Elastic films of single-crystal two-dimensional covalent organic frameworks.

The properties of polycrystalline materials are often dominated by defects; two-dimensional (2D) crystals can even be divided and disrupted by a line defect1-3. However, 2D crystals are often required to be processed into films, which are inevitably polycrystalline and contain numerous grain boundaries, and therefore are brittle and fragile, hindering application in flexible electronics, optoelectronics and separation1-4. Moreover, similar to glass, wood and plastics, they suffer from trade-off effects between mechanical strength and toughness5,6. Here we report a method to produce highly strong, tough and elastic films of an emerging class of 2D crystals: 2D covalent organic frameworks (COFs) composed of single-crystal domains connected by an interwoven grain boundary on water surface using an aliphatic bi-amine as a sacrificial go-between. Films of two 2D COFs have been demonstrated, which show Young's moduli and breaking strengths of 56.7 ± 7.4 GPa and 73.4 ± 11.6 GPa, and 82.2 ± 9.1 N m-1 and 29.5 ± 7.2 N m-1, respectively. We predict that the sacrificial go-between guided synthesis method and the interwoven grain boundary will inspire grain boundary engineering of various polycrystalline materials, endowing them with new properties, enhancing their current applications and paving the way for new applications.

Growth and Local Structures of Single Crystalline Flakes of Three-Dimensional Covalent Organic Frameworks in Water.

Due to the enormous chemical and structural diversities and designable properties and functionalities, covalent organic frameworks (COFs) hold great promise as tailored materials for industrial applications in electronics, biology, and energy technologies. They were typically obtained as partially crystalline materials, although a few single-crystal three-dimensional (3D) COFs have been obtained recently with structures probed by diffraction techniques. However, it remains challenging to grow single-crystal COFs with controlled morphology and to elucidate the local structures of 3D COFs, imposing severe limitations on the applications and understanding of the local structure-property correlations. Herein, we develop a method for designed growth of five types of single crystalline flakes of 3D COFs with controlled morphology, front crystal facets, and defined edge structures as well as surface chemistry using surfactants that can be self-assembled into layered structures to confine crystal growth in water. The flakes enable direct observation of local structures including monomer units, pore structure, edge structure, grain boundary, and lattice distortion of 3D COFs as well as gradually curved surfaces in kinked but single crystalline 3D COFs with a resolution of up to ∼1.7 Å. In comparison with flakes of two-dimensional crystals, the synthesized flakes show much higher chemical, mechanical, and thermal stability.

Nanoporous and Highly Thermal Conductive Thin Film of Single-Crystal Covalent Organic Frameworks Ribbons.

Nanoporous materials are widely explored as efficient adsorbents for the storage of gases and liquids as well as for effective low-dielectric materials in large-scale integrated circuits. These applications require fast heat transfer, while most nanoporous substances are thermal insulators. Here, the oriented growth of micrometer-sized single-crystal covalent organic frameworks (COFs) ribbons with nanoporous structures at an air-water interface is presented. The obtained COFs ribbons are interconnected into a continuous and purely crystalline thin film. Due to the robust connectivity among the COFs ribbons, the entire film can be easily transferred and reliably contacted with target supports. The measured thermal conductivity amounts to ∼5.31 ± 0.37 W m-1 K-1 at 305 K, which is so far the highest value for nanoporous materials. These findings provide a methodology to grow and assemble single-crystal COFs into large area ensembles for the exploration of functional properties and potentially lead to new devices with COFs thin films where both porosity and thermal conductivity are desired.

A High-Rate Two-Dimensional Polyarylimide Covalent Organic Framework Anode for Aqueous Zn-Ion Energy Storage Devices.

Rechargeable aqueous Zn-ion energy storage devices are promising candidates for next-generation energy storage technologies. However, the lack of highly reversible Zn2+-storage anode materials with low potential windows remains a primary concern. Here, we report a two-dimensional polyarylimide covalent organic framework (PI-COF) anode with high-kinetics Zn2+-storage capability. The well-organized pore channels of PI-COF allow the high accessibility of the build-in redox-active carbonyl groups and efficient ion diffusion with a low energy barrier. The constructed PI-COF anode exhibits a specific capacity (332 C g-1 or 92 mAh g-1 at 0.7 A g-1), a high rate capability (79.8% at 7 A g-1), and a long cycle life (85% over 4000 cycles). In situ Raman investigation and first-principle calculations clarify the two-step Zn2+-storage mechanism, in which imide carbonyl groups reversibly form negatively charged enolates. Dendrite-free full Zn-ion devices are fabricated by coupling PI-COF anodes with MnO2 cathodes, delivering excellent energy densities (23.9 ∼ 66.5 Wh kg-1) and supercapacitor-level power densities (133 ∼ 4782 W kg-1). This study demonstrates the feasibility of covalent organic framework as Zn2+-storage anodes and shows a promising prospect for constructing reliable aqueous energy storage devices.

