T. Dedova

Photoluminescence of spray pyrolysis deposited ZnO nanorods

Photoluminescence of highly structured ZnO layers comprising well-shaped hexagonal rods is presented. The ZnO rods (length 500-1,000 nm, diameter 100-300 nm) were grown in air onto a preheated soda-lime glass (SGL) or ITO/SGL substrate by low-cost chemical spray pyrolysis method using zinc chloride precursor solutions and growth temperatures in the range of 450-550°C. We report the effect of the variation in deposition parameters (substrate type, growth temperature, spray rate, solvent type) on the photoluminescence properties of the spray-deposited ZnO nanorods. A dominant near band edge (NBE) emission is observed at 300 K and at 10 K. High-resolution photoluminescence measurements at 10 K reveal fine structure of the NBE band with the dominant peaks related to the bound exciton transitions. It is found that all studied technological parameters affect the excitonic photoluminescence in ZnO nanorods.PACS: 78.55.Et, 81.15.Rs, 61.46.Km

ZnO Nanorods via Spray Deposition of Solutions Containing Zinc Chloride and Thiocarbamide

In this work we present the results on formation of ZnO nanorods prepared by spray of aqueous solutions containing ZnCl2and thiocarbamide (tu) at different molar ratios. It has been observed that addition of thiocarbamide into the spray solution has great impact on the size, shape and phase composition of the ZnO crystals. Obtained layers were characterized by scanning electron microscopy (SEM) equipped with energy selected backscattered electron detection system (ESB), X-ray diffraction (XRD) and photoluminescence spectroscopy (PL). Small addition of thiocarbamide into ZnCl2solution (ZnCl2:tu = 1:0.25) supports development of significantly thinner ZnO nanorods with higher aspect ratio compared to those obtained from ZnCl2solution. Diameter of ZnO rods decreases from 270 to 100 nm and aspect ratio increases from ∼2.5 to 12 spraying ZnCl2and ZnCl2:tu solutions, respectively. According to XRD, well crystallized (002) orientated pure wurtzite ZnO crystals have been formed. However, tiny ‘spot’—like formations of ZnS were detected on the side planes of hexagonal rods prepared from the thiocarbamide containing solutions. Being adsorbed on the side facets of the crystals ZnS inhibits width growth and promotes longitudinalc-axis growth.

Selective performance of sol-gel synthesised titanium dioxide photocatalysts in aqueous oxidation of various-type organic pollutants

Photocatalysts synthesized by sol-gel method inevitably incorporate carbon together with dopants. The objective of the research consists in the synthesis and testing of photocatalytic activity of carbon-containing titanium dioxide photocatalysts calcinated at various temperatures. The optical and structural properties of the catalysts were also studied. The activity was tested in visible light in aqueous photocatalytic oxidation of three various-type pollutants, methyl-tert-butyl ether, p-toluidine and phenol, where the divergent character of the C-TiO2 catalysts was distinctively observed: methyl-tert-butyl ether and p-toluidine were oxidized with the efficiency close to or even surpassing that of UV-irradiated P25 (Evonik), whereas phenol was oxidized poorly. The observed photocatalytic activity, where quantum efficiency varied from 0.6 to 2.3 and from 0.1 to 1.2% for p-toluidine and phenol degradation respectively, may be explained by the different electrostatic properties of the catalysts’ surface and the tested substances, i.e. their interaction. This compromises the widespread usage of phenol as a reference substance for comparison of catalytic activities of catalysts.

Aqueous Photocatalytic Oxidation of Doxycycline

Abstract The experimental research into the aqueous photocatalytic oxidation of doxycycline, a tetracycline family antibiotic, was undertaken. The objective of the study was to ensure the feasibility of doxycycline photocatalytic degradation by UVA irradiated titania coatings on granulated media to be used in fluidised bed photocatalytic reactor and by slurries of P25, Evonik, as well as by visible light-sensitive sol-gel synthesized carbon-containing titania. The parameters influencing doxycycline oxidation, like catalyst concentration, initial doxycycline concentration and pH with P25 TiO2 were studied. The impact of calcination temperature on the catalytic properties of carboncontaining titania and catalytic activity of titania film on expanded clay as bed material towards doxycycline degradation were also studied. Based on the examination of doxycycline photocatalytic oxidation by-products, possible doxycycline degradation pathways were proposed.

