ZnO Nanowire Arrays Research Articles

Piezoelectric properties of ZnO nanowire arrays/DAST-PDMS flexible nanogenerators

The piezoelectric properties of 4-(4-dimethylaminostyryl) methylpyridine p-toluene sulfonate (DAST)-polydimethylsiloxane (PDMS) composite thin film was investigated. Flexible nanogenerators based on zinc oxide (ZnO) nanowire (NW) arrays/DAST-PDMS were fabricated. DAST holds organic crystal structure, and it can possess piezoelectric properties, and it can enhance the piezoelectric properties of ZnO NW arrays. PDMS can not only mix DAST powder with a liquid to prepare a thin film but also protect ZnO NW arrays and DAST from deterioration. When applying pressure with a balance weight of 100 g, the flexible nanogenerator based on ZnO NW arrays/DAST-PDMS can generate an output voltage of 2.3 V, which is much larger than that of the nanogenerator based on ZnO NW arrays. The effect of the strength of vertical external force, frequency of vertical external force, and degree of bending deformation on the ZnO NW arrays/DAST-PDMS flexible nanogenerators were investigated in this Letter. In our experiments, the output voltage of the ZnO NW arrays/DAST-PDMS flexible nanogenerators can reach 3.3 V. After bending the nanogenerator 20 times, the energy collection device based on the ZnO NW arrays/DAST-PDMS flexible nanogenerator was able to light an LED bulb.

Enhancement of the performance of a ZnO-based nanostructured flexible UV photodiode grown on the carbon clothe by piezo-phototronic effect

The current study aims to evaluate the piezo-phototronic effect on the performance of the prepared ZnO-based UV Photodiodes (PDs). To this end, the electrochemical method was employed to facilitate the growth of ZnO Nanowires (NWs) on the Carbon Clothe (CC) substrate. The results obtained from Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) analyses demonstrated well-grown ZnO NWs arrays with high coverage density and crystal quality on the substrate. The current-voltage (I–V) measurement was employed in the UV illumination and dark conditions to determine the photo-responsivity and detectivity of the prepared device to the UV light. In addition, the photocurrent and overall device performances were modified under UV illumination and applying compressive strain, given its role in increasing the barrier height. As a result, more photo-generated charge carriers can migrate to the electrode without recombination in comparison with free strain conditions. This phenomenon is known as the piezo-phototronic effect. Further, the findings of this study revealed that CC could be an appropriate alternative to the fabricated flexible PDs instead of other expensive flexible substrates such as Indium Tin Oxide/Poly-Ethylene Terephthalate (ITO/PET).

Conformal Coverage of ZnO Nanowire Arrays by ZnMnO3 : Room-temperature Photodeposition from Aqueous Solution.

Compositionally and structurally complex semiconductor oxide nanostructures gain importance in many energy-related applications. Simple and robust synthesis routes ideally complying with the principles of modern green chemistry are therefore urgently needed. Here we report on the one-step, room-temperature synthesis of a crystalline-amorphous biphasic ternary metal oxide at the ZnO surface using aqueous precursor solutions. More specifically, conformal and porous ZnMnO3 shells are photodeposited from KMnO4 solution onto immobilized ZnO nanowires acting not only as the substrate but also as the Zn precursor. This water-based, low temperature process yields ZnMnO3 /ZnO composite electrodes featuring in 1 M Na2 SO4 aqueous solution capacitance values of 80-160 F g-1 (as referred to the total mass of the porous film i. e. the electroactive ZnMnO3 phase and the ZnO nanowire array). Our results highlight the suitability of photodeposition as a simple and green route towards complex functional materials.

