查看更多>>摘要：The cobalt-based absorbing materials with core-shell structure have been widely investigated and developed in the microwave absorption territory, but their shortcomings such as relatively high density and weak dielectric loss limit their practical applications. In this work, taking the modification of microstructure and coating material as the cut-in point, we fabricated the Co@void@polypyrrole (PPy) nanocomposites (NCs) with yolk-shell structure and conductive polymer PPy coating via an integration of hydrogen plasma-metal reaction (HPMR), in-situ SiO2/PPy coating and SiO2-etching approaches. The Co@void@PPy with a PPy layer thickness of 7.6 nm exhibits the optimal microwave absorption performance. The minimum reflection loss (RL) value comes up to ?28.4 dB at 1.4 mm, and the corresponding effective absorption bandwidth (EAB, RL≤ ?10 dB) is 5.7 GHz. The optimal EAB is 7.2 GHz with a thickness of only 1.6 mm, where the RLmin is ?23.4 dB. Such excellent dielectric loss property and attenuation ability is closely related to the PPy coating and the yolk-shell structure, which give rise to abundant interfaces between PPy and Co core and greatly promote multiple scattering and interface polarization. Accordingly, the yolk-shell structured Co@void@PPy NCs can be a competent candidate in the region of high-performance absorbers.
查看更多>>摘要：The novel A-doped Co3O2BO3 (A4+=Zr, Hf) ludwigites have been synthetized by the first time and investigated by X-ray diffraction, magnetization and specific heat experiments. The non-magnetic ions place mainly at sites 4 of the structure. This doping strengthens the magnetic interactions rising the magnetic transition temperatures from 42 K, for the undoped compound, to 71 K and 72 K for Zr and Hf, respectively. These magnetic transition temperature are ~ 10 K below that shown by the Sn4+-doped Co3O2BO3. As expected, all these isostructural and isovalent compounds exhibit the same magnetic features. However, low temperature specific heat experiments and magnetization curves with typical metamagnetic behavior revealed that doping with the non-magnetic open-shell ions d0 Zr and Hf preserves the two-dimensional antiferromagnetic character of the parent ludwigite Co3O2BO3 while the closed-shell d10 Sn leads to a three-dimensional magnetism. The experimental results are compatible with an antiferromagnetic structure with a ferromagnetic component for these two compounds. The difference in TN and dimensionality of these compounds are related to super-superexchange (SSE) interaction between two Co2+ mediated by the non-magnetic ion A4+. The non-magnetic closed-shell d10 ion turned out to be more effective in mediating SSE interactions between 1?2?3 magnetic layers.
查看更多>>摘要：The photothermal catalysis has attracted much attention as a new catalytic method. Utilization of self-generated heat instead of external heating source is an ideal approach for improving the performance of catalysts. Herein, a novel urchin-like hollow TiO2 photothermal nano-catalyst with spatially separated Pt and RuO2 dual cocatalysts combine with carbon layer (denoted as RuO2/TiO2/Pt/C) is reported for catalytic hydrogen evolution under visible light irradiation. The photothermal catalytic performance of the as-prepared catalysts was evaluated in relation to structural characterizations and the thermal effect of the carbon layer. The sandwich nanostructure of carbon layer, Pt NPs and TiO2 layer effectively support and protect Pt NPs from agglomeration and deactivation of Pt active sites. The hot electrons generated from carbon layer can participate in the photocatalytic reaction. Furthermore, the enhanced visible light absorption performance of TiO2 is explained by narrowing the band gap due to a small amount of doping carbon and reducing the penetration-loss of light via constructing the hollow structure. As a result, the synergy between the spatially separated Pt/RuO2 NPs and the thermal effect with carbon layer greatly improve the catalytic performance of the TiO2-based catalyst for hydrogen production under visible light irradiation.
