Zinc Oxide Phase Research Articles

Characterizations of octahedral zinc oxide synthesized by sonochemical method

The ultrasonic reaction of zinc nitrate hexahydrate (Zn(NO 3) 2·6H 2O) and hexamethylenetetramine (C 6H 12N 4) was investigated by varying the concentration of the reactants, the irradiation time, and the type of sonicator. The morphology, composition, and phase structure of the products were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) and ultraviolet–visible (UV–vis) spectroscopy. Octahedral zinc oxide (ZnO) micropowders were formed at low concentrations, 0.05 M, of Zn(NO 3) 2·6H 2O and C 6H 12N 4 in both lab-made sonicator and commercial ultrasonic bath. However, at concentrations between 0.1 and 1.0 M Zn(NO 3) 2–C 6H 12N 4 mainly plate-like zinc hydroxide nitrate hydrate (Zn 5(OH) 8(NO 3) 2(H 2O) 2) resulted with only a small fraction of ZnO, irrespective of the irradiation time employed, highlighting the sensitivity of the system to the concentration of the starting materials. Heat treatment of Zn 5(OH) 8(NO 3) 2(H 2O) 2 at 350 °C in air affords a ZnO phase of irregular morphology. Octahedral ZnO is found to exhibit slightly lower IR absorption and similar UV absorption to that of commercial prismatic hexagonal ZnO, although an extra peak due to small quantities of Zn 5(OH) 8(NO 3) 2(H 2O) 2 is observed.

Synthesis and characterization of ZnO/PET composite using supercritical carbon dioxide impregnation technology

A zinc oxide (ZnO) and poly(ethylene terephthalate) (PET) composite was obtained using a supercritical fluid deposition (SCFD) approach. The zinc precursor was solubilized in supercritical carbon dioxide (scCO2) and impregnated onto PET films. The PET film impregnated zinc precursor was chemically treated using a hydrazine alcoholic solution to obtain the ZnO/PET composite. The composite was characterized by photoacoustic spectroscopy UV–Vis, photoluminescence emission at room temperature, and scanning electron microscopy. The ZnO generated using hydrazine presented spherical shape with strong photoluminescence emission at 390nm (3.17eV), indicating the formation of a well-organized ZnO phase.

A MULTISCALE APPROACH TO THE REPRESENTATION OF 3D IMAGES, WITH APPLICATION TO POLYMER SOLAR CELLS

A multiscale approach to the description of geometrically complex 3D image data is proposed which distinguishes between morphological features on a ‘macro-scale’ and a ‘micro-scale’. Since our method is mainly tailored to nanostructures observed in composite materials consisting of two different phases, an appropriate binarization of grayscale images is required first. Then, a morphological smoothing is applied to extract the structural information from binarized image data on the ‘macro-scale’. A stochastic algorithm is developed for the morphologically smoothed images whose goal is to find a suitable representation of the macro-scale structure by unions of overlapping spheres. Such representations can be interpreted as marked point patterns. They lead to an enormous reduction of data and allow the application of well-known tools from point-process theory for their analysis and structural modeling. All those voxels which have been ‘misspecified’ by the morphological smoothing and subsequent representation by unions of overlapping spheres are interpreted as ‘micro-scale’ structure. The exemplary data sets considered in this paper are 3D grayscale images of photoactive layers in hybrid solar cells gained by electron tomography. These composite materials consist of two phases: a polymer phase and a zinc oxide phase. The macro-scale structure of the latter is represented by unions of overlapping spheres.

