查看更多>>摘要：? 2022 Elsevier B.V.Bi4Ti3O12 (BIT), a typical layered-structure ferroelectric with a high Curie temperature (TC), is a promising material for high-temperature sensors. Herein, W/Cr co-substitution at the B-site of BIT ceramics (BITWC100x) is carried out to investigate the phase structure, domain structure, and electrical properties. The W/Cr addition apparently reduces the concentration of oxygen vacancies, effectively improving the ferroelectric and piezoelectric properties as well as the resistivity of the BIT ceramics. The BITWC2 ceramic exhibits a high piezoelectric coefficient (d33 = 31.1 pC/N), a moderate TC (651 °C), a large remnant polarization (Pr = 12.2 μC cm?1), and a prominent direct current resistivity (5.49 ×106 Ω·cm at 500 °C). Moreover, the BITWC2 ceramic possesses a large d33 of 26.6 pC/N at an annealing temperature of 600 °C, indicating the excellent thermal stability of the piezoelectric coefficient. Overall, the BITWC100x ceramics can be used in piezoelectric devices at temperatures up to 500 °C.
查看更多>>摘要：? 2022 Elsevier B.V.Ba0.5Sr0.5TiO3-MgO composite ceramics have been prepared through spark plasma sintering (SPS) process. Phase composition, microstructures and dielectric properties have been systematically characterized. In this composite system, with the gradual increase of the MgO content, the dielectric constant of the composite ceramics drops drastically. On the contrary, when the MgO content varies between 0% and 30%, the tunability of composite ceramics have not decreased significantly, but increased instead. High tunability of 16.53% and relatively low dielectric constant of 415 are realized simultaneous at 3 kV/mm, 10 kHz when the dielectric content is 30%. Its tunability is even higher than pure Ba0.5Sr0.5TiO3 under the same electric field condition, which indicates that SPS is an effective means to suppress the ion diffusion between ferroelectric-dielectric composite ceramics and improve the tunability.
查看更多>>摘要：? 2022 Elsevier B.V.The present study is based on the adsorption of Ni2+ in aqueous solution on the spinel MgCo2O4 synthesized by nitrate route, followed by calcination at 500 °C. The powder was characterized by X-ray diffraction (XRD), FTIR spectroscopy, SEM/EDX analysis and specific surface area. It crystallizes in a cubic symmetry (Space Group: Fd-3m) and the SEM image shows hexagonal-shaped grains with visible porosity. The effects of the initial Ni2+ concentration, catalyst dose, temperature and pH were investigated. The optimization was found for 0.5 g/ L, 25 mg/ L, pH ～ 6 and 50 °C respectively with a maximum efficiency of 99%. The experimental data were analysed by different isotherms. The Langmuir model indicates a better representation with a high adsorption capacity of 140 mg/g and a correlation coefficient (R2) of 0.99, thus showing that MgCo2O4 is an efficient adsorbent for the Ni2+ recovery. The kinetic data are well fitted by the pseudo second-order model. The positive zeta potential leads to a high adsorption capacity. The thermodynamic parameters revealed that the Ni2+ adsorption on the spinel is endothermic (ΔH° = 27.236 kJ/ mol) and spontaneous (ΔG° = ?2.045 kJ/ mol). The spinel is regenerated with diluted HCl solution without noticeable loss of adsorption quality after continuous cycles (adsorption / desorption).
查看更多>>摘要：? 2022 Elsevier B.V.Molybdenum disulfide (MoS2) is a promising anode material in lithium ion batterys (LIBs). However, poor conductivity and stability severely hinder its application. Herein, carbon nitride nanotubes are used as template to in-situ grow ultrathin MoS2 nanosheets and after removing carbon nitride nanotubes, MoS2 nanosheets with an uniform tube-like structure can be obtained. Benefiting from hollow structure with long aspect ratio and well-dispersed ultrathin MoS2 layers, the obtained MoS2 nanotubes favor mass diffusion, shorten ion transfer distance and can effectively alleviate volume expansion. The obtained MoS2 nanotubes deliver a reversible capacity of 1112.3 mAh g?1 (0.5 A g?1 after 500 cycles), a good long cycling life (428 mAh g?1 at 2 A g?1 after 1000 cycles). For the MoS2-NT//LiCoO2 full cell, it exhibits stable cycling performance with discharge capacity of 143 mAh g?1 at 0.1 A g?1 after 100 cycles. The specific architecture of MoS2 nanotubes could provide a useful design idea for the electrode of next-generation LIBs.
