Spherical ZnO Research Articles

Effects of Oxide-Modified Spherical ZnO on Electrical Properties of Ag/ZnO Electrical Contact Material

Silver-zinc oxide (Ag/ZnO) electrical contact material is widely used as contacts of the medium duty switching devices. Effects of modified ZnO on properties of Ag/ZnO electrical contact material were investigated in this work. NiO and CuO were introduced to modify spherical ZnO by a chemical solution nano-coating method. Ag/ZnO contacts prepared using the modified spherical ZnO were produced by powder metallurgy (PM) method in a muffle furnace in temperature ranges from 750 to 900 °C. Results show that electrical conductivity, stability of relative density, and Vickers’ hardness of Ag/ZnO electrical contact material can be improved by the addition of NiO because of the formation of NiO solid solution Zn0.2Ni0.8O. The addition of CuO to Ag/ZnO electrical contact material makes arcing energy and mass loss lower. Since this is attractive for a longer service life, using NiO and CuO co-modified ZnO as a second phase may be a promising way to improve properties of Ag/ZnO electrical contact material. Hence, the presented results could also be useful for the design of a new Ag/ZnO electrical contact material.

ZnO hollow nanospheres via Laux-like oxidation of Zn0 nanoparticles

Zinc oxide hollow nanospheres were obtained via a Laux-like oxidation of zinc nanoparticles using nitrobenzene as oxidizing agent. The ZnO hollow nanospheres exhibit an outer diameter of 10.4 ± 1.3 nm and a well crystallized sphere wall with a thickness of 2.9 ± 0.4 nm. Laux-like oxidation and formation of the ZnO hollow nanospheres were performed instantaneously after sodium naphthalenide ([NaNaph]) driven reduction of ZnCl2 to Zn0 nanoparticles in the liquid phase without any separation of the intermediate Zn0 nanoparticles. The diameter of the resulting ZnO hollow nanospheres (10.4 ± 1.3 nm) reflects the diameter of the intermediate Zn0 nanoparticles (10.1 ± 2.3 nm). In accordance with the small diameter of the ZnO sphere wall, quantum-size effects occur with a band gap that is blue-shifted by 0.2 eV in comparison to bulk-ZnO.

Sonochemical synthesis and characterization of three nano zinc(II) coordination polymers; Precursors for preparation of zinc(II) oxide nanoparticles

Nanostructures of three Zinc(II) coordination polymers, [Zn(NNO)2(H2O)4]n (1), [Zn(PNNO)2(H2O)2]n (2) and [Zn(H2O)6]·(INNO)2 (3) {NNO: Nicotinic acid N-oxide, PNNO: Picolinic acid N-oxide and INNO: Isonicotinic acid N-oxide}, have been synthesized by a sonochemical process and reaction of ligands with Zn(CH3COO)2. The Zinc(II) oxide nano-particles have been synthesized from thermolysis of [Zn(NNO)2(H2O)4]n (1), [Zn(PNNO)2(H2O)2]n (2) and [Zn(H2O)6]·(INNO)2 (3) at two different methods (with surfactant and without surfactant) and two temperatures (200 and 600°C). The ZnO nanoparticles were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Comparison of the SEM images of ZnO nano-particles at two different methods and temperatures shows that higher temperature results in an increasing of agglomeration and thus small and spherical ZnO particles with good separation were produced by thermolysis of compounds at 200°C and by use of surfactant.

Novel synthesis of monodisperse ZnO-based core/shell ceramic powders and applications in low-voltage varistors

In this article, monodisperse ZnO microspheres were successfully prepared by a facile ultrasound irradiation method. Then, by using the microspheres as the templates, the novel uniform ZnO/Co2O3-Bi2O3 core/shell composites were successfully synthesized via a situ precipitation–coating route due to the electrostatic interaction of [BiEDTA]− and [Co(NH3)6]3+. Microstructural studies of the as-obtained powders were carried out using the techniques of the XRD, FTIR, SEM, TEM, TGA and EDS. The results show that the white ZnO powders as the core were spherical structure with the size of approximate 500nm and the thickness of the additive metal oxide shell was about 80nm, respectively. On the basis of the results, the spherical ZnO microspheres fully coated with additional transition metal oxides were identified and Bi12Co0.60O18.80 phase was observed after the ZnO composites were calcinated at 420°C for 4h. The formation mechanism of monodisperse ZnO microspheres and the ZnO-based core/shell structured composites were also brief introduced. The varistors ceramics sintered in air at 1250°C for 2h possesses a density of 5.64g/cm3 corresponding to 97.7% of the theoretical density, with breakdown voltage of 78.6V/mm and nonlinear coefficient of ~7.1.

