Dispersed Zinc Oxide Research Articles

Synthesis, Characterization and Dielectric Properties of Rodlike Zinc Oxide-Polyimide Nanocomposites

Novel polyimide-rodlike zinc oxide hybrid nanocomposite (PI-RL-ZnO) has been developed from the poly (amic acid) with different weight percentages (1, 3, 5 wt%) of using N-methyl-2-pyrrolidone (NMP) and N,N-dimethylacetamide (DMAc) as aprotic solvents. The prepared zinc oxide-polyimide nanocomposites were characterized for their structure, morphology, and thermal behavior employing Fourier transform infrared spectroscopy (FTIR), scanning electron micrograph (SEM), transmission electron micrograph (TEM), X-ray diffraction (XRD) and thermal analysis (DTA/TGA/DSC) techniques. These studies showed the homogenous dispersion of zinc oxide in the polyimide matrix with an increase in the thermal stability of the composites on zinc oxide loadings. More importantly, we intend to explore the possibility of incorporating ZnO particles through dispersion into the polyimide network to achieve the polyimide hybrid with lower dielectric constant (low-k). The lowest dielectric constant achieved of the PI-RL-ZnO material is 2.82 by incorporating 5 wt% ZnO (pure PI, k = 3.22). The reduction in the dielectric constants of the PI-RL-ZnO hybrids can be explained in terms of creating ZnO particles and the free volume increase by the presence of the ZnO particles resulting in a loose PI structure.

Fabrication of ZnO nano-structures using UV nanoimprint lithography of a ZnO nano-particle dispersion resin

Recently, nanoimprint lithography (NIL) has gained great attention as an effective patterning technology in the fields of light emitting diodes (LEDs), solar cells, and other optical devices, because of its simplicity and cost effectiveness. The aim of this study is the development of an imprint resin containing dispersed zinc oxide (ZnO) nano-particles that is applicable in the UV NIL process. UV NIL uses conventional monomer-based resins, which contain a UV initiator, but restricts the use of imprinted structures in optical devices due to their relatively low refractive index. In order to resolve this problem, an imprint resin containing dispersed ZnO nano-particles was prepared, using which submicron-scale structures were fabricated by the UV NIL process. The haziness of submicron-scale ZnO nano-particle resin structures and the refractive index of the ZnO nano-particle dispersion resin were measured to analyze the optical properties of the ZnO nano-particle dispersion resin and the resulting structures.

Zinc oxide nanoparticles: A study of defect level blue–green emission

Systematic investigation of the structural, morphological and optical properties of hexylamine capped zinc oxide (ZnO) nanoparticles is presented. Optical properties indicate the presence of sufficient amount of surface defects. These defects in highly dispersed ZnO nanoparticles have been studied by annealing the nanoparticles in air at various temperatures and recording the photoluminescence spectra. The annealing temperature was found to strongly influence the UV band edge emission and the blue–green defect level emission (DLE). At low annealing temperatures an increase in UV emission with temperatures is observed and this emission is proposed to be a result of desorption of surface adsorbed water and hydroxyl groups. The DLE of the synthesized sample is likely due to the presence of oxygen vacancies on the surface resulting in green emission.

Titanium dioxide and zinc oxide nanoparticles in sunscreens: focus on their safety and effectiveness

Sunscreens are used to provide protection against adverse effects of ultraviolet (UV)B (290-320 nm) and UVA (320-400 nm) radiation. According to the United States Food and Drug Administration, the protection factor against UVA should be at least one-third of the overall sun protection factor. Titanium dioxide (TiO2) and zinc oxide (ZnO) minerals are frequently employed in sunscreens as inorganic physical sun blockers. As TiO2 is more effective in UVB and ZnO in the UVA range, the combination of these particles assures a broad-band UV protection. However, to solve the cosmetic drawback of these opaque sunscreens, microsized TiO2 and ZnO have been increasingly replaced by TiO2 and ZnO nanoparticles (NPs) (<100 nm). This review focuses on significant effects on the UV attenuation of sunscreens when microsized TiO2 and ZnO particles are replaced by NPs and evaluates physicochemical aspects that affect effectiveness and safety of NP sunscreens. With the use of TiO2 and ZnO NPs, the undesired opaqueness disappears but the required balance between UVA and UVB protection can be altered. Utilization of mixtures of micro- and nanosized ZnO dispersions and nanosized TiO2 particles may improve this situation. Skin exposure to NP-containing sunscreens leads to incorporation of TiO2 and ZnO NPs in the stratum corneum, which can alter specific NP attenuation properties due to particle-particle, particle-skin, and skin-particle-light physicochemical interactions. Both sunscreen NPs induce (photo)cyto- and genotoxicity and have been sporadically observed in viable skin layers especially in case of long-term exposures and ZnO. Photocatalytic effects, the highest for anatase TiO2, cannot be completely prevented by coating of the particles, but silica-based coatings are most effective. Caution should still be exercised when new sunscreens are developed and research that includes sunscreen NP stabilization, chronic exposures, and reduction of NPs' free-radical production should receive full attention.

