Flower-like ZnO Nanostructures Research Articles

One-step solution synthesis and formation mechanism of flower-like ZnO and its structural and optical characterization

The regular hierarchical flower-like ZnO nanostructures assembled by nanosheets were successfully synthesized by one-step solution route with citrate assistance at room temperature. It was demonstrated that the concentration of citrate and the molar ratio of Zn2+/OH− had strong effect on the formation of nanosheets and self-assembly flower-like nanostructures. A reasonable formation mechanism of the flower-like nanostructures was proposed. According to UV–vis spectrum, the flower-like ZnO nanostructures exhibited strong light absorption, and the value of band gap of the obtained ZnO was estimated to be 3.26eV. Moreover, the room-temperature photoluminescence (PL) spectrum of the sample presented only a near-band edge emission at 382nm.

A facile salicylic acid assisted hydrothermal synthesis of different flower-like ZnO hierarchical architectures with optical and concentration-dependent photocatalytic properties

Different flower-like ZnO hierarchical architectures with wurtzite structure have been prepared by a facile salicylic acid (SA) assisted hydrothermal method, especially four flower-like ZnO nanostructures can be obtained simultaneously by using 18.00mmol of SA. The petals of the flower-like ZnO architectures are mainly assembled by many of single nanorods, a mixture of single nanorods and bundle (cluster) of nanorods, or bundle of nanorods respectively. The nanorod exhibits the taper-like, hexagonal prism-like, tower-like or bamboo shoot-shaped body and the pyramid-like or pencil-like tip. Photoluminescence (PL) study shows two tunable wavelengths (542nm and 565nm). All the samples exhibit the similar Raman spectra. With increasing the amount of SA, the peak at 441cm−1 increases. The photodegradation rates of MB are more effective than these of MO, and the sample from 22.50mmol of SA decomposes 55% of MB within 140min. The activity of photocatalysts is significantly affected by the concentration of SA. With the increase of SA, the number of nanorods of the flower-like ZnO nanostructures increases, and leads to the improvement of photocurrent response and photocatalytic performance.

Facile synthesis of triangular silver nanoplate-coated flower-like ZnO nanostructures

Triangular silver nanoplate-coated flower-like ZnO nanostructures were successfully fabricated via a facile hydrothermal method combined with a dual reduction method. The morphology, composition, and structural and optical properties of the as-synthesized materials were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), UV–vis absorption spectra, X-ray diffraction (XRD), and photoluminescence (PL) spectrum. Results show that the morphology of ZnO and Ag were flower-like and triangular nanoplate, respectively. Triangular silver nanoplates exhibit unique surface plasmon resonance (SPR) absorption spectra, and the PL intensity of flower-like ZnO decreased by coating triangular silver nanoplates. In addition, the growth process and possible mechanism of flower-like ZnO and triangular silver nanoplates are discussed in certain detail.

Solution self-assembly of flower-like ZnO nanostructures with nanosheets and their optical properties

A uniform flower-like ZnO materials assembled by nanosheets have been synthesised on a large scale by a facile, cost efficient and room temperature solution route without the assistance of any substrate, template or seed layers. X-ray diffraction and field emission scanning electron microscopy were employed to characterise the phase composition and morphology of the samples, and ultraviolet–visible (UV-vis) diffuse reflectance spectrum and photoluminescence (PL) spectrum were used to analyse the optical properties of the samples. The flower-like ZnO materials with an average diameter of ∼2 μm are composed of interacted nanosheets with an average thickness of ∼5 nm. A reasonable growth mechanism that the formation of this kind of flower-like ZnO structures experienced a two-stage nucleation growth process was discussed. Based on the UV-vis diffuse reflectance spectrum, the band gap of hierarchical flower-like ZnO materials was calculated to be 3·27 eV. The PL spectrum suggests that flower-like ZnO materials only emit UV light and possess good optical properties.

