Hydrothermal controllable synthesis to convert ZnO hexagonal nanotubes to hexagonal nanorods and their photocatalytic application

Zinc oxide (ZnO) thick films were analyzed by high-resolution X-ray diffraction (HR-XRD), field emission scanning electron microscopy, and photoluminescence (PL) spectroscopy at room temperature. The films were grown on glass substrates using different molar concentrations of aqueous solution (0.02, 0.04, and 0.06 M) via a simple hydrothermal method. This method uses glass bottles with rubber caps as reactor vessels (100 mL) and, thus, is classified as a green chemistry technique. Hexahedral zinc nitrate (Zn (NO₃)₂·6H₂O), hexamethylenetetramine (C₆H₁₂N₄), and deionized water were used as starting materials and were reacted in the presence of heat. HR-XRD measurements confirmed that the diffraction peaks of the polycrystalline structure films can be assigned to the hexagonal-shaped wurtzite ZnO. In addition, the PL spectra show that the integrated intensity decreases with the increase in ZnO content. The SEM images also revealed the existence of hexagonal ZnO nanotubes in the 0.02 M sample, and these nanotubes are gradually converted into hexagonal nanorods with the increase in ZnO content. Moreover, the photocatalytic activity of both nanostructures was measured based on the degradation of methyl blue (MB) by using ultraviolet light (λ = 366 nm). Results showed that the ZnO nanotubes degraded MB more effectively than the nanorods.     

Large-scale synthesis of hexagonal cone-shaped ZnO nanoparticles with a simple route and their application to photocatalytic degradation

We report the large-scale synthesis of hexagonal cone-shaped ZnO nanoparticles by the esterification between zinc acetate and alcohol. The morphology of the ZnO nanoparticles was investigated by transmission electron microscopy, selected area electron diffraction and scanning electron microscopy measurements. The synthesized ZnO nanoparticles are single-crystalline with hexagonal phase and show a strong UV emission at −378 nm due to the excellent crystallinity of particles. A possible formation mechanism of the hexagonal cone-shape structure is proposed. Furthermore, the as-prepared ZnO particles exhibit high photocatalytic activity for the photocatalytic degradation of Rhodamine B, indicating that the ZnO nanostructure is promising as a semiconductor photocatalyst.     

Hydrothermal synthesis of ultrathin ZnO nanosheets and their gas-sensing properties

Gas-sensing performances can often be enhanced significantly once the size of sensing nanomaterials approaches a critical value of 15 nm. Here, we synthesize, by a simple hydrothermal method accompanied by the calcination process, ultrathin ZnO nanosheets with a thickness as thin as 10–13 nm. We find that the prepared zinc hydroxide carbonate precursor is largely agglomerated, yet transformed to the ultrathin ZnO nanosheets in a dispersive fashion after the calcination process. The as-prepared ultrathin nanosheets exhibit excellent gas-sensing functions to ethanol gas at the optimal temperature as low as 300 °C under the concentration of 50 ppm, rendering them a promising sensing material for the on-site detection of ethanol.     

Solvothermal synthesis of hexagonal ZnO nanorods and their photoluminescence properties

Pure hexagonal ZnO nanorods were synthesized by low-temperature (90 °C) solvothermal treatment of zinc acetate in 40-80 wt.% hydrazine hydrate aqueous solutions. The products were characterized by means of powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electronic microscopy (TEM), selected area electron diffraction (SAED), and room temperature photoluminescence (RTPL) spectra. They show a strong UV emission at around 380 nm upon excitation at 360 nm using a Xe lamp at room temperature. The influence on the quality of the nanorods was investigated while the content of the solvent changed. The as-synthesized ZnO nanorods are promising materials for nanoscale optoelectronic devices due to their excellent UV emission properties.     

