Sheet-like ZnO Research Articles

Synthesis of two-dimensional ZnO nanosheet-structures for the application in dye-sensitized solar cells

A large amount of nano-ZnO with a thin sheet-like morphology has been manufactured by a simple citric acid assisted hydrothermal route. The influences on the morphologies and structures of ZnO products for the introduction of citric acid in the reaction system have been investigated. A dye-sensitized solar cell assembled by the ZnO nanosheets as photoanode shows an efficiency of 1.82 % with a short-circuit current density of 7.48 mA cm−2 which is over 1.5 times higher than the one without adding citric acid during the synthetic process. This result is mainly connected to the unique superiority of the two-dimensional sheet-like ZnO nanostructures for light scattering and dye loading.

Synthesis of sheet-like nanoscaled ZnO and Ag/ZnO composite nanocrystals and their electrocatalytic properties

Sheet-like ZnO Ag/ZnO composites were synthesised by calcination of each precursor prepared via a hydrothermal treatment. The samples were characterised by thermogravimetric analysis and differential thermal gravimetric analysis, X-ray diffraction, scanning electron microscopy and transmission electron microscopy technologies. The results showed that ZnO and Ag/ZnO composite nanosheets were composed of nanoparticles. The electrocatalytic performances of the samples modified on a glassy carbon electrode for p -nitrophenol, K2CrO4 and H2O2 reduction in a basic solution, respectively, were investigated using a cyclic voltammetry method. The results revealed that ZnO and Ag/ZnO composites with Ag content from 1 to 5% all exhibited an enhanced catalytic activity by comparing with a bare glassy carbon electrode. Among the samples, Ag/ZnO composite with 4% Ag displayed the highest catalytic activity for p -nitrophenol, and H2O2, but the one with 3% Ag content showed the highest catalytic activity for K2CrO4 reduction.

Two-step fabrication of ZnO nanosheets for high-performance VOCs gas sensor

Sheet-like ZnO nanostructure was successfully synthesized through a simple, cost-effective, and low-temperature sonochemical process followed by an etching treatment in an alkali environment at room temperature without any catalyst, template, or seed layer. The morphology and crystallinity of the products were examined by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The as-prepared nanosheets with high purity were single crystals and well-dispersed. A possible formation mechanism of ZnO nanosheets was proposed based on the experimental results. Micro gas sensor fabricated from the as-prepared ZnO nanosheets were tested to different concentration of volatile organic compounds (VOCs) gases. The gas-sensing results revealed that ZnO nanosheets-based micro sensor exhibited high sensitivity to acetaldehyde and formaldehyde with response time within 10 s and the detection limit down to 50 ppb. The excellent sensing property of ZnO nanosheets is mainly attributed to their large specific area, accessible surface, and less agglomerated configuration.

Facile synthesis of sheet-like ZnO assembly composed of small ZnO particles for highly efficient photocatalysis

We report an effective and green precursor-based route for preparing a sheet-like ZnO assembly composed of small ZnO particles, which showed good photocatalytic performance under UV light irradiation. The process involved first preparing a zinc glycerol precursor and then calcination to transform it into a sheet-like ZnO assembly. The microstructure of the sheet-like ZnO assembly, including the crystallite size, crystallinity degree and Brunauer–Emmett–Teller (BET) specific surface area, could be easily tuned by changing the calcination temperature. With an increase in calcination temperature, the crystallinity degree could be improved along with an increase in the crystallite size. Photocatalytic tests indicated that the as-prepared ZnO sheets showed good activity for photo-degradation of organic dye under UV light irradiation. ZnO-600 (calcination at 600 °C) exhibited the best photocatalytic activity, which was superior to that of P25 TiO2, a commercial benchmark photocatalyst. Furthermore, the sheet-like ZnO assembly could be readily separated from the reaction system by filtration or low-speed centrifugation (or natural sedimentation) after photocatalytic use due to the large particle size of 10 μm, which is favorable for separation and reuse. After 5 recycles, the ZnO-600 did not exhibit an obvious loss in activity, confirming its good activity upon recycling. By combining X-ray photoelectron spectroscopy (XPS) and BET tests, we found that the synergy of the BET surface areas and crystallinity resulted in the good performance of the sheet-like ZnO photocatalyst. In particular, due to the sheet-like structure, the ZnO could effectively combine with Ag particles, resulting in a large increase in the photocatalytic activity by more than 3 time by compounding with a small amount of Ag NPs (about 1% by mass). The present route is promising for the application of ZnO-based photocatalysts due to its easy handling process, good reproducibility, high yield and the good performance of the resulting materials.

Synthesis of large-scale uniform mulberry-like ZnO particles with microwave hydrothermal method and its antibacterial property

Large-scale uniform mulberry-like ZnO particles were successfully synthesized via a fast and simple microwave hydrothermal method. The formation mechanism of mulberry-like ZnO particles was investigated by adding different types of alkalis and different amounts of triethanolamine (TEA). Transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to observe the morphology and crystal structure of the obtained ZnO. The results revealed that the as-prepared ZnO products had an average diameter of about 150nm and polycrystalline wurtzite structure. The existence of TEA was vital for the formation of nanoparticle-assembled mulberry-like ZnO particles. These mulberry-like ZnO particles exhibited stronger antibacterial effects on Candida albicans than did sheet-like and flower-like ZnO.