Novel inkjet droplet method generating monodisperse hollow metal oxide micro-spheres

A novel method to synthesize monodisperse hollow TiO2, SnO2 and ZnO microspheres was developed. Water droplets generated from an inkjet nozzle contain clusters of polystyrene latex (PSL) particles covered with metal oxide nanoparticles were continuously dried up forming PSL clusters decorated with metal oxide nanoparticles. By heating the clusters up to 400°C, the PSL particles are evaporated forming hollow spheres. Monodisperse hollow TiO2, SnO2 and ZnO spheres in the size range of 5.1–8.6μm were consequently generated with a narrow particle size distribution. And the hollow TiO2, SnO2 and ZnO spheres have 41.0nm, 30.0nm, and 85.3nm sized pores, respectively. The method enables us to have simpler and faster process to generate hollow TiO2, SnO2 and ZnO spheres and to control the diameter of hollow spheres easily by adjusting waveform applied to a nozzle compared to other processes. A potential applicability to photoelectrochemical cells was demonstrated for the prepared hollow TiO2 grown a Si substrate.

Toward single-mode random lasing within a submicrometre-sized spherical ZnO particle film

We had recently reported unique random laser action such as quasi-single-mode and low-threshold lasing from a submicrometre-sized spherical ZnO nanoparticle film with polymer particles as defects. The present study demonstrates a novel approach to realize single-mode random lasing by adjusting the sizes of the defect particles. From the dependence of random lasing properties on defect size, we find that the average number of lasing peaks can be modified by the defect size, while other lasing properties such as lasing wavelengths and thresholds remain unchanged. These results suggest that lasing wavelengths and thresholds are determined by the resonant properties of the surrounding scatterers, while the defect size stochastically determines the number of lasing peaks. Therefore, if we optimize the sizes of the defects and scatterers, we can intentionally induce single-mode lasing even in a random structure (Fujiwara et al 2013 Appl. Phys. Lett. 102 061110).

Synthesis and optical properties of Au/ZnO core–shell nanorods and their photocatalytic activities

Gold nanoparticles with ZnO (sphere and rod) core–shell have been prepared from HAuCl4 containing aqueous solution using pot chemical and hydrothermal method. The nanoparticles were characterized by using X-ray diffraction, transmission electron microscopy, and UV–vis absorption spectroscopy. The effects of the concentration of zinc acetate, reaction temperature, and growth solution of zinc oxide were investigated. It was found that they strongly effect on the formation of the core–shell nanoparticles and optical properties of it. The high absorption peak in the visible region and more absorption intensity in UV region of Au/ZnO core–shell nanoparticles candidate it for photocatalytic applications.

Au Nanoparticles Supported Nanoporous ZnO Sphere for Enhanced Photocatalytic Activity Under UV-Light Irradiation

Monodispersed 200 nm-sized ZnO spheres (SPs) with porous structure emanating from 8 nm zinc oxide nanoparticles (NPs) composing the SPs were synthesized by dissolving zinc acetate dihydrate in diethylene glycol at 160 °C. The prepared SPs were employed in fabricating the gold (Au) loaded ZnO (Au/ZnO SP) composite materials, exhibiting high photocatalytic activity in decomposing salicylic acid under UV-light irradiation. It is deduced that its high catalytic activity originates from the charge separation by transferring photoinduced electrons from the conduction band (CB) of ZnO to Au, since the CB level of ZnO (−0.5 V vs. NHE) is located more negative side than that of Au (+0.5 V vs. NHE). The evidence for the charge separation was provided by monitoring.OH radical with bare ZnO SPs and Au/ZnO SP produced in the solution which readily react with 1,4-terephthalic acid (TA) inducing 2-hydroxy terephthalic acid (TAOH) that shows unique fluorescence peak at 426 nm.

Composite of ZnO spheres and functionalized SnO2 nanofibers with an enhanced ethanol gas sensing properties

Many studies have proven that composite type sensor utilizing two or multiple oxide material could prove to be an effective way to enhance the gas sensing performance. We have fabricated successfully the composite of ZnO spheres and functionalized SnO2 nanofibers as a novel sensing material. The structure and morphology of the samples were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and BET test. A systematic comparison study reveals an enhanced gas sensing performance for the sensor made of ZnO–SnO2 composite toward ethanol over undecorated ZnO spheres, SnO2 nanofibers. The enhanced gas sensing properties is attributed to the unique hierarchical and n–n heterojunction structures.

