Well-aligned ZnO Nanorod Arrays Research Articles

Effect of Ti and Au buffer layers on controlling the density and wettability of well-aligned ZnO nanorod arrays grown on different substrates.

ZnO nanorod arrays (NRAs) have potential applications as building blocks for nanoscale electronic, optoelectronic, and sensing applications. The density of ZnO NRAs is controlled by a simple low-cost hydrothermal growth process. It is shown that Ti and Au thin buffer layers can be used to control ZnO NRA density up to an order of magnitude on a wide variety of substrates including bare glass AZO, ZnO seeded AZO, FTO and ITO substrates, respectively. We investigate surface morphological, structural and optical properties of ZnO NRAs by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman, and photoluminescence spectroscopy measurements, respectively. To highlight the importance of NRA density, wettability measurements show large dependence on density and static water contact angles range from as low as ∼23° to as large as ∼142°. These results indicate that the capability to control the density of ZnO NRAs, and thus their wettability, can have additional implications such as in their use in biosensors, field emission, dye-sensitized solar-cells (DSSCs), and photocatalytic activity in addition to potential light trapping effects over wide spectral ranges.

Well-aligned ZnO nanorod array covered with ruthenium layers for alternative counter electrodes in dye-sensitized solar cells

As an alternative material for conventional counter electrodes (CEs), which are usually made from Pt/fluorine doped tin oxide (FTO), well aligned ZnO nanorod arrays have great potential, their extremely high surface area can significantly increase the number of interfacial reaction sites in contact with the electrolyte. However, in order to use ZnO nanorod arrays as CEs, inferior charge collecting efficiency is a crucial obstacle that must be overcome. Here, patterned ZnO nanorod arrays are synthesized using a hydrothermal method and an Ru metal layer is deposited using a radio frequency sputtering process. We found the optimal conditions for ZnO nanorod growth that enable us to form vertically aligned ZnO nanorod arrays on only the ZnO seed layer. The Ru metal layer, coated onto the ZnO nanorod array serves both the role of the catalyst and the charge collecting electrode, its deposition process is controlled in such a way to maximize electrode performance. The results found in this study reveal the combination of Ru metal and the ZnO nanorod array has great potential as a lower cost alternative to Pt and FTO.

UV-Enhanced Field-Emission Performances of Pd-Adsorbed ZnO Nanorods through Photochemical Synthesis

In this work, vertically oriented well-aligned palladium-adsorbed ZnO (PZO) nanorod (NR) arrays were successfully prepared on indium-tin-oxide (ITO) glass substrates via an aqueous solution method with photochemical synthesis. The nanostructures of the PZO NRs were characterized via a field-emission scanning electron microscopy (FE-SEM), a high-resolution transmission electron microscopy (HR-TEM), and the X-ray diffraction (XRD), which revealed that the PZO NRs show a hexagonal wurtzite structure and grew preferentially along the (002) crystal plane. The composition of the adsorbed sample was also confirmed by an X-ray photoelectron spectroscopy and an energy-dispersive X-ray spectroscopy. The PZO NRs exhibited superior field-emission (FE) performance under UV irradiation than in the dark with a low turn-on field value of 5.62 V μm−1 and an enhanced field enhancement factor (β) of 9145.07. It was found that the FE characteristics of the PZO NRs were improved by UV light irradiation, which attributed to generate a large number of electrons.

ZnO nanorod arrays assembled on activated carbon fibers for photocatalytic degradation: Characteristics and synergistic effects

Well-aligned ZnO nanorod arrays were assembled on activated carbon fibers by a stepwise sequence of sol-gel and hydrothermal synthesis methods. These ZnO nanorod arrays on activated carbon fibers having different characteristics such as surface area, rod concentration, aspect ratio and defect level, were applied as catalysts for the photodegradation of an aqueous methylene blue solution. They showed very promising methylene blue adsorbility in the dark (ca. 0.025–0.031 mg methylene blue m−2 catalyst, vs. 0.072 mg methylene blue m−2 activated carbon fibers). Significantly, the defect level of ZnO nanorod arrays has a major effect on the turnover frequency compared to other characteristics. A synergistic effect between activated carbon fibers and ZnO nanocrystals on enhancing turnover frequency was more significant for the well-assembled ZnO nanorod arrays on activated carbon fibers catalysts compared to the mechanically mixed ZnO powder with activated carbon fibers catalyst. Further, turnover frequency for the ZnO nanorod arrays on activated carbon fibers (0.00312 molmethylene blue molZnO−1 h−1) was twice higher than that for the corresponding bare ZnO nanorod arrays, and 3 times higher than that for a commercial ZnO powder. In addition, ZnO nanorod arrays on activated carbon fibers show high degradation (77.5%) and mineralization (55.0%) levels for methylene blue, and also good reusability (or stability) as demonstrated by a sequential 5-time recycle routine. These outstanding features indicate that activated carbon fibers supported ZnO nanorod arrays have significant potential to be used as catalysts for photodegradation.

