Flower-like ZnO Nanorods Research Articles

Synthesis of Template-free Flower-like ZnO Nanorods using a Simple Chemical Bath Technique

Flower-like ZnO nanorods were successfully synthesised using a template-free, low-temperature chemical bath deposition method. The effects of growth time on the structural, morphological, and vibrational properties of flower-like zinc oxide were investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) indicated that the crystallite size and density of flower-like ZnO nanorods increased with increasing growth time. Raman spectroscopy confirmed the existence of specific Raman modes that correspond to the wurtzite structure of ZnO. In addition, Raman measurements revealed that increased growth time increases the Raman modes intensity of the flower-like ZnO nanorods. Moreover, the measurements of the Au/ZnO nanorods/FTO Schottky diode showed that all devices functioned as Schottky diodes and rectifying; however, their ideality factor was greater than 1. In addition to the ideality factor, the Schottky barrier height was calculated and slightly increased with growth time. The values of Schottky barrier height obtained were 0.502 eV, 0.523 eV, 0.516 eV and 0.529 eV for samples grown at 1, 2, 3 and 4 h, respectively.

Au/CdS Core-Shell Sensitized Actinomorphic Flower-Like ZnO Nanorods for Enhanced Photocatalytic Water Splitting Performance.

Herein, a novel actinomorphic flower-like ZnO/Au/CdS nanorods ternary composite photocatalyst is prepared to extend the light-responsive range, reduce the photogenerated charge carriers recombination, and ultimately improve the water splitting performance. Flower-like ZnO nanorods are synthesized by a chemical bath method and the CdS nanoparticles are sensitized by successive ionic layer adsorption and reaction method. Then the Au nanoparticles as co-catalysts are introduced by the photodeposition method to modify the interface of ZnO/CdS for reducing the photogenerated electron recombination rate and further improving the performance of water splitting. Detailed characterizations and measurements are employed to analyse the crystallinity, morphology, composition, and optical properties of the flower-like ZnO/Au/CdS nanorods samples. As a result, the flower-like ZnO/Au/CdS nanorod samples present significantly enhanced water splitting performance with a high gas evolution rate of 502.2 μmol/g/h, which is about 22.5 and 1.5 times higher than that of the pure ZnO sample and ZnO/CdS sample. The results demonstrate that the flower-like ZnO/Au/CdS nanorods ternary composite materials have great application potential in photocatalytic water splitting for the hydrogen evolution field.

Hydrothermal synthesis and optical properties of Fe doped ZnO nanorods

ZnO nanopowders with hexagonal wurtzite structure were synthesized by hydrothermal method with different concentrations of Fe. X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, X-ray photoelectron spectroscopy The morphology, structure and optical properties of the samples were tested and characterized by XPS and (photoluminescence) PL spectra.The results show that the crystal structure of wurtzite ZnO does not change with the increase of Fe doping concentration, and Fe ions do not change into ZnO lattice instead of Zn ions. At the same time, the uniformity of flower-like ZnO nanorods deteriorates, Fe doping A small number of single nanorods with smaller sizes appeared in the hetero-ZnO nanorods.The PL spectrum shows that as the Fe doping concentration increases, the UV luminescence peak of the sample does not change significantly, and the intensity of the luminescence peak decreases first and then increases, indicating that the defect of the sample first decreases and then increases.When the concentration of Fe doping is 1.5%, the prepared ZnO flower-like nanorods have a relatively low visible luminescence peak, which has a small defect.

Graphene Oxide Concentration Effect on the Optoelectronic Properties of ZnO/GO Nanocomposites.

In this work, the effects of graphene oxide (GO) concentrations (1.5 wt.%, 2.5 wt.%, and 5 wt.%) on the structural, morphological, optical, and luminescence properties of zinc oxide nanorods (ZnO NRs)/GO nanocomposites, synthesized by a facile hydrothermal process, were investigated. X-ray diffraction (XRD) patterns of NRs revealed the hexagonal wurtzite structure for all composites with an average coherence length of about 40–60 nm. A scanning electron microscopy (SEM) study confirmed the presence of transparent and wrinkled, dense GO nanosheets among flower-like ZnO nanorods, depending on the GO amounts used in preparation. Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible (UV–Vis) absorption spectroscopy, and photoluminescence (PL) measurements revealed the impact of GO concentration on the optical and luminescence properties of ZnO NRs/GO nanocomposites. The energy band gap of the ZnO nanorods was independent of GO concentration. Photoluminescence spectra of nanocomposites showed a significant decrease in the intensities in the visible light range and red shifted suggesting a charge transfer process. The nanocomposites’ chromaticity coordinates for CIE 1931 color space were estimated to be (0.33, 0.34), close to pure white ones. The obtained results highlight the possibility of using these nanocomposites to achieve good performance and suitability for optoelectronic applications.

