Porous Crystalline Spherulite Superstructures

Streamlined synthesis of superstructure Ni-benzimidazole MOFs: Glucose electrochemical analysis

The design and synthesis of efficient electrochemical sensors are crucial transformation technologies in electrochemistry. We successfully synthesize a three-dimensional Ni-metal-organic framework (MOF) nanostructured material with a superior architecture using benzimidazole and nickel nitrate as precursors at room temperature which is being applied in glucose electrochemical sensors. The reaction mechanism of M-6 during glucose detection is thoroughly studied using various characterization techniques, such as in situ Raman spectroscopy, in situ ultraviolet-visible spectrophotometry, synchrotron radiography, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The research findings demonstrate that the M-6 material exhibits high sensitivity for glucose detection, with a sensitivity of 2199.88 mA M-1 cm-2. This study provides an important reference for designing more efficient electrochemical reaction systems and optimizing material performance. Furthermore, the superstructural design offers new ideas and possibilities for the development and application of similar materials.

Layered (AlO)2OH·VO3 composite superstructures for ultralong lifespan aqueous zinc-ion batteries

The unique superstructures electrode materials are of dominant significance for improving the performance of aqueous zinc-ion batteries (AZIBs). In this work, using nano MIL-96 (Al) as the precursor, a series of the layered (AlO)2OH·VO3 composite superstructures with different morphologies and V-oxide contents were prepared by combining calcination and hydrothermal synthesis. Among which, the HBC650·V4 superstructure is composed of the amorphous Al2O3/C, V-oxide, and the fluffy structure of (AlO)2OH, thus the superstructure can enhance the stability, increase the active center, and shorten Zn2+ diffusion, respectively. It is commendable that, the HBC650·V4 superstructure exhibits a high specific capacity of 180.1 mAh·g-1 after 300 cycles at 0.5 A·g-1. Furthermore, the capacity retention can be as high as 99.6 % after 5000 cycles at a high current density of 5.0 A·g-1, showing superior long cycling stability. Importantly, the in-situ XRD patterns and ex-situ analysis revealed the structural changes and reaction mechanisms of the HBC650·V4 superstructure during Zn2+ insertion/extraction. Therefore, the HBC650·V4 superstructure prepared using Al-MOF exhibits the advanced AZIBs performance. The preparation of nano-MOF into multifunctional superstructures through innovative strategies will be development trend in this field, which opens a new way to design AZIBs cathode materials.

Constructing Porous Energetic Spherulites via Solvation-Growth Coupling for Enhanced Combustion

The fabrication of materials with hierarchical structures has garnered great interest, owing to the potential for significantly enhancing their functions. Herein, a strategy of coupling molecular solvation and crystal growth is presented to fabricate porous spherulites of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), an important energetic material. With the addition of polyvinylpyrrolidone in the antisolvent crystallization, the metastable solvate of CL-20 is formed and grows spherulitically, and spontaneously desolvates to obtain the porous spherulite when filtration, in which the characteristic peak of the nitro group of CL-20 shifts detected by the in situ micro-confocal Raman spectroscopy. The effect of polyvinylpyrrolidone is thought to induce the solvation of CL-20, confirmed by density functional theory calculations, meanwhile acting on the (020) face of CL-20 to trigger spherulitic growth, demonstrated through infrared spectroscopy and Rietveld refinement of powder X-ray diffraction. Moreover, compared to common CL-20 crystals, porous spherulites exhibit enhanced combustion with increases of 6.24% in peak pressure, 40.21% in pressurization rate, and 9.63% in pressure duration effect, indicating the capability of hierarchical structures to boost the energy release of energetic crystals. This work demonstrates a new route via solvation-growth coupling to construct hierarchical structures for organic crystals and provides insight into the structure-property relations for material design.

Pentazolate Anion: A Rare and Preferred Five-Membered Ligand for Constructing Pentasil-Zeolite Topology Architectures

As the fourth full-nitrogen structure, the pentazolate anion (cyclo-N5 - ) was highly coveted for decades. In 2017, the first air-stable non-metal pentazolate salt, (N5 )6 (H3 O)3 (NH4 )4 Cl, was obtained, representing a milestone in this field. As the latest member of the azole family, cyclo-N5 - is comprised of five nitrogen atoms. Although significant attention has been paid to the potential of cyclo-N5 - as an energetic material, its poor thermostability hinders any practical application. However, the unique ring structure and multiple coordination capability of cyclo-N5 - provide a platform for the fabrication of various structures, among which pentasil-zeolite topologies are the most intriguing. In addition, the introduction of structure-directing auxiliaries enables the self-assembly of diverse topological architectures, potentially imparting cyclo-N5 - with the potential to impact wide-ranging areas of coordination chemistry and topology. In this minireview, different pentasil-zeolite topologies based on metal-pentazolate frameworks are evaluated. To date, three zeolitic and zeolite-like topologies have been reported, namely the melanophlogite (MEP), chibaite (MTN), and unj topologies. The MEP topology consists of two nanocages, Na20 N60 and Na24 N60 , whereas the MTN topology contains Na20 N60 and Na28 N80 nanocages. Furthermore, the unj topology features multiple homochiral channels consisting of two helical chains. Various possible strategies for obtaining additional pentasil-zeolite topologies are also discussed.

