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1.
To overcome the fast recombination rate of electron-hole pairs of individual SnS2, p-n heterojunction g-C3N4/SnS2 composites were fabricated as high-efficiency visible-light photocatalyst to photodegradate the organic dye MB. The morphologies, structures, compositions, and photocatalytic properties were characterized. The SnS2 shows two-dimensional layer structure with an average thickness of 20 nm and diameter size of about 2 μm, and the g-C3N4 nanoflakes were uniformly deposited on the surface of SnS2 nanosheets. In comparison with the bare g-C3N4 and SnS2, the composites show improved photocatalytic activity under visible light, which is sensitive to the content of g-C3N4. In particular, the 15% g-C3N4/SnS2 composites exhibit the highest photocatalytic activity and outstanding reusability, which can degrade 88.01% MB after only 1 h in the visible light (λ?>?420 nm) range. The g-C3N4/SnS2 heterojunction composites show outstanding reusability after four times cycling experiments. The improved photocatalytic activities of composites are attributed to abundant active species, increased charge separation, and decreased electron-hole pair recombination, which originated from the large specific surface area and efficient interfacial transport of photo-induced charge carriers between SnS2 and g-C3N4. These results suggest that the two-dimensional layered g-C3N4/SnS2 p-n heterojunction composites are promised to be a high-efficiency visible-light photocatalyst.  相似文献   

2.
Porous SnO2 nanoflakes with loose-packed structure were synthesized by calcination of SnS2 precursors that were obtained through solvothermal method at low temperature. The as-obtained SnO2 product had a three-dimensional porous structure with relatively high specific surface area. It was found that the SnO2 nanoflakes inherited the morphology of precursor while numerous pores were formed after the annealing process. The combined techniques of X-ray diffraction, energy-dispersive spectrum, field emission scanning electron microscopy, and (high-resolution) transmission electron microscopy were used for characterization of the as-prepared SnO2 product. Moreover, the porous SnO2 nanoflakes with loose-packed structure could be used as gas sensors for detecting ethanol and acted as anode for lithium ion batteries. Our study shows that the as-prepared SnO2 nanoflakes not only exhibit good response and reversibility to ethanol gas but also display enhanced Li-ion storage capability.  相似文献   

3.
The 2H polytype of a SnS2 layered crystal has been studied using Raman spectroscopy at pressures of up to 5 GPa in a diamond anvil cell. The Raman frequency of the intralayer mode increases linearly with increasing pressure at baric coefficients of 5.2 cm−1/GPa for P<3 GPa and 3.4 cm−1/GPa for P>3 GPa. This change in the baric coefficient for Raman scattering and the available data on X-ray measurements of the compressibility of 2H-SnS2up to 10 GPa suggest that the crystal structure undergoes a transformation at about 3 GPa.  相似文献   

4.
We report the synthesis of single-crystalline α-Fe2O3 nanoflakes from a simple Fe–air reaction within the temperatures range of 260–400 °C. The nanoflakes synthesized at the lowest temperature (260 °C) in this work show an ultra-sharp morphology: 5–10 nm in thickness, 1–2 μm in length, 20 nm in base-width and around 5 nm at the tips; successfully demonstrate the promising electron field emission properties of a large-scaled α-Fe2O3 nanostructure film and exhibit the potential applications as future field-emission (FE) electron sources and displays (FEDs). The formation and growth of α-Fe2O3 nanostructures were discussed based on the surface diffusion mechanism. PACS 79.60.Jv; 79.70.+q; 77.84.Bw  相似文献   

5.
In this work, a facile and low‐temperature water evaporation approach to prepare columnar superstructures consisting of face centered cubic (fcc) Cu2?xSe nanoflakes stacked along 〈111〉 direction is reported. Formation of such unique stacked nanoflake assemblies is resulted from oriented attachment of isolated hexagonal CuSe nanoflakes along the 〈001〉 direction with a ripening effect driven by solvent evaporation, and then followed by a phase conversion into fcc Cu2?xSe. Evolution from hexagonal CuSe nanoflakes to fcc Cu2?xSe columnar superstructures results in obvious red‐shift of band‐gap absorption edge from 670 to 786 nm and dramatically decreased Raman resonance band intensity of the Se–Se stretching mode at 259 cm?1 due to the phase conversion and composition variation. Remarkably, the Cu2?xSe columnar superstructures are employed as low‐cost and highly efficient counter electrodes (CEs) in quantum dot sensitized solar cells, exhibiting excellent electrocatalytic activity for polysulfide electrolyte regeneration. A ZnSe/CdSe cosensitized solar cell using the Cu2?xSe CE shows a significant increase in fill factor and short‐current density (JSC) and yields a 128% enhancement in power conversion efficiency as compared to the traditional noble metal Pt CE.  相似文献   