MOCVD of Vertically Aligned ZnO Nanowires Using Bidentate Ether Adducts of Dimethylzinc

AbstractThe dimethylzinc‐bidentate ether adducts [Me2Zn(1,4‐dioxane)] (1), [Me2Zn(1,2‐dimethoxyethane)] (2) and [Me2Zn(1,4‐thioxane)] (3) are used as precursors for the growth of vertically aligned zinc oxide (ZnO) nanowires (NWs) by liquid‐injection, metal‐organic (MO)CVD. The ZnO NWs are deposited on Si(111) and F‐doped SnO2/glass substrates in the absence of a seed catalyst. The precursors (1) and (2) are used to deposit ZnO NWs at substrate temperatures of 450 °C and 500 °C, whilst higher deposition temperatures of 550–600 °C are necessary to obtain ZnO NWs using (3). X‐ray diffraction (XRD) data show that the NWs grown from all three adduct precursors are deposited in the wurtzitic ZnO phase. Room‐temperature photoluminescence (PL) data for the ZnO NWs grown using (1) and (2) show an intense peak at 3.28 eV due to near band‐edge emission with a very low intensity of defect‐related green luminescence at 2.42 eV. In contrast, room‐temperature PL data for the ZnO NWs deposited using (3) is dominated by deep centre, defect‐related emission at 2.42 eV. Auger electron spectroscopy (AES) shows that the ZnO films deposited from (1) and (2) are high purity with no detectable carbon, but the ZnO films grown from (3) are contaminated with sulfur (1 at.‐%). Single‐crystal X‐ray structures show that (1) is polymeric containing bridging 1,4‐dioxane ligands while (2) is a monomeric complex featuring a chelating 1,2‐dimethoxyethane ligand. The wide [Me‐Zn‐Me] bond angles in (1) and (2) (152.0(3)° and 154.5(2)°, respectively) suggest moderately weak [Me2Zn]‐ligand interactions. Complex (3) is polymeric and exhibits nearly linear [Me‐Zn‐Me] bond angles, indicative of much weaker [Me2Zn]‐ligand interactions.

Synthesis and characterization of zinc/iron oxide composite nanoparticles and their antibacterial properties

Inorganic metal oxides may serve as effective disinfectants, due to their relatively non-toxic profile, chemical stability and efficient antibacterial activity. Among metal oxide nanoparticles, zinc oxide demonstrates significant bacterial growth inhibition on a broad spectrum of bacteria, mainly by catalysis of reactive oxygen species (ROS) formation from water and oxygen. Aqueous suspensions of ZnO nanoparticles (ZnO nanofluids) are the preferred formulation for using the antibacterial agent in liquid phases and for the incorporation of the nanoparticles in different commercial products. However, ZnO nanoparticles in aqueous media tend to aggregate into large flocculates, due to their hydrophobic nature, and thus do not interact with microorganisms effectively. In this study, zinc oxide was combined with iron oxide to produce magnetic composite nanoparticles with improved colloidal aqueous stability, together with adequate antibacterial activity. For this purpose, the Zn/Fe oxide composite nanoparticles were synthesized by basic hydrolysis of Fe2+ and Zn2+ ions in aqueous continuous phase containing gelatin. The obtained composite nanoparticles were composed of iron oxide, zinc oxide and zinc ferrite phases. The effect of the weight ratio [Zn]/[Fe] of the composite nanoparticles on their properties (composition, size, magnetic behavior and colloidal stability) was elucidated. The antibacterial activity of these nanoparticles was tested against Staphylococcus aureus and Escherichia coli and was found to be dependent on the weight ratio [Zn]/[Fe], i.e., the higher the ratio, the higher the antibacterial activity. In addition, the activity against Staphylococcus aureus was significantly higher than that observed against Escherichia coli.

Comparative Studies on Degradation of Methyl Orange by Nanostructured Zinc and Zinc Oxide Films

Nanostructured zinc and zinc oxide films were prepared by magnetron sputtering processes and succeeded air annealing treatments. Comparison of reductive degradation rate of methyl orange (MO) by zinc films and photocatalytic degradation rate of MO by zinc oxide films was carried out. Both reductive degradation and photocatalytic degradation process of MO by zinc and zinc oxide films can be described by first order kinetic model. It was found that although MO liquid was most quickly decolorized by metallic zinc films, the mineralization of MO was not thorough. Observation of extra ultraviolet absorption peaks indicated the formation of aromatic intermediates. On the other hand, although the photocatalytic degradation rate of MO liquid by ZnO films was only as about 1/4 large as the reductive degradation rate by zinc films, no signs of aromatic intermediates were found. Moreover, it was found that partially oxidized zinc oxide film showed higher photocatalytic efficiency than the totally oxidized ZnO films. Synergy effect between zinc and zinc oxide phase in the partially oxidized films was considered to be responsible for the higher photocatalytic efficiency.