Self-assembly of single-crystal ZnO nanorod arrays on flexible activated carbon fibers substrates and the superior photocatalytic degradation activity

The synthesis of one-dimensional nanocrystals on flexible substrates has attracted a great attention in the last decade. We here report an integrated approach using a sequential sol-gel and hydrothermal synthesis method to successfully assemble well-aligned single-crystalline wurtzite ZnO nanorod arrays (ZnO NRAs) on activated carbon fibers (ACFs). The ZnO NRAs, with high rod surface area (up to 20 m2 g−1), high aspect ratio (rod length/rod diameter, ca. 20:1) and high defect level (indicated by an extremely sharp blue emission, strong green and yellow emissions), were shown to grow nearly perpendicularly on the ACFs surface. The pre-coating of ZnO seed layers on ACFs surface during sol-gel synthesis is vital for the growth of the ordered ZnO nanorod arrays. The structural and optical properties of ZnO NRAs/ACFs can be adjusted by tuning the synthesis parameters for sol-gel and hydrothermal steps. As compared to the ZnO NRAs grown on the stiff substrates (e.g., silicon wafer, fluorine-doped tin oxide glass, GaN and metal sheets), ZnO NRAs grown on ACFs have very high surface area and intensive blue, green and yellow emissions. The novel ZnO NRAs/ACFs show excellent photocatalytic degradation of methylene blue and robust recyclability as compared to the individual ZnO nano particles (powder, NRs and NRAs).

Vertically aligned ZnO nanorods arrays grown by chemical bath deposition for ultraviolet photodetectors with high response performance

Well-aligned ZnO nanorods (NRs) arrays were grown on ZnO seed layer/ITO substrate using chemical bath deposition (CBD) technique and then fabricating ultraviolet (UV) photodetectors (PDs). The effect of precursor concentration of sols on the properties of ZnO seed layer was investigated, and indicated that the crystallinity and growth orientation of samples depend significantly on precursor concentration. ZnO NRs deposited on seed layer exhibit hexagonal wurtzite structure and found that changing the concentration not only affects seed layer, but also influence the rods growth, making it possible to improve the aspect ratio and crystallinity of ZnO NRs. Moreover, the performance of PDs was further discussed and suggested that the maximum signal-to-noise ratio (SNR) and sensitivity (S) of PDs are 67 dB and 2348, when the concentration is 0.5 mol/L, also the shortest rise time of 0.993 s and fall time of 2.036 s can be obtained in such preparation conditions, which is related to larger aspect ratio and higher crystal quality of ZnO NRs. The fabricated UV PDs with high performance are helpful to its application in ultraviolet astronomy, fire detection, especially in military fields, and also are promising for large-scale production.

Growth of Well-aligned Ag-doped ZnO Nanorods Arrays on FTO Substrate Using Electrochemical Approach: Optical Properties and Photocatalytic Activity

Growth of Well-aligned Ag-doped ZnO Nanorods Arrays on FTO Substrate Using Electrochemical Approach: Optical Properties and Photocatalytic Activity

ZnO nanorod arrays decorated with AgCl nanoparticles as highly efficient visible-light-driven photocatalyst

Well-aligned ZnO nanorod arrays (NRAs) are decorated with AgCl nanoparticles by an environment-friendly and low-cost route to achieve the highly efficient photocatalytic property under visible light. The content of AgCl is varied by controlling the times of successive ionic layer adsorption and reaction (SILAR). The photocatalytic results indicate that all ZnO/AgCl NRAs display outstanding photocatalytic activities as compared to pure ZnO NRAs, and the Ag/Zn molar ratios in ZnO/AgCl composites have an obviously influence on the decomposition of rhodamine B (RhB). ZnO/AgCl NRAs with the Ag/Zn molar ratio of about 3.26% achieve the best photocatalytic activity, which is about 5.4 times higher than that of pristine ZnO NRAs. Furthermore, ZnO/AgCl NRAs show the good stability, and ZnO/AgCl NRAs as photocatalysts are expected to be promising in sewage water treatment.

