| Semiconductor heterojunctions have unique optoelectronic properties,which have great potential and research value in optoelectronic applications and energy storage.In this paper,we have prepared hierarchical tree-shaped ZnO/Si nanowire arrays with pn heterojunctions on silicon substrates by a simple two-step method.Based on the nanomaterials,we studied their application and physical mechanism in Raman sensing and photocatalysis.In addition,due to the excellent properties of graphene materials,graphene/cobalt molybdate composites were prepared,and their electrical properties were investigated as supercapacitor electrode materials.The details are as follows:Firstly,tree-shaped nanowire arrays were prepared by a two-step hydrothermal method.The XRD analysis showed that they have higher crystal quality,and the metal-induced etching Si nanowires(Si-NWs)are evenly perpendicular to the substrate.The ZnO nanowires(ZnO-NWs)branches,grown by hydrothermal method,are uniformly perpendicular to the surface of Si-NWs.By using Raman spectral response of Rhodamine 6G(R6G),we found that silver-modified ZnO/Si nanowires(Ag/ZnO/Si)possessed better function than other samples which constituted with same chemical composition and size apart from morphology(thin film or nanowire).The ZnO/Si hierarchical array had the strongest Raman scattering peak and exhibited ideal detection capability with 1×10-8 mol/L detection sensitivity and 1.5×104 enhancement factor.Both the experimental design and band structure analysis showed that the electromagnetic effect of localized surface plasmon resonance(LSPR)of silver nanoparticles increased 8 times in Raman enhancement,while the chemical effect of the hierarchical array of ZnO/Si nanowires played a more critical role in Raman Sensitivity.Secondly,the Tree&TiO2&Ag and Tree&In2S3&Ag2S hierarchical nanowire composite arrays were prepared based on tree-shaped ZnO/Si nanowire arrays,and their photocatalytic degradation efficiency of methylene blue(MB)dyes was tested under UV irradiation.The UV-light intensity of the Tree&TiO2&Ag series samples was 4.0-4.3 mW/cm2.The Tree/Ag array exhibited the best catalytic efficiency(20.98%)due to the synergistic effect of LSPR of Ag nanoparticles and pn heterojunction.While for the poor crystal quality of Tree&TiO2,a large amount of impurities and holes in TiO2 greatly promoted the recombination of photogenerated electron-hole pairs,so that the degradation efficiency was the lowest.The UV-light intensity of the Tree&In2S3&Ag2S series samples was 3.0?3.2 mW/cm2,and the catalytic ability of these arrays was that Tree/In2S3/Ag2S>Tree/Ag2S>Tree/In2S3>Tree.Due to the synergistic effect of narrow band gap of In2S3 and Ag2S quantum dots,and the tree-shaped heterojunction promoting the light absorption efficiency,the degradation efficiency of Tree/In2S3/Ag2S array was up to 3 1.50%.Thirdly,graphene was grown on nickel foam(NF)as current collector by chemical vapor deposition,thereafter CoMoO4 was prepared on it by hydrothermal method then.In the early period of hydrothermal growth,Co2+ ions and MoO42-ions in the solution reacted into a nano-seed of CoMoO4 precursor,and the seed crystal tended to preferentially grow at crystal domain of the NF interface.As the reaction proceeded,the derivatized nucleation center grew into a petal-like CoMoO4 seed crystal,which then acted as a new nucleation site and grew into a nanoflower-like structure.We also prepared NF/CoMoO4,20min GNF/CoMoO4,30min GNF/CoMoO4,60min GNF/CoMoO4 electrode materials and tested their electrical properties.It was found that 30min GNF/CoMoO4 had the best capacitance performance at a current density of 0.5 A·g-1,The specific capacitance was 1119 F·g-1.It was shown that graphene modification greatly improved the capacitance performance of the electrode. |
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