Plasmon-enhanced nanoporous BiVO4 photoanodes for efficient photoelectrochemical water oxidation.

Conversion of solar irradiation into chemical fuels such as hydrogen with the use of a photoelectrochemical (PEC) cell is an attractive strategy for green energy. The promising technique of incorporating metal nanoparticles (NPs) in the photoelectrodes is being explored to enhance the performance of the photoelectrodes. In this work, we developed Au-NPs-functionalized nanoporous BiVO4 photoanodes, and utilized the plasmonic effects of Au NPs to enhance the photoresponse. The plasmonic enhancement leads to an AM 1.5 photocurrent of 5.1 ± 0.1 mA cm(-2) at 1.23 V versus a reverse hydrogen electrode. We observed an enhancement of five times with respect to pristine BiVO4 in the photocurrent with long-term stability and high energy-conversion efficiency. The overall performance enhancement is attributed to the synergy between the nanoporous architecture of BiVO4 and the plasmonic effects of Au NPs. Our further study reveals that the commendable photoactivity arises from the different plasmonic effects and co-catalyst effects of Au NPs.

Localization of oxygen interstitials in CeSrGa3O(7+δ) melilite.

The solubility of Ce in the La(1-x)Ce(x)SrGa3O(7+δ) and La(1.54-x)Ce(x)Sr0.46Ga3O(7.27+δ) melilites was investigated, along with the thermal redox stability in air of these melilites and the conductivity variation associated with oxidization of Ce(3+) into Ce(4+). Under CO reducing atmosphere, the La in LaSrGa3O7 may be completely substituted by Ce to form the La(1-x)Ce(x)SrGa3O(7+δ) solid solution, which is stable in air to ∼600 °C when x ≥ 0.6. On the other side, the La(1.54-x)Ce(x)Sr0.46Ga3O(7.27+δ) compositions displayed much lower Ce solubility (x ≤ 0.1), irrespective of the synthesis atmosphere. In the as-made La(1-x)CexSrGa3O(7+δ), the conductivity increased with the cerium content, due to the enhanced electronic conduction arising from the 4f electrons in Ce(3+) cations. At 600 °C, CeSrGa3O(7+δ) showed a conductivity of ∼10(-4) S/cm in air, nearly 4 orders of magnitude higher than that of LaSrGa3O7. The oxidation of Ce(3+) into Ce(4+) in CeSrGa3O(7+δ) slightly reduced the conductivity, and the oxygen excess did not result in apparent increase of oxide ion conduction in CeSrGa3O(7+δ). The Ce doping in air also reduced the interstitial oxide ion conductivity of La1.54Sr0.46Ga3O7.27. Neutron powder diffraction study on CeSrGa3O7.39 composition revealed that the extra oxygen is incorporated in the four-linked GaO4 polyhedral environment, leading to distorted GaO5 trigonal bipyramid. The stabilization and low mobility of interstitial oxygen atoms in CeSrGa3O(7+δ), in contrast with those in La(1+x)Sr(1-x)Ga3O(7+0.5x), may be correlated with the cationic size contraction from the oxidation of Ce(3+) to Ce(4+). These results provide a new comprehensive understanding of the accommodation and conduction mechanism of the oxygen interstitials in the melilite structure.

High energy density asymmetric quasi-solid-state supercapacitor based on porous vanadium nitride nanowire anode.

To push the energy density limit of asymmetric supercapacitors (ASCs), a new class of anode materials is needed. Vanadium nitride (VN) holds great promise as anode material for ASCs due to its large specific capacitance, high electrical conductivity, and wide operation windows in negative potential. However, its poor electrochemical stability severely limits its application in SCs. In this work, we demonstrated high energy density, stable, quasi-solid-state ASC device based on porous VN nanowire anode and VOx nanowire cathode for the first time. The VOx//VN-ASC device exhibited a stable electrochemical window of 1.8 V and excellent cycling stability with only 12.5% decrease of capacitance after 10,000 cycles. More importantly, the VOx//VN-ASC device achieved a high energy density of 0.61 mWh cm(-3) at current density of 0.5 mA cm(-2) and a high power density of 0.85 W cm(-3) at current density of 5 mA cm(-2). These values are substantially enhanced compared to most of the reported quasi/all-solid-state SC devices. This work constitutes the first demonstration of using VN nanowires as high energy anode, which could potentially improve the performance of energy storage devices.