Mobility enhancement of solution-processed Poly(3-Hexylthiophene) based organic transistor using zinc oxide nanostructures

This work reports the mobility enhancement of p-type organic transistors formed using Poly(3-Hexylthiophene) (P3HT) using the dispersion of ZnO (zinc oxide) nanostructures. The ZnO nanostructures considered here are nanorods that were fabricated via a simple one-step aqueous-based chemical approach. Organic Thin Film Transistors (OTFTs) based on these nanocomposites show a mobility enhancement of more than 60% for the P3HT/ZnO nanorod composite compared to its pristine state polymer devices. The results presented here show a great promise for the mobility enhancement of p-type solution processed OFETs and applications.

Enhanced light output power of GaN-based light-emitting diodes by nano-rough indium tin oxide film using ZnO nanoparticles

We demonstrate the performance improvement of GaN-based light-emitting diodes (LEDs) using zinc oxide (ZnO) nanoparticles inserted between the p-GaN and the indium tin oxide (ITO) layers. Upon deposition of an ITO film over the dispersed ZnO nanoparticles, the ITO surface tends to attain a nano-rough morphology due to the presence of ZnO nanoparticles. The light output power of the fabricated LEDs with ZnO nanoparticles is 39% higher than that of conventional LEDs at an injection current of 20 mA. This is attributed to the improved light extraction favored by the light scattering tendency of ZnO nanoparticles and the nano-roughened ITO film. In addition, the intermediate refractive index (n ∼2) of ZnO materials between those of the p-GaN (n ∼2.5) and the ITO (n ∼1.9) results in a broader critical angle and a reduction of total internal reflection.

Synthesis and photocatalytic properties of highly dispersed zinc oxide doped with iron

Synthesis and photocatalytic properties of highly dispersed zinc oxide doped with iron

Preparation of Self-Assembled Zinc Oxide Nanoparticles Multilayer Films Under Ultrasonic Irradiation

Zinc oxide nanoparticles were synthesized and self-assembled on the reactive surface of a glass slide functionalized with (3-mercaptopropyl)-trimethoxysilane under ultrasonic irradiation. The structure, morphology, and optical property of the zinc oxide nanoparticles were investigated by TEM, XRD, and UV-vis spectroscopy. The functionalized glass slide was soaked in an aqueous solution which dispersed zinc oxide nanoparticles under ultrasonic irradiation. Zinc oxide multilayer films grew up to several layers (up to 5 layers) depending on the immersion time. The self-assembled zinc oxide nanoparticles multilayer films were characterized using UV-vis spectroscopy and SEM. Ultrasonic irradiation was an efficient method to make multilayer films on the functionalized glass slide with zinc oxide nanoparticles.

The oxidation of zinc and barium chlorides with oxygen to obtain chlorine and finely dispersed zinc oxide

The regular features of the reaction of calcium, barium, and zinc chlorides with oxygen to form molecular chlorine and corresponding metal oxides are studied. The rate constants of the reaction were determined. The effective activation energies of oxidation of chloride ions were calculated with due to regard for the diffusion at the gas-chloride melt interface, which is especially pronounced at a temperature above 550°C. Zinc oxide being formed was separated from the reaction mixture, and the dispersion of its particles was determined.

In situ preparation of nano ZnO/hyperbranched polyimide hybrid film and their optical properties

Novel hybrid films of fluorinated hyperbranched polyimide (HBPI) and zinc oxide (ZnO) were prepared via the in situ sol–gel polymerization technique, in which mono-ethanolamine (MEA) was used as the coupling agent between the termini of HBPI and the precursor of ZnO. The hybrid films were characterized by transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) absorption, ultraviolet–visible (UV–vis) absorption, and fluorescent excitation/emission spectroscopy. The films, which originated from the colourless fluorinated HBPI structure and homogeneously dispersed ZnO nanoparticles, exhibited good optical transparency. Furthermore, two kinds of model compounds with and without ZnO and a HBPI film blended with ZnO microparticles were prepared to clarify the fluorescence mechanism in the pristine HBPI and in situ hybrid films. Efficient energy transfer from the ZnO nanoparticles to the aromatic HBPI main chains was observed in the in situ hybrid films, whereas energy transfer occurred only from the locally excited (LE) states to the charge-transfer (CT) state in the HBPI film. These facts demonstrate that the peripheral termini of HBPI are covalently bonded to ZnO particles via the MEA function, which operates as an effective pathway for energy transfer to give intense fluorescent emission.

