查看更多>>摘要：? 2022 Elsevier B.V.Here we report the development of a bifunctional magnetic composite that induces magnetic hyperthermia and shows stable paramagnetic defects after the irradiation with X-ray source. The composite is formed by Zn0.16Fe2.84O4 nanoparticles of 18 (3) nm of diameter embedded in a micrometric carbonated hydroxyapatite matrix. As the magnetic nanoparticles are fixed in the matrix, their magnetic properties were adjusted by the size and composition in order to induce local heating by magnetic losses in presence of an AC magnetic field due to the Néel relaxation mechanism. This behavior was confirmed by measuring the Specific Power Absorption (SPA) of 0.1 wt% of magnetic nanoparticles dispersed in media with different viscosity as chloroform (η = 0.56 cP) and butter oil (η = 174 cP) obtaining ~111(15) W/g in both cases. Consistently, the magnetic hydroxyapatite composite presents a comparable SPA= 126(19) W/g value. On the other hand, the carbonated hydroxyapatite and the magnetic carbonated hydroxyapatite composite were subjected to X-ray radiation with an equivalent dose of 3 kGy and the generated paramagnetic defects were evaluated by electron paramagnetic resonance spectroscopy. It was observed that the CO2? radical is the main defect produced by the irradiation, and its concentration stabilized after a month. These results confirm the potential of this composite to act as a local nanoheater and as a sensor of ionizing radiation, showing interesting possibilities to be used in studies of nanomedicine where the combination of magnetic hyperthermia and radiotherapy is proposed for oncological treatments.
查看更多>>摘要：? 2022 Elsevier B.V.Coating soft magnetic powders by an insulation layer is an effective way to improve the high-frequency performance of soft magnetic powder cores. The quality of insulation coating is highly dependent of the coating materials and the coating method. In the present work, a commercial amorphous powder (Fe73Si11B11C3Cr2) was primarily coated by a PDA/PEI layer by a co-deposition method in alkaline solution. A thick PDA/PEI layer with good homogeneity was co-deposited on the surface of amorphous soft magnetic powders. The high frequency core loss of magnetic powder cores was reduced by up to ~ 44 % at the magnetic induction of 0.1 T and the frequency of 100 kHz by primarily coating the amorphous powders by PDA/PEI. Microscopic images showed that the PDA/PEI coating layer on the amorphous powders does not peel off while being compressed. These results indicates that PDA/PEI insulation coating is a coating method which can effectively improve the comprehensive magnetic properties of magnetic powder cores.
查看更多>>摘要：? 2022 Elsevier B.V.Magnetic refrigeration is an energy-efficient, sustainable, environmentally-friendly alternative to the conventional vapor-compression cooling technology. There are several magnetic refrigerator device designs in existence today that are predicted to be highly energy-efficient, on condition that suitable working materials can be developed. This challenge in manufacturing magnetocaloric devices is unresolved, mainly due to issues related to shaping the mostly brittle magnetocaloric alloys into thin-walled channeled regenerator structures to facilitate efficient heat transfer between the solid refrigerant and the heat exchange fluid in an active magnetic regenerator (AMR) cooling device. To address this challenge, a novel extrusion-based additive manufacturing (AM) method has been developed to 3D print microchanneled magnetocaloric structures. The printing ink consists of magnetocaloric powders, a polymer binder, and multiple solvents to achieve desirable shear-thinning property, which is critical for a robust printing process. Acting as a sacrificial binding agent for the magnetic powders, the polymer binder holds the 3D printed structures in place and is removed subsequently using a two-step heat-treatment process. To demonstrate the effectiveness of the fabrication process, spatially designed microchannels with minimum dimensions of 150 μm were achieved using nanoscaled La0.6Ca0.4MnO3 powders (diameter~10 nm). Results indicate that the crystallographic properties and magnetofunctional response of the sintered 3D printed samples are comparable to that of the precursor powders. Overall, this study provides a promising route for realizing low-cost magnetic regenerators, thus potentially eliminating one of the main barriers to the commercialization of magnetic cooling technology.
