Sonochemical synthesis of CuO nanostructures and their morphology dependent optical and visible light driven photocatalytic properties

A controlled synthesis of CuO nanostructures with various morphologies were successfully achieved by presence/absence of low frequency (42 kHz) ultrasound with two different methods. The size, shape and morphology of the CuO nanostructures were tailored by altering the ultrasound, mode of addition and solvent medium. The crystalline structure and molecular vibrational modes of the prepared nanostructures were analysed through X-ray diffraction and FTIR measurement, respectively which confirmed that the nanostructures were phase pure high-quality CuO with monoclinic crystal structure. The morphological evaluation and elemental composition analysis were done using TEM and EDS attached with SEM, respectively. Furthermore, we demonstrated that the prepared CuO nanostructures could be served as an effective photocatalyst towards the degradation of methyl orange (MO) under visible light irradiation. Among the various nanostructures, the spherical shape CuO nanostructures were found to have the better catalytic activities towards MO dye degradation. The catalytic degradation performance of MO in the presence of CuO nanostructures showed the following order: spherical\nanorod \layered oval \nanoleaf \triangular \shuttles structures. The influence of loading and reusability of catalyst revealed that the efficiency of visible light assisted degradation of MO was effectively enhanced and more than 95 % of degradation was achieved after 3 cycle

Microstructure, vibrational and visible emission properties of low frequency ultrasound (42 kHz) assisted ZnO nanostructures

Size and shape tuneable ZnO nanostructures were prepared by a low frequency ultrasound (42 kHz) route using various organic solvents as the reaction media. The crystalline nature, lattice parameters and microstructural parameters such as microstrain, stress and energy density of the prepared ZnO nanostructures were revealed through X-ray diffraction (XRD) analysis. The organic solvents influenced the size and morphology of the ZnO nanostructures, and interesting morphological changes involving a spherical to triangular shaped transition were observed. The visible emission properties and lattice vibrational characteristics of the nanostructures were drastically modified by the changes in size and shape. Raman spectral measurements revealed the presence of multiphonon processes in the ZnO nanostructures. The intensity of the visible emission band was found to vary with the size and morphology of the structures. The strongest visible emission band corresponded to the structure with the largest surface/volume ratio and could be attributed to surface oxygen vacancies. The control over the size and morphology of ZnO nanostructures has been presented as a means of determining the intensity of the visible emission ban

Enhanced ultraviolet-blue emission and Raman modes in ZnO:Cr

We present secondary phase identification studies on Cr doped ZnO nanoparticles prepared by the sol-gel method. X-ray diffraction analysis confirms the formation of chromium oxides and there is found to be an increase of lattice parameter with thermal annealing. Scanning electron microscopic studies show the increase in the crystalline nature and particle size. Optical absorption measurements of the as prepared sample exhibit a strong band at 356 nm due to the free exciton absorption of the ZnO nanoparticles. An absorption band at 277 nm is due to the 3T1 →    3T2 transition in Cr4+ ions which appears only for the annealed samples. Photoluminescence studies show that deep level emission is completely suppressed after Cr2O3 formation/thermal annealing. Raman and FTIR spectra reveal formation of the Cr2O3 phase. Thermal annealing leads to the increase of crystalline nature which gives an enhancement to the Raman modes

Fabrication and spectroscopic investigation of sandwich-like ZnO:rGO:ZnO:rGO:ZnO structure by layer-by-layer approach

Transparent conducting materials (TCMs) are the heart of modern optoelectronic industries and the properties of TCMs could be improved by the introduction of 2D carbon materials. In this report, the influence of order layering on microstructural, transparency and emission characteristics of ZnO:rGO:ZnO:rGO:ZnO and rGO:ZnO:rGO:ZnO:rGO sandwich structures has been investigated. The layer-by-layer approach has been adopted for the fabrication of sandwich structured materials ZnO:rGO:ZnO:rGO:ZnO and rGO:ZnO:rGO:ZnO:rGO through the spin coating technique. The sandwich structures of ZnO and rGO exhibited hexagonal wurtzite structure of ZnO without any impurities were identified through XRD. The ordering of layer's influenced the microstructural parameters and were significantly altered. The spherical nature of the particles and the formation of the sandwich structures were confirmed by using SEM micrograph. The reduction in an optical transparency and narrowing bandgap of the ZnO upon the order of layering were identified through transmission spectra. The lower energy shift of near band edge (NBE) emission and reduction in the emission intensity with respect to pure ZnO nanostructures was observed. The present work provides a simple layer-by-layer approach to fabricating sandwich structures and improving the optical properties which have potential applications in various optoelectronic devices

A facile hydrothermal synthesis of CeO2 nanocubes decorated ZnO nanostructures: optical and enhanced photocatalytic properties

Synthesis of CeO2, ZnO, and CeO2 nanocubes decorated on the surface of ZnO ovals via a simple hydrothermal method was investigated. The crystalline nature and purity of CeO2, ZnO and CeO2 decorated ZnO were confirmed through X-ray diffraction (XRD) by the co-existence of cubic and hexagonal wurtzite phase of CeO2 and ZnO, respectively. The transmission electron microscopy (TEM) images revealed that CeO2 nanocubes were well decorated on the surface of ZnO in oval morphology. The optical properties of the prepared materials were investigated using diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) spectra and also, the oxidation species presented in the materials were identified through X-photoelectron spectroscopy (XPS) spectra survey. The photocatalytic activity of CeO2 decorated ZnO nanostructures against methylene blue (MB) as a model pollutant under visible light irradiation was enhanced when compared to those of the pure CeO2 and ZnO nanostructures. The reusability of catalyst studies revealed that the efficiency of the visibility light degradation of MB was increased upon the CeO2 deposited on the ZnO surfaces