Sphere-like ZnO Research Articles

Zinc oxide nanostructures: Experiments probing their transformation to nanorods

Due to their high length-to-diameter aspect ratio, ZnO nanorods (ZnO-NRs) are extensively used in different applications. However, how they form is not well understood. Here, we have investigated the formation of ZnO-NR by sequential, temporal evolution of ZnO nanostructures. We observe sphere-like ZnO nanoparticles (ZnO-NP), as early as 5–10 s. Subsequently, these spherical ZnO-NPs aggregate and form short chains, which transform into novel nanocones. This hitherto unseen ZnO nanocones (ZnO-NCs) are hollow on one side and has a pointed end on the other side. Two ZnO-NCs together form individual ZnO-NC pairs. High intrinsic surface energy may have caused a ZnO-NC to pair-up with another adjacent ZnO-NC. Later, each of these paired ZnO-NCs transform into ZnO-NRs. We find that, formation of ZnO-NR follows second-order rate kinetics with respect to zinc precursor and HMTA concentration. Additionally, temperature and HMTA concentration significantly influence the length of ZnO-NR.

GC/MS screening of buckthorn phytochemicals and their use to synthesize ZnO nanoparticles for photocatalytic degradation of malachite green dye in water.

Zinc oxide nanoparticles (ZnO NPs) were biosynthesized. According to gas chromatography/mass spectrometry analysis, chalcone, the main phytochemical, is probably complexed with Zn ions that are then oxidized to ZnO NPs by atmospheric O2 during heating. The ZnO NPs were characterized by thermogravimetric analysis, Fourier transform infrared spectroscopy, X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and Brunauer-Emmett-Teller surface area analysis. Sphere-like ZnO NPs were formed with 11 nm mean crystallite size, 5.2 m2 g-1 surface area, and 0.02 cm3 g-1 total pore volume. The synthesized ZnO showed excellent photocatalytic degradation (96.5±0.24% in 1 hour at 25 °C) of malachite green (MG) in aqueous solutions under ultraviolet light at optimum conditions; pH 10, MG initial concentration of 20 mg L-1, and ZnO dose of 1.5 g L-1. Also, ZnO showed very good reusability (92.9± 0.2% after five runs). The experimental data obeyed pseudo-first-order kinetics (R2 = 0.92). The photocatalysis process was dependent on the following species in the order: OH. > electron/positive hole pairs > O2.-. Moreover, photodegradation efficiency decreased in the presence of CO32-, HCO3-, and Cl-, but increased in the presence of NO3- and SO42- ions. Thus, the green synthesized ZnO NPs can be applied as an efficient photocatalyst for the removal of MG from aqueous media.

Hierarchical Sphere-Like ZnO–CuO Grown in a Controlled Boundary Layer for High-Performance H2S Sensing

Hierarchical Sphere-Like ZnO–CuO Grown in a Controlled Boundary Layer for High-Performance H2S Sensing

Sphere-like and flake-like ZnO immobilized on pineapple leaf fibers as easy-to-recover photocatalyst for the degradation of congo red

This work reports immobilization of ZnO photocatalyst on very fine pineapple leaf fiber (PALFs) by a by polyelectrolyte coating method, for the removal of colored pollutants from water stream, allowing for simple recovery after use. It also emphasizes on the effect of defect structure containing in ZnO of hierarchical sphere-like and flake-like morphologies on the color removal performance. The photocatalytic activity of ZnO/PALFs for degradation of congo red (CR) dye was examined under static (dark) and UV/visible irradiation conditions, and effective color removal (>95 %) was achieved, as the results of adsorption and photo-oxidation processes. Results from photoluminescence and X-ray photoelectron spectroscopy suggested that the sphere-like ZnO, bearing zinc vacancies (VZn), zinc interstitials (Zni), singly ionized oxygen vacancies (Vo+), and oxygen vacancies (Vo), has superior photocatalytic activity up to 3.6 times compared to that of flake-like ZnO. With the recyclability up to 3 cycles (>84 % color removal efficiencies), the ZnO immobilized on PALFs have shown a great promise as an easy-to-recover photocatalyst for the removal of colored pollutants in wastewater treatment processes.

