Precise Modulation of Carbon Activity Sites in Metal-Free Covalent Organic Frameworks for Enhanced Oxygen Reduction Electrocatalysis.

Metal-free carbon-based materials have gained recognition as potential electrocatalysts for the oxygen reduction reaction (ORR) in new environmentally-friendly electrochemical energy conversion technologies. The presence of effective active centers is crucial for achieving productive ORR. In this study, we present the synthesis of two metal-free dibenzo[a,c]phenazine-based covalent organic frameworks (DBP-COFs), specifically JUC-650 and JUC-651, which serve as ORR electrocatalysts. Among them, JUC-650 demonstrates exceptional catalytic performance for ORR in alkaline electrolytes, exhibiting an onset potential of 0.90 V versus RHE and a half-wave potential of 0.72 V versus RHE. Consequently, JUC-650 stands out as one of the most outstanding metal-free COF-based ORR electrocatalysts report to date. Experimental investigations and density functional theory calculations confirm that modulation of the frameworks' electronic configuration allows for the reduction of adsorption energy at the Schiff-base carbon active sites, leading to more efficient ORR processes. Moreover, the DBP-COFs can be assembled as excellent air cathode catalysts for zinc-air batteries (ZAB), rivaling the performance of commercial Pt/C. This study provides valuable insights for the development of efficient metal-free organoelectrocatalysts through precise regulation of active site strategies.

Quasi-Three-Dimensional Cyclotriphosphazene-Based Covalent Organic Framework Nanosheet for Efficient Oxygen Reduction.

Metal-free carbon-based materials are considered as promising oxygen reduction reaction (ORR) electrocatalysts for clean energy conversion, and their highly dense and exposed carbon active sites are crucial for efficient ORR. In this work, two unique quasi-three-dimensional cyclotriphosphazene-based covalent organic frameworks (Q3CTP-COFs) and their nanosheets were successfully synthesized and applied as ORR electrocatalysts. The abundant electrophilic structure in Q3CTP-COFs induces a high density of carbon active sites, and the unique bilayer stacking of [6 + 3] imine-linked backbone facilitates the exposure of active carbon sites and accelerates mass diffusion during ORR. In particular, bulk Q3CTP-COFs can be easily exfoliated into thin COF nanosheets (NSs) due to the weak interlayer π-π interactions. Q3CTP-COF NSs exhibit highly efficient ORR catalytic activity (half-wave potential of 0.72 V vs. RHE in alkaline electrolyte), which is one of the best COF-based ORR electrocatalysts reported so far. Furthermore, Q3CTP-COF NSs can serve as a promising cathode for Zn-air batteries (delivered power density of 156 mW cm-2 at 300 mA cm-2). This judicious design and accurate synthesis of such COFs with highly dense and exposed active sites and their nanosheets will promote the development of metal-free carbon-based electrocatalysts.

Dual-Porosity (Ta0.2Nb0.2Ti0.2Zr0.2Hf0.2)C High-Entropy Ceramics with High Compressive Strength and Low Thermal Conductivity Prepared by Pressureless Sintering.

Porous (Ta0.2Nb0.2Ti0.2Zr0.2Hf0.2)C high-entropy ceramics (HEC) with a dual-porosity structure were fabricated by pressureless sintering using a mixture powder of ceramic precursor and SiO2 microspheres. The carbothermal reduction in the ceramic precursor led to the formation of pores with sizes of 0.4-3 µm, while the addition of SiO2 microspheres caused the appearance of pores with sizes of 20-50 µm. The porous HECs exhibit competitive thermal insulation (4.12-1.11 W·m-1 k-1) and extraordinary compressive strength (133.1-41.9 MPa), which can be tailored by the porosity of the ceramics. The excellent properties are ascribed to the high-entropy effects and dual-porosity structures. The severe lattice distortions in the HECs lead to low intrinsic thermal conductivity and high compressive strength. The dual-porosity structure is efficient at phonon scattering and inhabiting crack propagations, which can further improve the thermal insulation and mechanical properties of the porous HECs.

YY1 affects the levels and function of fibulin-5 in ox-LDL-treated vascular smooth muscle cells.

