Ordered ZnO/AZO/PAM nanowire arrays prepared by seed-layer-assisted electrochemical deposition

An Al-doped ZnO (AZO) seed layer is prepared on the back side of a porous alumina membrane (PAM) substrate by spin coating followed by annealing in a vacuum at 400 °C. Zinc oxide in ordered arrays mediated by a high aspect ratio and an ordered pore array of AZO/PAM is synthesized. The ZnO nanowire array is prepared via a 3-electrode electrochemical deposition process using ZnSO₄ and H₂O₂ solutions at a potential of − 1 V (versus saturated calomel electrode) and temperatures of 65 and 80 °C. The microstructure and chemical composition of the AZO seed layer and ZnO/AZO/PAM nanowire arrays are characterized by field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), and energy-dispersive X-ray spectroscopy (EDS). Results indicate that the ZnO/AZO/PAM nanowire arrays were assembled in the nanochannel of the porous alumina template with diameters of 110–140 nm. The crystallinity of the ZnO nanowires depends on the AZO seed layer during the annealing process. The nucleation and growth process of ZnO/AZO/PAM nanowires are interpreted by the seed-layer-assisted growth mechanism.     

N-doped ZnO nano-arrays: A facile synthesis route, characterization and photoluminescence

Field emission scanning electron microscopy (SEM) investigation reveals that array-orderly novel nanostructures, which are nanorods with many nanoparticles on the surfaces, have been synthesized at low temperature (162 °C) via a one-step in-situ process in solution. High resolution transmission electron microscope (HRTEM) and energy-dispersive X-ray spectroscopy (EDS), coupled with X-ray powder diffraction (XRD) patterns and X-ray photoelectron spectra (XPS), reveal that the as-obtained products possess crystalline structure of N-doped ZnO. The room temperature photoluminescence (PL) spectrum has also been examined to explore the optical property. The present synthesis method possesses several advantages, which would be significant to be studied deeper in the future. It is also envisioned that this method could provide a new approach to synthesize ZnO:N and other ZnO-based adulterants at low temperature.     

Facile synthesis via a solvothermal route and characterization of Mg–Al layered double hydroxide (LDH) 3D micro–nano structures

Different Mg–Al layered double hydroxide (LDH) 3D micro–nano structures had been synthesized via a facile solvothermal method. By carefully controlling the fundamental experimental parameters, the morphologies of hexagonal nanoplates, rose-like micro–nano structures, chrysanthemum-like micro–nano structures, and spherical micro–nano structures have been efficiently obtained, respectively. And these micro–nano structures are formed from self-assembly of nanoplates in a spontaneous process in solvothermal system. It is also found that the concentration of the reactant and the dosage of CTAB have significant effects on the morphology of the products. The FT-IR spectra and thermal stability of the micro–nano structures were explored.     

Optimization of growth conditions of ZnO nano thin films by chemical double dip technique

Abstract

Zinc oxide (ZnO) nano thin films have been deposited by the chemical double-dip technique using aqueous ZnSO₄ and NaOH solutions. The ZnO films were characterized in terms of surface morphology by x-ray diffraction, energy-dispersive x-ray analysis (EDX), the use of a scanning electron microscope (SEM) and atomic force microscope (AFM) for surface morphology. The films exhibited a smooth morphology. The chemical states of oxygen and zinc in the ZnO nano thin films were also investigated by x-ray photoelectron spectroscopy (XPS). In the present investigations, highly textured ZnO thin films with a preferential (002)-orientation were prepared on glass substrates. The deposition conditions were optimized to obtain device-quality films for practical applications.     

Controllable synthesis of hexagonal ZnO–carbon core–shell microrods and the removal of ZnO to form hexagonal carbon microtubes

A simple and efficient approach was developed to produce regular and uniform shaped hexagonal ZnO–C core–shell micro-rods and carbon micro-tubes. A single-source raw material, zinc acetate dihydrate, has been used for the in situ generation of the hexagonal ZnO–C micro-rods in a sealed autoclave system at 500 °C for 12 h without a catalyst. The resulting products were characterized by X-ray powder diffraction, scanning and transmission electron microscopy, energy-dispersive X-ray analysis and room-temperature photoluminescence spectroscopy (PL). The partial or complete carbon coating on the ZnO surfaces plays an important role in modifying the PL properties. Impacting factors including thermolysis temperature, time and dose of the reactant on the evolution of the hexagonal shape were investigated. A possible formation diagram for the materials has been proposed and discussed based on the features of the reaction system.     