A Facile Method for the Synthesis Fluorescent Zinc Chalcogenide (ZnO, ZnS and ZnSe) Nanoparticles in PS and PMMA Polymer Matrix.

A simple method for the synthesis of fluorescent zinc chalcogenide (ZnO, ZnS and ZnSe) nanoparticles directly in the transparent PMMA and PS polymer matrices were reported. Highly dispersed small spherical ZnO nanoparticles (3-5nm) was obtained by hydrothermal reaction of PMMA/PS-Zn(acac)2H2O in toluene. ZnS and ZnSe nanoparticles were prepared by heterogeneous stirring of PMMA/PS-Zn(acac)2H2O in toluene with aqueous solution of thiourea or NaHSe. Interestingly, ZnO and ZnS-PMMA thin film showed strong fluorescence quenching upon exposure to ammonia.

Evaluation of gas-sensing properties of ZnO nanostructures electrochemically doped with Au nanophases.

A one-step electrochemical method based on sacrificial anode electrolysis (SAE) was used to deposit stabilized gold nanoparticles (Au NPs) directly on the surface of nanostructured ZnO powders, previously synthesized through a sol–gel process. The effect of thermal annealing temperatures (300 and 550 °C) on chemical, morphological, and structural properties of pristine and Au-doped ZnO nancomposites (Au@ZnO) was investigated. Transmission and scanning electron microscopy (TEM and SEM), as well as X-ray photoelectron spectroscopy (XPS), revealed the successful deposition of nanoscale gold on the surface of spherical and rod-like ZnO nanostructures, obtained after annealing at 300 and 550 °C, respectively. The pristine ZnO and Au@ZnO nanocomposites are proposed as active layer in chemiresistive gas sensors for low-cost processing. Gas-sensing measurements towards NO2 were collected at 300 °C, evaluating not only the Au-doping effect, but also the influence of the different ZnO nanostructures on the gas-sensing properties.

ZnO nanoflowers-based photoanodes: aqueous chemical synthesis, microstructure and optical properties

AbstractWe have developed an efficient, low temperature, synthetic route for ZnO nanoflowers (NFs) as photoanode material. This alternative route yields small flowerlike nanostructures, built from densely self-assembled tip-ended rod structures. The obtained ZnO NFs possess a large bandgap of 3.27 - 3.39 eV, enabling the generation of an average open current voltage of 0.56 V. Additionally, they show a high internal light harvesting of 14.6•10-7A-mol-1. The growth mechanism and self-assembly of ZnO NFs were studied in detail by joint spectroscopic-TEM investigations. It is shown that the ZnO crystallite size increases with increasing annealing temperatures and that the stress and the improved crystallinity are induced by annealing and reduce the lattice strain and the dislocation density. The bandgaps of ZnO are affected by the lattice strain revealing an optimal region of lattice strain to gain high bandgap energies. The properties of the synthesized ZnO NFs are compared with other morphologies, i.e. ZnO spherical aggregates (SPs) and ZnO nanorods (NRs), and are tested as electrode materials in dye-sensitized solar cells.

One-Step Electrodeposited Porous ZnO Thin Film Based Immunosensor for Detection of Vibrio cholerae Toxin

Here, we have reported one step fabrication of a porous thin film of the zinc oxide nanoparticles (ZnO NPs) directly onto the indium tin oxide (ITO) glass substrate by cathodic electrodeposition from an aqueous solution containing zinc nitrate. The morphological studies of a thin film of ZnO NPs suggest that the NPs formed a porous structure with irregular pore size distribution over the surface of ITO glass substrate. The average pore size and wall thickness of pores obtained as 620 nm and 50–120 nm, respectively. Transmission electron microscopic investigations reveal the growth of spherical ZnO NPs of size ranging from 20–30 nm. The surface charge on the electrodeposited ZnO NPs has shown a positive value of 18 mV as confirmed by zeta potential. This electrodeposited porous thin film of ZnO NPs has been employed for immobilization of monoclonal antibodies (Ab) specific to Vibrio cholerae for detection of Vibrio cholerae toxin B. Electrochemical studies reveal that these ZnO/ITO electrodes provide favorable conditions for immobilization of Ab with better orientation, resulting in enhanced electron transfer at the interface. This immunoelectrode exhibits improved biosensing characteristics as detection range varies from 12.5–500 ng mL−1, the sensitivity of 71 nA ng−1 mL cm−2, the low detection limit of 0.16 ng mL−1 and an association constant of 14.12 ng mL−1. Significantly, the electrodeposited ZnO thin films are uniform, cost-effective, reproducible and stable. This can be processed for commercialization.