A free-standing 3D nano-composite photo-electrode—Ag/ZnO nanorods arrays on Ni foam effectively degrade berberine

Berberine is a widely used antibiotic in China, its photocatalytic degradation is not well understood nor its efficient treatment reported. In this study, it is most quickly and efficiently degraded (97.9% under UV and 98.9% under visible light) using a free-standing 3D composite photo-electrode, with well dispersed Ag nanoparticles (Ag NPs) over well-aligned ZnO nanorods arrays (ZnO NAs) on Ni foam (NiF), compared to ZnO NAs/NiF, ZnO powder and P25. The composite photo-electrode was prepared by first directly growing ZnO NAs on NiF hydrothermally, followed by photo-deposition of Ag NPs, without any inactive binders or non-conductive substrates. It was characterized using scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray Diffraction (XRD), ultraviolet–visible spectrophotometry (UV–Vis) and electrochemical analysis (I-t, EIS). The highest activity of Ag NPs/ZnO NAs/NiF in degrading the target pollutant, is due to the synergy of easy pollutants diffusion and fast reaction on active sites, from suppressed electron-hole recombination by Ag NPs/ZnO NAs heterojunctions, extended light absorption by surface plasmon resonance (SPR) of Ag NPs and accelerated electron transport on the conductive macro-porous NiF. The reactive oxidizing species (OH, O2−, h±), degradation intermediates and possible degradation pathways of berberine over Ag NPs/ZnO NAs/NiF were examined respectively. This free-standing whole piece photo-electrode with UV–visible light response, is easy to recycle and assemble, that not only degrades pollutant, but also generates electricity as photo-anode in a photo-catalytic fuel cell reactor using carbon fiber cloth as cathode.

Pulsed Electrodeposition of Co3 O4 Nanocrystals on One-Dimensional ZnO Scaffolds for Enhanced Electrochemical Water Oxidation.

Invited for this month's cover are the collaborative groups of Dr. Yun Hau Ng at University of New South Wales, Australia and Dr. Yiming Tang at South China Normal University, China. The front cover picture shows ultrathin Co3 O4 nanoflakes that are deposited on ZnO nanorods by pulsed electrodeposition. The performance of the nanostructured hybrid Co3 O4 /ZnO anode in electrochemical O2 evolution is better than that of neat Co3 O4 . Well-aligned one-dimensional ZnO nanorod arrays are integrated as a scaffold which functions as a "highway" to facilitate improved charge transfer, while the porosity of the anode material allows the penetration of the electrolyte, thus promoting efficient utilization of the catalytically active species. Read the full text of the article at 10.1002/cplu.201800218.

Surface plasmon-driven photoelectrochemical water splitting of aligned ZnO nanorod arrays decorated with loading-controllable Au nanoparticles

In this paper, we designed a series of well-aligned ZnO nanorod arrays decorated with loading-controllable Au nanoparticles and studied their surface plasmon-driven photoelectrochemical (PEC) water splitting performances. The PEC water splitting ability of Au-ZnO nanorod arrays was evaluated under illumination with λ > 420 nm light. These nanorod arrays show remarkable PEC water splitting performances and achieve the highest photocurrent density of 30 μA cm−2 at 0.8 V versus Ag/AgCl. Furthermore, the PEC performance for heterogenous nanorod arrays can be effectively adjusted by controlling loading amounts of Au nanoparticles. We experimentally demonstrate that the Au-ZnO nanorod arrays show enhanced visible light absorption ability. The superior PEC performance of Au-ZnO nanorod arrays is attributed to the synergistic effects of plasmonic Au nanoparticles, ZnO semiconductor and Schottky barrier built in heterogenous nanorod array. This work provides a facile strategy to manipulate the PEC water splitting activity of Au-ZnO hybrid nanostructures by simply controlling the loading amounts of metallic Au nanoparticles. Furthermore, our research offers a potentially efficient strategy for the design and fabrication of new types of plasmonic-metal/semiconductor hybrid nanostructures with a plasmonic-enhanced PEC water splitting activity under the visible light, which are as valuable photocatalysts for solar-to-chemical/electrical energy conversion.