Synthesis of Mg-doped hierarchical ZnO nanostructures via hydrothermal method and their optical properties

Hierarchical flower-like ZnO nanostructures and Mg-doped ZnO flower-like hierarchical nanostructures composed of porous nanosheets were synthesized via a one-step hydrothermal method. In this method, Zn(NO3)2·6H2O was used as a precursor and Mg(NO3)2·6H2O was the dopant. FESEM, EDS, XRD, UV–vis absorption spectra and PL spectra were used to characterize the samples. It demonstrates that small portions of Mg are successfully incorporated into the lattice of the ZnO nanostructures. The incorporation of Mg into ZnO is supported by broadening and higher Bragg angle shift in XRD pattern and EDS analysis. Cell Parameters of hierarchical flower-like Mg-doped ZnO nanostructures are obtained from Rietveld analysis. The decrease of c-axis indicates that substitution by Mg2+ is the dominant doping form in the hierarchical ZnO nanostructures. PL spectra show that the effective Mg doping suppresses the near band gap emission and the green emission. The band edge emission shifts to the blue with increasing amount of Mg doping, reflecting the change in the excitons energy seen in the absorption spectra. The defect band is believed to be due to deep traps and becomes dominant at high levels of doping. All the results show that the molar ratio of Mg and Zn determines the structure, surface morphology and optical properties of the samples significantly.

CTAB-assisted synthesis of 3D Sn doped ZnO nanostructures with enhanced acetone sensing performance

The flowerlike Sn doped ZnO nanostructures were synthesized by a cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal process at low temperature (150°C). The morphology and structure of sample were characterized by XRD, EDS, XPS, SEM and TEM analysis. The results indicate that the sample is well crystallized wurtzite hexagonal phase of ZnO, and preferentially grows up along [0001] direction. The possible formation mechanism of flowerlike ZnO nanostructures is proposed. Moreover, the sensor based on flowerlike ZnO nanostructures exhibits enhanced sensing performances to acetone at 300°C. The response is up to 600 when the sensor is exposed to 100ppm acetone. The response and recovery times are about 24 and 8s, respectively. These results demonstrate that the Sn doped ZnO nanoflowers can be used as the sensing materials for fabricating high performance acetone sensor.

Synthesis of three-dimensional flower-like hierarchical ZnO nanostructure and its enhanced acetone gas sensing properties

A three-dimensional (3D) flower-like hierarchical ZnO nanostructure was successfully synthesized via a facile and efficient hydrothermal method. The sample was characterized by XRD, FESEM, Raman, UV–vis DRS and Photoluminescence (PL) techniques. The XRD pattern revealed that the sample was well-crystallized in a hexagonal wurtzite structure. FESEM images showed that the as-prepared ZnO exhibited a nanosheet-assembled hierarchical flower-like ZnO nanostructure, which was self-assembled by thin and uniform nanosheets with a thickness of approximately 30 nm. Raman spectra exhibited that the sample kept the crystal structure of the bulk ZnO and possessed more surface defects. UV–vis spectra showed that a significant blue-shift in the absorption edge for the as-prepared ZnO as compared to the commercial ZnO. PL spectra indicated that the concentration of surface oxygen vacancies in the as-prepared ZnO was much higher than that of the commercial ZnO. Furthermore, the nanosheet-assembled flower-like ZnO nanostructure exhibited excellent gas sensing properties towards acetone, indicating that the as-prepared ZnO architecture is a promising material for gas sensors.

Tartaric acid assisted hydrothermal synthesis of different flower-like ZnO hierarchical architectures with tunable optical and oxygen vacancy-induced photocatalytic properties