Growth of ZnO rods on FTO electrodes by spray pyrolysis

ZnO layers comprizing rods were deposited by chemical spray pyrolysis (CSP) method at 520 °C on different FTO (SnO2:F)/glass substrates using zinc chloride aqueous solutions. Substrates were purchased from different manufactures and differ by morphology, grain size and roughness of FTO electrode. FTO/glass substrates and ZnO layers grown on them were characterised with the help of XRD, AFM, high resolution SEM, EDX methods. The relationship between nanorod formation and substrate properties was studied. It was found that substrate roughness and grain size influence the ZnO rods formation. Deposition of rods (d=300 nm, L=1.4 μm) was successful on the FTO layers with grain sizes around 30–50 nm and roughness below 10 nm, whereas large-grained FTO (grain size > 130 nm) resulted in thick, low-aspect ratio crystals with diameter around 400 nm and length of about 400 nm.

ZnO Nanorods Grown Electrochemically on Different Metal Oxide Underlays

In this study we present results on electrochemically grown ZnO nanorods on different metal oxide underlays, such as ZnO seed layers with different morphologies, ZnS and TiO2 compact thin films produced by spray pyrolysis on transparent conductive oxide (TCO) substrates. Also in this work we present results on ZnO nanorods directly deposited on some chosen TCO substrates. The relationship between nanorod formation and substrate properties were studied. All ZnO nanorod layers were grown electrochemically using ZnCl2 aqueous solutions (c=0.2 mmol/L) at the bath temperature of 80 °C during one hour. The structural properties and morphology of metal oxide underlays and ZnO nanorods grown on them were studied by scanning electron microscopy (SEM), x-ray diffraction spectroscopy (XRD). Depending on the substrate morphology, ZnO rods with different dimension, orientation, shape and density were obtained. For instance, larger rods (d~200 nm, l~700 nm) were obtained on substrates, such as ITO/glass, FTO/glass and ZnO:In/ITO/glass. Smaller rods (d~60 nm, l~350 nm) were obtained on smooth, uniform and fine-grained underlays, such as ZnS and TiO2.

Template synthesis of titanium dioxide coatings and determination of their photocatalytic activity by aqueous oxidation of humic acid

In this work, aqueous photocatalytic oxidation of humic acid, present in various waters as naturally occurring compound or anthropogenic pollutant, was studied using self-synthesized titanium dioxide coatings. To obtain the latter, template synthesis, widely used for the production of photocatalysts with improved surface properties and activity, was applied with variations in template material, N-cetyl-N,N,N-trimethylammonium bromide content. The catalysts were characterized using XRD, UV-VIS spectroscopy, and SEM. The activity of TiO2 coatings in the degradation of humic acid proved to be superior to that of commercial photocatalyst P25 (Evonik) The dependence of the photocatalysts’ performance on the template content in the synthesis precursors, which was responsible for the various surface features of the coatings, was established and explained.

Structural and optical characterization of sprayed ZnS thin films

The cost-effective spray pyrolysis technique was applied to prepare ZnS thin films for large-scale applications. Aqueous solutions containing ZnCl2 and SC(NH2)2 were deposited onto glass and n-type Si(100) substrates at 430-600°C. The structure and phase composition were studied by XRD and FTIR, the surface morphology by SEM. The optical properties were determined from the transmittance and reflectance measurements in the UV-visible and near-IR regions. The phase composition, crystallinity, and surface morphology of the films could be controlled by the Zn:S molar ratio in the stock solution and the deposition temperature. Highly (001) oriented ZnS films with wurtzite structure were grown at temperatures above 500°C using the Zn:S molar ratio 1:2 in the solution. The sprayed films had high optical transmittance in a wide spectral range and the refractive index of up to 1.9 at 632.8 nm. It was also found that the sprayed ZnS films are capable of being used as antireflection coatings in Si-based devices.