查看更多>>摘要：Molybdenum and vanadium mixed oxides of Mo_6V_9O_(40) and Mo_6V_(8.5)Te_(0.5)O_(40) were synthesized by the modified sol-gel method. The phase formation and structure were investigated through X-ray powder diffraction (XRD) patterns. The optical absorption measurements show that the sample has an efficient light response covering the region UV-visible to near IR wavelength. The two Mo-V mixed oxides of Mo_6V_9O_(40) and Mo_6V_(8.5)Te_(0.5)O_(40) show an indirect forbidden transition with band energies of 1.67 eV and 1.64 eV, respectively. The multivalent cations (V and Mo ions) were confirmed via X-ray photoelectron spectroscopy (XPS) measurements. The effective photocatalysis of the samples was conducted via the photodegradation of RhB under visible-light irradiation (λ ≥ 420 nm). The conductivity properties and lifetime of charge carriers were characterized via impedance spectra and luminescence decay curves respectively. It was suggested that intrinsic redox couples in these Mo-V mixed oxides lead to intervalence transfer between V~(5+/4+) and Mo~(6+/5+) couples, which can improve photocatalysis. This work offers a potential alternative material with rich intrinsic redox couples and defects toward high-performance photocatalyst.
查看更多>>摘要：Room temperature (RT) gas sensors play a crucial role in the development of wearable and portable devices. Herein, a single hydrothermal approach was used to effectively rivet the α-Fe_2O_3 to the functionalized Ti_3C_2T_x MXene plates to prepare the α-Fe_2O_3/Ti_3C_2T_x MXene composites material with high specific surface area (29.2 m~2/g) and abundant functional groups, forming a hybrid heterojunction structure. A side-heated sensor was manufactured and its sensing performance for a variety of vapors were measured experimentally. The morphology and crystal phase of the composite products were analyzed through a range of testing technique. The rose-like α-Fe_2O_3/Ti_3C_2T_x MXene sensor revealed a response value and rapid response/recovery times of 18.3% and below 2.5 s for 5 ppm NH_3 gas at RT under relatively humidity (RH) of 22%. Meanwhile, it illustrated an excellent linear response in the vary of 5-100 ppm, excellent reversibility and the long-term stability. In addition, a plausible mechanism of the α-Fe_2O_3/Ti_3C_2T_x MXene sensor was predicted, and the adsorption capacity of composites material was confirmed by the support of density functional theory (DFT) calculations. This work is expected to provide a fresh idea for the design of other high properties RT gas sensors in the future.
查看更多>>摘要：In the present study, correlative corrosion testing and electron microscopy, including quasi-in-situ electron microscopy, are employed to investigate the corrosion behaviour of 2A97-T8 Al-Cu-Li alloy extrusion in 3.5 wt% NaCl solution. It is found that the corrosion behaviour of the alloy is influenced by synergetic effect of the plastic deformation introduced by the thermomechanical processing during alloy fabrication and the precipitation of T_1 phase during T8 treatment. Localized corrosion initiates and propagates preferentially within non-recrystallized regions of the partially recrystallized alloy. Corrosion initiated at coarse constituent intermetallic particles is confined to its periphery, which doesn't develop further when the particles are disconnected from alloy matrix.