Systematically controlled synthesis of shape-selective ZnO superstructures via sonochemical process

The controllable synthesis of shape-selective ZnO superstructures using a facile method is still great demand. Herein, ZnO nanostructures with different morphology were prepared via a simple sonochemical route with the help of ethylene glycol, such as sphere-like ZnO, twin-sphere-like ZnO, and bouquet-like ZnO. Control experiments were carried out to explore the growth mechanism of ZnO. The water content, ultrasound time, alkaline medium, and reaction pH were key factors for the morphology control of ZnO. Thereinto, the action of water content and ultrasound time could be regarded as the main factor. A formation mechanism of ZnO superstructures based on relocation, growth, and self-assembly of ZnO grains was proposed. Choosing the ammonia water as pH adjustment, the OH– ions were reacted with Zn2+ to form ZnO nuclei rapidly under the condition of pH = 8. Under the inducement of different water content and ultrasound time, the ZnO crystals were turned into irregular nanospheres, nanorods, or hexagonal prism. When the water content was 50%~70%, the ZnO units could be assembled into bouquet-like ZnO. Interestingly, ZnO superstructures with similar morphology could be obtained by the complementary of water content and ultrasound time, meaning that the morphology of ZnO prepared at high water content was the same as that prepared at long ultrasound time or vice versa.

Effect of size and shape on the excitonic stimulated emission process in ZnO microstructures

There has been some (partly controversial) discussion about the role of excitons in room-temperature laser emission of ZnO. Recently, we have demonstrated from temperature and excitation-density-dependent photoluminescence measurements on a ZnO film consisting of well crystallized micrometer-sized grains that the mechanism of optical gain at temperatures below ∼150 K is the exciton-exciton (ex-ex) scattering, whereas at temperatures from ∼150 K to room temperature, the gain results from the exciton-electron (ex-el) scattering without any contribution from electron-hole plasma lasing [R. Matsuzaki et al., Phys. Rev. B 96, 125306 (2017)]. However, the mechanism of optical feedback inside these ZnO microstructures is not fully understood. In this work, we investigate the emission properties of various ZnO microcrystals with different size and shape in the temperature region from 3 to 300 K using a nanosecond pulsed laser as an excitation source. We found that room temperature stimulated emission is observed only from the sphere-like ZnO particles with the size of a few micrometers in diameter. We also found the temperature-induced transition between ex-ex and ex-el scattering processes at a temperature of ∼150 K, similar to the case of the ZnO film consisting of micrometer-sized grains reported previously. The close similarity observed between the two different types of ZnO microstructures allows us to deduce that the temperature-dependent excitonic stimulated emission characteristics are common in micrometer-sized ZnO crystals with a low-loss feedback mechanism.

Controllable preparation of porous ZnO microspheres with a niosome soft template and their photocatalytic properties

Using Span80/ polyethyleneglycol 400 (PEG400)/H2O niosome as a soft template, Zn(NO3)2·6H2O as zinc source, urea as alkali source and cinnamate as directing agent, three dimensional (3D) sphere-like ZnO hierarchical nanostructures assembled with numerous nanospheres were fabricated by a simple, one-step hydrothermal route. In the process, cinnamate played a crucial role for the formation of ZnO hierarchical nanostructures, which was acted as morphology director, and demonstrate that the zinc carbonate hydroxide hydrate(ZCHH) precursor can be transformed utterly to ZnO porous microspheres after calcination. The effects of reactant and additive concentrations on the morphology and size of the nanospheres were studied and the possible formation mechanism of the ZHC nanostructures is discussed in this paper. Based on the statistical results from SEM images of the nanospheres, these hydrozincite nanospheres assemble into the sphere-like ZCHH respectively. Results indicate that ZnO retained the morphology of the ZCHH precursor following calcination at 400°C for 2h. The photocatalytic results indicated that the ZnO exhibited higher photocatalytic activity than that of the reported nanostructured ZnO, The great enhancement was mainly ascribed to their unique hierarchical nanostructures and high BET surface.

