Reticular Synthesis of Highly Crystalline Three-Dimensional Mesoporous Covalent-Organic Frameworks for Lipase Inclusion.

The synthesis and application of three-dimensional (3D) mesoporous covalent-organic frameworks (COFs) are still to be developed. Herein, two mesoporous 3D COFs with an stp topology were synthesized in a highly crystalline form with aniline as the modulator. The chemical composition of these COFs was confirmed by Fourier transform infrared (FT-IR) and 13C cross-polarization magic angle spinning nuclear magnetic resonance (NMR) spectroscopies. These 3D mesoporous COFs were highly crystalline and exhibited permanent porosity and good chemical stability in both aqueous and organic media. The space group and unit cell parameters of COF HFPTP-TAE were verified by powder X-ray diffraction (PXRD), small-angle X-ray scattering, and three-dimensional electron diffraction (3D ED). The appropriate pore size of the COF HFPTP-TAE facilitated the inclusion of enzyme lipase PS with a loading amount of 0.28 g g-1. The lipase⊂HFPTP-TAE (⊂ refers to "include in") composite exhibited high catalytic activity, good thermal stability, and a wide range of solvent tolerance. Specifically, it could catalyze the alcoholysis of aspirin methyl ester (AME) with high catalytic efficiency. Oriented one-dimensional (1D) channel mesopores in HFPTP-TAE accommodated lipase, meanwhile preventing them from aggregation, while windows on the wall of the 1D channel favored molecular diffusion; thus, this COF-enzyme design outperformed its amorphous isomer, two-dimensional (2D) mesoporous COF, 3D mesoporous COF with limited crystallinity, and mesoporous silica as an enzyme host.

Constructing Intrapenetrated Hierarchical Zeolites with Highly Complete Framework via Protozeolite Seeding.

Creation of intrapenetrated mesopores with open highway from external surface into the interior of zeolite crystals are highly desirable that can significantly improve the molecular transport and active sites accessibility of microporous zeolites to afford enhanced catalytic properties. Here, different from traditional zeolite-seeded methods that generally produced isolated mesopores in zeolites, nanosized amorphous protozeolites with embryo structure of zeolites were used as seeds for the construction of single-crystalline hierarchical ZSM-5 zeolites with intrapenetrated mesopores (mesopore volume of 0.51 cm3 g-1 ) and highly complete framework. In this strategy, in contrast to the conventional synthesis, only a small amount of organic structure directing agents and a low crystallization temperature were adopted to promise the protozeolites as the dominant growth directing sites to induce crystallization. The protozeolite nanoseeds provided abundant nucleation sites for surrounding precursors to be crystallized, followed by oriented coalescence of crystallites resulting in the formation of intrapenetrated mesopores. The as-prepared hierarchical ZSM-5 zeolites exhibited ultra-long lifetime of 443.9 hours and a high propylene selectivity of 47.92 % at a WHSV of 2 h-1 in the methanol-to-propylene reaction. This work provides a facile protozeolite-seeded strategy for the synthesis of intrapenetrated hierarchical zeolites that are highly effective for catalytic applications.

Silanol-Engineered Nonclassical Growth of Zeolite Nanosheets from Oriented Attachment of Amorphous Protozeolite Nanoparticles.

Zeolite nonclassical growth via particle attachment has been proposed for two decades, yet the attachment mechanism and kinetic regulation remain elusive. Here, nonclassical growth of an MFI-type zeolite has been achieved by using amorphous protozeolite (PZ) nanoparticles containing encapsulated TPA+ templates and abundant silanols (Si-OH) as sole precursors under hydrothermal conditions. The silanol characteristics of the precursor were studied by two-dimensional (2D) solid-state nuclear magnetic resonance (NMR) correlation spectroscopy, which were proven to play critical roles in determining precursor attachment behavior and crystal growth orientation. Under mechanical ball-milling or tablet-pressing process, pressure drove the fusion of spherical PZ into platelet-like integrated PZ (IPZ) coupled with transformations of external silanols from evenly distributed to curvature-dependent distributed and internal silanols from isolated to spatially proximate. Compared to isolated silanols, the spatially proximate silanols possessed a stronger correlation with TPA+, benefiting the formation of Si-O-Si bonds via silanol condensation. Subsequently, driven by minimization of surface energy, particle attachment of the platelet-like IPZ precursor preferentially occurred at high-curvature surfaces with high-density silanols, leading to anisotropic rates of nonclassical growth and thus the formation of high-aspect-ratio MFI-type zeolite nanosheets. Advanced electron microscopy provided direct evidence of attachment of amorphous IPZ precursors to crystalline intermediate surfaces along the c-axis direction with the formation of amorphous-crystalline interfaces, followed by interface elimination and structural evolution to a single-crystalline phase. Our findings not only unravel the zeolite nonclassical growth mechanism but also reveal the critical role of silanol chemistry in kinetic regulation, which is of great importance for pursuing a tailored zeolite synthesis.