Fibulin-5 is reportedly involved in the pathological process of atherosclerosis (AS) where low expression has been frequently observed in ruptured atherosclerotic plaques. The aim of the present study was to determine the effects of fibulin-5 on the responses of vascular smooth muscle cells (VSMC) to oxidized low-density lipoprotein (ox-LDL). The expression of fibulin-5 was studied in human aortic-VSMCs (HA-VSMCs) treated with ox-LDL. Fibulin-5 was first overexpressed by the transfection of Ov-Fibulin-5 plasmids in HA-VSMCs challenged with ox-LDL to investigate its influence on cell proliferation, migration and invasion using Cell Counting Kit-8, wound healing and Transwell assays. Yin Yang-1 (YY1) was bioinformatically predicted to bind to the promoter sites of fibulin-5, which was subsequently confirmed by dual-luciferase reporter gene assay. Fibulin-5 overexpression was able to suppress cell proliferation, invasion and migration, which was effectively reversed by YY1 silencing by the transfection of siRNA-Fibulin-5 plasmids which could induced fibulin-5 silencing. YY1 binding sites in the promoter region of fibulin-5 were identified and confirmed in vitro by chromatin immunoprecipitation assay and dual-luciferase reporter gene assay. The present results suggested that as a modulator of fibulin-5, YY1 alleviated ox-LDL-induced proliferation, invasion, migration and phenotypic transition from differentiated contractile phenotype to dedifferentiated phenotype in VSMCs. However, the mechanism underlying the YY1-mediated regulation of fibulin-5 expression needs to be confirmed further in vivo. Nevertheless, targeting fibulin-5 and YY1 could be further developed for AS therapy.

Gating Effects for Ion Transport in Three-Dimensional Functionalized Covalent Organic Frameworks.

The development of bioinspired nano/subnano-sized (<2 nm) ion channels is still considered a great challenge due to the difficulty in precisely controlling pore's internal structure and chemistry. Herein, for the first time, we report that three-dimensional functionalized covalent organic frameworks (COFs) can act as an effective nanofluidic platform for intelligent modulation of the ion transport. By strategic attachment of 12-crown-4 groups to the monomers as ion-driver door locks, we demonstrate that gating effects of functionalized COFs can be activated by lithium ions. The obtained materials exhibit an outstanding selective ion transmission performance with a high gating ratio (up to 23.6 for JUC-590), which is among the highest values in metal ion-activated solid-state nanochannels reported so far. Furthermore, JUC-590 offers high tunability, selectivity, and recyclability of ion transport proved by the experimental and simulated studies.

Fabrication of electron-acceptor staggered AB Covalent triazine-based frameworks for enhanced visible-light-driven H2 evolution.

Covalent triazine-based frameworks (CTFs) have been emerged as a promising organic material for photocatalytic water splitting. However, all of the CTFs only are in the form of AA stacking model to participate in water splitting. Herein, two CTF-1 isomers with different stacking models (eclipsed AA, staggered AB) were obtained by modulating the reaction temperature. Interestingly, experimental and theoretical calculations showed that the crystalline AB stacking CTF-1 possessed a much higher activity for photochemical hydrogen evolution (362 µmol g-1 h-1) than AA stacking CTF-1 (70 µmol h-1 g-1) for the first time. The outstanding photochemical performance could be attributed to its distinct structural feature that allows more N atoms with higher electron-withdrawing property to be involved in the water reduction reaction. Notably, as a cathode material for PEC water reduction, AB stacking CTF-1 also demonstrated an excellent saturated photocurrent density up to 77 µA cm-2 at 0 V vs. RHE, which was superior to the AA stacking CTF-1 (47 µA cm-2). Furthermore, the correlation between stacking models and photocatalytic H2 evolution of CTF-1 were investigated. This study thus paves the path for designing optimal photocatalyst and extending the novel applications of CTF-based materials.

Three-Dimensional Triptycene-Based Covalent Organic Frameworks with ceq or acs Topology.

The growth of three-dimensional covalent organic frameworks (3D COFs) with new topologies is still considered as a great challenge due to limited availability of high-connectivity building units. Here we report the design and synthesis of 3D triptycene-based COFs, termed JUC-568 and JUC-569, following the deliberate symmetry-guided design principle. By combining a triangular prism (6-connected) node with a planar triangle (3-connected) or another triangular prism node, the targeted COFs adopt non-interpenetrated ceq or acs topology, respectively. Both materials show permanent porosity and impressive performance in the adsorption of CO2 (∼98 cm3/g at 273 K and 1 bar), CH4 (∼48 cm3/g at 273 K and 1 bar), and especially H2 (up to 274 cm3/g or 2.45 wt % at 77 K and 1 bar), which is highest among porous organic materials reported to date. This research thus provides a promising strategy for diversifying 3D COFs based on complex building blocks and promotes their potential applications in energy storage and environment-related fields.

