Photocatalytic activity of TiO2 nanotube layers loaded with Ag and Au nanoparticles

Ag and Au nanoparticles were found to significantly enhance the photocatalytic activity of self-organized TiO₂ nanotubular structures. The catalyst systems are demonstrated to be highly efficient for the UV-light induced photocatalytic decomposition of a model organic pollutant – Acid Orange 7. The metallic nanoparticles with a diameter of ∼10 ± 2 nm (Ag) and ∼28 ± 3 nm (Au) were attached to a nanotubular TiO₂ layer that consists of individual tubes of ∼100 nm of diameter, ∼2 μm in length and approx. 15 nm of wall thickness. Both metal particle catalyst systems enhance the photocatalytic decomposition significantly more on the nanotubes support than placed on a compact TiO₂ surface.     

Chemical bath deposition of CdS quantum dots on vertically aligned ZnO nanorods for quantum dots-sensitized solar cells

Formation of CdS quantum dots (Q dots) on the vertically aligned ZnO nanorods electrode was carried out by chemical bath deposition. The diameter and thickness of ZnO nanorods are ～100–150 nm and ～1.6 μm, respectively, and CdS Q dots on ZnO nanorods have a diameter of smaller than 15 nm. In application of the Q dots-sensitized solar cells, composite film exhibited a power conversion efficiency of 0.54% under air mass 1.5 condition (80 mW/cm²), and incident-photon-to-current conversion efficiency showed 18.6%.     

Synthesis of rod-shaped La0.7Sr0.3MnO3 by a simple solid state ceramic route

The manganese oxides La_0.7Sr_0.3MnO₃ with rod shape have been synthesized by a simple solid state ceramic method. The morphology and magnetic properties of La_0.7Sr_0.3MnO₃ have been studied by XRD, SEM, TEM and VSM. The diameters of rod-shaped oxide were ranging from 180 nm to1.5 μm and the length was averaging 20 μm. The ratio of length to diameter could reach more than 35:1. The magnetic results showed that the Curie temperature of rod-shaped La_0.7Sr_0.3MnO₃ is far lower than single crystal.     

Short aspect ratio gold nanorods prepared using gamma radiation in the presence of cetyltrimethyl ammonium bromide (CTAB) as a directing agent

The synthesis of short aspect ratio gold nanorods using gamma radiation method by incorporating cetyltrimethyl ammonium bromide (CTAB) as a directing agent is reported in this communication. The radiolysis of Au⁺, in the presence of 2.5 nm Au seeds and 0.1 mol dm^?3 isopropanol, results in the formation of Au spheres as evident from surface plasmon resonance band at 527 nm. However, by carrying out radiolysis at lower radiation dose rate, short aspect gold nanorods having surface plasmon bands at 513 and 670 nm have been prepared. The formation of rods at low radiation dose rate was observed to be governed by the kinetics of particle growth. The TEM of as-synthesized nanoparticles confirmed the formation of uniform sized nanorods having an aspect of 2.4.     

Synthesis of gold nanorods using concentrated aerosol OT in hexane and its application as catalyst for the reduction of eosin

The microemulsion method for the preparation of nanoparticles is well known. We have used the aqueous core of highly concentrated aerosol OT in hexane solution to synthesize gold nanorod by utilizing the aqueous core of surfactant aggregates as host nanoreactor. The shape and size of the aqueous core as well as the particles formed inside the core can be controlled by changing the parameter W₀ (water to surfactant ratio), concentration of gold salt and the concentration of surfactant. When the concentration of the surfactant is very high the shape of the aqueous droplet does not remain spherical but take the shape of prolate. In our study we have made gold nanorods by the reduction of gold chloride with sodium borohydride in the aqueous core of 1 M AOT hexane at a W₀ of 10. The rods are highly monodispersed with a diameter of about 20 nm and a length of 200 nm with an aspect ratio of 10. The absorption spectra of the gold nanorods show two different peaks one at 535 nm and the other at 965 nm. The particles were used as a catalyst for the reduction of eosin with sodium borohydride. The rate constant comes out be very large in comparison with that of uncatalysed reaction. The reaction was carried out at various temperatures between 20 and 60 °C and the activation energy of the reaction was calculated using Arrhenius plot between–ln k and 1/T. The activation energy of the gold nanorods catalysed reaction comes out to be more than two times as compared to uncatalysed reaction.     