Transplantation of Wnt5a-modified Bone Marrow Mesenchymal Stem Cells Promotes Recovery After Spinal Cord Injury via the PI3K/AKT Pathway.

Spinal cord injury (SCI) is a severe neurological condition that can lead to paralysis or even death. This study explored the potential benefits of bone marrow mesenchymal stem cell (BMSC) transplantation for repairing SCI. BMSCs also differentiate into astrocytes within damaged spinal cord tissues hindering the cell transplantation efficacy, therefore it is crucial to enhance their neuronal differentiation rate to facilitate spinal cord repair. Wnt5a, an upstream protein in the non-classical Wnt signaling pathway, has been implicated in stem cell migration, differentiation, and neurite formation but its role in the neuronal differentiation of BMSCs remains unclear. Thus, this study investigated the role and underlying mechanisms of Wnt5a in promoting neuronal differentiation of BMSCs both in vivo and in vitro. Wnt5a enhanced neuronal differentiation of BMSCs in vitro while reducing astrocyte differentiation. Additionally, high-throughput RNA sequencing revealed a correlation between Wnt5a and phosphoinositide 3-kinase (PI3K)/protein kinase B(AKT) signaling, which was confirmed by the use of the PI3K inhibitor LY294002 to reverse the effects of Wnt5a on BMSC neuronal differentiation. Furthermore, transplantation of Wnt5a-modified BMSCs into SCI rats effectively improved the histomorphology (Hematoxylin and eosin [H&E], Nissl and Luxol Fast Blue [LFB] staining), motor function scores (Footprint test and Basso-Beattie-Bresnahan [BBB]scores)and promoted neuron production, axonal formation, and remodeling of myelin sheaths (microtubule associated protein-2 [MAP-2], growth-associated protein 43 [GAP43], myelin basic protein [MBP]), while reducing astrocyte production (glial fibrillary acidic protein [GFAP]). Therefore, targeting the Wnt5a/PI3K/AKT pathway could enhance BMSC transplantation for SCI treatment.

Defect structure, phase separation, and electrical properties of nonstoichiometric tetragonal tungsten bronze Ba(0.5-x)TaO(3-x).

New insight into the defect chemistry of the tetragonal tungsten bronze (TTB) Ba(0.5-x)TaO(3-x) is established here, which is shown to adapt to a continuous and extensive range of both cationic and anionic defect stoichiometries. The highly nonstoichiometric TTB Ba(0.5-x)TaO(3-x) (x = 0.25-0.325) compositions are stabilized via the interpolation of Ba(2+) cations and (TaO)(3+) groups into pentagonal tunnels, forming distinct Ba chains and alternate Ta-O rows in the pentagonal tunnels along the c axis. The slightly nonstoichiometric Ba(0.5-x)TaO(3-x) (x = 0-0.1) compositions incorporate framework oxygen and tunnel cation deficiencies in the TTB structure. These two mechanisms result in phase separation within the 0.1< x < 0.25 nonstoichiometric range, resulting in two closely related (TaO)(3+)-containing and (TaO)(3+)-free TTB phases. The highly nonstoichiometric (TaO)(3+)-containing phase exhibits Ba(2+) cationic migration. The incorporation of (TaO)(3+) units into the pentagonal tunnel and the local relaxation of the octahedral framework around the (TaO)(3+) units are revealed by diffraction data analysis and are shown to affect the transport and polarization properties of these compositions.

Comparative investigation of the performances of hematite nanoplates and nanograins in lithium-ion batteries.

In this work, we selectively prepared two samples with quite different nanocrystal shapes, i.e. nanoplates and nanograins but with almost identical surface areas to make a clear comparison of nanocrystal shapes on electrochemical performance. The electrochemical results indicate that the thinner hexagonal α-Fe2O3 nanoplates considerably enclosed by two larger (0001) basal surfaces exhibit higher capacity and stability than thicker α-Fe2O3 nanograins enclosed by a variety of crystal facets. During the conversion reaction, an orientated growth of porous nanostructure with orientated nanowalls as a stable framework is observed for the nanoplate, readily supplying a pathway for long and easy lithiation-delithiation cycling. The improved electrochemical performance of α-Fe2O3 nanoplates is surely related to the nanostructure with significantly stacked (0001) lattice planes along [0001] direction for orientated growth of γ-Fe2O3 nanodomains along one [111] direction.

Stabilized TiN nanowire arrays for high-performance and flexible supercapacitors.

