The Role of Cuprous Oxide Seeds in the One‐Pot and Seeded Syntheses of Copper Nanowires

This paper demonstrates that Cu₂O nanoparticles form in the early stages of a solution‐phase synthesis of copper nanowires, and aggregate to form the seeds from which copper nanowires grow. Removal of ethylenediamine from the synthesis leads to the rapid formation of Cu₂O octahedra. These octahedra are introduced as seeds in the same copper nanowire synthesis to improve the yield of copper nanowires from 12% to >55%, and to enable independent control over the length of the nanowires. Transparent conducting films are made from nanowires with different lengths to examine the effect of nanowire aspect ratio on the film performance.     

Synthesis of Cu<Subscript>2</Subscript>O nanowire mesocrystals using PTCDA as a modifier and their superior peroxidase-like activity

Cu₂O nanowire mesocrystals (NWMCs), which possess well-defined octahedral morphology and high-porosity architecture with anisotropic interpenetrating nanowires, have attracted considerable attention owing to their superior physical and chemical properties. However, the current synthetic approach for Cu₂O NWMCs using graphene oxide as modifier leads to uncontrollable products and low productivity (~30 %), which largely hinder their further industrial application. Herein, we report a modified synthetic approach for controllable and large-scale preparation of Cu₂O NWMCs using perylene-3,4,9,10-tetracarboxylic dianhydride molecule as modifier. The effects of growth time and initial pH on the morphology of final products have been systemically investigated. Under the optimal reaction condition with initial pH of 5.3 and reaction time of 15 h, the well-defined octahedral Cu₂O NWMCs can be obtained with a productivity as high as ~75 %. In addition, this synthetic approach can be easily scaled up from 50 to 500 mL autoclave. The ability of high productivity and reproducibility in synthesis of Cu₂O NWMCs enable us to further study their peroxidase-like activity by catalyzing the oxidation of o-phenylenediamine in the presence of H₂O₂. The Cu₂O NWMCs have exhibited a superior catalytic activity with the K _cat of 1.14 × 10^?2, 10 times higher than that of horseradish peroxidase. Moreover, the Cu₂O NWMCs can also retain 69.5 % of their initial activities after 10-batch redox reactions. Our results provide a facile approach to controllable and large-scale synthesis of Cu₂O NWMCs using homogeneous molecule modifier and open up opportunities to use Cu₂O NWMCs as nanozyme for future industrial application.     

Characterization of ordered Cu2O nanowire arrays prepared by heat treated Cu/PAM composite

Cu nanowire arrays were synthesized via a porous alumina membrane (PAM) template with a high aspect ratio, uniform pore size (120–140 nm), and ordered pore arrangement. The Cu₂O nanowire arrays were prepared from the oxidization of Cu metal nanowire arrays. The electrochemical deposition potential of Cu metal nanowires (?180 mV vs. SCE) was determined from X-ray diffraction (XRD) patterns. The microstructure and chemical composition of Cu nanowire arrays were characterized using field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), and X-ray diffraction (XRD). Results indicate that the Cu/Cu₂O nanowire arrays assembled into the nanochannel of the porous alumina template with diameters of 120–140 nm. The valence of copper was controlled by the porous alumina template during the annealing process. Copper nanowires transformed to the Cu₂O phase with the space limitation of the PAM template. Single-crystal Cu₂O nanowire arrays were also obtained under the template embedded.     

Synthesis and formation mechanism of Cu3V2O7(OH)2·2H2O nanowires

Cu₃V₂O₇(OH)₂·2H₂O nanowires have been synthesized in high yield through a simple and facile low-temperature hydrothermal approach without any template or surfactants. XRD, TG, FE-SEM, TEM and HRTEM were used to characterize the product. The results indicated that the product consisted of wirelike crystals about 80 nm in diameter and length up to several micrometers. The formation of wirelike structure of Cu₃V₂O₇(OH)₂·2H₂O depended crucially on the reaction time and pH value of the precursor suspensions. The optical absorption spectrum indicates that the Cu₃V₂O₇(OH)₂·2H₂O nanowires have a direct band gap of 1.94 eV.     

