. Based on complementary properties of crystallinity, softness, organic-inorganic nature, and complex hierarchy, a description of how such artificial materials have extended their impact on applied physics to become the mainstream in material science is offered.

A sulfur coordination polymer with wide bandgap semiconductivity formed from zinc(II) and 5-methylsulfanyl-1,3,4-thiadiazole-2-thione

The sulfur coordination polymer catena-poly[zinc(II)-μ2-bis[5-(methylsulfanyl)-2-sulfanylidene-2,3-dihydro-1,3,4-thiadiazol-3-ido-κ2 N 3:S]], [Zn(C3H3N2S3)2] n or [Zn2MTT4] n , constructed from Zn2+ ions and 5-methylsulfanyl-1,3,4-thiadiazole-2-thione (HMTT), was synthesized successfully and structurally characterized. [Zn2MTT4] n crystallizes in the tetragonal space group I\overline{4} (No. 82). Each MTT− ligand (systematic name: 5-methylsulfanyl-2-sulfanylidene-2,3-dihydro-1,3,4-thiadiazol-3-ide) coordinates to two different ZnII ions, one via the thione group and the other via a ring N atom, with one ZnII atom being in a tetrahedral ZnS4 and the other in a tetrahedral ZnN4 coordination environment. These tetrahedral ZnS4 and ZnN4 units are alternately linked by the organic ligands, forming a one-dimensional chain structure along the c axis. The one-dimensional chains are further linked via C—H...N and C—H...S hydrogen bonds to form a three-dimensional network adopting an ABAB-style arrangement that lies along both the a and b axes. The three-dimensional Hirshfeld surface analysis and two-dimensional (2D) fingerprint plots confirm the major interactions as C—H...S hydrogen bonds with a total of 35.1%, while 7.4% are C—H...N hydrogen-bond interactions. [Zn2MTT4] n possesses high thermal and chemical stability and a linear temperature dependence of the bandgap from room temperature to 270 °C. Further investigation revealed that the bandgap changes sharply in ammonia, but only fluctuates slightly in other solvents, indicating its promising application as a selective sensor.

Improving photoelectrochemical response of ZnO nanowire arrays by coating with p-type ZnO-resembling metal-organic framework

Coupling semiconducting metal-organic frameworks (MOFs) with metal oxide (MO) semiconductor nanowires is an efficient solution to tune the photoelectric properties of both the parties. In this report, we demonstrate a facile surfactant-free growth strategy for modification of zinc oxide (ZnO) single-crystal nanowire arrays (NWAs) with the MOF zinc glycolate (noted as Zn-GA) that contains an embedded continuous 3D Zn-O network. Due to the structural resemblance of the Zn-O network between Zn-GA and ZnO, the prepared ZnO@Zn-GA nanowires present a tight contact at the core-shell interface in a partially epitaxial manner, and the loading amount of Zn-GA can be well controlled in the synthetic process. The inherent p-type Zn-GA in combination with the widely available n-type ZnO assures the construction of tandem n-p heterojunctions at the core-shell interface, which is confirmed by Mott-Schottky analysis. By implementation of the ZnO@Zn-GA NWAs as photoanodes for photoelectrochemical oxidation of water and oxalic acid, improved photocurrent responses are obtained relative to the primary ZnO NWAs. The most significant photoresponse is observed in the ZnO nanowires shelled by a compact Zn-GA particulate thin film with the largest junction region. These results are elucidated by the enhanced spatial separation efficiency of photogenerated charge carriers, which is favored by the built-in electric field at the interface of the n-p heterojunctions.