查看更多>>摘要：In this study, a three-component nanocatalyst consisting of cobalt oxide (Co3O4), nickel sulfide (Ni3S4), and reduced graphene oxide (rGO) is synthesized by the hydrothermal method. Physical characterization confirmed the successful synthesis of these nanocatalysts. In this study, Co3O4- Ni3S4 (CN) and Co3O4- Ni3S4 -rGO (CNR) is reported for application in alcohol fuel cells for the first time. Electrochemical investigations show that both nanocatalysts have relatively good efficiencies in the methanol and ethanol electrooxidation process. Adding rGO to the CN structure causes the nanocatalyst to gain a higher specific surface area and increase its electrical conductivity. CNR showed 96% stability in the methanol oxidation reaction (MOR) process and 94% stability in the ethanol oxidation reaction (EOR) process. The electron transfer kinetics are investigated in the MOR and EOR processes. CNR indicates the exchange current of 8.61 × 10?7 mA/cm2 in MOR and 1.87 × 10?7 mA/cm2 in EOR that is higher than the exchange current of CN, which proves a clear reason for the excellent effect of adding rGO to the nanocatalyst. In this work, the synergistic effect of Co3O4 as metal oxide and Ni3S4 as metal sulfide, and rGO as a conductive substrate is investigated. Finally, CN and CNR nanocatalysts introduce as stable and inexpensive catalysts in MOR and EOR processes for use in alcoholic fuel cells.
查看更多>>摘要：Constructing metal-oxide-based composites with the multiple valence-states and redox-couples has been proved as an effective strategy to enhance the performance of non-enzymatic glucose sensing. Herein, we report a mild and efficient method to prepare multiple-valent copper-based oxide composite nanofibers (CuxO CNFs) through introducing the TiO2 photosensitizer into the CuO NFs for actuating the localized phase transition from tenorite CuO (Cu2+) to cuprite Cu2O (Cu+) upon UV–visible light irradiation. The sensitivity of the obtained TiO2/Cu2O/CuO CNFs for glucose sensing (0–2 mM) could be enhanced by 1.12–1.31 times as compared to that of the TiO2/CuO CNFs. The enhanced sensitivity is dependent on the TiO2-content in the primal TiO2/CuO CNFs. When introducing 5.0 at.% of TiO2 into the CuO nanofibers, the photoinduced phase-transition process could result in the formation of optimal TiO2/Cu2O/CuO CNFs with the component ratio of Cu2O to CuO at 0.46:1. This TiO2/Cu2O/CuO CNFs (2074.7 μA·mM?1·cm?2; 0.25 μM) exhibited nearly 1.32-fold improvement on the sensitivity and 3.0-fold enhancement on the detection limit as compared to the corresponding values of the pure CuO electrospun nanofibers (1581 μA·mM?1·cm?2; 0.75 μM). After the continuous measurements for 14 days, the sensitivity of the optimal sample could maintain 89.4% of its initial value. Notably, its sensitivity could be further recovered to 97.4% of the initial value after UV–visible light irradiation for 1 h.
查看更多>>摘要：Inspired by animal blood as a biowaste rich in biological enzymes with molecular Fe–N centers, Fe doped g-C3N4 (FCN) photocatalyst was successfully prepared by one-step thermal polymerization with pig blood and melamine to produce an efficient photocatalyst with Fe–N active sites for photo-Fenton degradation of tetracycline (TC) under visible light irradiation. The photocatalytic TC degradation results exhibited that FCN-1 sample possesses optimal photocatalytic degradation activity for TC (50 mg/L) in the presence of H2O2 system and a broad range over pH adaptation. The optimum photo-Fenton degradation activities of TC (50 mg/L) under visible-light irradiation for FCN-1/H2O2 system reach to 84.9% and 0.034 min?1 within 120 min under acidic conditions (pH = 3.1) and to 85% and 0.093 min?1 (first 20 min) in alkaline environment. Enhanced photocatalytic activity is mainly attributed to the positive roles of Fe-N bonds in FCN during the photo-Fenton process as follows: (i) improving the absorbance and separation efficiency in electron-hole pairs; (ii) accelerating the catalytic cycles between Fe2+/Fe3+ to produce more ?OH in acidic condition; (iii) serving as active sites to boost the production of more photon-generated carriers in alkaline environment. Our work overcame the defect of low photocatalytic activity in photo-Fenton process under alkaline conditions, and provided a simple design idea for the low-cost synthesis of visible-light-driven photocatalyst with high efficiency applied to photo-Fenton reaction.
