Flower-like ZnO Nanostructures Research Articles

Carbon-decorated flower-like ZnO as high-performance anode materials for Li-ion batteries

As a potential anode material for Li-ion batteries, ZnO has been intensively studied owing to its high theoretical capacity and low cost. However, low electronic conductivity restricted the application of ZnO in Li-ion batteries. It has been well recognized that morphology-controlled ZnO nanostructures can serve as high-performance anode materials. Here carbon-decorated flower-like ZnO nanostructures have been synthesized by microwave-assisted hydrothermal reactions. The carbon decoration on the flower-like ZnO surface not only suppresses the growth of ZnO crystals but also increases the electronic conductivity of ZnO. The results indicate that the nanocarbon-decorated flower-like ZnO materials can be employed as high-performance anode materials for advanced Li storage.

A green approach to the microwave-assisted synthesis of flower-like ZnO nanostructures for reduction of Cr(VI)

Zinc oxide nanostructures with different morphologies were prepared via a microwave-assisted method and used as photocatalysts for reduction of chromium(VI) under ultraviolet-B illumination. X-ray diffraction revealed that as-made ZnO samples have wurtzite hexagonal structure. Scanning electron microscopy demonstrated that the morphology of the ZnO crystals could be easily modified from star-shaped to chrysanthemum flower-like structure by changing the ratio of zinc nitrate and sodium hydroxide. X-ray photoelectron spectroscopy and energy dispersive X-ray analysis confirmed the stoichiometry of pure ZnO. Its optical properties were also investigated by UV-Vis diffuse reflectance spectroscopy, which indicated that the prepared ZnO possessed a band gap value of 3.2 eV. Photocatalytic activity studies revealed that the ZnO (1:6) (1 × 10−3 mol zinc nitrate: 6 × 10−3 mol sodium hydroxide) catalyst exhibited a significantly faster reduction rate of Cr(VI) compared to ZnO (1:5) and ZnO (1:4). More than 95% of Cr(VI) at a concentration of 10 mg/L has been reduced to Cr(III).

Synthesis and Characterization of AgCl/ZnO Nanocomposites for High Efficiency Photodegradation of Methylene Blue

AgCl/ZnO nanocomposites with different contents of loaded AgCl were synthesized by deposition-precipitation method. The analytical results showed that cubic AgCl nanoparticles supported on the surface of self-assembled nanopetals of flower-like ZnO nanostructure. The photocatalytic properties of AgCl/ZnO nanocomposites were investigated through the photodegradation of methylene blue induced by UV radiation. In this research, the AgCl/ZnO nanocomposites have higher photocatalytic activity than pure ZnO.

Chemical Sensing Performance of Flower-Like ZnO/PSi Nanostructures via Electrochemical Impedance Spectroscopy Technique

ZnO nanostructures were synthesized on porous Si (PSi) structures using a method developed by this study known as electric field-assisted aqueous solution technique. The detailed characterization of this nanostructure was performed using atomic force microscopy, field emission scanning electron microscopy, x-ray diffraction, room-temperature photoluminescence and Raman spectroscopy. Electrochemical impedance spectroscopy (EIS) technique was used to detect two classifications of chemical solvents, namely polar and non-polar solvents. Nyquist plots in EIS were utilized to detect chemical solvents (ethanol, acetone, toluene and benzene) exposed to ZnO/PSi nanostructure arrays. The results showed that the grown flower-like ZnO nanostructure arrays served as good chemical sensors with high sensitivity and low power consumption. Meanwhile, the ZnO/PSi nanoflowers exposed to ethanol showed the highest sensitivity (94.6% response) compared to other chemical solutions with the least response exhibited by benzene (68.4% response). It was postulated that the interaction between the solution and oxygen species of ZnO/PSi nanostructure surface induced a resistance change resulting in the release of free electrons that migrated to the conduction band of ZnO/PSi nanoflower structures and reduced the number of surface-adsorbed oxygen species. Subsequently, the changes observed in the Nyquist semicircle diameter and Warburg impedance led to the chemical sensing response.