Self-assembly of graphenelike ZnO superstructured nanosheets and their application in hybrid photoconductors

Photoconductors require high charge-carrier mobilities, sensitivity over a wide range of light levels, and good stability. Combining an organic semiconductor with environmentally benign inorganic nanoparticles is a rational means to develop photoconductors with such properties. However, an inhomogeneous distribution of nanoparticles in the active layer restricts both charge-carrier mobility and charge collection at an electrode. In this paper, ultrathin ZnO superstructured nanosheets are successfully synthesized by a solvothermal method. Time-dependent investigations show that the superstructured nanosheets assemble in solution during the growth process. Given that high-quality ZnO nanosheets are obtained, a hybrid photoconductor device with P3HT is fabricated and investigated. Sensitivity above 200% under simulated sunlight is obtained with good air stability. This study demonstrates a general approach to design photoconductors using hybrid nanomaterials.     

One-pot synthesis of porous hematite hollow microspheres and their application in water treatment

Alpha-Fe2O3 hollow micospheres have been successfully synthesized by solvothermal method at 200 degrees C. The synthesized products are characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and the nitrogen adsorption-desorption isotherm technique. The alpha-Fe2O3 hollow microspheres have an average diameter of 2-3 microm, the shell consists of numerous aligned nanorods with length of about 200-400 nm. The effects of solvent and reaction time have been studied. The Ostwald ripening mechanism is proposed to account for the formation of alpha-Fe2O3 hollow microspheres. Because of the porous hollow microstructure and large specific surface area, the microspheres were found to be effective sorbents for the removal of Cr(VI) ions from wastewater.     

One-pot synthesis of ZnO/Ag nanospheres with enhanced photocatalytic activity

ZnO/Ag composite nanospheres with an average diameter of about 440 nm, were synthesized through a facile one-pot solvothermal reaction, using a kind of biomolecular sodium alginate as template, H₂O and diethanolamine as solvents, followed by the assembly of ZnO and Ag nanoparticles in-situly produced. The composite spheres were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and energy disperse X-ray spectrum. Moreover, the results showed that the as-made ZnO/Ag assembled nanospheres exhibited better photocatalytic performance than the pure ZnO nanoparticles and this one-pot synthesis method has great potential to be extended for the synthesis of other metallic oxide/metal spheres.     

温和条件下氧化铜纳米片层的制备与电化学催化性质研究

为实现特定形貌CuO纳米材料的温和可控合成,增强该材料作为电化学催化剂的催化活性,利用亚铜离子在碱性溶液中的氧化沉淀反应,制备了形貌均一稳定的CuO纳米片层。采用粉末X射线衍射、扫描电子显微镜、透射电子显微镜、X射线光电子能谱与电化学催化反应等手段,研究了不同合成参数对产物的形貌、价态与电化学催化性能的影响。研究结果表明:当产物投料比为0.01 g CuCl/10 mL TBAOH时,产物的电化学催化性质最好;在200℃下煅烧后,催化性能得到进一步提高。利用具有特殊分子结构的四丁基氢氧化铵作为模板剂,能够实现CuO纳米片层的简单、快速、温和制备;同时,产物中低价态Cu离子的存在可提高催化剂的电化学催化活性。通过煅烧提高产物的结晶性,能够进一步增强材料的电化学催化活性。     

ZnO nanonails: synthesis and their application as glucose biosensor

Well-crystallized zinc oxide nanonails were grown in a high density by thermal evaporation process and were used as supporting matrixes for glucose oxidase (GOx) immobilization to construct efficient glucose biosensor. The GOx attached to the surfaces of ZnO nanonails had more spatial freedom in its orientation, which facilitated the direct electron transfer between the active sites of immobilized GOx and electrode surface. The fabricated biosensor showed a high sensitivity of 24.613 microA cm(-2) mM(-1) with a response time less than 10 s. Moreover, it shows a linear range from 0.1 to 7.1 mM with a correlation coefficient of R = 0.9937 and detection limit of 5 microM.     