Three-Dimensional Large-Pore Covalent Organic Framework with stp Topology.

Three-dimensional (3D) covalent organic frameworks (COFs) are excellent crystalline porous polymers for numerous potential applications, but their building units and topological nets have been limited. Herein we report the design and synthesis of the first 3D large-pore COF with the stp topology constructed from a 6-connected triptycene-based monomer. The new COF (termed JUC-564) has a high specific surface area (up to 3300 m2 g-1), the largest pore size among 3D COFs (43 Å), and record-breaking low density among crystalline materials reported to date (0.108 g cm-3). The large pore size of JUC-564 was confirmed by the incorporation of a protein. This study expands the structural varieties of 3D COFs based on the deliberate symmetry-guided design principle as well as their applications for adsorption and separation of large biological molecules.

Metal-Free Thiophene-Sulfur Covalent Organic Frameworks: Precise and Controllable Synthesis of Catalytic Active Sites for Oxygen Reduction.

Defective or heteroatom-doped metal-free carbon materials (MFCMs) have been regarded as efficient oxygen reduction reaction (ORR) catalysts in the past decade. However, the active centers for ORR in MFCMs are hard to confirm precisely and synthesize controllably through common methods such as high-temperature pyrolysis or heteroatom doping. To verify the precise structure acting as the active center for the ORR, we first report two crystalline metal-free thiophene-sulfur covalent organic frameworks (MFTS-COFs) as ORR catalysts. The MFTS-COFs show more positive catalytic capability than the thiophene-free COF, indicating that pentacyclic thiophene-sulfur building blocks act as active centers to induce ORR catalytic activity. MFTS-COFs with higher contents of thiophene-sulfur exhibit better ORR performance. The experimental identification is supported by density functional theory calculations. These results thus demonstrate that rational design and precise synthesis of metal-free crystalline organic materials can promote the development of new ORR catalysts.

Three-Dimensional Tetrathiafulvalene-Based Covalent Organic Frameworks for Tunable Electrical Conductivity.

The functionalization of three-dimensional (3D) covalent organic frameworks (COFs) is essential to broaden their applications. However, the introduction of organic groups with electroactive abilities into 3D COFs is still very limited. Herein we report the first case of 3D tetrathiafulvalene-based COFs (3D-TTF-COFs) with non- or 2-fold interpenetrated pts topology and tunable electrochemical activity. The obtained COFs show high crystallinity, permanent porosity, and large specific surface area (up to 3000 m2/g). Furthermore, these TTF-based COFs are redox active to form organic salts that exhibit tunable electric conductivity (as high as 1.4 × 10-2 S cm-1 at 120 °C) by iodine doping. These results open a way toward designing 3D electroactive COF materials and promote their applications in molecular electronics and energy storage.

Co,N-Codoped porous vanadium nitride nanoplates as superior bifunctional electrocatalysts for hydrogen evolution and oxygen reduction reactions.

Developing efficient and low-cost bifunctional electrocatalysts as candidates for Pt-based materials to satisfy commercial applications in the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) is still very challenging. Herein, we show that Co,N-codoped porous vanadium nitride (VCoN) nanoplates are successfully synthesized via a simple one-step pyrolysis protocol without the use of NH3 gas. We also demonstrate that the crystallization, surface chemical state and porosity of vanadium nitride are well modulated by inventively using Co dopants as structural inducers. The resulting VCoN material exhibits an excellent catalytic activity towards the HER in alkaline media, with an extremely low onset potential of -0.03 V, an overpotential of 179 mV at 10 mA cm-2, and a remarkable durability for over 100 h. Moreover, it shows a superior ORR performance, which compares favorably with commercial 20% Pt/C, exhibiting an onset potential of ∼1.02 V, a half-wave potential of ∼0.91 V and a weak potential shift (-5 mV) after 2000 cycles at 1600 rpm in 0.1 M KOH. Such excellent electrocatalytic performance primarily contributes to the unique structural features of the heteroatom N (pyrrolic and graphitic N) and Co codoping in favor of improving the electrical conductivity and the high porosity contributing to exposing numerous catalytic active sites.

