Dumbbell-like ZnO Research Articles

Al-Doped Dumbbell-Like ZnO for Enhanced Ethanol Sensing Performance

A dumbbell-like Al doped ZnO(AZO) microstructure was successfully synthesized via a facile, controllable and one-pot hydrothermal method. The samples were characterized by XRD, SEM, EDS and TEM. It showed that all the samples present dumbbell-like structure composed of highly crystalline hexagonal wurtzite ZnO. The dumbbell-like structure is formed through the self-assembly of Al-dopled ZnO nanodisks. Gas sensing tests reveal that the Al-doped dumbbell-like ZnO microstructure (3 at %) shows excellent gas sensing response (5.37 for ethanol with 1 ppm) for ethanol with shorter response-recovery time (53 s/21 s). The notable sensing performance could be mainly attributed to the increased content of oxygen vacancy in ZnO due to the Al doping. Thus, the Al-doped dumbbell-like ZnO microstructures could provide an inspiration for the design and preparation of the highly sensitive ethanol gas sensor with the controllable electronic structure.

Synthesis and photocatalytic activity of dumbbell-like mesoporous ZnO micro-nanomaterials with tetrasulfonatomethyl-n-hexyl calix [4]resorcinarene tetrasodium salt as hard-soft template

Dumbbell-like ZnO micro-nanomaterials with uniform morphology were prepared with tetrasulfonatomethyl-n-hexyl calix [4]resorcinarene tetrasodium salt (THCRT) by a simple reflux method. The ZnO samples were characterized by X-ray diffraction, field emission scanning electron microscope, transmission electron microscopy, high-resolution transmission electron microscopy, thermogravimetric analysis, Brunauer-Emmett-Teller technique, Fourier transform infrared spectroscopy, ultraviolet–visible diffuse reflectance spectra, and Photoluminescence. The as-prepared ZnO micro-nanomaterials with a hexagonal wurtzite structure exhibited dumbbell-like morphology with a length of 700–900 nm and a hemisphere diameter of 500–700 nm. The THCRT was involved in the formation of ZnO nanostructure framework during the assembly and stacking of ZnO nanoparticles. The as-obtained dumbbell-like micro-nanomaterials possessed obvious mesoporous structure after the calcination at 500 °C and 650 °C, which is due to the rigid hydrophobic cavity of THCRT as hard template. The effects of the zinc sources, amount of THCRT, surfactants and amount of ammonia on the size and morphology of the ZnO samples were studied. The results indicate that THCRT with multi-head and multi-tail as soft template has a good protective effect on the growth of ZnO crystals. This study shows that the as-prepared ZnO product has a dumbbell-like mesoporous micro-nanostructure due to the special structure of THCRT which consists of rigid cup cavity, hydrophilic heads and hydrophobic tails. The evolution process of the dumbbell-like ZnO micro-nanostructures was investigated by FE-SEM, and a possible formation mechanism was proposed. The as-prepared ZnO micro-nanomaterials exhibited good adsorption capacity without calcination and excellent photocatalytic activity for degradation of methyl violet after calcination. Due to the excellent properties of micro-nanoscale, suitable pore size, high specific surface and good photoabsorption, the as-prepared dumbbell-like mesoporous ZnO micro-nanomaterials exhibit potential application as photocatalyst.

Tetrasulfonate substituted phthalocyaninatozinc (II) (ZnTSPc) modification on the two dimensional surface of ZnO: On-surface synthesis, interface characteristics, and its selective photodegradation under visible irradiation