Growth of Well-Aligned ZnO Nanorod Arrays and Their Application for Photovoltaic Devices

We have fabricated well-aligned ZnO nanorod arrays (ZNRAs) on indium tin oxide-coated glass substrates by a facile chemical bath deposition method. We used field-emission scanning electron microscope, x-ray diffraction and UV–Vis absorption spectroscopy to study the morphology, crystalline structure and optical absorption of the fabricated ZNRAs, respectively. The results showed that ZnO nanorods stood almost perpendicularly on the substrate, were about 30–50 nm in diameter and 800–900 nm in length, and were wurtzite-structured (hexagonal) ZnO. In addition, well-aligned ZNRAs exhibited a weak absorption in the visible region and had an optical band gap value of 3.28 eV. Furthermore, a hybrid ZNRAs/polymer photovoltaic device was made, under 1 sun AM 1.5 illumination (light intensity, ∼100 mW/cm2), and the device showed an open circuit voltage (V oc) of 0.32 V, a short circuit current density (J sc) of 7.67 mA/cm2, and a fill factor (FF) of 0.37, yielding an overall power conversion efficiency of 0.91%. Also, the exciton dissociation and transportation processes of charge carriers in the device under illumination were explained according to its current density–voltage (J–V) curve and the energy level diagram.

Morphology-controllable growth of vertical ZnO nanorod arrays by a polymer soft template method: Growth mechanism and optical properties

Vertically well-aligned ZnO nanorod arrays were synthesized on silicon substrate by a novel polymer soft template method. The ZnO nanorod arrays have been deposited by immersing a silicon substrate into an aqueous solution containing Zn(CH3COO)2·2H2O, Polyvinylpyrrolidone (PVP) and NH3·H2O at 99 °C and then being annealed in oxygen atmosphere. The effects of reaction conditions on the morphology, structure and optical properties of ZnO nanostructures were investigated. The morphology of ZnO nanostructures was demonstrated to be controllable by adjusting the pH values of PVP-Zn2+ complex solution, zinc acetate concentration and growth time, respectively. The nanorod arrays were hexagonal zincite ZnO and the c-axis orientation growth trend of ZnO became more and more obvious with increasing the pH values of PVP-Zn2+ complex solution from 7.5 to 10.5, the zinc acetate concentration from 5 mM to 200 mM, and the growth time from 1 h to 3 h, respectively. The concentration of deep level defects in ZnO was reducing with increasing the pH values of PVP-Zn2+ complex solution, zinc acetate concentration and growth time, respectively. A growth mechanism of vertical ZnO nanorod arrays based on PVP soft template is proposed.

Chemical bath deposition of well-aligned ZnO nanorod arrays on Ag rods for photoelectrocatalytic degradation of rhodamine B

ZnO nanorod arrays (NAs) were prepared by a simple two-step process on the Ag rods. The X-ray diffraction and HRTEM characterizations indicated that ZnO nanorods were hexagonal wurtzite single crystalline structure. Photoelectrocatalytic performances of Ag rods with ZnO NAs (ZnO NAs/Ag rods) were studied systematically for the removal of rhodamine B (RhB). Under the optimal condition, the photoelectrocatalytic efficiency was nearly twice the photocatalytic efficiency, which can be attributed to the more efficient separation of photo-generated carriers. Our results show that ZnO NAs/Ag rods should be a promising photoelectrode for photoelectrocatalysis progress.

Epitaxial growth of ZnO nanorod arrays via a self-assembled microspheres lithography

Through a simple hydrothermal method, well-aligned and periodic honeycomb-like ZnO nanorod arrays were fabricated on a c-plane sapphire with an aluminum-doped ZnO (AZO) seed layer. Vertical and highly ordered ZnO nanostructures with the <0002> orientation were synthesized by employing a self-assembled monolayer of polystyrene (PS) microspheres as a mask. The optimal growth conditions allowed the growth of only one rod in the confined space between the microspheres. A ϕ-scan exhibited six-fold symmetry, which indicates a favorable epitaxial relationship between the ZnO nanorods, seed layer, and c-plane sapphire substrate. The epitaxial relation is as follows: [0001]ZnO∥[0001]AZO∥[0001]c-planesapphire. These results indicate that the AZO seed layer acts as a buffer layer that can relax the strain between ZnO and c-plane sapphire generated by the large lattice mismatch of 18%. The size of the resulting ZnO nanorods of diameter 20–90nm could be tuned by varying the concentration of the solution, pH, and duration of reaction. The large aspect ratio of the ZnO nanorod arrays can serve as a template for high-surface-area applications.

