查看更多>>摘要：? 2022In this work, we present detailed structural, magnetic, dielectric, and transport properties as well as electronic structure studies of a Mn2.4Ni0.6O4 system. The Mn2.4Ni0.6O4 system acquires cubic Fd3?m crystal structure at room temperature and exhibits a ferrimagnetic transition around 108 K. The pristine Mn3O4 acquires a tetragonal I41/amd structure at room temperature and exhibits ferrimagnetic transition and magneto-dielectric coupling at around 43 K. The magneto-dielectric coupling is found to be absent in cubic Mn2.4Ni0.6O4, but still shows interesting transport behavior. The resistivity results show semiconducting behavior of the system, but interestingly, this semiconducting behavior weakens at low temperatures. This is evident from the decreased rate of change of resistivity with decreasing temperature. X-ray absorption spectra results have confirmed that to compensate for the charge imbalance caused by Ni2+ cations at the octahedral-site, a few Mn3+ cations transform into Mn4+. The density of state calculations reveal that at Fermi-level, Mn2.4Ni0.6O4 exhibits small but finite bands in the majority channel while a band gap of 1.5 eV exists in the minority channel. The ground state electronic structure of Mn2.4Ni0.6O4 predicts a half-metallic character for the system. The partial density of states analysis of Mn2.4Ni0.6O4 suggests that the bands near the Fermi-level are predominantly contributions of Mn3+, Mn4+ and O2-. We further discuss the origin of the weak semiconducting behavior of Mn2.4Ni0.6O4 at low temperatures.
查看更多>>摘要：? 2022The effects of hot-rolling on the secondary electron property evolution of activated Cu-2.7Be sheets were investigated in this study. The microstructures of both pristine and activated Cu-2.7Be alloys subjected to different hot-rolling temperatures were characterized. Their phase compositions were found to comprise an α matrix and eutectoid phases (α + γ). Using electron back-scattered diffraction, the initial average grain size (d0) was found to vary from 6.45 μm to 15.63 μm as the hot-rolling temperature increased from 680 °C to 830 °C. Scanning electron microscopy and X-ray photoelectron spectroscopy studies of the activated Cu-2.7Be sheets revealed that the amount of BeO increased with a decrease in the average grain size, resulting in the enhancement of the peak secondary electron emission yield. Scanning Kelvin probe force microscopy measurements confirmed that the main contributor to the BeO enhancement was the α matrix, while transmission electron microscopy analysis showed that BeO formed preferentially from sub-grain boundaries, indicating the importance of grain boundaries for BeO formation. Moreover, the peak secondary electron yield (δm) exhibited a linear relationship with d0?0.5 similar to the Hall-Petch relation. The results in this study will be important for enhancing the secondary electron yield of Cu-Be dynodes used in photomultiplier tubes and electron multipliers.
查看更多>>摘要：? 2022 Elsevier B.V.W-Mo/Mo-V/V-W co-doped TiO2 photocatalyst for the effective degradation of MB (methylene blue) dye under sunlight irradiation was successfully prepared by one-step Plasma Electrolytic Oxidation (PEO) process. The XRD, XPS, and EDS results revealed that W/Mo/V were co-doped in the TiO2 lattice. The highest redshift in the light absorption edge is recorded for the sample MV (Mo-V co-doped TiO2) with a bandgap of 2.51 eV, whereas the bandgaps for WM (W-Mo co-doped TiO2) and VW (V-W co-doped TiO2) are recorded as 2.96 eV and 2.58 eV, respectively. The co-doped photocatalysts show a typical PEO structure with a high degree of porosity favouring the dye adsorption ability. EIS, LSV, and PL analysis confirmed that the co-doped coatings pose a high degree of charge separation, suppressed charge carriers' recombination, and increased the ability to produce photocurrent. Under direct sunlight irradiation, the sample MV showed the highest photocatalytic efficiency, confirmed by MB dye degradation, then the other co-doped and undoped TiO2. This can be attributed to the synergetic effects of intense visible light absorption in the solar spectrum and the reduced charge carriers' recombination rate by acting as the trapping sites for photogenerated electrons and holes. Finally, this immobilised co-doped photocatalyst developed by the PEO process is a promising system in the quest to establish a renewable energy-assisted strategy for textile wastewater treatment application.