High-yield chemical synthesis of hexagonal ZnO nanoparticles and nanorods with excellent optical properties

Large yield and low temperature growth of nanostructures are key requirements for fulfilling the demand of large scale applications of nanomaterials. Here, we report a highly efficient chemical method to synthesize high quality hexagonal ZnO nanoparticle and nanorods utilizing the low temperature oxidation of metallic zinc powder in the presence of an appropriate catalyst. This one-step method has advantages such as low temperature (90 degrees C) and atmospheric pressure synthesis and a high yield (> 90%). Microstructure and optical properties of the as-synthesized ZnO nanoparticles are found to be identical or better than those of the commercial ZnO nanopower (Sigma-Aldrich). In particular, in comparison to the commercial nanopowder the as-grown ZnO nanorods and nanoparticles exhibit stronger UV absorption at 376 nm and intense UV photoluminescence emission at -382 nm, with negligible defect emission band. This method is suitable for large-scale production of nanosized ZnO and could be extended for the synthesis of other metal oxides.     

Fabrication of ZnO films consisting of densely accumulated mesoporous nanosheets and their dye-sensitized solar cell performance

Nanocrystalline and mesoporous ZnO films approximately 4 μm in thickness were fabricated through a simple chemical deposition of Zn₄CO₃(OH)₆·H₂O in an aqueous solution of zinc nitrate and urea and subsequent pyrolysis at a low temperature of 300 °C. Microscopic observation of the films revealed that they were composed of mesoporous nanosheets accumulating with submicrometer-order spacing between them on conducting glass substrates. Adsorption of N-719 dye onto the ZnO surface, for application to dye-sensitized solar cells, led to dye-loading of 1.1 × 10^− 7 mol/cm² in spite of the relatively small thickness. The resultant ZnO/N-719 photoanode exhibited a short-circuit photocurrent density of 13.8 mA/cm², which is of the highest level ever reported for ZnO. An overall light-to-electricity conversion efficiency of 3.3% was achieved under 1 sun AM1.5 illumination without any optimization in view of the other cell components.     

The facile synthesis of nickel silicide nanobelts and nanosheets and their application in electrochemical energy storage

Ni silicides in the form of nanobelts and nanosheets were synthesized for the first time based on the chemical reaction of Ni substrate with SiHCl(3) under H(2) atmosphere at 900?°C. Their morphological, structural and compositional features were characterized in detail using scanning electron microscopy, transmission electron microscopy, electron diffraction, energy-dispersive x-ray spectroscopy and x-ray diffraction. It was found that the nanobelts, 120-180?nm in thickness and 1-5?μm in width, comprise a single Ni(3)Si phase and the nanosheets 20-80?nm in thickness consist of Ni(3)Si and Ni(31)Si(12), which is influenced by the concentration ratio of SiHCl(3) to H(2). Moreover, the potential application of these Ni silicides in electrochemical energy storage was also investigated. The results indicate that the nanosheets have excellent electrochemical performance when used as anode material for high energy density lithium ion batteries: a reversible capacity of more than 540?mA?h?g(-1) can be maintained even for the 20th cycle in a standard Li(+) half-cell.     

Sono-chemical synthesis of ZnO nano-particles and their application in hydrogen sulphide gas sensing

Herein we describe synthesis of ZnO nanoparticles by using alkaline solution of ZnX2 (X = NO3, Cl) under ultrasound energy of 20 KHz. The reaction can be completed in about 1-2 hours. As prepared powders were analyzed by XRD measurement to find that the product is hexagonal phase pure ZnO. UV-Visible measurement of aq. solution showed absorption band at -365 nm and photoluminescence (PL) indicated multiple bands in visible region due to deep traps owing to high temperature sintering. The hydrophilicity can be imparted by use of a suitable polyelectrolyte. Freshly prepared samples showed good dispersion in aqueous and alcoholic medium. The thick films derived from the ZnO nano-particles showed excellent sensing for hydrogen sulphide gas.     

