One-dimensional Nanostructure Arrays Research Articles

One-dimensional nanostructure arrays with Schottky Junction enhanced charge separation for the photoelectrocatalytic selective removal of Uranium from wastewater

The photoelectrocatalytic reduction of soluble U(VI) to relatively insoluble U(IV) is a promising method for uranium wastewater treatment. However, the strong reliance on sacrificial agents and an inert atmosphere due to the rapid charge reorganization remains a great challenge. The construction of an inner electrical field at a heterojunction interface accompanied by an external electric field provides a promising strategy for enhancing charge transfer. Herein, a photoelectrode was proposed by in-situ coating nano-TiO2 cone arrays (NTCA) on a titanium mesh, and used for uranium removal from complex effluents under air conditions without sacrificial agents. The enhanced spatial charge separation driven by the Schottky junction built-in electric field and an external bias voltage, coupled with rapid fluid diffusion, granted the photoelectrode an outstanding photoelectrocatalytic uranium removal performance with photocurrent densities of up to 3 mA cm−2 at −0.55 VAg/AgCl. The impressive uranium removal performance was maintained in a wide range of chemical conditions, as well as in real seawater and industrial wastewater. Theoretical calculation revealed that uranyl ions were confined on the NTCA surface as [UO2(H2O)5]2+, further reduced to UO2. This work demonstrated a viable route for uranium separation from aqueous solutions with inexhaustible solar energy and minimal electrical energy.

Ion Beam Etching of Anodic Aluminium Oxide Barrier Layer for Au Nanorod-Based Hyperbolic Metamaterials

Porous anodic aluminium oxide (AAO) is widely used as a template for the electrodeposition of ordered arrays of one-dimensional nanostructures. Prior to template filling, the barrier layer, which blocks the...

In2O3 anchored Fe2O3 nanorod arrays for enhanced photoelectrochemical performance

Fe2O3 is supposed to be one of the most promising photoanode materials. In terms of charge collection and transfer efficiencies, one-dimensional nanostructure arrays exhibit superior performance with great application potential in different fields. In the articles, Fe2O3 nanorod arrays (Fe2O3NRA) have been fabricated on the conductive fluorine-doped tin dioxide glasses by the hydrothermal method, In2O3 with different times cycles anchored Fe2O3NRA photoelectrode was also prepared by a simple dip-coating process. The structure, morphology, crystalline and optical property of the as-prepared photoelectrode were characterized by X-ray diffraction, Raman spectra, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, etc. The photoelectrochemical performance of the samples was investigated under visible light irradiation. A highest photocurrent density of 23 μA/cm2 at 1.23 V (versus the reversible hydrogen electrode) is obtained for the In2O3 with 4 times cycle anchored Fe2O3NRA photoelectrode in a 1 M Na2SO4 aqueous solution. The maximum applied bias photon-to-current efficiency is observed for the In2O3 with 4 times cycle anchored Fe2O3NRA photoelectrode with values 0.0033%. The results indicated that the appropriate decoration amount of In2O3 nanoparticles significantly hinders the recombination process of electron-hole pairs and improves the separation efficiency of photogenerated charge carriers of Fe2O3NRA.

Recent Advances in Electrode Design Based on One-Dimensional Nanostructure Arrays for Proton Exchange Membrane Fuel Cell Applications

Abstract One-dimensional (1D) Pt-based electrocatalysts demonstrate outstanding catalytic activities and stability toward the oxygen reduction reaction (ORR). Advances in three-dimensional (3D) ordered electrodes based on 1D Pt-based nanostructure arrays have revealed great potential for developing high-performance proton exchange membrane fuel cells (PEMFCs), in particular for addressing the mass transfer and durability challenges of Pt/C nanoparticle electrodes. This paper reviews recent progress in the field, with a focus on the 3D ordered electrodes based on self-standing Pt nanowire arrays. Nanostructured thin-film (NSTF) catalysts are discussed along with electrodes made from Pt-based nanoparticles deposited on arrays of polymer nanowires, and carbon and TiO2 nanotubes. Achievements on electrodes from Pt-based nanotube arrays are also reviewed. The importance of size, surface properties, and the distribution control of 1D catalyst nanostructures is indicated. Finally, challenges and future development opportunities are addressed regarding increasing electrochemical surface area (ECSA) and quantifying oxygen mass transport resistance for 1D nanostructure array electrodes.

