ZnO Nanowire Arrays Research Articles

Ni nanoparticles‐loaded ZnO nanowire as an efficient and stable catalyst for reduction of 4‐nitrophenol

AbstractAn amorphous Ni nanoparticles‐loaded ZnO nanowire array is controllably constructed on stainless steel mesh through combined electrodeposition and hydrothermal reaction. Its nano‐arrayed structure not only provides a platform to achieve stable and good dispersion of Ni nanoparticles, but also helps improve their ability to adsorb 4‐nitrophenolate ions and to capture hydrogen radicals, thereby accelerating the hydrogen transfer from metal hydride complex to 4‐nitrophenol. Benefiting from the abovementioned unique features, it outperforms most Ni‐based catalysts. While a 30‐s re‐electrodeposition of Ni can provide it extra 150 min of high catalytic activity towards the reduction of waste 4‐nitrophenol to valuable 4‐aminophenol, further demonstrating its outstanding reusability. The highly general methodology reported here paves the way to economically and effectively synthesize various other metal nanoparticles‐loaded ZnO nanowire arrays on different conductive substrates, which not only enrich the nanowire‐arrayed catalysts, but also significantly promote their practical utilizations in a wide range of environment‐related fields.image

Preparation and Properties of Nano ZnO Dye Sensitized Solar Cells on (Titanium) Substrates

Nowadays, the development of science and technology has been increasing demand for energy. Energy problem has become a bottleneck to restrict the development of international social economy. People pay more and more attention to the development and research of renewable resources. Solar energy is a kind of renewable resource with great potential and no pollution. The commercialized solar cells are mainly silicon solar cells, among which the conversion efficiency of single silicon solar cells is the highest, but the cost of silicon solar cells is high. Therefore, people have been exploring new materials, among which titanium based nano ZnO dye sensitized solar cells have been paid more and more attention by scientists at home and abroad. Based on this, the preparation and performance of nano ZnO dye sensitized solar cells based on titanium are studied. In this paper, the optical anode materials of DSSC are used as the research objects. Three-dimensional ZnO nanoband, one-dimensional graded ZnO nanotube array and one-dimensional sub grade ZnO nanowire array are prepared by anodizing and hydrothermal synthesis. The photovoltaic properties of the three materials are studied. One dimensional graded ZnO, nanotube array films were prepared by two-step hydrothermal synthesis. One dimensional hierarchical ZnO nanowire array is obtained by two-step hydrothermal synthesis. The results show that DSSC is assembled by one-dimensional graded ZnO nanotube array film, and the photoelectric conversion efficiency is 5.1%. Compared with one-dimensional ZnO nanowire array, the efficiency is improved by nearly 90%. The ZnO nanowire of the sub grade is used instead of DSSC The efficiency of photoelectric conversion is only 4% in the photoanode, which is higher than that of the smooth ZnO nanowire photocell.

ZnO nanowire arrays with in situ sequentially self-assembled vertically oriented CdS nanosheets as superior photoanodes for photoelectrochemical water splitting

High-density CdS nanosheets were vertically self-assembled on ZnO nanowire arrays, forming a photoanode with superior performance toward water splitting.

Photoelectrochemical Immunosensor for Archaeological Silk Microtrace Detection Based on Tailored Monoclonal Antibody and ZnO Nanowires Array

Photoelectrochemical Immunosensor for Archaeological Silk Microtrace Detection Based on Tailored Monoclonal Antibody and ZnO Nanowires Array