Low-temperature performance of Al4B2O9 nanowires

In this paper we report on the synthetic investigation of single-crystalline aluminum borate (Al₄B₂O₉) nanowires in large scale by a direct calcination of a precursor powder made of Na₂B₄O₇·10H₂O and Al (NO₃)₃·9H₂O at a low temperature of 850 °C. The nanowires, with the diameter of 20-40 nm and the length up to several micrometers, possess smooth surfaces and uniform sizes along the entire wire. The growth mechanism of the nanowires is attributed to a solid-liquid-solid process, which controls the nanowire morphology.     

One-step chemical bath deposition and photocatalytic activity of Cu2O thin films with orientation and size controlled by a chelating agent

Nanocrystalline cuprous oxide (Cu₂O) thin films were prepared via a one-step chemical bath deposition (CBD) method. The effects of a chelating agent on the orientation, morphology, crystallite size, and photocatalytic activity of the thin films were carefully examined using X-ray diffractometry, scanning electron microscopy, and UV–vis spectrophotometry. The results confirmed that the crystallite size as well as the orientation of the films was dependent on the volume of trisodium citrate (TSC), demonstrating that the band gap ranged from 2.71 eV to 2.49 eV. The morphology and number density of the thin films also depended on the volume of TSC. In addition, the obtained Cu₂O thin films could degrade methyl orange (MO) efficiently in the presence of H₂O₂ under visible-light irradiation, and the mechanism for the enhanced photocatalytic activity of the Cu₂O thin films with the assistance of H₂O₂ was also explored in detail.     

Well‐Defined Cu2O/Cu3(BTC)2 Sponge Architecture as Efficient Phenolics Scavenger: Synchronous Etching and Reduction of MOFs in confined‐pH NH3⋅H2O

Fabrication of low‐dimensional nano‐MOFs as well as nanoparticles/metal‐organic frameworks (MOFs) hybrids has sparked new scientific interests but remains a challenging task. Taking Cu₃(BTC)₂ as a proof of concept, it is demonstrated thats NH₃?H₂O solution of a confined pH value can readily shape the bulk Cu₃(BTC)₂ into nanoscale Cu₃(BTC)₂, beyond the need to control the crystal growth kinetics of MOFs. Adjusting the pH of NH₃?H₂O within a much small range (10–11) allows fine tuning over the size and shape of nanoscale Cu₃(BTC)₂. Particularly at pH = 11, NH₃?H₂O exhibits weak reducibility that triggers a reduction of part of Cu₃(BTC)₂ into Cu₂O, while shaping the other into Cu₃(BTC)₂ nanowires. Benefiting from the coincidence of reduction and etching effects, the newly generated Cu₂O dots can in situ anchor onto adjacent Cu₃(BTC)₂ nanowires at highly dispersive state, forming a well‐defined sponge‐like architecture built of Cu₂O dots and nano‐Cu₃(BTC)₂. The CuO_x derived from annealing of the Cu₂O dots/nano‐Cu₃(BTC)₂ hybrid preserves the sophisticated sponge architecture and high porosity, and exhibits promising applications in phenol scavenging, with efficiency outperforming its counterparts and many other Cu‐based catalysts reported in literature. It is anticipated that the findings here pave the way for the rational design of intricate nano‐MOFs in a more efficient way.     

Hydrothermal synthesis of titanate nanowire arrays

A simple templateless synthesis strategy for titanate nanowire arrays was developed by employing hydrothermal reactions. Hydrothermal treatment of metallic titanium powder with H₂O₂ in a 10 M NaOH solution produced a new sodium titanate compound, Na₂Ti₆O₁₃·xH₂O (x ∼ 4.2), as arrays of nanowires of lengths up to 1 mm. The nanowires were characterized by using XRD, SEM, TGA, and TEM. The nanowires have exceptionally large aspect ratios of 5000 or higher, and they can form arrays over a large area of 2 × 3 cm². Investigations on the reaction products in varied conditions indicate that the array formation requires simultaneously controlled formation and crystal growth rates of the Na₂Ti₆O₁₃·xH₂O phase.     

