Papers by Keyword: Zinc Oxide (ZnO)

Abstract: In this study, we investigated the photoconductivity of pharma-grade zinc oxide (ZnO) which was excited under ultraviolet - long wavelength (UVA) and white light illumination. The morphological structures of ZnO were studied using field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The ZnO sample was composed of micro/nanorods, slabs, tripods, tetrapods and irregular-shaped particles. The energy-dispersive X-ray spectroscopy (EDS) result revealed the high purity of ZnO, with the relative O/Zn atomic ratio lower than 1. The absorption spectrum of ZnO suspension was performed using UV-Visible spectroscopy. ZnO sample exhibited strong absorption at 387 nm, corresponding to optical bandgap of 3.23 eV. The ZnO powder was converted into pellets to study its photoconductivity under different intensity of UVA (0.5-2.0 mW/cm^-2) and white light exposure (200-1000 lux) from conventional fluorescent lamp. The significant increase in surface conductivity of the ZnO pellets could be due to UVA illumination that produces photo-generated charge carriers on the surface of ZnO pellet. There was a small persistency of current flow after the UVA exposure was terminated. Under the white light exposure, the surface conductivity was slightly higher than that of dark condition. This is probably due to the small amount of defects, particularly oxygen vacancies and zinc interstitials that produce some light-generated charges on the ZnO crystal structures. The white light exposure may cause the excitation of electrons from the defects energy level to the conduction band, this being the underlying cause for the increase in the conductivity. ZnO pellet exhibited a dramatic enhancement of photoconductivity under UVA illumination if compared with small improvement of photoconductivity under white light exposure.

Abstract: In this study, silver-doped zinc oxide (ZnO) nanorods were grown by a solution method and the effect of varying the doping concentration on the electrical property and component characteristics of the synthesized ZnO nanorods were studied. The ZnO nanorods were grown in the mixed solution of zinc nitrate hexahydrate (Zn (NO₃)₂·6H₂O), hexamethylenetetramine (C₆H₁₂N₄), and silver nitrate (AgNO₃) at 90^oC for 2 hours. The purpose of silver nitrate was to supply dopant atoms. Field-emission scanning electron microscopy (FE-SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD) were used to investigate the surface morphology, chemical compositions, and microstructure of silver-doped ZnO nanorods, and the electrical properties were determined by Hall effect measurement. As found by EDS results, dopant atoms Ag have been successfully incorporated into the crystalline structure of ZnO nanorods, and the conductivity, concentration and mobility of majority carrier in ZnO nanorods have been modified accordingly.

Abstract: Zinc acetate (ZnAc)/PVP composite fibers were prepared by electrospinning technique and pure inorganic ZnO nanofibers were then obtained after the calcination of the composite fibers at 600°C for 2.5h. The effects of the parameters during the spinning process on the composite fibers and ZnO nanofibers were investigated. Uniform in diameters and continuous nanofibers without liquid beads could be obtained with the polymer concentration of 15%, the spinning voltage of 11kV, the receiving distance of 20cm and the rate of sample propulsion of 1.5uL/min. The XRD detection demonstrated the construction of ZnO for nanofibers after the calcinations of the composite fibers.

Abstract: The first-principles with pseudopotentials method based on the density functional theory was applied to calculate the formation energy of impurities and the electronic structure of ZnO doped with Na. In Na-doped ZnO, Na_O is the most unstable than the other cases. Simultaneously, Na_Zn is more stable than Na_i according to that Na_Zn have smaller formation energy. Furthermore, the electronic structure of Na-doped ZnO indicates that that Na_Zn behaves as an acceptor, while Na_i behaves as a donor.

Abstract: The high solid loading slurries with ZnO-Al₂O₃ powders stabilized with polyelectrolytes have been studied. The influence of Sodium poly(acrylate) (PA 30) on the fluidity and stablility of the slurries was investigated. Morphological features of ZnO-Al₂O₃ powders in suspension and fracture surface of green compact were observed using TEM and SEM. The slurries with pH 9 were prepared after milled using ZnO mixed powders and the PA 30 solution of pH 8. As 0.2 wt% PA 30 added, the lowest viscosity and the highest sediment were obtained. ZnO and Al₂O₃ particles had been homogeneous dispersed. The maximum density (66.7 %TD) of green compact was obtained.

