High quality ZnO/CuO nanocomposites synthesized by microwave assisted reaction

Highly crystalline zinc oxide (ZnO) and ZnO/CuO nanocomposite powders have been synthesized by a facile microwave irradiation method. The resulting powders were characterized in terms of structural, optical and morphological properties by X-ray diffraction (XRD), room temperature photoluminescence (PL) spectroscopy and scanning electron microscopy (SEM), respectively. XRD patterns revealed the formation of ZnO/CuO nanocomposites with good crystalline quality. SEM images displayed the formation of hexagonal ZnO and flower shaped agglomeration of ZnO/CuO nano-flakes with uniform production. The strong UV emission peak observed at around 380 nm show enhanced intensity for ZnO/CuO nanocomposite. Compared to ZnO nanoparticles, ZnO/CuO composites exhibit good transparency with sharp absorbance edges. The simplicity of synthesis route coupled with better optical and PL emission properties propose the microwave synthesized ZnO/CuO nanocomposite powders a promising material for optoelectronic devices.     

Photoluminescence and photoconductivity studies of ZnO nanoparticles prepared by solid state reaction method

In the present work, the effect of annealing temperature on the luminescence and photoconductivity properties of ZnO nanoparticles (NPs) has been investigated. The ZnO NPs have been prepared at low temperature by a simple one step solid state reaction method using ZnSO₄·7H₂O as a starting precursor. X-ray diffraction results show, the prepared samples have a hexagonal wurtzite structure of ZnO NPs. FE-SEM reveals that the prepared ZnO nanoparticles have perfect spherical shape with little agglomeration. UV–visible absorption spectrum of as-prepared ZnO sample shows an absorbance peak at ~372 nm (~3.32 eV), which is blue shifted as compared to bulk ZnO (~386 nm). The annealed sample exhibits red shift of absorption peak. The photoluminescence spectra of as-prepared sample as well as annealed samples show one emission peak in UV region, and violet, blue, blue-green and green emissions in visible region. The sample annealed at 650 °C results in a significant reduction in luminescence as compared to that of the sample annealed at 450 °C. The photoconductivity properties such as voltage dependence of photocurrent, growth and decay of photocurrent as well as wavelength dependence of photocurrent have been studied in detail.     

Influence of synthetic parameters on the enhanced photocatalytic properties of ZnO nanoparticles for the degradation of organic dyes: a green approach

Herein, we report a green synthetic strategy using aqueous leaves extract of Actinodaphne madraspatna Bedd (AMB) for the synthesis of ZnO NPs. The physical shape, size, thermal stability, surface area, surface composition and chemical state, morphological and optical properties of the synthesized ZnO NPs are well characterized through UV–Visible diffuse reflectance spectroscopy (DRS UV), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman spectroscopy, thermal gravimetric analysis–differential thermal analysis (TGA–DTA), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET) and X-ray photon spectroscopy (XPS). FT-IR spectrum of ZnO NPs showed a characteristic peak at 416.62 cm^?1. Optical studies of prepared ZnO NPs showed the bandgap values are reduced in the range of 3.05 to 2.96 eV. The XRD and TEM data revealed the synthesized ZnO NPs exist in wurtzite crystal structure with crystallite sizes of 18 nm to 68 nm range. The variation in bandgap, surface area and crystallite structure of ZnO NPs would be achieved by changing the experimental parameters. FESEM showed spherical-shaped structure. XPS result confirmed the atomic states of Zn and O. The green synthesized ZnO NPs were examined for the photocatalytic degradation of methylene blue (MB) and acid violet 17 (AV17) dyes under UV light and the rate constants ‘k’ was calculated. It is found that the green synthesized ZnO NPs with reduced bandgap showed enhanced photocatalytic activity with higher rate constant.