OPTICAL AND ELECTRICAL CHARACTERIZATION OF ZnO THIN FILM

The optical and electrical studies on ZnO thin film are reported. Thin film of ZnO is deposited on glass substrate by physical vapor deposition method. In this method, Zn powder is evaporated at a temperature of 400°C in the presence of oxygen and argon gases, and the resulting ZnO is deposited on the glass substrate which is kept at liquid nitrogen temperature. The crystallinity of this ZnO film is studied using XRD technique. The XRD pattern suggests that the nature of this film is polycrystalline. The prominent peaks observed at 31.78, 34.34, 36.18, and 56.32 correspond to the (100), (002), (101), and (110) planes, confirming the formation of hexagonal zinc oxide phase (JCPD 36-1451 for wurtzite zinc oxide). The XRD spectrum very clearly demonstrates that the film deposited in oxygen atmosphere has a dominant (101) orientation. The d hkl values are estimated for this as-deposited ZnO thin-film. It is observed that these calculated values in close agreement with the reported d hkl values for ZnO . Debye–Scherrer equation is used to estimate the size of these nanoparticles. It is found that size estimated by Debye–Scherrer equation agrees well with the size observed by TEM images. It is clear from the transmission electron microscope (TEM) images that the film contains nanoparticles of ZnO and the diameter of these nanoparticles varies from 5–20 nm. In optical properties, the UV visible spectrum of these nanoparticles is recorded in the wavelength range (300–900 nm). The absorption coefficient increases exponentially with the increase in photon energy. The direct optical band gap is calculated which comes out to be 3.54 eV. The value of Urbach energy (E U ) is also calculated using the slope of the plot ln α versus photon energy and it comes out to be 805.8 meV. For electrical properties, the DC conductivity of ZnO film deposited on glass substrate is measured in the temperature range of 450–300 K. On the basis of temperature dependence of DC conductivity of ZnO film, it is suggested that the conduction takes place via thermally activated process.

Growth and Surface Structure of Zinc Oxide Layers on a Pd(111) Surface

The growth and geometric structure of ultrathin zinc oxide films on Pd(111) has been studied by scanning tunneling microscopy, low-energy electron diffraction, and density functional theory calculations. For sub-monolayer coverages, depending on the oxygen pressure, two well-ordered zinc oxide phases with (4 × 4) and (6 × 6) coincidence structures form, which are attributed to H-terminated Zn6O5 and graphite-like Zn6O6 layers, respectively. The (6 × 6) phase exhibits a pronounced oxygen pressure dependence: at low p(O2) a well-ordered (6 × 6) two-dimensional array of O vacancies develops, yielding a layer with a formal Zn25O24 stoichiometry, while at high p(O2) the Zn6O6 monolayer transforms into bilayer islands. For oxide coverages up to 4 monolayers the graphite-like Zn6O6 structure is thermodynamically the most stable phase over a large range of oxygen chemical potentials, before it converges to the bulk-type wurtzite structure. Under oxygen-poor conditions a compressed overlayer of Zn adatoms can be stabilized on top of the Zn6O6 structure.

Synthesis, Characterization, and Performance of LaZnxFe1-xO3 Perovskite Nanocatalysts for toluene combustion

Nanostructured LaFeO3 and substituted LaZnxFe1-xO3 (x = 0.01, 0.05, 0.1, 0.2, and 0.3) perovskites were synthesized by the sol-gel auto-combustion method and used in the catalytic combustion of toluene. Their structures and surface properties were investigated by X-ray diffraction, Fourier transmission infrared spectroscopy, BET surface area, and scanning electron microscopy. Characterization data revealed that the total insertion of zinc into LaFeO3 takes place when x ≤ 0.1. However, ZnO segregation occurs to some extent, especially at x > 0.1. The performance of these perovskites was evaluated by toluene combustion. The catalytic activity of the catalysts increased substantially with an increase in zinc substitution. These results can be attributed to the cooperative effect between LaZnxFe1-xO3 and the zinc oxide phases. The relative concentration of these phases determines their oxygen activation ability and reactivity.

