Dependence of optical properties on doping metal, crystallite size and defect concentration of M-doped ZnO nanopowders (M = Al, Mg, Ti)

ZnO, Al-, Mg- and Ti-doped ZnO nanopowders were synthesized from CTAB-assisted oxalate intermediate by thermal decomposition method at 600 °C in air. All samples presented a hexagonal wurtzite structure. The spherical nanoparticles assembled in a porous octahedron-like shape for all samples. The size of Al-doped ZnO nanopowders increased as a function of Al ion concentration whereas the size of Mg- and Ti-doped ZnO nanopowders decreased when Mg and Ti ion concentrations were increased. The increment and reduction of their sizes can be explained by the Zener pinning effect. The E_g value of Al-doped ZnO nanopowders slightly decreased when Al ions were increased due to the crystallite size and defect concentration increased. In contrast, the E_g value of Mg- and Ti-doped ZnO nanopowders increased as a function of Mg and Ti ion concentration which can be explained by the Moss-Burstein effect.     

Optical and photocatalytic properties of La-doped ZnO nanoparticles prepared via precipitation and mechanical milling method

The synthetic method used for preparing ZnO nanoparticles strongly influenced the products obtained. The ZnO powders incorporated more La when prepared by the mechanical milling method whereas the La₂O₃/ZnO composite nanoparticles were formed better using the precipitation method. The phase formations were detected by the X-ray diffraction technique and the morphology of the samples was followed by scanning electron microscopy. The La contents affected the crystallite size. This was explained by the formation of LaOZn on the surface of the samples and by the Zener pinning effect. The band gap energy of the samples was influenced by repulsion between the valence and conduction bands and the presence of a secondary phase. The photocatalytic degradation of a methylene blue solution by the samples depended upon the number of oxygen vacancies.     

The wide band gap of highly oriented nanocrystalline Al doped ZnO thin films from sol–gel dip coating

Undoped and Al doped ZnO thin films were prepared on glass substrate by sol–gel dip coating from PVP-modified zinc acetate dihydrate and aluminium chloride hexahydrate solutions. The XRD patterns of all thin films indexed a highly preferential orientation along c-axis. The AFM images showed the average grain size of undoped ZnO thin film was about 101 nm whereas the smallest average grain size at 8 mol% Al was about 49 nm. The values of direct optical band gap of thin films varied in the range of 3.70–3.87 eV.     

Structure,morphology, photocatalytic and antibacterial activities of ZnO thin films prepared by sol–gel dip-coating method

ZnO thin films were deposited on soda lime glass substrates by the sol–gel dip-coating method with variations of the initial Zn²⁺ concentrations. Various techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and transmission electron microscopy (TEM) were used to investigate the effects of the initial Zn²⁺ concentrations on the structure, and surface morphology and topography of the prepared films. All prepared ZnO thin films showed a high transparency of over 88% in the visible region. The particle size increased with an increased initial Zn²⁺ concentration. This also reduced the surface denseness and the energy band gap of the ZnO thin films. All the prepared films showed photocatalytic properties through photodegradation of the methylene blue (MB) dye. The ZnO thin film prepared from the 0.1 M Zn²⁺ concentration showed the greatest efficiency as it had the highest surface area because of its greatest surface roughness. Furthermore, the prepared ZnO thin film showed antibacterial activities against the Escherichia coli bacterium.     

Evolution and temperature dependence of ZnO formation by high power sonication

The sonochemical reaction between varying concentrations of zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O) and hexamethylenetetramine (C₆H₁₂N₄) in a 150 W dual transducer sonicator resulted in different phases of zinc compounds. Single phase zinc oxide (ZnO) was exclusively obtained in the case of 0.05 M. By tracking the products synthesized at 50 °C, zinc hydroxide (Zn(OH)₂) was formed in the first 40 min and replaced by ZnO after prolonged sonication. Zn(OH)₂ was also present in a mixed phase with ZnO when the reagent concentration was reduced to 0.01 M. The increase in the synthesis temperature up to 80 °C reduced defects and free radicals but introduced zinc hydroxide nitrate hydrate (Zn₅(OH)₈(NO₃)₂(H₂O)₂) which is a dominant phase from the reaction between highly concentrated reagents (0.1 M). High temperature and sonication power in this system tend to cause agglomerations into irregular microparticles.     