The photo-degradative selectivity for a photocatalyst is strongly dependent to the specific interaction between the photocatalyst and substrate. Here, a hydrophilic functional molecule, tetrasulfonate substituted phthalocyaninatozinc (II) (ZnTSPc) was modified on the two dimensional (2D) surface of ZnO via an on-surface synthesis. In the synthetic process, the dangling bonds of zinc ions on the high active facet ((001) and (100)) of dumbbell-like ZnO (ZnO ZDs) were used as a template of cyclotetramerization reaction for ZnTSPc by an on-surface process, where 4-(potassium sulfonate) phthalonitrile was used as a precursor. Compared with pure ZnTSPc, a significant fluorescence quenching (96.3 %) for ZnTSPc/ZnO happened. The photogenerated electron-hole pairs were effectively separated by photoexcited electrons injecting from ZnTSPc into ZnO ZDs conduction band with a rapid charge transfer rate (6.1 × 107s−1). Under visible light irradiation, ZnTSPc/ZnO as a photocatalyst illustrates higher catalytic degradation rate for both phenol (PL) and methylene blue (MB) than those by using ZnO ZDs. Due to the hydrophilicity of sulfo groups on the peripheral substituted ZnTSPc, MB as a hydrophilic dye had strong attraction towards super-hydrophilic ZnTSPc/ZnO via π-π conjugation, but PL with hydrophobicity. The relative degradation rate of MB by using ZnTSPc/ZnO is 4.19 times faster than that of PL, illustrating ZnTSPc/ZnO with distinct photocatalytic selectivity under visible irradiation. The energy-band feature and mechanism for photoexcited electrons transition are illustrated based on electrochemical analysis.

Dumbbell-like ZnO nanoparticles-CeO2 nanorods composite by one-pot hydrothermal route and their electrochemical charge storage

Dumbbell-like ZnO nanoparticles-CeO2 nanorods (ZnONPs-CeO2NRs) composites with superior electrochemical performance were fabricated by one-pot hydrothermal process and characterized by X-ray diffraction, an energy dispersive spectrum, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and nitrogen adsorption–desorption isotherms. The ZnONPs-CeO2NRs nanostructure possessed larger Brunauer–Emmett–Teller (BET) surface, crystallinity, lower resistance. The specific capacitance of ZnONPs-CeO2NRs composite (162.08mFg−1) was higher than that of precursor CeO2NRs (151.43mFg−1) in galvanostatic charge/discharge, and the super-capacitor charge storage of ZnONPs-CeO2NRs (581.39Fg−1) was more 12 times than the precursor (46.63Fg−1). The improved electrochemical performances could be ascribed to the import of ZnONPs, which induced variations in the structure, conductivity and surface morphology.

Synthesis of dumbbell-like ZnO microcrystals via a simple solution route

Uniform dumbbell-like ZnO microcrystals had been successfully fabricated on a large scale via a facile solution technique under mild conditions. Obtained ZnO, with length of 1.2 to 1.6 μm and diameters of 350 to 600 nm, exhibited well-defined dumbbell-like morphology and hexagonal wurtzite structure and grew along the [001] direction. Effects of the reactant concentration on the sizes and morphologies of the ZnO products had been investigated, indicating that the reactant concentration played a crucial role in determining final sizes and shapes of the samples. In addition, the growth process of the dumbbell-like ZnO microcrystals was studied, and a possible formation mechanism was proposed. Furthermore, the optical properties of ZnO samples obtained at various reaction times were also investigated by photoluminescence (PL) spectroscopy. The PL spectra of the as-prepared dumbbell-like ZnO microcrystals showed a strong UV emission peak.

Strong violet emission from zinc oxide dumbbell-like microrods and nanowires

ZnO of different morphologies with controlled size and aspect ratio (l/d) such as dumbbell-like microrods, thick nanowires and thin nanowires were prepared by a hydrothermal method. Possible mechanisms for the formation of ZnO crystals with the different morphologies were discussed. Strong violet photoluminescence bands at∼413nm (3.0eV) without band edge emission were observed from the dumbbell-like ZnO microrods and thick nanowires. Correspondingly, the thin nanowires showed a weak shoulder UV photoluminescence band at∼390nm. Such result indicates that the photoluminescence properties could be improved by the morphologies or aspect ratio (l/d) and the potential fabrication violet-light-emitting devices.