查看更多>>摘要：? 2022 Elsevier B.V.Industrial Mg alloys scraps containing 3% of Al and 3% of Zn (and about 20% of MgO and Mg(OH)2) were ball milled with the addition of 5 wt% C and 5 wt% of Ni, Cu, Co or SiO2. 3 h of ball milling were needed to obtain optimum hydrolysis performances of the mixtures (e.g. yields of almost 90% obtained within 1 min). Pellets of such obtained powder were prepared as it is easier for an application. The shape of the hydrolysis curves highlights first an incubation period depending on the compactness of the pellets and then a second part with a logarithmic shape. A new model is presented that allows to take into account both parts of the hydrolysis curve. The model is applied successfully to all the pellets having various compactness.
查看更多>>摘要：? 2022 Elsevier B.V.The development of highly-sensitive and moisture resistant semiconductor metal oxide (SMO) gas sensors for practical application remains a challenge. Here, a three-dimensional ordered macroporous (3DOM) SnO2 decorated with Au nanoparticles (NPs) was obtained via a facile self-assembly template method and the Au content was optimized. The resulting 3DOM Au/SnO2 gas sensor displayed remarkable performance, with its response and lower actual detection limit to formaldehyde 10.2 times higher and 500 times lower, respectively, compared to the undecorated 3DOM SnO2 sensor at 110 °C. Meanwhile, the fast response-recovery process and the repeatability, stability, and selectivity of the sensor indicate that it can meet the requirements for practical application. Density functional theory (DFT) calculations revealed that the Au/SnO2 NPs have strong adsorption energies and electrical conductivity, allowing for selective formaldehyde detection. Further, the 3MCM-48 layer protects the 3DOM Au/SnO2 layer from moisture, allowing at least 80 % of the initial response value to formaldehyde to be maintained even at> 90 % relative humidity. Hence, the proposed strategy represents, for the first time, a universal and effective way to achieve high response and moisture-resistant formaldehyde sensors and demonstrates the potential of SMO gas sensors for indoor air monitoring.
查看更多>>摘要：? 2022 Elsevier B.V.Lightweight and multifunctional aerogel has attracted increasing attention in microwave absorption, thermal insulation and pollutant recovery due to the increase of electromagnetic radiation and pollution, global warming and environmental pollution, which is an ideal material to meet the technical needs of today's society. In this study, aerogel composites (M-AMF), consisted of aramid nanofiber, multiwall carbon nanotubes and Fe3O4 nanoparticles modified by methyl trimethoxy silane, are prepared via a combination of a facile vacuum assisted filtration, freeze drying and vapor deposition, which show superhydrophobic property, low density and high mechanical properties. M-AMF32 aerogel composite as microwave absorber shows that a minimum reflection loss can reach up to ‐45.83 dB at microwave frequency of 5.46 GHz and a maximum effective absorption bandwidth is 4.0 GHz. Moreover, surface temperature of M-AMF aerogel composite as thermal insulation material is only 50 °C after placed on heating plate of 100 °C. The adsorption capacity of M-AMF32 aerogel can still maintain at about 30 g/g after 100 cycles for oil. Moreover, M-AMF aerogel exhibits excellent thermal insulation performance and certain selective absorbability to non-polar liquids, which can be applied in the harsh environment applications and the treatment of pollutants.