Different flower-like ZnO hierarchical architectures were prepared by tartaric acid assisted hydrothermal synthesis, especially four flower-like ZnO nanostructures were obtained simultaneously under the same reaction condition. The cauliflower-like ZnO is assembled by spherical shaped nanoparticles, and the chrysanthemum-like and other flower-like ZnO nanostructures are assembled by hexagonal rods/prisms with from planar to semi-pyramid, and to pyramid tips. TA acts as a capping agent and structure-directing agent during the synthesis. All ZnO possess the hexagonal wurtzite structure. The PL spectra can be tuned by changing TA concentration. XRD, PL and Raman spectra confirmed that oxygen vacancies mainly come from the ZnO surface. The flower-like samples of 1:4.5 and 1:3 with the largest aspect ratios have highest photocatalytic performance. They decompose 85% MB within 60min. Combining PL Gaussian fitting with K, the higher content of oxygen vacancy is, the higher photocatalytic activity is. The enhanced photocatalytic performance is mainly induced by oxygen vacancy of ZnO. The possible formation mechanism, growth and change process of flower-like ZnO were proposed.

Synthesis of flower-like ZnO nanostructures by sonochemical route and their photocatalytic activity

In this study, the flower-like ZnO nanostructures have been fabricated using zinc chloride and potassium hydroxide as precursors by sonochemical technique. The as-prepared ZnO nanostructures were characterized by SEM, XRD, Fourier Transform Infrared Spectroscopy (FTIR), Raman spectra and UV–vis spectroscopy. The results indicated that the synthesized zinc oxide posses a flower shape with diameters in the range of 4–6μm. Meanwhile, every single flower is composed of needle-like crystals of 200–300nm in diameter irradiated from the center. The morphologies of the obtained product at different sonochemical time were experimentally studied. The formation mechanism is discussed in detail. Additionally, photocatalytic activity of the prepared ZnO sample was evaluated by the degradation of methylene blue under UV irradiation.

Enhancement of NH3 sensing performance in flower-like ZnO nanostructures and their growth mechanism

ZnO nanostructures hold substantial promise for gas-sensing applications owing to their outstanding ethanol sensing performance, yet their sensing performance toward NH3 has rarely been reported. Here, we report on a successful preparation of sunflower-like ZnO nanostructures and ZnO nanoparticle via a facile hydrothermal method, and demonstrate that the ZnO nanoflowers have high gas-sensing performances toward NH3 under a low concentration of 10–50ppm. Further structural characterization reveals that the sunflower-like nanostructure comprises six triangles-like and one sphere-like nanostructures, and the triangle-like nanostructure is single crystalline with {001} crystal face. As a consequence of their unique morphology, the nanoflowers show much improved NH3 sensing performances than the nanoparticles with a high sensitivity of 49.5.

A highly efficient urea detection using flower-like zinc oxide nanostructures.

A novel matrix based on flower-like zinc oxide nanostructures (ZnONF) has been fabricated using hydrothermal method and exploited successfully for the development of urea biosensor. Urease (Urs) is physically immobilized onto the ZnO nanostructure matrix synthesized over platinized silicon substrate. The surface morphology and crystallographic structure of the as-grown ZnONF have been characterized using a scanning electron microscope (SEM) and X-ray diffraction (XRD) techniques. The fabricated amperometric biosensor (Urs/ZnONF/Pt/Ti/Si) exhibits a linear sensing response towards urea over the concentration range 1.65 mM to 16.50mM with an enhanced sensitivity (~132 μA/mM/cm(2)) and a fast response time of 4s. The relatively low value of Michaelis-Menten constant (Km) of 0.19 mM confirms the high affinity of the immobilized urease on the nanostructured ZnONF surface towards its analyte (urea). The obtained results demonstrate that flower-like ZnO nanostructures serve as a promising matrix for the realization of efficient amperometric urea biosensor with enhanced response characteristics.

