Highly efficient PdCu<Subscript>3</Subscript> nanocatalysts for Suzuki–Miyaura reaction

Suzuki–Miyaura reactions, involving the activation of carbon–halogen bonds, especially C–Cl bonds, have drawn widespread attention because of their huge industrial potential. However, these reactions are dependent on the development of highly active and stable catalysts. Herein, we developed a convenient one-pot wet route to synthesize Pd _x Cu _y bimetallic nanocrystals for the Suzuki–Miyaura reaction. By introducing Cu, an earth-abundant element, the catalytic activity was greatly enhanced while the amount of Pd required was reduced. Pd _x Cu _y nanocrystals of different compositions, including Pd₃Cu, Pd₂Cu, PdCu, PdCu₂, and PdCu₃, were successfully synthesized by tuning the Pd:Cu ratio. Their catalytic performance in Suzuki–Miyaura reactions between phenylboronic acid and halobenzenes (iodo-, bromo-, or chlorobenzene) showed that PdCu₃ nanocatalyst demonstrated the best efficacy.

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Synthesis of supported SnO<Subscript>2</Subscript>–CeO<Subscript>2</Subscript> catalysts for the deep oxidation of methane

A new method has been proposed for the synthesis of catalytically active 80 wt % SnO₂ + 20 wt % CeO₂ materials supported on glass fiber, which involves the use of an ethanolic film-forming solution based on cerium(III) nitrate and salicylic acid, with the addition of tin(IV) chloride. We have studied the morphology of the materials thus prepared and assessed their catalytic activity for the deep oxidation of methane. The results indicate that the appreciable catalytic activity of the materials is ensured by their uniform distribution over the support surface and the small oxide aggregate size ( 10 μm), which is due to the use of the filmforming solution of the proposed composition.     

Activity of carbon-fiber-supported Fe–Co catalysts in the CO<Subscript>2</Subscript> methanation reaction

The catalytic activity of Fe–Co catalysts applied on carbon fibers of various morphologies was studied in the CO₂ methanation reaction The catalysts produced by applying the active mass on the cleaned oxygenated or cleaned reduced carbon fibers exhibited a lower activity. It was demonstrated by the SEM method that an increase of the amount of oxygen-containing functional groups on the carrier surface has a negative influence on the catalytic activity of the samples in the methanation reaction and hinders the processes of metal nitrates adjoining the carrier surface and the reduction of the active mass during the synthesis of catalysts. The sample Fe: Co = 86: 14 applied on the non-modified cleaned carbon fibers (T ₆₅ = 390°C, with \({S_{C{H_4}}}\)) showed the greatest activity in the CO₂ methanation reaction.     

Vertical α-FeOOH nanowires grown on the carbon fiber paper as a free-standing electrode for sensitive H<Subscript>2</Subscript>O<Subscript>2</Subscript> detection

Highly sensitive,selective,and stable hydrogen peroxide (H2O2) detection using nanozyme-based catalysts are desirable for practical applications.Herein,vertical α-FeOOH nanowires were successfully grown on the surface of carbon fiber paper (CFP) via a low-temperature hydrothermal procedure.The formation of vertical α-FeOOH nanowires is ascribed to the structure-directing role of sodium dodecyl sulfate.The resulting free-standing electrode with one-dimensional (1D)nanowires offers oriented channels for fast charge transfer,excellent electrical contact between the electrocatalyst and the current collector,and good mechanical stability and reproducibility.Thus,it can serve as an efficient electrocatalyst for the reduction and sensitive detection of H2O2.The relation of the oxidation current of H2O2 with the concentration is linear from 0.05 to 0.5 mM with a sensitivity of-0.194 mA/(mM.cm2) and a low detection limit of 18 μM.Furthermore,the portability in the geometric tailor and easy device fabrication allow extending the general applicability of this free-standing electrode to chemical and biological sensors.     

MoS<Subscript>2</Subscript> yolk–shell microspheres with a hierarchical porous structure for efficient hydrogen evolution

Yolk–shell architectures have attracted extensive attention owing to their unique structure and infusive applications. MoS₂ is regarded as one of the most promising catalytic materials for hydrogen evolution by the splitting of water. In this work, a simple self-template solvothermal approach is developed for the synthesis of novel MoS₂ yolk–shell microspheres with a hierarchical porous structure by reacting MoO₂ microspheres with L-cysteine. A dissolutionrecrystallization formation mechanism is proposed for the MoS₂ yolk–shell microspheres. Owing to structural superiority, the new material architecture exhibits improved photoelectrochemical properties, including efficient hydrogen evolution reaction catalytic activities, a high photocurrent density, a small overpotential, and a low charge-transfer resistance.