Fabrication of flower-like hierarchical ZnO nanostructures with enhanced photocatalytic activity

Flower-like hierarchical ZnO nanostructures (FHZNs) have been successfully obtained through the hydrothermal method at the temperature of 120 °C for 7 h. The as-synthesized FHZNs was characterized by SEM, XRD, EDS, and XPS. Flower-like structure was formed by the simultaneous presence of urea and glycerol. A possible reaction mechanism was proposed based on a range of experiments. It could be described as nucleation, growth and self-assembly of nanosheets. Simultaneously, the photocatalytic properties of the product were also tested.

Flower-like ZnO Nanostructures as Gas Sensor

In this work, we report the synthesis of ZnO nanostructures using a simple solvothermal method and then investigate their use in sensing of ammonia (NH3) and some volatile organic compounds (VOC) such as ethanol and methanol. Electron microscopic analysis shows that the synthesized nanorods are arranged in a flower-like array while UV-Vis absorption spectroscopy shows a peak at 380 nm confirming presence of ZnO. Resistances measured across a thin film of the ZnO nanoflowers show sharp decrease when exposed to ammonia and the VOCs with highest sensitivity recorded for ethanol suggesting its potential use in sensing of these gases.

Microwave-assisted solution synthesis and photocatalytic activity of Ag nanoparticles supported on ZnO nanostructure flowers

Ag nanoparticles supported on the surface of three-dimensional (3D) flower-like ZnO nanostructure were synthesized by a microwave-assisted solution method. The obtained products were characterized by X-ray diffraction analysis, field-emission scanning electron microscopy, Fourier-transform infrared spectroscopy, Raman spectrophotometry, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy. The analytical results confirmed homogeneously distributed Ag nanoparticles supported on the surface of flower-like ZnO nanostructure. The photocatalytic effect of the heterostructure Ag/ZnO nanocomposites was investigated using photodegradation under ultraviolet (UV) light of methylene blue as model dye. The heterostructure Ag/ZnO nanocomposites exhibited much higher photocatalytic activity than pure ZnO flowers. The improved photocatalytic properties are attributed to formation of a Schottky barrier at the metal–semiconductor interface of the Ag/ZnO nanocomposites.

Photochemistry and the role of light during the submerged photosynthesis of zinc oxide nanorods

Recently, metal oxide nanocrystallites have been synthesized through a new pathway, i.e., the submerged photosynthesis of crystallites (SPSC), and flower-like ZnO nanostructures have been successfully fabricated via this method. However, the photochemical reactions involved in the SPSC process and especially the role of light are still unclear. In the present work, we discuss the reaction mechanism for SPSC-fabricated ZnO nanostructures in detail and clarify the role of light in SPSC. The results show that both photoinduced reactions and hydrothermal reactions are involved in the SPSC process. The former produces OH radicals, which is the main source of OH− at the ZnO crystal tips, whereas the latter generates ZnO. Although ZnO nanocrystals can be obtained under both UV irradiation and dark conditions with the addition of thermal energy, light promotes ZnO growth and lowers the water pH to neutral, whereas thermal energy promotes ZnO corrosion and increases the water pH under dark conditions. The study concludes that the role of light in the submerged photosynthesis of crystallites process is to enhance ZnO apical growth at relatively lower temperature by preventing the pH of water from increasing, revealing the environmentally benign characteristics of the present process.

Enhanced photocatalytic activity of Au-doped Au@ZnO core-shell flower-like nanocomposites

We introduce a simple and low-cost three-step hydrothermal and pulsed laser ablation technique for the fabrication of flower-like pure ZnO nanostructures, Au@ZnO core-shell nanocomposites, and Au@ZnO/Au core-shell nanocomposites doped with various concentrations (5, 10, and 15 wt%) of Au nanoparticles without using surfactants or catalysts to enhance the catalytic performance of ZnO under UV–visible irradiation. The decoration of Au nanoparticles on the surface of ZnO promoted the absorption of visible light due to the surface plasmon resonance of Au. Further, we evaluated the photocatalytic performance of the nanocomposites in the degradation of methylene blue (MB). Our findings revealed that the Au@ZnO/Au core-shell nanocomposites with 5 wt% of doped Au NPs demonstrated the highest photocatalytic activity. In addition, radical-scavenging experiments were conducted to determine the main reactive species formed in the reaction mixture, and accordingly, a plausible photocatalytic reaction mechanism for the enhanced photodegradation of MB is presented.