查看更多>>摘要：White-emitting Na5Y1-yLny(MoO4)4:Dy3+ (Ln = La, Gd) phosphors were synthesized by a sol-combustion method. The effects of Ln3+ partial introduction on the structure and photoluminescence of Na5Y1-yLny(MoO4)4:Dy3+ (Ln = La, Gd) phosphors were studied. The X-ray diffraction and chemical composition results verified the successful introduction of Dy3+, La3+ and Gd3+ into the Na5Y(MoO4)4 lattice. Under the excitation of ultraviolet at 352 nm, the as-prepared phosphors showed a white emission with characteristic emission peaks at 577 nm (yellow) and 485 nm (blue), corresponding to the 4F9/2→6H13/2 and 4F9/2→6H15/2 transitions of Dy3+ ions, respectively. By substituting Y3+ ion with La3+ and Gd3+, the photoluminescence intensity of Na5Y(MoO4)4:Dy3+ sample was obviously enhanced due to the crystal field effect surrounding the luminescence center Dy3+. The chromaticity coordinates of all phosphors were located at the white light region, and the substitution of La3+ or Gd3+ could realize a higher color rendering index of white emission. Therefore, the as-prepared white-emitting Na5Y0.90La0.06(MoO4)4:0.04Dy3+ and Na5Y0.88Gd0.08(MoO4)4:0.04Dy3+ phosphors could be used as single-component phosphor for w-LEDs application.
查看更多>>摘要：Novel (Zr-Hf-Nb-Ta)C-xCo (x = 5, 10, 20 wt%) high entropy cermets (HEC4-Co) were successfully synthesized and densified using a simple two-step high temperature process. The high entropy carbide was first synthesized by solid state reaction at 1800 ℃ of a mixed powder compact. The reacted and partially sintered compact was then pressureless melt infiltrated with cobalt at 1600 ℃. The results show that degassing of the powders in the first step, before the infiltration step, significantly reduced the defects in the cermets. The HEC4-Co cermets consisted of a single-phase high entropy carbide (Zr-Hf-Nb-Ta)C in a single-phase cobalt matrix. The maximum hardness was achieved for a Co content of 10 wt%, 15.38 GPa (1569HV1), while the cermet with a Co content of 20 wt% had the highest indentation crack resistance, 9.72 MPa m1/2.
查看更多>>摘要：Transparent oxyfluoride glass ceramics (GCs) comprised of a uniform oxide glass phase and a well-distributed fluoride crystal phase are regarded as suitable optical gain materials because of the combination of facile fabricability of glass and low phonon energy of nanocrystals. Here, oxyfluoride GCs containing NaYF4: Er3+/Ho3+/Dy3+ nanocrystals were controllably prepared. Due to the preferential incorporation of rare-earth ions into NaYF4 nanocrystals with low phonon energy and the efficient energy transfer between active ions, enhanced and broadband mid-infrared (MIR) emission at 2.5–3.3 μm was obtained from the GCs, which was nearly unobserved in precursor glass (PG) because of the high phonon energy of glass matrix. Compared with Er3+ singly-doped sample, the full width at half maximum (FWHM) is more than 3 times broader in Er3+/Ho3+/Dy3+ triply-doped sample. Furthermore, by the match of the refractive index of glass with NaYF4 nanocrystal, transparent GCs with average crystal size of 80 nm and high transmittance over 80% were achieved simultaneously. The desirable optical properties endow the GCs with potential applications in MIR broadband tunable lasers.
查看更多>>摘要：The worldwide application of lithium-sulfur (Li–S) batteries is severely hampered by the low utilization of sulfur, rapid capacity fading, and poor rate performance. Herein, an efficient functional V2CTx/CNT framework is constructed and employed as an anchoring-catalysis modified layer of the separator to improve the performance of Li–S batteries. CNT acts as the foundation of the structure due to its impressive conductivity, continuous framework, and satisfactory mechanical stability, which provides a conductive surface and prevents the structure from collapsing during cycling progress as well. While V2CTx nanoribbons, strengthen the chemical anchoring to lithium polysulfides (LiPSs), facilitate the further conversions of the LiPSs in the liquid phase, and induce the Li2S homogeneous nucleation, restraining the shuttle effect and accelerating redox reactions. Benefiting from the anchoring-catalysis effect, the Li–S battery with V2CTx/CNT separator delivers an outstanding rate performance of 893.6 mAh g?1 at 2 C. The average capacity decay per cycle within 1000 cycles at 1 C is as low as 0.047%. This work provides a rewarding view to develop the practical application of Li–S batteries with a functional separator.