Effect of synthesis conditions on the growth of various ZnO nanostructures and corresponding morphology-dependent photocatalytic activities

Well-aligned ZnO nanorod arrays have been prepared by using seed-assisted hydrothermal method, in which the c-axis oriented ZnO films prepared by a soft-chemical were used as the seed layers on quartz glass. The epitaxial growth mechanisms and corresponding morphology effect of samples are discussed. The results show that the morphology of ZnO nanorod arrays is closely related to the hydrothermal temperature, pH value and initial concentration of Zn source in precursor solution. The as-prepared samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer-Emmett-Teller (BET), Raman spectroscopy, photoluminescence (PL) spectra and UV–vis spectra. The well-aligned ZnO nanorod arrays exhibit improved photocatalytic degradation with Rhodamine 6G (R6G) solution under UV radiation, according with the UV–vis spectra investigation and photocatalytic improvement speculation. Noteworthy, the photocatalytic properties of well-aligned ZnO nanorod arrays have obviously improved comparing with other ZnO samples without proper alignment. The oxygen vacancies suppressed recombination process of photon induced electrons and holes, as the oxygen vacancy trapped the charge carriers.

Synthesis of well-aligned ZnO nanorod arrays from mixed sulfide-oxide lead and zinc ore

A novel process of recovery of zinc from mixed sulfide-oxide lead and zinc ore was presented in this paper. ZnO nanorod arrays (ZNRAs) on FTO substrate pre-coated with a layer of ZnO seeds was synthesized successfully from the mixed ore via the oxidative ammoniacal leaching process and a two-step process including precipitation and hydrothermal synthesis. The characterization results from the XRD, SEM and UV–vis spectrophotometer analysis showed that the as-prepared ZNRAs was well-aligned, large-scale, perpendicular to the FTO substrate and had a reduced band gap energy of 3.03eV. XPS analysis indicated that the grown ZNRAs were doped by a small quantity of carbon and did not contain any other impurities particularly Fe and Pb. The total zinc extraction can reach 92.4% after the oxidative ammoniacal leaching process and the precipitation process. The elimination of conventional purification process in zinc production was achieved due to the efficient and selective oxidative ammoniacal leaching process.

Continuous wet-process growth of ZnO nanoarrays for wire-shaped photoanode of dye-sensitized solar cell

Well-aligned ZnO nanorod arrays have been grown on metal-plated polymer fiber via a mild wet process in a newly-designed continuous reactor, aiming to provide wire-shaped photoanodes for wearable dye-sensitized solar cells. The growth conditions were systematically optimized with the help of computational flow-field simulation. The flow field in the reactor will not only affect the morphology of the ZnO nanorod⧹nanowire but also affect the pattern distribution of nanoarray on the electrode surface. Unlike the sectional structure from the traditional batch-type reactor, ZnO nanorods with finely-controlled length and uniform morphology could be grown from the continuous reactor. After optimization, the wire-shaped ZnO-type photoanode grown from the continuous reactor exhibited better photovoltaic performance than that from the traditional batch-type reactor.

Obtaining a Well-Aligned ZnO Nanotube Array Using the Hydrothermal Growth Method / Labi Sakārtotu Zno Nanocauruļu Kopu Iegūšana, Izmantojot Hidrotermālo Metodi

Abstract Optimal growing parameters have been found using the hydrothermal method to obtain well-aligned vertical ZnO nanorod and nanotube arrays. The influence of different growing factors (such as temperature, growing solution concentration, method of obtaining seed layer and condition) on nanotube morphology and size is described in the paper. Well-structured ZnO nanotubes have been obtained by using a selfselective etching method with lowering temperatures of growth during the hydrothermal process. It is shown that the optical properties of the nanostructure arrays obtained are sensitive to the medium in which they are placed, which is why they can be used as sensors for pure substance detection and in different solutions for impurity determination.

Controllable Growth of Highly Oriented ZnO Nanorod Arrays on Copper by a Two-Step Route

Highly oriented and well-aligned ZnO nanorod arrays were synthesized by low-temperature solution phase method on copper substrate under different conditions. Results illustrated that dense ZnO nanorods were vertically and uniformly distributed on the substrate. The effects of precursor concentration, growth temperature and time on the morphologies of nanorod arrays were investigated systematically. It is demonstrated that the controllable growth of well-aligned ZnO nanorods can be realized by readily adjusting the preparation parameters. The high quality ZnO nanorod arrays could be achieved via the chemical approach at low temperature.