     

Optical humidity sensor based on in situ and ex situ synthesized nAg/0.1%PVP composite coated on self supported PVP substrate

An optical based humidity sensor having linear response (R²?=?0.99) over a wide range (06–94%RH) and high sensitivity is reported using nAg/0.1%PVP nanocomposite. Nanocomposite is prepared using in-situ and ex-situ approaches by chemical reduction method with silver salt (AgNO₃) as precursor, tri sodium citrate as reducing agent and PVP as capping agent. The nanocomposite is dip coated on hydrophilic PVP substrate of 80 µm thickness. The material is characterized by using UV–Vis, TEM and FTIR techniques. UV–Vis and TEM analysis are complementary to each other for exhibiting dependence of particle size on preparation approach ??10 nm (in-situ) to 40 nm (ex-situ). Humidity sensing mechanism is explained on the basis of FTIR spectra. Co-ordination between tertiary nitrogen ( Open image in new window ) and C=O group with nAg particles during nanocomposite formation is evidenced from low humidity FTIR. Breaking of these bonds is evidenced from high humidity FTIR. In/PVP/6-PVP sensors offer higher sensitivity (~?0.68?±?0.04 (1/% RH)) as compared to Ex/PVP/4:5-PVP sensors [~?0.31?±?0.04 (1/% RH)].     

Poly(3-hexylthiophene)/hexamine modified ZnO hybrid nanocomposite: structural,optical, thermal and electrical transport studies

This paper reports the synthesis of poly(3-hexylthiophene) (P3HT)/HA@ZnO nanocomposite by in situ polymerization and demonstrates their thermal, morphological and optoelectronic properties. Zinc oxide (ZnO) nanoparticles were prepared by the simple approach of co- precipitation method using zinc acetate dihydrate as precursor modified by hexamine (HA) acting as a capping agent. Structural and photo physical studies shows that conjugated polymer chains intimately contact with the inorganic semiconductor. ZnO has wurtzite structure with average crystallite size of 40 nm. The emission spectra indicate that modified ZnO nanoparticles results in more efficient photo induced charge transfer than that of the simple nanocomposite of P3HT/ZnO. The morphological studies revealed that the transformation of granular morphology of P3HT to the clusters in P3HT/HA@ZnO hybrid nanocomposites. Cyclic voltammeter elucidates the electrochemical behavior and the HOMO–LUMO energy levels of the nanocomposites. The results indicate that the P3HT/HA@ZnO nanocomposite has energy gap of 0.72 eV, indicating this composite has potential for the fabricating hybrid organic–inorganic solid state solar cells. A solar to electric energy conversion efficiency of 0.1238 % was attained with the system.     

Nonlinear optical investigations on Al doping ratio in ZnO thin film under pulsed Nd:YAG laser irradiation

In the present study, it has been reported on the effect of Al doping on linear and nonlinear optical properties of ZnO thin films synthesized by spray pyrolysis method. The structural properties of ZnO thin films with different Al doping levels (0–4 wt%) were analyzed using X-ray diffraction (XRD). The results obtained from XRD analysis indicated that the grain size decreased as the Al doping value increased. The UV–Vis diffused refraction spectroscopy was used for calculation of band gap. The optical band gap of Al-doped ZnO (AZO) thin films is increased from 3.26 to 3.31 eV with increasing the Al content from 0 to 4 wt%. The measurements of nonlinear optical properties of AZO thin films have been performed using a nanosecond Nd:YAG pulse laser at 532 nm by the Z-scan technique. The undoped ZnO thin film exhibits reverse saturation absorption (RSA) whereas the AZO thin films exhibit saturation absorption (SA) that shows RSA to SA process with adding Al to ZnO structure under laser irradiation. On the other hand, all the films showed a self-defocusing phenomenon because the photons of laser stay on below the absorption edge of the ZnO and AZO films. The third-order nonlinear optical susceptibility, χ⁽³⁾, of AZO thin films, was varied from of the order of 10^?5–10^?4 esu. The results suggest that AZO thin films may be promising candidates for nonlinear optical applications.     