Study on the optoelectronic properties of Zn and Mg doped CuGaO2 nanoplates

In this study, significant optoelectronic performance boost was observed after Mg and Zn doping of hexagonal CuGaO2 (CGO) nanoplates (NPs) by the hydrothermal method. Details effects of dopant are studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), absorption spectra, and photoluminescence (PL)spectrum. There is a sharp peak at 700 nm in the PL spectrum of pure CGO NPs ascribed to the intrinsic defect caused by Cu vacancy (VCu) and the peak increases dramatically in intensity as elements doping. To deeply understand the enhancement mechanism in PL intensity of Zn-doped CGO (ZCGO) NPs and Mg-doped CGO (MCGO) NPs, the band diagram and radiation transition of divalent ions doped CGO NPs are investigated in detail. These results reveal that the divalent element doping (ZCGO especially) could increase the carrier concentration of CGO material effectively and form stable and high-intensity PL emission. In addition, photodetection performance of pure CGO NPs and doping CGO NPs has been demonstrated, which could be enhanced by constructing non-planar heterojunction of nanoplate and ZnO nanowire arrays. And Zn doping has a significantly better effect than Mg doping in absorption, photoluminescence and ultraviolet (UV) detection. The findings can play an important role in the regard of optoelectronic performance enhancement of CGO NPs, which common used in optoelectronic devices such as red light emitters and ultraviolet (UV) detectors.

ZnO nanowires for photoelectric converter applications

This work is focused on the creation and study of photosensitive structures based on zinc oxide nanofibers, which are promising for solar energy. Zinc oxide nanowires were obtained on the porous zinc selenide surface. The porous substrate was obtained by electrochemical etching of a low-resistance n-ZnSe plate (110) with a polished surface. Nanowires were deposited by radical-beam epitaxy. The annealing temperature was varied from 400° C to 500° C. The oxygen radical flux was 1.5∙1017 cm-2s-1. The process duration was 50 minutes. According to the scanning electron microscopy results, the nanowires length reaches 10 μm, the nanowires diameter is ~1 μm. The predominant X-ray diffraction reflex at 2θ=34.44° indicates the polycrystalline nature of the manufactured ZnO coatings with a wurtzite-type hexagonal lattice. The study of nanowires ZnO luminescence at room temperature contains an ultraviolet peak around 385 nm. This peak is related to the zinc oxide edge luminescence. Based on the fabricated structure, the design of the photoconverter was developed. The upper contact of the fabricated photoelectric converter was created by vacuum thermal sputtering of aluminum through a mask. The deposition was carried out at a substrate temperature of 200° C. Ohmic contacts were made using conductive silver paste. The reverse ohmic contact was formed by applying Al paste to the entire reverse side of the surface. The upper layer of the structure is an array of ZnO nanowires. The active base layer is ZnSe. The light volt-ampere characteristics of the obtained structure were measured in the AM 1.5 illumination mode. No-load voltage Uxx, short-circuit current Isc and the fill factor of the current-voltage characteristic FF of the solar element were measured. The efficiency of the manufactured photoconverter was 13.7 %.

Fully Vacuum-Sealed Diode-Structure Addressable ZnO Nanowire Cold Cathode Flat-Panel X-ray Source: Fabrication and Imaging Application.

A fully vacuum-sealed addressable flat-panel X-ray source based on ZnO nanowire field emitter arrays (FEAs) was fabricated. The device has a diode structure composed of cathode panel and anode panel. ZnO nanowire cold cathodes were prepared on strip electrodes on a cathode panel and Mo thin film strips were prepared on an anode panel acting as the target. Localized X-ray emission was realized by cross-addressing of cathode and anode electrodes. A radiation dose rate of 10.8 μGy/s was recorded at the anode voltage of 32 kV. The X-ray imaging of objects using different addressing scheme was obtained and the imaging results were analyzed. The results demonstrated the feasibility of achieving addressable flat-panel X-ray source using diode-structure for advanced X-ray imaging.