Preparation of Dumbbell-Like ZnO Microcrystals and Characterization of their Thermal Radiation Properties

3D-ordered dumbbell-like ZnO microcrystals were prepared under hydrothermal conditions without using any additive, template or surfactant. FE-SEM images show that 3D-ordered dumbbell-like ZnO microcrystals are made of two elements-(Ⅰ) dumbbell-like microrods and (Ⅱ) nanorods that grow on the two ends of microrods. The thermal radiation properties of 3D-ordered dumbbell-like ZnO microcrystals were discussed in detail.

Synthesis and characterization of ZnO with hexagonal dumbbell-like bipods microstructures

High crystalline ZnO with hexagonal dumbbell-like bipods morphology was successfully synthesized via N-cetyl-N,N,N-trimethyl ammonium bromide (CTAB)-assisted hydrothermal microemulsion route. X-ray diffraction, scanning electron microscopy, photoluminescence spectrum and Ultraviolet and Visible absorption spectroscopy were used to characterize the structure, morphologies and properties of the as-prepared samples. The results demonstrated that the hydrothermal reaction time had obvious influence on the shape and size of the ZnO products. The Ultraviolet and Visible absorption spectra indicated that the as-prepared ZnO had a strong and broad absorption band from ultraviolet to visible region. The photoluminescence spectra of the synthesized ZnO exhibited a very strong UV emission at ∼380 nm, indicative of their high crystal quality. Meanwhile, the possible growth mechanism for the formation of hexagonal dumbbell-like ZnO microstructures was proposed.

Dynamic transition between Zn-HDS and ZnO; growth and dissolving mechanism of dumbbell-like ZnO bipod crystal

The dumbbell (DB) ZnO bipod crystal is directly grown from acetate anion intercalated Zn based hydroxyl double salts (Zn-HDS). Our results suggest that the (0001)-to-(0001) plane orientation of the DB ZnO crystal comes from the acetate anions intercalated into the Zn-HDS. The DB ZnO crystal is dynamically changed to tube, nanoplate, and the new Zn-HDS with interlayer spacing of 20.0Å by etching the (000-1) surface.

Synthesis of porous and nonporous ZnO nanobelt, multipod, and hierarchical nanostructure from Zn-HDS

Zn based hydroxide double salts (Zn-HDS) with an interlayer spacing of 20 Å was produced by dissolving dumbbell-like ZnO crystal. The resulting Zn-HDS with a ribbon-like shape has a suitable morphology to explore the remarkably mild procedure for synthesis of ZnO nanobelts. We found that the intercalated water molecules into the Zn-HDS could play a key role in the ZnO nanobelts porosity. The nonporous ZnO nanobelts were successfully synthesized from the Zn-HDS by soft-solution process at 95 °C through mild dehydration agent as Na 2CO 3. As-synthesized ZnO nanobelts were grown along not only the [0 1 −1 0], but also the [2 −1 −1 0]. On the other hand, the porous ZnO nanobelts were obtained from the Zn-HDS by calcinations at 200 and 400 °C. In addition, flower-like ZnO multipod and hierarchical nanostructures were produced from the Zn-HDS by using of strong dehydration agent (NaOH) through hydrothermal reaction at 150 and 230 °C.

Control of the Surface of ZnO Nanostructures by Selective Wet-Chemical Etching

In this article, we demonstrate successful application of a top-down strategy based on a selective wet-chemical etching technique in fabrication of nanostructures with a special morphology. Pagoda-like and hexagonal pyramidal ZnO nanostructures with the polar (0001) and {1011} planes as exposed surfaces have been synthesized by refluxing ZnO columns mainly bounded with {1010} nonpolar faces in the mixed solvent of oleic acid (OA) and 1-octylamine. Adequate evidence demonstrates that OA in the mixed solvent acts as the etchant in the process of morphology evolution, and the appropriate proportion of OA, reaction time, and reaction temperature are crucial for controlling the etching degree of ZnO. Through the selective wet-chemical etching, it has been confirmed that the dumbbell-like ZnO is of twinning morphologies growing along contrary direction on both sides of the (0001) twinning plane. Therefore, our present work provides a simple way to estimate the complicated twinning phenomena.