6.
A simple and economical route based on a K2CO3 mediated process was developed to synthesize three-dimensional (3D) flower-like Fe3O4 micro/nanoflakes on the surface of iron plates by a direct in-situ hydrothermal synthesis method. The prepared micro/nanoflakes were characterized by X-ray diffraction and scanning electron microscopy. It was found that the width of the nanoflakes ranges from 50 to 100 nm, and the length of the flakes is about 3 μm. The morphology of Fe3O4 nanostructures can be tuned from simple isolated nanoflakes to the ordered 3D flower-like shape by increasing the reaction temperature. The wettability of the surface with 3D flower-like micro/nanoflakes was changed from hydrophilicity to superhydrophobicity by chemical modification with vinyl tirethoxy-silane. The static contact angles for water on both of the modified surfaces were larger than 150°, which was closely related to the chemical modification and hierarchical structure. Furthermore, the surfaces retained good superhydrophobic stability in long-term storage as well, which should be critical to the application of iron materials in engineering.  相似文献   

7.
Based on density functional theory, we systematically study the mechanical and electronic properties of monolayer and bilayer SnS2 and SnSe2. The electronic properties of these layers can be significantly tuned by applying in-plane strains and electric fields perpendicular to the sheets. The band gaps of monolayer SnS2 and SnSe2 slightly increase with the in-plane tensile strains, and they start to decrease after critical strains (5% for monolayer SnS2 and 7% for monolayer SnSe2). The band gaps of bilayer SnS2 and SnSe2 have a similar tendency to the monolayers with smaller critical strains (1% for bilayer SnS2 and 2% for bilayer SnSe2), which enables a semiconductor-to-metal transition at 10% strain for bilayer SnSe2. We also find that an external electric field perpendicular to bilayer SnS2 and SnSe2 modulates their electronic band gaps. Semiconductor-to-metal transitions are achieved at the electric fields of 0.27 V/Å for bilayer SnS2 and 0.13 V/Å for bilayer SnSe2.  相似文献   

8.
Ultrathin epitaxial films of YBa2Cu3O7– on SrTiO3 prepared by Direct Current (DC) sputtering and pulsed laser deposition were imaged by Atomic Force Microscopy (AFM) to follow the different stages of growth of the thin films. Series of films with thicknesses between 1.2 nm and 12 nm (1–10 monolayers of YBa2Cu3O7–) were prepared under identical conditions, optimized with respect to electrical and structural properties, to obtain information on the mechanisms responsible for the formation of growth spirals which are commonly observed in films having a thickness of several 10 nm or more. It could be shown that few layers are formed by a layered growth mode where material is attached laterally to 2D islands which are only one c-axis unit cell in height. In a later stage of growth when about 8–10 layers have been formed, the growth process changes to a mode which is mediated by growth spirals. This could be directly monitored in the AFM images where different defect structures like vertically sheared growth fronts and dendrite-like terraces of stacked islands as well as the resulting growth spirals could be identified.  相似文献   

9.
Transition metal dichalcogenides (TMDs), such as MoS2, MoSe2, WS2, and WSe2, are layered materials with strong in-plane ionic-covalent bonds and weak out-of-plane van der Waals interactions, enabling formation of various nanostructures, such as nanotubes, nanoribbons, nanoflakes, and fullerene-like nanoparticles. Various remarkable properties have been found recently in these nanostructures, opening up brand new opportunities for their applications in nanoelectronics, optoelectronics, spintronics and structural materials. In this article, we present recent advances in the study of two-dimensional TMDs and their derivatives with special emphasis on structures, morphologies, properties (electronic, magnetic, thermal, mechanical), and applications (transistors, sensors, catalysts, lubricants, and composite materials). In addition, routes for modifying these properties by chemical doping, defect engineering, strain engineering, and electric fields are discussed. Our intent is to present a state-of-the-art view in this fast evolving field, with a balanced theoretical and experimental perspective.  相似文献   

10.
We have studied the growth characteristics, structure, and parameters of the epitaxial heterostructures (001)NdBa2Cu3O7−δ /(100)SrTiO3/(001)NdBa2Cu3O7−δ grown by laser ablation on a (100)LaAlO3 substrate with a thin (∼2 nm) YBa2Cu3O7−δ intermediate layer. The use of an YBa2Cu3O7−δ intermediate layer promotes layered growth of the (200 nm) NdBa2Cu3O7−δ layer, whose free-surface roughness is 4–5 nm. The resistance of the NdBa2Cu3O7−δ layers began to fall off abruptly at T=92 K, and at T≈87 K it vanished completely. The critical current density in the NdBa2Cu3O7−δ layers at T=76 K exceeded 106 cm2 A/cm2. The dielectric constant of the (400 nm) SrTiO3 layer sandwiched between the NdBa2Cu3O7−δ epitaxial layers grew by roughly threefold as the temperature was lowered in the interval 300–4.2 K. When a bias voltage of ±2.5V was applied to the NdBa2Cu3O7−δ electrodes, the relative dielectric constant of the (400 nm) SrTiO3 intermediate layer fell from 1150 to 400 (T=32 K, f=100 kHz). The conductivity of the SrTiO3 intermediate layer in the direction perpendicular to the substrate plane increased with temperature and the electric field strength. Fiz. Tverd. Tela (St. Petersburg) 41, 395–403 (March 1999)  相似文献   

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