Abstract: We demonstrate the vertically well-aligned zinc oxide (ZnO) nanowires synthesized on amorphous borosilicate glass (BSG) via simple chemical vapor deposition (CVD) process with a vapor trapping approach. During the process, zinc precursor was put inside a glass vial with the vial’s opening was directed towards the BSG substrate, which is being placed downstream from the gas flow and approximately 30-40 mm from the precursor. The BSG substrates were coated with Nichrome (NiCr) and gold (Au) coating prior to the synthesis process. Vertically aligned nanowires with a high aspect ratio was found to be deposited in total operating pressure of 20-25 bar with an Oxygen flow rate range of 5-10 sccm and argon flow rate range of 30-50 sccm. This vapor trapping approach using BSG substrates provided a good alternative towards controllable growth of ZnO NWs on any much cheaper amorphous substrates for future development of low cost energy-converter heat cell devices based on ZnO nanowires.

Abstract: Synthesising zinc oxide nanoparticles to get certain specific characteristics to be applied in Enhanced oil recovery (EOR) is still challenging to date. In this work, zinc oxide (ZnO) nanoparticles were synthesised using the sol-gel method by dissolving zinc nitrate hexahydrate in nitric acid. The ZnO crystal and particles morphology and structure were determined using X-ray Diffractometer (XRD) and Field Emission Scanning Electron Microscope (FESEM). In this study, a microwave oven was used for annealing ZnO without insulating a sample in any casket. The results show that 30 and 40 minutes of annealing and stirring for 1 hour influenced the morphology and size of zinc oxide particles in nanoscale. These parameters could be tailored to generate a range of nanoparticle morphology (agglomerated nanoparticles in a corn-like morphology), a crystal size with the mean size of 70.5 and 74.9 nm and a main growth at the peak [10. EOR experiment were conducted by dispersing 0.10 wt% ZnO NPs in distilled water to form a ZnO nanofluid. Then the fluid was injected into the medium in the 3^rd stage of the oil recovery to present EOR stage. It was found that ZnO nanofluid has the ability to extract 8% of the original oil in place (OOIP).

Abstract: In this paper, the novel ZnO nanophosphors is synthesized by solgel method. The study exposed ZnO nanophosphors samples in Gamma (y) radiation to investigate their thermo-luminescence (TL) intensity as a function of temperature. The thermo-luminescence response has been studied in the dose range 0.291.16 kGy and it is observed that the thermo-luminescence response increases with increase in the dose. Moreover, the TL intensity increases with temperature and attains its maximum value near 200 Cand decreases after this temperature. Keywords: Dosimetry; Thermo-luminescence; Zinc oxide; Nanophosphors.

Abstract: Zinc oxide nanostructures have been done by many scientists but amongst the soft chemistry methods, chelating agents are normally used. In this work zinc oxide nanostructures have been synthesized using a soft chemistry method without using a chelating agent. The precursor were annealed at various temperatures of 400 °C, 500 °C, 600 °C, 700 °C, 800 °C and 1200 °C for 24 h. Nanostructures are found with rod-like shapes and they are compared with larger oval morphology. X-Ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), and UV-Vis spectroscopy were used for characterization. XRD results confirm that all peaks were pure and single phase without the presence of any impurities. It was found from electron microscopy results that the morphology of the materials annealed at 400 °C possesses nanorod shape and as the calcination temperature increases, the material consists of mixed rod, spherical and oval shapes. The aspect ratio of the materials decreases when the annealing temperature increases. The absorption edges of the materials annealed at higher temperatures show a red-shift implying that narrowing of the band gaps occur in the materials. Band gap were evaluated and found to be between 3.32 to 3.19 eV.

Abstract: In this paper we have reported excellent luminescence properties of novel nanophosphors synthesized through solgel method with narrow size distribution. The size and morphology of the prepared ZnO nanophosphors has been confirmed through XRD and SEM. We have investigated their photo-luminescence (PL) intensity as a function of wavelength. We have prepared ZnO nanophosphor of size 6 nm. It is observed two different emission peaks near 375 nm in the ultraviolet (UV) and near 525 nm in the visible region. The prepared ZnO nanophosphor has enough potential for optoelectronic applications. Keywords: Dosimetry; Thermo-luminescence; Zinc oxide; Nanophosphors.