CO2-mediated synthesis of ZnO nanorods and their application in sensing ethanol vapor

High-purity ZnO nanorods have been synthesized via a two-step route using zinc acetate as a precursor without any surfactant and additive. In this method, ZnCO3 fibers were first formed in the CO2-ethanol solution, which directed the formation of ZnO nanorods by subsequent treatment in KOH aqueous solution. The as-prepared nanorods were fully characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and Fourier transform Infrared spectroscopy. It was found that the as-obtained ZnO nanorods were single crystals with uniform diameter around 150 nm and length of 4 microm. The nanorod crystals were prismatic with hexagonal cross sections, consistent with the wurtzite lattice structure. Moreover, the sensing properties of the as-prepared ZnO nanorods were also investigated. It was demonstrated that they exhibited good performance for detecting ethanol vapor even at 380 and 250 degrees C.     

One-step large-scale synthesis of porous ZnO nanofibers and their application in dye-sensitized solar cells

A one-step thermal evaporation and vapor-phase transport method was utilized to synthesize porous ZnO nanofibers in large scale. The synthesized nanofibers are highly porous, with diameters in the range of 200–700 nm and lengths of several micrometers. The addition of the CuCl₂·2H₂O into the Zn precursor powder was proved to be critical for the formation of the porous structures, which were proposed to be resulted from the decomposition of the unstable Cl-containing intermediate products such as zinc hydroxide chloride or zinc oxide chloride hydrate phases. In addition, a demonstration of applying the porous ZnO nanofibers as the photoanode of dye-sensitized solar cells is provided.     

Microwave synthesis of ZnO microcrystals with novel asymmetric morphology

This paper reports a discovery of novel morphological features of ZnO asymmetric micron-sized single crystals synthesized by microwave irradiation of W/O emulsions containing a Zn source in the inner aqueous phase. The influence of the zinc ion concentration on the size and shape is studied in detail. The morphological and structural properties show that the obtained ZnO powders are almost mono-dispersed ZnO single crystals with a novel morphology of truncated hexagonal pyramids ca. 1 μm in diameter. A scanning precession electron diffraction analysis reveals that the asymmetrically shaped ZnO single crystals thus obtained have a crystallographic c-axis perpendicular to the bottom hexagonal flat surfaces, and annular bright-field imaging indicates that the bottom surfaces are Zn-terminated ZnO(0001)-Zn polar faces. These new findings are led from a combination of well-controllable liquid-phase emulsion synthesis of the oxide powders and highly advanced atomic-resolution TEM imaging technique, suggesting for the first time a highly probable relationship between the polarity of the wurtzite-type crystal structure and the novel asymmetric morphology of the ZnO microcrystals obtained in this study.     

Low-temperature synthesis of ZnO nanoparticles for inverted polymer solar cell application

Zinc oxide (ZnO) nanoparticles were synthesized by a simple wet chemical method at low temperature. Morphologies, crystalline structure, and optical transmission of ZnO nanoparticles were investigated. The results showed that the average diameter of as-synthesized ZnO nanoparticles was about 4.9 nm, the nanoparticles were wurtzite-structured (hexagonal) ZnO and had optical band gap of 3.28 eV. Very high optical transmission (>80 %) in visible light region of ZnO nanoparticulate thin films was achieved. Furthermore, an inverted polymer solar cell consisted of ZnO nanoparticles and polymer were fabricated. The device exhibited an open circuit voltage (V_oc) of 0.50 V, a short circuit current density (J_sc) of 1.76 mA/cm², a fill-factor of 38 %, and a power conversion efficiency of 0.42 %.     

One-pot size and interior-cavity controlled synthesis of ZnO hollow micro-/nano-structured spheres

In this work, ZnO hollow micro-/nano-structured microspheres were prepared via a one-pot solution route. The size and interior-cavity of these microspheres could be easily controlled by varying the precursor concentration. The hollow spherical assemblies were composed of short rod-like building units at low precursor concentration. When the precursor concentration increased, one-dimensional (1D) "pearl-chain-like" building units formed firstly and then self organized into hollow microspheres. The organization process and ripening of "pearl-chain-like" building units could be modulated by simply altering the reaction time. When tested in photocatalytic experiments, the hollow microspheres composed of loosely packed 1D "pearl-chain-like" building units showed higher activity than the densely packed ones. This method is very simple, mild, and may provide a new strategy to synthesize hierarchical self-assembled hollow structures.