Application of ZnO Nanoparticles EM Wave Detector Prepared by Sol-Gel and Self-Combustion Techniques

Zinc oxide (ZnO) has found many important applications such as optoelectronic devices, sensors and varistors. The challenging part however is synthesizing ZnO nanoparticles and its utilisation as EM detectors. Sol-gel and self-combustion techniques were chosen in this study due to the ability to produce single phase and nano-size samples. The starting mixture consists of 10 grams of zinc (II) nitrate, Zn(NO3)2.6H2O salt which was dissolved in 50 mL of nitric acid, HNO3.The solution was stirred at 250 rpm continuously for 1 day. The mixture was then gradually heated for every 15 minutes until it combusted at 110oC for the self-combustion technique. For the sol-gel technique, the dissolved mixture was heated at 40oC, 50oC, 60oC and 70oC until the gelatine was formed. After the drying process, the as-prepared samples were annealed at 100oC and 200 oC for 1 hour for each technique. Characterizations were performed by using X-Ray Diffraction (XRD), Raman Spectra and Scanning Electron Microscopy (SEM).The XRD analysis showed a major peak of [101] plane at 2Ө for the self-combustion technique and the sol-gel technique. Raman results for the samples prepared via sol-gel and self-combustion techniques had shown the major peak of ZnO that is located at the Raman shifts of 437.67 cm-1. Using the Scherrer equation, single crystal nano particle of ZnO was successfully obtained in the range of 38.49 nm to 50.70 nm for the sample prepared via the sol gel technique. By the self-combustion technique, the average dimension of the as-prepared sample is in the range of 34-49 nm. Further heat treatment resulted in a major change of the Raman shift corresponding to the single phase ZnO nano particles. The best samples were used as electromagnetic (EM) detectors. The EM detectors are polymer based composite which were prepared using a casting technique.

Physical properties of ZnO thin films deposited at various substrate temperatures using spray pyrolysis

Zinc oxide (ZnO) thin films have been deposited with various substrate temperatures by spray pyrolysis technique onto glass substrates. X-ray diffraction (XRD) results showed the random growth orientation of the crystallites and the presence of the wurtzite phase of ZnO. The x-ray photoelectron spectroscopy (XPS) measurements reveal the presence of Zn 2+ and chemisorbed oxygen in ZnO thin films. Atomic force micrograms (AFM) revealed a granular, polycrystalline morphology for the films. The grain size is found to increase as the substrate temperature increases. All films exhibit a transmittance of about 85% in the visible region. The photoluminescence (PL) measurements indicated that the intensity of emission peaks significantly varying with substrate temperature. Electrical resistivity has been found to decrease; while the carrier concentration increases with substrate temperature.

Nonhydrolytic Route for Synthesis of ZnO and Its Use as a Recyclable Photocatalyst

A simple, convenient and versatile synthetic approach has been demonstrated for large-scale synthesis of zinc glycerolate microcrystals having preferential growth along the (100) axis. Glycerol has been used both as a ligand and as a solvent. This glycerolate precursor has subsequently been converted into the hexagonal phase of zinc oxide (ZnO) with wurtzite structure by calcining in air. A number of techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, solid-state 13C NMR spectroscopy, and thermogravimetric analysis (TGA) measurements have been used to investigate the morphology, crystallinity, and structure of the products obtained before and after calcination. Furthermore, the room-temperature photoluminescence (PL) of the ZnO nanocrystals has also been investigated along with rhodamine B degradation. The latter has been used as a probe reaction to evaluate the photocatalytic performance of the ZnO nanoparticles for as many as three recycles.