Solution Growth of BiSI Nanorod Arrays on a Tungsten Substrate for Solar Cell Application

One-dimensional nanostructure arrays hold great promise for orthogonalizing light absorption and carrier collection, and thus have been attractive building blocks for next-generation solar cells. T...

Activation of carbon cloth and concurrent precipitation of titania nanowires for enhanced adsorption and photocatalysis performance

Vertically aligned TiO2 nanowires exhibit excellent photoactivity because of the high specific surface area and increased charge separation; yet the limited adsorption capacity towards target pollutants hinders the photocatalytic degradation of pollutants in water. We report herein a mild solution approach to precipitate anatase TiO2 nanowire arrays, with a tunable thickness of 1.5–4.5 μm, on carbon cloth to achieve simultaneously high adsorption capacity and excellent photoactivity. When compared with TiO2 nanowire arrays precipitated on metallic Ti substrates, which possess a negligible adsorption capacity, TiO2 nanowires loaded on the activated carbon cloth substrates exhibit a higher efficiency towards photocatalytic degradations of both rhodamine B dye molecules and colorless sulfosalicylic acid in water under UV light illumination. The increasing film thickness is more effective to increase the photoactivity of TiO2 nanowires loaded on the activated carbon cloth than those on metallic Ti foil. The current investigation establishes the feasibility to greatly improve the photoactivity of one-dimensional nanostructured TiO2 arrays by using a highly adsorptive substrate.

Metal oxide heterojunction (NiO/ZnO) prepared by low temperature solution growth for UV-photodetector and semi-transparent solar cell

Wide bandgap inorganic metal oxide heterojunctions p-NiO/n-ZnO have been prepared by two low temperature solution growth techniques. Namely, one-dimensional ZnO nanostructure arrays electrodeposited in a pulsed mode, and nanocrystalline NiO films synthesized via Successive Ionic Layer Adsorption and Reaction (SILAR). The crystal structure, morphology, and optical properties of NiO films and NiO/ZnO heterostructures were investigated both before and after annealing in air. The analysis of the dark current vs. voltage characteristics and temporal response curves of the NiO films and corresponding NiO/ZnO heterostructures have shown the promise of their use in the effective UV-photodetectors. Poor photovoltaic characteristics of the test samples on the base of obtained NiO/ZnO heterostructures probably associated with their not quite optimal design, and with too large series resistances and diode ideality factors of the manufactured p-NiO/n-ZnO heterojunctions, that will be corrected by scrutinizing the defects in the metal oxides and through the improvement of the NiO/ZnO heterostructure design. Solving these problems will provide the effective application of the wide bandgap metal oxide NiO/ZnO heterostructures prepared by low temperature solution growth in the UV-active semi-transparent solar cells.

UV and visible light photocatalytic activity of Au/TiO2 nanoforests with Anatase/Rutile phase junctions and controlled Au locations

To magnify anatase/rutile phase junction effects through appropriate Au decorations, a facile solution-based approach was developed to synthesize Au/TiO2 nanoforests with controlled Au locations. The nanoforests cons®isted of anatase nanowires surrounded by radially grown rutile branches, on which Au nanoparticles were deposited with preferred locations controlled by simply altering the order of the fabrication step. The Au-decoration increased the photocatalytic activity under the illumination of either UV or visible light, because of the beneficial effects of either electron trapping or localized surface plasmon resonance (LSPR). Gold nanoparticles located preferably at the interface of anatase/rutile led to a further enhanced photocatalytic activity. The appropriate distributions of Au nanoparticles magnify the beneficial effects arising from the anatase/rutile phase junctions when illuminated by UV light. Under the visible light illumination, the LSPR effect followed by the consecutive electron transfer explains the enhanced photocatalysis. This study provides a facile route to control locations of gold nanoparticles in one-dimensional nanostructured arrays of multiple-phases semiconductors for achieving a further increased photocatalytic activity.