Hydrothermal synthesis of hierarchical flower-like ZnO nanostructure and its enhanced ethanol gas-sensing properties

Abstract ZnO nanoparticles, nanoplates and nanoflowers have been successfully synthesized via a facile hydrothermal route, and their microstructures and gas-sensing properties to ethanol were investigated. Among all the nanostructures, the nanoplates-assembled nanoflowers exhibited significantly higher gas-sensing performances than the others, which may ascribe to their hierarchical architectures with large specific area and abundant spaces for gas diffusion. Furthermore, we surprisingly found that the concentration of surfactant CTAB used had an essential effect on the ultimate morphology of the hierarchical nanoflowers. We hoped our findings could be in favor of further investigations on the fabrication of perfect hierarchical architectures.

Aqueous norfloxacin sonocatalytic degradation with multilayer flower-like ZnO in the presence of peroxydisulfate

Multilayer ZnO nanoflowers were synthesized through a simple precipitation method and characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectra (XPS) and nitrogen absorption-desorption techniques. The FE-SEM images show the integrated morphology of an individual flower-like ZnO nanostructure, which is made of nano-platelets with uniform thickness (20–30nm). The average pore size and Brunauer-Emmet-Teller (BET) surface area of the as-synthesized ZnO were 27.25nm and 13.53m2/g. The sonocatalytic ability of the prepared samples was evaluated through norfloxacin (NF) degradation in an aqueous system using ultrasound (US) irradiation. To improve degradation efficiency, peroxydisulfate (Na2S2O8) was introduced to develop a US/ZnO/peroxydisulfate system, which exhibited an excellent synergistic effect. The effects of ZnO dosage, Na2S2O8 concentration, pH, and initial NF concentration were studied to determine the performances of the US/ZnO/peroxydisulfate process. Corresponding results showed that NF degradation rate increased with the increase of ZnO dosage but decreased with the increase of initial NF concentration. Under the optimal Na2S2O8 concentration of 0.1gL−1 at pH 9, the best degradation efficiency can be achieved. Moreover, based on the scavenging experiment results and literatures, NF degradation through US/ZnO/peroxydisulfate system is majorly induced by OH and SO4− radicals.

Role of defects in one-step synthesis of Cu-doped ZnO nano-coatings by electrodeposition method with enhanced magnetic and electrical properties

We report the growth of flower-like ferromagnetic Cu-doped ZnO (CZO) nanostructures using electrochemical deposition on FTO-coated glass substrates. X-ray photoelectron spectroscopy studies affirmed the presence of Cu in ZnO with an oxidation state of 2+. In order to find the optimized dopant concentration, different Cu dopant concentrations of 0.28, 0.30, 0.32, 0.35, 0.38, and 0.40 mM are applied and their magnetic, optical, and electrical properties are studied. Magnetic moment increased with the increasing dopant concentration up to 0.35 mM and then decreased with further increase in the concentration. Diamagnetic pure ZnO showed ferromagnetic nature even with a low doping concentration of 0.28 mM. Band gap increased with the increasing Cu concentration until a value of 0.35 mM and then remained the same for the higher dopant concentrations. It is ascribed to the Burstein–Moss effect. Defect-related broad photoluminescence (PL) peak is observed for the pure ZnO in the visible range. In contrast, Cu-doped samples showed a sharp and intense PL peak at 426 nm due to increased Zn interstitials. Kelvin probe measurements revealed that the Fermi level shifts toward the conduction band for the Cu-doped samples with respect to pure material. Electron transport mechanism in the samples is observed to be dominated by space charge-limited current and Schottky behavior with improved ideality factor up to 0.38 mM Cu.