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Self-healing superhydrophobic polyvinylidene fluoride/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@polypyrrole fiber with core–sheath structures for superior microwave absorption

Self-healing superhydrophobic polyvinylidene fluoride/Fe₃O₄@polypyrrole (F-PVDF/Fe₃O₄@PPy _x ) fibers with core–sheath structure were successfully fabricated by electrospinning of a PVDF/Fe₃O₄ mixture and in situ chemical oxidative polymerization of pyrrole, followed by chemical vapor deposition with fluoroalkyl silane. The F-PVDF/Fe₃O₄@PPy_0.075 fiber film produces a superhydrophobic surface with self-healing behavior, which can repetitively and automatically restore superhydrophobicity when the surface is chemically damaged. Moreover, the maximum reflection loss (R _L) of the F-PVDF/Fe₃O₄@PPy_0.075 fiber film reaches ?21.5 dB at 16.8 GHz and the R _L below ?10 dB is in the frequency range of 10.6–16.5 GHz with a thickness of 2.5 mm. The microwave absorption performance is attributed to the synergetic effect between dielectric loss and magnetic loss originating from PPy, PVDF and Fe₃O₄. As a consequence, preparing such F-PVDF/Fe₃O₄@PPy _x fibers in this manner provides a simple and effective route to develop multi-functional microwave absorbing materials for practical applications.

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Effect of Ca doping on the performance of CeO<Subscript>2</Subscript>–NiO catalysts for CH<Subscript>4</Subscript> catalytic combustion

Methane catalytic combustion was carried out over the Ce_0.9–xNi_0.1Ca_xO_δ (0 < x ≤ 0.3) catalysts prepared by a citric acid complexation–combustion method. When x ≤ 0.1, the presence of Ca can enhance the surface area and reduce the crystalline size, and improve the reduction of the dispersed NiO species in catalyst, resulting in an improvement of the catalytic activity of Ce_0.9–xNi_0.1Ca_xO_δ. The XRD and Raman results show that Ce_0.9–xNi_0.1Ca_xO_δ (x ≤ 0.1) solid solution can form by Ni and Ca incorporation in the CeO₂ lattices. TEM and etching results reveal that part of Ni disperses well on the surface of Ca-doped sample. FT-IR testing shows that with an increase in Ca amount (x > 0.1), more carbonate species (mainly carbonate calcium) can form on the catalyst surface, which would severely debase the catalytic activity of Ce_0.9–xNi_0.1Ca_xO_δ.     

Solid–Liquid Equilibria for the CO<Subscript>2</Subscript> + R23 and N<Subscript>2</Subscript>O + R23 Systems

A recently built experimental setup was employed for the estimation of the solid–liquid equilibria of alternative refrigerant systems. In this paper two binaries, i.e., carbon dioxide + trifluoromethane (CO₂ + R23) and nitrous oxide + trifluoromethane (N₂O + R23), were studied down to temperatures of 117 K. In order to check the reliability of the apparatus, the triple points of the pure fluids contained in the mixture were measured, revealing good consistency with the literature. The results obtained for the mixtures were interpreted by means of the Schröder equation.     

Structure,electrical, and optical properties of ZnO-substituted PbO for the Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript> co-doped Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–GeO<Subscript>2</Subscript>–Na<Subscript>2</Subscript>O glass system

Glasses of the 0.5Er³⁺/2.5Yb³⁺ co-doped (40Bi₂O₃–20GeO₂–(30 − x)PbO–xZnO–10Na₂O system where x = 0.0, 5, 10, 15, 20, 25, and 30 mol%) have been characterized by FT-IR spectroscopy measurements to obtain information about the influence of ZnO-substituted PbO on the local structure of the glass matrix. The density and the molar volume have been determined. The influences of the ZnO-substituted PbO on the structure of glasses have been discussed. The dc conductivity measured in the temperature range 475–700 K obeys Arrhenius law. The conductivity decreases while the activation energy for conduction increases with increase ZnO content. The optical transmittance and reflectance spectrum of the glasses have been recorded in the wavelength range 400–1100 nm. The values of the optical band gap E _opt for all types of electronic transitions and refractive index have been determined and discussed. The real and imaginary parts ε₁ and ε₂ of dielectric constant have been determined.     