Template-Assisted Electrodeposition of Urchin-Like Ag-Nanoplate-Assembled Nanorod Arrays and Their Structurally Enhanced SERS Performance

An effective template-assisted electrodeposition approach is demonstrated for growing large-area, hexagonally arranged arrays of urchin-like Ag-nanoplate-assembled nanorods grafted on the polystyrene spheres (PSs) as homogeneous and sensitive surface-enhanced Raman scattering (SERS) substrates. The urchin-like Ag-nanoplate-assembled nanorod arrays are fabricated by first transferring the ordered hexagonally arranged PS colloidal monolayer onto the silicon wafer as the template, and then electrodepositing ZnO nanorods onto the surface of each PS, and finally assembling Ag-nanoplates onto each ZnO nanorod on the PSs via electrodeposition in silver nitrate and citric acid electrolyte. Because of the ordered arrangement of the PS arrays and the high-density sub-10 nm gaps between the neighboring building blocks, the hierarchical urchin-like Ag-nanoplate-assembled one-dimensional nanostructure arrays can offer uniform and abundant “hot spots” for sensitive and reproducible SERS effect. Using the urchin-like hierarchical Ag-nanoplate-assembled nanorod arrays as SERS substrates, 1 pM rhodamine 6 g (R6G), 10pM para-aminothiophenol (p-ATP), and 1 μM PCB-77 (one congener of polychlorinated biphenyl, a notorious member of persistent organic pollutant) are identified respectively, showing promising potentials in rapid detection of organic environmental pollutants.

Porosimetry and packing morphology of vertically aligned carbon nanotube arrays via impedance spectroscopy

Vertically aligned one-dimensional nanostructure arrays are promising in many applications such as electrochemical systems, solar cells, and electronics, taking advantage of high surface area per unit volume, nanometer length scale packing, and alignment leading to high conductivity. However, many devices need to optimize arrays for device performance by selecting an appropriate morphology. Developing a simple, non-invasive tool for understanding the role of pore volume distribution and interspacing would aid in the optimization of nanostructure morphologies in electrodes. In this work, we combined electrochemical impedance spectroscopy (EIS) with capacitance measurements and porous electrode theory to conduct in situ porosimetry of vertically aligned carbon nanotube (VA-CNT) forests non-destructively. We utilized the EIS measurements with a pore size distribution model to quantify the average and dispersion of inter-CNT spacing (Γ), stochastically, in carpets that were mechanically densified from tubes cm−2 to tubes cm−2. Our analysis predicts that the inter-CNT spacing ranges from over 100 ± 50 nm in sparse carpets to sub 10 ± 5 nm in packed carpets. Our results suggest that waviness of CNTs leads to variations in the inter-CNT spacing, which can be significant in sparse carpets. This methodology can be used to predict the performance of many nanostructured devices, including supercapacitors, batteries, solar cells, and semiconductor electronics.

Photoelectrochemical and structural properties of TiO2 nanotubes and nanorods grown on FTO substrate: Comparative study between electrochemical anodization and hydrothermal method used for the nanostructures fabrication

Titanium dioxide in the form of one-dimensional (1D) nanostructure arrays represent widely studied morphological arrangement for light harvesting and charge transfer applications such as photocatalysis and photoelectrochemistry (PEC). Here we report a comparative structural and PEC study of variously grown 1D TiO2 nanostructures including i) nanorod arrays prepared by a hydrothermal method (TNR), ii) nanotube arrays fabricated by a two-step hydrothermal method using a ZnO nanorod array film as a template (THNT) and finally iii) nanotubes grown by self-organized electrochemical anodization of Ti films deposited on the FTO substrate (TNT). These nanostructures are assumed to be utilized as photoanodes in PEC water splitting devices. Field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), TEM images and UV–vis absorption spectra were used to characterize TiO2 nanostructures. The SEM and TEM morphology images revealed that the main difference among the nanostructures grown on the FTO are the shape and diameter of the individual nanotubes/nanorods and also the array’s density in the range of TNR>THNT>TNT and the degree of organization in the range of TNT>TNR>THNT. The obtained photocurrents at 0V vs. Ag/AgCl increased in the order of THNT (110μAcm−2)<TNT (185μAcm−2)<TNR (630μAcm−2). Extended electron lifetime and light absorption shifted to the longer wavelengths were attributed to the enhanced PEC performance of TNR.

An efficient route to Cu2O nanorod array film for high-performance Li-ion batteries

Fabrication of well-organized one-dimensional nanostructured arrays on conducting substrates as binder free electrodes allows us to synergize and integrate multi-functionalities into lithium ion batteries. In this contribution, we report a metal-induced thermal reduction (MITR) method to prepare free-standing Cu2O nanorod array film with average diameters of 400±100nm and lengths of several microns on copper substrates by direct thermal reduction of Cu(OH)2 nanorod arrays on copper foils in nitrogen atmosphere at 500°C. The presence of Cu substrates reduces the Cu(OH)2 to Cu2O and decreases the reduction temperature significantly through changing the reaction Gibbs energy. Compared with some previously-reported methods about thermal reduction, the MITR method is facile, controllable, efficient and low energy consumption. The free-standing Cu2O nanorod array film on Cu substrates as anode can achieve high rate capability (315mAhg−1 at 10 C) and good cyclability (358mAhg−1 after 200cycles at 1 C), demonstrating their excellent electrochemical performance in lithium ion batteries, which results from relatively faster electron and ion transport, easier electrolyte diffusion and better accommodation of strains from the repeated conversion reactions based on their one-dimensional nanostructured arrays.

