查看更多>>摘要：? 2022 Elsevier B.V.Herein, we report an intrinsic fluorescence in polyethylene glycol (PEG) coated manganese ferrite (MnFe2O4) magnetic nano particles (MNPs). Generally, nano ferrites (NFs) do not show fluorescence characteristics, however, imparting fluorescence in these materials can be valuable for many applications as the stipulation of external control over the properties by external field provides an opportunity to develop active-controlled devices. In the present work, PEG-200 coated MnFe2O4 MNPs have been synthesized by a large-scale, facile one-pot hydrothermal method. The optical properties of MnFe2O4 MNPs have been by photoluminescence (PL) spectroscopy suggest that the prepared sample is showing sharp emission spectra at 422 nm, corresponding to the violet band, and second at 458 nm corresponding to the blue band. The presence of oxygen vacancy created at both tetrahedral and octahedral sites and shallow hole defects are responsible for the PL behavior in the PEG-coated MnFe2O4. The time-resolved PL (TRPL) results suggest that the MnFe2O4 MNPs have two decay times τ1=1.29ns and τ2=6.85ns which are non-correlated and correspond to different defect states. The electronic bandgap of the MNPs is 3 eV obtained from the Tauc plot using UV absorption spectra. Moreover, the structural analysis has been carried out using X-ray diffraction and various optical and magnetic properties have been correlated to structural parameters and cation distribution. The ferromagnetic resonance (FMR) spectra of the MnFe2O4 MNPs sample show a broad single peak which confirms the ferromagnetic characteristics of the sample and the g-value obtained for the sample is 1.98 which suggests that the super exchange interactions (SEI) dominates over the dipolar interaction. The M-H loop confirms the single domain nature of the sample and the saturation magnetization (SM) is 68 emu/g. The obtained value of SM is higher than the previously reported literature due to an increase in the occupancy of Fe3+ and Mn2+ ions at octahedral sites (Neel's model). Further, the FTIR spectra confirm the spinel phase formation, and the size distribution and average size are obtained using electron microscopy analysis. The intrinsic fluorescent PEG-coated MnFe2O4 are highly suitable for a diverse range of biomedical (bio-imaging, sensing, magnetic resonance imaging (MRI) contrast agent), optoelectronics, and optical applications.
查看更多>>摘要：? 2022 Elsevier B.V.The scanning electron microscopy, X-ray diffraction, positron annihilation spectroscopy, M?ssbauer spectrometry, and measurements of magnetic characteristics by vibrating sample magnetometer complemented by theoretical simulations are applied in the present investigations of the Fe-Al-Co alloys with 25 at% Al and Co substituting Fe in amount of 15 at% or 25 at%. The alloys prepared by slightly different technologies resulting in different structural morphologies are subjected to thermal treatment followed by slow cooling and water cooling. It is shown that the alloy with lower Co content and the initial A2 structure is more sensitive to the thermal treatments from the viewpoints of changes in morphology, defects concentration and magnetic properties in comparison to the other one with the initial B2 structure. This is reflected almost in all experimentally obtained results.
查看更多>>摘要：? 2022 Elsevier B.V.Chemically architectured alloys are a new concept of microstructure in which two phases are separated by a 3D network of fluctuations of composition, which is called interphase, and which induces a strengthening. Chemically architectured alloys were processed by spark plasma sintering of a mixture of pure Ni and CoCrFeMnNi high entropy alloy with varying conditions. They were characterized by scanning electron microscopy coupled with energy dispersive spectroscopy and electron backscattered diffraction, microhardness and compression tests. It was shown that the width of the interphase can be decreased by decreasing the sintering temperature and increasing the applied pressure. The strengthening effect of the interphase increases when its width decreases and its volume fraction increases. The microstructure of the chemically architectured alloys can be finely controlled by the processing parameters which will permit to maximize the strengthening. Chemical architecturation is thus an efficient and tunable strengthening mechanism.