查看更多>>摘要：Ultra-fine Ta_4HfC_5 and TaHfC_2 powders were prepared through the pyrolysis of a precursor synthesised by using a facile one-pot reaction. HfCl_4, TaCl_5, and phenolic resins were used as the sources of hafnium (Hf), tantalum (Ta), and carbon (C), respectively. The as-synthesised precursors were further utilised to prepare Ta_4HfC_5- and TaHfC_2-modified carbon/carbon (C/C-Ta_4HfC_5 and C/C-TaHfC_2) composites through precursor infiltration and pyrolysis. The transformation of Ta_4HfC_5 and TaHfC_2 precursors into ultra-fine ceramic powders and anti-ablation performance of the C/C-Ta_4HfC_5 and C/C-TaHfC_2 composites were investigated. The carbothermal reduction of Ta_2O_5 and Hf_6Ta_2O_(17) and the solid solution reaction between HfC and TaC occur successively during the pyrolysis of Ta_4HfC_5 precursors. HfC and TaC undergo a sufficient solid solution reaction at 1800 °C to form the Ta_4HfC_5 solid solution with a particle size of 200-300 nm. The pyrolysis products of TaHfC_2 precursors acquired at 1400-1600 °C are composed of TaC, HfC and TaHfC_2. High-temperature pyrolysis promotes the solid solution reaction between TaC and HfC. The TaHfC_2 solid solution with a particle size of 100-150 nm is formed at 1800 °C. The introduction of TaHfC_2 and Ta_4HfC_5 solid solutions into the C/C composite substantially enhances their anti-ablation performance. The linear ablation rates of C/C-Ta_4HfC_5 and C/C-TaHfC_2 are 11.04 and 16.97 um/s, respectively, which are considerably lower than that of the C/C composite. The good anti-ablation performance of the C/C-Ta_4HfC_5 and C/C-TaHfC_2 composites can be attributed to the formation of the Ta_2O_5 and Hf_6Ta_2O_(17).
查看更多>>摘要：Nitrogen-doped bamboo-like carbon nanotubes with embedded Fe/Fe_3C nanoparticles (NPs) (Fe/Fe_3C@ NCNTs) were successfully fabricated by the pyrolysis of the metal organic framework. When the pyrolysis temperature was 800 °C, the length and diameter of NCNTs were in the ranges 8-20 um and 17-130 nm, respectively. Remarkably, the wall thickness of the NCNTs was merely 5.0 nm. The Fe/Fe_3C@NCNTs-800 exhibits enhanced dielectric and magnetic loss performance attributing to its excellent electrical conductivity, massive interfaces between Fe/Fe_3C and NCNTs, and a large number of defects and void spaces between bamboo joints. In addition, the Fe/Fe_3C@NCNTs-800 also has outstanding impedance matching characteristic, and thus its minimal reflection loss and effective absorption bandwidth reached -50.8 dB with a thickness of 1.6 mm and 4.3 GHz with a thickness of 1.4 mm, respectively. The results of this study demonstrate the Fe/Fe_3C@NCNTs-800 as a promising candidate for electromagnetic wave absorption.
查看更多>>摘要：This work focuses on the electrical properties of Ni/n-GaN Schottky barrier diodes (SBDs) fabricated on GaN bulk substrates with different crystal orientations. For the SBDs on a-plane, m-plane, and s5-plane GaN, the Schottky barrier heights (SBHs) exhibited magnitudes of 0.65 eV, 0.69 eV, and 0.75 eV, respectively. The relatively small SBH of a-plane devices results in a relatively larger reverse leakage current than that of m-plane and s5-plane. In addition, the carrier concentrations extracted by C-V characteristics are comparable for the GaN substrates with different crystal orientations. The temperature-dependent I-V characteristics indicate how the barrier inhomogeneity of the Ni/GaN Schottky contacts on the a-plane GaN is smaller than the others. Based on the XPS spectra results, the discrepancy in Schottky contact characteristics stems from the different polarization charges and/or surface oxides of the different crystal planes. The low GaOx density on a-plane GaN surface contributes to the minimum barrier inhomogeneity of the corresponding SBD devices.
查看更多>>摘要：In this work, metal-free hexagonal boron nitride (h-BN) was incorporated into BiFeO_3 and MnFeO_3 type perovskites by facile impregnation method for the first time and the catalysts presented excellent photocatalytic activity towards various antibiotics and dyes. The characterization tests were carried out by SEM-EDS, TEM, XPS, FTIR, XRD, BET, PL and DRS techniques. The narrower band gap of Type-II heterojunction improved the photodegradation of tetracycline which the reaction rates were calculated as 2.5 times higher than raw perovskites. The outstanding photocatalytic performance of heterojunc-tions was explained by extended excitation wavelength and hindered recombination rate of charge-carriers. In lake and sea water media, 86% and 72% degradation degrees were achieved aver BiFeO_3/h-BN and MnFeO_3/h-BN, respectively, suggesting their practical utilization. BiFeO_3/h-BN and MnFeO_3/h-BN catalysts also exhibited superior catalytic performances for the elimination other contaminants namely, ciprofloxacin, Orange II and Indigo carmine yielding approximately 75% removal at the end of photo-Fenton catalysed reaction. The heterojunctions effectively removed nearly -50% and -70% of ibuprofen from the real pharmaceutical wastewater. The incorporation of hexagonal boron nitride offers an innovative and ideal way to enhance the photocatalytic activity of perovskite catalysts for the elimination of organic pollutants.