Synthesis,structural and optical properties of Er doped,Li doped and Er + Li co-doped ZnO nanocrystallites by solution-combustion method

Pure zinc oxide (ZnO) and 2 mol% of Er, 1 mol% of Li individually doped and Er + Li co-doped ZnO nanopowders were synthesized by auto-combustion method. Crystal structure and grain size were characterized by X-ray diffractometer and found that all synthesized samples have hexagonal wurtzite crystal structure. Scanning electron microscope (SEM) and Transmission electron microscope (TEM) studies were used to determine the morphology and size of the nanocrystallites. A UV–VIS measurement shows four absorbance peaks in the visible regions and the band gap is slowly blue shifted after annealing at 800 °C. The presence of Er, Li and the hexagonal wurtzite structure was confirmed by FT-IR studies. FT-Raman spectroscopy has been employed to study the crystalline quality and structural disorders.     

Processing,characterization, and bactericidal activity of undoped and silver-doped vanadium oxides

Vanadium oxide (V) and silver-doped vanadium oxide (Ag-V) powders were prepared via sol–gel processing. Structural evolution and bactericidal activity was examined as a function of temperature ranging from 250, 350, 450 and 550 °C. Powders were characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Raman spectroscopy. Results from all techniques showed vanadium pentoxide (V₂O₅) is the predominant phase regardless of heat treatment temperature or the addition of silver (Ag). XRD analysis suggests Ag is present as AgCl in samples heat treated to 250, 350, and 450 °C and as AgV₆O₁₅ at 550 °C. Bactericidal activity was evaluated against Escherichia coli using the agar disk diffusion method considering both Ag-V and undoped, V powders. While the addition of Ag significantly increased bactericidal properties, the specific Ag valency, or crystal structure and morphology formed at higher temperatures, had little effect on functionality.     

Synthesis and characterization of ZnO nanowires for nanosensor applications

In this paper we report the synthesis of ZnO nanowires via chemical vapor deposition (CVD) at 650 °C. It will be shown that these nanowires are suitable for sensing applications. ZnO nanowires were grown with diameters ranging from 50 to 200 nm depending on the substrate position in a CVD synthesis reactor and the growth regimes. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and Raman spectroscopy (RS) have been used to characterize the ZnO nanowires. To investigate the suitability of the CVD synthesized ZnO nanowires for gas sensing applications, a single ZnO nanowire device (50 nm in diameter) was fabricated using a focused ion beam (FIB). The response to H₂ of a gas nanosensor based on an individual ZnO nanowire is also reported.     

Fabrication of TiO2/ZnO composite nanofibers by electrospinning and their photocatalytic property

TiO₂/ZnO composite nanofibers with diameters in the range of 85–200 nm were fabricated via the electrospinning technique using zinc acetate and titanium tetra-isopropoxide as precursors, cellulose acetate as the fiber template, and N,N-dimethylformamide/acetone 1:2 (v/v) mixtures as the co-solvent. After treated with 0.1 mol/L NaOH aqueous solution, TiO₂/zinc acetate/cellulose acetate composite nanofibers were transformed into TiO₂/Zn(OH)₂/cellulose composite nanofibers. TiO₂/ZnO composite nanofibers were obtained by calcinating the hydrolyzed composite fibers at 500 and 700 °C for 5 h. The structure and morphology of composite nanofibers were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. With the blending of ZnO into TiO₂, a new crystallite ZnTiO₃ was formed in addition to the ZnO and TiO₂ crystallites, and the ultraviolet light absorption efficiency was enhanced according to the UV–vis diffuse reflectance spectroscopy. The photocatalytic activity of TiO₂/ZnO composite nanofibers toward the decomposition of Rhodamine B and phenol was investigated. Almost 100% Rhodamine B and 85% phenol were decomposed in the presence of TiO₂/ZnO composite nanofibers under mild conditions. The results demonstrated that the blending of ZnO in the TiO₂/ZnO composite nanofibers increased the photocatalytic efficiency. The optimum ZnO content in the TiO₂/ZnO composite nanofibers was 15.76 wt% to reach the most efficient photocatalytic activity. A schematic diagram of photocatalytic mechanism of TiO₂/ZnO composite nanofibers was also presented.     

Controlled morphology of ZnO nanostructures by adjusting the zinc foil heating temperature in an air-filled box furnace

By heating zinc foil in an air-filled box furnace, one-dimensional ZnO nanorods, two-dimensional ZnO nanoplates and three-dimensional ZnO nanotetrapods were prepared by adjusting the temperature in the furnace in the ranges of 500–600, 650–750 and 800–900 °C, respectively. The morphologies, structures and emissions of the synthesized ZnO nanostructures were investigated by scanning electron microscopy, X-ray diffractometry, transmission electron microscopy, selected area electron diffraction and photoluminescence spectroscopy. Mechanisms on the control of the morphology and photoluminescence were discussed in terms of the crystal growth habits combined with the temperature-dependent diffusions of zinc and oxygen atoms in the ZnO lattices.     