Enhancement of the optical and mechanical properties of chitosan using Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles

In this work, the optical and mechanical properties of Fe₂O₃ nanoparticles (NPs)/chitosan nanocomposite films have been investigated. Nanocomposite films of different weight ratios of Fe₂O₃ NPs/chitosan (0, 1, 5, 10, 20 and 30 wt%) were fabricated using casting technique. The optical properties of colloidal Fe₂O₃ NPs and Fe₂O₃ NPs/chitosan nanocomposite films were recorded using UV–visible spectrophotometer. As the ratio of Fe₂O₃ NPs to chitosan increases from 0 to 30%, the energy band gap of Fe₂O₃ NPs/chitosan films decreases from 3.16 to 2.11 eV. This decrease is due to quantum confinement effect. The mechanical properties of the nanocomposite films as a function of sweeping temperature were measured using a dynamic mechanical analyzer. An enhancement in storage modulus, stiffness and glass transition temperature (T_g) has been observed as the ratio of Fe₂O₃ NPs/chitosan increases. T_g of Fe₂O₃ NPs/chitosan nanocomposite film shifts towards higher temperature side with respect to pure chitosan film from 152.1 to 166.3?°C as the ratio of Fe₂O₃ NPs/chitosan increases from 0 to 30 wt%. The increase in T_g is mainly attributed to the decrease in free volumes and vacancies in the nanocomposite films as the weight ratio of Fe₂O₃ NPs/chitosan increases.     

Synthesis of fluorescent PVA/polypyrrole-ZnO nanofibers

Electro spinning is a simple and efficient technique to produce polymer nanofibers. Here, we describe the preparation of electrospun PVA/PPy–ZnO fluorescent fibers and discuss their characterization by use of UV–Vis and Fourier transform infrared spectroscopies, and fluorescence and scanning electron microscopies. These hybrid organic–inorganic fibers exhibit a visible emission of 526 nm with a well-defined green color, as the ZnO–NPs fluorescence emission at 390 nm is quenched. The scanning electronic microscopy images reveal that the fibers present an average diameter of 324 nm and good surface quality. We have observed that their Ohmic behavior is light sensitive as the charge transport along the fibers is highly affected by UV illumination. Since this is a reversible effect, and a quick recovery of the electrical resistance original value occurs right after the incident UV light is turned off, we suggest that these organic–inorganic materials can find useful applications in the preparation of various polymer-based micro and nano optoelectronic devices, such as low-cost flexible photovoltaic devices and UV sensors.     

Thermal blooming and photoluminescence characterizations of sol–gel CdO–SiO<Subscript>2</Subscript> with different nanocomposite

The CdO NPs was synthesized using the sol–gel method and the nanoparticles were characterized using an UV–Vis spectrophotometer, with shape and size were examined by SEM and XRD. The XRD analysis respects the Bragg’s law and confirmed the crystalline nature of CdO nanoparticles. From the XRD, the average size of CdO NPs was found to be around 41 nm. The photoluminescence spectra of the CdO NPs, as recorded at room temperature, were excited at 300 nm wavelength. The broad emission peaks were between 600 and 650 nm (orange emission). The optical limiting performance of the nanocomposite was described in the sol–gel state. Also, this study has observed and studied the diffraction rings generated in CdO NPs using the same CW laser. The number of rings increases almost exponentially with an increasing volume fraction of SiO₂ in the nanocomposites. The refractive index change, Δn, and effective nonlinear refractive index, n ₂, were found to be 10^?4 and 10^?8 cm²/W, respectively. The effective nonlinear refractive index, n ₂, was determined based on the observed number of rings. The threshold values of the CdO, CdO–2SiO₂ and CdO–5SiO₂ nanocomposites are 7.1, 6.55 and 6.34 mW, respectively. This large nonlinearity is attributed to the thermal effect. The present studies suggest that the nanocomposite is a potential candidate for optical device applications such as the optical limiters. The thermal blooming technique was applied to evaluate the thermo-optic coefficient and thermal diffusivity of the CdO NPs. In the thermal blooming experimental setup a transistor–transistor logic modulated CW laser of wavelength 532 nm was used as the excitation source.     