TiO2-Coated ZnO Nanowire Arrays: A Photocatalyst with Enhanced Chemical Corrosion Resistance

Photocatalysis is proven to be the most efficient and environmentally friendly method for the degradation of organic pollutants in water purification. To meet the requirement of large-scale water treatment, there are two important points: One is the lifetime and chemical stability of the photocatalyst material, especially in the complex and harsh aqueous conditions. The other is the ease of synthesis of such photocatalysts with specific nano-morphology. In this work, two common photocatalyst materials, zinc oxide (ZnO) and titanium dioxide (TiO2), are selected to form more sustainable photocatalysts with high chemical stability. This involves the combination of both TiO2 and ZnO in a two-step simple synthesis method. It appears advantageous to exploit the conformal deposition of atomic layer deposition (ALD) to achieve nanometer-thick TiO2 coating on ZnO nanowires (NWs) with a high aspect ratio, which are firmly anchored to a substrate and exhibit a large specific surface area. The high chemical stability of the ALD TiO2 coating has been investigated in detail and proven to be effective under both strong acid and strong alkaline aqueous solutions. In addition, photocatalysis experiments with organic dyes show that via this simple two-step synthesis method, the produced ZnO/TiO2 tandem photocatalysts does indeed exhibit improved chemical stability in a harsh environment, while allowing efficient photodegradation.

A low-dimensional hybrid p-i-n heterojunction neuromorphic transistor with ultra-high UV sensitivity and immediate switchable plasticity

We demonstrate a photoelectric neuromorphic transistor (PENT), consisting of a hybrid p-i-n heterojunction channel of vertically phase-separated 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) /poly(methyl methacrylate) (PMMA) as a two-dimensional (2D) sheath and highly-aligned array of long continuous zinc oxide (ZnO) nanowires (NWs) as a quasi-one dimensional (Q1D) core. This is the first report of a hybrid p-i-n heterojunction being developed on a NW-based PENT. The device integrates both optical sensing and electrical processing functionalities. In optical sensing, the device could respond to ultraviolet (UV) light with low intensity down to microwatts per square centimeter, representing so far the most UV-sensitive nonvolatile optoelectronic neural device. In electrical-processing, the PENT demonstrates a mechanically immediate switchable plasticity between short-term and long-term by altering charge carriers in the conductive channel; this emulates the selective release of different neurotransmitters, i.e. dopamine and noradrenaline, from a same axon, for pain-avoiding and pleasure-inducing patterns of Skinner Box for the first time. Furthermore, a new strategy for gesture recognition was developed. This approach can be applied to control and design multipurpose neuromorphic systems by combining brain-like processing and artificial sensory nerves.

Hydrothermal growth optimization of vertically aligned ZnO nanowire arrays and their dye-sensitized solar cell performance under air/oxygen environments

In this work, the hydrothermal growth parameters of vertically aligned ZnO nanowire arrays on FTO substrates were optimized for best surface coverage and minimal stacking and entanglement between nanowires for dye-sensitized solar cell (DSSC) application. The concentration of seed layer solution was found to be essential in reducing the stacking effect of adjacent nanowires. The growth temperature study has revealed a remarkable existence of a temperature window in the range 90 °C–110 °C, beyond which the nanowire lengths start to decline. We attributed the nanowire length regression above 110 °C to the enhanced homogeneous nucleations in the growth solution. Nanowire entanglement started to be observable at ∼100 °C for a growth duration of 2 h. DSSCs were fabricated using the grown ZnO nanowire arrays that are post-annealed under air and pure oxygen gas environments. Oxygen post-annealing resulted in a remarkable decrease in the open circuit voltage (VOC), which we attributed to the large impact of band bending.

Characterization of DBD plasma actuator with ZnO nanowire arrays

Researches in the plasma actuation are increasingly scrutinizing the methodology to enhance the thrust density for the application in the aerodynamic flow control. In this paper, a new method has been proposed and experimentally evaluated. This method is based on the deposition of nanoscaled structures on the electrode surface and the tuning of the applied voltages and frequency. It is found that the thrust enhancement rate resulted from the incorporation of the nanostructures could be approximately 78%, relative to the controlled group, under 14 kV and 7 kHz. However, a threshold effect has been founded across all of the tested samples, where lower applied voltage and frequency could lead to the decrease in the thrust generation. Capacitor charging effects are basically not sensitive to the introduction of the nanostructures in electrical characteristic. Other experimental features and electric field simulation results also indicate the effectiveness of introducing nanoscaled structures into DBD plasma actuators, thus providing a new way to improve mechanical performance.