查看更多>>摘要：? 2022 Elsevier B.V.In this study, reduced graphene oxide-based graphitic carbon nitride (rGO/g-C3N4) composite was fabricated via thermal polymerization-hydrothermal method and were utilized to activate peroxydisulfate (PDS) under simulated solar light irradiation. The as-synthesized rGO/g-C3N4 was demonstrated to effectively remove methyl orange (MO) in wastewater. Notably, 92.3% of MO (15 mg/L) was removed within 120 min in the presence of 0.2 g/L rGO/g-C3N4 and 0.225 g/L PDS. The influence of activator dosage, PDS concentration and co-existing solution matrix on the removal efficiency was investigated. Free radical capture experiments confirmed that SO4ˉ·, photogenerated holes (h+), O2ˉ· and non-radical reaction initiated by rGO played a major role in MO removal. Furthermore, PDS and rGO acted as the electron acceptor and transfer carrier of the photogenerated charges, respectively, resulting in the efficient activation of PDS. The promoting visible light absorption might be ascribed to the defect sites on the surface of rGO/g-C3N4, which generated from the rGO loading. This study revealed that the as-synthesized rGO/g-C3N4 composite exhibits wide promising application prospects as a photocatalytic activator of PDS for the degradation of azo dyes in textile wastewater.
查看更多>>摘要：? 2022 Elsevier B.V.In this work, magnetic nanocomposites Ba0.5Sr0.5Fe12O19/x(Ni0.5Zn0.5)Fe2O4 with the compositions x = 10, 20, 30, and 50 wt%, arising from nickel-zinc ferrite added to barium strontium hexaferrite were prepared and characterized. The samples were synthesized using co-precipitation and ball milling methods. X-ray powder diffraction measurements validated the synthesis of nanocomposite with high purity and crystallinity. A transmission electron microscope was also used to analyze the morphology of the nanocomposites that demonstrated hexagonal platelet-like and spherical-like shapes for hard and soft phases, respectively. Also, multiple shapes of different grain sizes were formed, and their grain size decreased upon the addition of the soft phase. Besides, the elemental compositions and the oxidation states of (Ba2+, Sr2+, Ni2+, Ni3+, Zn2+, Fe2+, Fe3+and O2-) constituting the nanocomposites were investigated, using X-ray photoelectron spectroscopy. Additionally, the magnetic properties were examined using a vibrating sample magnetometer. According to Henkel plots, the existence of a weak exchange coupling interaction and the dominance of dipolar interactions were visible upon the addition of Ni0.5Zn0.5Fe2O4. Furthermore, the maximum energy product, (BH)max, is the energy density that a hard ferrite can store with low magnetic anisotropy. (BH)max of the nanocomposite containing 10 wt% of soft phase increased by 10% when compared to pure hard phase, reaching the highest value of (BH)max equal to 22.89 kJ/m3.
查看更多>>摘要：? 2022 Elsevier B.V.Snoek relaxation in bcc crystals is the delayed strain response to an applied stress resulting from the interaction of the interstitial atoms with the stress field. It is responsible for the Snoek peak observed in internal friction measurements of ferrite. However, although martensite is carbon supersaturated, several authors denied the possibility of Snoek relaxation in bct-martensite. We investigated this matter by means of Monte Carlo simulations and mean-field thermo-kinetic modeling. Our results show that Snoek relaxation does occur in bct-martensite. The computed Snoek profiles of temperature-dependent and frequency-dependent internal friction exhibit unexpected features: both peak height and peak temperature decrease when the carbon content is increased. We explain this behavior in the frame of the linear-response approximation. Our theoretical predictions are in qualitative agreement with experiments.
