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排序方式: 共有639条查询结果,搜索用时 15 毫秒
71.
《Ceramics International》2023,49(20):33099-33110
In this study, spinel Ni0.5Zn0.5Fe2O4 doped with transition metal ions as well as rare-earth ions Ni0.4Zn0.4M′0.2Fe2O4 (M′ = Cu, Dy, Gd and Lu) and M″0.5Zn0.5Fe2O4 (M″ = Ni, Mn and Co) are developed using the sol-gel auto-combustion route, and the role of substitution on electromagnetic properties is investigated. The powder X-ray diffraction accompanied by Rietveld refinement signifies a single-phase spinel ferrite that belongs to Fd-3m space group for all the compositions. Rietveld refinement confirms that doped Cu2+, Dy3+, Gd3+ and Lu3+ ions are at random distribution between spinel tetrahedral and spinel octahedral sites against their preferential occupancy. The saturation magnetisation (MS) of Ni0.5Zn0.5Fe2O4 (MS = 50.5 emu/g) increased with partial doping showing MS = 60.08 emu/g for transition-metal doped Ni0.4Zn0.4Cu0.2Fe2O4 and MS = 109.7 emu/g for rare-earth doped Ni0.4Zn0.4Dy0.2Fe2O4, which was the highest among all the doped compositions. Doping enhances the dielectric permittivity of Ni0.5Zn0.5Fe2O4 from 4.2 to 6.5 for Ni0.4Zn0.4Cu0.2Fe2O4 and 7.7 for Ni0.4Zn0.4Dy0.2Fe2O4. Further, the reflection coefficient (RL) of all the doped compositions of Ni0.4Zn0.4M′0.2Fe2O4 (M′ = Cu, Dy, Gd and Lu) was less than −8 dB (85% absorption) throughout the frequency band of 8–12 GHz with an optimum material thickness of 3.5 mm. Transition metal ion doped Ni0.4Zn0.4Cu0.2Fe2O4 resulted in further improvement of its absorption characteristics of the incident EM waves with reflection coefficient (RL) less than −10 dB (between 84.15% and 90%) between 10 and 12 GHz at a material thickness of 3.5 mm in the X-band frequency range. 相似文献
72.
《International Journal of Hydrogen Energy》2023,48(15):5755-5763
The electrochemical water splitting into hydrogen and oxygen is the promising way for renewable hydrogen production as a carbon-neutral fuel, along with oxygen as a by-product. Herein, a novel nanoporous CoCu-layered double hydroxide (LDH) bifunctional electrocatalyst is fabricated by the hydrothermal method. The outstanding activity is mainly attributed to the incorporation of Cu2+ that promotes conductivity and enhances the electrochemical properties. As-prepared CoCu-LDH nanostructure works as efficient and stable water-splitting-electrolyzer and produces the voltage of 1.60 V at the current density of 10 mA cm?2, which is better than catalyst based on the combination of commercial IrO2 and Pt/C. Due to high electrocatalytic performance, together with its low cost and natural abundance of LDHs, it is expected that CoCu LDH can act as a candidate catalyst in the commercial alkaline overall water splitting. 相似文献
73.
《International Journal of Hydrogen Energy》2023,48(60):22865-22874
Nanoparticles (NPs) thanks to their unique features such as large surface area, high catalytic activity and intra-cellular electron transfer ability used as an enhancement additive in biohydrogen production. Up to date, inorganic, organic and their mixtures of various NPs were produced from different input sources and synthesis methodology. The NPs properties and cost minimization are the critical factors for the scale up studies of industrial applications. Nevertheless, there have not been any study on the determination of the most efficient and feasible NPs in biohydrogen production for the scaling up the process. In this study, the NPs used for biohydrogen production enhancement over Clostridium sp. by dark fermentation were examined and these studies were evaluated to determine the most effective and feasible NPs using the two-stage TOPSIS method. As a result, iron-containing NPs (hematite, magnetite) were determined as the most effective and economical NPs for increasing the yield. 相似文献
74.