查看更多>>摘要：? 2022 Elsevier B.V.The influence of Zn and/or Ag additions on the microstructure and properties of Al-Mg based alloys has been investigated. In the as cast condition, β-Al3Mg2 was dominated in Al-5 wt% Mg alloy with the addition of 0.66 wt% Zn. However, a further addition of Zn up to 2.55 wt% promotes the formation of T-Mg32(Al,Zn)49 phase. With the addition of Ag, no new intermetallic phase was observed. However, Ag partitions into the T-Mg32(Al,Zn)49 phase and thereby the T-Mg32(Al,Zn)49 phase transforms to Ag-containing T phase (T-Mg32(Al,Zn,Ag)49 phase) during solidification. After ageing treatment, the addition of Zn can promote the precipitation kinetics and thereby improve the strength of Al-Mg based alloys. Similar to the addition of Zn, the addition of Ag also promotes the precipitation kinetics and improve the strength of Al-Mg based alloys. This investigation can provide guidance for the alloy design of Al-Mg based alloys.
查看更多>>摘要：? 2022 Elsevier B.V.Antimony-based anodes possessing advantages of stable operating voltage and high theoretical capacity can replace graphene as alloy-based electrodes material in LIBs applications. However, the problems of capacity decaying and poor stability of Sb-based materials due to volume expansion and structural crushing during the long-term cycling remain to be solved. Therefore, we propose a strategy of using S and N co-doped carbon nanofibers encapsulated with Sb nanoparticles to overcome the above problems. The proposed material exhibits an excellent lithium storage performance with a high reversible specific capacity of 734 mAh g?1 at 0.1 A g?1 after 50 cycles (474.8 mAh g?1 at 1 A g?1 after 800 cycles, 394.5 mAh g?1 at 2 A g?1 after 2000 cycles). Importantly, a specific capacity of 288.5 mAh g?1 remains after more than 5000 cycles. The superior electrochemical performance of the S and N co-doped electrode is attributed to the proven structure and stability of the carbon matrix alleviating the volume changes of Sb during the process of lithium intercalation and extraction. The alloying/de-alloying reactions of the S@Sb@N-CNFs composite in the first charging/discharging process were systematically investigated by ex-situ XRD. This strategy of S and N co-doped carbon matrix could establish Sb-based materials as potential high-performance anodes for LIBs.
查看更多>>摘要：? 2022 Elsevier B.V.In this study, we report reduced graphene oxide wrapped Fe3O4@TiO2 yolk–shell nanostructures (G-Fe3O4@TiO2) as a magnetic recyclable photocatalytic antibacterial agent for medical wastewater treatment. The yolk–shell structure with a magnetic oxide core was synthesized using a template-assisted route and graphene wrapping was added using the one-step method. The obtained samples were characterized by TEM, XRD, XPS, FTIR, Raman and BET analysis. Owing to the photocatalysis property, TiO2 exhibits certain antibacterial effect by generating reactive oxygen species (ROS). As an excellent conductor, Fe3O4 improves the photocatalytic performance of TiO2 after forming a yolk–shell structure. Moreover, the synergistic effect of Fe3O4 magnetism and graphene adsorption ensure bacteria removal under external magnetic field. Graphene inhibits the recombination of photogenerated electron–hole pairs, maximizing the bactericidal activity of the material. With the dual functions of photocatalytic bactericidal and magnetic targeting to separate bacteria, the removal percentage of Staphylococcus aureus (S. aureus) cocultured with G-Fe3O4@TiO2 reached up to 99.9% in 4 h exposure to visible light and external magnetic field, higher than 61% in Escherichia coli (E. coli). Therefore, G-Fe3O4@TiO2 could effectively remove typical bacteria on the premise of biosafety, which provided an ideal recyclable material for medical wastewater treatment.
查看更多>>摘要：? 2022 Elsevier B.V.Here a novel composite material that is described by the MnFe2O4 with spinel structure in-situ grown on the biomass-derived amorphous porous carbon (PC@MFO) is proposed as a cathode material for aqueous zinc-ion batteries (AZIBs). This electrode has an excellent initial discharge capacity of 168 mA h g?1 at 0.3 A g?1 and superior cycle stability with capacity retention rate of 92% over 900 cycles even at a high rate of 1 A g?1. The excellent charge/discharge performance of PC@MFO electrode is attributed to some beneficial synergistic effects including increasing good electrode conductivity and high ion transmission speed and more reactive points and avoiding the rapid collapse of the structure of the MnFe2O4 electrode produced by the introduction of mesoporous carbon, which promotes and stabilizes charge/discharge reaction of multivalent redox (Mn2+/Mn4+, Fe2+/Fe3+). The rapid electrochemical kinetic behavior of the PC@MFO electrode is also analyzed by cyclic voltammetry, where the kinetic process of electrochemical reaction involving the diffusion control faraday process and capacitance control behavior is revealed and the capacitance contribution rate of about 88.19% is attained. Moreover, the galvanostatic intermittent titration technique (GITT) also explains that this PC@MFO electrode has a high Zn2+ ion diffusion capacity and the diffusion coefficient can reach 10?14~10?10 cm2 s?1. In addition, the reaction mechanism and structural evolution of this electrode is also studied by ex-situ X-ray photoelectron spectroscopy (XPS) and X-ray diffraction test (XRD) from different cycle stages. XPS and XRD reveal the strong deintercalation ability of Zn2+ ions in the highly stable MFO which grows in biomass-derived porous carbon. The present result implies that such a PC@MFO composite material could be a promising cathode material for AZIBs.