Investigation of ethanol vapor sensing properties of ZnO flower-like nanostructures

ZnO flower-like nanostructures were synthesized using zinc nitrate, zinc acetate and zinc sulfate precursors by hydrothermal method. The samples were characterized by X-ray diffraction, scanning electron microscopy and Fourier transform infrared analyses. All of the ZnO samples synthesized by the different precursors were crystallized in a same wurtzite hexagonal structure with different properties such as various morphologies, effective surface areas, concentrations of OH− surface groups, and gas sensing performances. It was observed that flower-like ZnO nanostructures grown by zinc nitrate and zinc acetate included nanopetals with thicknesses of 30 and 50nm, respectively. For the ZnO sample based on zinc sulfate, microspheres were constructed from nanoplatelets with thickness of ∼100nm. The gas sensing properties of the samples toward ethanol vapor were examined and compared at various working temperatures. It was observed that ZnO[nitrate] nanoflower sample was the optimal choice for practical applications (with considerable sensitivity of 70% beside fast response time of 25–27s at low working temperature of 130°C). The suitable ethanol sensing characteristics of ZnO[nitrate] sample was explained by its highly porous structure as the mean surface area of the samples calculated from BET method followed from ZnO[nitrate]>ZnO[acetate]>ZnO[sulfate] sequence.

Controllable synthesis of hierarchical flower-like ZnO nanostructures assembled by nanosheets and its optical properties

The uniform and regular hierarchical flower-like ZnO nanostructures assembled by nanosheets have been controllably synthesized by a facile and efficient solution route on a large scale without using any templates, substrate or seed layers. The results of the experiment indicated that reaction temperature, time and the molar ratio of Zn2+/OH− had a strong influence on the formation of the hierarchical flower-like ZnO nanostructures. ZnO with flower-like nanostructures can be controllable synthesized with appropriate temperature, time and the molar ratio of Zn2+/OH−. The optical properties of the as-synthesized ZnO were investigated by UV–Vis absorption and photoluminescence. Consequently, the value of the band gap for this kind of ZnO crystals was calculated to be 3.26eV and the ZnO nanostructures possess a relatively strong UV emission, violet emission and a blue emission. Moreover, The ZnO may be tempting for further application such as photocatalyst, gas sensors and UV lasers. The facile and efficient solution route has high potentials to synthesize ZnO crystals on a large scale for industry application.

CTAB-assisted synthesis of unique 3D ZnO and the acetone sensing performances

Flower-like ZnO nanostructure composed of orderly nanoplates was synthesized by a cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal method. The unique ZnO nanostructure was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy analysis. The possible formation mechanism of flower-like ZnO nanostructure is proposed. The positively charged CTA+ surfactant can act as an ionic carrier, as well as an agglomeration inhibitor in the orientation growth of ZnO nanoplates. Moreover, the gas sensing properties for acetone were also investigated. The sensor shows high response and good selectivity to acetone gas at the optimum operating temperature of 300°C. The excellent gas sensing performances of the flower-like ZnO indicate that ZnO sensor synthesized by the CTAB-assisted hydrothermal method can be used as a promising sensing material for fabricating acetone sensors.

Comparison of physical and electrochemical properties of ZnO prepared via different surfactant-assisted precipitation routes

The flakes-, hexagons-, nanoparticle-, and flower-like ZnO nanostructures have been synthesized via different surfactant-assisted precipitation routes. The XRD of all ZnO nanostructures is hexagonal single crystalline in nature and the UV–Vis absorption spectra showed blue shift in wavelength corresponding to bulk. The synthesized zinc-oxide nanopowders were used to fabricate dye solar cells sensitized by N719 dye. The comparative study of cells prepared by above ZnO nanopowders has been done. The highest conversion efficiency (2.48 %) for the cell is shown by flower-like ZnO than the others. The difference in photovoltaic parameters for the ZnO nanopowders is due to the difference in surfactants which directly correlate with surface area and dye loading.

Simple chemical aqueous synthesis of dahlia nanoflower consisting of finger-like ZnO nanorods and observation of stable ultraviolet photoluminescence emission

In this work, we have reported the synthesis of dahlia flower-like ZnO nanostructures consisting of human finger-like nanorods by the hydrothermal method at 120°C and without using any capping agent. Optical properties of the samples, including UV–vis absorption and photoluminescence (PL) emission characteristics are determined by dispersing the samples in water as well as in ethanol media. The quenching of PL emission intensity along-with the red shifting of the PL emission peak are observed when the samples are dispersed in water in comparison to those obtained after dispersing the samples in ethanol. It has been found that PL emission characteristic, particularly the spectral nature of PL emission, of the samples remains almost unaltered (except some improvement in UV PL emission) even after thermally annealing it for 2h at the temperature of 300°C. Also the synthesized powder samples, kept in a plastic container, showed a very stable PL emission even after 15 months of synthesis. Therefore, the synthesized samples might be useful for their applications in future optoelectronics devices.