查看更多>>摘要：? 2022 Elsevier B.V.A nitrogen-doped carbon-based catalyst (Fe-C-CG) to oxygen reduction reaction (ORR) is synthesized by pyrolyzing a precursor from coffee grounds, iron chloride and commercial carbon black in ammonia atmosphere. The coffee grounds are pyrolyzed to carbon particles with diameters about 20 nm with the facilitation of carbon black. The carbon nanoparticles show higher reactive activity with ammonia to achieve the doping of nitrogen atoms to carbon with 3.33 at% of content in Fe-C-CG, which is greater than 0.47 at% in the product from commercial carbon black (Fe-C). Resultantly, the Fe-C-CG exhibits high ORR activity with 0.87 V of half wave potential and 5.48 mA cm?2 of limited diffusion current, which highly surpass the 0.71 V, 4.19 mA cm?2 for Fe-C, and are comparable with 0.86 V and 4.52 mA cm?2 for Pt/C catalyst, respectively. The Zn-air battery assembled with Fe-C-CG delivers 142 mW cm?2 of maximum power density and 774 mAh g?1Zn of specific capacity, and can stably work at 1.212–1.257 V of discharge voltage at 10 mA cm?2. This work provides a strategy to prepare a nonprecious metal and nitrogen doped carbon catalyst to ORR by using biomass as the basic material.
查看更多>>摘要：? 2022 Elsevier B.V.For transition metal oxyhydroxides, morphology modification and ion doping are widely used strategies for improving the performance of water catalytic oxidation. However, how to distinguish the contribution of different factors to the oxygen evolution reaction (OER) performance is still a serious challenge. In this study, Al ions can control the morphology of CoOOH in cycle of nanosphere-nanosheet-nanosphere, and Ce-doping can significantly improve the OER activity of CoOOH, with an overpotential of 263 mV@50 mA cm?2 and low Tafel slope of 53.74 mV dec?1. In order to explain the above interesting experimental phenomena, detailed characterization has been carried out, such as high-resolution transmission electron microscopy (HRTEM) and electrochemical tests. At the same time, the mechanism of OER performance improvement was discussed based on electrochemical testing and density functional theory (DFT) calculations. Subsequently, the OER activities of different reactive sites, such as Al, Co, Ce, and oxygen vacancies (Ov), have been compared. As the main active center of OER, Ce ion has a minimum potential barrier of 1.71 eV. The results show that the adjustment of the adsorption intensity of the oxygen-containing species by Ce ions dominants the potential-determining step. Meanwhile, the synergistic effect of Ce and Co has also been confirmed based on the d-band theory.
查看更多>>摘要：? 2022 Elsevier B.V.In this work, core CdTe, core-shell CdTe/CdSe and alloy CdTeSe QDs are synthesized by aqueous solvent. TEM visually shows the rod-shaped core-shell structure with a transverse to longitudinal ratio of 6.5 and the ellipsoidal alloy structure with different crystal planes competing for growth. The XRD and Raman spectra of the three QDs illustrate the characteristics of the internal lattice structure. With the increase of reaction time, CdTe emission maximum (EM) shows a red shift of 84 nm. Stokes shift changes little, and full width half maximum (FWHM) increases slightly. Compared with the CdTe, the red shift of CdTe/CdSe EM is slowly first and then faster, with a total shift of 125 nm. Stokes shift increases obviously. The initial FWHM is larger than CdTe and the widening speed is gradually accelerated. The initial EM of CdTeSe is red shifted compared with CdTe, and the total red shift of EM is 72 nm. Stokes shift increases obviously. The initial FWHM is significantly wider than CdTe. FWHM first decreases and then increases with reaction time. CdTe shows obvious band edge exciton absorbance of photoluminescence excitation (PLE) spectrum between 356 nm and 400 nm. CdTe/CdSe shows double band edge exciton absorption at 354–373 nm and 401–436 nm due to wave function separated of core-shell structure. The PLE spectrum of CdTeSe shows an obvious upward trend at 306–373 nm due to high energy level nonradiation. The average lifetime of CdTe/CdSe increases by 53 ns compared with CdTe due to the spatially separated electrons and holes. The defect state of CdTeSe increases the proportion of fast delay, which is 2 ns shorter than the average lifetime of CdTe. The transition mechanism of core-shell indirect band gap and alloy direct band gap is explained according to the valence bands of each element shown by XPS and the simulation of energy band density of states. The thickness shell and the doping elements can be adjusted to provide rich variation in the optical properties. This provides a more definite direction for the applications of cadmium chalcogenide in the fields of photoelectric devices and biology.
