查看更多>>摘要：The effect of Sn on the hardening and corresponding precipitation behavior of as-quenched Al–0.4Mg–1.0Si alloy at different aging temperatures was investigated with hardness tests, differential scanning calorimetry analysis, and transmission electron microscopy. The hardness of the Sn-free alloy was higher than that of the Sn-added alloys during under-aging, but the tendency is reversed during over-aging. The effect of Sn on the hardening behavior of these alloys is not substantially affected by the aging temperature, i.e., the addition of Sn can improve resistance to over-aging softening at different aging temperatures. The reason for the resistance to over-aging softening by the addition of Sn is related to the increase in the number density of precipitates during under-aging and the decrease in precipitates size during over-aging.
查看更多>>摘要：Materials combining d0 and p cations with stereo-active lone pair electrons have excellent polarization for photoelectric applications. This work reports the modifications of photochemical properties via Nb5+-, Ta5+-doping in Te-V mixed oxide Te2V2O9 with d0-(V5+) and p-(Te4+) cations. Nb5+-, Ta5+-doped Te2V2O9 nanobelts were prepared using the sol-gel method. The structure, morphologies, and optical absorption properties were reported. The calculation and experimental results indicate that the Te-V mixed oxide Te2V2O9 has an indirect transition with band energy of 2.19 eV. The photodegradation of RhB dye solutions was conducted under the irradiation of visible-light irradiation (λ ≥ 420 nm). The conductivity properties, lifetime of charge carriers were characterized via impedance spectra and decay curves, respectively. The multivalent cations were confirmed via XPS measurements. The experiments concluded that both Nb5+ and Ta5+ ions can depressed the luminescence, and enhanced photocatalysis to some extent. While, compared with Ta5+, the Nb5+ doping shows much more significant improvement of photodegradation. It was concluded that the redox couples V5+/4+ induced by Nb5+ doping attribute to the photocatalysis. This work offers an effective method to modify the photochemical properties via the redox couples and defects induced by heterovalent substitution on the cations.
查看更多>>摘要：The aim of this paper was to study the isothermal forward martensitic transformation in binary, ternary, and quaternary NiTi-based shape memory alloys to find the origin of this phenomenon. The results obtained showed that the isothermal B2 → B19′ transformation was observed only in the NiTi-based alloys with substitutional defects. The critical concentration of copper was found that completely suppressed the martensitic transformation both on cooling or isothermal holding in Ti-Hf-Ni-Cu alloys. The thermodynamics of the martensitic transformation that occurred in the presence or absence of the substitutional defects was discussed, and the reason for the influence of the substitutional defects on the martensitic transformation was clarified. It was verified that the formation of the martensite phase on isothermal holding was caused by the local fluctuation of the substitutional defect concentration which led to fulfilment of the thermodynamic condition for the martensitic transformation. It was shown that the maximum volume fraction of the isothermal martensite was limited by the maximum volume of martensite that corresponded to the thermal elastic equilibrium and appeared on cooling of the alloy without substitutional defects. The results allowed to conclude that the martensitic transformation remained to be thermal elastic in the NiTi-based alloys with a non-stoichiometric composition however, the martensite nucleation was controlled by the thermally activated migration of substitutional defects.
查看更多>>摘要：Owing to the ease of catalyst separation and recycling, magnetically sensitive catalysts are essential for developing a cost-effective method for the photocatalytic degradation of aqueous organic pollutants. This study demonstrates the efficacy of a magnetically sensitive TiO2 hollow sphere/Fe3O4 (THS/FO) core-shell hybrid catalyst for the sunlight-assisted degradation of aqueous antibiotic pollutants, namely amoxicillin (AMC) and levofloxacin (LVF). To fabricate this core-shell hybrid catalyst, THS was first synthesized via a wrap–bake–peel approach using SiO2 templates and FO nanoparticles were then carefully deposited on the THS surface via an in situ growth method. The THS/FO core-shell hybrid catalyst exhibited significantly higher activity for degrading AMC and LVF than THS under simulated sunlight. Moreover, the activity results indicate that the proposed hybrid catalyst outperforms numerous reported photocatalysts owing to its strong optical response properties and the synergistic effect of THS and FO due to the core-shell configuration of the hybrid catalyst, which facilitates charge separation. Additionally, due to the strong magnetic properties of the hybrid catalyst, the catalyst can be magnetically recovered and reused in the AMC and LVF degradation processes without exhibiting a significant loss in its activity even after five consecutive test cycles. Thus, the hybrid catalyst designed herein promotes the use of practical photocatalytic techniques for treating aqueous antibiotic pollutants.