Thermal Evaporation Synthesis, Optical and Gas-Sensing Properties of ZnO Nanowires

The purpose of this study is to synthesize and explore the relationship between the optical properties and gas-sensing performance of ZnO nanowires (NWs). Well-aligned ZnO nanowire (NW) arrays were synthesized on a silicon substrate using the thermal evaporation method without any catalyst or additive. The structures, surface morphologies, chemical compositions, and optical properties of the products were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) together with energy-dispersive spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectroscopy, and their gas-sensing properties for NO2 were examined. The results showed that single-crystalline ZnO NWs with high density grow uniformly and vertically on a Si substrate. The FESEM and TEM images indicate that ZnO NWs have an average diameter of roughly 135–160 nm with an average length of roughly 3.5 μm. The results from XRD confirm that the ZnO NWs have a hexagonal wurtzite structure with high crystalline quality and are highly oriented in the [0001] direction (i.e., along the c-axis). The deconvoluted O 1s peak at ~531.6 eV (29.4%) is assigned to the oxygen deficiency, indicating that the ZnO NWs contain very few oxygen vacancies. This observation is further confirmed by the PL analysis, which showed a sharp and high-intensity peak of ultraviolet (UV) emission with a suppressed deep-level (DL) emission (very high: IUV/IDL > 70), indicating the excellent crystalline quality and good optical properties of the grown NWs. In addition, the gas-sensing properties of the as-prepared ZnO NWs were investigated. The results indicated that under an operating temperature of 200 °C, the sensor based on ZnO NWs is able to detect the lowest concentration of 1.57 ppm of NO2 gas.

Performance of flexible ZnO nanowire piezoelectric generators enhanced by bifacial superposition

High performance piezoelectric nanogenerators have important applications in many fields. In this work, we report a bifacial superposed zinc oxide piezoelectric nanogenerator that shows better performance than a single unit. A stainless steel substrate with both front and back zinc oxide nanowire arrays is an elementary unit. Then we engage in an alternating superposition of two elementary units with a carbon-contained polyurethane foil. Multiple units can be similarly assembled by adding alternating structures to further enhance the piezoelectric output performance. Nanogenerators obtained by the above bifacial method are flexible and stability with high output. The method can be used to increase the overall piezoelectric performance and is expected to have a wide application in self-powered device fields.

Effect of Hydrogen Plasma Treatment on the Sensitivity of ZnO Based Electrochemical Non-Enzymatic Biosensor.

Information on vitamin C-ascorbic acid (AA)-content is important as it facilitates the provision of dietary advice and strategies for the prevention and treatment of conditions associated with AA deficiency or excess. The methods of determining AA content include chromatographic techniques, spectrophotometry, and electrochemical methods of analysis. In the present work, an electrochemical enzyme-free ascorbic acid sensor for a neutral medium has been developed. The sensor is based on zinc oxide nanowire (ZnO NW) arrays synthesized via low-temperature chemical deposition (Chemical Bath Deposition) on the surface of an ITO substrate. The sensitivity of the electrochemical enzyme-free sensor was found to be dependent on the process treatments. The AA sensitivity values measured in a neutral PBS electrolyte were found to be 73, 44, and 92 µA mM-1 cm-2 for the ZnO NW-based sensors of the pristine, air-annealed (AT), and air-annealed followed by hydrogen plasma treatment (AT+PT), respectively. The simple H-plasma treatment of ZnO nanowire arrays synthesized via low-temperature chemical deposition has been shown to be an effective process step to produce an enzyme-free sensor for biological molecules in a neutral electrolyte for applications in health care and biomedical safety.

Fabrication of transparent TiO2-GO nanocomposites deposited on vertically aligned ZnO nanowire arrays as hybrid nanostructured photo-anode for dye-sensitized solar cells