Multifocal and Multicentric Breast Carcinoma: A Significantly More Aggressive Tumor than Unifocal Breast Cancer.

BACKGROUND/AIM: There are still many questions that surround multifocal or multicentric breast carcinoma (MMBC). The aim of this study was to analyze the clinicopathological characteristics of MMBC and provide feasible suggestions for therapy. PATIENTS AND METHODS: A total of 156 cases of MMBC in 3,597 invasive ductal breast carcinomas were collected and reviewed. Some factors related with prognosis such as tumor size, lymph node metastasis and others were assessed in each tumor focus, and mismatches among foci were recorded. RESULTS: The majority of MMBC had aggregate dimensions over 2 cm (85.90%). The rate of axillary lymph node metastasis was 56.41% (88/156) compared to unifocal tumors of 33.01% (1,136/3,441). Most cases had higher Ki-67 proliferative indices (91/156). Mismatches in ER status were present in 6 cases, PR in 4 cases, proliferative index (Ki-67) in 9 cases and HER2-positive status in 2 cases. CONCLUSION: The larger aggregate dimension of tumor, the higher metastatic rate of axillary lymph node and the high Ki-67 proliferative index seen in most cases, suggest that MMBC is biologically more aggressive than unifocal breast cancer. In addition, every focus should be tested owing to the existence of different expressions of immunostaining between foci.

ZnO based heterojunctions and their application in environmental photocatalysis.

As an alternative to TiO2 photocatalysts, ZnO exhibits a large potential for photocatalytic (PC) applications in environmental treatments, such as degradation of wastewater, sterilization of drinking water, and air cleaning. However, the efficiency achieved with ZnO to date is far from that expected for commercialization, due to rapid charge recombination, photo-corrosion as well as poor utilization of solar energy. Fortunately, in recent years, a great number of breakthroughs have been achieved in PC performance (including activity and stability) of micro-/nano- structured ZnO by forming heterojunctions (HJs) with metal nanoparticles (NPs), carbon nanostructures and other semiconductors. In most cases, the improvement of PC performance was ascribed to the better charge separation at the interfaces between ZnO and the other components. Sometimes, the formation of hybrids is also in favor of visible light harvesting. This review summarizes recent advances in the fields of environmental photocatalysis by ZnO based HJs, and especially emphasizes their abilities in degradation of organic pollutants or harmful substances in water. We aim to reveal the mechanism underlying the enhanced PC performance by constructing HJs, and extend the potential of ZnO HJ photocatalysts for future trends, and practical, large-scale applications in environment-related fields.

Ti-O-O coordination bond caused visible light photocatalytic property of layered titanium oxide.

The layered titanium oxide is a useful and unique precursor for the facile and rapid preparation of the peroxide layered titanium oxide H1.07Ti1.73O4·nH2O (HTO) crystal with enhanced visible light photoactivity. The H2O2 molecules as peroxide chemicals rapidly enter into the interlayers of HTO crystal, and coordinate with Ti within TiO6 octahedron to form a mass of Ti-O-O coordination bond in the interlayers. The introduction of these Ti-O-O coordination bonds result in lowering the band gap of HTO, and promoting the separation efficiency of the photo induced electron-hole pairs. Meanwhile, the photocatalytic investigation indicates that such peroxide HTO crystal has the enhanced photocatalytic performance for RhB degradation and water splitting to generate oxygen under visible light irradiating.

Enhanced fluorescence of graphene oxide by well-controlled Au@SiO2 core-shell nanoparticles.

Graphene and graphene derivatives, including graphene oxide (GO) and reduced GO (rGO), have attracted remarkable attention in different fields due to their unique electronic, thermal, and mechanical properties, whereas the fluorescence property is rarely been studied. This paper reports on metal-enhanced fluorescence Au@SiO2 composite nanoparticles adsorbed graphene oxide nanosheets, where the silica-shell is used to control the distance between gold-core and fluorophore GO, and a positively charged polyelectrolyte poly(allylamine hydrochloride) (PAH) is used to adsorb the negatively charged silica-shell and GO by layer-by-layer assembly (LbL) approach. The silica-shell around the 80 nm gold-core can be well-controlled by ending the reaction at different times. Various analytical techniques were applied to characterize the morphology and optical characters of the as-prepared particles. A more than three-fold increase of the fluorescence intensity of GO was obtained.