1D ZnO Nanorods Research Articles

Synthesis of novel AuPd nanoparticles decorated one-dimensional ZnO nanorod arrays with enhanced photoelectrochemical water splitting activity

The vertically aligned one-dimensional (1D) ZnO nanorod arrays decorated with AuPd alloy nanoparticles have been synthesized with ZnO nanorod arrays as template via a mild hydrothermal method. In this work, the as-prepared AuPd/ZnO nanorod arrays demonstrated high light-harvesting efficiency. The microstructures, morphologies and chemical properties of the obtained AuPd/ZnO composite photocatalyst were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–vis diffuse reflectance spectra (DRS) and X-ray photoelectron spectroscopy (XPS). The photoelectrochemical (PEC) performances of as-obtained AuPd/ZnO nanorod arrays were examined, and the photocurrent density was up to 0.98mAcm−2 at 0.787V versus Ag/AgCl, which was about 2.4 times higher than the pure ZnO sample. A possible photocatalytic mechanism of the AuPd/ZnO hybrid nanostructures under the simulated sunlight irradiation was proposed to guide further improvement of other desirable materials. According to the above experiment results, it can be clearly found that AuPd/ZnO composite nanorod arrays showed excellent PEC performance and had promising applications in the utilization of solar energy.

Constructing n-ZnO@Au heterogeneous nanorod arrays on p-Si substrate as efficient photocathode for water splitting

Developing ingenious heterostructure photoelectrodes in photoelectrochemical (PEC) cells to both harvest more solar photons and steer desired charge separation flow is a prerequisite challenge for PEC water splitting. Herein a hierarchical p-Si/n-ZnO@Au heterostructure was constructed via large-area growth of one-dimensional (1D) ZnO nanorod arrays (NRAs) on p-Si substrate followed by decorating with Au nanoparticles (NPs), which exhibited remarkably improved photocathode activity for PEC water splitting relative to the bare Si and Si/ZnO NRAs photocathodes. In addition to structural superiorities of 1D NRAs, a series of dynamic contributions from complementary band-gap structure, p–n heterojunctions and Au plasmon towards photon harvesting and charge separation were demonstrated to ensure a well-steered collection of photoelectrons at the exposed ZnO nanorods and Au NPs, enabling substantially improved photocathode performance.

Atomic Layer Deposition on Block Copolymer Membranes with Gyroidal Nanopores Toward Periodically Nanostructured Vapor Sensors: Nanotubes versus Nanorods

3D gyroidal networks of ZnO nanorods or nanotubes are synthesized by replicating block copolymer (BCP) templates with gyroidal nanopores via atomic layer deposition (ALD). The generation of 3D ZnO nanorods or nanotubes depends on the thicknesses of deposited ZnO layers, which can be easily and precisely controlled by adjusting ALD cycles. The as‐obtained ZnO nanostructures have porosities as high as 77% for gyroidal nanorods and 86% for gyroidal nanotubes due to their unique interconnected structures and rough surfaces. Both gyroidal ZnO nanostructures are used as vapor sensors to detect ethanol with different concentrations. Gyroidal ZnO nanotubes show higher ethanol sensitivity than nanorods because of the inherently interconnected nanotubes and larger porosity. Gyroidal ZnO nanotubes can also act as formaldehyde sensors with the sensitivity as high as 42 to 50 ppm formaldehyde, which is much higher than previously reported sensors based on ZnO nanorods or nanotubes.

Effects of multilayer buffer on structural properties of ZnO nanostructures grown using a solvothermal method

This paper reports on a solvothermal method used in the fabrication of vertically aligned two-dimensional (2D) ZnO nanowall networks and one-dimensional (1D) ZnO nanorods with overlapping structures. The introduction of an Al thin film as a doping source was shown to alter the morphology from rods to walls. The proposed multilayer buffer results in the formation of two types of nanostructure (nanowalls and rods) and also increased the length to which the nanorods grow at the same time. Analysis based on transmission electron microscopy (TEM) and selected area electron diffraction (SAED) led us to formulate a possible growth mechanism and elucidate the optical properties of the ZnO nanostructures.

