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Photocatalytic activity of anatase titanium dioxide nanostructures prepared by reactive magnetron sputtering technique
摘要： In this work, nanostructured titanium dioxide (TiO2) photocatalysts with high optical and structural homogeneity were successfully synthesized by dc reactive magnetron sputtering technique. The TiO2 thin films were produced with high structural homogeneity without any heat treatment. Analysis of the X-ray diffraction patterns and UV–visible spectroscopy gave an indication that the structure of prepared films is anatase with energy band gap of 3.23 eV. The Fourier-transform infrared spectroscopy has confirmed the formation of Ti–O bond. The average size of TiO2 particles in the deposited films was ranging in 5–7 nm. These nanostructures are very applicable as photocatalysts as their photocatalytic activity was determined from the degradation rate with UV irradiation time as the first order reaction rate constant was determined to be 2.4 × 10?3 min?1.
关键词： Anatase phase,Titanium dioxide,Nanostructures,Photocatalysis
更新于2025-09-23 15:22:29
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Optical Band Gap, Local Work Function and Field Emission Properties of MBE Grown β-MoO3 Nanoribbons
摘要： Monoclinic molybdenum trioxide (β-MoO3) nanostructures (shaped like nanoribbons: NRs) were grown on Si(100), Si(5512) and fluorine-doped tin oxide (FTO) by molecular beam epitaxy (MBE) technique under ultra-high vacuum (UHV) conditions. The dependence of substrate conditions and the effective thickness of MoO3 films on the morphology of nanostructures and their structural aspects were reported. The electron microscopy measurements show that the length and the aspect ratio of nanostructures increased by, 260% without any significant change in the width for a change in effective thickness from 5 nm to 30 nm. NRs are grown along <011> for all the effective thickness of MoO3 films. Similarly, when we increased the film thickness from 5 nm to 30 nm, the optical band gap decreased from 3.38± 0.01eV to 3.17± 0.01eV and the local work function increased from 5.397 ± 0.025 eV to 5.757 ± 0.030 eV. Field emission turn-on field decreased from 3.58 V/μm for 10-μA/cm2 to 2.5 V/μm and field enhancement factor increased from 1.1×104 to 5.9×104 for effective thickness variation of 5 nm to 30 nm β-MoO3 structures. The β-MoO3 nanostructures found to be much better than the α-MoO3 nanostructures due to low work function, low turn on field and high field enhancement factor, and are expected to be useful applications.
关键词： β-MoO3 nanostructures,Field emission and Kelvin probe force microscopy (KPFM),Optical band gap,Molecular beam epitaxy (MBE),Electron microscopy
更新于2025-09-23 15:22:29
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Preparation of La doped ZnO ceramic nanostructures by electrospinning–calcination method: Effect of La3+ doping on optical and photocatalytic properties
摘要： Ceramic nanostructures of ZnO doped with La3+ ions (0.02%, 1%, 2% and 4%) were prepared by electrospinning-calcination method. Polyvinylpyrrolidone (PVP) was used as an additional polymer to promote the electrospinning. And, the intermediate electrospun products were processed thermically at 700 °C for 3 h. The produced materials were characterized morphologically and structurally by using scanning/transmission electron microscopy (SEM/TEM) and X-ray diffraction (XRD). The XRD patterns showed the successful incorporation of La ions in the hexagonal wurtzite structure of ZnO. Optical band gaps of these ceramic nanostructures were estimated from reflectance data using Kubelka-Munk theory and were found to vary from 2.589 to 2.889 eV, depending on La3+ doping concentration. Photoluminescence spectra of undoped/doped ZnO with different contents of La3+ ion were investigated. The decay curves for the La3+ ion doped ZnO nanostructures were measured and the average lifetime was found to increase from 2.69 to 2.80 ns when La3+ content increased from 0 to 4%. The photocatalytic activity of doped products (ZnO:La) was investigated by using Congo-Red dye as a probe molecule for degradation under UV-light. Maximal color removal efficiency (97.63%) was observed experimentally for ZnO doped with 2% La3+ in dosage of 0.283 g/L. Finally, the recovered catalyst was thermally activated at 700 °C (1 h) and then successfully reused for the dye photodegradation.