Effect of microwave power on the morphology and optical property of zinc oxide nano-structures prepared via a microwave-assisted aqueous solution method

The effect of the microwave power on the morphology and optical properties of zinc oxide nanostructures prepared using a microwave-assisted aqueous solution method has been investigated. The ZnO nanostructures were synthesized from zinc chloride and sodium hydroxide mixed aqueous solutions exposed for 5 min to microwave radiation at four different powers, namely 150, 450, 700 and 1000 W. The morphologies of the samples have been characterized by transmission electron microscope (TEM) and scanning electron microscope (SEM). The results showed that the power of microwave radiation influenced the shape and size of the synthesized nanostructures. It is also found that the average particle size of nanostructures decreased with decreasing microwave power. The results of X-ray diffraction (XRD) showed that all the as-prepared ZnO nanostructures are in crystalline form with high purity. The infrared (IR) spectra indicated that the as-prepared nano ZnO product can be used as infrared gas sensors such as an infrared carbon dioxide (CO₂) and/or CO sensor. Optical properties of the as-prepared ZnO nanostructures were investigated by UV–vis spectroscopy and showed that the optical properties of as-synthesized ZnO samples are sensitive to the variation of the power of microwave radiation.     

Selective H2S detection by CuO functionalized ZnO nanotetrapods at room temperature

ZnO nanotetrapods have been synthesized by carbothermal method. The structure, phase, morphology of the synthesized sample were investigated by X-ray diffraction and X-ray photoelectron spectroscopy, Scanning electron microscopy, Transmission electron microscopy and Selected area electron diffraction. The gas-sensing characteristics of thick films of pure and CuO-functionalized ZnO Nanotetrapods have been compared. Pure ZnO nanotetrapod films were found to be sensitive to both H₂S and NO with similar sensitivities, at a temperature of 250–300 °C. It is demonstrated that functionalization of ZnO nanotetrapods with CuO, results in selectivity towards H₂S at a lower temperature of 50 °C.     

Fabrication of TiO<Subscript>2</Subscript>/ZnO composite nanofibers with enhanced photocatalytic activity

TiO₂/ZnO composite nanofibers have been successfully prepared by electrospinning technique. X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, Raman spectrum, X-ray photoelectron spectroscopy and UV–Vis diffuse reflectance spectroscopy, were used to characterize the as-synthesized nanofibers. The photocatalytic studies revealed that the TiO₂/ZnO nanofibers exhibited enhanced photocatalytic efficiency of photodegradation. Additionally, the recycling experiment of TiO₂/ZnO nanofibers had been done, demonstrating that TiO₂/ZnO nanofibers have high efficiency and stability.     

Facile preparation of Ag/ZnO nanoparticles via photoreduction

Ag/ZnO nanoparticles can be obtained via photocatalytic reduction of silver nitrate at ZnO nanorods when a solution of AgNO₃ and nanorods ZnO suspended in ethyleneglycol is exposed to daylight. The mean size of the deposited sphere like Ag particles is about 5 nm. However, some of the particles can be as large as 20 nm. The ZnO nanorods were pre-prepared by basic precipitation from zinc acetate di-hydrate in the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide. They are about 50–300 nm in length and 10–50 nm in width. Transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDS), X-ray powder diffraction (XRD), UV–Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) were used to characterize the resulting Ag/ZnO nanocomposites.     

Effect of sintering aid on microwave dielectric behaviors of Ni0.5Ti0.5NbO4 ceramics for LTCC applications

The effects of ZnO glass addition on the microwave dielectric properties of Ni_0.5Ti_0.5NbO₄ (NTN) ceramics prepared by solid-state reaction method have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The pure NTN ceramics have ε_r of 60.6, Q × f value of 70,100 GHz, and τ_f value of 76.6 ppm ^°C⁻¹ sintered at 1140 °C for 6 h. The results indicate that the addition of ZnO can effectively benefit the densification and further improve the dielectric constant. Moreover, the lower sintering temperature of NTN ceramics from 1140 to 930 °C is obtained by the addition of ZnO glass. However, an excess of ZnO suppresses the grain growth and decreases the Q × f value of NTN ceramics. The NTN ceramics with 2 wt% ZnO sintered at 930 °C for 6 h possess promising microwave dielectric properties: ε_r of 56.3, Q × f value of 67,000 GHz, and τ_f value of 78.6 ppm °C⁻¹, which shows that the materials are suitable for low-temperature co-fired ceramics applications.     