Synthesis,characterization and bactericidal activity of silica/silver core–shell nanoparticles

Silica/silver core–shell nanoparticles (NPs) were synthesized by coating silver NPs on silica core particles (size ~300 ± 10 nm) via electro less reduction method. The core–shell NPs were characterized for their structural, morphological, compositional and optical behavior using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis and UV–Visible spectroscopy, respectively. The size (16–35 nm) and loaded amount of silver NPs on the silica core were found to be dependent upon reaction time and activation method of silica. The bactericidal activity of the NPs was tested by broth micro dilution method against both Bacillus subtilis (gram positive) and Escherichia coli ATCC25922 (gram negative) bacterium. The bactericidal activity of silica/silver core–shell NPS is more against E. coli ATCC25922, when compared to B. subtilis. The minimal inhibitory concentration of the core–shell NPs ranged from 7.8 to 250 μg/mL and is found to be dependent upon the amount of silver on silica, the core. These results suggest that silica/silver core–shell NPs can be utilized as a strong substitutional candidate to control pathogenic bacterium, which are otherwise resistant to antibiotics, making them applicable in diverse medical devices.     

Preparation,characterization, and photoluminescence study of PVA/ZnO nanocomposite films

ZnO nanoparticles with average diameter of 25 nm were synthesized by a modified sol–gel method and used in the preparation of (in wt.%) (100 − x) poly(vinyl alcohol) (PVA)/x ZnO nanocomposite films, with x = 0, 1, 2, 3, 4, and 5. The PVA/ZnO films were exposed to UV radiation for 96 h and their thermal, morphological, and spectroscopic properties were investigated. In inert atmosphere, the nanocomposite films showed lower thermal stability than the pure PVA film, and the calorimetric data suggest an interaction between PVA and ZnO in the nanocomposite films. Some crystalline phases could be seen in the films with ZnO, and a direct dependence on the ZnO concentration was also observed. The original structure of ZnO nanoparticles remained unaltered in the PVA matrix and they were uniformly distributed on the film surface. The roughness of the PVA film was not modified by the addition of ZnO; however, it increased after 96 h of UV irradiation, more significantly in the nanocomposite films. The films showed an absorption band centered at 370 nm and a broad emission band in the UV–vis region when excited at 325 nm.     

Structural and optical characterization of (Sn/Li) co-doped ZnO thin films deposited by spray pyrolysis technique

(Sn/Li) co-doped ZnO (LTZO) thin films have been deposited by spray pyrolysis technique and their structural, morphological and optical properties have been investigated. The films were characterized by X-ray diffractometer (XRD), field-emission scanning electron micrograph (FESEM), (UV–Vis) spectroscopy and photoluminescence spectroscopy. XRD results revealed that all thin films (LTZO) are polycrystalline with à hexagonal wurtzite structure, moreover when the Li reach (5 at.%) content, the surface thin films of (LTZO5) become covered with bigger and clear nano-sized crystallites and the average value of grain size is 147 nm with mainly hexagonal grains. The (UV–Vis) spectroscopy showed high transmittance in the visible region, which varied between 84% and 93% and the doping of 5 at.% for all the films of Li content thin films (LTZO5) red shifted. The doping ZnO with lithium and tin were eliminates the deep-level emission in orange/red bands (around to 600 nm).     

Structural transition of ZnO thin films produced by RF magnetron sputtering at low temperatures

Zinc oxide (ZnO) thin films were prepared using reactive radio-frequency magnetron sputtering of a pure metallic zinc target onto glass substrates. The evolution of the surface morphology and the optical properties of the films were studied as a function of the substrate temperature, which was varied from 50 to 250 °C. The surface topography of the samples was examined using atomic force microscopy (AFM), and their optical properties were studied via transmittance measurements in the UV–Vis–NIR region. DRX and AFM analyses showed that the surface morphology undergoes a structural transition at substrate temperatures of around 150 °C. Actually, at 50 °C the formation of small grains was observed while at 250 °C the grains observed were larger and had more irregular shapes. The optical gap remained constant at ~3.3 eV for all films. In the visible region, the average optical transmittance was 80 %. From these results, one can conclude that the morphological properties of the ZnO thin films were more greatly affected by the substrate temperature, due to mis-orientation of polycrystalline grains, than were the optical properties.     

