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This article deals with the Raman spectroscopic research of aluminum–graphene (Al–Gr) composites obtained by aqueous suspension-based mixing to improve dispersion of graphene sheets in composite powders. Raman spectra of composite powders reflect encapsulated nanostructure of Al–Gr composite powders and chemical interaction of oxygen groups on graphene oxide (GO) with magnesium ions (Mg2+), depending on the added Mg2+ content. First, the enhanced Raman signal for our composite powders is an apparent evidence of that graphene sheets with uniform dispersion on Al matrix are in close contact with the spherical surface of Al powders. The polarization dependence of the Raman spectra, which are dependent on the incident laser spot, also confirms that the graphene sheets surrounded the spherical powder. SEM image, XPS and FT-IR spectra for the composite powders provide additional data to decipher the Raman analysis results. [ABSTRACT FROM AUTHOR]

In this work, a new route for preparation of graphene reinforced aluminum (Al) matrix composites with enhanced dispersion and strength has been discussed based on aqueous suspension mixing procedure. Mg 2+ ions added into mixture were used as binding bridge that anchored graphene sheets to the surface of Al powder, improving affinity and binding capacity of graphene sheets with Al matrix. Graphene nanosheets have double dispersion behaviors on Al matrix with increasing of Mg 2+ concentration following colloidal theory (DLVO theory and Schulze-Hardy rule). Although composite billet consolidated through spark plasma sintering (SPS) has only 3 wt% content of graphene, but it was significantly reinforced in strength affected by the dispersion degree of graphene on composite matrix. [ABSTRACT FROM AUTHOR]

Fine control over the physicochemical structures of carbon electrocatalysts is important for improving the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in rechargeable Zn–air batteries. Covalent organic frameworks (COFs) are considered good candidate carbon materials because their structures can be precisely controlled. However, it remains a challenge to impart bifunctional electrocatalytic activities for both the ORR and OER to COFs. Herein, a pyridine‐linked triazine covalent organic framework (PTCOF) with well‐defined active sites and pores is readily prepared under mild conditions, and its electronic structure is modulated by incorporating Co nanoparticles (CoNP‐PTCOF) to induce bifunctional electrocatalytic activities for the ORR and OER. The CoNP‐PTCOF exhibits lower overpotentials for both ORR and OER with outstanding stability. Computational simulations find that the p‐band center of CoNP‐PTCOF down‐shifted by charge transfer, compared to pristine PTCOF, facilitate the adsorption and desorption of oxygen intermediates on the pyridinic carbon active sites during the reactions. The Zn–air battery assembled with bifunctional CoNP‐PTCOF exhibits a small voltage gap of 0.83 V and superior durability for 720 cycles as compared with a battery containing commercial Pt/C and RuO2. This strategy for modulating COF electrocatalytic activities can be extended for designing diverse carbon electrocatalysts. [ABSTRACT FROM AUTHOR]

This study deals with the fabrication of a fine-grained Ti−22Al−25Nb alloy from elemental powders by mechanical alloying (MA) and subsequent spark plasma sintering (SPS). The effect of SPS parameters on the microstructure and mechanical properties of sintered compacts was investigated and discussed. The (Ti, Al, Nb) bcc solid solution with a chemical composition of Ti−22Al−25Nb was produced by MA for 40 h with a rotation speed of 400 rpm, and subsequently consolidated by SPS at a temperature range of 950–1300 °C for 5, 7 and 10 min, respectively, followed by furnace cooling. The sintered compact showed the microstructure consisting of fine equiaxed B2 grains, fine O-phases with a lath shape or an equiaxed shape, ultrafine acicular O-phases inside the B2 grains, and ultrafine equiaxed α 2 -phases along the rim of B2 grains. The best combination of mechanical properties was exhibited in the Ti−22Al−25Nb alloy sintered at 1200 °C/10 min/35 MPa; the yield strength and the fracture strain were 1652 MPa and 32.2% at room temperature, and 1163 MPa and 56.7% at 650 °C, respectively. [ABSTRACT FROM AUTHOR]

Precise control over doping of photocatalysts is required to modulate their photocatalytic activity in visible light-driven reactions. Here, a single precursor-employing bottom-up approach is developed to produce different heteroatom-doped graphene quantum dots (GQDs) with unique photocatalytic activities. The solvothermal reaction of a norepinephrine precursor with redox active and condensable moieties effectively produces both nitrogen/sulfur codoped GQDs (NS-GQDs) and nitrogen-doped GQDs (N-GQDs) by simply varying solvents (from dimethyl sulfoxide to water) under microwave irradiation. As-prepared NS-GQDs and N-GQDs show similar lateral sizes (3-4 nm) and heights (1-2 nm), but they include different dopant types and doping constitution and content, which lead to changes in photocatalytic activity in aerobic oxidative coupling reactions of various amines. NS-GQDs exhibit much higher photocatalytic activity in reactions under visible light than N-GQDs and oxygen-doped GQDs (O-GQDs). The mechanism responsible for the outstanding photocatalytic activity of NS-GQDs in visible light-driven oxidative coupling reactions of amines is also fully investigated. [ABSTRACT FROM AUTHOR]