In this article, we report the fabrication of hybrid nanostructures comprised of vertically aligned Zinc Oxide (ZnO) nanowires (NWs) coated with titanium dioxide-graphene oxide (TiO2-GO) nanocomposites by easy, cost-effective, chemical method and demonstrate their utilization as photo-anode for dye-sensitized solar cells (DSSCs). A thin layer of transparent TiO2 with varying GO amount is deposited on top of vertical ZnO NW arrays by sol-gel spin coating method. A conventional DSSC structure is fabricated by using hybrid structure as photo-anode, ruthenium based N3 dye as photosensitizers, iodine solution (I−/I3+) as electrolyte and fluorine-doped tin oxide (FTO) coated glass substrate as counter electrode. The fabricated hybrid nanostructure based DSSC exhibits enhanced power conversion efficiency (η) compared to that of pristine ZnO NW photo-anode. Also, other characteristic parameters of DSSCs like open-circuit voltage (Voc), short-circuit current density (Jsc) and fill factor (FF) are estimated from the current density-voltage (J-V) relation measured under illumination of 1 sun (100 mW/cm2) solar spectrum for ZnO NW/TiO2-GO hybrid nanostructures. Improvement in these obtained parameters is observed with increasing GO amount in the TiO2-GO nanocomposite layers deposited on top of ZnO NW arrays. Best performance is delivered by the hybrid nanostructure consists of ZnO NW/TiO2-GO (10%)with optimized value of η ∼0.72% along with Voc ∼491 mV, Jsc ∼2.19 mA/cm2 and FF ∼0.66. This betterment in performance is attributed to the combined effects of improvement in charge transport through the axis of ZnO NWs, increment in contact area and modulation of conductivity of TiO2 by inclusion of conducting GO network. The modulation in charge transport properties of hybrid nanostructures with varying GO amount is studied by complex impedance spectroscopic analyses. The study indicates that particular amount of GO significantly modifies the interfacial effects in fabricated hybrid nanostructures to facilitate better charge transportation.

Silver nanoparticles decorated ZnO–CuO core–shell nanowire arrays with low water adhesion and high antibacterial activity

Nanostructured surfaces based on silver nanoparticles decorated ZnO–CuO core–shell nanowire arrays, which can assure protection against various environmental factors such as water and bacteria were developed by combining dry preparation techniques namely thermal oxidation in air, radio frequency (RF) magnetron sputtering and thermal vacuum evaporation. Thus, high-aspect-ratio ZnO nanowire arrays were grown directly on zinc foils by thermal oxidation in air. Further ZnO nanowires were coated with a CuO layer by RF magnetron sputtering, the obtained ZnO–CuO core–shell nanowires being decorated with Ag nanoparticles by thermal vacuum evaporation. The prepared samples were comprehensively assessed from morphological, compositional, structural, optical, surface chemistry, wetting and antibacterial activity point of view. The wettability studies show that native Zn foil and ZnO nanowire arrays grown on it are featured by a high water droplet adhesion while ZnO–CuO core–shell nanowire arrays (before and after decoration with Ag nanoparticles) reveal a low water droplet adhesion. The antibacterial tests carried on Escherichia coli (a Gram-negative bacterium) and Staphylococcus aureus (a Gram-positive bacterium) emphasize that the nanostructured surfaces based on nanowire arrays present excellent antibacterial activity against both type of bacteria. This study proves that functional surfaces obtained by relatively simple and highly reproducible preparation techniques that can be easily scaled to large area are very attractive in the field of water repellent coatings with enhanced antibacterial function.

Investigation of hydrothermal growth time and temperature for optimized ZnO nanowire arrays toward photovoltaics

The challenge of meeting energy demands has led to the development of nanotechnology. Semiconductor nanowires are considered a promising option among various nanomaterials for efficiently capturing solar radiation in an axial geometry. This work presents the growth of ZnO nanowire arrays on seeded-coated glass substrates using a two-step hydrothermal method, by examining the effect of two crucial hydrothermal growth parameters: time and temperature of growth. X-ray diffraction (XRD) spectra showed the hexagonal wurtzite shape of the ZnO nanowires which displayed a preferred (002) axial orientation. To estimate the crystallite size, strain, stress, and energy density values, we used the Modified Williamson-Hall models. Scanning electron microscopy (SEM) observations showed that the growth time and temperature have a significant impact on the length and diameter of the nanowires, which increase with increasing time and temperature. A clear correlation was also observed between the diameter and density of the nanowires. Optical analysis showed that ZnO nanowires exhibited good transmittance of about 90% in the near ultraviolet and visible spectrum, but this decreased with increasing growth time and temperature. The measured bandgap energy showed a red shift, which confirmed its correlation with the structural characteristics. The improved optical and structural features of ZnO nanowires were analyzed with regards to their potential use in photovoltaics.