查看更多>>摘要：The single-phase disordered alloys of RAlGe (R = Dy, Ho) are successfully prepared by arc-melting, and their structures and physical properties are investigated by X-ray diffraction, magnetization, specific heat, electric transport and magnetoresistance measurements. RAlGe crystallizes into an orthorhombic YAlGe-type structure with a space group of Cmcm, and three kinds of crystal positions are randomly occupied by (Al, Ge) at 4a (0, 0, 0) site, (R, Al) at 4c (0, 0.31, 0.25) site, and (Ge, R) at 4c (0, 0.61, 0.25) site, respectively. RAlGe exhibits strong relation effect among magnetic and electric as well as thermal properties, it shows that the magnetic, thermal and electric phase transitions simultaneously occur. The thermal and electric phase transitions are associated with the magnetic transition. The magnetoresistance shows the dynamic evolution from positive to negative with increasing temperature from the magnetic transition temperature Tt to Néel temperature TN. It is suggested to be due to the temperature induced magnetic phase transition from AFM-I to AFM-II, which causes the decrease of spin disordered scattering.
查看更多>>摘要：Designing high-efficiency catalysts with earth-abundance elements for overall water splitting (OWS) in alkaline electrolyte has been unsettled owing to the non-negligible overpotential of oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). An electrocatalyst with decent HER and OER activities in the same electrolyte is crucial for sustainable energy storage and conversion device. In this work, a nitrogen-doped porous carbon confined yolk/shell OWS catalyst of WC/Co3W3N/Co@NC has been prepared via calcination polyhedron encapsulation structure PW12 @ZIF-8 @ZIF-67 generated by the epitaxial method. Because of the optimized chemical composition, the derived WC/Co3W3N/Co@NC multisite catalyst has outstanding OWS performance in 1 M KOH solution. For example, to reach a current density of 10 mA cm-2, it only needs low overpotentials of 141 and 280 mV for the HER and OER, respectively. By using the easy operation and classical bubble extraction method, we find that the Faraday efficiencies of the catalyst for HER and OER are 94.3% and 97.4%, respectively. Moreover, taking advantage of the micropores and mesopores in the yolk/shell structure, it exhibits enhanced stability and promoted diffusion kinetics. This work initiates an effortless approach to the synthesis of the highly efficient yolk/shell carbon-based OWS electrocatalyst.
查看更多>>摘要：Realization of an anti-pulverization electrode structure is extremely important for developing high-performance Li/Na storage, and yet this technology is still challenging. Herein, the yolk-shell Co9S8/ZnS heterostructure encapsulated by N, S-doped carbon (YS Co9S8/ZnS@SNC) is successfully synthesized from solid CoZn glycerate microsphere for the first time and utilized as the anode materials for Li/Na storage. Consequently, the optimized YS Co9S8/ZnS@SNC electrode exhibits superior Li/Na storage performance, involving excellent reversible capacity and outstanding rate capability with high specific capacity. The superior performances of the electrode are attributed to the two factors: ⅰ) The YS structure can not only accommodate the volume variation effectively to resist pulverization during Li/Na-ions insertion/extraction, but also enable sufficient contact of Co9S8/ZnS and electrolyte to improve electron/ion transportation in the electrode; ⅱ) in-situ constructed Co9S8/ZnS heterostructure and its surface coated SNC layer can provide a high efficient transfer path for electrons. Density functional theory calculations further confirm the excellent conductivity of the Co9S8/ZnS and its delocalized electron distribution. Importantly, the strategy provides a new opportunity to realize high-performance energy storage from various glycerate template-based transition metal compounds.