查看更多>>摘要：? 2022Metal-organic frameworks (MOFs) have attracted extensive attention as electrode material for supercapacitor in view of their rich active sites and excellent chemical compatibility. However, the insufficient conductivity and easy agglomeration make the directly use of MOFs show impoverished electrochemical performance. Thus, constructing unique nanostructured electrode materials of MOFs or their derivatives remains a great challenge. Here, the ZIF-67-derived CoSe2/Ni3Se4 nanosheets anchored vertically on the MXene nanosheets substrate, effectively alleviating the agglomeration of CoSe2/Ni3Se4 nanosheets. Meanwhile, the introduction of highly conductive MXene enhances the holistic conductivity, and in turn prevents the restacking of MXene flakes. Furthermore, the close combination between CoSe2/Ni3Se4 nanosheets and MXene nanosheets promotes faster charge transfer rate and improves the durability of the structure. Consequently, as an electrode materials for supercapacitors, the honeycomb-like MXene@CoSe2/Ni3Se4 achieves a high specific capacitance (283 mAh g?1 at 1 A g?1) and an outstanding capacitance retention rate with 80% after 5000 cycles. The design strategy proposed by this work provides a novel method for developing high-performance two-dimensional nanostructured electrode materials.
查看更多>>摘要：? 2022 Elsevier B.V.Recently, Al2O3 has been demonstrated to be an effective material type for perovskite photoelectric device performance improvement. It is therefore essential to investigate the interfacial electronic characteristics and the energy-level diagrams of perovskite/Al2O3 heterojunctions in depth. In this research, we fabricated an MAPbBr3 microcrystal/Al2O3 film heterojunction and determined the band offset by performing X-ray photoelectron spectroscopy measurements. The resulting valence band offset of ΔEv = 0.87 ± 0.01 eV and the conduction band offset of ΔEc = 3.03 ± 0.01 eV indicated occurrence of a type-I band alignment at the MAPbBr3/Al2O3 heterointerface. The carrier confinement effect was reflected in the photoluminescence spectra obtained for the heterojunction sample. This work will be valuable for optimization of the energy level alignment of perovskite/metallic oxide heterojunctions during the design of photoelectric devices.
查看更多>>摘要：? 2022 Elsevier B.V.Pure and vanadium (V) doped ZnO nanoparticles (NPs) were successfully synthesized via a modified sol-gel method. The wurtzite crystal structure of ZnO remained intact with the vanadium doping concentrations under the present synthesis environment as confirmed by an array of advanced analytical techniques; such as Rietveld refined X-ray diffraction (XRD) pattern, as well as bond valence sum (BVS) analysis. SEM and TEM techniques were used to examine the morphology of the samples. UV-Vis-NIR spectra showed an absorption band in the UV range with reduction in the band gap from 3.23 eV to 3.20 eV when V content increases. Photoluminescence (PL) shows that doping with V causes the creation of some defects in the band gap of ZnO. The energy position of the obtained PL emission introduces a blue shift when the measurement temperature increases. The M-T curve is successfully fitted using both three dimensional (3D) spin wave model and Curie-Weiss law which attests to the mixed state existence of ferromagnetic (FM) and paramagnetic (PM) phases. The electron paramagnetic resonance (EPR) analysis supports the XRD results and provides evidence of oxygen vacancies (VO). Magnetic interaction is quantitatively studied and explained by polaronic percolation of bound magnetic polarons (BMP) produced by VO defects.
查看更多>>摘要：? 2022According to the well-known Hall-Petch theory, grains refinement is one of the most effective routes to improve the mechanical properties of Mg. Understanding the Hall-Petch relationship of Mg can provide guidance for improving the mechanical strength of Mg through grain refinement. In this study, pure Mg samples with average grain sizes ranging from 9.8 μm to 31 nm were prepared, and the grain size dependence of the deformation microstructure, dislocation density, strain rate sensitivity, activation volume and mechanical properties were investigated. Moreover, the Hall-Petch relationship of pure Mg and the mechanism that caused the transformation of the Hall-Petch relationship were explored. It is found that there are three Hall-Petch relationships for pure Mg: positive correlation with large stress concentration factor and the dominated deformation mechanism of twin (>2.4 μm), positive correlation with small stress concentration factor and the dominated deformation mechanism of dislocation (between 2.4 μm and 93 nm) and an inverse correlation with negative stress concentration factor and the dominated deformation mechanism of GB motion (<93 nm).
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