Surface Of ZnO Particles Research Articles

Charge-transfer induced ferromagnetism in nanostructured ZnO/Al powders: An x-ray absorption near edge structure study

The correlation between the x-ray absorption spectra and the magnetic properties for Al doped ZnO nanostructures prepared by mechanical alloying has been studied in order to clarify the origin of the room-temperature ferromagnetism in the Al doped ZnO nanostructures. Room-temperature ferromagnetism is induced in nanostructured ZnO-Al powders by milling without any ferromagnetic dopant. The O and Al K-edge x-ray absorption spectra acquired from the ferromagnetic ZnO-Al powders indicate a clear sign of a charge transfer from Al to O on ZnO. The comparison of the florescence yield and total electron yield spectra suggests that this charge transfer takes place mostly at the surface of ZnO particles. Our results show that the surface charge transfer between Al and O plays an important role in the induction of spontaneous magnetization in the Al doped ZnO.

Sodium-phosphorylated chitosan/zinc oxide complexes and evaluation of their cytocompatibility: An approach for periodontal dressing

The aim of this study was to evaluate the possibility of metal complex formation between sodium-phosphorylated chitosan (PCTS) and ZnO. The polymer-metal complex formation was investigated in terms of thermal degradation. The structure deduction of the PCTS/ZnO complex was investigated by means of Fourier transform infrared spectroscopy and X-ray diffraction (XRD). The PCTS/ZnO complexes were formed by the sharing of lone pairs of electrons from the N atoms in the amine groups and O atoms in the phosphate and hydroxyl groups of PCTS to the protonated hydroxyl species on the ZnO surface. Because complex formation occurred at the surface of ZnO particles, it did not change the ZnO crystalline structure. Cytotoxicity, evaluated by a direct contact test with primary human gingival fibroblast cells, revealed that PCTS was biocompatible and reduced the cytotoxicity of ZnO by complexation, making PCTS/ZnO complexes potentially biocompatible. Within the limits of these data, it appears that PCTS could be used as a reaction rate-modifying agent in periodontal dressings.

Acetylene sensor based on Pt/ZnO thick films as prepared by flame spray pyrolysis

ZnO nanoparticles loaded with 0.2–2.0at.% Pt have been successfully produced in a single step by flame spray pyrolysis (FSP) technique using zinc naphthenate and platinum(II) acetylacetonate, as precursors dissolved in xylene and their acetylene sensing characteristics have been investigated. The particle properties were analyzed by XRD, BET, TEM, SEM and EDS. Under the 5/5 (precursor/oxygen) flame condition, ZnO nanoparticles and nanorods were observed. The crystallite sizes of ZnO spherical and hexagonal particles were found to be ranging from 5 to 20nm while ZnO nanorods were seen to be 5–20nm in width and 20–40nm in length. In addition, very fine Pt nanoparticles with diameter of ∼1nm were uniformly deposited on the surface of ZnO particles. From gas-sensing characterization, acetylene sensing characteristics of ZnO nanoparticles is significantly improved as Pt content increased from 0 to 2at.%. The 2at.% Pt loaded ZnO sensing film showed an optimum C2H2 response of ∼836 at 1% acetylene concentration and 300°C operating temperature. A low detection limit of 50ppm was obtained at 300°C operating temperature. In addition, Pt loaded ZnO sensing films exhibited good selectivity towards hydrogen, methane and carbon monoxide.

Modification of optical properties in ZnO particles by surface deposition and anchoring of NiO nanoparticles

Nanodispersion of NiO nanoparticles on the surface of ZnO microparticles has been carried out by means of a low energy dry mixing method. This method keeps the shape and size of the ZnO microparticles that served as support to hold the NiO nanoparticles. The dispersion and anchoring of the NiO nanoparticles takes place by means of an electrochemical reaction with the OH-groups present at the ZnO surface. The process took place at room temperature and cation interdiffusion between ZnO and NiO have not been detected by structural analysis. Nevertheless, changes in the optical properties of semiconductor ZnO particles have been observed due to the deposition of the nanoparticles. These changes correlate with the amount of NiO nanoparticles at the ZnO particle surface. The amount of defects, i.e. oxygen vacancies, interstitial oxygen and zinc vacancies, rises with the increasing NiO content.