Synthesis and Characterization of Highly Fluorescent Water Dispersible ZnO Quantum Dots

We report the synthesis of stable and water dispersible fluorescent zinc oxide (ZnO) quantum dots (QDs). Hydrophilic polyethyleneimine (PEI) was used to stabilize QDs in water and trisodiumcitrate was used as linker between ZnO and PEI. X-ray diffraction reveals the nanocrystalline nature and hexagonal wurtzite structure of as synthesized ZnO QDs. High-resolution transmission electron micrograph suggests nearly spherical particles of size 3-6 nm and lattice spacing of 0.28 nm corresponding to the (100) plane of zinc oxide. Water dispersed ZnO QDs exhibit efficient yellow-green fluorescence centered at 555 nm (2.23 eV) with an excitation wavelength of 360 nm, which is found to be stable for two month revealing the high stability of QDs in water.

Mechanism of formation of finely dispersed zinc oxide in homogeneous hydrolysis of zinc nitrate in the presence of hexamethylenetetramine

Mechanism of formation of finely dispersed zinc oxide in homogeneous hydrolysis of zinc nitrate in the presence of hexamethylenetetramine

Zinc Bioavailability Is Improved by the Micronised Dispersion of Zinc Oxide with the Addition of L-Histidine in Zinc-Deficient Rats

Zinc fortification of milk or soft drinks is usually used to combat zinc deficiencies in developing countries. Water-soluble zinc compounds, such as zinc sulfate or zinc citrate, are better absorbed but have an unacceptable taste. A micronised, dispersible zinc oxide (MDZnO), which does not have such a problem concerning taste, had higher solubility compared to ZnO (zinc oxide) in an artificial gastric solution. MDZnO was tested for its bioavailability using zinc-deficient Wistar rats. Prior to the experiment, rats were fed zinc-deficient diet for 3 wk and were orally administered control (distilled water) or zinc solutions (ZnO, ZnO+L-histidine (His), MDZnO, MDZnO+His, 1 mg zinc/kg or 3.2 mg His/kg body weight). Compared to ZnO, MDZnO showed a lag in peak time and a lengthy period of continued high plasma zinc concentration after the single oral administration of zinc compounds. Addition of His to MDZnO elevated serum zinc concentration. Serum zinc concentration (area under the curve) in rats administered MDZnO with His was significantly higher than in rats administered distilled water (p<0.05). Liver zinc level was significantly higher in rats administered MDZnO with His compared with control rats (p<0.05), although the level was not affected by the administration with ZnO alone, ZnO+His, or MDZnO alone. In conclusion, the solubility of ZnO was elevated by the micronised dispersion tecnique and an in vivo study using zinc-deficient rats confirmed that its bioavailability was significantly improved compared to ZnO and the coadministration of His additively enhanced the bioavailability of MDZnO.

Preparation of ZnO/Eu mixed films by electrochemical precipitation

The electrochemical preparation of europium doped zinc oxide and europium oxide/hydroxide as thin films is investigated. First, a thermodynamic study of the Eu–Cl–H 2O system has been carried out at 25 and 70 °C in order to predict the electrochemical behaviour of Eu(III) dissolved in aqueous solution containing chloride ions. A comparison of the Eu–Cl–H 2O and Zn–Cl–H 2O systems indicates the possible coprecipitation of ZnO and Eu(OH) 3 from deposition solutions containing well-adjusted Eu(III)/Zn(II) concentrations ratio. The thermodynamic predictions have been confirmed experimentally by the electrochemical co-deposition of ZnO/Eu thin films on conducting electrode substrates at −1.4 V versus MSE. The presence of europium in the film is detected for Eu(III)/Zn(II) concentration ratio at (0.6 mM/5 mM) which is lower than the predicted value. Increasing Eu(III) concentration leads to the rapid appearance of two phases: dispersed zinc oxide nanorods and, at the bottom of the rods, a covering layer containing Eu(OH) 3 and zinc. The density of ZnO rods decreases and the rod size increases with increasing Eu(III) concentration in the bath. Above 1 mM EuCl 3, a dramatic fall in the current density is observed with the formation of a less conducting ZnO/Eu mixed deposit.

The Study of Morphology and Mechanical Properties of Compatibilized Polypropylene/Zinc Oxide Composites

The paper studies the influence of compatibilizer (polypropylene-graft-maleic anhydride, PP-g-MA) on morphology and mechanical properties of polypropylene/zinc oxide composites. Polypropylene (PP) and zinc oxide (ZnO) composites were prepared by melt mixing technique in a twin screw extruder. The Young's modulus and impact strength of the composites increased as ZnO loading increased, but the impact strength was decreased with the addition of the compatibilizer. The tensile strength of the composites before and after adding compatibilizer was almost the same with the pure PP. The dispersion of ZnO in the matrix polymer was investigated using scanning electron microscope (SEM). The results obtained show that the addition of a small of PP-g-MA compatibilizer during melt extrusion improved the dispersion of ZnO particles.