Controlled assembly of one-dimensional MoO3@Au hybrid nanostructures as SERS substrates for sensitive melamine detection

A new, feasible, and highly efficient platform was developed using self-assembly of (3-aminopropyl) diethoxymethylsilane (ATES) to create metallic oxide-based noble metal nanoparticle hybrid materials. The ex situ approach for fabricating 1D MoO3-nanowires (MoO3-NWs) or ZnO-nanorods (ZnO-NRs) @Au-nanoparticles (Au-NPs) hybrid surface-enhanced Raman scattering (SERS) substrates not only provides a simple route for the decoration of noble metal nanoparticle on metallic oxide nanomaterials, but also realizes the controllable assembly/co-assembly of pre-synthesized nanoparticles with distinctively different sizes, compositions, shapes, and properties. Control over the self-assembly synthesis for morphology and SERS activity was demonstrated by several parameters: (i) coupling agent of ATES, (ii) ATES content, (iii) Au-NPs content, (iv) Au-NP sizes, and (v) other metallic oxide such as ZnO-NRs. The finite difference time domain (FDTD) method was employed to visualize the enhancement mechanism distribution of the hybrid substrate. Furthermore, the optimized MoO3-NW@Au-NPs SERS substrate manifests high SERS sensitivity to melamine with a limit of detection (LOD) of 0.1 ppb (0.08 nM) and excellent uniformity (RSD = 9.26%). The LOD was much lower than the maximal residue limit (MRL) of 2.5 ppm in food prescribed by the US Food and Drug Administration (FDA).

A facile and green strategy for the synthesis of 1-dimensional luminescent ZnO nanorods and their reduction behavior for aromatic nitro-compounds

This article illustrates a facile microwave assisted synthesis of 1D ZnO nanorods using lauric acid.

ZnO/ZnS heterostructured nanorod arrays and their efficient photocatalytic hydrogen evolution.

Semiconducting heterostructures have been widely applied in photocatalytic hydrogen evolution due to their variable band gaps and high energy conversion efficiency. As typical semiconducting heterostructures, ZnO/ZnS heterostructured nanorod arrays (HNRAs) have been obtained through a simple anion-exchange process in this work. Structural characterization indicates that the heterostructured nanorods (HNRs) are all composed of hexagonal wurtzite ZnO core and cubic zinc-blende ZnS shell. As expected, the as-obtained one-dimensional heterostructures not only lower the energy barrier but also enhance the separation ability of photogenerated carriers in photocatalytic hydrogen evolution. Through comparisons, it is found that 1D ZnO/ZnS HNRAs exhibit much better performance in photocatalytic hydrogen evolution than 1D ZnO nanorod arrays (NRAs) and 1D ZnS NRAs. The maximum H2 production is 19.2 mmol h(-1) for 0.05 g catalyst under solar-simulated light irradiation at 25 °C and the corresponding quantum efficiency is 13.9 %, which goes beyond the economical threshold of photocatalytic hydrogen evolution technology.

Zinc oxide–nickel cermet selective coatings obtained by sequential electrodeposition

The investigation of pulse electrodepositing modes influence on crystal structure, morphology and optical properties of ZnO has revealed the conditions in which quasi-one-dimensional (1D) ZnO nanorod arrays are formed as separate nanorods. Due to a sufficiently high resistance of zinc oxide, the electrodeposition of nickel on the fluorine doped tin oxide (FTO)/ZnO surfaces carried out in space between the ZnO nanorods. An incomplete filling of the gaps between nanorods by the nickel nanoparticles through subsequent Ni electrodeposition ensured the creation of ZnO–Ni graded cermets. The cermets, in which electrochemical filling of the spaces between ZnO nanorods by Ni, was performed in the pulse mode. It provided higher absorption of visible and near IR light. It was shown that the manufactured ZnO–Ni graded cermets have high light absorption combined with comparatively low thermal losses, so these cermets are promising cheap and affordable selective coatings for solar heat collectors.