查看更多>>摘要：? 2022 Elsevier B.V.Phase transition and defect relaxation behavior of a Fe-7Mn-0.1C medium manganese steel have been systematically studied mainly by using internal friction (IF) technique. From temperature-dependent IF curves in both heating and cooling processes, two relaxation IF peaks (the P1 located at ~ 200 °C on heating and the P2 at ~ 550 °C on cooling) and two phase transition IF peaks (the Ptr1 located at ~ 670 °C on heating and the Ptr2 at ~ 300 °C on cooling) were observed. The P1 peak disappears when the cementite (θ) particles and/or retained austenite (γR) exist in the microstructure, and is associated with the Snoek-Kê-K?ster relaxation (SKK relaxation). The P2 peak is suggested to be originated from grain boundary relaxation in austenite (γ). The formation mechanisms of the Ptr1 and the Ptr2 come from reverse austenitic transformation (RAT) and martensitic transformation (MT), respectively. In addition, the apparent asymmetry of the Ptr1, the variation of peak height, the difference between the Ptr1 and Ptr2 peaks, and the effect of IF studies on the mechanical properties are discussed in detail in the present work. These results provide a valuable reference for the design of high-performance medium Mn steels.
查看更多>>摘要：? 2022 Elsevier B.V.To reduce the risk of implant failure caused by “stress shielding” and bacterial infection, a porous Cu-bearing Ti-based BMG with high porosity (48.5%), hierarchical holes ranging from 0 to 600 μm in diameter and mechanical characteristics (162 MPa and 22.8 GPa) close to bone tissue was developed by a space holder method via SPS. With the aid of the space holder's size effect, the porosity and strength of the BMG have been further improved under the low Young's modulus without triggering the “stress shielding”. Furthermore, the addition of porous structures increases the rate of Cu ion release and significantly improves the antibacterial activity of the porous BMG without destroying biocompatibility. Taken together, the porous Ti-based BMG shows great potential as an ideal substitute for natural bone.
查看更多>>摘要：? 2022 Elsevier B.V.In this paper, pure and silver doped (3% and 5%) α-Fe2O3 semiconductor nanoparticles were synthesized with co-precipitation from Fe2+, Fe3+ and Ag+-(doped samples) containing salts and subsequent thermal annealing at 400 °C of the precipitate. The structural, optical (absorption and emission), and surface electronic properties of α-Fe2O3 nanoparticles and the effect of silver doping were characterized by powder x-ray diffraction, Raman spectroscopy, diffuse reflectance spectroscopy, Fourier transform infrared spectroscopy, photoluminescence and x-ray photoelectron spectroscopy. Powder x-ray diffraction confirms the synthesis of pure alpha phase and mixed phases of iron oxide for undoped and Ag doped samples, respectively. The crystallite size and structural parameters were estimated with Debye Scherer and Williamson-Hall methods. The bandgap of iron oxide semiconductor nanoparticle samples was calculated by Tauc's plot, showing the marginal increase in the bandgap with Ag content. To investigate the effect of Ag doping in the recombination rate of photogenerated charge-carrier, room temperature photoluminescence spectra of the nanoparticles were recorded at the excitation wavelength of 450 nm. Vibrational spectroscopy was utilized to find the chemical structure changes of iron oxide nanoparticles on Ag doping. Also, the dye degradation efficiency which includes surface adsorption and photocatalysis of dye with the iron oxide nanocatalysts is improved with Ag doping.
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