Rapid preparation and photocatalytic properties of octahedral Cu2O@Cu powders

To improve the photocatalytic properties of Cu₂O, octahedral Cu₂O@Cu powders were prepared by a convenient and rapid two-step liquid phase reduction method. Glucose (C₆H₁₂O₆) and thiourea dioxide (CH₄N₂O₂S, TD for short) were used as pre-reductant and secondary-reductant separately. The microstructure and composition of the products obtained after the reduction processes were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). With the increasing of TD content, the secondary reduced products changed from solid octahedral Cu₂O to octahedral Cu₂O@Cu composites and finally hollow octahedral Cu₂O/Cu composites. The corresponding calculated mass of Cu increased from 6.2 wt% to 80.2 wt%. The photocatalytic behavior of the reduced particles were analyzed by monitoring the degradation of methyl orange solution (MO for short) and electrochemical tests. Photocatalytic performance tests showed that octahedral Cu₂O@Cu powders had an excellent photocatalytic activity. The MO degradation rate was improved from 1.4% for photocatalysts without CuNPs to 92.9% after introducing 13.4 wt% CuNPs under visible light irradiation for 60 min. This simple and rapid synthesis process allowed for the fabrication of octahedral Cu₂O@Cu material with photocatalytic performance superior to pure octahedral Cu₂O and hollow octahedral Cu₂O/Cu materials.     

Hydrothermal synthesis and characterization of Bi2O3 nanowires

An alternative two-step method has been proposed for the synthesis of Bi₂O₃ nanowires with a diameter of about 40 nm from common and cost-effective Bi(NO₃)₃·5H₂O, Na₂SO₄, and NaOH. That is, first, Bi₂O(OH)SO₄ nanowires were prepared through the precipitation reaction of Bi(NO₃)₃·5H₂O and Na₂SO₄ in distilled water under the ambient condition and second, monoclinic phase Bi₂O₃ nanowires were prepared via the hydrothermal reaction of Bi₂O(OH)SO₄ and NaOH at 120 °C for 12 h. The resultant products were characterized by X-ray diffraction, field emission scanning electron microscope, and high resolution transmission electron microscopy. In addition, the photocatalytic studies indicated that the as-synthesized Bi₂O₃ nanowires were a kind of promising photocatalyst in remediation of water polluted by some chemically stable azo dyes.     

Shape controlled synthesis of Cu2O and its catalytic application to synthesize amorphous carbon nanofibers

Octahedral Cu₂O particles and Cu₂O nanowires were synthesized by a simple solution-phase route using N₂H₄·H₂O as reducing agent at room temperature. Amorphous carbon nanofibers were synthesized using octahedral Cu₂O particles and an acetylene gas source at atmospheric pressure. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and thermogravimetric (TG) analysis. SEM and TEM images indicated that most of the obtained octahedral Cu₂O particles had an edge length of 400-700 nm. The obtained nanowires had uniform diameters of about 15 nm, and the length of the nanowires ranged from 5 to 10 μm. The XRD result revealed the amorphous feature of the nanofibers. IR spectrum revealed that the nanofibers consist of -CH, -CH_2, -CC- and -CH₃ groups. The concentrations of N₂H₄·H₂O and NaOH played important roles in controlling the geometric shape of the Cu₂O.     

TiO2/Si nanowires hybrid system for efficient photocatalytic degradation of organic dye

Herein, titanium dioxide (TiO₂)-coated vertically aligned silicon nanowires (SiNWs/TiO₂) were fabricated and evaluated for photocatalytic degradation of organic dyes. Aligned SiNWs arrays were prepared by facile metal-assisted chemical-etching process with varying the etching time that was followed by TiO₂ nanoparticles coating using sputtering technique. The TiO₂ film crystallized in pure anatase phase with an average crystalline size of 50 nm, as was elucidated with X-ray diffraction studies. SEM analysis showed nanowires with varying lengths from 2.5 to 13.5 µm and confirmed the homogenous surface decoration with TiO₂. The homogeneous distribution of TiO₂ nanoparticles on nanowires was co-evidenced with Energy-Dispersive X-ray spectroscopy (EDX) and Raman spectra analysis. The developed SiNWs/TiO₂ was exploited for photocatalytic degradation of methylene blue; the role of hydrogen peroxide was also elucidated. The highest photocatalytic efficiency of 96% was achieved for SiNWs/TiO₂ with optimum nanowire length of 3.5 μm. The developed photocatalyst was found to be almost stable even after 190 days (~?5 months) and could be used as reusable and easily removable photocatalysts. The current study highlighted the SiNWs/TiO₂/H₂O₂ system as excellent candidate for water remediation applications.