Effect of pH on Zinc Oxide Powder Prepared by a Chemical Co-Precipitation Method

Zinc oxide powder was prepared by a chemical co-precipitation method. Zinc nitrate and ammonium hydroxide were used as the starting precursors. The white precipitated powder was formed after adding ammonium hydroxide until the pH of final solution was 7-9. The powder was filtered and dried at 100 °C for 24h. The phase of zinc oxide powder was studied by X-ray diffractometer (XRD). Hexagonal single phase of zinc oxide was obtained without calcination step. The morphology of zinc oxide powder was investigated by scanning electron microscope (SEM). The particle was irregular in shape and highly agglomerated with an average particle size of 0.1 µm. The chemical composition of zinc oxide powder was determined by energy dispersive X-ray spectrometer (EDXS). The elemental composition of zinc oxide showed the characteristic X-ray energy value as follows: zinc of Lα = 1.012 keV, Kα = 8.630 keV and Kβ = 9.570 keV and oxygen of Kα = 0.525 keV, respectively.

Propriedades eletrônicas, estruturais e constantes elásticas do ZnO

The electronic, structural properties and elastic constants of the wurtzite phase of zinc oxide, ZnO, was investigated using computer simulation at Density Functional Theory level, with B3LYP hybrid functional and Hartree-Fock methodology. The electronic properties as well the band energy was investigated through the analysis of the band structures and density of states (DOS), and the mechanical properties was studied through the calculus of the elastic constants C11, C33, C44, C12 e C13. The results are in good agreement with experimental data found in the literature and in accordance with results obtained by another theoretical methodology.

Synthesis of zinc oxide nanocrystalline powders for cosmetic applications

The synthesis of zinc oxide (ZnO) nanocrystalline powders for cosmetic applications by a coprecipitation process has been investigated. When the Zn(OH) 2 precipitates are calcined at 373 K for 10 min, the crystalline phases comprise the major phase of Zn(OH) 2 and the minor phase of ZnO. XRD pattern shows that only ZnO is present and no other phase is detected when the Zn(OH) 2 precipitates calcined at 413 K for 10 min. The nanocrystallite size of ZnO increases slightly from 32.3 to 44.3 nm when the calcination temperature increases from 413 to 873 K. The activation energy of ZnO nanocrystallite growth is 2.02 kJ/mol, which reveals that the nanocrystalline ZnO is easily grown at low temperature. The UV transmission of ZnO nanocrystallites in the wavelength range from 290 to 375 nm is about 35%, indicating that the ZnO nanocrystallites have an excellent UV-absorbing capability.

An Investigation on Co-Precipitation Derived ZnO Nanospheres

This paper describes a simple chemical co-precipitation method for preparing nano-sized zinc oxide (ZnO) nanospheres. The morphological, thermal, structural, and chemical features of ZnO nanospheres were systematically studied and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermo gravimetric analysis-differential scanning calorimetric analysis, X-ray diffraction (XRD), and Fourier transform infrared spectroscopy. The SEM micrographs reveal that the particles are spherical in nature and the precipitating agent ammonia plays a critical role in controlling the morphology of the nanospheres. Crystalline ZnO phase is obtained at higher annealing temperature and there by reduce the contents of the hydrated species. Powder XRD pattern indicated that the nanospheres exhibit wurtzite hexagonal ZnO phase. The average crystallite sizes of the ZnO nanospheres were calculated to be 14 nm for as-prepared sample and 16 nm for 500 degrees C annealed sample. The peak broadening in ZnO nanospheres due to lattice deformation was analyzed by plotting various modified form of W-H analysis such as uniform deformation model, uniform stress deformation model, and uniform deformation energy density model. From the three models, the strain values epsilon and the crystallite size D(v) were estimated and tabulated. The growth and the formation of ZnO were predicted and the results were confirmed by FT-IR studies.