Solution-derived ZnO nanoflowers based photoelectrodes for dye-sensitized solar cells

Flower-like ZnO nanostructures, composed of hexagonal nanorods were manipulated, via a low temperature hydrothermal method from an aqueous solution using polyethyleneimine (PEI) as a surfactant in the seed sole. It was found that the PEI in the seed sole not only affected the geometrical shape of ZnO flowers but also changed the length and spacing of the petals. These flower-like nanostructures were used as photoelectrodes in dye-sensitized solar cells. Compared to rod-like flowers (sample X1), the blade-like flowers (sample X2) nanostructures demonstrate increased power conversion efficiency (η) of about 106%. Meanwhile, short-circuits current density (JSC), open-circuit voltage (VOC), and fill factor (FF) are all substantially improved. The enhancement of η, VOC and FF in the blade-like-flower photoelectrodes were mainly ascribed to the enlargement of internal surface area between the blades for higher dye loading and the improved light harvesting from efficient light scattering. The band gap energies were 3.31eV and 3.27eV for rod-like flowers and blade-like flowers respectively. The decrease in the optical band gap with the increase of film roughness was due to decrease of lattice defects.

Flower-like ZnO nanostructure assisted loop-mediated isothermal amplification assay for detection of Japanese encephalitis virus

In this study, we described a novel and effective flower-like ZnO nanostructure assisted Reverse Transcription Loop-Mediated Isothermal Amplification (RT-LAMP) method to detect Japanese Encephalitis Virus (JEV). The effects of different concentrations of ZnO nanoflower on the RT-LAMP reaction were investigated. With the increase of concentration of ZnO nanoflower, RT-LAMP reaction obtained optimization, until the concentration exceeded 1.5nM, RT-LAMP reaction was inhibited. Made 1nM as optimum concentration of ZnO nanoflower, we found that optimum RT-LAMP reaction temperature and time were 60°C and 30min, respectively. The optimization might be connected with good adsorption to DNA and thermal conductivity of ZnO nanoflower, but mechanism of the RT-LAMP reaction affected by ZnO nanoflower needs to be explored further.

Growth and optical properties of hierarchical flower-like ZnO nanostructures

The integration of low dimensions nanoscale building blocks into 3D architectures has attracted great scientific attention. We have obtained the novel hierarchical flower-like ZnO nanostructures self-assembled by nanorods via a facile hydrothermal method. The as-synthesized samples were characterized with various technologies. The field emission scanning electron microscope (FESEM) images indicated that hydroxide ions play a significant role on the formation of hierarchical flower-like ZnO nanostructures. The X-ray diffraction (XRD) result proved that the nanocrystals were well crystallized hexagonal wurtzite structure. A possible growth mechanism of the nanostructures was proposed based on the effects of hydroxide ions. And the TEM imagines provided some important evidence for the proposed growth mechanism. UV–vis adsorption and photoluminescence (PL) spectra results indicated that the obtained ZnO nanostructurs have a good optical-absorption and photoluminescence property. The as-synthesized ZnO nanostructures exhibited superior photocatalytic performance, which was higher than that of commercially available ZnO.

Morphology dependent thermal conductivity of ZnO nanostructures prepared via a green approach

In this study, a green synthesis route for the preparation of ZnO nanostructures with different morphologies was demonstrated. The morphological, structural, elemental composition and thermal properties of the synthesized ZnO nanostructures are characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and thermal conductivity. The prepared ZnO nanostructures are well crystalline nature with a wurtzite structure. The FE-SEM results demonstrated that the ZnO nanostructures with different morphologies such as clusters of coral particles, flower-like particles, ovoid-like particles and spherical particles were obtained via changing the experimental conditions. The flower-like ZnO nanostructures revealed a better thermal conductivity of about 0.34 to 0.22 Wm−1K−1 measured in the temperature range of 298–673 K by coupling of thermal diffusivity and heat capacity.

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

Herein, hierarchical flower-like ZnO nanostructures and S-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 CS(NH2)2 was the dopant. Field emission scanning electron microscope (FESEM), Energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), UV–Vis absorption spectra and photoluminescence spectra (PL) were used to characterize the samples. It demonstrates that small portions of S are successfully incorporated into the lattice of the ZnO nanostructures. The incorporation of S into ZnO is supported by broadening and lower Bragg angle shift in XRD pattern and EDS analysis. Cell Parameters of hierarchical flower-like S-doped ZnO nanostructures are obtained from Rietveld Analysis. The results show that the molar ratio of Zn and S determines the structure, surface morphology and optical properties of the samples significantly. PL spectra show that the effective S doping enhances the green emission and suppresses the near band gap emission.