ZnO nanosheets assembled different hierarchical structures and their gas sensing properties

We fabricated successfully scroll-like, lung lobe-like, flower-like and sphere-like ZnO via the simple hydrothermal method and investigated their gas-sensing properties. The structures and morphologies of samples were investigated by X-ray diffraction, scanning electron microscopy and Brunauer–Emmett–Teller method. On the basis of those characterizations, it was found that all the nanostructures were self-assembled by ZnO nanosheets, and the sphere-like ZnO possess unique three-dimensional hierarchical structures with the largest specific surface area. Further gas-sensing measurements reveal that the sensor based on sphere-like ZnO exhibited the highest gas response, shortest response and recovery time, indicating that the sphere-like ZnO might be promising f promising for the development of a sensor device for the effective on-site detection of ethanol gas.

Preparation of doped ZnO nanopowders by refluxing method and applications in high voltage varistors

The doped ZnO nanopowders were successfully prepared via simple hydrolysis followed by refluxing route in alcohol medium. Several analytic techniques such as XRD, TEM and SEM were used to make characterizations of the as-synthesized samples. The influence of refluxing time on the morphology and average size of the products was investigated. Rod-like doped ZnO powders were easily prepared by refluxing for 5 h. With the elevation of the refluxing time to 20 h, nearly monodispersed sphere-like ZnO nanoparticles can be obtained and the diameter is about 30–50 nm. The results show that refluxing time plays an important role in the formation and oriented growth of ZnO nanocrystals. The powders were consolidated into dense varistors discs by compaction, sintering and evaluated for their electrical characteristics. The varistors can be produced possessing a nonlinear coefficient of ~56, a breakdown voltage of ~7.09 kV/cm.

Characterization, growth mechanism and gas sensing properties for ZnO microflowers with mesoporous nanosheets

Flower-like ZnO microstrucutures (ZMFs) self-assembled by nanosheets were fabricated by a simple template-free hydrothermal method, and the nanosheets were observed with a great many of mesopores. Without adding NaOH, sphere-like ZnO microstrucutures (ZMSs) which were covered by nanosheets were obtained. Subsequently, according to the characterization of SEM and TEM for ZMFs nanosheets, the possible formation mechanisms and simulation of ZMFs were discussed. The novel ZMFs presented numerous mesopores of size around 6 nm and high BET specific area (about 36.886 m2/g) which contributed to its high gas-sensing performance. In comparison with the ZMSs-based sensor, the ZMFs-based sensor displayed excellent gas-sensing performance to the ethanol gas with high sensitivity of nearly 35 at the concentration of 250 ppm.

Controlled Growth of ZnO Nanoparticles with Different Morphologies Using Sol-Gel Technique

A low temperature sol-gel approach was demonstrated to prepare ZnO nanoparticles with controlled morphologies. By changing the concentration of NH4OH, the ZnO nanoparticles evolves from sphere-like, star-like and sheet-like structures. No peak of additional phase was observed in the XRD patterns except the diffraction peaks of ZnO. The estimated crystallite size of ZnO nanoparticles decreases with the increase of NH4OH. It is also found that the morphology of nanoparticles affects the optical bandgap of ZnO. The optical bandgap of sphere-like,star-like, and sheet-like ZnO nanoparticles are 3.55 eV, 3.48 eV and 3.45 eV, respectively. The growth mechanism of ZnO nanoparticles was discussed.