Hierarchical ZnO microspheres built by sheet-like network: Large-scale synthesis and structurally enhanced catalytic performances

Large-scale novel hierarchical ZnO microspheres were fabricated by a facile precursor procedure in the absence of self-assembled templates, organic additives, or matrices. A field emission scanning electron microscopy (FESEM) image reveals that the ZnO microspheres with diameter of 5–18μm are built by sheet-like ZnO networks with average thickness of 40nm and length of several microns. High resolution transmission electron microscopy (HRTEM) image indicates that the building blocks, sheet-like ZnO networks, are porous mesocrystal terminated with {01−10} crystal planes. A potential application of the ZnO microspheres as a catalyst in the synthesis of 5-substituted 1H-tetrazoles was investigated. It was found that the hierarchical ZnO microsphere catalyst exhibits structure-induced enhancement of catalytic performance and a strong durability.

Hierarchical ZnO microrods: synthesis, structure, optical and photocatalytic properties

Hierarchical ZnO microrods have been prepared by cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal process at low temperature. Sheetlike or fluffy ZnO nanostructures have been developed in a large density on the surface of the microrods. The ZnO cores grow preferentially along [001]; the nanosheets are single crystalline and grow in two dimensions along the [001] and [120] directions. The formation of hierarchical structures has been attributed to the presence of CTAB in the solution, which facilitates the secondary nucleation and growth. The nanosheet-covered hierarchical microrods have been analyzed by Raman and photoluminescence spectroscopy, and they exhibit a blue emission at 465 nm and a strong orange emission at 640 nm. Photocatalytic activities of the products have been examined, and the nanosheet-covered hierarchical microrods display the best activity in photodegradation of phenol due to their unique surface features and high surface area.

Synthesis, characterization and optical properties of sheet-like ZnO

Sheet-like ZnO with regular hexagon shape and uniform diameter has been successfully synthesized through a two-step method without any metal catalyst. First, the sheet-like ZnO precursor was synthesized in a weak alkaline carbamide environment with stirring in a constant temperature water-bath by the homogeneous precipitation method, then sheet-like ZnO was obtained by calcining at 600 °C for 2 h. The structures and optical properties of sheet-like ZnO have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), photoluminescence (PL) and UV–vis-NIR spectrophotometer. The results reveal that the product is highly crystalline with hexagonal wurtzite phase and has appearance of hexagon at (0 0 0 1) plane. The HRTEM images confirm that the individual sheet-like ZnO is single crystal. The PL spectrum exhibits a narrow ultraviolet emission at 397 nm and a broad visible emission centering at 502 nm. The band gap of sheet-like ZnO is about 3.15 eV.

Synthesis and photocatalysis properties of ZnO structures with different morphologies via hydrothermal method

The special flower-like and sheet-like ZnO structures were successfully synthesized by hydrothermal method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The photocatalytic activity of different morphologies of ZnO structures was evaluated by degradating of methyl orange (MO). The photocatalytic degradation process was monitored in terms of decolorization and total organic carbon (TOC) removals. The results indicated that the flower-like ZnO structures were consisted of numerous flower-like aggregates with the size of 2 μm. The sheet-like ZnO nanostructures were obtained by increasing the reaction time. They exhibited higher photodegradation efficiencies under UV light irradiation than flower-like ZnO structures due to the blue shift of the band gap. The photodegradation could be described as the pseudo-first-order kinetics with apparent rate constants ranging from 1.17 × 10 −2 to 3.42 × 10 −2 min −1, which were based on the morphology of the structures. The photodegradation was faster than the mineralization, indicating that the accumulation of by-products were resistant to photocatalytic degradation.

HIERARCHICAL Zn5(OH)6(CO3)2 STRUCTURE ASSEMBLED IN AN AQUEOUS SOLUTION

Hydrothermal technique is demonstrated for achieving Zn 5( OH )6( CO 3)2 microstructure consisting of nanosheets on zinc foils in the presence of formamide. Formamide concentration and reaction temperature have significant influences on the size and shape of hierarchical Zn 5( OH )6( CO 3)2 structures. A self-assembly mechanism is proposed to explain the growth of Zn 5( OH )6( CO 3)2 microstructure, which can be transformed into sheet-like dense ZnO architectures without loss of the shape features by calcining in air.

Studies on the adsorption of RuN 3 dye on sheet-like nanostructured porous ZnO films

The interface between the ZnO and dye directly impacts the dye-sensitized solar cell (DSSC) performance. Nanostructured porous ZnO film was developed by a simple chemical solution process. Scanning electron microscope (SEM) images demonstrated the uniform ZnO films with sheet-like nanostructure. Adsorption studies indicated that the maximum adsorption capacity of RuN 3 dye on the surface of ZnO films was approximately 0.016 mmol RuN 3/g ZnO films. Adsorption studies were conducted at 25 and 40 °C. The results showed that the dye adsorption was significantly influenced by temperatures. Moreover, the problem of the dye aggregation on the ZnO surface was reduced at higher adsorption temperatures. The adsorption chemistry was studied with Raman spectroscopy.

Two Growth Modes of Metal Oxide in the Colloidal Crystal Template Leading to the Formation of Two Different Macroporous Materials

The experimental results show that there are two growth modes of crystalline metal oxide in the colloidal crystal template, which depend on the quality of the colloidal crystal. In well-ordered colloidal crystal templates, the metal oxide growth follows the structure of the colloidal crystal; and high quality three-dimensional ordered macroporous (3DOM) Cu2O or ZnO are formed. In contrast, in less-ordered colloidal crystal templates, metal oxide is grown according to its own capital structure, and cubic-shaped macroporous Cu2O or sheetlike macroporous ZnO are formed. Our method provides an easy and convenient way to prepare three-dimensional ordered macroporous materials or shaped macroporous materials via adjusting the level of ordered arrangement of the colloidal crystal templates.