Flower-Like ZnO Nanorods Synthesized by Microwave-Assisted One-Pot Method for Detecting Reducing Gases: Structural Properties and Sensing Reversibility.

In this work, flower-like ZnO nanorods (NRs) were successfully prepared using microwave-assisted techniques at a low temperature. The synthesized NRs exhibited a smooth surface and good crystal structure phase of ZnO. The sharp peak of the XRD and Raman spectrum confirmed the high crystallinity of these ZnO NRs with a pure wurtzite structure. The nanorods were ~2 μm in length and ~150 nm in diameter, respectively. The electron diffraction pattern confirmed that the single crystal ZnO nanorods aligned along the [001] plane. The NRs were applied to fabricate a gas sensor for reducing gases such as CH4, CO, and H2. The sensor showed a good performance and sensitivity toward the target gases. However, its response toward CH4 and CO was higher compared to H2 gas. Although the operating temperature was varied from room temperature (RT) up to 350°C, the sensor did not show a response toward any of the target gases in the range of RT-150°C, but dramatic enhancement of the sensor response was observed at 200°C, and up to higher temperatures. This behavior was ascribed to the activity of the smooth surface and the reactivity of surface oxygen species with the targeted gases. The sensor response was measured at various gas concentrations, where the calibration curve was shown. The gas sensing mechanism was described in terms of the reaction of the gases with the transformed oxygen species on the surface of the oxides.

Synthesis of ZnO Hierarchical Structures and Their Gas Sensing Properties.

Firecracker-like ZnO hierarchical structures (ZnO HS1) were synthesized by combining electrospinning with hydrothermal methods. Flower-like ZnO hierarchical structures (ZnO HS2) were prepared by a hydrothermal method using ultrasound-treated ZnO nanofibers (ZnO NFs) as raw material which has rarely been reported in previous papers. Scanning electron microscope (SEM) and transmission electron microscope’s (TEM) images clearly indicated the existence of nanoparticles on the ZnO HS2 material. Both gas sensors exhibited high selectivity toward H2S gas over various other gases at 180 °C. The ZnO HS2 gas sensor exhibited higher H2S sensitivity response (50 ppm H2S, 42.298) at 180 °C than ZnO NFs (50 ppm H2S, 9.223) and ZnO HS1 (50 ppm H2S, 17.506) gas sensors. Besides, the ZnO HS2 sensor showed a shorter response time (14 s) compared with the ZnO NFs (25 s) and ZnO HS1 (19 s) gas sensors. The formation diagram of ZnO hierarchical structures and the gas sensing mechanism were evaluated. Apart from the synergistic effect of nanoparticles and nanoflowers, more point–point contacts between flower-like ZnO nanorods were advantageous for the excellent H2S sensing properties of ZnO HS2 material.

Facile fabrication of porous hierarchical SnO2 via a self-degraded template and their remarkable photocatalytic performance

In this paper, a novel hierarchical SnO2 assembled of nanotubes was successfully prepared using flower-like ZnO nanorods as self-etching template. Alkaline reaction environment led to the removal of the template without post-treatment. The as-prepared samples were characterized by X-ray powder diffraction (XRD), fourier transform infrared (FTIR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscope (HRTEM), photoluminescence (PL), Brunauer–Emmett–Teller (BET) and Zeta potential analysis. The as-prepared hierarchical SnO2 nanostructure showed uniform flower-like morphology, small grain size, and good crystallinity even without annealing. The product also had a very rough surface with a high specific area about 80 m2 g−1. The porous hierarchical SnO2 demonstrated high degradation rate (∼94%) for methylene blue (MB) in 30 min under UV light. Furthermore, the photocatalytic performance was sustained over 3 cycles, indicating it may have potential applications in wastewater treatment.