Site-selective superassembly of biomimetic nanorobots enabling deep penetration into tumor with stiff stroma.

Chemotherapy remains as the first-choice treatment option for triple-negative breast cancer (TNBC). However, the limited tumor penetration and low cellular internalization efficiency of current nanocarrier-based systems impede the access of anticancer drugs to TNBC with dense stroma and thereby greatly restricts clinical therapeutic efficacy, especially for TNBC bone metastasis. In this work, biomimetic head/hollow tail nanorobots were designed through a site-selective superassembly strategy. We show that nanorobots enable efficient remodeling of the dense tumor stromal microenvironments (TSM) for deep tumor penetration. Furthermore, the self-movement ability and spiky head markedly promote interfacial cellular uptake efficacy, transvascular extravasation, and intratumoral penetration. These nanorobots, which integrate deep tumor penetration, active cellular internalization, near-infrared (NIR) light-responsive release, and photothermal therapy capacities into a single nanodevice efficiently suppress tumor growth in a bone metastasis female mouse model of TNBC and also demonstrate potent antitumor efficacy in three different subcutaneous tumor models.

Characterization of Tunneled Wide Band Gap Mixed Conductors: The Na2O-Ga2O3-TiO2 System.

This article focuses on the Na2O-Ga2O3-TiO2 system, which is barely explored in the study of transparent conductive oxides (TCOs). NaxGa4+xTin-4-xO2n-2 (n = 5, 6, and 7 and x ≈ 0.7-0.8) materials were characterized using neutron powder diffraction and aberration-corrected scanning transmission electron microscopy. Activation energy, as a function of different structures depending on tunnel size, shows a significant improvement in Na+ ion conduction from hexagonal to octagonal tunnels. New insights into the relationship between the crystal structure and the transport properties of TCOs, which are crucial for the design and development of new optoelectronic devices, are provided.

Edge-Site-Free and Topological-Defect-Rich Carbon Cathode for High-Performance Lithium-Oxygen Batteries.

The rational design of a stable and catalytic carbon cathode is crucial for the development of rechargeable lithium-oxygen (LiO2 ) batteries. An edge-site-free and topological-defect-rich graphene-based material is proposed as a pure carbon cathode that drastically improves LiO2 battery performance, even in the absence of extra catalysts and mediators. The proposed graphene-based material is synthesized using the advanced template technique coupled with high-temperature annealing at 1800 °C. The material possesses an edge-site-free framework and mesoporosity, which is crucial to achieve excellent electrochemical stability and an ultra-large capacity (>6700 mAh g-1 ). Moreover, both experimental and theoretical structural characterization demonstrates the presence of a significant number of topological defects, which are non-hexagonal carbon rings in the graphene framework. In situ isotopic electrochemical mass spectrometry and theoretical calculations reveal the unique catalysis of topological defects in the formation of amorphous Li2 O2 , which may be decomposed at low potential (∼ 3.6 V versus Li/Li+ ) and leads to improved cycle performance. Furthermore, a flexible electrode sheet that excludes organic binders exhibits an extremely long lifetime of up to 307 cycles (>1535 h), in the absence of solid or soluble catalysts. These findings may be used to design robust carbon cathodes for LiO2 batteries.

Can NbO Keep nbo Topology under Electrons? -Unveiling Novel Aspects of Niobium Monoxide at the Atomic Scale.

A precise investigation of NbO has been carried out by advanced electron microscopy combined with powder and single crystal X-ray diffraction (XRD). The structure of pristine NbO has been determined as Pm-3 m space group (SG) with a = 4.211 Šand the positions of Nb and O at the 3c and 3d Wyckoff positions, respectively, which is consistent with previous report based on powder XRD data. Electron beams induced a structural transition, which was investigated and explained by combining electron diffraction and atomic-resolution imaging. The results revealed that the electron beam stimulated both Nb and O atom-migrations within each fcc sublattice, and that the final structure was SG Fm-3 m with a = 4.29 Å, Nb and O at the 4a and 4b with 75 % occupancy and same chemical composition. Antiphase planar defects were discovered in the pristine NbO and related to the structural transformation. Theoretical calculations performed by density functional theory (DFT) supported the experimental conclusions.