Synthesis of porous spherical ZnO nanoparticles and measurement of their gas-sensing property

In present work, porous sphere-like and coralline-like ZnO nanoparticles (NPs) are synthesized by precipitation method at different calcination temperatures (400 and 450°C). The temperature of calcinations plays an important role in formation of NPs morphology. A formation mechanism of porous sphere-like ZnO NPs is proposed. The response of gas sensing for different concentrations of acetone (1–10,000ppm) at optimum temperature (310°C) is shown. Besides, the ZnO NPs (400°C) exhibits fast response and recovery time (average value is about 9s and 6s). These results demonstrate that the ZnO NPs (400°C) can be used as an ideal candidate for fabricating high response (130–100ppm) acetone sensor.

Nanoparticle morphology and film-forming behavior of polyacrylate/ZnO nanocomposite

Film-forming agents of polyacrylate/ZnO nanocomposite are formed by in situ emulsion polymerization of acrylate monomers in the presence of ZnO nanostructures with various morphologies including sphere-like, rod-like, sheet-like, needle-like and flower-like. Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were used to quantify the nanocomposites thus obtained. Nuclear magnetic resonance (NMR) was employed to investigate the intermolecular interactions in the polyacrylate/ZnO nanocomposites. The impact of ZnO nanostructures with various morphologies on the antibacterial behavior, water vapor permeability and mechanical properties is established. ZnO nanoparticles are well dispersed in polyacrylate matrix. Flower-like ZnO nanoparticles exhibit weak interactions with the polymer chains, while those containing flower-like or sphere-like ZnO show improved antibacterial effects against both aspergillus flavus and candida albicans. Water vapor permeability of polyacrylate/ZnO nanocomposites were increased by 122.17% with the addition of the flower-like ZnO nanoparticles. In comparison, sphere-like ZnO is favorable for improving the mechanical behavior.

Flower-like and hollow sphere-like ZnO assisted by microorganisms and their UV absorption and photo catalytic performance

Microorganisms were used to assist to synthesize two unique ZnO assembly structures via an easy and low cost two-step method in two experiments in this paper. The flower-like and hollow sphere-like ZnO were obtained by adding two different bacteria, respectively, through chemical deposition and self-assembly processes. The bacteria cells were removed easily at 550 °C, and it was revealed by TG/DSC. The unique structures obtained in two experiments were characterized by XRD, SEM and TEM and demonstrated the unique structures obtained were pure ZnO products. Furthermore, the mechanisms of the whole experiments were analyzed and it was indicated that the bacteria were served as template in chemistry deposition and self-assembly phase, and TEA coated on the bacteria promoted the ZnO particles to assemble around bacteria by an orient process. Finally, the UV–vis absorption spectrums of as-prepared samples assumed a red shift. Moreover, photo catalysis measurements exhibited that flower-like and hollow sphere-like ZnO have excellent ability to accelerate MB decolorize. It is verified bacteria are excellent templates for prepare unique ZnO structures to improve UV–vis absorbtion and photo catalytic performance.

Effect of 3D ZnO:Fe morphology on the photocatalytic activity under solar irradiation

Nanoparticles, microsphere, hedgehog sphere-like and flower-like ZnO:Fe photocatalysts were prepared by the hydrothermal method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet/visible absorption spectra (UV–Vis). The results show that the ZnO:Fe photocatalysts with different 3D morphologies are a hexagonal wurtzite structure with space group of p63mc. The pH value of the precursor has a great influence on various morphologies of ZnO:Fe photocatalysts. The flower-like and hedgehog sphere-like ZnO:Fe photocatalysts exhibit the high solar photocatalytic behavior on methylene blue (MB). The ZnO:Fe order of photocatalytic activity is as follows: flower > hedgehog sphere > microsphere > nanoparticle. The flower-like ZnO:Fe is optimal, which exhibits the highest degradation rate of 98% for light time of 5 h.