X-ray peak broadening analysis in ZnO nanoparticles

Zinc oxide (ZnO) nanoparticles were synthesized by a hydrothermal process at 120 ∘C. XRD results reveal that the sample product is crystalline with a hexagonal wurtzite phase. TEM results confirm that the morphology of the annealed ZnO is rod shaped with an aspect ratio (length/diameter) of ∼3.2. We also investigate the crystallite development in nanostructured ZnO by X-ray peak broadening analysis. The individual contributions of small crystallite sizes and lattice strain to the peak broadening in as-prepared and annealed ZnO nanoparticles were studied using Williamson-Hall (W–H) analysis. All other relevant physical parameters including strain, stress and energy density value were calculated more precisely for all the reflection peaks of XRD corresponding to wurtzite hexagonal phase of ZnO lying in the range 20 ∘–65 ∘, from the modified form of W–H plot assuming the uniform deformation model (UDM), uniform stress deformation model (USDM) and uniform deformation energy density model (UDEDM). The root mean square (RMS) lattice strain 〈 ε R M S 〉 calculated from the interplanar spacing and the strain estimated from USDM and UDEDM are different due to consideration of anisotropic crystal nature. The results obtained show that the mean particle size of ZnO nanoparticles estimated from TEM analysis, Scherer’s formula and W–H method are highly inter-correlated. All the physical parameters from W–H plot are tabulated, compared, and found to match well with the value of bulk ZnO.

Effect of annealing on the conversion of ZnS to ZnO nanoparticles synthesized by the sol-gel method using zinc acetate and thiourea

A systematic study is presented on the conversion of zinc sulfide to zinc oxide nanoparticles as a function of annealing temperature. Zinc acetate dihydrate (Zn(CH3COO)2.2H2O) and thiourea (NH2CSNH2) are used as precursors to synthesize ZnS and then ZnO. The aqueous solution of the precursor was refluxed at 90 °C for over 12 h. The synthesized complex was then annealed at 300 °C, 500 °C, 700 °C, and 900 °C in air for one hour. From elemental analyses, it was found that the as-synthesized powder is a mixture of ZnS and ZnO, which annealing later converts to the zinc oxide phase only. The morphological observations revealed spherical particles of various sizes (20 nm to 300 nm) while increasing the annealing temperatures. A drastic change in the vibration bands is noticed with annealing. Photoelectron peaks related to sulfur and carbon are observed for synthesized powder, whereas, these peaks disappeared when annealed at 500 °C.

Deactivation of a Zn/TiO2 catalyst in the course of methanol steam reforming in a microchannel reactor

The service life tests of a Zn/TiO2 catalyst deposited on the microchannel plates of copper foam, nickel foam, and corrugated brass foil in the process of methanol steam reforming demonstrated that the catalyst stability and operation time depend on microchannel plate material. The rate of catalyst deactivation correlated with the thermal conductivity of the microchannel plate material. It was found that catalyst deactivation resulted from the decomposition of zinc titanates, which are active components, and it was accompanied by the appearance of a zinc oxide phase. The best results in the service life tests were obtained with the microchannel plates of copper foam. A microchannel reactor containing 16 copper plates continuously operated at 400°C for 150 h; in this case, the conversion of methanol decreased by 8%. The subsequent microreactor operation for 500 h caused a decrease in the methanol conversion by 26%. It was found that the loss of the catalyst activity was a reversible process, and the activity can be restored by annealing in air.

The effect of heat treatment on the physical properties of sol–gel derived ZnO thin films

Zinc oxide (ZnO) thin films were deposited on microscope glass substrates by sol–gel spin coating method. Zinc acetate (ZnAc) dehydrate was used as the starting salt material source. A homogeneous and stable solution was prepared by dissolving ZnAc in the solution of monoethanolamine (MEA). ZnO thin films were obtained after preheating the spin coated thin films at 250 °C for 5 min after each coating. The films, after the deposition of the eighth layer, were annealed in air at temperatures of 300 °C, 400 °C and 500 °C for 1 h. The effect of thermal annealing in air on the physical properties of the sol–gel derived ZnO thin films are studied. The powder and its thin film were characterized by X-ray diffractometer (XRD) method. XRD analysis revealed that the annealed ZnO thin films consist of single phase ZnO with wurtzite structure (JCPDS 36-1451) and show the c-axis grain orientation. Increasing annealing temperature increased the c-axis orientation and the crystallite size of the film. The annealed films are highly transparent with average transmission exceeding 80% in the visible range (400–700 nm). The measured optical band gap values of the ZnO thin films were between 3.26 eV and 3.28 eV, which were in the range of band gap values of intrinsic ZnO (3.2–3.3 eV). SEM analysis of annealed thin films has shown a completely different surface morphology behavior.