Hierarchical Nano-Electrocatalytic Reactor for High Performance Polysulfides Redox Flow Batteries

The aqueous polysulfides is an important Earth-abundant and multielectron redox couple to construct high capacity density and low-cost aqueous redox flow batteries (RFB) ; nevertheless, the sluggish conversion and kinetic behavior of S2-/Sx2- result in a low power density output and poor active material utilizations. Herein, we present nanoconfined self-assembled ordered hierarchical porous Co and N codoped carbon (OHP-Co/NC) as an electrocatalytic reactor to enhance the mass transfer and redox activity of aqueous polysulfides. Finite element method simulation proves that the OHP-Co/NC with interconnected macropores and mesopores exhibits an enhanced mass transfer and delivers a larger redox electrolyte utilization of 50.1% compared to 23.3% of conventional Co/NC. Notably, the OHP-Co/NC obtained at 850 °C delivers the smallest redox peak potential difference (ΔE = 99 mV). Comparison studies of in operando Raman for aqueous polysulfides in the redox electrolyte and in situ electrochemical Raman on the single OHP-Co/NC particle for the adsorbed polysulfides were carried out. And it confirms that the OHP-Co/NC-850 catalyst has a strong adsorption of S42- and can retard the strong disproportionation and hydrolysis behavior of polysulfides on the electrocatalyst interface. Therefore, the polysulfide/ferrocyanide RFB with an OHP-Co/NC-850 based membrane-electrode assembly (MEA) exhibited a high power density of 110 mW cm-2, as well as a steady capacity retention over 99.7% in 300 cycles.

Single-Crystal Superstructures via Hierarchical Assemblies of Giant Rubik's Cubes as Tertiary Building Units

Intricate superstructures possess unusual structural features and promising applications. The preparation of superstructures with single-crystalline nature are conducive to understanding the structure-property relationship, however, remains an intriguing challenge. Herein we put forward a new hierarchical assembly strategy towards rational and precise construction of intricate single-crystal superstructures. Firstly, two unprecedented superclusters in Rubik's cube's form with a size of ≈2×2×2 nm³ are constructed by aggregation of eight {Pr₄ Sb₁₂ } oxohalide clusters as secondary building units (SBUs). Then, the Rubik's cubes further act as isolable tertiary building units (TBUs) to assemble diversified single-crystal superstructures. Importantly, intermediate assembly states are captured, which helps illustrate the evolution of TBU-based superstructures and thus provides a profound understanding of the assembly process of superstructures at the atomic level.

Growth mechanism and microstructures of Cu2O/PVP spherulites

Cu₂O spherulites are solvothermaly fabricated by using Cu(NO₃)₂ as the starting material and polyvinylpyrrolidone (PVP) as a multifunctional growth agent. The specimens at different growth stages are investigated by using X-ray diffraction, electron microscopy, energy dispersive X-ray spectroscopy, soft X-ray emission spectroscopy and infrared spectroscopy. The formation mechanism of Cu₂O spherulites is proposed accordingly. Hierarchically, the spherulites are composed of needle-like submicron-rods lying along the radial orientations. The submicron-rods are constructed by piling up of small Cu₂O/PVP spheres. The embedded Cu₂O nanocrystallites can generate a dipolar field in each along the [100] direction. They deposit at the surface of a negatively charged PVP-containing spherical core, and self-oriented along the radial directions. Therefore, all the Cu₂O nanocrystallites would have their positively charged (100) facet facing to the core and their negatively charged (1̄00) facet turning towards to the spherulite surface, leading to a negatively charged surface of spherulites. Unlike randomly oriented nanocrystallites embedded in polymer microspheres, the spherulites would not undergo surface recrystallisation into a single crystal shell due to the restricted potential of local shift and rotation of the nanocrystallites by the Coulomb force from the core. This work provides new perspective towards the formation of spherulites and their structural properties.

Cu₂O/PVP spherulites are synthesised using Cu(NO₃)₂ as precursor, PVP as a reductant/capping-agent and DMF as the solvent. The interaction between dipoles of Cu₂O nanocrystals and a negatively charged core plays an important role in their formation.