A nanohybrid of platinum nanoparticles-porous ZnO–hemin with electrocatalytic activity to construct an amplified immunosensor for detection of influenza

In this work, a nanohybrid of platinum nanoparticles-porous ZnO spheres-hemin (Pt–pZnO–hemin) was synthesized for construction of alkaline phosphatase-based immunosensor for detection of influenza. Briefly, porous ZnO spheres (pZnO) were prepared using soluble starches as the capping agent, followed by surface functionalization of platinum nanoparticles via a hydrothermal method (Pt–pZnO). Then, hemin with carboxylic functionality was spontaneously adsorbed onto Pt–pZnO by ester-like binding between carboxylic group of hemin and ZnO. Compared with platinum nanoparticles and hemin, the resulting Pt–pZnO–hemin nanohybrid showed more excellent electrocatalysis activity toward 1-naphthol (1-NP). Taking advantage of the Pt–pZnO–hemin, we have developed an amplified electrochemical immunosensor based on in situ generation of redox probe by alkaline phosphatase (ALP) and Pt–pZnO–hemin as signal enhancer. Herein, electrochemically active 1-NP was generated by enzymatic hydrolysis of inactive 1-naphthyl phosphate by ALP, then Pt–pZnO–hemin was used as catalyst to catalytically oxidize 1-NP, resulting in electrochemical signal amplification. Furthermore, in comparison with other nanomaterials including Au–pZnO, Pt–pZnO and Au–pZnO–hemin, the excellent catalytical property of Pt–pZnO–hemin make it a promising nanohybrid material for ALP-based immunosensor for signal amplification.

Zinc oxide and zinc hydroxide formation via aqueous precipitation: Effect of the preparation route and lysozyme addition

Aqueous precipitation products of Zn(NO3)2 and NaOH obtained by changing the method of combining the reactants and by using lysozyme as an additive were investigated. In the case of single addition method, octahedral ε-Zn(OH)2 and plate-like β-Zn(OH)2 structures formed in the absence and in the presence of lysozyme, respectively. Calcination of these Zn(OH)2 samples at 700 °C yielded porous ZnO structures by conserving the template crystals. When zinc source was added dropwise into NaOH solution, predominantly clover-like ZnO crystals were obtained independent of lysozyme addition. Mixed spherical and elongated ZnO morphology was observed when NaOH was added dropwise into Zn(NO3)2 solution containing lysozyme. Lysozyme contents of the precipitation products were estimated as in the range of ∼5–20% and FTIR indicated no significant conformational change of lysozyme in the composite. These results suggest that lysozyme-ZnO/Zn(OH)2 composite materials may have a value as an antibacterial material.

Tunable ZnO spheres with high anti-biofilm and antibacterial activity via a simple green hydrothermal route

A family of distinct ZnO morphologies – hollow, compartmented, core–shell and full solid ZnO spheres, dispersed or interconnected – is obtained by a simple hydrothermal route, in the presence of the starch biopolymer. The zinc-carbonaceous precursors were characterized by infrared spectroscopy, thermal analysis and scanning electron microscopy, while the ZnO spheres, obtained after the thermal processing, were investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, UV–VIS spectroscopy, photoluminescence measurements, antimicrobial, anti-biofilm and flow cytometry tests. The formation mechanism proposed for this versatile synthesis route is based on the gelling ability of amylose, one of the starch template constituents, responsible for the effective embedding of zinc cations into starch prior to its hydrothermal carbonization. The simple variation of the raw materials concentration dictates the type of ZnO spheres. The micro-sized ZnO spheres exhibit high antibacterial and anti-biofilm activity against Gram-positive (Staphylococcus aureus, Bacillus subtilis) and Gram-negative (Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa) reference and methicillin resistant clinical strains especially for Gram-negative biofilms (P. aeruginosa), demonstrating great potential for new ZnO anti-biofilm formulations.

