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Thick ZnO/ZnAl2O4 coatings were synthesized on zinc alloy Z1 substrates through plasma electrolytic oxidation (PEO) for different anodization times. The prepared coatings were characterized by scanning SEM, XRD, diffuse reflectance and photoluminescence spectroscopy in order to establish the relationship between their structural and optical properties and PEO processing parameters. Under different PEO processing conditions (anodization time—1–10 min and applied voltage—370 and 450 V) ceramic coatings with a mean thickness of 2–12 μm were prepared. XRD analysis explored the coating structure composed of zinc oxide (wurtzite) and zinc aluminate spinel. The content of ZnAl2O4 in the coatings grows with increasing the applied voltage and anodization time. Photoluminescence (PL) measurements showed that the PEO coatings have several bands in the visible and near-infrared regions associated with their composite structure. The PL spectra significantly depend on the PEO processing parameters due to varying ZnO and ZnAl2O4 content in the coatings. The insight in the relationship between the ZnAl2O4 structure and the photoluminescent properties of ZnO/ZnAl2O4 coatings has been provided using the combination of XRD and luminescence spectroscopy. [ABSTRACT FROM AUTHOR]

Photoactive Cu-doped ZnO–ZnAl2O4 ceramic nanocomposites and coatings were prepared by polymer-salt method. The luminescent spectroscopy, scanning electron microscopy (SEM) and X-ray diffraction methods were used for the study the structure, morphology and materials properties. The nanocomposites consist of small hexagonal ZnO and cubic ZnAl2O4 nanocrystals having size about 10 nm. The study of luminescence properties shows that prepared nanocomposites can be used as light down-converters that transfer short-wave ultraviolet (UV-C) radiation into long-wave ultraviolet (UV-A) and visible spectral range. These nanocomposites can be very attractive in photovoltaic applications as spectral down-converters. Also obtained nanocomposites demonstrate the ability to generate chemically active singlet oxygen under UV-A radiation and blue light. The experiments show that Cu-doped ZnO–ZnAl2O4 materials demonstrate antibacterial activity against gram-positive bacteria. [ABSTRACT FROM AUTHOR]

We have investigated various Zn-based catalysts for their interaction with methanol (MeOH). MeOH is one of the most critical molecules being studied extensively, and Zn-based catalysts are widely used in many industrially relevant reactions involving MeOH. We note that the same element (Zn and O, in the present study) exhibits different catalytic activity in different environments. The changing environment is captured in the underlying electronic structure of the catalysts. In the present work, we compared the electronic structure of Zn-based systems, i.e., ZnAl 2 O 4 and ZnO along with oxygen preadsorbed Zn (O-Zn) and metallic Zn. We demonstrate the one-to-one correlation between the p DOS of the bare facet and the outcome of that facet's interaction (i.e. either adsorption or dissociation of MeOH) with MeOH. These findings would pave the way towards the in-silico design of catalysts. [Display omitted] • Electronic properties of many Zn-based systems investigated for their reactivity. • pDOS of bare facets is correlated with the outcome of methanol interaction with a facet. • Dissociation of MeOH is associated with presence of energy states near the Fermi. • Adsorption (chemi/physi) is associated with absence of energy states near the Fermi. [ABSTRACT FROM AUTHOR]

Abstract: Zinc oxide (ZnO) thin films on c-sapphire substrates were synthesized by spin-coating aqueous polymeric precursors. The effects of annealing at 1000°C on crystallinity, surface morphology, and optical properties of ZnO thin films, with varying thicknesses, were studied. Single-layered ZnO thin films are polycrystalline with wurtzite structure and preferentially oriented along the (002) plane. X-ray diffraction pattern also reveals the presence of spinel zinc aluminate (ZnAl2O4) peaks. ZnO films have highly faceted granular morphology. Multilayered ZnO films, annealed twice at 1000°C, do not exhibit any ZnO peaks but only ZnAl2O4 peaks. Moreover, the surface morphology was smooth with ridges. These films do not exhibit the band gap or ultra-violet emission photoluminescence characteristics of ZnO. On annealing, there is an interfacial reaction between ZnO and sapphire resulting in ZnAl2O4. [Copyright &y& Elsevier]

ZnO and ZnAl2O4 coated aluminium borate whisker (ABOw) reinforced pure aluminium composites were fabricated by squeeze casting. The effects of the coatings on the bending properties of the composites were investigated. On the analysis of fractographs, the fracture mechanisms of the composites under bending were also investigated. The results show that both ZnO and ZnAl2O4 coatings of ABOw can significantly increase the bending properties of ABOw reinforced aluminium composite. In ABOw/Al, ABOw/ZnO/Al and ABOw/ZnAl2O4/Al composites, the interface debonding, near interface fracture and near interface fracture and ABOw fracture dominate the fracture of each composite during bending respectively. [ABSTRACT FROM AUTHOR]