Electrodeposition of monodispersed metal nanoparticles in a nafion film: Towards highly active nanocatalysts

We have explored a new and facile method for the fabrication of metal nanoparticles on the electrode surface. The approach for fabricating metal nanoparticles was carried out by two steps consisting of ion-exchange in nafion film coated on the electrode and subsequent reduction of metal ions to metallic nanoparticles by electrochemical method. The results of characterization by TEM show that metal nanoparticles were nearly monodispersed in the whole nafion film. The average diameters of Cu, Co and Ni nanoparticles were statistically measured to be 5.1 nm ± 0.2 nm, 4.6 nm ± 0.2 nm and 4.7 nm ± 0.2 nm, respectively. The amount of metal nanoparticles can be readily controlled by the amount of nafion coated on the electrode. By performing the H₂O₂ reduction at the obtained Cu nanoparticles, the high electrocatalytic activity of metal nanoparticles fabricated has been confirmed.     

Dye-sensitized solar cells using anodic TiO2 mesosponge: Improved efficiency by TiCl4 treatment

In the present work, we produce 15 μm thick titania mesosponge layers (TMSL) by a Ti anodization/etching process and use the layers in dye-sensitized solar cells (DSCs). We show that the solar cell efficiency can considerably be improved by a TiCl₄ hydrolysis treatment (increase of approx. 40% to an overall value of 4.9% under AM 1.5 illumination). This beneficial effect is due to the decoration of the ～10 nm wide channels present in TMSL with TiO₂ nanoparticles of approx. 3 nm diameter, which allow for a significantly higher specific dye loading of the TMS structure.     

A novel waist-regulable dumbbell-like nanosuperstructure of (3-carboxy-1-acyl-propyl)-ferrocene

Dumbbell-like nanosuperstructures of (3-carboxy-1-acyl-propyl)-ferrocene were successfully prepared by ultrasonic–pHcontrolling–reprecipitation method. The scanning electron microscope shows that as-obtained products were composed of nanorods. The length of the products is about 6–12 μm, the diameter of the two polar coronas and the middle part (waist) are respectively about 2–8 μm and 0.5–2 μm. The diameter of the nanorods that are the basic unit of the superstructures, is about 0.3 μm. X-ray diffraction analysis of the products indicated that the superstructures keep original crystal structure. The optical properties of the products were characterized by FT-IR spectrometer and UV spectrometer, and they display quantum size effect. This paper provides a novel method that has potential application in preparing other organometallic compounds superstructures, and more importantly, the as-obtained superstructures have widely applications. The possible mechanism was also proposed.     

Assembly of NaTaO3 porous microspheres via imperfect oriented attachment mechanism

Spongy-like NaTaO₃ mesoporous microspheres are assembled from nanoparticles via imperfect oriented attachment. Study shows that the NaTaO₃ spongy microspheres with the diameters of ～1 μm are composed of the fundamental building blocks of ～50 nm NaTaO₃ nanospheres. The high-resolution transmission electron microscopy further reveals that these fundamental building blocks are assembled from primary building blocks of ～10 nm NaTaO₃ nanocrystals. The pore diameters of these spongy microspheres are ca. 30 nm and the Brunauer–Emmett–Teller (BET) surface area is calculated to be 57.8 m² g^?1. This interesting ternary alkali metal composite oxide of NaTaO₃ spongy microspheres with high specific surface area and strong stability will be favorable for their practical application in photocatalysis. This synthesis route may throw light on the fabrication of the binary or ternary porous metal oxides by geometrical stacking of the nanobuilding blocks via imperfect oriented attachment.     

TiO2@CdS core–shell nanorods films: Fabrication and dramatically enhanced photoelectrochemical properties

In this paper, we prepared TiO₂@CdS core–shell nanorods films electrodes using a simple and low-cost chemical bath deposition method. The core–shell nanorods films electrodes were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and UV–vis spectrometry techniques. After applying these TiO₂@CdS core–shell nanorods electrodes in photovoltaic cells, we found that the photocurrent was dramatically enhanced, comparing with those of bare TiO₂ nanorods and CdS films electrodes. Moreover, TiO₂@CdS core–shell nanorods film electrode showed better cell performance than CdS nanoparticles deposited TiO₂ nanoparticles (P25) film electrode. A photocurrent of 1.31 mA/cm², a fill factor of 0.43, an open circuit photovoltage of 0.44 V, and a conversion efficiency of 0.8% were obtained under an illumination of 32 mW/cm², when the CdS nanoparticles deposited on TiO₂ nanorods film for about 20 min. The maximum quantum efficiency of 5.0% was obtained at an incident wavelength of 500 nm. We believe that TiO₂@CdS core–shell heterostructured nanorods are excellent candidates for studying some fundamental aspects on charge separation and transfer in the fields of photovoltaic cells and photocatalysis.     