Polymer-controlled crystallization of dumbbell-like ZnO hollow architectures

Dumbbell-like ZnO hollow architectures have been achieved on a large scale by a facile solution-based method by using water-soluble polymer (poly(sodium 4-styrenesulfonate)) as crystal growth modifier. The as-prepared ZnO architectures were in fact assembled by numerous sheet-like particles with an average size of ~ 10 nm. Studies found that the existence of PSS played an important role in the formation of these unique ZnO microstructures. The possible formation mechanism has been discussed based on the experimental results and the function of organic molecules. The hollow ZnO architectures exhibit unique photoluminescence characteristics at room temperature, suggesting promising potential for optoelectronic applications.

Phase transformation and resistivity of dumbbell-like ZnO microcrystals under high pressure

High-pressure Raman spectra and in situ electrical resistivity measurement of the dumbbell-like ZnO microcrystals have been investigated by using the diamond-anvil-cell technique at room temperature. The dumbbell-like ZnO microcrystals were synthesized via a facile solution method under mild conditions. In terms of the Raman results, the dumbbell-like ZnO microcrystals underwent a transition from wurtzite to rock-salt structure with increasing pressure and the phase-transition pressure was about 11.13 GPa. In situ electrical resistivity measurement of the dumbbell-like ZnO microcrystals was performed on a designed diamond anvil cell. The change in electrical resistivity related to the phase structure for the ZnO microcrystals was observed with the applied pressure of up to 34.86 GPa. Moreover, the pressure dependence of the electrical resistivity for the dumbbell-like ZnO microcrystals annealed at different conditions was also investigated.

Selective acetone sensor based on dumbbell-like ZnO with rapid response and recovery

Dumbbell-like ZnO microcrystals have been obtained through a facile solution method. The structure, morphology and optical properties of the as-prepared ZnO microcrystals have been characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy and photoluminescence. The as-prepared ZnO microcrystals exhibit excellent sensing properties against acetone at an operating temperature of 300 °C. The response and recovery times are found to be 1.5 and 3 s, respectively. Moreover, the sensor holds the successful discrimination between acetone and ethanol, which makes our product a good candidate in fabricating highly selective sensors in practice.

Growth of Dumbbell-like ZnO Microcrystals under Mild Conditions and their Photoluminescence Properties

Large-scale uniform dumbbell-like ZnO microcrystals were successfully synthesized via a facile solution method under mild conditions. The as-prepared dumbbells, with lengths of 3.5-5.4 microm and diameters of 1.3-1.8 microm, possess a single-crystal hexagonal structure and grow along the [0001] direction. The influence of the reactant concentration on the size and shapes of the ZnO samples had been studied, and the results revealed that the reactant concentration plays a crucial role in determining final morphologies of the samples. Moreover, the evolution process of the dumbbell-like ZnO microcrystals was viewed by field-emission scanning electron microscopy (FE-SEM) characterization, and a possible formation mechanism was proposed. In addition, optical properties of the ZnO samples prepared at different reaction times were also investigated by photoluminescence (PL) spectroscopy. The room-temperature PL spectrum of the dumbbell-like ZnO microcrystals shows a strong UV emission peak. The UV emission is further identified to originate from the radiative free-exciton recombination by the temperature-dependent PL.

Controllable Growth of ZnO Microcrystals by a Capping-Molecule-Assisted Hydrothermal Process

Different shapes of ZnO microcrystals have been achieved controllably by a capping-molecule-assisted hydrothermal process. The flowerlike, disklike, and dumbbell-like ZnO microcrystals of hexagonal phase have been obtained respectively using ammonia, citric acid (CA), and poly(vinyl alcohol) (PVA) as the capping molecules. Only a very strong UV emission at ∼380 nm is observed in the photoluminescence (PL) spectra of the three kinds of ZnO microcrystals, indicative of their high crystal quality. The formation mechanisms for the hydrothermally synthesized microcrystals in different morphologies have been phenomenologically presented.