Tuning the SERS Capabilities of ZnO Nanowire Arrays Functionalized with Au Quantum Dots for Highly Sensitive Detection of Methylene Blue

AbstractThe development of a surface enhanced Raman scattering (SERS) substrate capable of sensing the target analyte at low concentration has always been demanding. In this prospective, ZnO−Au quantum dots (QDs) hybrid structure with tunable surface properties and high chemical stability is considered a promising material for SERS applications. Here, a novel ZnO@Au QDs hybrid structures with various amounts of Au QDs (ZnO−Aux QDs, where x=0.2, 0.4, 0.6 and 1.0) was synthesized by employing solvothermal along with electrodeposition approach. The optimized substrate, ZnO@Au QDs (0.6) exhibits excellent SERS sensitivity for the detection of MB up to 1 nM with a good reproducibility. The chemical and compositional analysis show that the surface defects are formed due to the interface interactions which not only promote charge transfer between ZnO nanowires and Au QDs complex but also enhanced the Raman scattering of target analyte. The developed substrate demonstrates excellent SERS uniformity which makes them reliable choice for the detection of multi‐analyte for practical applications.

On-Chip Ultralow-Threshold Tunable CdSSe Nanobelt Lasers Excited by the Emission of Linked ZnO Nanowire.

The integration of optical waveguide and on-chip nanolasers source has been one of the trends in photonic devices. For on-chip nanolasers, the integration of nanowires and high antidamage ability are imperative. Herein, we realized the on-chip ultralow-threshold and wavelength-tunable lasing from alloyed CdSSe nanobelt chip that is excited by the emission from linked ZnO nanowires. ZnO nanowire arrays are integrated into CdSSe nanobelt chips by the dry transfer method. A one-dimensional (1D) ZnO nanowire forms high-quality optical resonators and serves as an indirect pumping light to stimulate CdSSe nanobelt chips, and then wavelength-tunable lasing is generated with the ultralow threshold of 3.88 μW. The lasing mechanism is quite different than direct excitation by nanosecond laser pulse and indirect pumping by ZnO emission. The ZnO-CdSSe blocks provide a new solution to realize nanowire lasing from linked nanowires rather than direct laser pumping and thus avoid the light direct damage under general nanosecond laser excitation.

Catalytic transformation of 4-nitrophenol into 4-aminophenol over ZnO nanowire array-decorated Cu nanoparticles

To realize economical and effective removal of hazardous 4-nitrophenol from the environment, we developed an easily recyclable ZnO nanowire array decorated with Cu nanoparticles. Its salix argyracea-shaped structure not only provides a platform to achieve stable and good dispersion of Cu nanoparticles, but also offers a great deal of catalytically active sites. The density functional theory calculations reveal that ZnO and Cu have a very beneficial synergistic effect on their catalytic capability. This synergy is ascribed to the electronic localization occurring at ZnO/Cu interface, which helps improve Cu nanoparticle's ability to adsorb electro-negatively 4-nitrophenolate ions and to capture hydrogen radicals, thereby accelerating the hydrogen transfer from metal hydride complex to 4-nitrophenol. Benefiting from these characteristics, it exhibits high efficiency and reusability towards the catalytic reduction of waste 4-nitrophenol to valuable 4-aminophenol with a rate constant of 43.02 × 10−3 s−1 and an average conversion of 96.5% in 90 s during 10 cycles. This activity is superior to that of most reported noble- or non-noble-metal powder, bulk, coating, and array catalysts, indicating its competitive advantages in cost and efficiency, as well as enticing application prospects.

Enhanced H2S Gas-Sensing Performance of Ni-Doped ZnO Nanowire Arrays.