关键词： La-doped ZnO nanostructures,Photodegradation kinetics,Photocatalyst,Optical properties,Electrospinning
更新于2025-09-23 15:22:29
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Zinc blende and wurtzite crystal structure formation in gold catalyzed InGaAs nanowires
摘要： III-V semiconductor nanowires made of materials which have the zinc blende crystal structure in bulk are well known to exhibit either the zinc blende or the wurtzite crystal structure. Understanding and controlling which crystal structure that forms is of highest importance for nanowire applications in a variety of areas. In addition to this, composition control in ternary nanowires is another key technology area for successful nanowire applications. We derive a general model, based on two-component nucleation theory, which we use to explain the so far less understood experimental observations of zinc blende, wurtzite, and mixed crystal structure as a function of growth conditions and composition, x, in gold catalyzed InxGa1-xAs nanowires. An interesting theoretical finding is that the wurtzite and zinc blende phases have different compositions, even if they are nucleated from the same catalyst particle at the same conditions.
关键词： A1. Nanostructures,A1. Nucleation,A1. Crystal structure,B2. Semiconducting III-V materials,B2. Semiconducting ternary compounds
更新于2025-09-23 15:22:29
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Influence of gold nanolayer coating on the continuous-wave laser ablation of a pure aluminum surface: Evaluations of structural and optical features
摘要： In this paper, formation of uniform and large-area micro/nanostructures on pure aluminum surfaces using a continuous-wave laser irradiation is presented. Gold nanolayer coating was utilized as a confinement layer for controlling the possible hydrodynamic phenomena in a molten area. Dependency of the laser-induced morphology on the thickness of a gold coating was investigated in this regard. Scanning electron microscopy, energy dispersive spectroscopy, grazing test of the X-ray diffraction, and optical absorption/reflection spectroscopy in UV/visible/IR ranges were employed to characterize the samples. Results showed that the formation of uniform structures of average sizes of 50 nm-5μm on aluminum surface was possible following the irradiation of a continuous-wave CO2 laser, delivering 130 W beam power. Alterations of the surface morphology brought about an increase in specific absorption peaks at the UV region and the appearance of an absorption peak in the visible range. In addition, these structure-covered surfaces provided interesting reflection behaviors in different spectral areas, which can clearly reflect their high potential to be used as selective solar absorbers. The results of this investigation indicated that optical characteristics such as absorption and emission coefficients as well as ξ factor were 0.98, 0.13, and 7.53, respectively. It can therefore be concluded that this process can be considered an efficient and fast technique to fabricate selective solar absorbers.
关键词： Nanostructures,Aluminum,Selective solar absorber,Sputtering,Nanolayer,Continuous-wave CO2 laser,Gold,Black carbon
更新于2025-09-23 15:22:29
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Reduced Graphene Oxide-Nanostructured Silicon Photosensors With High Photoresponsivity at Room Temperature
摘要： We have created nanostructured Si (~3 nm) with a direct band gap of 1.37 eV on electrically conducting reduced graphene oxide (rGO) for a highly efficient photosensor. This robust photosensor is fabricated using a non-equilibrium processing route, where nanosecond excimer laser pulses melt the alternating layers of Si and amorphous carbon to form micropillars and nanoreceptors of Si on rGO layers. The incident white light generates free carriers in the Si microstructures and nanoreceptors which are ballistically transported (via rGO layers) to the external circuit under the application of a voltage bias. The responsivity of rGO-Si devices to light (resistance vs time) and I-V measurements indicate an exponential drop in resistance with the incidence of white light and non-rectifying nature, respectively. Photoresponsivity of the rGO-Si devices is calculated to be 3.55 A/W at room temperature, which is significantly larger than the previously fabricated graphene-based Ohmic photosensors. Temperature-dependent resistance measurements of rGO-Si structures follow Efros-Shklovoskii variable range hopping (ES-VRH) electrical conduction in the low-temperature region (<100 K) and Arrhenius conduction in the high-temperature region (>100 K). In rGO, the localization length, hopping energy, and activation energy are calculated to be 17.58 μm, 3.15 meV, and 1.67 meV, respectively. The 2D nature of highly reduced and less defective rGO also render an interesting negative magnetoresistance (~2.5 %) at 5 K, thereby indicating potential implications of rGO-Si in opto-spintronics. The large-area integration of rGO-Si structures with sapphire employing nanosecond pulsed laser annealing and its exciting photosensing properties will open a new frontier for further extensive research in these functionalized 2D materials.