Hybrid Structure of a ZnO Nanowire Array on a PVDF Nanofiber Membrane/Nylon Mesh for use in Smart Filters: Photoconductive PM Filters

A nanofiber membrane with a high surface-to-volume ratio has advantages in applications such as those used for particulate matter filtration and gas detection. To maximize the potentials of the membrane structure, recent research has been attempted to control nanofiber geometries. In this paper, surface modification of a nanofiber membrane with a metal/ceramic nanostructure is performed to improve multi-functional filter performance, enhancing fine particle filtration and toxic gas absorption. Here, a smart filter is fabricated by electrospinning polyvinylidene difluoride (PVDF) nanofiber onto a nylon mesh and hydrothermal synthesis of ZnO nanoparticles onto a nanowire array on a PVDF nanofiber surface. On the ZnO nanowires–PVDF nanofiber layer filter, the pressure difference (ΔP = 4.13 kPa) is higher than the pure PVDF nanofiber layer. However, the filtration efficiency is 94.3% for a 0.3 μm particle size, which is higher than that of other sizes. Additionally, a ZnO nanowire array with high density on a PVDF nanofiber layer affects sensitivity (S = 39.37), with high resolution. The photocurrent characteristics of a smart filter have the potential for a photo-assisted redox reaction to detect toxic polar molecules in continuous airflow in real-time in indoor environments.

Emerging of Ag particles on ZnO nanowire arrays for blue-ray hologram storage

Noble-metal/metal-oxide-semiconductor nanostructures as an important material platform have been applied in massive data storage. ZnO exhibits excellent optical modulation ability. However, plasmon induced charge separation effect in Ag/ZnO systems is very weak due to the low chemical activity on surface of the oxide. Herein, we prepare ZnO nanowire arrays via the hydrothermal method, and measure their absorption spectra, photoluminescence spectra and electron paramagnetic resonance, proving the existence of oxygen defects in ZnO. Accordingly, an idea of “electron reverse transfer” is proposed such that blue-ray (403.4 nm) induces reduction of Ag+ ions through the excitation of ZnO. Rod-like and spherical silver nanoparticles emerge on the surface and in the gap of ZnO nanowire arrays, respectively, after the visible light stimulus. It is found that nanowire density, oxygen defects and surface roughness are dependent on hydrothermal time. The optimized diffraction efficiency of 0.08% is obtained for reconstructing hologram in the nanocomposite film. This work provides a bright way for construction of ZnO-based optoelectronic integrated devices.

Optimization of aluminum doped ZnO nanowires for photoelectrochemical water splitting

Undoped and aluminum-doped ZnO nanowire (NW) arrays with high aspect ratio and doping concentration up to 2.0 at.% in Al, were prepared by chemical bath deposition (CBD) technique onto FTO/glass substrates. The morphological, structural, and optical properties of the as-grown NWs were investigated by using electron microscopy, diffraction, and spectroscopic techniques. The prepared samples were used as photoanodes in a photoelectrochemical cell and their effectiveness for water splitting was evaluated. The optimum doping concentration was found to be 0.5 at.%. The increase of the photocurrent density normalized by the specific surface reaches up to 110% (in relation to the neat ZnO photoanode at 1.23 V) for this concentration The improved photocurrent density cannot be accounted for solely by the improvement of the conductivity by Al doping and the change in morphology; hence, the promoting effect of Al ions and the photoactivation of a larger fraction of sites has been evoked.