Field electron emission from structure-controlled one-dimensional CuO arrays synthesized by wet chemical process

One-dimensional CuO nanostructure arrays have been synthesized on Cu foil by a low-temperature wet chemical process. Different CuO nanostructures including nanorods with facet heads, nanorods with needle-like tips and nanotubes are shaped simply by varying the concentration of oxidant. Field emission measurements show that CuO nanorods with needle-like tips are of superior performance than other shapes, having a turn-on field of 3.5V/μm and a field enhancement fact or of 2107. The good field emission performance is assigned to the sharp tips contributing to the high field enhancement effect and to the moderate density reducing the field screening effect.

Chemical replacement route to Cu2−xSe-coated CuO nanotube array anode for enhanced performance in lithium ion batteries

The utilization of well-aligned hybrid one-dimensional hollow nanostructured arrays is a promising strategy for the development of transition metal oxides as high-cycle-life stability and high-rate performance electrode materials for lithium ion batteries. Here we report a chemical replacement route to prepare well-aligned Cu2−xSe-coated CuO nanotube arrays with diameters of 400 nm and length of several micrometers, based on Cu(OH)2 nanotube arrays grown on a copper substrate as precursors. As an integrated anode for lithium ion batteries, the Cu2−xSe-coated CuO nanotube array on a copper substrate is capable of delivering a high cycling capacity of 764 mA h g−1 after 100 cycles at a current density of 0.08 mA cm−2 (0.1 C), and retains a discharge capacity of 382.5 mA h g−1 and 94.5 mA h g−1 at current densities of 10 mA cm−2 (12.5 C) and 20 mA cm−2 (25 C), respectively, exhibiting superior performance to the bare CuO nanotube array film. The synergistic effect of the successful integration of the CuO nanotubes with the Cu2−xSe semiconducting coating layer significantly contributes to the enhanced electrochemical properties of the Cu2−xSe-coated CuO nanotube array anode.

Fabrication of hollow-sphere films of wurtzite CuInS2 on copper substrate

As important semiconductors, I–III–VI2 compounds have attracted wide attention, among which the wurtzite structured CuInS2 has been the research focus due to its metastable phase. In this paper, the wurtzite CuInS2 hollow-sphere films have been successfully prepared on copper substrate in a self-designed solvothermal detached system. The films of Cu(OH)2 one-dimensional nanostructure arrays and thioacetamide were used as the precursors and triethylene glycol was used as the solvent. Experiments showed that the amount of indium trichloride played a determinative role in the final morphology of the products. Meanwhile, the one-dimensional nanostructure arrays and the detached solvothermal system have great influences on the crystal shape as well. Based on the experimental results, a possible formation mechanism for the CuInS2 hollow spheres was also proposed. The UV–Vis absorption spectrum showed a broad absorption over the entire visible light and extending into the near-infrared region and presented the band gap of 1.53 eV for the as-prepared wurtzite CuInS2, which indicates the potential applications in solar cells.

Surface Morphology-Dependent Photoelectrochemical Properties of One-Dimensional Si Nanostructure Arrays Prepared by Chemical Etching

Maximizing the optical absorption of one-dimensional Si nanostructure arrays (1DSiNSAs) is desirable for excellent performance of 1DSiNSA-based optoelectronic devices. However, a quite large surface-to-volume ratio and enhanced surface roughness are usually produced by modulation of the morphology of the 1DSiNSAs prepared in a top-down method to improve their optical absorption. Surface recombination is mainly determined by the surface characteristics and significantly affects the photogenerated carrier collection. In this paper, we systematically investigated the photoelectrochemical characteristics of 1DSiNSAs with various morphologies prepared by the metal-assisted chemical etching of Si wafers. Our results show that the saturation photocurrent density and photoresponsivity of 1DSiNSAs first increased and then gradually decreased with an increasing etching time, while the reflection spectrum was gradually suppressed to the measurable minimum. To identify the behaviors of the photoresponsivity and optical absorption of the various 1DSiNSAs, we analyzed the morphology, structure, and minority-carrier lifetime. Additionally, device physics simulations were used to confirm the significance of surface recombination. We proposed that future directions for the design of nanostructure-based optoelectronic devices should include not only strong optical absorption but also low surface carrier recombination. High-performance devices could be obtained only by balancing the requirements for light absorption and photogenerated carrier collection.