Coherent hexagonal platinum skin on nickel nanocrystals for enhanced hydrogen evolution activity.

Metastable noble metal nanocrystals may exhibit distinctive catalytic properties to address the sluggish kinetics of many important processes, including the hydrogen evolution reaction under alkaline conditions for water-electrolysis hydrogen production. However, the exploration of metastable noble metal nanocrystals is still in its infancy and suffers from a lack of sufficient synthesis and electronic engineering strategies to fully stimulate their potential in catalysis. In this paper, we report a synthesis of metastable hexagonal Pt nanostructures by coherent growth on 3d transition metal nanocrystals such as Ni without involving galvanic replacement reaction, which expands the frontier of the phase-replication synthesis. Unlike noble metal substrates, the 3d transition metal substrate owns more crystal phases and lower cost and endows the hexagonal Pt skin with substantial compressive strains and programmable charge density, making the electronic properties particularly preferred for the alkaline hydrogen evolution reaction. The energy barriers are greatly reduced, pushing the activity to 133 mA cmgeo-2 and 17.4 mA µgPt-1 at -70 mV with 1.5 µg of Pt in 1 M KOH. Our strategy paves the way for metastable noble metal catalysts with tailored electronic properties for highly efficient and cost-effective energy conversion.

Conjugated Nonplanar Copper-Catecholate Conductive Metal-Organic Frameworks via Contorted Hexabenzocoronene Ligands for Electrical Conduction.

Conductive metal-organic frameworks (c-MOFs) with outstanding electrical conductivities and high charge carrier mobilities are promising candidates for electronics and optoelectronics. However, the poor solubility of planar ligands greatly hinders the synthesis and widespread applications of c-MOFs. Nonplanar ligands with excellent solubility in organic solvents are ideal alternatives to construct c-MOFs. Herein, contorted hexabenzocoronene (c-HBC) derivatives with good solubility are adopted to synthesize c-MOFs. Three c-MOFs (c-HBC-6O-Cu, c-HBC-8O-Cu, and c-HBC-12O-Cu) with substantially different geometries and packing modes have been synthesized using three multitopic catechol-based c-HBC ligands with different symmetries and coordination numbers, respectively. With more metal coordination centers and increased charge transport pathways, c-HBC-12O-Cu exhibits the highest intrinsic electrical conductivity of 3.31 S m-1. Time-resolved terahertz spectroscopy reveals high charge carrier mobilities in c-HBC-based c-MOFs, ranging from 38 to 64 cm2 V-1 s-1. This work provides a systematic and modular approach to fine-tune the structure and enrich the c-MOF family with excellent charge transport properties using nonplanar and highly soluble ligands.

Direct Construction of 2D Conductive Metal-Organic Frameworks from a Nonplanar Ligand: In Situ Scholl Reaction and Topological Modulation.

Two-dimensional conductive metal-organic frameworks (2D c-MOFs) are an emerging class of promising porous materials with high crystallinity, tunable structures, and diverse functions. However, the limited topologies and difficulties in synthesizing suitable organic linkers remain a great challenge for 2D c-MOFs synthesis and applications. Herein, two layered 2D c-MOF polymorphs with either a rhombus structure (sql-TBA-MOF) or kagome structure (kgm-TBA-MOF) were directly constructed via in situ Scholl reaction and coordination chemistry from a flexible and nonplanar tetraphenylbenzene-based ligand (8OH-TPB) in a one-pot manner. Interestingly, the kgm-TBA-MOF comprising hexagonal and triangular dual pores exhibit higher conductivities of 1.65 × 10-3 S/cm at 298 K and 3.33 × 10-2 S/cm at 353 K than that of sql-TBA-MOF (4.48 × 10-4 and 2.90 × 10-3 S/cm, respectively). Moreover, the morphology and topology can be modulated via the addition of ammonium hydroxide as modulator. The present work provides a new pathway for design, synthesis, and topological regulation of 2D c-MOFs.

Atomic-level structural responsiveness to environmental conditions from 3D electron diffraction.

Electron microscopy has been widely used in the structural analysis of proteins, pharmaceutical products, and various functional materials in the past decades. However, one fact is often overlooked that the crystal structure might be sensitive to external environments and response manners, which will bring uncertainty to the structure determination and structure-property correlation. Here, we report the atomic-level ab initio structure determinations of microcrystals by combining 3D electron diffraction (3D ED) and environmental transmission electron microscope (TEM). Environmental conditions, including cryo, heating, gas and liquid, have been successfully achieved using in situ holders to reveal the simuli-responsive structures of crystals. Remarkable structural changes have been directly resolved by 3D ED in one flexible metal-organic framework, MIL-53, owing to the response of framework to pressures, temperatures, guest molecules, etc.