Hybrid ZnO/MoS2 Core/Sheath Heterostructures for Photoelectrochemical Water Splitting

The rational synthesis of semiconducting materials with enhanced photoelectrocatalytic efficiency under visible light illumination is a long-standing issue. ZnO has been systematically explored in this field, as it offers the feasibility to grow a wide range of nanocrystal morphology; however, its wide band gap precludes visible light absorption. We report on a novel method for the controlled growth of semiconductor heterostructures and, in particular, core/sheath ZnO/MoS2 nanowire arrays and the evaluation of their photoelectrochemical efficiency in oxygen evolution reaction. ZnO nanowire arrays, with a narrow distribution of nanowire diameters, were grown on FTO substrates by chemical bath deposition. Layers of Mo metal at various thicknesses were sputtered on the nanowire surface, and the Mo layers were sulfurized at low temperature, providing in a controlled way few layers of MoS2, in the range from one to three monolayers. The heterostructures were characterized by electron microscopy (SEM, TEM) and spectroscopy (XPS, Raman, PL). The photoelectrochemical properties of the heterostructures were found to depend on the thickness of the pre-deposited Mo film, exhibiting maximum efficiency for moderate values of Mo film thickness. Long-term stability, in relation to similar heterostructures in the literature, has been observed.

Hydrothermal synthesis of brush-like ZnO NWAs@CC composites with enhanced photocatalytic and field emission performance

Flexible substrates are very advantageous for optimal performance of highly ordered nanoscale semiconductor nanowire arrays, which is beneficial for flexible device fabrication. Herein, the highly vertically alignment ZnO NWAs (Zinc oxide nanowires arrays) have been successfully fabricated on the high-conductivity flexible CC (Carbon cloth) substrates spin-coated with ZnO seed layers to form a brush-like ZnO NWAs@CC heterojunction composites. XPS spectra shows the C–O–Zn interface chemical bonds between the CC and ZnO seed layers, which not only reduces the contact resistance between ZnO NWAs and CC substrates, but also conducive to the transfer of efficient electrons. The brush-like ZnO NWAs@CC-18 composites were demonstrated to possess excellent photocatalytic activity under visible light irradiation (degradation of 91.65% for 120 min for MB (Methyl blue) dyes) and field emission properties (the turn-on and threshold field of 0.32 V/μm and 1.02 V/μm, the field enhancement factor of 64438), suggesting a promising flexible cold candidate for photocatalytic decontamination and field emission (FE) devices.

Synthesis of Self-Supporting ZnO Nanowire Array Film and its Optical Property and Room Temperature Ferromagnetism

X-ray diffractometer, field emission scanning electron microscope (SEM, Hitachi S-4800), laser confocal micro-region Raman spectrometer and vibration sample magnetometer were used to systematically study the effects of polyethyleneimine concentrations and exposure time on the morphology and size of ZnO nanowire arrays. The photoelectric property and the relationship between the morphology of nanowire arrays and ferromagnetism at room temperature were also analyzed. Under 15 min exposure time, when the polyethyleneimine concentration is 2.25 g / L, the obtained ZnO nanowire array film exhibits the smallest size, the optimal density and vertical orientation. According to the study of luminescence and room temperature magnetism, it is shown that the optical and ferromagnetic property are related to the variation tendency of oxygen defects and surface defects of the ZnO nanowires.

Characterizing and Optimizing Piezoelectric Response of ZnO Nanowire/PMMA Composite-Based Sensor.

Due to the outstanding coupling between piezoelectric and semiconducting properties of zinc oxide nanowires, ZnO NW-based structures have been demonstrating promising potential with respect to their applicability in piezoelectric, piezotronic and piezo-phototronic devices. Particularly considering their biocompatibility and biosafety for applications regarding implantable medical detection, this paper proposed a new concept of piezoelectric composite, i.e., one consisting of vertically aligned ZnO NW arrays and an insulating polymer matrix. First, the finite element method (FEM) was employed to drive optimization strategies through adjustment of the key parameters such as Young’s modules and the dielectric constant of the dielectric constituents, together with the density and dimension of nanowire (NW) itself. Second, to investigate the functionality of each individual layer of composite, different designed structures were fabricated and characterized in terms of electrical and piezoelectric properties. Next, experimental and simulation tests were performed, indicating that the decreasing thickness of the top poly(methyl methacrylate) layer (PMMA) can substantially enhance the piezoelectric sensitivity of the ZnO NW composite. Besides the further benefit of no polarization being needed, our material has a comparable charge coefficient (d33) with respect to other lead-free alternatives (e.g., BaTiO3), confirming the high sensing abilities of the developed structure based on vertically aligned ZnO NW arrays. Finally, a time-varying model combining piezoelectricity and electric circuit modules was investigated in detail, giving rise to an estimation of the d33 coefficient for ZnO NWs. Based on this study, the developed material is revealed to be highly promising in medical applications, particularly regarding the FFR technique, where coronary pressure can be measured through a piezoelectric sensor.