Effects of constant magnetic field on the electrodeposition reactions and cobalt–tungsten alloy structure

The paper presents a study of the effect of constant magnetic field (CMF) on the basic processes of cobalt–tungsten alloys electrodeposition. To the author's knowledge, such an investigation has been performed for the first time for cobalt–tungsten alloys. The applied research methods included scanning electron microscopy (SEM), energy dispersive X-ray (EDX) microanalysis, energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). SEM images of cobalt–tungsten alloys revealed numerous fractures on the samples surface, formed as a result of residual stress during alloy deposition without CMF. In CMF such fractures disappeared. The cobalt content increased, with a simultaneous decrease of the tungsten content, under CMF condition. The XRD study of cobalt–tungsten alloys allowed to identify phase Co₃W in a hexagonal system, phase Co₇W₆ in a trigonal (orthorhombic) system, phase α-Co in a regular system and phase W in a regular system. Under CMF conditions some crystal planes were deflected at angles ranging from 10 to 20°. The exposure to CMF caused also an increase of the volume fraction (by about 9% by volume) of the dominant phase (Co₃W and Co₇W₆) in the alloy. The reason for these changes was the fact that the Lorentz force, generated in CMF, caused the magnetohydrodynamic (MHD) effect. This induced movement of the electrolyte. The Nernst diffusion layer was depleted, whereas a new Navier–Stokes hydrodynamic layer appeared, which determined the velocity of electroactive molecules flow to the working electrode under CMF conditions.     

pH-dependant structural and morphology evolution of Ni(OH)2 nanostructures and their morphology retention upon thermal annealing to NiO

Nickel hydroxide nanosheets, nanobelts and nanorods were prepared by hydrothermal treatment of the precipitates obtained at different pH values. The morphology and crystal structure of the products could be controlled simply by adjusting the pH value at precipitation. Interconnected nanosheets of hexagonal β-Ni(OH)₂ with thickness around 10–20 nm were formed at pH ∼ 11, whereas nanobelts with typical widths around 40–80 nm, and nanorods with diameters around 50–60 nm of phase pure α-Ni(OH)₂ containing intercalated sulphate ions were obtained in the pH range ∼9.5–8.5. Thermal annealing of the hydroxides at 500 °C yielded cubic phase NiO with morphologies similar to their hydroxide precursors. X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and energy dispersive X-ray (EDX) analysis were used to characterize the as-prepared products. The role of pH in controlling the phase and morphology of the products was discussed.     

Fabrication of ZnO submicrorod films with water repellency by surface etching and hydrophobic modification

Superhydrophobic ZnO submicrorod films have been fabricated on zinc sheets through an H₂O₂-assisted surface etching process and subsequent surface modification with a monolayer of 1H,1H,2H,2H-perfluorodecyltriethoxysilane (FDS). The crystal structure, chemical compositions, morphologies, and wettability of the resultant ZnO films were analyzed by means of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and water contact angle measurements. It is found that the surface of the as-prepared ZnO films on zinc substrate was hydrophobic with a water contact angle of 95 ± 2°, whereas after modification with FDS, the film exhibited superhydrophobicity and the water CA increased to 154 ± 2°. It is shown that both the higher surface roughness and the lower surface free energy play an important role in creating the superhydrophobic films.     

Growth of ZnO nanostructure on Cu0.62Zn0.38 brass foils by thermal oxidation

Cu_0.62Zn_0.38 brass foil was heated at temperatures of 400–700 °C in flowing N₂–5%O₂ at a pressure of 1 atm. for 1–24 h. The oxidized specimens were characterized with a scanning electron microscope, an X-ray diffractometer and a transmission electron microscope. The results show that hexagon ZnO nanowires and nanowalls grew on convoluted oxide scales when brass foils were oxidized at 500 and 600 °C. Thermodynamics of forming ZnO is analyzed based on oxidation theory of an alloy. Pilling–Bedworth ratio of Cu–Zn alloy is calculated based on the volume differences between the formed oxide and the consumed metal. The growth stresses caused by Pilling–Bedworth ratio of the alloy and stress relief of oxide scale at different oxidation temperature are analyzed. The mechanism of forming nanostructural ZnO on the convoluted oxide scales is explained by the change in the growth stresses and stress relief of oxide scale during thermal oxidation.     

Growth and optical properties for non-catalytically grown ZnO micro-tubules by simple thermal evaporation

A simple synthesis technique to grow ZnO micro-tubules in large quantities from ZnO powders in one step at ~ 1000 °C ± 50 °C is discussed. The micro-tubules were formed in the form of small chunks or ingots as well as sticking to the walls of the crucible. Most of those micro-tubules are formed radially outwards of the ingots and that self-alignment may be attributed to the local balance of vapors as well as the steady state of vapor flow. The morphology, structure and optical properties of ZnO microtubes were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and Photoluminescence (PL) respectively. The growth of ZnO micro-tubules would be of interest in the future for the technological revolution of useful application such as in catalytic and optoelectronics.