Direct TEM Observation of Vacancy-Mediated Heteroatom Incorporation into a Zeolite Framework: Towards Microscopic Design of Zeolite Catalysts.

Incorporating hetero-metal-atom, e.g., titanium, into zeolite frameworks can enhance the catalytic activity and selectivity in oxidation reactions. However, the rational design of zeolites containing titanium at specific sites is difficult because the precise atomic structure during synthesis process remained unclear. Here, a titanosilicate with predictable titanium distribution was synthesized by mediating vacancies in a defective MSE-type zeolite precursor, based on a pre-designed synthetic route including modification of vacancies followed by titanium insertion, where electron microscopy (EM) plays a key role at each step resolving the atomic structure. Point defects including vacancies in the precursor and titanium incorporated into the vacancy-related positions have been directly observed. The results provide insights into the role of point defects in zeolites towards the rational synthesis of zeolites with desired microscopic arrangement of catalytically active sites.

Counting charges per metal nanoparticle.

Charges on a metal nanoparticle are measured with precision by electron holography.

Synchronous quantitative analysis of chiral mesostructured inorganic crystals by 3D electron diffraction tomography.

Chiral mesostructures exhibit distinctive twisting and helical hierarchical stacking ranging from atomic to micrometre scales with fascinating structural-chiral anisotropy properties. However, the detailed determination of their multilevel chirality remains challenging due to the limited information from spectroscopy, diffraction techniques, scanning electron microscopy and the two-dimensional projections in transmission electron microscopy. Herein, we report a general approach to determine chiral hierarchical mesostructures based on three-dimensional electron diffraction tomography (3D EDT), by which the structure can be solved synchronously according to the quantitative measurement of diffraction spot deformations and their arrangement in reciprocal space. This method was verified on two samples-chiral mesostructured nickel molybdate and chiral mesostructured tin dioxide-revealing hierarchical chiral structures that cannot be determined by conventional techniques. This approach provides more precise and comprehensive identification of the hierarchical mesostructures, which is expected to advance our understanding of structural-chiral anisotropy at the fundamental level.

Rational design of mixed-matrix metal-organic framework membranes for molecular separations.

Conventional separation technologies to separate valuable commodities are energy intensive, consuming 15% of the worldwide energy. Mixed-matrix membranes, combining processable polymers and selective adsorbents, offer the potential to deploy adsorbent distinct separation properties into processable matrix. We report the rational design and construction of a highly efficient, mixed-matrix metal-organic framework membrane based on three interlocked criteria: (i) a fluorinated metal-organic framework, AlFFIVE-1-Ni, as a molecular sieve adsorbent that selectively enhances hydrogen sulfide and carbon dioxide diffusion while excluding methane; (ii) tailoring crystal morphology into nanosheets with maximally exposed (001) facets; and (iii) in-plane alignment of (001) nanosheets in polymer matrix and attainment of [001]-oriented membrane. The membrane demonstrated exceptionally high hydrogen sulfide and carbon dioxide separation from natural gas under practical working conditions. This approach offers great potential to translate other key adsorbents into processable matrix.

Protozeolite-Seeded Synthesis of Single-Crystalline Hierarchical Zeolites with Facet-Shaped Mesopores and Their Catalytic Application in Methanol-to-Propylene Conversion.

Hierarchical zeolites integrating intrinsic micropores with secondary meso- and/or macropores afford superior catalytic properties for enhanced mass transportation and more accessible active sites. The mesopores generated by using mesoporogens or framework etching are usually irregular with abundant defective sites and low hydrothermal stability. Here, using protozeolite nanoparticles as seeds, we succeeded in the synthesis of single-crystalline hierarchical ZSM-5 zeolites with hexagonal mesopores faceted by complete microporous frameworks. The protozeolites played a key role in the formation of faceted mesopores achieved via intraparticle ripening process. Thanks to the unique texture properties and more accessible acid sites at the open location, the as-prepared zeolites exhibited remarkedly long lifetime (18 h) and high propylene selectivity (52.7 %) with propylene/ethylene ratio of 3.64 in the methanol-to-propylene reaction (WHSV=12.5 h-1 ) compared to the counterparts.

Superassembly of Surface-Enriched Ru Nanoclusters from Trapping-Bonding Strategy for Efficient Hydrogen Evolution.