Abstract: Layered double hydroxides (LDH) containing zinc and aluminium within the brucite-like layers and carbonate as the interlayer anion have been used as precursors for the preparation of mixed metal oxides by calcination. Zinc oxide and the ZnAl2O4 spinel were formed with different degree of crystallinity depending of two parameters, i.e., the Zn2+/Al3+ molar ratio and the calcination temperature (500–800°C) of the LDH precursor. A pure spinel phase was obtained to remove ZnO upon a basic post-treatment in NaOH solution of the samples calcined at 800°C. All the samples were tested for the photodegradation of 2-propanol in gas–solid regime. All the samples resulted active as heterogeneous photocatalysts. The photocatalytic activity increased by increasing the Zn2+/Al3+ molar ratio and the calcination temperature of the solids. [Copyright &y& Elsevier]

Abstract: ZnO and ZnAl2O4-coated Al18B4O33 whisker reinforced pure aluminum composites were fabricated by squeeze casting. The effects of the coating contents on the ultimate tensile strength (UTS), 0.2% proof stress (σ 0.2) and elongation to fracture (δ) of the composites were investigated. The results show that the UTS of ZnO-coated Al18B4O33 whisker reinforced aluminum composites increases almost linearly as the coating contents increase. However, the UTS of ZnAl2O4-coated Al18B4O33 whisker reinforced aluminum composites declines initially and increases later. The ZnAl2O4 coating of the whiskers is more favorable for an increase in the σ 0.2 of the composites. The δ of the composites obtains its maximum value with an appropriate coating content. Fracture mechanisms of the composites were also investigated. [Copyright &y& Elsevier]

Abstract: Pd and Pd–Zn alloy were supported on various supporting materials using impregnation, co-precipitation and microemulsion methods, and their catalytic performances in oxidative methanol reforming (OMR) were investigated. Pd/ZnO exhibited much higher selectivity than either Pd/Al2O3 or Pd/ZrO2 in the OMR for hydrogen production. This was attributed to the presence of Pd–Zn alloy on the ZnO support. Elemental Pd on Al2O3 or ZrO2 promotes methanol decomposition reaction and increases CO formation. Using a microemulsion method, a highly selective Pd/ZnO can be obtained with much lower Pd loading than that in samples prepared by co-precipitation. Modification of Al2O3 with ZnO produced a ZnAl2O4 phase, which was found to be a good support for the Pd/ZnO catalyst. Highly active and selective Pd/ZnO/ZnAl2O4 catalysts for the OMR reaction, containing much lower Pd loadings have been developed by impregnation of the supports with an aqueous solution of Pd(NO3)2 +Zn(NO3)2. [Copyright &y& Elsevier]

• Almost pure ZnAl 2 O 4 containing PEO coating was obtained. • Coatings are highly stressed and tend to flake off. • Combined constant current/constant voltage mode was successfully applied to release stresses. In the frame of this work, plasma electrolytic oxidation of a zinc alloy was performed in a phosphate-aluminate electrolyte as a first approach. Phase composition and microstructure of the formed PEO coating was analysed as a function of treatment time and applied current density. The coatings are mainly composed out of ZnAl 2 O 4 and ZnO with some smaller amounts of AlPO 4 and Zn 2 P 2 O 7. The coating formation starts with ZnO at lower discharge energies and changes to the reactive formation of ZnAl 2 O 4 when the discharge energy is increasing. The phase composition is only influenced by the final voltage and not by the current density. Latter is only determining the growth rate of the coating. However, stresses in the coatings are high and the layers are cracked and seems to flake-off already during PEO processing, thus at longer treatment times the coating thickness is not increasing anymore. To prevent extensive flaking-off of the coating a constant voltage PEO "repair" mode was introduced partly successfully at the end of the treatment. [ABSTRACT FROM AUTHOR]

Three dimensional (3D) ZnO/ZnAl2O4 nanocomposites (ZnnAl-MMO) were synthesized by a simple urea-assisted hydrothermal process and subsequent high-temperature calcination. The as-prepared samples and their precursors were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), UV-Vis diffuse reflectance spectroscopy (DRS), and Photoluminescence spectra (PL). It was observed that the morphology of ZnnAl-MMO nanocomposites could be tuned from cubic aggregates, hierarchically flower-like spheres to porous microspheres by simply changing the molar ratio of metal cations of the starting reaction mixtures. The photocatalytic performance of ZnO/ZnAl2O4 nanocomposites in the photoreduction of aqueous Cr(VI) indicated that the as-prepared 3D hierarchical sphere-like ZnnAl-MMO nanocomposite showed excellent photocatalytic activity of Cr(VI) reduction under UV light irradiation. The results indicated that the maximum removal percentage of aqueous Cr(VI) was 98% within four hours at 10 mg/L initial concentration of Cr(VI), owing to the effective charge separation and diversion of photogenerated carriers across the heterojunction interface of the composite. Our study put forward a facile method to fabricate hierarchical ZnO/ZnAl2O4 composites with potential applications for wastewater treatment. [ABSTRACT FROM AUTHOR]