Metal nitrides have received increasing attention as electrode materials for high-performance supercapacitors (SCs). However, most of them are suffered from poor cycling stability. Here we use TiN as an example to elucidate the mechanism causing the capacitance loss. X-ray photoelectron spectroscopy analyses revealed that the instability is due to the irreversible electrochemical oxidation of TiN during the charging/discharging process. Significantly, we demonstrate for the first time that TiN can be stabilized without sacrificing its electrochemical performance by using poly(vinyl alcohol) (PVA)/KOH gel as the electrolyte. The polymer electrolyte suppresses the oxidation reaction on electrode surface. Electrochemical studies showed that the TiN solid-state SCs exhibit extraordinary stability up to 15,000 cycles and achieved a high volumetric energy density of 0.05 mWh/cm(3). The capability of effectively stabilizing nitride materials could open up new opportunities in developing high-performance and flexible SCs.

Dual-mobility cup total hip arthroplasty improves the quality of life compared to internal fixation in femoral neck fractures patients with severe neuromuscular disease in the lower extremity after stroke: a retrospective study.

Background: This study aimed to demonstrate that dual-mobility cup total hip arthroplasty (DMC-THA) can significantly improve the quality of life (QOL) of elderly femoral neck fracture patients with severe neuromuscular disease in unilateral lower extremities due to stroke hemiplegia compared to internal fixation (IF). Methods: Fifty-eight cases of severe neuromuscular disease in the unilateral lower extremities with muscle strength < grade 3/5 due to stroke were retrospectively examined From January 2015 to December 2020. Then, patients were divided into DMC and IF groups. The QOL was examined using the EQ-5D and SF-36 outcome measures. The physical and mental statuses were assessed using the Barthel Index (BI) and e Fall Efficacy Scale-International (FES-I), respectively. Results: Patients in the DMC group had higher BI scores than those in the IF group at different time point. Regarding mental status, the FES-I mean score was 42.1 ± 5.3 in the DMC group and 47.3 ± 5.6 in the IF group (p = 0.002). For the QOL, the mean SF-36 score was 46.1 ± 18.3 for the health component and 59.5 ± 15.0 for the mental component in the DMC group compared to 35.3 ± 16.2 (p = 0.035), and 46.6 ± 17.4 (p = 0.006) compared to the IF group. The mean EQ-5D-5L values were 0.733 ± 0.190 and 0.303 ± 0.227 in the DMC and IF groups (p = 0.035), respectively. Conclusion: DMC-THA significantly improved postoperative QOL compared to IF in elderly patients with femoral neck fractures and severe neuromuscular dysfunction in the lower extremity after stroke. The improved outcomes were related to the enhanced early, rudimentary motor function of patients.

Porous Pr(OH)3 nanostructures as high-efficiency adsorbents for dye removal.

Herein we report the electrochemical synthesis of porous Pr(OH)(3) nanobelt arrays (NBAs), nanowire arrays (NWAs), nanowire bundles (NWBs), and nanowires (NWs) and their applications as dye absorbents in water treatment. These Pr(OH)(3) nanostructures exhibit high efficient and selective adsorption of the dyes with amine (-NH(2)) functional groups such as Congo red, reactive yellow, and reactive blue. The high efficiency and selectivity is attributed to the large effective surface area of the porous structure, plentiful hydroxyl groups, and basic sites on the Pr(OH)(3) surface. Furthermore, the toxicity studies of these porous Pr(OH)(3) nanostructure show a negligible effect on seed germination, indicating that they hold great potential as environmentally friendly absorbents in water treatment.

Formation mechanism of CaTiO3 hollow crystals with different microstructures.

The crystal growth of CaTiO(3) hollow crystals with different microstructures has been investigated. In a water-free poly(ethylene glycol) 200 (PEG-200) solution, CaTiO(3) nanocubes formed first. The nanocubes underwent an oriented self-assembly into spherical particles, enhanced by the surface-adsorbed polymer molecules. Since the growth of nanocubes and their aggregation took place simultaneously, the nanocubes in the outer shells were larger than those in the cores. Disappearance of the small nanocubes in the cores of the spheres during an Ostwald ripening process led to spherical hollow crystals. Addition of a small amount of water (1.25 vol %) in the polymer solution enhanced surface recrystallization of the aggregated spheres, forming a cubic morphology. The orthorhombic distortion of the perovskite CaTiO(3) structure did not have a significant effect on the nanocube aggregation, resulting in a domain structure in the shells. Single-crystalline hollow cubes were produced with a slightly higher water content, e.g., 5 vol %. This process of (1) aggregation of nanocubes and (2) surface crystallization followed by (3) surface-to-core extension of recrystallization gives a good example of the reversed crystal growth route in ceramic materials. The proposed formation mechanism of the hollow CaTiO(3) crystals would enable us to control the microstructures of these materials and to explain the formation of many other hollow crystals.