A novel synthesis of ultrathin CoPt3 nanowires by dealloying larger diameter Co99Pt1 nanowires and subsequent stress-induced crack propagation

A novel approach to the fabrication of ultrathin CoPt₃ nanowires with a diameter of a few nanometers has been developed, by taking advantage of the volume shrinkage and formation of nanoporous structures upon dealloying electrodeposited Co₉₉Pt₁ nanowires (28 nm in diameter), followed by an ultrasonication treatment. The as-produced ultrathin CoPt₃ nanowires have an average diameter of 5 nm and lengths of up to 10 μm, and are found to be ferromagnetic at room temperature.     

PVP-Assisted ZrO2 coating on LiMn2O4 spinel cathode nanoparticles prepared by MnO2 nanowire templates

LiMn₂O₄ spinel nanorods prepared from nanowire MnO₂ templates were capped with polyvinyl pyrrolidone (PVP) and coated with ZrC₂O₄ precursors in aqueous solution. Upon annealing at 600 °C in air, an amorphous ZrO₂ nanoscale coating layer was obtained on the spinel nanoparticles with a particle size of <100 nm that formed from the splitting of the original spinel nanorods. The electrochemical cycling results clearly showed that nanoscale ZrO₂ coating significantly improved the rate capability and cycle life at 65 °C in spite of very high surface area of the spinel nanoparticles.     

Electrochemical synthesis of Au/polyaniline–poly(4-styrenesulfonate) hybrid nanoarray for sensitive biosensor design

Au/polyaniline (PANI)–poly(4-styrenesulfonate) (PSS) hybrid nanoarray is fabricated for biomolecular sensing in neutral aqueous solutions. Firstly, an array of one-dimensional Au nanorods (diameter = ca. 200 nm, length = ca. 3 μm) is formed by a template-electrodeposition method using a porous anodic alumina membrane, and then a thin PANI–PSS composite layer is electropolymerized on the surface of the Au nanorods. The resulting Au/PANI–PSS hybrid nanoarray exhibits a quasi-reversible redox electrochemical process at ca. +0.11 V and electrocatalytic oxidation of reduced β-nicotinamide adenine dinucleotide (NADH) is attained with a detection limit of 0.3 μM in a neutral solution.     

Enhancing the bioactivity of zirconium with the coating of anodized ZrO2 nanotubular arrays prepared in phosphate containing electrolyte

Bioactive zirconium oxide nanotubular arrays on zirconium alloys are prepared electrochemically in fluoride and phosphate containing electrolyte. Geometric factors of the ZrO₂ nanotubular layers, particularly the pore diameter and thickness, are affected by the electrochemical conditions, including applied potential and anodization time. Under specific sets of conditions, highly ordered ZrO₂ nanotubular arrays are formed with diameters varying from 30 nm to 75 nm and lengths varying from 2 μm to 12 μm. XPS shows that the nanotubular layer contains a significant amount of phosphate species distributed almost homogeneously over the entire tubular length. The ZrO₂ nanotubular layer formed in fluoride and phosphate containing electrolyte highly enhances the formation of bioactive hydroxyapatite coating in simulated biological fluid (SBF).     

In situ growth of LiFePO4 nanorod arrays under hydrothermal condition

A novel in situ combinatorial method has been developed to fabricate LiFePO₄ nanorod arrays, during which anodized alumina oxide (AAO) was employed as the template and ethylene glycol/water medium is used to ensure mass transportation rates of different chemicals to match each other. The samples were then characterized by X-ray diffractometer (XRD), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and energy dispersive X-ray spectroscopy (EDX). After being hydrothermally processed at 160 °C, the highly-crystallized LiFePO₄ arrays were directly obtained, which are composed of single crystal nanorods with a diameter of 200 nm and a length of 3 μm. The reported synthesis is simple, mild and energy-efficient. A noteworthy advantage over conventional sol–gel–template methods is the elimination of high-temperature annealing.     