     

Synthesis and photocatalytic properties of BiOCl nanowire arrays

Bismuth oxychloride (BiOCl) nanowire arrays have been successfully prepared employing the Anodic Aluminum Oxide (AAO) template assisted sol-gel method. Nanowires of 100 nm diameter and length 2-6 μm, assembled in the porous of AAO templates, were formed. XRD and HRTEM results show that the nanowires are pure BiOCl polycrystal phase without Bi₂O₃ or BiCl₃. The photocatalytic activity of BiOCl nanowire arrays was investigated by the degradation of Rhodamine B dye solution under UV irradiation.     

Facet‐Dependent Optical Properties of Semiconductor Nanocrystals

Recent observations of facet‐dependent electrical conductivity and photocatalytic activity of various semiconductor crystals are presented. Then, the discovery of facet‐dependent surface plasmon resonance absorption of metal–Cu₂O core–shell nanocrystals with tunable sizes and shapes is discussed. The Cu₂O shells also exhibit a facet‐specific optical absorption feature. The facet‐dependent electrical conductivity, photocatalytic activity, and optical properties are related phenomena, resulting from the presence of an ultrathin surface layer with different band structures and thus varying degrees of band bending for the {100}, {110}, and {111} faces of Cu₂O to absorb light of somewhat different wavelengths. Recently, it is shown that the light absorption and photoluminescence properties of pure Cu₂O cubes, octahedra, and rhombic dodecahedra also display size and facet effects because of their tunable band gaps. A modified band diagram of Cu₂O can be constructed to incorporate these optical effects. Literature also provides examples of facet‐dependent optical behaviors of semiconductor nanostructures, indicating that optical properties of nanoscale semiconductor materials are intrinsically facet‐dependent. Some applications of semiconductor optical size and facet effects are considered.     

Enhanced electrochemical reduction of hydrogen peroxide by Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanowire electrode

Crystalline Co₃O₄ nanowire arrays with different morphologies grown on Ni foam were investigated by varying the reaction temperature, the concentration of precursors, and reaction time. The Co₃O₄ nanowires synthesized under typical reaction condition had a diameter range of approximately 500–900 nm with a length of 17 µm. Electrochemical reduction of hydrogen peroxide (H₂O₂) of the optimized Co₃O₄ nanowire electrode was studied by cyclic voltammetry. A high current density of 101.8 mA cm^?2 was obtained at ?0.4 V in a solution of 0.4 M H₂O₂ and 3.0 M NaOH at room temperature compared to 85.8 mA cm^?2 at ?0.35 V of the Co₃O₄ nanoparticle electrode. Results clearly indicated that the Ni foam supported Co₃O₄ nanowire electrode exhibited superior catalytic activity and mass transport kinetics for H₂O₂ electrochemical reduction.     

Joule Heating a Palladium Nanowire Sensor for Accelerated Response and Recovery to Hydrogen Gas

The properties of a single heated palladium (Pd) nanowire for the detection of hydrogen gas (H₂) are explored. In these experiments, a Pd nanowire, 48–98 µm in length, performs three functions in parallel: 1) Joule self‐heating is used to elevate the nanowire temperature by up to 128 K, 2) the 4‐contact wire resistance in the absence of H₂ is used to measure its temperature, and 3) the nanowire resistance in the presence of H₂ is correlated with its concentration, allowing it to function as a H₂ sensor. Compared with the room‐temperature response of a Pd nanowire, the response of the heated nanowire to hydrogen is altered in two ways: First, the resistance change (ΔR/R₀) induced by H₂ exposure at any concentration is reduced by a factor of up to 30 and second, the rate of the resistance change – observed at the beginning (“response”) and at the end (“recovery”) of a pulse of H₂ – is increased by more than a factor of 50 at some H₂ concentrations. Heating nearly eliminates the retardation of response and recovery seen from 1–2% H₂, caused by the α → β phase transition of PdH_x, a pronounced effect for nanowires at room temperature. The activation energies associated with sensor response and recovery are measured and interpreted.     

