查看更多>>摘要：As a typical metal sulfide, tungsten disulfide (WS2) with high theoretical capacity has attracted significant attention as the anode for sodium-ion batteries (SIBs). However, WS2 bulk material usually displays poor rate performance and fast capacity fading in practical applications due to its low conductivity and structural instability. Herein, we propose an in-situ confinement strategy for synthesizing low-crystallinity and ultrafine WS2 nanosheets within carbon nanofibers (WS2-CNF) by the simple heat treatment of electrospun polyacrylonitrile/ammonium tetrathiotungstate (PAN/(NH4)2WS4) nanofibers. The low-crystallinity structure of WS2 with ultrasmall size and rich defects can greatly reduce the volume change and shorten the ion diffusion length. WS2 nanosheets are confined in the CNF matrix, which is capable of effectively improving its electronic conductivity and structural stability. Based on these advantages, the WS2-CNF composite electrode demonstrates fast and ultrastable Na+ storage performance with a high capacity of 182 mAh g–1 after 6000 cycles at 5.0 A g?1. Therefore, this work provides a simple and facile strategy for developing high-performance WS2 anodes for SIBs.
查看更多>>摘要：Thermal instability of InxGa1?x N quantum wells (QWs) is an obstacle to construct efficient blue and green LEDs and laser diodes. Structural degradation of QWs with indium content above 15% becomes severe at temperatures above 930 °C leading to formation of extended non-radiative areas within the active region. Our previous studies (Smalc-Koziorowska, 2021) indicated a relationship between the degradation process and metal vacancies present in the layers adjacent to the QWs. In this work, we show a method to overcome this problem by using heavy Si doping of the GaN barrier layers. In particular, such barrier layer grown on the top of n-type GaN layer below the InGaN QWs can act as a diffusion barrier for vacancies. The presence of silicon atoms increases the energy barrier for gallium vacancies migration. This effectively reduces possibility of diffusion of gallium vacancies from the n-type layer to the active region. As a result, improved thermal stability of QWs was achieved and significant degradation was not observed up to temperatures of 980 °C in comparison to 930 °C for the undoped structure.
查看更多>>摘要：Nanospheres were widely utilized as atomic clusters for the self-assembly and modification of functional nanomaterials. In this study, by using the laser-induced deposition in a liquid medium, the spherical Silver (Ag) and Tin dioxide (SnO2) nanocomposites were successfully prepared. The characteristics of the product, such as morphologies, components, structures and optical properties were obtained by STEM, EDS, ICP-OES, XPS, XRD, UV-Vis and PL instruments, respectively. During the laser-induced liquid deposition, the pristine Ag nanoparticles were melted to be spheres with the average particle size decreased and welded with the SnO2 nanomaterials under the laser heating and liquid quenching. The photocatalytic performance of the synthesized nanocomposites was evaluated by the degradation of methylene blue aqueous solution as a model organic pollutant. The results indicated that, for the spherical Ag and SnO2 nanocomposites, the reaction rate constant was enhanced 3.1 times than the pure-SnO2 nanomaterials and 13.3 times than the pure-Ag nanoparticles, respectively, with a high value of 0.08 min?1. Where 99.1% methylene blue can be removed in 60 min by using Ag and SnO2 nanocomposites as catalysts under ultraviolet lamp irradiation. This performance performed better than the previous reports in similar physical conditions. The possible enhanced mechanism was analyzed, where the spherical Ag anchoring on the surface of SnO2 induced the perturbation of SnO2 bandgap, the free electrons transfer of spherical Ag promoted the separation of photogenerated electron-hole pairs, increased the formation of superoxide and hydroxyl radicals for methylene blue effectively removal via a redox reaction.
查看更多>>摘要：Green synthesis of nanostructures is an alternative method to physical and conventional chemical methods, which is cost-effective and environmentally friendly. This study focuses on the synthesis of nanostructured multilayer graphene and zinc oxide nanocomposites from natural extracts and their utilization for photodegradation of brilliant black (BB) under solar light irradiation. The fabricated ZnO and graphene nanostructures were used to fabricate multilayer graphene/zinc oxide (MLG/ZnO) nanocomposites, with different ratios of MLG to ZnO (1:1, 1:2, 1:3) through ex-situ casting of the two materials. Various characterization techniques such as XRD, SEM, HR-TEM, EDS, BET, UV-Vis, and Raman were used to study the physico-chemical properties of the synthesized materials. The XRD profiles and Raman spectra exhibited predominant features of MLG and the characteristic wurtzite structure of ZnO in the nanocomposites. The UV-Vis absorbance spectra analysis revealed that combining MLG and ZnO reduced the energy band gap of ZnO nanoparticles, consequently improving the light absorption of the ZnO in the visible range. The overall percentage photodegradation of BB under sunlight by MLG, ZnO, MLG/ZnO_1, MLG/ZnO_2 and MLG/ZnO_3 were found to be 7%, 63%, 39%, 81% and 93%, respectively. Scavenger experiments confirmed that holes played a significant role in the photodegradation of BB followed by superoxide radicals and hydroxyl radicals being the least. The results of this study showed that MLG/ZnO nanocomposite can be adopted for beneficial application in the removal of pollutants from water using natural solar light irradiation.