Formation of porous TiOx biomaterials in H3PO4 electrolytes

In this work, formation of porous TiO_x layers and theirs corrosion behavior were studied. Application of H₃PO₄ electrolytes results in porous TiO_x formation. The process is enhanced by small amount of HF content in the electrolyte. The HF results in higher current density, enhancing dissolution. Small 0.5% HF concentration results in nanopores formation, with pore diameter of about 45 nm. Increase of HF concentration up to 10% results in pores with average diameter of about 5.2 μm. An increase of etching time results in larger pore diameter, but between large 2–5 μm diameter pores smallest ones were observed with diameter below 200 nm. In the initial etching process a remnants of the flat surface are presents with initial cracks in the surface, indicating places for growth of the pores.The TiO_x layers can be used as a biomaterial. The corrosion behavior of the layer investigated in Ringer’s solution, revealed an excellent corrosion resistance, with respect to pure Ti.     

Fabrication and electrochemical properties of the Sn–Ni–P alloy rods array electrode for lithium-ion batteries

A new ternary Sn–Ni–P alloy rods array electrode for lithium-ion batteries is synthesized by electrodeposition with a Cu nanorods array structured foil as current collector. The Cu nanorods array foil is fabricated by heat treatment and electrochemical reduction of Cu(OH)₂ nanorods film, which is grown directly on Cu substrate through an oxidation method. The Sn–Ni–P alloy rods array electrode is mainly composed of pure Sn, Ni₃Sn₄ and Ni–P phases. The electrochemical experimental results illustrate that the Sn–Ni–P alloy rods array electrode has high reversible capacity and excellent coulombic efficiency, with an initial discharge capacity and charge capacity of 785.0 mAh g^?1 and 567.8 mAh g^?1, respectively. After the 100th discharge–charge cycling, capacity retention is 94.2% with a value of 534.8 mAh g^?1. The electrode also performs with an excellent rate capacity.     

Electrochemically synthesized CdS nanoparticle-modified TiO2 nanotube-array photoelectrodes: Preparation,characterization, and application to photoelectrochemical cells

A novel electrodeposited CdS nanoparticle-modified highly-ordered TiO₂ nanotube-array photoelectrode and its application to photoelectrochemical cells is reported. Results show formation of a thin, nanoparticulate CdS layer, comprised of sphere-like 10–20 nm diameter nanoparticles, on the anodic synthesized TiO₂ nanotube-array (inner diameter of 70 nm, wall thickness 25 nm and ca. 400 nm length) electrode. The resulting CdS–TiO₂ photoelectrode has an as-fabricated bandgap of 2.53, and 2.41 eV bandgap after sintering at 350 °C in N₂ ambient. Photoelectrochemical properties are described in detail.     

Chrysanthemum-like Co3O4 architectures: Hydrothermal synthesis and lithium storage performances

Three-dimensional chrysanthemum-like Co₃O₄ was prepared via a facile hydrothermal route without any template, and a subsequent calcination process. With a controlled concentration of the homogeneous precipitation agent, urea, a chrysanthemum-like precursor was hydrothermally obtained at 120 °C for 20 h, and the morphology was kept for Co₃O₄ after a subsequent calcination at 300 °C for 2 h. Co₃O₄ chrysanthemum-like architectures are assemblies of nanorods radiating from a common centre, and the nanorods consisted of interconnected nanoparticles with the size of about 30 nm. When tested as an anode material of Li-ion batteries, chrysanthemum-like Co₃O₄ presented a discharge capacity of ∼450 mA h/g after 50 discharge/charge cycles.     

Titanium oxide nanotubes prepared in phosphate electrolytes

In the present communication, we report the electrochemical formation of self-organized titanium oxide nanotubes (π-TiO₂) prepared in fluoride ion containing phosphate electrolytes. The morphology of the π-TiO₂ layers (particularly the pore diameter and length) is affected by the electrochemical conditions used (applied potential, electrolyte composition, pH, and anodizing time). Under specific sets of conditions highly self-organized titanium oxide nanotubes are formed with diameters varying from approx. 40 nm to 100 nm and length from approx. 100 nm to 4 μm. XPS investigations show that the nanotubes formed in phosphate solutions contain a significant amount of phosphorous species.