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Band gap engineered zinc oxide nanostructures <i>via</i> a sol–gel synthesis of solvent driven shape-controlled crystal growth
摘要： A reliable sol–gel approach, which combines the formation of ZnO nanocrystals and a solvent driven, low shape-controlled, crystal-growth process to form well-organized ZnO nanostructures at temperature is presented. The sol of ZnO nanocrystals showed shape-controlled crystal growth with respect to the solvent type, resulting in either nanorods, nanoparticles, or nanoslates. The solvothermal process, along with the solvent polarity facilitate the shape-controlled crystal growth process, augmenting the concept of a selective adhesion of solvents onto crystal facets and controlling the final shape of the nanostructures. The XRD traces and XPS spectra support the concept of selective adhesion of solvents onto crystal facets that leads to yield different ZnO morphologies. The shift in optical absorption maxima from 332 nm in initial precursor solution, to 347 nm for ZnO nanocrystals sol, and finally to 375 nm for ZnO nanorods, evidenced the gradual growth and ripening of nanocrystals to dimensional nanostructures. The engineered optical band gaps of ZnO nanostructures are found to be ranged from 3.10 eV to 3.37 eV with respect to the ZnO nanostructures formed in different solvent systems. The theoretical band gaps computed from the experimental XRD spectral traces lie within the range of the optical band gaps obtained from UV-visible spectra of ZnO nanostructures. The spin-casted thin film of ZnO nanorods prepared in DMF exhibits the electrical conductivity of 1.14 × 10?3 S cm?1, which is nearly one order of magnitude higher than the electrical conductivity of ZnO nanoparticles formed in hydroquinone and ZnO sols. The possibility of engineering the band gap and electrical properties of ZnO at nanoscale utilizing an aqueous-based wet chemical synthesis process presented here is simple, versatile, and environmentally friendly, and thus may applicable for making other types of band-gap engineered metal oxide nanostructures with shape-controlled morphologies and optoelectrical properties.
关键词： electrical conductivity,ZnO nanostructures,optical band gap,shape-controlled crystal growth,sol–gel synthesis
更新于2025-11-19 16:56:42
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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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Methodical engineering of defects in MnXZn1-X O(x?=?0.03, and 0.05) nanostructures by electron beam for nonlinear optical applications: A new insight
摘要： A series of MnxZn1-xO (x = 0.03, 0.05) nanostructures have been grown via the solution based chemical spray pyrolysis technique. Electron beam induced modifications on structural, linear and nonlinear optical and surface morphological properties have been studied and elaborated. GXRD (glancing angle X-ray diffraction) patterns show sharp diffraction peaks matching with the hexagonal wurtzite structure of ZnO thin films. The upsurge in e-beam dosage resulted in the shifting of XRD peaks (101) and (002) towards lower angle side, and increase in FWHM value. Gaussian deconvolution on PL spectra reveals the quenching of defect centers, implying the role of electron beam irradiation regulating luminescence and defect centers in the nanostructures. Irradiation induced spatial confinement and phonon localization effects have been observed in the films via micro Raman studies. The later are evident from spectral peak shifts and broadening. Detailed investigations on the effect of electron beam irradiation on third order nonlinear optical properties under continuous and pulsed mode of laser operation regimes are deliberated. Third order absorptive nonlinearity of the nanostructures evaluated using the open aperture Z-scan technique in both continuous and pulsed laser regimes shows strong nonlinear absorption coefficient β eff of the order 10-4 cm/W confirming their suitability for passive optical limiting applications under intense radiation environments. Laser induced third harmonic generation (LITHG) experiment results supports the significant variation in nonlinearities upon electron beam irradiation, and the effect can be utilized for frequency conversion mechanisms in high power laser sources and UV light emitters.
关键词： Mn:ZnO nanostructures,8MeV e-beam,Spatial confinement effects,Defects quenching,Third harmonic generation
更新于2025-09-19 17:15:36
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[IEEE 2019 IEEE SENSORS - Montreal, QC, Canada (2019.10.27-2019.10.30)] 2019 IEEE SENSORS - Room temperature gas sensors based on laser-annealed ZnO nanostructures for gaseous pollutants detection
摘要： To effectively control gaseous pollutants in air it is mandatory to fabricate reliable and non-expensive monitoring systems that can be easily deployed in urban areas. Sensing devices based on metal oxide nanostructures offer many advantages respect bulk material in detecting multiple hazardous gases such as, high stability, easy surface functionalization and temperature. Among diverse potentially nanostructures, ZnO nanorods can be obtained with low cost and simple process at a low manufacturing temperature opening the possibility to integrate the material with flexible substrates. Additionally, laser annealing procedure can be exploited to improve or tune the morphology and the electrical properties of these materials. In this work, we present a comparison between the performance of as deposited and laser-annealed devices in the detection of NO and NO2. Different sensors characteristics at increasing gas concentrations and dynamic behaviors are shown and discussed evaluating the mechanisms involved in the diverse pollutant detection. As result, the laser-annealed sensor exhibits a sensitivity one-order higher respect to as-grown sample in detecting NO (3.9x10-3 vs 2.7x10-4 [1/ppm]) while for NO2 sensitivity is more than four times higher (3.8x10-3 vs 8.4x10-4 [1/ppm]).
