查看更多>>摘要：? 2022 Elsevier B.V.As a classic two-dimensional material, graphene has attracted worldwide attention in the fields of electromagnetic shielding and microwave absorption. However, the excellent electrical conductivity makes it challenging to achieve impedance matching, which significantly limits its application microwave absorption. Here, we propose a strategy for the modification of graphene by low-temperature oxygen plasma that precisely regulates the electromagnetic parameters of the graphene material by adjusting the plasma irradiation time. This approach controls the electrical conductivity of graphene for impedance matching and creates enriched defects that effectively improve the material permittivity loss capability. Owing to these advantages, the sample (O-MW-rGO-60) irradiated by plasma for 60 min showed excellent microwave absorption properties with a minimum reflection loss of ?54.11 dB at a matched thickness of 1.7 mm and an effective absorption bandwidth of 5.68 GHz at a thin thickness of 2.0 mm. In addition, CST simulation is used as an intelligent design strategy to verify a product's radar wave absorption capability under realistic conditions. The RCS values of the model covered with the O-MW-rGO-60 sample coating are significantly lower than those of the metal substrate, which confirms its excellent microwave absorption properties and provides new insights into the future development of microwave absorbing materials.
查看更多>>摘要：? 2022In this work, type II heterojunctions were constructed by in suit loading of ZnIn2S4 (ZIS) nanosheets onto S-doped g-C3N4 (SCN) nanosheets by a simple hydrothermal synthesis method. The formation of heterojunction induced rapid electron-hole separation, while the introduction of SCN reduced the internal resistance of photogenerated carriers to transfer. When the mass fraction of SCN was 20 %, the best photocatalytic hydrogen production performance was 1.63 mmol g?1 h?1 under visible light irradiation (λ > 420 nm), which was 7.7 and 2.8 times higher than SCN (0.21 mmol g?1 h?1) and ZIS (0.57 mmol g?1 h?1), respectively. The enhanced photocatalytic activity was mainly due to greater light utilization achieved by band gap adjustment through constructing heterojunctions and improved electron-hole separation efficiency. This method can effectively improve the photocatalytic performance of ZIS-based photocatalysts in a simple way.
查看更多>>摘要：? 2022 Elsevier B.V.Binary metal selenides (BMSs) have attracted considerable interest as potential anode materials for sodium-ion batteries (SIBs) due to significantly improved sodium storage performance resulting from higher intrinsic ionic conductivities and richer redox-active sites, particularly when compared to mono-metal selenides. In addition, the accumulation of binder in slurry preparation for electrodes not only accumulates dead weight but also diminishes the extent of the exposed surface area of active material. Henceforth, hierarchical nanostructures of nickel-cobalt selenide (NCSe) and iron-cobalt selenide (FCSe) bearing high surface area were deposited directly over carbon fibers and employed as free-standing anodes for SIBs (termed as NCSe/CFs and FCSe/CFs, respectively). A facile hydrothermal strategy, followed by optimized gas selenization was used to acquire hierarchical nanowire-like morphologies of BMSs on carbon fibers. Carbon fibers substrates not only provide current collecting pathways for electron transport during charging/discharging but also exhibit the high strength required for the free-standing electrode for battery assembly. When these electrodes were employed as an anode in SIBs, they exhibited adequately high initial energy capacities (i.e., 665 mA h g?1 by FCSe/CFs and 589 mA h g?1 by NCSe/CFs at 0.1 A g?1) and high-rate capabilities. Furthermore, these electrodes delivered outstanding stability in long-term cyclic performance over 1000 cycles at 1 A g?1. We believe that this simple strategy will further open a pathway toward the facile synthesis of numerous BMSs with carbon fiber composites as free-standing anodes for energy storage and conversion systems.