查看更多>>摘要：SrFe12O19 (M-type hexaferrite) and NiFe2O4 (spinel) nano ferrite powders were synthesized in the presence of Calotropis gigantea (crown) flowers extract separately. SrFe12O19/NiFe2O4 nanocomposites were prepared in the presence of crown flowers extract and the effect of different weight ratios (M:S – 9:1, 8:2, 7:3, 6:4, 5:5) on structural, microstructural, magnetic, electrical transport, and dielectric properties were studied. The average crystallite size of nanocomposites was found from 25 nm to 44 nm. In addition, it was observed that the crystallite size of the M-phase decreased when the spinel phase increased. XRD analysis depicts the presence of both M and S phases in composites. The M-H loops analysis of SrFe12O19/NiFe2O4 composites indicates that the coercivity (3181–326 Oe), and saturation magnetization (57.5 Am2/kg. - 40 Am2/kg.) decreased when the spinel phase amount increased. Nanocomposites with weight ratios 9:1, 8:2, 7:3, 6:4 belong to a hard ferrite, while 5:5 shows soft magnetic nature. However, prepared composites possess a multi-domain structure. The weak exchange coupling interactions were found in composites 9:1 and 8:2, whereas the partial exchange coupling interactions were observed in composites 7:3, 6:4, and perfect exchange coupling interaction was noticed in 5:5.
查看更多>>摘要：With the rapid development of telecommunication technologies and highly integrated electronic devices, researchers show great interest in nanocrystalline soft magnetic thin films with unique characteristics for microwave applications. An important direction of the current research in this field is the study of high-frequency magnetization dynamics that directly depends on the damping processes in a magnetic medium. This paper reports on the effect of sharp broadening and shift of the ferromagnetic resonance (FMR) line revealed experimentally in a 40-nm-thick nanocrystalline permalloy (Fe20Ni80) thin film at a frequency of about 5 GHz. The effect arises only in films with crystallite size exceeding some critical value Dcr. The micromagnetic simulation demonstrates that exchange and dipolar interactions between randomly oriented crystallites form in the film a quasiperiodic magnetic structure with a characteristic wavelength in the range from 36 nm to 3.3 μm. An analysis of the two-magnon scattering model and simulation results shows that the formed magnetic structure provides the energy transfer from uniform magnetization oscillations (uniform FMR) to spin waves, which results in an additional energy dissipation channel and, consequently, sharp FMR line broadening. A theoretical estimate of the critical crystallite size Dcr based on this model yields a value of ~14.3 nm for 40-nm-thick Fe20Ni80 films.
查看更多>>摘要：A novel method of “fully covered + friction stir welding + accumulative roll bonding” was developed to prepare an Al/Mg/Al laminated composite material (LCM). This work presents a rolling simulation of an Al/Mg/Al LCM using the DEFORM software and processing maps to show the hot rolling mechanism. The single pass reduction should be set at approximately 3–4 mm by finite element simulation. The edge damage value of the core Mg alloy plate in the Al/Mg/Al LCM decreased with the increasing hot rolling temperatures. The optimum process parameters were obtained by processing maps for deformation temperatures from 250 °C to 300 °C and 350–400 °C in the strain rate range of 0.01 s?1 to 0.1 s?1. The hot rolling temperature for the 11.5 mm-thick Al/Mg/Al LCM should be controlled at 400 °C, and the single pass processing rate should be selected in the range of 20–40%. With each increase in heat treatment temperature and time, the compound gradually increased, and the thickness of the transition layer gradually increased at the Mg/Al interface. The growth kinetic model formulas of the interface layer for the 1060/AZ31/1060 LCM under different rolling strain fields were obtained, which could have been predicted by the interface layer thickness at different rolling reduction rates and heat treatments.
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Elsevier