查看更多>>摘要：It is possible to exploit graphene's superior mechanical and thermal properties at the bulk level by reinforcing it in the metal matrix via advanced manufacturing processes. In the present study, the influence of graphene reinforcement on the coefficient of thermal expansion (CTE) and thermal conductivity (TC) of 3D printed graphene/AlSi10Mg composite was evaluated in the temperature range of 25 °C to 500 °C. The composite samples were prepared by conducting ball-milling of graphene (0.1 and 0.2 wt%)-AlSi10Mg powder followed by powder bed fusion (PBF) process. Relative densities of the prepared samples were evaluated by Archimedes' method. A relative density of 99.1% was achieved for 0.1 wt% graphene/AlSi10Mg composite and unreinforced samples, whereas 98.4% was obtained for 0.2 wt% graphene/AlSi10Mg composite sample. Uniform dispersion of graphene in the matrix was achieved through micron-scale melt processing during PBF, which was ensured using Raman spectroscopy. X-ray photoelectron spectroscopy results suggested that graphene is not reacting with the matrix even after laser fusion. The atom probe tomography results further demonstrated the stability of graphene in the matrix. Stable graphene platelets inside the AlSi10Mg matrix were responsible for ~10% reduction in the CTE of the composite owing to the negative CTE of graphene. A slight increment in thermal diffusivity was observed due to a smoother phonon transition at the graphene matrix interface.
查看更多>>摘要：One of the key efficient strategies to optimize the silicon micro-structure and to improve the lithium-storage electrochemical performance is to introduce the metallic phase into silicon matrix to realize the silicon-metal recombination as well as the nanocrystallization of silicon structure. The present research introduced metallic titanium to synthesis TiSi2/Si nanocomposites by the aid of electrolyzing SiO2/TiO2 in molten salt. The reduced nanocomposites exhibited excellent lithiation stability with the initial discharging specific capacity of 2107 mA h/g and the first columbic efficiency of 89.96%. Particularly benefiting from the compositional TiSi2 phase and the structural superiority of silicon nanowires surrounded by the alloyed nanoparticles, the as-obtained anode also delivered a high rate capacity. The major objective of this study is to establish the technology for molten salt electrolytic preparation of TiSi2/Si nanocomposites for lithium-ion batteries and further to offer solutions for modifying the silicon anode materials.
查看更多>>摘要：To improve the visible-light photocatalytic performance of BiOI, it is extremely desired to boost charge transfer and separation. Herein, a novel ternary Au/BiOCl/BiOI photocatalyst with enhanced separation efficiency and prolonged lifetime of photogenerated carrier was successfully in-situ prepared via a facile thermal reduction method. The Au nanoparticles uniformly distributed on BiOI and BiOCl acted as an electron-bridge, which could promote the transfer of electron from BiOI to BiOCl, forming a high-speed spatial electron transfer channel. In addition, BiOCl provided a high-energy-level platform to prolong charge lifetime by receiving high-energy electrons of BiOI to alleviate the relaxation to the valence band and recombination with the holes on the valence band. The synergistic effect of Au and BiOCl largely improved the separation efficiency of BiOI photogenerated carrier, ultimately the photocatalytic performances of Au/BiOCl/BiOI nanocomposites for RhB degradation in static system (97%) and dynamic system (85.52%) and NO removal (65.4%) were enhanced by 1.52, 1.71 and 1.32 times compared to BiOI, respectively. Thus, this work can provide new insights into understanding the important role of electron-bridge in accelerating electron transfer and designing the suitable high-energy-level platform to prolong charge lifetime.
查看更多>>摘要：We report on structural, magnetic properties of Na-doped La0.8Sr0.15Na0.05MnO3 (LSNMO) nanoparticles (NP) with size about 50 nm elaborated via sol-gel route. The chemical composition was verified using the energy dispersive X-ray analysis (EDAX) and by X-ray photoelectron spectroscopy (XPS). Magnetic characterizations demonstrate that LSMNO exhibits a coexistence of interacting superparamagnetic (ISPM) phase with blocking temperature TB = 194 K and a ferromagnetic phase with Curie temperature TC = 255.5 K. At low temperatures, the SPM state undergoes a collective freezing state at Tf = 46 K. the high-temperature regime (well above TC) reveals that NP-LSNMO has a strengthened Griffiths-like phase compared to their bulk counterpart. An itemized investigation of the critical behavior of the material was carried out in the vicinity of TC. The critical exponents [β = 0.546(7), γ = 0.972(6), and δ = 2.94 (5)] were found to be in close agreement with of the mean-field theory. The maximum magnetic entropy change (?ΔSMpk) is about 1.41 Jkg-1 K-1 and the refrigeration capacity (RC) is 288 Jkg-1 for a field change of 5 T at T = 215 K. This magnetocaloric response is reasonably high for nanomaterials and, together with its cost-effectiveness, makes NP LSMNO a potential candidate material for active magnetic refrigerators. Besides, the ISPM properties are desirable for hyperthermia applications. Our findings suggest that the magnetic inhomogeneity and the dipolar interaction between the SPM and FM phases in the range TB<T<TC are crucial factors in determining the magnetic properties of NP-LSNMO.