Hydrogen evolution reaction (HER) through water splitting is a potential technology to realize the sustainable production of hydrogen, yet the tardy water dissociation and costly Pt-based catalysts inhibit its development. Here, a trapping-bonding strategy is proposed to realize the superassembly of surface-enriched Ru nanoclusters on a phytic acid modified nitrogen-doped carbon framework (denoted as NCPO-Ru NCs). The modified framework has a high affinity to metal cations and can trap plenty of Ru ions. The trapped Ru ions are mainly distributed on the surface of the framework and can form Ru nanoclusters at 50 °C with the synergistic effect of vacancies and phosphate groups. By adjusting the content of phytic acid, surface-enriched Ru nanoclusters with adjustable distribution and densities can be obtained. Benefiting from the adequate exposure of the active sites and dense distribution of ultrasmall Ru nanoclusters, the obtained NCPO-Ru NCs catalyst can effectively drive HER in alkaline electrolytes and show an activity (at overpotential of 50 mV) about 14.3 and 9.6 times higher than that of commercial Ru/C and Pt/C catalysts, respectively. Furthermore, the great performance in solar to hydrogen generation through water splitting provides more flexibility for wide applications of NCPO-Ru NCs.

General Synergistic Capture-Bonding Superassembly of Atomically Dispersed Catalysts on Micropore-Vacancy Frameworks.

Atomically dispersed catalysts are a new type of material in the field of catalysis science, yet their large-scale synthesis under mild conditions remains challenging. Here, a general synergistic capture-bonding superassembly strategy to obtain atomically dispersed Pt (Ru, Au, Pd, Ir, and Rh)-based catalysts on micropore-vacancy frameworks at a mild temperature of 60 °C is reported. The precise capture via narrow pores and the stable bonding of vacancies not only simplify the synthesis process of atomically dispersed catalysts but also realize their large-scale preparation at mild temperature. The prepared atomically dispersed Pt-based catalyst possesses a promising electrocatalytic activity for hydrogen evolution, showing an activity (at overpotential of 50 mV) about 21.4 and 20.8 times higher than that of commercial Pt/C catalyst in 1.0 M KOH and 0.5 M H2SO4, respectively. Besides, the extremely long operational stability of more than 100 h provides more potential for its practical application.

Kinetics-Regulated Interfacial Selective Superassembly of Asymmetric Smart Nanovehicles with Tailored Topological Hollow Architectures.

Hollow nanoparticles featuring tunable structures with spatial and chemical specificity are of fundamental interest. However, it remains a significant challenge to design and synthesize asymmetric nanoparticles with controllable topological hollow architecture. Here, a versatile kinetics-regulated cooperative polymerization induced interfacial selective superassembly strategy is demonstrated to construct a series of asymmetric hollow porous composites (AHPCs) with tunable diameters, architectures and components. The size and number of patches on Janus nanoparticles can be precisely manipulated by the precursor and catalyst content. Notably, AHPCs exhibit excellent photothermal conversion performance under the irradiation of a near infrared (NIR) laser. Thus, AHPCs are utilized as NIR light-triggered nanovehicles and cargos can be controllably released. In brief, this versatile superassembly approach offers a streamlined and powerful toolset to design diverse asymmetric hollow porous composites.

In Situ Mapping and Local Negative Uptake Behavior of Adsorbates in Individual Pores of Metal-Organic Frameworks.

Herein, we report the adsorbate behavior in individual local pores of MIL-101, which is a metal-organic framework (MOF) with two heterogeneous mesopores and different metal sites, by combining adsorbate isotherms and in situ crystallography profiles. The in situ mapping shows that the substrate-adsorbate interaction affects the initial adsorption and pore condensation steps. The monolayer adsorption gradient changes greatly depending on the framework metal-adsorbate attraction force. Also, broad inflection points are found in adsorption isotherms, and the initial shape depends on the different metals. Besides, the capillary condensation at a pore draws adsorbates from other local pores. This leads to the local negative uptake behavior in individual pore isotherms. At higher pressure, they move to a larger space, whereas in a relatively low-pressure range the attraction force between the MOF framework and guest molecule influences the amount of rearranged guest molecules. Furthermore, the origin of the characteristic adsorption behavior based on the metals constituting the MOFs and the relative strength of substrate-adsorbate and adsorbate-adsorbate interactions are elucidated through the combined study of electron densities in pores, electron paramagnetic resonance spectroscopy spectra, and density functional theory and Monte Carlo simulations to uncover the previously veiled information on adsorption behavior.