Aqueous Protein-Polymer Bioconjugation via Photoinduced RAFT Polymerization Using High Loading Heterogeneous Catalyst

Light-driven polymerization, such as photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization, enables biological benign conditions and versatile functional polymer structure design, which is readily used in protein-polymer bioconjugates. However, conventional metalloporphyrinic homogeneous catalysts for PET-RAFT polymerization suffer from limited aqueous solubility and tedious purification. Here we demonstrate the design of PET-RAFT photocatalyst from the reticular assembled Zr-porphyrinic metal-organic frameworks (MOFs), along with a biomacromolecule-based chain transfer agent, as efficient bioconjugation tools in water. Our methodology offers manufacturing advantages on bioconjugates under mild conditions such that MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) and cytotoxicity assays have shown the preservation of the protein integrity, bioactivity, and high cell viability after PET-RAFT polymerization. We find that the fast kinetics are benefiting from the ultrahigh loading of metalloporphyrins in MOF-525-Zn. This heterogeneous catalyst also allows us to maintain living characteristics to incorporate myriads of monomers into block copolymers. Other advantages like easy postreaction purification, reusability, and high oxygen tolerance even in an open system are demonstrated. This study provides a tool of highly efficient heterogeneous photocatalysts for polymer-protein bioconjugation in aqueous media and paves the road for biological applications.

Unusual Surface Texture, Dimensions and Morphology Variations of Chiral and Single Crystals*

We demonstrate here a unique metallo-organic material where the appearance and the internal crystal structure are in contradiction. The egg-shaped (ovoid) crystals have a brain-like texture. Although these micro-sized crystals are monodispersed; like fingerprints their grainy surfaces are never exactly alike. Remarkably, our X-ray and electron diffraction studies unexpectedly revealed that these structures are single-crystals comprising a continuous coordination network of two differently shaped homochiral channels. By using the same building blocks under different reaction conditions, a rare series of crystals have been obtained that are uniquely rounded in their shape. In stark contrast to the brain-like crystals, these isostructural and monodispersed crystals have a comparatively smooth appearance. The sizes of these crystals vary by several orders of magnitude.

MOF-74-type frameworks: tunable pore environment and functionality through metal and ligand modification

This highlight demonstrates a comprehensive overview of MOF-74-type frameworks in terms of synthetic approaches and pre- or post-synthetic modification approaches.

Hierarchy in Metal-Organic Frameworks

Sequence-defined nucleic acids and proteins with internal monomer sequences and arrangement are vital components in the living world, as a result of billions of years of molecular evolution. These natural hierarchical systems have inspired researchers to develop artificial hierarchical materials that can mimic similar functions such as replication, recognition, and information storage. In this Outlook, we describe the conceptual introduction of hierarchy into the design of metal-organic framework (MOF) materials. Starting with a history and background of hierarchical MOF synthesis and applications, we discuss further mesoscopic assembly strategies of MOF crystallites into hierarchical primary, secondary, tertiary, and quaternary architectures. This is followed by a highlight of the utilization of modular total synthesis for crafting MOFs with hierarchical compositions. The multiscale control over hierarchical MOF architecture formation can be rationally achieved by designing stepwise synthetic routes based on the knowledge from various fields including coordination chemistry, organic chemistry, reticular chemistry, and nanoscience. Altogether, this outlook is expected to shed light on these essential but embryonic materials and might offer inspiration for the development of the next generation of smart MOF materials with controllable heterogeneity and tailorable architectures.

Seed-mediated evolution of hierarchical metal-organic framework quaternary superstructures

Varying levels of hierarchy in metal–organic framework (MOF) superstructures are achieved through seed-mediated evolution of multiple MOF modules.

The idea of hierarchy, widely observed in natural and artificial worlds, has been extensively explored in chemistry and materials science. Similar to proteins which contain primary, secondary, tertiary and quaternary structures, varying levels of hierarchy in metal–organic framework (MOF) superstructures can also be achieved. In this work, we initiate a systematic study on the morphological evolution of hierarchical superstructures with the assistance of seeded growth and explore the assembly of multiple modular MOFs into superstructures with enhanced hierarchy and diversity. By utilizing MOF-74-III spherulite superstructures as seeds, multiple quaternary architectures were obtained depending on the lengths of organic linker precursors. The resulting superstructures with superior hierarchy represent a unique porous material which contains multiple modules with diverse morphologies. To the best of our knowledge, this is the first report that utilizes tertiary superstructures as seeds in MOF synthesis, which leads to unusual and diverse behaviors during secondary growth. This synthetic approach not only provides a facile method to establish hierarchy in porous materials, but also enables the fabrication of multiscale heterostructures through secondary growth on MOF seeds.

A general strategy based on the self-evolution of building blocks for the construction of one-dimensional hierarchically super-structured TiO2 fibres

We provide a general strategy based on the self-evolution of building blocks to fabricate one-dimensional hierarchically superstructured metal-doped titanate and TiO₂ materials with coated-nanosheet and interconnected meso-/macropores.