Multipod structures of ZnO hydrothermally grown in the presence of Zn3P2

Zinc phosphide (Zn3P2) is used in the present contribution as an inorganic additive for the surfactant-free hydrothermal synthesis of ZnO structures with controlled morphology. Postulated as a suitable dopant candidate for generating P-related acceptor defects inside the wurtzite structure of ZnO, the obtained results however reveal that a stable P:ZnO solid solution is never formed in the binary ZnO–Zn3P2 system. Instead the amorphized phosphide particles may preferentially locate at the surface of ZnO particles, exerting a strong effect on the morphological development of the material and controlling its crystal growth habit: with the incorporation of Zn3P2 the system evolves from a situation in which just hexagonal bipods are observed to another one in which the ZnO particles merge to form spherical ball-shaped structures and flower-like architectures. The high propensity of ZnO polar structure to twin is behind the observed growth mechanism.

Correlation of structural properties with energy transfer of Eu-doped ZnO thin films prepared by sol-gel process and magnetron reactive sputtering.

We investigated the structural and optical properties of Eu-doped ZnO thin films made by sol-gel technique and magnetron reactive sputtering on Si (100) substrate. The films elaborated by sol-gel process are polycrystalline while the films made by sputtering show a strongly textured growth along the c-axis. X-ray diffraction patterns and transmission electron microscopy analysis show that all samples are free of spurious phases. The presence of Eu(2+) and Eu(3+) into the ZnO matrix has been confirmed by x-ray photoemission spectroscopy. This means that a small fraction of Europium substitutes Zn(2+) as Eu(2+) into the ZnO matrix; the rest of Eu being in the trivalent state. This is probably due to the formation of Eu(2)O(3) oxide at the surface of ZnO particles. This is at the origin of the strong photoluminescence band observed at 2 eV, which is characteristic of the (5)D(0)-->(7)F(2) Eu(3+) transition. In addition the photoluminescence excitonic spectra showed efficient energy transfer from the ZnO matrix to the Eu(3+) ion, which is qualitatively similar for both films although the sputtered films have a better structural quality compared to the sol-gel process grown films.

Characterization and Bacterial Response of Zinc Oxide Particles Prepared by a Biomineralization Process

In this paper, olive-like ZnO particles were successfully synthesized via a facile biomineralization process in the template of silk fibroin (SF) peptide at room temperature. The coat of SF peptide on the surface of ZnO particles had a substantial influence on their morphology during the biomineralization. Room-temperature photoluminescence behavior of ZnO particles indicated that the visible blue emission peak centered at 410 nm was enhanced with the mineralization time. Bacteriological tests revealed that the mineralized ZnO particles with SF peptide were not toxic for Staphylococcus aureus, Escherichia coli, and Streptococcus agalactiae, presenting good cytocompatibility due to the surface coat of peptide. Their potential applications in bio-optical detectors could be envisioned.

Ag-modification improving the electrochemical performance of ZnO anode for Ni/Zn secondary batteries

Ag-modified ZnO was prepared by a facile silver mirror reaction process. The average size of silver particles was about 45 nm and they were modified on the part surface of ZnO particles. The electrochemical performance of ZnO as active materials for Ni/Zn batteries was investigated by charge/discharge cycling test, slow rate cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The Ag-modified ZnO anode showed the better cycle stability than unmodified ZnO. The discharge capacity maintained 456 mAh g −1 throughout 65 cycling tests, and the fading rate of the discharge capacity was only 0.89 mAh per cycle. At the same time, it also exhibited the higher midpoint discharge voltage and the lower midpoint charge voltage. The better cycle performance was ascribed to that Ag nanoparticles on the surface of ZnO improved the conductivity of the electrode and inhibited the dissolution of ZnO.

Single-crystal ZnO flocky sphere formed by three-dimensional oriented attachment of nanoparticles

The nanostructure of a single-crystal ZnO flocky sphere was synthesized by using a simple chemical route in the Zn 2+–triethanolamine system. Formation of such quasi-single-crystal nanostructures was achieved through oriented attachment of a large number of ZnO nanoparticles in three dimensions. It is suggested that the adsorption of triethanolamine molecules on the surface of ZnO particles plays an important role in their oriented attachment, leading to the formation of flocky spheres with single-crystal structure.