A comparative study of physical properties of pure and In-doped nanostructured ZnO polycrystalline thin film for optoelectronic applications

In this research work a comparative study of pure and In-doped ZnO polycrystalline thin films was made successfully deposited onto fused silica by reactive e-beam thermal evaporation at 300 °C. The structural and optical properties were assessed by employing X-ray diffraction (XRD), Raman spectroscopy, photoluminescence atomic force microscopy and spectroscopic ellipsometry (SE). XRD pattern, EDS and the principal Raman phonon band at 438 cm^?1 confirmed purely polycrystalline wurtzite structured ZnO and incorporation of In at the Zn lattice sites. In studying the structural properties, the characteristic (002) plane was used as the focal point. Structural analysis showed that with In incorporation, the crystallites exhibited a preferential orientation along (002) c-plane perpendicular to the substrate. With In-doping (3.9 at.%), the optical band-gap increased and compressive strains were developed within the film. The prominent optical phonon mode at 587 cm^?1 presented a low Raman intensity for the sample prepared in the oxygen environment and was assigned to oxygen vacancies. The film thickness and optical constants [refractive index (n), extinction coefficient (k)] were determined by SE study using Cauchy curve fitting model. PL emission spectra showed strong UV emission at 370–373 nm and a feeble visible (green) emission at 512–520 nm. The UV emission showed Stoke’s shift with incorporation of In at the lattice sites as the emitted energy is lower that the band-gap energy of ZnO. The observed properties showed that ZnO can be made significantly important an electronic and optical material for various optoelectronic applications by incorporating In as the dopant material.     

Influence of In doping on electro-optical properties of ZnO films

Thin metallic films of Zn and In/Zn were deposited onto glass substrates by thermal evaporation under vacuum. The metallic films were submitted to a thermal oxidation in air, at 623 K, for different oxidation times (30–90 min), in order to be oxidized. Structural and morphological analyses (X-ray diffraction, transmission electron microscopy and scanning electron microscopy) revealed that the obtained undoped and In-doped ZnO thin films possess a polycrystalline structure. Transmission spectra were recorded in spectral domain from 280 to 1400 nm. The influence of In doping and oxidation parameters as well, on the optical parameters (transmittance, optical bandgap, Urbach energy) were analysed. It was clearly evidenced that by In doping, the optical properties of ZnO films were improved. The temperature dependence of electrical conductivity was studied using surface-type cells with Ag electrodes. The obtained results indicate that In-doped ZnO films exhibit an enhancement of electrical conductivity with few orders of magnitude when compared with non-doped ones.     

Synthesis and characterization of SnS/ZnO nanocomposite by chemical method

SnS nanorods and SnS/ZnO nanocomposite have been synthesized by chemical method. Structure and phase purity of the samples were confirmed by powder X-ray diffraction. Transmission electron microscope image of SnS nanorods showed the average diameter of nanorods was about 85 nm and length was several micrometers. Transmission electron microscope image of SnS/ZnO nanocomposite showed the average particle size of ZnO nanoparticle was about 12 nm. The formation of SnS/ZnO nanocomposite was confirmed by elemental analysis using energy dispersive X-ray spectroscopy. From the microRaman spectrum of SnS/ZnO nanocomposite, it was observed that the intensity of B_2g mode of SnS nanorods decreased dramatically compared to that of pure SnS nanorods, since the surface of the SnS nanorods were coated with ZnO nanoparticles. Both direct and indirect band gap transitions were observed for SnS nanorods from the optical absorption spectrum and the optical absorption spectrum of SnS/ZnO nanocomposite showed absorption in the visible region.     

Influence of oxygen vacancies on the structural,dielectric, and magnetic properties of (Mn,Co) co-doped ZnO nanostructures