Synthesis and enhanced gas sensing properties of flower-like ZnO/α-Fe2O3 core-shell nanorods

This paper reports a facile two-step synthesis route for the preparation of flower-like ZnO/α-Fe2O3 nanorods (NRs). Flower-like ZnO NRs with the average diameter about 810nm and length about 4.5µm were firstly synthesized via a chemical solution method, and then ZnO NRs was coated with a continuous α-Fe2O3 layer to form ZnO/α-Fe2O3 core-shell structure through an ionic-layer adsorption and reaction method. The gas-sensing results show that the ZnO/α-Fe2O3 NRs exhibit excellent sensitivity, selectivity, and response-recovery capacity to ethanol vapor at a low optimum temperature of 240°C. In particular, compared with pure ZnO NRs and α-Fe2O3 nanoparticles (NPs), the ZnO/α-Fe2O3 NRs show an obvious improvement in gas sensing properties. The substantial improvement of sensing properties may be attributed to the unique microstructure and heterojunction formed between ZnO and α-Fe2O3.

Synthesis and enhanced gas sensing properties of flower-like ZnO nanorods decorated with discrete CuO nanoparticles

Flower-like CuO/ZnO hierarchical structures were prepared via a flexible two-step synthesis method, in which nanorods-assembled flower-like ZnO microstructures with the diameter about 430–1680nm and the length about 3.6–8.8μm were prepared in advance through a chemical solution method, and then a frost-like layer of CuO nanoparticles (NPs) decorated on the surface of ZnO nanorods (NRs) via an ionic-layer adsorption and reaction method. Compared with pure ZnO NRs, the flower-like CuO-decorated ZnO NRs show an obvious improvement in gas sensing performance. The gas sensing mechanism of the CuO-decorated ZnO NRs was discussed in relation to the catalytic effect of CuO and the introduction of the p-n junction between CuO and ZnO.

Synthesis and characterization of ZnO flower-like structures

The flower-like ZnO nanorods have been successfully synthesized by a surfactant-assisted hydrothermal method. The nanostructures formed by ZnO nanorods were synthesized and deposited without seeding in glass flask by a hexamethylenetetramine (HMTA)-assisted hydrothermal method at low temperature with NaOH as surfactant and catalyst. The synthesized ZnO flowers comprise of several spike structures that have hexagonal cross section and taper toward the end. The structures are investigated using X-ray diffraction, scanning electron microscope and transmission microscope. The optical properties are studied with UV-VIS, FTIR, and Raman spectroscopy. The process of synthesis is simple and highly reproducible. The synthesized flower-like structures are suitable for use as sensors applications.

Flower-like ZnO nanorod arrays grown on HF-etched Si (111): constraining relation between ZnO seed layer and Si (111)

We demonstrate the formation of self-assembled homogenous flower-like ZnO nanorods over a ZnO seed layer deposited on a HF-etched Si (111) substrate. The typical flower-like morphology of ZnO nanorod arrays is ascribed to the formation of the island-like seed layer which is deposited by the drop method followed by annealing at 300 °C. The island-like ZnO seed layer consists of larger ZnO grains, and is built by constraining of the Si (111) surface due to pattern matching. Pattern matching of Si with ZnO determines the shape and size of the seed layer and this controls the final morphology of ZnO nanorods to be either flower like or vertically aligned. The high quality of the island-like ZnO seed layer enhances the diameter and length of ZnO nanorods. Besides, while the amorphous layer formed during the annealing process would influence the strained ZnO grain, that subsequent amorphous layer will not block the constraining between the ZnO grain and the substrate.

Three-photon-induced blue emission with narrow bandwidth from hot flower-like ZnO nanorods.

ZnO nanorods (NRs) self-organized into flowers were synthesized at different temperatures ranging from 100°C to 180°C by using the hydrothermal method. The existence of Zn interstitials (Zn(i)) was confirmed by X-ray photoelectron spectroscopy and a larger amount of Zn(i) was found in the ZnO NRs prepared at higher temperatures. A redshift of the emission peak of more than 15 nm was observed for the ZnO NRs under single photon excitation. The nonlinear optical properties of the flower-like ZnO NRs were characterized by using focused femtosecond laser light and strong three-photon-induced luminescence was observed at an excitation wavelength of ~750 nm. More interestingly, a large redshift of the emission peak was observed with increasing excitation intensity, resulting in efficient blue emission with a narrow bandwidth of ~30 nm. It was confirmed that the large redshift originates from the heating of the ZnO NRs to a temperature of more than 800°C and the closely packed ZnO NRs in the flowers play a crucial role in heat accumulation. The stable and efficient three-photon-induced blue emission from such ZnO NRs may find potential applications in the fields of optical display, high-temperature sensors and light therapy of tumors.