Site-specific nucleation and controlled growth of a vertical tellurium nanowire array for high performance field emitters

We report the controlled growth of highly ordered and well aligned one-dimensional tellurium nanostructure arrays via a one-step catalyst-free physical vapor deposition method. The density, size and fine structures of tellurium nanowires are systematically studied and optimized. Field emission measurement was performed to display notable dependence on nanostructure morphologies. The ordered nanowire array based field emitter has a turn-on field as low as 3.27 V μm−1 and a higher field enhancement factor of 3270. Our finding offers the possibility of controlling the growth of tellurium nanowire arrays and opens up new means for their potential applications in electronic devices and displays.

Hole-induced large-area homoepitaxial growth of CdSe nanowire arrays for photovoltaic application

Traditionally, lattice-matched substrates are a requisite for the epitaxial growth of one-dimensional (1D) semiconductor nanostructure arrays, while the lack of suitable substrates seriously limits the nanowire (NW) arrays available for future nanoelectronic and nano-optoelectronics applications. In this work, we reported a new strategy for achieving the one-step homoepitaxial growth of highly aligned CdSe NW arrays by utilizing porous silicon as substrates. The porous Si with dense holes could promote the nucleation of CdSe micro-crystals at the early stage of vapor phase transport owing to its high surface energy. Subsequently, the epitaxial growth of CdSe NW arrays would take place on the top surfaces of the micro-crystals, resulting in large-area highly aligned NW arrays. As compared with the conventional epitaxial methods, the hole-induced method is greatly simplified because no lattice-matched substrates or catalysts are needed; furthermore, the universality of the proposed method was demonstrated for a variety of II–VI NW arrays. As a demonstration of the potential applications, preliminary studies on CdSe NW array/Si p–n heterojunction solar cells were shown with an efficiency of ∼0.43% under AM 1.5G illumination.

Colorful InAs Nanowire Arrays: From Strong to Weak Absorption with Geometrical Tuning

One-dimensional nanostructure arrays can show fascinatingly different, tunable optical response compared to bulk systems. Here we study theoretically and demonstrate experimentally how to engineer the reflection and absorption of light in epitaxially grown vertical arrays of InAs nanowires (NWs). A striking observation is optically visible colors of the array, which we show can be tuned depending on the geometrical parameters of the array. Specifically, larger diameter NW arrays absorb light more effectively out to a longer wavelength compared to smaller diameter arrays. Thus, controlling the diameter provides a way to tune the optically observable color of an array. We also find that arrays with a larger amount of InAs material reflect less light (or absorb more light) than arrays with less material. On the basis of these two trends, InAs NW arrays can be designed to absorb light either much more or much less efficiently than a thin film of an effective medium containing the same amount of InAs as the NW array. The tunable absorption and low area filling factor of the NW arrays compared to thin film bode well for III-V photovoltaics and photodetection.

Composition-Graded ZnxCd1–xSe@ZnO Core–Shell Nanowire Array Electrodes for Photoelectrochemical Hydrogen Generation

One-dimensional oxide nanostructure arrays are widely investigated as photoelectrodes in solar cells or photoelectrochemical (PEC) solar hydrogen generation applications, for which it is highly desirable for the electrode to have a broad light absorption and an efficient charge separation. In this work, a composition-graded ZnxCd1–xSe@ZnO core–shell nanowire array is prepared through temperature-gradient chemical vapor deposition (CVD) of ZnxCd1–xSe layer onto the pregrown ZnO nanowires. The core–shell nanowire array photoelectrodes yield a continuous absorption edge from 2.7 (460 nm) to 1.77 eV (700 nm) across the sample surface. The core–shell heterostructure facilitates the photogenerated electron–hole pair separation and the electron transfer from ZnCdSe to ZnO. By using such core–shell nanowire arrays as photoanodes for solar hydrogen generation via a PEC cell, a photocurrent density of ∼5.6 mA/cm2 is achieved under 1 sun solar light illumination at zero bias versus Ag/AgCl. This method may be useful...