Photocatalytic degradation of dye by Ag/ZnO prepared by reduction of Tollen’s reagent and the ecotoxicity of degraded products

A heterostructure of Ag/ZnO powder was prepared by a reduction of Ag(NH₃) ₂ ⁺ ions in a basic solution or Tollen’s reagent. From this method, the existence of a metallic Ag coating on the ZnO surface was confirmed by transmission electron microscope and x-ray photoelectron spectroscopy. The photocatalytic activity of the Ag/ZnO powders was investigated by analyzing the degradation of an aqueous methylene blue solution under a blacklight irradiation. Furthermore, the parameters, including Ag content, catalyst loading, initial dye concentration and pH, were also studied. After the methylene blue solution was irradiated for 30min under a blacklight illumination, total mineralization was not observed as the presence of some carbon compound species was indicated in a mass spectrum. Furthermore, the toxicity of the treated methylene blue solution produced by the Ag/ZnO powders was also investigated by a test for the inhibition of the growth of Chlorella vulgaris.     

Effect of Ag loading on activated carbon doped ZnO for bisphenol A degradation under visible light

Silver modified activated carbon doped zinc oxide (Ag/AC-ZnO) was synthesized via a calcination-electroless deposition route. The samples were characterized by X-ray powder diffractometry, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and UV–vis diffuse reflectance spectroscopy. The photocatalytic activity of the Ag/AC-ZnO was evaluated for bisphenol A degradation in the presence of H₂O₂ under visible light irradiation. The archived results showed that the photocatalytic activity of the Ag/AC-ZnO was higher than that of AC-ZnO and pure ZnO. The cytotoxicity of the bisphenol A after photocatalysis under visible light irradiation was tested using L929 mouse fibroblast cells and the obtained results indicated that the treated bisphenol A solution exhibited no cytotoxicity against normal cells.     

Dependence of β-Co(OH)2/ZnO heterostructural composite prepared by one-pot hydrothermal method on visible-light-driven photocatalytic degradation of organic dye

Journal of Materials Science: Materials in Electronics - A β-Co(OH)2/ZnO heterostructural composite was successfully prepared via a simple one-pot hydrothermal method. The β-Co(OH)2/ZnO...     

Structural,optical and antibacterial properties of nanocrystalline Zn1–xLaxO compound semiconductor

The Zn_1–xLa_xO powders were synthesized by the planetary ball milling method. An accumulated milling time of 15 h with a milling speed of 400 rpm were found to be the optimum milling conditions. The crystal structure, morphology, selected area electron diffraction, and elemental analysis were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy dispersive spectroscopy. The solubility limit of La that could substitute at the Zn sites was only 5 mol% or x=0.05. The dependence of the crystallite size on the La doping content can be explained by the Zener pinning effect. The particle size of the milled ZnO powder was about 34.03 nm and the particle size was reduced to 30.90 nm when doped with 10 mol% La. The particles of all milled samples could agglomerate as a cluster. The largest E_g value of 3.14 eV was obtained from the Zn_0.97La_0.03O powder due to this sample having the smallest crystallite size. The Zn_1–xLa_xO powders can inhibit Staphylococcus aureus better than Escherichia coli due to the presence of an extra lipopolysaccharide layer on the outer surface of the latter.     

Surface and photocatalytic properties of ZnO thin film prepared by sol-gel method

ZnO films were prepared on glass substrates by a sol-gel dip-coating technique. The films showed a polycrystalline phase without any preferable orientation. By decreasing the withdrawal speed, the surface of the ZnO films became denser because of a decrease in particle sizes. This reduces the distance between the supported solids under the water droplet that could increase the degree of the pinning effects, and leads to increase the water contact angle. Furthermore, these prepared ZnO films showed photocatalytic properties indicating by photocatalytic degradation of methylene blue under a blacklight illumination. By increasing the calcination temperature, the water contact angle value decreases due to the grain coalescence which increases the gap between these supported solids. On the other hand, this enhances the photocatalytic activity caused by the improving of the crystallinity and the surface roughness of ZnO thin films with an increase in calcination temperature.