关键词： Pulsed laser annealing,Raman spectroscopy,Variable range hopping,Nanostructures,Reduced graphene oxide
更新于2025-09-23 15:22:29
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Enhanced generation of reactive oxygen species and photocatalytic activity by Pt-based metallic nanostructures: the composition matters
摘要： The modification of semiconductor nanostructures with metallic nanocomponents can promote the separation of electron/hole from photoexited semiconductors by forming heterojunctions, thus exhibit enhanced photocatalytic activities and potential applications. In this study, Pt-based NPs, including Pt, PtCu, and PtCuCo are employed as model co-catalysts to comparatively study their capability to enhance the photocatalytic activity of TiO2 nanosheets. It was found that each of Pt, PtCu, and PtCuCo can greatly enhance the photocatalytic activity of TiO2 toward degradation of organic dyes. Using electron spin resonance spectroscopy, we demonstrated that deposition of Pt-based NPs resulted in more production of reactive oxygen species including hydroxyl radicals, superoxide, and singlet oxygen. The enhancing effects of Pt-based NPs on generation of ROS and photocatalytic activity showed same trend: PtCuCo > PtCu > Pt. The mechanism underlying the enhancement differences in Pt-based NPs may be mainly related to electronic structure change of Pt in alloying with Cu and Co. These results are valuable for designing hybrid nanomaterials with high photocatalytic efficiency for applications in water purification and antibacterial products.
关键词： photocatalysis,hybrid nanostructures,reactive oxygen species,PtCuCo,TiO2
更新于2025-09-23 15:22:29
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Systematic λ/21 resolution achieved in nanofabrication by two-photon-absorption induced polymerization
摘要： Photopolymerization, based on two-photon absorption in resins, has been recognized as one of the enabling technologies to fabricate three-dimensional micro/nanostructures with a sub-diffraction-limit resolution. This work focuses on improving the spatial resolution using femtosecond laser, λ=780 nm, with a systematic nanofabrication process which we developed. We discuss the factors influencing the spatial resolution, including the laser intensity, the exposure time, and the scanning speed by fabricating polymerized-voxels, nano-lines, and suspended nano-fibers in a photoresist based on a methyl-methacrylate monomer. We show that a resolution of ~36 nm, corresponding to ~λ/21, is achieved. Stable 3D microstructures can be fabricated by using our custom made set up.
关键词： Voxel,Resolution,Two Photon Polymerization,Micro/Nanostructures,Femtosecond Laser,Suspended Polymerized Fibers
更新于2025-09-23 15:22:29
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Production of Methanol from Aqueous CO <sub/>2</sub> by Using Co <sub/>3</sub> O <sub/>4</sub> Nanostructures as Photocatalysts
摘要： In this work, we report for the first time the photocatalytic activity of Co3O4 nanostructures for the reduction of aqueous CO2 to methanol (MeOH). This could be considered a simple example of artificial photosynthesis. The photocatalysis experiments were developed under simulated solar light of 100 mW/cm2 and without using any sacrificial agent. To carry out this study, nanostructured mixed valence cobalt oxide (Co3O4) powders, with porous nanoparticle aggregates of different morphologies, have been prepared by two synthesis methods. The characterization of structural (PXRD, XPS, SEM, and TEM) and optical (UV-vis-NIR, Raman, and FT-IR) properties, magnetization curves, and surface area (BET) was accomplished.
关键词： Co3O4,photocatalysis,artificial photosynthesis,CO2 reduction,nanostructures,methanol
更新于2025-09-23 15:22:29
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Multicomponent Metal Oxide Nanostructures: Fabrication and Study of Core Issues to Improve Gas Sensing Performance
摘要： We have obtained and studied the sensing properties of porous titania-based nanostructures. The materials have been prepared using cost-effective techniques. The morphological and structural analyses of the prepared materials have been performed. The sensing properties of the samples have been studied towards carbon monoxide. The obtained results demonstrate that the prepared structures are promising for the potential applications in the area of chemical sensors for the environmental monitoring.
关键词： metal oxide,nanostructures,chemical gas sensor
更新于2025-09-23 15:22:29