查看更多>>摘要：The construction of gas sensors with excellent gas sensitivity and low operating temperature is of great importance while challenging. In this work, using indium nitrate, urea, and sucrose as precursors, In2O3 nanomaterials with the porous rod-like structure were prepared via hydrothermal method combined with high-temperature calcination. FTIR and TGA methods verified the growth process of porous rod-like In2O3 nanomaterials. Significantly, due to the doping of carbon in In2O3, the sensor based on porous rod-like In2O3 nanomaterials showed an enhancement response to NO at room temperature. The porous structure of In2O3 nanomaterials facilitates the diffusion of gas, shortening the response time. The developed materials provide insight into the fabrication of porous nanomaterials and the detection of NO at room temperature.
查看更多>>摘要：In this paper, three different morphologies of NiCo2O4 nanoarrays, namely, nanosheet (S-NiCo2O4), nanoneedle (N-NiCo2O4) and their hybrid nanostructure (M-NiCo2O4) were successfully prepared on flexible carbon cloth (CC) by a hydrothermal method. The structures, surface morphologies and compositions of the samples were respectively characterized by XRD, SEM, EDS, and XPS, and the effect of NiCo2O4 morphologies on the electrochemical performances was systematically investigated. It is found that the M-NiCo2O4/CC electrode demonstrates the best supercapacitive performance among the three kinds of samples, typically its specific capacitance is 1347.4 F/g at 1 A/g (1509.1 F/cm2 at 1 mA/cm2), much higher than that of S-NiCo2O4 (938.4 F/g at 1 A/g) and N-NiCo2O4 (1022.4 F/g at 1 A/g). Meanwhile, the M-NiCo2O4/CC sample exhibits excellent rate capability (81.6%, from 1 A/g to 15 A/g) and cycling stability (92.4% retention after 10,000 cycles). In addition, an flexible solid-state asymmetric supercapacitor (ASC) with M-NiCo2O4/CC as positive electrode manifests great capacity retention (94% after 5000 cycles) and outstanding energy density of 41.7 Wh/kg at the power density of 750 W/kg. Moreover, the charge-discharge time shows no significant change after 2000 bends, demonstrating its application potential in the field of flexible SCs. The excellent performance is attributed to the unique hybrid porous structure of one-dimensional (1D) nanoneedles and two-dimensional (2D) nanosheets.
查看更多>>摘要：In order to more effectively alleviate the volume extension and shrinkage of the Si anode during Li intercalation/deintercalation processes, and also to improve the electron and ion transport dynamics, carbon coated Si-porous carbon composite fibres with a sandwich structure were prepared using a sacrificial template (ZIF-8) to construct mesoporous carbon, combined with electrospinning technology and subsequent hydrothermal carbon coating. The carbon fibre skeleton and carbon-coated sandwich structure provide support for the volume extension and shrinkage of Si, avoiding Si from directly contacting with the electrolyte, and forming a stable solid electrolyte interphase film. Furthermore, the polyvinylpyrrolidone spinning solution assists ZIF-8 to obtain a mesoporous structure inside the carbon fibre, which improves the specific surface area and pore volume of the composite material. In this case, the mesoporous structure also helps to alleviate the volume extension and shrinkage of Si during the charging /discharging processes and improves the transmission dynamics of lithium ions and electrons. Benefit from the unique structural features, this anode composite material exhibits enhanced electrochemical properties for Li-ion batteries, with a reversible specific capacity of 1114 mAh g?1 at 1 A g?1, and demonstrates a capacity retention rate of 66% with a specific capacity of 740 mAh g?1 after 400 cycles.
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