查看更多>>摘要：? 2022 Elsevier B.V.A novel strategy was reported to improve electrocatalytic activity of NiCo2O4 by doping Fe. It is interesting to find that the doping of Fe induces formation of nanorod composing with crystalline core and thin amorphous shell. The composition, structure and properties of NiCo2O4 are well characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry and amperometric method. The results display that the presence of thin amorphous shell is conducive to accelerating electron transfer rate and exposing more effective active sites, therefore making the sensor based on Fe-doped NiCo2O4 detect glucose in a wide linear range from 0.2 μM to 3.1 mM with a high sensitivity of 3055.7 μA mM?1 cm?2 and a low detection limit of 0.19 μM. This unique crystalline core/amorphous shell-structured NiCo2O4 demonstrates promising potential as an effective electrocatalyst for glucose sensing.
查看更多>>摘要：? 2022 Elsevier B.V.The rational design and development of a highly efficient and sustainable heterogeneous catalyst has become a limiting factor for the practical application of persulfate-based advanced oxidation processes in organic dye degradation. Herein, a nitrogen-doped porous carbon-coated CoFe2O4 core–shell composite (CoFe2O4 @NPC) was synthesized by in-situ growth of cobalt/iron bimetallic zeolitic imidazolate framework-9 (Co/Fe-ZIF-9) on graphene oxide (GO) nanosheets followed by one-step calcination of the bimetallic ZIF-GO composite in nitrogen. The textural, chemical, and magnetic properties of the composites were comprehensively characterized using various analytical techniques. The catalytic performances of the as-prepared CoFe2O4 @NPC in activating PMS to decompose Rhodamine B (RhB) were then systematically evaluated. The composite calcined at 600 °C exhibited the highest catalytic activity. The maximum RhB degradation efficiency of 99.05% and pseudo-second-order kinetic constant of 0.0766 L/(mg·min) were achieved after 20 min at 25 °C. Moreover, CoFe2O4 @NPC displayed excellent recyclability and stability with negligible leaching of Co and Fe ions into the solution. Subsequently, electron spin resonance, reactive oxygen species quenching, and X-ray photoelectron spectroscopy were conducted to clarify the PMS activation mechanisms. Results suggested that SO4?? and ?OH were generated during PMS activation and that SO4?? was the predominant radical involved in RhB degradation. In addition, Co(II), Fe(III), and structured nitrogen, especially pyridinic and graphitic N groups, participated in the PMS activation. Some insights into possible mechanisms of RhB degradation were also attained from spectral analyses. All these results suggested that CoFe2O4 @NPC had excellent potential as a PMS activator for application in dye-contaminated wastewater treatment.
查看更多>>摘要：? 2022 Elsevier B.V.Reducing annealing twin boundary (ATB) density was proposed to substantially improve the shape memory effect (SME) of Fe–Mn–Si-based alloys, irrespective of their composition, deformation temperature and thermomechanical treatments. Here, we re-examined the effect of reducing ATB density on the SME of a Fe[sbnd]20Mn[sbnd]5.5Si[sbnd]9Cr[sbnd]5Ni (wt%) alloy. We set off with three starting states, i.e., the as-cast state, the hot forged and solution-treated (ST) state as well as the subsequently δ-annealed (DA) state. Our results reveal that the as-cast sample with the lowest ATB density exhibits the lowest shape recovery ratios, while the shape recovery ratios of the DA sample are close to those of the ST sample although the ATB density in the former is only ~1/3 of that in the latter. In other words, reducing ATB density does not necessarily lead to the improvement of SME. Compared to the ST sample, the lower ATB densities in the as-cast and DA samples are actually concomitant with higher densities of low angle grain boundaries (LAGBs), larger γ grain sizes and a limited amount of χ precipitates (volume fraction < 1.6%). The increase of LAGB density and the precipitation of elongated χ precipitates are deleterious to the SME, while the increase of γ grain size improves the SME. Thus, reducing ATB density cannot result in a monotonic change to the SME, given that the decrease of ATB density is concomitant with other microstructural changes.
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