Aspect-Ratio Dependent Electron Transport and Recombination in Dye-Sensitized Solar Cells fabricated with one-dimensional ZnO nanostructures

Though one-dimensional (1-D) ZnO nanrods are promising transport electron transport material in the photoanode of Dye Sensitized Solar Cells (DSSC), 1-D ZnO nanorod based DSSCs exhibit poor energy conversion efficiencies. In this study, DSSCs were fabricated with 1-D ZnO nanorods having different aspect ratio and the dependence of solar cell performance on aspect ratio of ZnO nanorods was investigated. Photoanodes fabricated with different 1-D ZnO nanorods having aspect ratios of 4.4, 5.4, 5.8, 6.8 and 7.6 showed increasing solar cell performance with the increase of aspect ratio where 2.1 and 4.7% light conversion efficiencies were observed respectively for the lowest and highest aspect ratio of 1-D ZnO nanostructures. We study the electrical and operational differences between DSSC made with ZnO nanostructures with different aspect ratio. Electrochemical impedance spectroscopy (EIS) is used to quantify the aspect ratio depended electron transport properties, charge recombination, life-time and charge diffusion lengths of excited electrons in 1D ZnO nanorods and electron transport properties are correlated to the observed cell performance. In addition, effect of aspect ratio of ZnO nanorods on dye loading amount and light scattering properties were also investigated.

Hierarchically CdS Decorated 1D ZnO Nanorods‐2D Graphene Hybrids: Low Temperature Synthesis and Enhanced Photocatalytic Performance

A simple, low‐temperature synthesis approach is reported for planting CdS‐sensitized 1D ZnO nanorod arrays on the 2D graphene (GR) sheet to obtain the ternary hierarchical nanostructures, during which graphene oxide (GO) as the precursor of GR acts as a flexible substrate for the formation of ZnO nanorod arrays. The hierarchical CdS‐1D ZnO‐2D GR hybrids can serve as an efficient visible‐light‐driven photocatalyst for selective organic transformations. The fast electron transport of 1D ZnO nanorods, the well‐known electronic conductivity of 2D GR, the intense visible‐light absorption of CdS, the unique hierarchical structure, and the matched energy levels of CdS, ZnO and GR efficiently boost the photogenerated charge carriers separation and transfer across the interfacial domain of hierarchical CdS‐1D ZnO‐2D GR hybrids under visible light irradiation via three‐level electron transfer process. Furthermore, the superior reusability of ternary hybrids is achieved by controlling the reaction parameters, i.e., using visible light irradiation and holes scavenger to prevent ZnO and CdS from photocorrosion. This work demonstrates a facile way of fabricating hierarchical CdS‐1D ZnO‐2D GR hybrids in a controlled manner and highlights a promising scope of adopting integrative photosensitization and co‐catalyst strategy to design more efficient semiconductor‐based composite photocatalysts toward solar energy capture and conversion.

Electrochemical cortisol immunosensors based on sonochemically synthesized zinc oxide 1D nanorods and 2D nanoflakes

We report on label free, highly sensitive and selective electrochemical immunosensors based on one-dimensional 1D ZnO nanorods (ZnO-NRs) and two-dimensional 2D ZnO nanoflakes (ZnO-NFs) which were synthesized on Au-coated substrates using simple one step sonochemical approach. Selective detection of cortisol using cyclic voltammetry (CV) is achieved by immobilizing anti-cortisol antibody (Anti-Cab) on the ZnO nanostructures (NSs). 1D ZnO-NRs and 2D ZnO-NFs provide unique sensing advantages over bulk materials. While 1D-NSs boast a high surface area to volume ratio, 2D-NSs with large area in polarized (0001) plane and high surface charge density could promote higher Anti-Cab loading and thus better sensing performance. Beside large surface area, ZnO-NSs also exhibit higher chemical stability, high catalytic activity, and biocompatibility. TEM studies showed that both ZnO-NSs are single crystalline oriented in (0001) plane. The measured sensing parameters are in the physiological range with a sensitivity of 11.86µA/M exhibited by ZnO-NRs and 7.74µA/M by ZnO-NFs with the lowest detection limit of 1pM which is 100 times better than conventional enzyme-linked immunosorbant immunoassay (ELISA). ZnO-NSs based cortisol immunosensors were tested on human saliva samples and the performance were validated with conventional (ELISA) method which exhibits a remarkable correlation. The developed sensors can be integrated with microfluidic system and miniaturized potentiostat for point-of-care cortisol detection and such developed protocol can be used in personalized health monitoring/diagnostic.