查看更多>>摘要：The effect of heat treatment of Co-based amorphous microwires at temperatures near the crystallization (Tcr) onset on micromagnetic structure, magnetostriction, and magnetoimpedance (MI) was investigated. As the annealing temperature approaches Tcr, the hysteresis loops abruptly change the shape from almost rectangular to inclined with a small coercivity and remanence magnetization. This behavior is quite unique since even partial crystallization deteriorates soft magnetic properties. The Kerr-microscopy confirmed the formation of a fine circular domain structure and an easy anisotropy direction of a helical type. Both current and furnace annealing with appropriate high temperatures produce similar magnetic transformation. The origin of the formed easy anisotropy is different from that induced by current annealing at temperatures below the Curie temperature and is associated with a change in the magnetostriction constant, which drops from positive to negative values. This could be explained by structural relaxation leading to amorphous phase decomposition at the very initial stage of crystallization. The effect is not specific for the Co-rich alloy composition and was observed in microwires of two compositions: Co71Fe5B11Si10Cr3 and Co66.6Fe4.28B11.51Si14.48Ni1.44Mo1.69 which in the as-prepared state have axial and circumferential anisotropies, respectively. The obtained combination of magnetic anisotropy, magnetostriction and temperature stability leads to useful MI properties, in particular, at Gigahertz frequencies.
查看更多>>摘要：Enhancement of photocatalytic activity of ZnO nanoplates was achieved by loading FeV2O4. The coexistence of FeV2O4 and ZnO in a single crystalline material was ensured by obtaining XRD pattern. XPS confirmed the chemical states present in FeV2O4-ZnO nanocomposites (NCs). The octahedral/tetrahedral M─O bonds presence was indicated in FTIR. High surface area (49.36 m2/g) was observed in NCs. White-light harvesting was facilitated due to the narrow bandgap in NCs (2.41 eV) compared with pure ZnO (3.1 eV). The magnetic property of NCs was validated by VSM analysis. The photocatalytic activity of NCs was 3.6 folds enhanced than pristine counter parts. Dye degradation is primarily carried out by generated ·OH radicals. The photocatalysis performance was almost same even after 5th cycle. The NCs exposure to Escherichia coli and Bacillus subtilis showed enhanced growth inhibition. The magnetically-removable FeV2O4-ZnO NCs can be applied for environmental remediation and antimicrobial application.
查看更多>>摘要：In this study, an efficient heterojunction photocatalyst, g-C3N4/ZnO (CNZn), was successfully produced by coupling graphitic carbon nitride (g-C3N4) with hierarchical zinc oxide nanoparticles (ZnO) using a facile wet-chemical strategy. Electron microscope results showed that CNZn is characterized by a unique three-dimensional flower-like porous architecture. The physicochemical properties of the synthesized photocatalysts were determined by using energy dispersive X-ray spectroscopy, fourier transform infrared spectra and X-ray powder diffractometry. The photocatalytic properties of the prepared catalysts were evaluated based on their photodegradation of methylene blue (MB) under ultraviolet (UV) and solar irradiation. The results indicated that the CNZn composite exhibited superior photocatalytic properties compared with pristine g-C3N4 and ZnO alone, which could be ascribed to the effective establishment of heterojunctions between g-C3N4 and ZnO. It was also found that the catalytic activity of the CNZn composite can be further enhanced by modifying reaction parameters including the illumination source, catalyst dosage and solution pH. Meanwhile, trapping experiments of reactive species suggested that holes and superoxide radicals played a major role in promoting the MB photodegradation. This study could shed light for the construction of high-performing photocatalysts.
NSTL
Elsevier