Effect of the mixing rate on the morphology and photocatalytic activity of ZnO powders prepared by a precipitation method

The urchin-like shape of ZnO powders was prepared by mixing of Zn²⁺ and NaOH solutions at various mixing rates. In this work, ε-Zn(OH)₂ was the first precipitant that was subsequently transformed to ZnO in the alkaline medium during heating. The size of the urchin-like shape of the ZnO powder decreased with a decrease of the mixing rate. The large urchin-like shape also had a large diameter of its hexagonal facet (0 0 0 1) and showed the highest photocatalytic degradative activity on methylene blue.     

Dependence of photocatalytic activity on structural and optical properties of nanocrystalline ZnO powders

Nanocrystalline ZnO powders were prepared from cetyltrimethylammonium bromide (CTAB)-modified NaOH, NH₄OH and (CH₂)₆N₄ solutions. The calcined ZnO powders exhibited a hexagonal structure without any secondary phase. Different shapes of ZnO powders were formed depending on CTAB concentration and type of precipitating agent. As (CH₂)₆N₄ solution was used, rod-like ZnO structure was changed to a spherical shape when CTAB concentration was increased. The widest E_g value of approximately 3.23 eV was obtained from the sample containing the lowest defect concentration. The decolorization efficiency was higher than 90% after irradiating for 90 min and the sample with higher E_g value showed higher decolorization efficiency.     

Synthesis, photocatalytic and antibacterial activities of ZnO particles modified by diblock copolymer

Various shapes of ZnO particles were synthesized through a precipitation method as a low cost technique. The morphological changes due to the use of poly(ethylene oxide)-b-poly(propylene oxide) copolymer as a stabilizer and precipitation from pH solutions of 8, 10 and 12 were investigated. The ZnO powder that was prepared from pH 10 showed the highest efficiency for degrading the dyes methylene blue, rhodamine B and reactive orange under backlight fluorescent tubes. This may be due to the highest surface area obtained from precipitation at this pH. These prepared ZnO particles also exhibited antibacterial effects that were stronger on Staphylococcus aureus than on Escherichia coli.     

Improvement of optical properties of nanocrystalline Fe-doped ZnO powders through precipitation method from citrate-modified zinc nitrate solution

Nanocrystalline Zn_1−xFe_xO (where x = 0, 0.01 and 0.02) powders were successfully synthesized by a precipitation method from citrate-modified zinc nitrate solution. X-ray powder diffraction, Fourier transformed infrared spectroscopy, field emission scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy were used to study the structural properties. The optical properties were determined by UV–vis spectrophotometer and luminescent spectrometer. In this study, the optical band gap of nanocrystalline ZnO powder increased from 3.170 eV to 3.214 eV when the Fe concentration in the solution was increased up to 2 mol. %.     

Extrinsic and intrinsic magnetic properties of Co1−x Fex Sb3

We report magnetic properties of iron in Co_1−x Fe_x Sb₃ for x in the range 0<x<0.2, since x=0.2 is found to be the limit of solubility of iron in the skutterudite lattice. The magnetic ions diluted in the matrix carry a small magnetic moment reduced to that of the spin-only S=1/2 value of the Fe³⁺ in the low spin d⁵ configuration in presence of a strong crystal field that screens the orbital momentum. The magnetic properties give evidence that a small fraction of iron is spin-frozen in magnetite ferrimagnetic clusters, and antiferromagnetic FeO clusters. Because both types of clusters represent only very minor phases, their detection by the usual analytical means such as X-rays is not possible. The remaining part is diluted in the matrix to form a semimagnetic semiconductor characterized by a Fe–Fe nearest-neighbor exchange interaction J that is antiferromagnetic, with |J|/k_B19.6  K.     

Preparation and characterization of nanocrystalline La-doped ZnO powders through a mechanical milling and their optical properties

Structural and optical properties of mechanically milled La-doped ZnO powders are presented in this paper. The Zn_1−xLa_xO phase formed when x varied in a range of 0.02-0.06 and milled at 400 rpm for 20 h. The secondary La₂O₃ phase occurred with an increase of La content. The crystallite and particle size decreased as a function of La content as x = 0-0.14 due to the effect of Zener pinning and solute drag. The absorption edge shifted to a lower wavelength when La content was increased to x = 0.14 because of the size effect. The energy band gap of Zn_1−xLa_xO powders varied in a range of 2.96-3.12 eV depending on the crystallite size. The broad emission bands in a visible region centered at about 640 nm are attributed to oxygen deficiency.     

Synthesis, characterization and optical properties of Zn1−xTixO nanoparticles prepared via a high-energy ball milling technique

Zn_1−xTi_xO (x = 0, 0.01, 0.03 and 0.05) nanoparticles were prepared by high-energy ball milling at 400 rpm. The milled powders were characterized by X-ray diffractometer (XRD) and the results exhibited that Ti-doped ZnO nanoparticles consisted of single phase with hexagonal structure when the mixtures of ZnO and TiO₂ powders were milled for 20 h. The crystallite size reduced as a function of the doping content and milling time from 1 to 10 h then increased after milling for 20 h and when the annealing temperature increased. The strain changed inversely to the crystallite size. A wider band-gap was obtained by increasing the doping content and annealing temperature because of a reduction in defect concentration. Both ZnO- and Ti-doped ZnO nanoparticles caused damage to S. aureus, E. coli, P. mirabilis, S. typhi and P. aeruginosa.     

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.