Facile electrochemical synthesis of single crystalline CeO2 octahedrons and their optical properties.

We developed a simple electrochemical process for the large-scale fabrication of single crystalline CeO(2) octahedrons and nanospheres from DMSO aqueous solution. The octahedrons with some structural defects have a size ranging from 200 to 300 nm. Moreover, highly crystalline CeO(2) nanospheres were also obtained via this electrochemical process based on the oriented attachment mechanism. The absorption edge of octahedrons and spheres shows a red-shift, and that of the octahedrons was near the visible region.

Continuous shape- and spectroscopy-tuning of hematite nanocrystals.

Uniform hexagonal hematite (α-Fe(2)O(3)) nanoplates have been synthesized by a facile alcohol-thermal reaction, and a new nanostructure of α-Fe(2)O(3) has been proposed. Each nanoplate is enclosed by (0001) basal planes and {1012} side surfaces. The phase, size, shape, and growth orientation of these nanocrystals were characterized by powder X-ray diffraction and electron microscopy. The thickness and diameter of these nanocrystals could be finely tuned by the selective use of alcohol solvent with increasing carbon atom number in the linear alkyl chain. A variety of nanocrystals with systemically changeable shapes from nanoplates to nanograins have been obtained. Specific adsorption of alcohol molecules on polar (0001) facets is proposed to be the main issue to modify the growth behavior of hematite nanocrystals. The presence of distilled water and the addition of sodium acetate have also been investigated. Either of them has a great influence on the growth of hematite nanocrystals, and shape-controlled growth can be rationally achieved. In addition, the post-aging of as-grown hematite nanocrystals in alcohol and distilled water has also been described. Both vibration spectroscopy (i.e., FTIR and Raman) and electronic spectra (diffused reflectance spectra) of these nanocrystals with a continuing shape change show a highly shape-dependent nature.

Facile fabrication of hierarchical SnO(2) microspheres film on transparent FTO glass.

Hierarchical SnO(2) microspheres consisting of nanosheets on the fluorine-doped tin oxide (FTO) glass substrates are successfully prepared via a facile hydrothermal synthesis process. The as-prepared novel microsphere films were characterized in detail by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy. Moreover, SnO(2) nanoparticles with 30-80 nm in size covered on the surface of nanosheets/microspheres were also obtained by optimizing the hydrothermal reaction temperature, time, or volume ratio of acetylacetone/H(2)O. The detailed investigations disclose the experimental parameters, such as acetylacetone, NH(4)F, and seed layer play important roles in the morphology of hierarchical SnO(2) microspheres on the FTO glass. The formation process of SnO(2) microspheres is also proposed based on the observations of time dependent samples.

Interlayer gap widened α-phase molybdenum trioxide as high-rate anodes for dual-ion-intercalation energy storage devices.

Employing high-rate ion-intercalation electrodes represents a feasible way to mitigate the inherent trade-off between energy density and power density for electrochemical energy storage devices, but efficient approaches to boost the charge-storage kinetics of electrodes are still needed. Here, we demonstrate a water-incorporation strategy to expand the interlayer gap of α-MoO3, in which water molecules take the place of lattice oxygen of α-MoO3. Accordingly, the modified α-MoO3 electrode exhibits theoretical-value-close specific capacity (963 C g-1 at 0.1 mV s-1), greatly improved rate capability (from 4.4% to 40.2% at 100 mV s-1) and boosted cycling stability (from 21 to 71% over 600 cycles). A fast-kinetics dual-ion-intercalation energy storage device is further assembled by combining the modified α-MoO3 anode with an anion-intercalation graphite cathode, operating well over a wide discharge rate range. Our study sheds light on a promising design strategy of layered materials for high-kinetics charge storage.

Hollow single-crystal spinel nanocubes: the case of zinc cobalt oxide grown by a unique Kirkendall effect.

Small hollow nanocubes of the ternary spinel Zn x Co 1- x Co 2O 4 of ca. 18 nm dimension were prepared via a facile hydrothermal route. A growth mechanism is suggested in which solid single-crystal Co 3O 4 nanocubes are gradually converted to hollow single-crystal Zn x Co 1- x Co 2O 4 nanocubes with preservation of the spinel framework through differential diffusion of Zn (2+) and Co (2+) ions. With the cation exchange, the chemical composition and thus physical properties can be tailored.