Microstructure dependence of the magnetic properties of sintered Ni–Zn ferrites by solid-state reaction doped with V<Subscript>2</Subscript>O<Subscript>3</Subscript>

In order to improve the frequency range operation of Ni–Zn ferrites with the Ni_0.7Zn_0.3Fe₂O₄ stoichiometry in this study, they were doped with V₂O₃ at different concentrations (0, 0.25, 0.50, and 0.75 wt%). The samples were prepared by the solid-state reaction at 1250 °C for 24 h. The content and location of Vanadium in these ferrites allow us to determine its influence on their microstructure and magnetic properties. A single cubic spinel phase with lattice parameter variation was determined by the refinement of X-ray diffraction patterns. This refinement was achieved using the Rietveld method. The lattice parameter presents a slight enhancement with increasing Vanadium content up to 0.50 wt% of V₂O₃. The increase of intragrain porosity and the segregation of Vanadium at the grain boundary in samples with higher concentration of Vanadium show a narrow grain-size distribution that leads to a resonant character of the magnetic domain wall. A wide grain-size distribution determined in lower concentration of Vanadium results in a mixed resonant-relaxation dispersion. The use of V₂O₃ as a dopant in Ni–Zn ferrites increases the frequency operation and coercivity, H _c, without abruptly degrading the saturation magnetization, M _s. We, therefore conclude, that Vanadium may be used as a strong dopant for the preparation of ferrites for any particular high-frequency application.     

The effect of preparation method on the activities of Pd–Fe–O<Emphasis Type="Italic">x</Emphasis>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for CO oxidation

The Pd–Fe–Ox/Al₂O₃ catalysts were prepared by co-impregnation (co-Pd–Fe–Ox/Al₂O₃) and sol–gel method (sol–gel–Pd–Fe–Ox/Al₂O₃) and characterized by N₂ adsorption–desorption, X-ray diffraction (XRD), H₂-temperature programmed reduction (H₂-TPR), and X-ray photoelectron spectroscopy (XPS). The CO catalytic oxidation was investigated over Pd–Fe–Ox/Al₂O₃ catalysts prepared by different methods. The 100% conversion temperature (T ₁₀₀) over pre-reduced co-Pd–Fe–Ox/Al₂O₃ (co-Pd–Fe–Ox/Al₂O₃–R) and pre-reduced sol–gel–Pd–Fe–Ox/Al₂O₃ (sol–gel–Pd–Fe–Ox/Al₂O₃–R) is 90 and 25 °C when fed with the reaction mixture containing 1 vol.% CO and a balance of air, respectively. XRD results indicate that the sol–gel method is favorable for the high dispersion of PdO particles compared with co-impregnation method. H₂-TPR results suggest that the interaction between Pd and Fe is existent over both sol–gel–Pd–Fe–Ox/Al₂O₃ and co-Pd–Fe–Ox/Al₂O₃ catalysts, while the interaction in former catalyst is stronger than that in the latter. The XPS results show that the Pd species on the surface of both sol–gel–Pd–Fe–Ox/Al₂O₃–R and co-Pd–Fe–Ox/Al₂O₃–R catalysts are the mixture of oxide and metal state, leading to the high activity for CO oxidation. Furthermore, the different Pd²⁺/Pd⁰ ratio may be the reason for the different activity between sol–gel–Pd–Fe–Ox/Al₂O₃–R and reduced co-Pd–Fe–Ox/Al₂O₃–R catalysts.     