Morphology of ZnO nanoparticles bound to carbon nanotubes affects electrocatalytic oxidation of phenolic compounds

The electrocatalytic activity of ZnO nanoparticles attached to carboxylic acid functionalized multi-walled carbon nanotubes (MWCNTs) was investigated controlling the morphology and size of ZnO nanoparticles hydrothermally synthesized. A strong dependence of electrocatalytic activity on nanosized ZnO shape toward electrochemical oxidation of dopamine, hydroquinone, and tert-butylhydroquinone is demonstrated. High activity was verified for the oxidation of all phenolic molecules when ZnO nanoparticles were hydrothermally produced at 120°C for 120min, which resulted in nanosized flower-shape nanoparticles. Two other procedures for production of ZnO were evaluated using the microwave hydrothermal method and resulted in spherical and non-uniform ZnO nanoparticles. The cyclic voltammetry experiments in Britton–Robinson buffer revealed that the composite ZnO/MWCNT using the nanosized flower-shape ZnO nanoparticles provided intense (around 4-fold) increase in current and decrease in peak-to-peak separation for the electrochemical oxidation of the three phenolic molecules in comparison with the other ZnO/MWCNT composites and with MWCNT-modified electrodes. Improved performance of this sensor was in agreement with electrochemical impedance spectroscopy measurements. Amperometric measurements also revealed the improved performance of the composite ZnO/MWCNT using the nanosized flower-shape ZnO (superior sensitivity).

Facile synthesis of high tap density ZnO microspheres as advanced anode material for alkaline nickel-zinc rechargeable batteries

Anode active materials, high tap-density ZnO microspheres, with enhanced volumetric capacity and improved cycling performance for nickel-zinc rechargeable batteries have been synthesized via a novel complexing co-precipitation method. The physical and electrochemical properties of the obtained ZnO microsphere are investigated. Notably, tap-density of the resultant ZnO microspheres can reach 3.00g cm−3, three times higher than the commercial conventional ZnO. Compared with the conventional ZnO, the obtained ZnO microspheres have demonstrated superior electrochemical properties, including higher volume specific capacity, improved high-rate ability, and better cyclic stability. At rates of 0.2C and 2C, the obtained ZnO microspheres deliver volumetric capacities of ∼1450 and ∼1110mAhcm−3, respectively, which are about three times higher than those of the conventional ZnO. These performance improvements are attributed to its unique more dense spherical microstructure, thus leading to better reaction reversibility, excellent anti-corrosion ability, lower charge transfer resistance and better inhibiting effect on shape change of the material. Owing to its facile synthesis and outstanding electrochemical properties, this high-density spherical ZnO sample is a promising anode material for fabricating high performance Ni-Zn secondary batteries.

Unravelling the origin of the giant Zn deficiency in wurtzite type ZnO nanoparticles.

Owing to its high technological importance for optoelectronics, zinc oxide received much attention. In particular, the role of defects on its physical properties has been extensively studied as well as their thermodynamical stability. In particular, a large concentration of Zn vacancies in ZnO bulk materials is so far considered highly unstable. Here we report that the thermal decomposition of zinc peroxide produces wurtzite-type ZnO nanoparticles with an extraordinary large amount of zinc vacancies (>15%). These Zn vacancies segregate at the surface of the nanoparticles, as confirmed by ab initio calculations, to form a pseudo core-shell structure made of a dense ZnO sphere coated by a Zn free oxo-hydroxide mono layer. In others terms, oxygen terminated surfaces are privileged over zinc-terminated surfaces for passivation reasons what accounts for the Zn off-stoichiometry observed in ultra-fine powdered samples. Such Zn-deficient Zn1-xO nanoparticles exhibit an unprecedented photoluminescence signature suggesting that the core-shell-like edifice drastically influences the electronic structure of ZnO. This nanostructuration could be at the origin of the recent stabilisation of p-type charge carriers in nitrogen-doped ZnO nanoparticles.

Optimization of process parameters and its effect on particle size and morphology of ZnO nanoparticle synthesized by sol–gel method

In the present work, a systematic basic research has been performed for finding out the effect of various process parameters viz. molar ratio of zinc sulfate and sodium hydroxide, reaction time and calcination temperature on size and morphology of ZnO nanoparticles synthesized using zinc sulfate as a precursor by sol–gel method. Taguchi design method, ANOVA and regression analysis were used to find out the effect of various process parameters on the response in terms of narrow particle size distribution and crystal size. Characterization was done to find out the response such as particle size distribution and crystal size by using TEM and XRD. Results revealed molar ratio of 1:2, and calcination temperature of 700 °C could significantly form uniform-sized spherical ZnO nanoparticles (85 nm) with narrow size distribution. However, significant increase in crystal size of ZnO nanoparticles was observed with increase in calcination temperature from 300 to 700 °C. This may be primarily due to governing of higher diffusion rate at high temperature which resulted in enhanced growth rate of ZnO crystals.