Template-free sonochemical synthesis of flower-like ZnO nanostructures

Abstract Flower-like ZnO nanostructures have been successfully synthesized via a facile and template-free sonochemical method, using zinc acetate and potassium hydroxide as reactants only. The as-synthesized flower-like ZnO nanostructures were composed of nanorods with the width of ∼ 300 – 400 nm and the length of ∼ 2 – 3 μm . The structures, morphologies and optical properties of the as-prepared products were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscopy, UV-Vis spectrophotometry and Raman-scattering spectroscopy. A plausible formation mechanism of flower-like ZnO nanostructures was studied by SEM which monitors an intermediate morphology transformation of the product at the different ultrasonic time ( t = 80 , 90 , 95 , 105 , and 120 min ).

Improvement of gas-sensing property by defect engineering in microwave-assisted synthesized 3D ZnO nanostructures

In this paper, 3D ZnO nanostructures were synthesized by microwave-assisted method, and an improvement of the gas-sensing property of the ZnO nanostructures by defect engineering was reported. The experimental results indicated that the urchin-like and flower-like ZnO nanostructures could be synthesized by tuning the dosage of urea, and the ethanol responses of the flower-like ZnO were higher than those of the urchin-like ones. Defect engineering in the flower-like ZnO nanostructures was used to further enhance the sensing responses, which was accomplished by post-treatment of the flower-like ZnO nanostructures with different calcination temperatures and atmospheres. Defect structures were characterized by PL, Raman, XPS and EPR techniques. Moreover, the possible sensing mechanism and the relationship between the sensing response and the content of defect were proposed. The flower-like ZnO annealed at 500°C in N2 had the most donor defects (zinc interstitial and oxygen vacancy) which were beneficial to the formation of active oxygen and ethoxy. The active oxygen would further interact with the ethoxy, and released electrons which resulted in the decrease of the resistance of sensor. Therefore, ZnO–N2 had the highest response to ethanol.

A facile room temperature synthesis of ZnO nanoflower thin films grown at a solid–liquid interface

Hierarchical ZnO films consisting of nanoflower particulates are successfully grown by a solid–liquid interface reaction technique at room temperature without additives like surfactants, capping agent, or complexing agent. The structural, morphological, and photocatalytic properties of these films are studied using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and UV–Vis spectroscopy. The nucleation, growth processes and hence the resulting morphology of the end product can be regulated by changing the concentration of LiOH and the time of reaction. SEM throws light on the chronology of the flower formation by studying the intermediate morphology. Electron microscopy results indicated that these ZnO nanostructures self-assembled to produce flower-like nanostructures. The highest photocatalytic efficiency was observed for the films prepared at the concentration of LiOH 0.5 mg/mL in ethanol at 24 h. On the basis of the results, a plausible growth mechanism for the formation of flower-like ZnO nanostructures is discussed.

Synthesis and characterization of flower-like ZnO nanostructures via flower-like ZnOHF intermediate

Flower-like ZnO nanostructures were obtained by annealing flower-like ZnOHF by a simple hydrothermal route. The experiments could be carried out under mild conditions in an inexpensive and environmental-friendly way. The surface morphology and microstructure of these as-prepared ZnO nanostructures were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The optical property of the prepared flower-like ZnO nanostructures was investigated by room-temperature photoluminescence (PL) spectra as well. The PL spectra confirmed that ZnO flower-like nanostructures exhibited emission band centered at 382nm in UV region, which came from the characteristic emission of ZnO. Meanwhile, weak and broad emission peak centered at about 540nm, which may be come from the defects existed in ZnO nanostructures.