Custom Synthesis of ZnO Nanowires for Efficient Ambient Air-Processed Solar Cells.

Nanostructuration of solar cells is an interesting approach to improve the photovoltaic conversion efficiency (PCE). This work aims at developing architectured 3D hybrid photovoltaic solar cells using ZnO nanowires (ZnONWs) as the electron transport layer (ETL) and nanocollectors of electrons within the active layer (AL). ZnONWs have been synthesized using a hydrothermal process with a meticulous control of the morphology. The AL of solar cells is elaborated using ZnONWs interpenetrated with a bulk heterojunction composed of donor (π-conjugate low band gap polymer: PBDD4T-2F)/acceptor (fullerene derivate: PC71BM) materials. An ideal interpenetrating ZnONW-D/A system with predefined specific morphological characteristics (length, diameter, and inter-ZnONW distances) was designed and successfully realized. The 3D architectures based on dense ZnONW arrays covered with conformal coatings of AL result in an increased amount of the ETL/AL interface, enhanced light absorption, and improved charge collection efficiency. For AL/ZnONW assembly, spin-coating at 100 °C was found to be the best. Other parameters were also optimized such as the D/A ratio and the pre/post-treatments achieving the optimal device with a D/A ratio of 1.25/1 and methanol treated on ZnONWs before and after the deposition of AL. A PCE of 7.7% (1.4 times better than that of the 2D cells) is achieved. The improvement of the performances with the 3D architecture results from both of: (i) the enhancement of the ZnO/AL surface interface (1 μm2/μm2 for the 2D structure to 6.6 μm2/μm2 for the 3D architecture), (ii) the presence of ZnONWs inside the AL, which behave as numerous nanocollectors (∼60 ZnONW/μm2) of electrons in the depth of the AL. This result validates the efficiency of the concept of nanotexturing of substrates, the method of solar cell assembly based on the nano-textured surface, the chosen morphological characteristics of the nanotexture, and the selected photoactive organic materials.

Thermal Evaporation Synthesis of Vertically Aligned Zn2SnO4/ZnO Radial Heterostructured Nanowires Array.

The construction of a heterostructured nanowires array allows the simultaneous manipulation of the interfacial, surface, charge transport, and transfer properties, offering new opportunities to achieve multi-functionality for various applications. Herein, we developed facile thermal evaporation and post-annealing method to synthesize ternary-Zn2SnO4/binary-ZnO radially heterostructured nanowires array (HNA). Vertically aligned ZnO nanowires array (3.5 μm in length) were grown on a ZnO-nanoparticle-seeded, fluorine-doped tin oxide substrate by a hydrothermal method. Subsequently, the amorphous layer consisting of Zn-Sn-O complex was uniformly deposited on the surface of the ZnO nanowires via the thermal evaporation of the Zn and Sn powder mixture in vacuum, followed by post-annealing at 550 °C in air to oxidize and crystallize the Zn2SnO4 shell layer. The use of a powder mixture composed of elemental Zn and Sn (rather than oxides and carbon mixture) as an evaporation source ensures high vapor pressure at a low temperature (e.g., 700 °C) during thermal evaporation. The morphology, microstructure, and charge-transport properties of the Zn2SnO4/ZnO HNA were investigated by scanning electron microscopy, X-ray diffraction, Raman spectroscopy, transmission electron microscopy, and electrochemical impedance spectroscopy. Notably, the optimally synthesized Zn2SnO4/ZnO HNA shows an intimate interface, high surface roughness, and superior charge-separation and -transport properties compared with the pristine ZnO nanowires array.