Gan Ye Meng Zheng Qiuli Zhang Jun Zhou Lei Wu Jin Wang 《Small (Weinheim an der Bergstrasse, Germany)》2023,19(38):2301035
Stable platforms of host–guest catalysts are indispensable in the field of heterogeneous catalysis, however, clarifying the specific effect of host remains challenging. Herein, polyoxometalate (POM) is encapsulated in three types of UiO-66(Zr) with different controlled densities of defects by the aperture opening and closing strategy at ambient-temperature. It is found that catalytic activity of POM for oxidative desulfurization (ODS) at room temperature is turned on when encapsulated in the defective UiO-66(Zr), and the sulfur oxidation efficiency shows an obvious increasing trend (from 0.34 to 10.43 mmol g−1 h−1) with the increased concentration of defects in UiO-66(Zr) host. The as-prepared catalyst with the most defective host displays ultrahigh performance which removed 1000 ppm sulfur with exceptionally diluted oxidant at room-temperature within 25 min. The turnover frequency can reach 620.0 h−1 at 30 °C, which surpassed all the reported MOFs based ODS catalysts. A substantial guest/host synergistic effect mediated by the defective sites in UiO-66(Zr) is responsible for the enhancement. Density functional theory calculations reveal that OH/OH2 capped on the open Zr sites of host UiO-66(Zr) can decompose H2O2 to OOH group and enables the formation of WVI-peroxo intermediates that determine the ODS activity. 相似文献
75.
《Carbon》2015
A novel kind of N-doped hierarchically porous carbon materials (HPC-Ns) has been successfully synthesized with hierarchically macro/mesoporous silica as a hard template followed by a simple N-doping procedure using low-cost and nontoxic urea as the nitrogen source. The synthesized HPC-N samples demonstrated extensive three-dimensional (3D) connected macroporosity and partially ordered mesoporosity, extremely large specific surface area, favorable graphitization degree, and high relative content of pyridinic N, which is active to the oxygen reduction reaction (ORR). Due to the combined contributions of the above features, the metal-free HPC-Ns demonstrated excellent performance in ORR with a highly comparable limiting current density but much higher current output stability and resistance towards the fuel crossover effect compared to the commercial Pt/C, as well as the dominant 4 e− reduction mechanism. Thus, it is believed that HPC-N has the potential to be used in polymer electrolyte membrane fuel cells. 相似文献
76.
77.
This review highlights the synthesis, physical properties, and emerging technologies of state-of-the-art segmented copolymers containing amide hydrogen bonding sites. Amide hydrogen bonding plays a crucial role in the physical properties associated with amide-containing segmented copolymers. Amide hard segments are accessible in many different forms from amorphous alkyl amides to crystalline aramids and greatly influence copolymer morphology and mechanical properties. Variations in copolymer structure allow for the fine tuning of physical properties and the ability to predict mechanical performance based upon structural modifications. This review includes various synthetic methods for producing well-defined amide-containing segmented copolymers as well as common applications. Also, the morphological and mechanical properties associated with modifications in copolymer structure are discussed. 相似文献
78.
《Carbon》2015
The synthesis and electrochemical performance of a composite of Co9S8 nanoparticles and amorphous carbon is studied as an anode material for sodium-ion batteries. The Co9S8–carbon composite powder was fabricated through a one-pot spray pyrolysis process using thiourea and polyvinylpyrrolidone as sulfur and carbon sources, respectively. The Co9S8 nanoparticles are entirely covered by an amorphous carbon layer. The initial discharge and charge capacities of the Co9S8–carbon composite powder were 689 and 475 mA h g−1, respectively, at a current density of 0.5 A g−1. The Co9S8–carbon composite powders exhibited a stable cyclability with a reversible capacity of 404 mA h g−1 for the 50th cycle and a superior rate capability compared with bare Co1−xS powder. The improvement of Na-storage performance could be attributed to the small size and entanglement of the Co9S8 nanoparticles within the carbon matrix. 相似文献
79.
80.
《Ceramics International》2015,41(8):9373-9382
The aim of this work was to study the bioactivity of systems based on a clinically tested bioactive glass (BG) particulates (mol%: 4.33 Na2O−30.30 CaO−12.99 MgO−45.45 SiO2−2.60 P2O5−4.33 CaF2) and organic carriers. The cohesiveness of injectable bone graft products is of high relevance when filling complex volumetric bone defects. With this motivation behind, BG particulates with mean sizes within 11−14 μm were mixed in different proportions with glycerol (G) and polyethylene glycol (PEG) as organic carriers and the mixtures were fully injectable exhibiting Newtonian flow behaviors. The apatite forming ability was investigated using X-ray diffraction and field emission scanning electron microscopy under secondary electron mode after immersion of samples in simulated body fluid (SBF) for time durations varying between 12 h and 7 days. The results obtained revealed that in spite of the good adhesion of glycerol and PEG carriers to glass particles during preparation stage, they did not hinder the exposure of bioactive glass particulates to the direct contact with SBF solution. The results confirmed the excellent bioactivity in vitro for all compositions expressed by high biomineralization rates with the formation of crystalline hydroxyapatite being identified by XRD after 12 h of immersion in SBF solution. 相似文献