查看更多>>摘要：Despite the ultrahigh theoretical capacity of Si anodes, their commercial application is severely restricted due to the lack of scalable and low-cost methods to overcome their considerable volume deformation and poor electrical connectivity. Herein, a novel hierarchical porous silicon/N-doped carbon composite (Si/N-PC) is successfully fabricated via simple biomass fermentation with inexpensive wheat flour, and this composite is then used as a high-performance lithium-ion battery (LIB) anode. Wheat flour blended with silicon na-noparticles can be fermented under the action of yeast while releasing carbon dioxide to construct a unique hierarchical porous structure. The added cationic surfactant hexadecyltrimethylammonium bromide not only helps uniformly deposit the Si particles in the wheat flour under the action of electrostatic forces but also forms an N-doped carbon layer in combination with the protein in the wheat flour, realizing full utilization of the raw materials. Systematic tests verify that the N-doped hierarchical porous structure contributes to mitigating the volume change, ensuring electrode stability and enhancing the electrical conductivity of the Si/N-PC composite during the charge-discharge process. As anticipated, the obtained Si/ N-PC composite electrode can maintain a reversible discharge capacity of 696.1 mAh g~(-1) for over 300 cycles at a current density of 1 A g~(-1) exhibiting a 0.17% capacity loss per cycle from the 3rd to 300th cycle. Additionally, this composite electrode delivers a superior rate capability of 946.1 mAh g~(-1) at a high current density of 2 A g~(-1), showing the synergistic benefit of the hierarchical porous structure and N doping. This is the first time that a hierarchical porous silicon/N-doped carbon composite has been prepared via biomass fermentation treatment for use in high-performance LIBs. The overall fabrication process of the Si/N-PC composites is low cost and scalable, providing a sustainable strategy for the production of high-performance Si/C anode materials.
查看更多>>摘要：Heat treatment strategy has been initially used to prepare boron doped graphite carbon nitride nanodots (BCNDs)/carbon-rich g-C_3N_4 nanosheets (CNS) heterojunction catalysts. The overall procedure involved three stages. First, BCNDs were prepared by the molten salt method. Next, BCNDs were dispersed onto CNS via heat treatment. Finally, the prepared heterojunction catalysts were test for photocatalytic water splitting hydrogen evolution. The experiment results show that the highest photocatalytic hydrogen evolution activity reached 6260.5 umol-g~(-1)-h~(-1) which was approximately 15.7, 7.2 and 3.1 folds higher than that of bulk carbon nitride (bulk C_3N_4), CNS and BCNDs/CNS-H prepared by hydrothermal method, respectively. The enhanced photocatalytic performance may be attributed to the synergistic effect of the formation of heterojunction and the increase of C content in carbon nitride. This work provides reliable guideline for the design of a novel and simple method for composite photocatalyst.
查看更多>>摘要：Crystal structures, electronic, and magnetic properties of RbCeX_2 (X = S, Se, Te) crystals are investigated using periodic density functional theory (DFT) calculations under hydrostatic pressures up to 10 GPa. The ferromagnetic phase is slightly more stable than the anti-ferromagnetic one for all compounds and pressures. A pressure-induced transition from a magnetic semiconductor (MS) to a spin gapless semiconductor (SGS) is observed only in the case of the X = Te compound. In absence of imposed pressure, the X = Te exhibits a direct a-spin gap of 0.46 eV while its β-gap is 2.30 eV. A pressure of 10 GPa completely suppresses the a-spin gap of RbCeTe_2 and reduces it β-gap to 1.63 eV. This pressure-induced elimination of only one spin gaps is exclusive to the X = Te compound. This property distinguishes the Te compound from its two congeners. The pressure-response characteristics of RbCeTe_2 renders this compound a potential pressure-induced MS → SGS switching material.
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