Hydrothermal synthesis and photocatalytic activity of highly dispersed ZnO powders

Considerable attention of researchers in Russia and abroad has been given recently to the design and study of materials based on zinc oxide. This high interest is due to the unique electrophysical properties of these materials. Zinc oxide can be used as a component of gas sensors, transparent conductors, luminescent materials, solar cells, UV lasers, piezoelectric devices, and others [1]. Special attention is given to studies of the photocatalytic activity of ZnO. Photocatalytic purification of sewage has several advantages over presently used ozonation, chlorination, electrochemical oxidation, and decomposition by hydrogen peroxide and potassium permanganate [2‐4]. A possibility to prepare ZnO samples with photocatalytic activity comparable with that of commercial TiO 2 samples has been shown [5 − 8]. Thus, zinc oxide is considered as a cheaper alternative to TiO 2 . Highly dispersed zinc oxide is presently prepared by different methods: ceramic technology, sol‐gel process, pyrolysis of aerosols, and others [9]. Here we used the hydrothermal method to synthesize zinc oxide. This method makes it possible to vary the micromorphology of the synthesized materials through changing the synthesis parameters. Other advantages of the method are its ecological safety, economy, and relative simplicity [10]. The purpose of this work is to study the micromorphology and photocatalytic activity of ZnO as dependent on the hydrothermal synthesis parameters.

Synthesis and Use of Highly Dispersed Zinc Oxide

Methods for synthesis of zinc oxide hydrosols by peptization and condensation were developed. The basic colloid-chemical properties of the sols were determined: electrokinetic properties, size and phase composition of particles, and stability of hydrosols against introduction of electrolytes. The possibility of obtaining antibacterial and UV-protecting cosmetic preparations from the hydrosols obtained was demonstrated.

Adsorption of polyelectrolyte on the surface of ZnO nanoparticles and the stability of colloidal dispersions

The present study focuses on the adsorption of a polyelectrolyte, the component of which is a polymer of maleic anhydride sodium salt, on the surface of nanometric zinc oxide particles and the colloidal stability of aqueous dispersions. FTIR spectroscopic data provided evidence in support of hydrogen bonding and chemical interaction in the case of the polyelectrolyte-ZnO system. The adsorption isotherms showed the influences of polyelectrolyte concentration, pH and ionic strength on the adsorption. With the increase of pH the saturated adsorbed amount decreased, while the thickness of adsorption layer increased. The saturated adsorbed amount increased with increasing salt concentration, and decreased with further increasing salt concentration. It should be noted that in the presence of a CaCl2 solution the adsorbed amount and the adsorption layer thickness were greater than those in the NaCl solution of the same concentration. The change of the absorbance of zinc oxide dispersions showed that the absorbance decreased slowly at high pH. There was a maximum point for the absorbance of the zinc oxide dispersions in the presence of various polyelectrolyte concentrations. The change of dispersion stability resulted from the change of macromolecular chains conformation at the interface.

Highly dispersed zinc oxide species on silica as active sites for photoepoxidation of propene by molecular oxygen

The activity of silica-supported zinc oxide containing from 0.01 to 5 mol% of Zn was investigated in the photoepoxidation of propene by molecular oxygen at room temperature. With an increase in the Zn loading amount, the conversion of propene increased monotonically, while the yield of propene oxide (PO) increased up to 1 mol% of Zn and then decreased. The selectivity to PO was almost constant up to 0.1 mol% of Zn and then decreased. By means of XRD, UV-vis, and XANES/EXAFS spectroscopy, it was found that the highly dispersed (isolated) tetrahedral zinc oxide species were predominant in the ZnO/SiO 2 samples of low Zn loading amounts, while the aggregated species such as [ZnO] n clusters were dominant in the ZnO/SiO 2 samples of higher Zn loading. The former species were found to be responsible for the photoepoxidation of propene.

Adsorption of Polyacrylic Acid and Its Copolymers with Acrylonitrile on Zinc Oxide Particles

Adsorption of polyacrylic acid and its copolymers with acrylonitrile, containing different quantities of carboxyl groups, on the dispersion of zinc oxide was investigated. The kinetics of polymer desorption was investigated based on data concerning the change in concentration of free carboxylic groups of polymer and zinc ions in solution. The concentration of free carboxyl groups decreases and the concentration of zinc ions in the liquid phase above the residue after separation of zinc oxide particles increases with time, reaching a constant value. The dependence of the concentration of free carboxyl groups and zinc ions in the liquid phase on the initial concentration of polymer in the plateau section of the kinetic curve was investigated. Adsorption isotherms of copolymers depend on their solubility in water and can be described by different mathematical models.