查看更多>>摘要：? 2022 Elsevier B.V.The Yb3+/Ho3+/Tb3+ co-doped Na2O-Y2O3-SiO2 system transparent glass-ceramics containing oxyapatite-type Na3YSi2O7 (NYS) crystals were prepared. The structure of the crystal was characterized by XRD and TEM. The most suitable heat treatment process was confirmed by DSC and TEM results. The strongest emission peak in the fluorescence spectra relates to the Tb3+: 5D4→7F5 transition. In the CIE chromaticity diagram, the luminescence is concentrated in the green area. The emission intensity of the glass-ceramic is increased by 7 times compared with the precursor glass. The increase in emission intensity is caused by the entry of rare-earth ions into the Na3YSi2O7 grains to replace the positions of Y3+ ions. The fluorescence properties of the glass-ceramics containing Na3YSi2O7 crystals were tested at different temperatures. It is demonstrated that the luminescent materials show good thermal stability. The obtained glass-ceramic would be a candidate material for green diode elements.
查看更多>>摘要：? 2022 Elsevier B.V.Cu-26Zn-5Al shape memory alloy (SMA) was produced by accumulative roll bonding (ARB) and subsequent heat treatment. In this regard, different austenitization cycles and cooling conditions, including furnace, air, cold-water, and boiling-water cooling were experimented. The heat-treated specimens were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and X-ray diffraction (XRD). The corrosion behavior of the specimens was also studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in a 3.5 wt% NaCl solution. The results revealed that only by cooling in the boiling- and ice-water environments, a fully martensitic microstructure showing the shape memory effect is obtained. In contrast, by using the other cooling conditions, different phases like α-phase (Cu-saturated solid solution) are formed as well as martensite. From the corrosion testing results, it was found that the SMA specimens with the fully martensitic microstructure have the highest corrosion resistance, where cooling in boiling water was recognized to be optimal. In conclusion, Cu-26Zn-5Al SMA with an improved corrosion resistance can be produced by ARB followed by controlled heat treatment.
查看更多>>摘要：? 2022 Elsevier B.V.Energy harvesting technology is in high demand for self-powered devices. Flexible thermoelectric generators (f-TEGs) have attracted considerable attention for application in wearable electronics, which can be applied to healthcare and smart clothing. However, previous f-TEGs still have limitations such lack of novel research focus concerning its wearable applications and complicated and high-cost fabrication procedures. This study reports an f-TEG comprising Bi2Te3-based thermoelectric composite films on a flexible substrate to demonstrate thermoelectric energy conversion from the human body. To verify the thermoelectric energy harvesting efficiency of the energy harvester based on temperature gradients, an f-TEG was developed by placing p-type Bi0.5Sb1.5Te3 (BST) of 133 μWm?1K?2 and n-type Bi2Te2.7Se0.3 (BTS) of 124 μWm?1K?2 thermoelectric films. The fabricated f-TEG harvested an output voltage of 18.13 mV, current signal of 2.74 μA, and output power of ≈ 12.6 nW at ΔT = 25 K. The theoretical thermoelectric potential distribution of the f-TEG was confirmed by finite element analysis using multiphysics simulation. Furthermore, we investigated the biological output performance of the f-TEG on the human body, which showed the output performance of ≈ 0.38 μA and ≈ 2.3 mV. This study presents the possibility of harvesting thermal energy from human body heat, which will be useful for improving wearable device applications.
查看更多>>摘要：? 2022 Elsevier B.V.Bulk (Mo2N) and supported molybdenum nitride (Mo2N/TiO2, Mo2N/CeO2) were synthesized by reduction-nitridation of bulk and supported MoO3 under a mixture of N2/H2. We investigated the mechanism of formation of molybdenum nitrides by coupling elemental analysis, in situ and ex situ XRD, Raman spectroscopy, in situ XPS/UPS spectroscopy and DFT calculation. We showed that it is possible to control the crystallographic phase and degree of nitridation (i.e. nitrogen vacancies) by adjusting the parameters of the synthesis, including the heating rate and final temperature, the nature, composition and flow of gas during reduction/nitridation and cooling. We demonstrated that β-Mo2N and γ-Mo2N go through the same intermediates: molybdenum bronze, MoO2 and Mo. The final crystallographic phase of the nitride depends mainly on the temperature rate and gas hourly space velocity employed during the synthesis, as they impact the crystallite size of the intermediates and the kinetics of reduction and nitridation. Molybdenum nitride clusters (<0.5 nm) are formed on TiO2.