查看更多>>摘要：In this work, novel Ni0.6CoMn1.4O4: x wt%Ag (NCMO: Ag-x, x = 0, 5, 7.5, 10, 12.5, and 15) composite ceramics were successfully fabricated by combining chemical reduction with solid-state coordination reaction method. The phase composition, microstructure, element distribution, and electrical properties are systematically investigated. The introduced Ag nanoparticles formed heterogeneous interfaces with the NCMO particles and were uniformly distributed in the samples. Due to the introduction of Ag, the Co2+ content increases from 33.2% to 50.0%. The average valence state of Mn ions increases from 2.91 to 3.17, then it decreases to 2.89. The Ag addition does facilitate the remarkable reduction of room temperature resistivity from 250.38 to 7.61 Ω cm and makes the resistivity drift below 2.57%, while B value decreases from 3145 to 1909 K, which are caused by the decreases of grain resistance and grain boundary resistance. Moreover, space electronic transmission mechanism is also proposed to further explain the positive effect of Ag introduction on electrical properties of the NCMO/Ag composite ceramics.
查看更多>>摘要：Ta4C3 as one of the MXene has been widely investigated in the application of materials chemistry, biomedicine, electrochemical energy storage and other fields. However, the study of its optical properties and applications remains rare. In this work, few-layer Ta4C3 MXene are prepared and its optical properties and applications are systematically investigated. We develop few-layer Ta4C3 MXene through the liquid phase exfoliation (LPE) method, and prepare it as Ta4C3 saturable absorber (SA). To obtain femtosecond pulses, the Ta4C3-SA is inserted further to an erbium-doped fiber laser (EDFL) cavity. It is worth noting that in the experiment the EDFL composed of Ta4C3-SA can generate stable femtosecond pulses, and the spectral bandwidth and duration of the femtosecond pulses are 1559.6 nm and 350 fs, respectively. Meanwhile, the numerical simulation results consistent with the experimental results. The results reveal that Ta4C3 MXene has great application potential in nonlinear optics and ultrafast photonics.
查看更多>>摘要：Niobium carbide (NbC) catalytic films were deposited on vanadium (V) foils by magnetron sputtering to prepare the NbC/V composite membranes for high temperature hydrogen separation. It is found that the sputtering power and substrate bias largely affect the structure and catalytic activity of the NbC films, and thus the hydrogen permeability of the NbC/V composite membranes. Optimized conditions for membrane preparation were obtained, which generated a pronounced high hydrogen permeability, particularly ~5.85 × 10?8 mol H2 m?1 s?1 Pa?0.5 at 650 °C. This is 1.9 times that of pure palladium (Pd). The high hydrogen permeability of the NbC/V membranes can be attributed to the high catalytic activity of the NbC films towards hydrogen dissociation, as the cubic NbC phase in the films exhibits preferential growth along the catalytically dominated crystalline plane and a relatively high percentage. This work demonstrates that the NbC/V system shows high potential as a new non-precious metal membrane for hydrogen separation and purification at high temperatures.
查看更多>>摘要：This work reports the detailed analysis of the structure and optoelectronic properties of spin coated Zn2?xPbxSnO4 nanostructured films. XRD studies reveal the polycrystalline cubic inverse spinel structure while Raman spectra show the dominance of T2 g(3) mode and decrease in intensity of A1 g mode with Pb doped ZTO films. X-ray photoelectron spectroscopy substantiates the dominance of atom in multiple charge states and their possible substitutions in the host lattice. The maximum average transparency of 87% in 400–650 nm spectral region for x = 0.08 sample while the decrease in optical gap from 4.32 to 4.14 eV with minimal value of 4.04 eV for x = 0.04 is found. The refractive index at 500 nm is calculated using Swanepoel's method and found to decrease from 1.72 for ZTO and 1.59 for x = 0.08 sample. The carrier concentration increases from 1018 cm?3 for ZTO to 1020 cm?3 for x = 0.08 sample. The minimal value of electrical resistivity of 2.17 × 10?3 Ω-cm and maximal Haacke's Figure of merit (FOM) of 1.1 × 10?3/ Ω is obtained for x = 0.08. These results are significant advancement to the development of ZTO based transparent conductors for highly efficient futuristic optoelectronics and photovoltaic devices.
查看更多>>摘要：Rational design of self-supporting and well-aligned MOF-derived electrode materials is a great challenge. In this work, we report a novel strategy for preparing nickel-cobalt double hydroxide (NiCo-DH) array on nickel foam with template-directed growth of MOF array as the precursor. The obtained sample can be directly applied to both Ni-Zn aqueous secondary battery and hybrid supercapacitor. Due to the many advantages inherited from the MOFs material, the NiCo-DH array displays an ultrahigh reversible specific capacitance (325.6 mAh g?1 at 2 mA cm?2) and excellent rate performance (75.5% of initial capacity retention under 40 mA cm?2). As a cathode for NiCo-Zn batteries, the NiCo-DH electrode exhibits a high specific capacity of 329 mAh g?1 and satisfactory cycling stability. Moreover, the assembled NiCo-DH //active carbon asymmetric supercapacitor exhibited a remarkable capacity of 0.359 mAh cm?1 at 0.5 mA cm?1 and exhibited excellent durability (capacitance retention of 91% after 5 000 cycles). Furthermore, the hybrid device exhibited an impressive energy density of 50.5 Wh kg?1 at a power density of 750 W kg?1. The presented strategy for controlled design and synthesis of MOF-derived self-supported electrode offers prospects in developing highly electrochemical active electrode materials in energy storage devices.
查看更多>>摘要：Locating pressure and temperature conditions relevant to concurrent diamond-anvil-cell (DAC) experiments is imperative for the discovery of new high–pressure nitrogen-rich compounds. In this work we provide a pressure-temperature phase diagram of the iron–nitrogen system for pressures up to 200 GPa and temperatures up to 4000 K through a combination of Density Functional Theory computations and thermodynamic calculations. The work includes an assessment of the chemical potential of nitrogen and its change at high pressure and high temperature. We deliver stability fields of various Fe–N compounds in the presence of excess nitrogen. Our results are in agreement with recent synthesis of FeN2 and FeN4, and predict a hitherto unknown FeN8 attainable at 100 GPa and 1500 K.
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