查看更多>>摘要：? 2022 Elsevier B.V.Graphitic carbon nitride (g-C3N4) shows a graphite-like layered structure, which provides a high theoretical value for solar-to-hydrogen evolution especially for a 2D nanostructure. However, conventional polycondensation induces a strong agglomeration and collapse of nanostructure, resulting in a relatively poor photocatalytic performance. To overcome this problem, we develop a gas bubbling exfoliation strategy with NH4Cl assistant to make ultrathin 2D g-C3N4 nanosheets self-assembled into a 3D macroporous network on a large scale. The hierarchical structure significantly improves the specific surface area to 176.4 m2 g?1 (11.6 times higher than the reference g-C3N4), which allows a large water/g-C3N4 interface for photocatalytic water reduction reaction. The ultrathin 2D g-C3N4 nanosheets show a thickness of about 1.4 nm, which greatly suppress photoinduced carriers recombination and enhance charge transfer at the interface. Furthermore, the doping of N and Cl is achieved during synthesis. As a result, the resulting g-C3N4 demonstrates a remarkable improvement in H2 production of 12.89 mmol g-1 h?1, which is 21 times higher than the g-C3N4 obtained from the conventional condensation method. These explorations provide a facile guidance for the quasi 3D g-C3N4 hierarchical architecture engineering even for various energy-related applications.
查看更多>>摘要：? 2022 Elsevier B.V.The study of the mechanical spectroscopy (MS) behaviour in archaeological bone remains samples recovered from the Boca de Lega site (Santa Fe, Argentina) in the temperature range between 450 K and 673 K has been performed. Moreover, to our knowledge the mechanical spectroscopy behaviour as a function of temperature in archaeological bones is for first time reported. The present obtained results are of high value from the archaeological point of view due to they suggest that the bone remains were used probably for culinary activities by the preterite societies that habited this area. Attention is putted in the relaxation processes which appear at around of 510 K and 570 K and their relation with the diagenetic degree of the polypeptide chains of bone remains, inferred from the depositional effects from the soil and the replacement of calcium by sodium and potassium. The damping peaks in the archaeological bones are analysed though the study of the behaviour of the parameters corresponding to the fitted Havriliak-Negami (HN) equations. In addition, samples of fresh bones are also measured by means of MS during successive heating and cooling runs for determining the HN parameters in fresh bones for obtaining a reference state. Results from scanning electron microscopy, energy dispersive spectroscopy, differential thermal analysis and thermogravimetry are also coupled for the discussion of the present work.
查看更多>>摘要：? 2022 Elsevier B.V.Nanosized vanadium nitride (VN) wrapped onto carbon fibers was synthesized by a molten salt disproportionation synthesis method at 800–1,000 oC, using V and melamine as raw materials in molten (Li,K)Cl salts. Molten salts could accelerate the formation of nanosized VN at a lower temperature, which is possibly associated with the disproportionation reaction of V-ions on g-C3N4 surface. VN displays remarkable application prospects as an anode material for lithium-ion batteries (LIBs), delivering a reversible discharge capacity of 320.1 mAh·g?1 at 1.0 A·g?1 after 500 cycles and 669.4 mAh·g?1 at 0.1 A·g?1 after 230 cycles without capacity attenuation. Such a remarkable cyclability of VN is attributed to the increased surface area and superior structural stability, induced by the dispersion of VN nanoparticles onto high-conductive carbon fibrous network. Li-ions storage mechanism of VN is pseudocapacitive, accompanied with the conversion-type electrochemcial reaction of VN with Li-ions during the de-/lithiation process.
查看更多>>摘要：? 2022 Elsevier B.V.The spinel LiNi0.5Mn1.5O4 (LNMO) material is considered as a promising cathode in high-voltage lithium-ion batteries due to its advantageous voltage and capacity. Previous results indicate that the electrodes constructed by LNMO with the same compositions while differing in the crystallite geometries always exhibit various electrochemical performances. Here, to probe the relationships between the crystalline geometry of the obtained cathodes and their electrochemical properties, we synthesized different facet-exposed LNMOs with the same compositions using a template method. We demonstrate that the crystallite geometries of the hydroxide precursors can be tuned easily via varying the synthesize parameters, while the tuned precursors can be employed as the templates during the final product preparation. LNMOs enclosed by single {111} facets (LNMO-OH) and both {110} and {100} facets (LNMO-HP) are obtained and employed to elucidate the particle geometry-dependent electrochemical properties. Despite better rate capabilities exhibited for LNMO-HP because of the higher lithium diffusion coefficients along these crystal orientations, inferior cycling performance is released compared with its LNMO-OH counterpart. These insights can provide informative guidance in particle geometry-dependent material construction, thus helpful in realizing high-performance LNMO cathode.
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