Selective, Spontaneous One-Way Oil-Transport Fabrics and Their Novel Use for Gauging Liquid Surface Tension

Thin porous materials that can spontaneously transport oil fluids just in a single direction have great potential for making energy-saving functional membranes. However, there is little data for the preparation and functionalities of this smart material. Here, we report a novel method to prepare one-way oil-transport fabrics and their application in detecting liquid surface tension. This functional fabric was prepared by a two-step coating process to apply flowerlike ZnO nanorods, fluorinated decyl polyhedral oligomeric silsesquioxanes, and hydrolyzed fluorinated alkylsilane on a fabric substrate. Upon one-sided UV irradiation, the coated fabric shows a one-way transport feature that allows oil fluid transport automatically from the unirradiated side to the UV-irradiated surface, but it stops fluid transport in the opposite direction. The fabric still maintains high superhydrophobicity after UV treatment. The one-way fluid transport takes place only for the oil fluids with a specific surface tension value, and the fluid selectivity is dependent on the UV treatment time. Changing the UV irradiation time from 6 to 30 h broadened the one-way transport for fluids with surface tension from around 22.3 mN/m to a range of 22.3-56.7 mN/m. We further proved that this selective one-way oil transport can be used to estimate the surface tension of a liquid simply by observing its transport feature on a series of fabrics with different one-way oil-transport selectivities. To our knowledge, this is the first example to use one-way fluid-transport materials for testing the liquid surface tension. It may open up further theoretical studies and the development of novel fluid sensors.

FACILE HYDROTHERMAL SYNTHESIS OF FLOWER-LIKE ZNONANORODS WITHOUT CATALYSTS

A very simple hydrothermal method (one step) was used at low temperature to synthesis flower-like ZnOnanorods on glass substrate without any template, catalyst or buffer layer before the reaction. Flower-like ZnOnanorods were synthesized by hydrothermally heating 0.1 M precursor solution of hexahedral zinc nitrate Zn(NO3)2.6H2O, hexamethylenetetramine (HMT) and NaOH were the starting materials for the chemical reaction under stirring. The field emission scanning electron microscopy (FE-SEM) images showed that the flower-like structures were formed in 3.5 h hydrothermally-heated for sample, whereas the experimental pattern of the films by X-ray diffraction show that diffraction peaks can be assigned to the wurtzite hexagonal-shaped ZnO as shown in the (FE-SEM) images, also the morphology of the films studied by atomic force microscope (AFM) shows that the films have high roughness. The energy gap was estimated and optical behavior was investigated.

A highly sensitive and recyclable SERS substrate based on Ag-nanoparticle-decorated ZnO nanoflowers in ordered arrays.

Using a patterned sapphire substrate with a hemisphere array, flower-like ZnO nanorods grouped in a highly ordered array were fabricated on the wafer scale by routine solution growth. After decorating with high-density Ag nanoparticles (NPs), the ZnO nanoflower arrays were used as the substrates for surface enhanced Raman scattering (SERS). Using Rhodamine 6G as the probe molecules with a concentration down to 10(-10) M, the SERS substrates present an as high as 10(10) Raman enhancement with good reproducibility. The influence of Ag NP decoration on the SERS activity was explored and the sub-10 nm nanogaps between the adjacent Ag NPs were proved to be the primary electromagnetic "hot spots" responsible for the significant Raman enhancement. The Ag-NP-decorated ZnO nanoflower arrays were demonstrated to possess a self-cleaning function enabled by UV irradiation via photocatalytic degradation of the analyte molecules. In addition, the SERS substrate exhibited an extremely long service lifetime, possibly due to its superhydrophobicity and storage in the dark and a dry environment.

Thermally decomposition of high quality flower-like ZnO nanorods from zinc acetate dihydrate

In the present work, high purity flower-like ZnO nano-rods have been synthesized by thermal decomposition method maintained at 300°C in air without using any organic solvent additive surfactant or catalyst. The phase and structural analysis were characterized by X-ray diffraction (XRD) which confirmed the high crystal quality of ZnO with hexagonal (Wurtzite phase) crystal structure. The morphology was carried out by scanning electron microscopy (SEM) which indicates that the formation of well-formed ZnO nanorods as a flower-like ZnO structure. The optical bandgap of synthesized ZnO nanorods found as 3.37eV for all samples by using UV–vis absorption spectra and further verified by diffuse reflectance spectroscopy analysis. The room-temperature photoluminescence (PL) spectrum of all samples shows strong UV emission peak at ~384nm and a weak broad green–yellow due to the defects in the samples. The Raman spectroscopy was performed for the studies of vibrational bands and the quality of the crystalline structure of flower-like ZnO nanorods.