查看更多>>摘要：? 2022 Elsevier B.V.Using nebulizer spray pyrolysis method, we investigate the optoelectronic properties of Erbium (Er:2 %), Yttrium (Y:2 %) and Terbium (Tb:2 %) doped CdS thin films. The pure CdS film belongs to the II-IV semiconductor chalcogenide family, and it has good optical properties, making it appropriate for photo-detector applications. In addition, rare earth (RE) elements such as Erbium (Er), Yttrium (Y) and Terbium (Tb) doped CdS thin film is more suitable for photo sensing applications due to their good physical and optical properties. The polycrystalline structure of pure and doped CdS films with the structure of hexagonal and preferential orientation (002) was shown by structural analysis (XRD). In addition, the phase purity of RE doped CdS thin films was confirmed using Raman spectra. The direct bandgap values fell (2.52–2.47 eV) for the RE dopant, reaching a minimum for the film formed with RE of high ionic radius Tb. Three emission peaks were discovered in photoluminescence (PL) spectra: a strong dominant peak at 525 nm due to interband transitions and a peak with minimum intensity at 475 and 640 nm. With the exception of two RE materials, Er and Y, the CdS film coated with Tb had improved photo-sensitivity characteristics. Responsivity (3.32 AW?1), detectivity (2.82 × 1011 Jones), and external quantum efficiency (883 %) are the photo sensing values of Tb doped CdS film. The Tb coated films were found to exhibit good optical properties, making them suitable for photodetector applications.
查看更多>>摘要：? 2022 Elsevier B.V.The electronic structure of the novel intercalation compound Cu0.3ZrTe2 was analyzed using the X-ray photoelectron spectroscopy, resonant photoelectron spectroscopy and DFT calculations. The resonant photoemission enhancement of the valence band features of Cu0.3ZrTe2 at the Zr 3p→4d and Cu 3p→3d photo absorption thresholds was studied. The tetrahedral coordination of the Cu atoms by the Te atoms was shown to be responsible for the strong chemical bonding of the Cu atoms within the ZrTe2 lattice through the Cu 3d/Te 5p hybridization. These findings were confirmed by theoretical density of states (DOS) calculations performed for CuxZrTe2 (x = 0.25 and 0.5) with the Cu atoms tetrahedrally and octahedrally coordinated by Te atoms. It was concluded that the substitution of atoms in the CuxTiSe2 system with heavier and polarizable ones (Se→Te, Ti→Zr), i.e. an increase in the lattice polarizability, destabilizes the octahedral coordination of the Cu atoms by the Se/Te ones. This limits the stability of the phases characterized by quantum states with a charge density wave and superconductivity.
查看更多>>摘要：? 2022 Elsevier B.V.Inspired by the successful preparation of Janus transition metal dichalcogenides MoSSe with hexagonal structure, we investigated the electronic and thermoelectric properties of a new Janus Pd-based material with pentagonal crystal structure, Janus PdSeTe, by first-principles calculations together with Boltzmann transport theory. This work reports that the Janus PdSeTe is a direct band gap semiconductor, and exhibits anisotropic electronic and thermoelectric properties. The weak electron-phonon coupling of hole leads to excellent electronic transport properties for the p-doping. A high power factor of 104 mWm?1K?2 at 300 K is obtained for the p-type PdSeTe along y-direction. The enhanced electronic transport properties and low thermal conductivity lead to a high ZT value and the ZT maxima of p-type PdSeTe reaches to 3.1 at 700 K. The results suggest that the Janus materials with pentagonal crystal structure are the potential promising thermoelectric candidates.
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