Ni-doped ZnO nanowire arrays (Ni-ZnO NRs) with different Ni concentrations are grown on etched fluorine-doped tin oxide electrodes by the hydrothermal method. The Ni-ZnO NRs with a nickel precursor concentration of 0-12 at. % are adjusted to improve the selectivity and response of the devices. The NRs' morphology and microstructure are investigated by scanning electron microscopy and high-resolution transmission electron microscopy. The sensitive property of the Ni-ZnO NRs is measured. It is found that the Ni-ZnO NRs with an 8 at. % Ni precursor concentration have high selectivity for H2S and a large response of 68.9 at 250 °C compared to other gases including ethanol, acetone, toluene, and nitrogen dioxide. Their response/recovery time is 75/54 s. The sensing mechanism is discussed in terms of doping concentration, optimum operating temperature, gas type, and gas concentration. The enhanced performance is related to the regularity degree of the array and the doped Ni3+ and Ni2+ ions, which increases the active sites for oxygen and target gas adsorption on the surface.

High-Performance Near-Infrared Photodetector Based on PbS Colloidal Quantum Dots/ZnO-Nanowires Hybrid Nanostructures.

Quantum dots have found significant applications in photoelectric detectors due to their unique electronic and optical properties, such as tunable bandgap. Recently, colloidal quantum dots (CQDs) have attracted much interest because of the ease of controlling the dot size and low production cost. In this paper, a high-performance ZnO/PbS heterojunction photodetector was fabricated by spin-coating PbS CQDs onto the surface of a hydrothermally grown vertical array of ZnO nanowires (NWs) on an indium tin oxide (ITO) substrate. Under 940 nm near-infrared light illumination, the device demonstrated a responsivity and detectivity of ~3.9 × 104 A/W and ~9.4 × 1013 Jones, respectively. The excellent performances and low cost of this nanocomposite-based photodetector show that it has the potential for widespread applications ranging from medical diagnosis to environmental monitoring.

Room Temperature Synthesis of Branched ZnO Nanowires Array with Tunable Morphology

Herein, a novel method is proposed to synthesize B-ZnO NWA by simply immersing the Zn NWA in NaOH solution at room temperature (25 °C). Based on the systematic investigation of various factors that affect the growth of B-ZnO NWA, the growth mechanism of B-ZnO NWA is clarified. Guided by the growth mechanism, the control of the morphology of B-ZnO NWA is achieved by adjusting the pore structure of anodized aluminum oxide templates, hot-pressing parameters, NaOH concentration, solution temperature, and immersion time. In contrast to previous reports, the prepared B-ZnO NWA has hollow trunks, which can further increase the specific area of B-ZnO NWA. Considering the facile, environmental, and low-cost synthesis, the prepared B-ZnO NWA with tunable morphology has great prospects in a wide range of applications, especially those related to the conversion and utilization of solar energy, which are gaining increasing interest nowadays.

Alleviating Zn Dendrites by Growth of Ultrafine ZnO Nanowire Arrays through Horizontal Anodizing for High-Capacity, Long-Life Zn Ion Capacitors.

Zn ion capacitors (ZICs) composed of a carbon-based cathode and a Zn anode are one of the most promising energy storage devices due to their inherent safety and high-power output. However, their poor cycling stability originating from the Zn dendrites' formation and low energy density limited by insufficient activated carbon properties remain major challenges for development of high-performance ZICs. Hence, we constructed a facile and effective strategy to alleviate "edge effects" and suppress Zn dendrites by growing ZnO nanowire arrays on Zn foil (ZnO@Zn) using a horizontally potentiostatic anodizing technique. The electrochemical characterizations and in situ optical microscopy observation revealed that the introduction of ZnO nanowire arrays can significantly suppress the growth of Zn dendrites and enhance the cycling stability of the Zn anode. The superfine and interlaced ZnO nanowire arrays provide uniform nucleation sites and high electrical conductivity for the Zn metal anode, reducing the local current density and promoting the rapid diffusion and migration of Zn ions on the Zn anode surface. As a result, the ZnO@Zn electrode has a very low nucleation overpotential and excellent cycle stability, far superior to the bare Zn anode. Furthermore, a ZnO@Zn//NPHC ZIC assembled with an N, P-codoped hard carbon (NPHC) cathode delivers a high specific capacity of 110.3 mAh g-1 at 0.1 A g-1 and achieves outstanding cycling stability with 90% capacity retention together with ∼100% Coulombic efficiency after 20000 cycles.