关键词： ZnO nanostructures,gaseous pollutants,room temperature gas sensing,laser annealing
更新于2025-09-16 10:30:52
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A study of 8 MeV e-beam on localized defect states in ZnO nanostructures and its role on Photoluminescence and third harmonic generation
摘要： In this article we have explored an effect of electron beam irradiation (EBI) on physical and nonlinear optical properties ZnO thin nano films. Nanostructured ZnO thin films were grown by low cost spray pyrolysis technique. The irradiation dosage has been fixed at 5kGy, 10kGY, 15kGy and 20kGy. The structural investigation by Glancing angle X-Ray Diffractometer (GAXRD) confirms a polycrystalline phase of ZnO with wurtzite structure. The variation in the surface morphology upon EBI has been demonstrated using 2D and 3D Atomic force microscopy (AFM) images. Nanoscope software analysis quantifies the variation in surface roughness and average particle height upon EBI. The defect states created in the films upon irradiation experiments were investigated using UV- visible spectrophotometer, Room temperature Photoluminescence (RTPL), Raman and X-ray photoelectron spectroscopy (XPS). The increase in urbach tail validates the creation of localized defect states in the films The Gaussian fitting on RTPL spectra shows the quenching in the luminescent centers upon irradiation arised as result of recombination of vacancy defects. Phonon confinement model fitting on Raman spectra endorses that shift in the phonon modes observed on irradiation is due to spatial confinement of phonons. The elemental composition and impurity states of the EBI ZnO thin films were studied using XPS spectra. The shift in the binding energy of Zn and O elements infers the electron beam induced changes in the films. The electron beam irradiation has resulted in the increment of third order optical susceptibility χ(3) from 3.5×10-4esu to 8.13×10-3esu due to the enhancement of electronic transition to different defect levels formed in the films and through local heating effects arising due to continuous wave (CW) laser illumination. The enhanced THG signal investigated using Nd:YAG laser at 1064nm and 8 ns pulse width shows the promising features of EBI ZnO films for frequency tripling applications.
关键词： Electron beam irradiation,Phonon confinement model,third harmonic generation,ZnO nanostructures,Localized defect states
更新于2025-09-10 09:29:36
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Effect of the zinc salt concentration on the ZnO thin films properties grown by MWCBD
摘要： Nanostructured ZnO thin films with different surface morphologies have been synthesized by the microwave assisted chemical bath deposition technique (MWCBD), adjusting the pH of the reaction solution between 9 and 11.14. Newest results are presented in this work supported by previous investigations. Morphology, structure and optical properties of the films have been studied by scanning electron microscopy (SEM), X-ray diffraction (XRD) and room temperature photoluminescence (PL) techniques. It has been observed that the zinc salt concentration and the pH of the reaction solution determines the reaction kinetics, affecting strongly the morphology of the final product. However, the rapid heating in microwave irradiation process facilitates the crystallization of the formed nano-/microstructures. Effects of composition and morphology of the grown nano-/microstructures on their photoluminescence (PL) behaviors have been discussed.
关键词： Optical properties,Microwave deposition,ZnO nanostructures,Morphology control
更新于2025-09-10 09:29:36
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Photocatalytic Reduction of Bicarbonate to Formic Acid using Hierarchical ZnO Nanostructures
摘要： Zinc oxide (ZnO) is an earth abundant, non-toxic, and low-cost material that has been used widely for photocatalytic water splitting, gas sensing, and dye degradation. In this study, several ZnO structures were tested for the photochemical reduction of bicarbonate to formic acid, an intermediate to methanol, a high-octane-number fuel with higher energy density than compressed hydrogen. The different ZnO morphologies studied included micron- and nano-particulate ZnO, rods, wires, belts, and flowers. ZnO was also synthesized from the direct calcination of zinc acetate, which provided a cheap and large-scale synthesis method to produce ZnO. The photocatalytic efficiency of the synthesized ZnO was compared to commercial micron- and nano-particulate ZnO, and was proven to be just as efficient. ZnO flowers, possessing the largest surface area of 12.9 m2/g, were found to be the most efficient reaching an apparent quantum efficiency (AQE) of 10.04±0.09%, with a superior performance over commercial TiO2 (P25), a benchmark photocatalyst. This is the first study to compare different shapes and sizes of ZnO for bicarbonate reduction in an aqueous system with excellent photocatalytic performance.
关键词： solar fuels,ZnO nanostructures,zincite,bicarbonate photoreduction
更新于2025-09-10 09:29:36
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Enzyme Biosensing Based on Zinc Oxide Nanostructures as Active Surface
摘要： Ag/ZnO mesostructures deposited onto substrates different were analysed in order to use ZnO as bioactive surface. This paper presents the results obtained at the eNDE of strips gratings deposited on different substrates used as bioactive surface using the EM sensor with MM lens in order to improve the emphasizing of the evanescent waves appeared when the slits of MSG are filled with immobilized enzymes.
关键词： EM sensor,enzyme biosensing,bioactive surface,evanescent waves,ZnO nanostructures
更新于2025-09-09 09:28:46
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Improved Hydrophobicity of Polydimethylsiloxane (PDMS) Coating with ZnO Nanostructures
摘要： In this present work, an environmentally safe hydrophobic cotton surface comprising of PDMS and different morphology of Zinc oxide (ZnO) nanostructures via simple dip coating method was developed. ZnO nanosphere and ZnO nanoflakes were synthesized via sol gel method while ZnO nanorods were synthesized via solution precipitation method. The precursors used to prepared ZnO nanospheres, nanoflakes and nanorods are zinc acetate dehydrate, zinc chloride and zinc nitrate tetrahydrate respectively. ZnO nanostructures were analysed using FESEM and XRD. The hydrophobic cotton surface was characterized via FT-IR and WCA analysis. A WCA of 144.15° was achieved when coating the cotton with ZnO nanoflakes (ZnO-NF:PDMS).
关键词： ZnO nanostructures,Polydimethylsiloxane,Solution precipitation method,Hydrophobicity,Sol gel method,Dip coating
更新于2025-09-04 15:30:14