• Novel O 2 -mediated solvothermal radical reaction (OSRR) was developed. • Co/N-doped carbon nanohybrid electrocatalysts (CoCNs) were designed by OSRR. • The physical/chemical structures of CoCNs were modulated by molecular engineering. • The catalytic activities of CoCNs for ORR & OER depended strongly on the structures. • The Zn-air battery assembled with CoCNs showed superior performance and durability. Modulating the physicochemical structures of carbon-based electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in Zinc-air batteries is extremely important. However, it still remains a challenge to control these geometric and chemical nanostructures in a single reaction process under the same conditions. Herein, an approach based on an O 2 -mediated solvothermal radical reaction (OSRR) to control the physicochemical conformations of Co/N-doped carbon electrocatalysts in a single reaction is reported. Atomic Co/N-doped carbon (CoCN), nanoparticulate Co/N-doped carbon (AP-CoCN), atomic Co/N-doped hollow carbon (PCA-CoCN-1), and nanoparticulate Co/N-doped porous carbon (PCA-CoCN-2) nanostructures are effectively designed by adjusting the molecular interactions between the organic precursors and metal ions in the OSRR. The activities of the electrocatalysts depend strongly on their structures where PCA-CoCNs exhibit the most outstanding activity and stability for ORR while AP-CoCN displays the most excellent activity and stability for OER. The simulations suggest that the back side carbon of Co-pyridinic N doped nanostructures is an active site for ORR and OER. The Zn-air battery employing PCA-CoCN-1 and AP-CoCN exhibits a lower charge-discharge overpotential and greater durability than the Pt/C and RuO 2 assembly. The OSRR can provide a new avenue for designing diverse carbon-based catalysts with desired structures and activities. [ABSTRACT FROM AUTHOR]

In order to improve the corrosion resistance of magnesium alloys, environmentally friendly anti-corrosive composite coatings were fabricated on AZ31B Mg alloy. Mg alloys were first treated by plasma electrolytic oxidation (PEO) technique and then modified by phytic acid/3-aminopropyltrimethoxysilane (PA/APTMS) hybrid. Besides, the technique parameters were optimized. The composition and structure of the composite coatings were characterized by SEM, EDS, IR and XPS, the corrosion resistance was evaluated by electrochemical tests in 3.5% NaCl solution and the possible corrosion resistance mechanism was proposed as well. The results showed that the composite coating's corrosion resistance was remarkably improved by two or three orders of magnitude, compared with Mg alloy substrate and the single PEO coating. The PA/APTMS hybrid in network structure and the stable covalent bonds within the composite coatings effectively restricted the penetration of a corrosive medium into the Mg alloy surface, representing an excellent corrosion barrier effect. [ABSTRACT FROM AUTHOR]

Non-covalent adsorption and desorption of oligonucleotides on two-dimensional nanosheets are widely employed to design nanobiosensors for the rapid optical detection of targets. A precise control over the weak interactions between nanosheet interfaces and oligonucleotides is crucial for a high-sensing performance. Herein, the interface of ultrathin WS 2 nanosheets used as a fluorescence quencher was engineered by four different dextran polymers in an aqueous solution to control the adsorption kinetics and thermodynamics of the DNA probe. The WS 2 nanosheets, functionalized by the carboxyl group-bearing dextran (CM-dex-WS 2) or the trimethylammonium-modified dextran (TMA-dex-WS 2), exhibited 3.6-fold faster adsorption rates of the fluorescein-labeled DNA probe (FAM-DNA), which led to the effective fluorescence quenching of FAM, compared to the nanosheets functionalized with pristine dextran (dex-WS 2) or the hydrophobic phenoxy groups-bearing dextran (PhO-dex-WS 2). Isothermal titration calorimetry measurements showed that the adsorption strength of FAM-DNA for CM-dex-WS 2 was one order of magnitude greater than its hybridization energy for a target microRNA (miR-29a) that is well-known as an Alzheimer's disease (AD) biomarker, leading to the unfavorable desorption of the DNA probe from the surface. In contrast, TMA-dex-WS 2 exhibited the proper adsorption strength of FAM-DNA, which was lower than its hybridization energy for miR-29a, leading to its favorable desorption from the nanosheet surface along with the noticeable restoration of the quenched fluorescence after its hybridization with miR-29a. Finally, the interface modulation of WS 2 nanosheets allowed the selective and sensitive recognition of miR-29a against non-complementary RNA and single base-mismatched RNA in human serum via increases in target-specific fluorescence. Image 1 • The interface of WS 2 nanosheets was modulated by polymeric phases to design FRET-based biosensors. • DNA adsorption kinetics and thermodynamics were controlled by different polymeric phases on WS 2. • TMA-dex-WS 2 exhibited suitable adsorption and desorption properties for a probe DNA and miRNA. • A WS 2 nanosheet FRET sensor selectively detected miRNA specific for Alzheimer's disease in serum. [ABSTRACT FROM AUTHOR]