Synthesis and optical properties of nano-ZnO particles/mesostructured SnO 2 composite

Through self-assembly approach, ZnO nanoparticles were prepared in the pores of mesostructured SnO 2 and the assembled composite of ZnO nanoparticles/mesostructured SnO 2 was obtained. Powder X-ray diffraction (XRD) results clearly showed the existence of mesostructure in the assembled composite after calcining at high temperature. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to observe the morphology and showed ZnO nanoparticles in pores of mesostructured SnO 2. Room temperature photoluminescence (RTPL) of the assembly solid of ZnO nanoparticles/mesostructured SnO 2 was measured. Two emission bands were observed, one being an exciton emission with the peak position of about 406 nm and the other the visible emission with the peak position of about 500 nm. Compare with the nanostructured ZnO bulk, the photoluminescence intensity of the assembled composite of ZnO nanoparticles/mesostructured SnO 2 was enhanced. The luminescence intensity of the assembled composite of ZnO nanoparticles/mesostructured SnO 2 is five to six times higher than that of nanostructured ZnO bulk. It was suggested that the intensity enhancement of the exciton emission was due to band-edge exciton transition and the green emission was corresponded to the increase of the oxygen defect states in ZnO particle surface.

Self-assembly prismatic aggregates formed during the calcination of ZnO powders: In situ monitoring by ETA technique and their photocatalytic properties

This paper describes a unique phenomenon occurred during the calcination of ZnO powders, i.e., the ZnO particles self-assembled to form prismatic aggregates with a clear edges and faces. Field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) were used to characterize the particle morphology and crystal structure of the calcined sample. The emanation thermal analysis (ETA) technique was used to monitor the changes of ZnO particle surface and subsurface microstructure irregularities and the occurrence of interparticle compaction phenomena under in situ conditions of heating and cooling. It was assumed from the ETA results that the driven force of the self-assembly of ZnO particles towards prismatic aggregates originated from the solid state diffusion and migration of grain boundaries. The photocatalytic tests indicated that the prismatic aggregates of ZnO calcined at 800 °C demonstrated a highest photocatalytic activity for acetaldehyde decomposition because of the enhancement of the surface-exposed high-active crystal face of ( 10 1 ¯ 0 ).

Dimethylammonium dimethyldithiocarbamate‐accelerated sulfur vulcanization. I. Thermal stability and reactions with curatives

AbstractTo investigate its thermal stability and reactivity towards other accelerators dimethylammonium dimethyldithiocarbamate ((dma)dmtc) was heated at programmed heating rates in sealed and open pans in a differential scanning calorimeter and on a thermobalance. (Dma)dmtc was heated on its own, in rubber compounds and in mixes with tetramethylthiuram disulfide, zinc dimethyldithiocarbamate, and ZnO. In open systems (dma)dmtc readily sublimes at temperatures well below its melting point, and it is almost as rapidly lost when compounded on its own with rubber. No decomposition is observed at vulcanization temperatures and (dma)dmtc is unreactive towards tetramethylthiuram disulfide and zinc dimethyldithiocarbamate. Moisture does not promote its decomposition. Reaction with ZnO to give zinc dimethyldithiocarbamate is restricted to the surface of ZnO particles. (Dma)dmtc is soluble in water in which it dissociates. It must be concluded that when its is included in formulations, (dma)dmtc, per se, would act as a vulcanization accelerator; it does not decompose to dimethyldithiocarbamic acid and dimethylamine, both of which are known accelerators. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3067–3073, 2001

Über die spektrale Sensibilisierung von Zinkoxid: I. Sorptionsverhalten von o,o′‐Dihydroxyazofarbstoffen

Abstracto,o′‐Dihydroxyazo compounds are spectral sensitizers for the photosemiconductor properties of zinc oxide. It is shown that 1‐(2‐hydroxyphenylazo‐)‐2‐naphthol (II) forms a 1:1 Zn complex on the surface of ZnO particles if adsorbed from toluene solution. With most samples of ZnO a Langmuir type adsorption isotherm is obtained. The concentration of the dye at saturation relative to the BET surface of the ZnO particles correponds to a slightly oblique edge‐on arrangement of the dye molecules on the surfaces.In the case of ZnO pretreated with propionic acid and having taken up dye in excess of a monolayer, it can be shown by electron microscopy that tail‐like complexes (zinc: dye ratio = 1:1) are formed, and that these complexes contain zinc which was originally on the particle surfaces.