Wastewater treatment: A universal, scalable and recyclable catalyst with adjustable activity for diverse dyes degradation

The growing concern over water shortage and pollution is propelling and accelerating the development of sewage treatment technologies. Among them, the catalytic hydrogenation method is highly recommended from a sustainable perspective, because it can turn toxic pollutants into valuable raw materials. The catalyst with excellent activity and stability plays a critical role in this “trash to treasure” approach. Herein, we proposed a novel economical, scalable and recyclable candidate catalyst, i.e., the copper nanoparticles supported on zinc oxide nanowire array (Cu–ZnO NWA), for realizing efficient and stable dye wastewater treatment. The salix argyracea-shaped Cu–ZnO NWA displays very outstanding universality and controllability towards the catalytic hydrogenation reactions of diverse dyes, owing to the fact that ZnO nanowire array not only offers a platform to realize stable and homogeneous dispersion of Cu nanoparticles, but also provides a large quantity of catalytically active sites. More attractively, its synthetic method can be facilely extended to various conductive substrates through combined electrodeposition and hydrothermal technique, showing its general applicability for the surface assembly of sewage treatment facilities. Benefiting from above advantages, this proposal offers an attractive approach for large-scale and continuous decolorization of dye wastewater, and presents a broad application prospect in the textile printing industry.

Rapid precipitation-free synthesis of zinc oxide nanowire arrays

The microwave-assisted hydrothermal method is cost-effective for rapidly producing zinc oxide (ZnO) nanowire array. However, microwave-assisted heating can make many bulk crystals that may contaminate the nanowire array. The precipitated contamination on the ZnO nanowire array formed using the microwave-assisted hydrothermal method is grossly underreported in the literature. ZnO is usually prepared in a high basic condition to reduce the bulk nucleation, using ammonia or amine complexes. As microwave-assisted synthesis is preferred in open reactors to avoid high-pressure development and design complexity, amine-based components are particularly unsuitable for such reactions due to high volatility. In this work, the ZnO nanowire array was synthesized using the microwave-assisted hydrothermal method in an open reactor using a basic non-volatile compound, Sodium hydroxide (NaOH). Rapid growth of ZnO nanowires was achieved at a rate of 4.6 μm/h without having precipitated materials using NaOH. In contrast, ammonia-assisted synthesis showed a large number of precipitates on the array. High and low-magnified field emission scanning electron microscopy images revealed the formation of pristine ZnO nanowires and debris/contaminant-free arrays using a non-volatile hydrolyzing agent. Speciation data shows that various ionic species of Zn under different basic conditions using ammonia and NaOH can control the bulk nucleation of ZnO.

Synthesis of a ZnO nanowire array within minutes.

A ZnO nanowire array was successfully synthesized within 10 minutes, for the first time, through electrodeposition of a Zn nanocrystal coating followed by a microwave hydrothermal treatment, representing the cheapest and fastest route from aqueous solutions so far. This simple, economical, efficient, flexible and scalable method shows attractive prospects for industrial application.

Antibacterial fabrics based on synergy of piezoelectric effect and physical interaction

Antibacterial clothes play a key role in reducing the spreading threat of bacteria, thus protecting people’s health. In this work, several kinds of fabrics with high antibacterial efficiency have been demonstrated based on piezoelectric effect of ZnO nanowire (NW) arrays and their physical interaction with bacteria. Piezoelectric effect of NWs under bending can generate interface electrons, and electrons transfer between the bacteria and the NWs can hinder growth of bacteria and cause bacteria death. Electron transfer accounts for about 70 % of bacteria death, while residual 30 % of death is due to the puncture of NWs. The fabrics show remarkable antibacterial properties against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), with the bactericidal rate of 99.99 %, promising their practical applications. The antibacterial fabrics demonstrated in this work lay a solid foundation for antibacterial clothes.