CdS sensitized 3D hierarchical TiO2/ZnO heterostructure for efficient solar energy conversion.

For conventional dye or quantum dot sensitized solar cells, which are fabricated using mesoporous films, the inefficient electron transport due to defects such as grain boundaries and surface traps is a major drawback. To simultaneously increase the carrier transport efficiency as well as the surface area, optimal-assembling of hierarchical nanostructures is an attractive approach. Here, a three dimensional (3D) hierarchical heterostructure, consisting of CdS sensitized one dimensional (1D) ZnO nanorods deposited on two dimensional (2D) TiO2 (001) nanosheet, is prepared via a solution-process method. Such heterstructure exhibits significantly enhanced photoelectric and photocatalytic H2 evolution performance compared with CdS sensitized 1D ZnO nanorods/1D TiO2 nanorods photoanode, as a result of the more efficient light harvesting over the entire visible light spectrum and the effective electron transport through a highly connected 3D network.

Preparation of 1D or 3D Nano ZnO Crystals in High-Viscosity Solvent

1D or 3D nanoZnO crystals were prepared in diethylene glycol (DEG) via solvothermal process without surfactants at 160oC. Zinc acetate dihydrate was elected as zinc source, while water, sodium hydroxide, or ammonia solution was respectively as assistant agents. The morphologies of the products were characterized by field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED). With a certain content of water or sodium hydroxide, 1D ZnO nanorods were gained, having diameters of 20-90 nm and lengths of 0.04-1.8μm. With a certain content of ammonia solution, 3D shiitake-like ZnO hierarchical structures were gained. The pileus of shiitake structure composes of nanorods with diameters of 35-40 nm, while the stipe composes of one hexagonal rod with diameters of 250-350nm, or many hexagonal rods with diameters of 100-200nm. The morphology and size could be regulated by changing the amount of water, NaOH, or ammonia solution. Solvothermal process in high-viscosity solvent may provide a facile method for preparing nanomaterials.

Preparation and enhanced photocatalytic performance of one‐dimensional ZnO nanorods

One dimensional (1D) ZnO nanorods were successfully synthesized via a facile solution route by refluxing their acetate precursors in diethylene glycol medium at 160°C. The as‐prepared ZnO nanorods were characterized by field emission scanning electron microscopy, X‐ray diffraction, and Fourier transform infrared spectroscopy. Experimental results demonstrated that the resultant products showed a 1D rod‐like hexagonal wurtzite crystal structure with diameters of about 5 nm and lengths of up to 100–200 nm. A possible growth mechanism of ZnO nanorods was tentatively proposed. Photocatalytic measurements demonstrated that the as‐prepared ZnO nanorods showed higher photocatalytic activities than the commercial photocatalyst TiO2 P25 nanoparticles. In addition, the effect of solution pH values and initial solution concentrations on the photocatalytic activities of as‐prepared ZnO nanorods was also evaluated. © 2014 American Institute of Chemical Engineers Environ Prog, 34: 74–80, 2015

Synthesis of ZnO nanorod–nanosheet composite via facile hydrothermal method and their photocatalytic activities under visible-light irradiation

ZnO composite films consisting of ZnO nanorods and nanosheets were prepared by low-temperature hydrothermal processing at 80°C on seeded glass substrates. The seed layer was coated on glass substrates by sol–gel dip-coating and pre-heated at 300°C for 10min prior to hydrothermal growth. The size of the grain formed after pre-heat treatment was ~40nm. A preferred orientation seed layer at the c-axis was obtained, which promoted vertical growth of the ZnO nanorod arrays and formation of the ZnO nanosheets. X-ray diffraction patterns and high-resolution transmission electron microscope (HR-TEM) images confirmed that the ZnO nanorods and nanosheets consist of single crystalline and polycrystalline structures, respectively. Room temperature photoluminescence spectra of the ZnO nanorod–nanosheet composite films exhibited band-edge ultraviolet (UV) and visible emission (blue and green) indicating the formation of ZnO crystals with good crystallinity and are supported by Raman scattering results. The formation of one-dimensional (1D) ZnO nanorod arrays and two-dimensional (2D) ZnO nanosheet films using seeded substrates in a single low-temperature hydrothermal step would be beneficial for realization of device applications that utilize substrates with limited temperature stability. The ZnO nanorods and nanosheets composite structure demonstrated higher photocatalytic activity during degradation of aqueous methylene blue under visible-light irradiation.