We analysed the variation and effect of oxygen vacancies on the structural, dielectric and magnetic properties in case of Mn (4%) and Co (1, 2 and 4%) co-doped ZnO nanoparticles (NPs), synthesized by chemical precipitation route and annealed at 750 °C for 2 h. From the XRD, the calculated average crystallite size increased from15.30?±?0.73 nm to 16.71?±?012 nm, when Co content is increased from 1 to 4%. Enhancement of dopants (Mn, Co) introduced more and more oxygen vacancies to ZnO lattice confirmed from EDX and XPS. The high-temperature annealing leads to reduction of the dielectric properties due to enhancement in grain growth (large grain volume and lesser number of grain boundaries) with the incorporation of Co and Mn ions into the ZnO lattice. The electrical conductivity of the Mn doped and (Mn, Co) co-doped ZnO samples were enhanced due to increase in the volume of conducting grains and charge density (liberation of trapped charge carriers in oxygen vacancies and free charge carriers at higher frequencies). The Mn-doped and (Mn, Co) co-doped ZnO NPs show ferromagnetic (FM) behaviour. The saturation and remnant magnetizations (M_s and M_r) elevates from (0.235 to 1.489)?×?10^?2 and (0.12 to 0.27)?×?10^?2 emu/g while Coercivity (H_c) reduced from 97 to 36 Oe with enhancement in the concentration of dopants in ZnO matrix. Oxygen vacancies were found to be the main reason for room-temperature ferromagnetism (RTFM) in the doped and co-doped ZnO NPs. The results show that the enhanced dielectric and magnetic properties of Mn doped and (Mn, Co) co-doped ZnO is strongly correlated with the concentration of oxygen vacancies. The observed enhanced RTFM, dielectric properties and electrical conductivity makes TM doped ZnO nanoparticles suitable for spintronics, microelectronics and optoelectronics based applications.     

Fast one-step synthesis of ZnO sub-microspheres in PEG200

ZnO sub-microspheres were synthesized via a new, simple, and one-step method by using zinc acetate dihydrate as a precursor and PEG200 as a solvent and modifier. The effect of temperature (160–210 °C) on the crystallization, surface morphology, and luminescence properties of ZnO spheres was investigated using different characterization techniques, including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, UV–Vis spectroscopy, and room temperature photoluminescence. The results show that the ZnO crystal has a hexagonal wurtzite structure. The products have monodispersed spherical morphology with diameters in the range of 200–600 nm. They have intensive UV emission peaks at ~380 nm and relatively weak and broad green peaks at ~550 nm. The PEG200 molecules adsorb on the surface of ZnO spheres. On the basis of the experimental results, a mechanism was proposed to elucidate the formation of ZnO sub-micron spheres.     

The effect of molybdenum on optical properties of ZnO nanoparticles in Ultraviolet–Visible region

Zn_1?xMo_xO (x = 0.0, 0.01, 0.03, and 0.05) nanoparticles (NPs) are synthesized by using gelatin, via the sol-gel method. A calcination temperature of 600 °C is maintained for 2 h. The influence of molybdenum concentration on the structural and optical properties of these NPs is demonstrated. Synthesized NPs are characterized using X-ray diffraction (XRD), UV–vis spectroscopy, and transmission electron microscopy (TEM). XRD patterns reveal the crystallite nature of samples that exist in the hexagonal wurtzite phase. TEM images manifest the existence of nearly spherically-shaped NPs. The UV–vis spectroscopy results showed that the absorption edge of ZnO nanoparticles is red-shifted by adding molybdenum. Finally, the optical parameters of the refractive index and permittivity of the synthesized samples were calculated using Kramers-Kronig relations using the UV–vis spectra.     

Effect of carbon nanotubes shape on the properties of multiwall carbon nanotubes/polyethylene flexible transparent conductive films

Transparent conductive material is used in a wide range of applications and is particularly interesting. In the present work, a series of multiwall carbon nanotubes/low density polyethylene nanocomposites with different carbon nanotubes were prepared via solution casting method. The optical transparency, morphology, and resistivity of transparent conductive films have been characterized by using UV–Vis Spectrophotometer, Field emission scanning electron microscope and Multimeter, respectively. Their electrically conductive and optically transparent properties were studied and compared. The result showed that thinner and longer multiwall carbon nanotubes were more suitable for the fabrication of flexible transparent conductive nanocomposites. The sample filled with 1 wt% of T.1 (outside diameter <8 nm, length 10–30 μm) had good transparent conductive properties (volume conductivity of 3.12 × 10^?3 S m^?1 and optical transmittance of 62.8 % at the light wavelength of 600 nm). The high volume conductivity and optical transparency demonstrated that such kind of nanocomposite films had favorable potential in the applications from electromagnetic interference shielding to transparent electrodes.