Novel hybrid self-assembly of an ultralarge ZnO macroflower and defect intensity-induced photocurrent and photocatalytic properties by facile hydrothermal synthesis using CO(NH2)2–N2H4 as alkali sources

Different flower-like ZnO nanoarchitectures were synthesized by a facile hydrothermal method using CO(NH2)2 and N2H4 as alkali sources simultaneously. A novel ultralarge ZnO macroflower was constructed by the ultrathin leaf-like nanobelts, hollow semisphere-like, sphere-like and apple-shaped nanoparticles simultaneously. The diameter of an individual flower can reach 90µm. Meanwhile, three or five flower-like ZnO nanostructures with different diameters, lengths and tips (Planar, semi-pyramid, and/ or pyramid tips) were formed simultaneously under the same reaction condition. XRD shows that all the ZnO crystals possess the hexagonal wurtzite structure. When the samples range from S1 to S5, the crystallinity is improved. EDX shows that the Zn/ O atom ratio of S1–S5 is close to the 1:1 stoichiometric ratio, and that of S3 is almost equal to 1:1. FTIR indicates that S4 and S5 are pure. However, the surface of S1, S2 and S3 adsorbs the CO32− group. The reflectance of S1–S4 in the range of 300–370nm is inversely proportional to that in visible region. Meanwhile, when the grain size of S1–S4 decreases, their band gap increases. The Raman results of S1 and S5 are different from those of S4 and exhibit the higher crystal quality, which are favorable for the improvement of photocatalytic performance. S1 and S5 exhibit the highest photocatalytic performance and decompose 65% and 70% of MB within 50min respectively. The photocatalytic activity and photocurrent strongly depend on the defect intensity of the ZnO crystals. The ZnO photocatalyst of S5 is still stable and efficient after three cycles. However, the photocatalytic activity of S1 decreases continuously, due to its unique morphology and the adsorption of intermediates. In addition, A hybrid self-assembly process of the ultralarge ZnO macroflower was proposed.

Fabrication and characterisation of flower‐like ZnO nanostructures grown chemically on flexible PEN substrate

Flower-like ZnO nanostructures were successfully produced on a polyethylene naphthalate (PEN) substrate through a chemical bath deposition method. Field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), photoluminescence (PL), and ultraviolet-visible were utilised to investigate the structural and optical properties of grown flower-like ZnO nanostructures. FESEM image indicates that fabricated ZnO nanostructures formed from the ZnO nanoflowers with different shape and the petals of the ZnO nanoflower grow symmetrically and radially from the centre. XRD pattern of the ZnO nanoflowers indicate that the ZnO nanorods of the nanoflowers were preferentially grown along the c-axis. The PL results of the ZnO nanoflowers exhibited a strong violet and indigo emission peaks are centred approximately at 413 and 425 nm, respectively.

Controllable ZnO nanostructures evolution via synergistic pulsed laser ablation and hydrothermal methods

We report the morphology-controlled ZnO nanostructures (ZNSs) evolution synthesized via a novel and facile technique at different growth times, where the pulse laser ablation in liquid (PLAL) is creatively combined with hydrothermal (H) method (hereafter called PLAL-H technique). Four types of ZNSs with varying sizes and shapes such as tapers, multipods, flowers, and hollow flowers are produced on Si substrate via PLAL-H technique. Furthermore, multipod- and flower-like ZNSs are grown using direct hydrothermal method to compare them with the one obtained via synergistic effects of PLAL-H method. This catalyst-free fabrication method is not only cost-effective but greatly useful for the rapid production of different quality of ZNSs at low temperature. ZNSs synthesized under prolonged growth time (60min) exhibited structural deformation. Growth technique and time dependent morphology, structure, composition, and optical properties of these as-grown ZNSs are characterized using FESEM, X-ray diffraction, FTIR, photoluminescence, and UV–vis measurements. Synthesized ZNSs revealed excellent crystallinity and growth process dependent variation in the physical and optical features. The ZNSs growth mechanism is understood. Excellent features of the results demonstrate that this synergized new growth technique may constitute a basis for modifying the morphology, sizes, and optical properties of ZNSs in a controllable manner useful for diverse applications.