Novel SiQDs–MoS<Subscript>2</Subscript> heterostructures with increasing solar absorption for the photocatalytic degradation of malachite green

Novel heterostructures based on silicon quantum dots and molybdenum disulfide nanosheets (SiQDs–MoS₂) were synthesized by a hydrothermal method, in which the introduced SiQDs play a determining role in manipulating the morphology, phase and band structure of MoS₂. The resultant SiQDs–MoS₂ is uniform flowerlike 3D microspheres assembled from petallike 2D MoS₂ nanosheets anchored with 0D SiQDs, possessing abundant active sites. Besides, the primary MoS₂ nanosheets consist of both semiconductive 2H and metallic 1T phases accompanied with intralayer mesopores and expanded interlayer spacing, endowing the resulting architectures with effective electron transfer. Significantly, the as-synthesized SiQDs–MoS₂ exhibits intense full solar-spectrum absorption, indicating efficient solar energy harvesting. First-principles calculations simulate similar increased spectral absorption of monolayer MoS₂ adhered with a Si cluster, suggesting the existence of new energy states associated with the integration of SiQDs and MoS₂ nanosheets as evidenced by photoluminescence (PL) spectral analysis. As expected, the current SiQDs–MoS₂ heterostructures demonstrate substantial photocatalytic activity even under visible and near-infrared (NIR) light on degradation of malachite green (MG). The type II electronic structure of SiQDs–MoS₂ was proposed, enabling sufficient photogenerated electrons and holes for the photocatalytic reactions. This study may establish a new frontier on the rational design and feasible development of the hybrid structures with the desirable morphologies, phase compositions and band structures for the catalysis and beyond.     

Refinement of primary Si and modification of eutectic Si for enhanced ductility of hypereutectic Al–20Si–4.5Cu alloy with addition of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles

It is very difficult to simultaneously refine and modify Si particles in hypereutectic Al–Si–Cu alloys to enhance their ductility. This study investigates how nanoparticles affect Si particles during solidification in hypereutectic Al–Si–Cu alloys. 0.5 wt% γ-Al₂O₃ nanoparticles were added in hypereutectic Al–20Si–4.5Cu alloy melt and further dispersed through an ultrasonic-cavitation-based technique. The as-cast Al–20Si–4.5Cu–Al₂O₃ nanocomposites showed marked enhancements in both ductility and strength. The ductility of Al₂O₃ nanocomposite was more than two times higher than that of the monolithic alloy without the nanoparticles. Microstructural analysis with optical and scanning electron microscopy revealed that both the primary and eutectic Si particles were significantly refined. The primary Si particles were refined from star shapes to polygon or blocky shapes, and their edges and corners were much smoother. The large plate eutectic Si particles were also modified into the fine coralline-like ones. The porosity of alloy was also reduced with the addition of γ-Al₂O₃ nanoparticles. Study suggests that γ-Al₂O₃ nanoparticles simultaneously refine and modify Si particles as well as reduce porosity in cast Al–20Si–4.5Cu, resulting in unusual ductility enhancement that could have great potential for numerous applications.     

Uniformly dispersed FeO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> atomic clusters by pulsed arc plasma deposition: An efficient electrocatalyst for improving the performance of Li–O<Subscript>2</Subscript> battery

The present study explored a new method to improve the catalytic activity of non-precious metals, especially in electrochemical reactions. Highly ionized Fe plasma produced by arc discharge was uniformly deposited on a porous carbon substrate and formed atomic clusters on the carbon surface. The as-prepared FeO _x /C material was tested as a cathode material in a rechargeable Li–O₂ battery under different current rates. The results showed significant improvement in battery performance in terms of both cycle life and reaction rate. Furthermore, X-ray diffraction (XRD) and scanning electron microscopy (SEM) results showed that the as-prepared cathode material stabilized the cathode and reduced side reactions and that the current rate was a critical factor in the nucleation of the discharge products.

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Composite materials of diamond–(Co–Cu–Sn) system with improved mechanical characteristics. Part 2. The influence of CrB<Subscript>2</Subscript> additive on the structure and properties of diamond–(Co–Cu–Sn) composite

The structural alterations in the diamond–metallic binder transition zone in the diamond(78.4Co–11.76Cu–7.84Sn–2CrB₂) composite upon its sintering in a mold in hydrogen atmosphere at 800°C for 1 h have studied versus the hot re-pressing parameters, and the influence of such alterations on physical-mechanical and tribological properties of the composites has been clarified. Adding 2 wt % CrB₂ to the starting diamond?(80Co–12Cu–8Sn) composite is shown to raise the ultimate compression strength from 816 to 1720 MPa, bending strength from 790 to 1250 MPa, and wear resistance by a factor of 2.4. The improvement of properties of the composite and the increase of its wear resistance are provided due to the formation of Cr₃C₂ nanocarbide in the transition zone and the uniform distribution of Co, CrB₂ phases and CoSn inclusions in the volume of the metallic binder.