Low-cost synthesis of hollow Cu2O octahedra with more than one shell

Inorganic materials with hollow and multilayer structures have attracted many interests because of their special applications. In this paper we reported a low-cost synthetic route for hollow cuprous oxide octahedra with more than one shell. Various characterizations identified the as-obtained powder as pure, uniform, and monodispersed Cu₂O octahedra wrapped by the {111} faces. To determine the formation mechanism, the time-dependent experiments were conducted and the results showed that the intermediate phase, CuO, precipitated out first and its reduction by amino acids led to the formation of hollow Cu₂O structures.     

Coordination state of Nb5+ ions in silicate and gallate glasses as studied by Raman spectroscopy

Raman spectra of K₂O-Nb₂O₅-SiO₂ glasses are measured in order to compare the coordination state of Nb⁵⁺ ions in gallate glasses with that in silicate glasses. It is found that less-distorted NbO₆ octahedra with no non-bridging oxygens as well as NbO₆ octahedra with non-bridging oxygens and/or with much distortion are present in the K₂O-Nb₂O₅-SiO₂ glasses. The Raman band in the 800 to 900 cm^–1 region is attributed to the NbO₆ octahedra with non-bridging oxygens and/or with much distortion. The broad bands in the 600 to 800 cm^–1 region are attributed to less-distorted NbO₆ octahedra with no non-bridging oxygens. An increase in the molar ratio Nb₂O₅/K₂O leads to an increase in the oxygens shared by more than two polyhedra and/or a decrease in non-bridging oxygens for the NbO₆ octahedra which possess non-bridging oxygens, or to an increase of distortion for much-distorted NbO₆ octahedra. At the same time, an increase in the molar ratio Nb₂O₅/K₂O increases the less-distorted NbO₆ octahedra with no non-bridging oxygens. In short, GaO₄ tetrahedra and NbO₆ octahedra compete to attract alkali ions in gallate glasses but such competition is not found in silicate glasses.     

PABA-assisted hydrothermal fabrication of W18O49 nanowire networks and its transition to WO3 for photocatalytic degradation of methylene blue

W₁₈O₄₉ nanowire networks have been fabricated by a facile hydrothermal method. In this method, p-aminobenzoic acid (PABA) was used as an assistant agent to control the morphology transformation. W₁₈O₄₉ and its products annealed at different temperature were characterized by XRD, SEM, TEM, UV–vis absorption spectroscopy, XPS, TGA, and FTIR. Formation mechanism and thermal stability of W₁₈O₄₉ nanowire networks were studied in detail. The experiment data showed that PABA played an important role in the induced crystal growth of W₁₈O₄₉ nanowires along [0?1?0] axis. In transformation, the structure of samples was controlled: from irregular particles to nanowire networks. W₁₈O₄₉ nanowire networks were annealed at different temperature. The nanowire networks collapsed at 450?°C, while WO₃ nanocrystals were obtained. The W₁₈O₄₉ nanowire networks annealed at 400?°C have a superior photocatalytic performance to degrade methylene blue and its specific surface area was up to 147?m²?g^?1.     

Preparation and characterization of Cu2O-TiO2: Efficient photocatalytic degradation of methylene blue

A series of copper-deposited titania were prepared by photoreduction method under irradiation with a 125-W high-pressure mercury lamp. From XPS and AES results, the deposited-copper formed Ti-O-Cu bond on the surface of TiO₂, and the Cu species on the surface of copper-deposited TiO₂ can be identified as Cu(I). The photocatalytic degradation activity of methylene blue for the Cu₂O-TiO₂ series increased with increasing Cu₂O-deposited content, and then decreased. The highest photocatalytic degradation activity of methylene blue was obtained for 0.16% Cu₂O-TiO₂. When copper-deposited content reached to 0.32%, the photocatalytic activity was lower than that of pure TiO₂. It is shown that Cu₂O on the surface of TiO₂ can trap electrons from the TiO₂ conduction band, and the electrons trapped on the Cu₂O-TiO₂ site are subsequently transferred to the surrounding adsorbed O₂, thereby avoiding electron-hole recombination, and enhancing the photocatalytic activity. Excess copper loading may screen the photocatalyst from the UV source, so the photocatalytic activity diminishes with increasing Cu₂O.