A highly sensitive UV sensor composed of 2D NiO nanosheets and 1D ZnO nanorods fabricated by a hydrothermal process

A highly sensitive UV sensor was fabricated using a low-cost, low temperature, and scalable solution-based process. The p–n heterojunction sensor composed of p-type two dimensional (2D) NiO nanosheets (NS) and n-type one dimensional (1D) ZnO nanorods (NRs) exhibited a highly increased UV response compared to 2D NiO NS or 1D ZnO NR alone. Photoluminescence (PL) spectra revealed a decrease of the trap-state emission and recombination of excitons in the NiO NS/ZnO NR structure, which could be responsible for the enhanced UV response.

3D-ZnO Nanorods Photoelectrodes for Quantum-Dot Sensitized Solar Cells

In this study, the three dimensional ZnO (3D-ZnO) nanorods were synthesized by a simple chemical solution method, which were used as photoelectrodes, and CdS QDs were deposited on the surface of the 3D-ZnO nanorods to act a light absorber by using the successive ionic layer adsorption and reaction (SILAR) method. The photovoltaic performances of the semiconductor quantum dots sensitized solar cells based on CdS QDs/3D-ZnO photoelectrodes were investigated. A maximum 5.06 mA/cm2short circuit current density and 1.03% conversion efficiency under one sun illumination has been achieved. These results demonstrate that the CdS QDs-sensitized 3D-ZnO nanorods photoelectrode has a potential application in solar cells.

Controlled Synthesis and Gas-Sensing Properties of One Dimensional Zinc Oxide Architectures

One-dimensional (1D) ZnO nanorods with different shapes and high aspect ratio were successfully synthesized using a cetyltrimethylammonium bromide (CTAB)-assisted or sodium dodecyl sulfate (SDS)-assisted hydrothermal process at 90°C for 5h. The surface morphology and structure of nanocrystals were characterized by FE-SEM and XRD. Experimental results showed that the typical morphology of ZnO crystals grown with additive of CTAB was pencil-like rods, while the ZnO crystals grown with SDS showed needle-like rods. The gas sensors had been fabricated using 1D ZnO powders to examine the response towards 40ppm NO2 in the range of operating temperature from 150 oC to 450 oC. Compared with needle-like ZnO crystals, the NO2 gas sensor based on pencil-like ZnO nanostructure had better selectivity at the same gas concentration.

Highly sensitive NO2 sensors based on local p–n heterojunctions composed of 0D CuO nanoparticles and 1D ZnO nanorods

AbstractA novel and highly sensitive p–n heterojunction sensor composed of zero‐dimensional (0D) CuO nanoparticles (NPs) and one‐dimensional (1D) ZnO nanorods (NRs) was fabricated using a solution‐based process. The structures were characterized with scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS). The formation of electron depletion layers in the p‐CuO and n‐ZnO is believed to increase the adsorption of NO2, resulting in a 6‐fold response improvement and a 13‐fold increased sensitivity compared to ZnO NRs alone. We believe that this type of heterojunction device can be applied to many different sensing applications.

Chemically grown vertically aligned 1D ZnO nanorods with CdS coating for efficient quantum dot sensitized solar cells (QDSSC): a controlled synthesis route

In the present article, vertically aligned ZnO nanorod arrays were synthesized by an aqueous chemical growth (ACG) route on a fluoride doped tin oxide (FTO) coated glass substrate. These nanorods were further sensitized with cadmium sulfide (CdS) quantum dots (QDs) by a successive ionic layer adsorption and reaction (SILAR) technique. The synthesized CdS coated ZnO nanorods were characterized for their structural and morphological properties with X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microscopy (FESEM). Finally, prepared CdS coated 1D ZnO photoelectrodes were tested for their photoelectrochemical performance. Our results show that the sample deposited after 40 SILAR cycles shows 5.61 mA cm(-2) short current density (JSC) with η = 1.61% power conversion efficiency.