Effects of various physicochemical characteristics on the toxicities of ZnO and TiO 2 nanoparticles toward human lung epithelial cells

Although novel nanomaterials are being produced and applied in our daily lives at a rapid pace, related health and environmental toxicity assessments are lagging behind. Recent reports have concluded that the physicochemical properties of nanoparticles (NPs) have a crucial influence on their toxicities and should be evaluated during risk assessments. Nevertheless, several controversies exist regarding the biological effects of NP size and surface area. In addition, relatively few reports describe the extents to which the physicochemical properties of NPs influence their toxicity. In this study, we used six self-synthesized and two commercial ZnO and TiO 2 nanomaterials to evaluate the effects of the major physicochemical properties of NPs (size, shape, surface area, phase, and composition) on human lung epithelium cells (A549). We characterized these NPs using transmission electron microscopy, X-ray diffraction, the Brunauer–Emmett–Teller method, and dynamic laser scattering. From methyl thiazolyl tetrazolium (MTT) and Interleukin 8 (IL-8) assays of both rod- and sphere-like ZnO NPs, we found that smaller NPs had greater toxicity than larger ones—a finding that differs from those of previous studies. Furthermore, at a fixed NP size and surface area, we found that the nanorod ZnO particles were more toxic than the corresponding spherical ones, suggesting that both the size and shape of ZnO NPs influence their cytotoxicity. In terms of the effect of the surface area, we found that the contact area between a single NP and a single cell was more important than the total specific surface area of the NP. All of the TiO 2 NP samples exhibited cytotoxicities lower than those of the ZnO NP samples; among the TiO 2 NPs, the cytotoxicity increased in the following order: amorphous > anatase > anatase/rutile; thus, the phase of the NPs can also play an important role under size-, surface area-, and shape-controlled conditions.

Ethylene Glycol Assisted Hydrothermal Synthesis of Flower-Like and Sphere-Like ZnO

ZnO microsturctures with flower-like and sphere-like morphologies have been successfully synthesized in ethylene glycol (EG) -water solution at 160 through a hydrothermal method. The volume ratio of EG to H2O plays an important role on the morphology control of ZnO. CH3COONH4 and NaOH were used as hydroxide source as well as complexing agents. The ZnO samples were characterized by XRD, FTIR and SEM. The optical properties of the final products were investigated by UV-vis absorption spectrometer and photoluminescence. The formation mechanism was also discussed.

Soft Solution Synthesis of ZnO Films with Developed Superstructures

A novel and simple two-step solution approach to prepare ZnO thin film consisted of 3D flower-like superstructure was demonstrated. The uniform, nano-dimensional scale and sphere-like ZnO crystals were first prepared on the borosilicate glass substrate in mild solution at 95 degrees C for 3 h, then introduced into 0.02 mol L(-1) hexamethylenetetramine (HMT, C6H12N4) aqueous solution and heated at the same temperature for 3 d. The obtained ZnO thin films were characterized by XRD, SEM and photoluminescence. The results indicated that the thin film with 3D flower-like superstructure possessed high crystallinity, high surface-volume ratio microstructure and excellent photoluminescence property. It is a potential way to prepare nano-structured materials by the mentioned simple and novel two-step solution synthesis process.

Synthesis and characterization of porous sphere-like ZnO with dendrite nanocrystals from layered inorganic–organic nanocomposite on titanium substrate

The porous sphere-like ZnO inorganic–organic nanocomposites have been prepared by self-assembly at the present of CTAB (cetyltrimethylammonium bromide, CH 3(CH 2) 15N +(CH 3) 3Br −) surfactant on the titanium substrate. After high temperature oxidation, all the organic were removed and the porous sphere-like ZnO dendrite nanocrystals were obtained. The resultant products have been characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The XRD pattern shows that the as-synthesized porous sphere-like is multilayered inorganic–organic nanocomposite, and the sample calcined at 500 °C for 2 h has a hexagonal wurtzite crystal structure. FE-SEM and TEM images demonstrate that porous sphere-like ZnO dendrite nanocrystals are formed. A possible formation mechanism is preliminary proposed for the formation of the novel nanostructure.