The mesoscopic structure of flower-like ZnO nanorods for acetone detection

The flower-like zinc oxide mesoscopic structure was successfully synthesized by a novel solution route with the assistance of polyvinyl pyrrolidone (PVP). These ZnO nanoflowers were composed of uniform and long nanorods. PVP and ammonia water played a key role in nanorods growth and the possible growth mechanism was tentatively proposed based on the experiment results. Furthermore, the gas sensor based on this mesoscopic structure with large specific surface area has an optimum operating temperature of 420°C and exhibits high sensitivity, quick response and good selectivity for acetone. The sensitivity is about 1170 and the response time is around 7s for 1000ppm acetone. The results suggest that the mesoscopic structure of flower-like ZnO nanorods is a good candidate for fabricating effective acetone sensor.

A Possible Growth Mechanism for ZnO-TiO2 Composite Nanostructured Films Prepared by Electrodeposition

ZnO-TiO2 composite nanostructured films were successfully prepared on fluorine doped tin oxide conducting glasses, from aqueous solutions, using a two-step electrochemical deposition process. The architecture of the ZnO nanorods arrays was strongly modified by the presence of TiO2 nanoparticles either on the seed layer formation or during the growth process, although the solution stirring parameter also contributed to the film arrangement. ZnO nanorods with well-defined hexagonal facets (002) were grown almost vertically over the entire substrate if no solution stirring was used during growth process. The formation of flower-like ZnO nanorods, consisting of many aggregative nanorods, requires the presence of TiO2 nanoparticles on the seed layer formation or during the growth process. In this case, the clusters of one-dimensional ZnO nanorods forming flowers were made up of numerous hexagonal straight nanorods and small clusters/agglomerates of TiO2 particles. The results showed that the diameter and length of the flower-like ZnO nanorods increased with solution stirring and, on the other hand, decreased with increase of TiO2 nanoparticles content in the bath. A possible crystal growth mechanism of ZnO and ZnO-TiO2 nanocomposites is suggested.

Hydrothermal Synthesis of Various Hierarchical ZnO Nanostructures and Their Methane Sensing Properties

Hierarchical flower-like ZnO nanorods, net-like ZnO nanofibers and ZnO nanobulks have been successfully synthesized via a surfactant assisted hydrothemal method. The synthesized products were characterized by X-ray powder diffraction and field emission scanning electron microscopy, respectively. A possible growth mechanism of the various hierarchical ZnO nanostructures is discussed in detail. Gas sensors based on the as-prepared ZnO nanostructures were fabricated by screen-printing on a flat ceramic substrate. Furthermore, their gas sensing characteristics towards methane were systematically investigated. Methane is an important characteristic hydrocarbon contaminant found dissolved in power transformer oil as a result of faults. We find that the hierarchical flower-like ZnO nanorods and net-like ZnO nanofibers samples show higher gas response and lower operating temperature with rapid response-recovery time compared to those of sensors based on ZnO nanobulks. These results present a feasible way of exploring high performance sensing materials for on-site detection of characteristic fault gases dissolved in transformer oil.

Hydrothermal Synthesis of Various Hierarchical ZnO Nanostructures and Their Methane Sensing Properties

Hierarchical flower-like ZnO nanorods, net-like ZnO nanofibers and ZnO nanobulks have been successfully synthesized via a surfactant assisted hydrothemal method. The synthesized products were characterized by X-ray powder diffraction and field emission scanning electron microscopy, respectively. A possible growth mechanism of the various hierarchical ZnO nanostructures is discussed in detail. Gas sensors based on the as-prepared ZnO nanostructures were fabricated by screen-printing on a flat ceramic substrate. Furthermore, their gas sensing characteristics towards methane were systematically investigated. Methane is an important characteristic hydrocarbon contaminant found dissolved in power transformer oil as a result of faults. We find that the hierarchical flower-like ZnO nanorods and net-like ZnO nanofibers samples show higher gas response and lower operating temperature with rapid response-recovery time compared to those of sensors based on ZnO nanobulks. These results present a feasible way of exploring high performance sensing materials for on-site detection of characteristic fault gases dissolved in transformer oil.