Hydrothermal growth of TiO2 nanowire membranes sensitized with CdS quantum dots for the enhancement of photocatalytic performance

In this paper, TiO₂ nanowires (NWs) on Ti foils were prepared using a simple hydrothermal approach and annealing treatment. CdS quantum dots (QDs) were assembled onto the crystallized TiO₂ NWs by sequential chemical bath deposition. Ultraviolet-visible absorption spectra showed that CdS adds bands in the visible to the TiO₂ absorption and exhibited a broad absorption band in the visible region, which extended the scope of absorption spectrum and helped improve the photocatalytic degradation efficiency. The results of photocatalytic experiment revealed that CdS-TiO₂ NWs possessed higher photocatalytic activities toward methyl orange than pure TiO₂ nanowires. The degradation efficiency of 96.32% after ten cycles indicated that the as-prepared CdS-TiO₂ composite exhibited excellent long-time recyclable ability and can be reused for the degradation of contaminants.     

Ag nanowires and its application as electrode materials in electrochemical capacitor

Silver nanowires were synthesized on a large scale by using anodic aluminum oxide (AAO) film as templates and serving ethylene glycol as reductant. Their morphological and structural characterizations were characterized with field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and selected area electron diffraction (SAED). The electrochemical properties of silver nanowires as electrode materials for electrochemical capacitors were investigated by cyclic voltammetry (CV) and galvanostatic charge/discharge technique in 6 M KOH aqueous electrolyte. The Ag₂O/Ag coaxial nanowires were formed by the incomplete electrochemical oxidation during the charge step. The maximum specific capacitance of 987 F g^?1 was obtained at a charge–discharge current density of 5 mA cm^?2.     

Electrodeposition: a versatile and inexpensive tool for the synthesis of nanoparticles,nanorods, nanowires,and nanoclusters of metals

The synthesis of various nanoscale materials, such as nanoparticles, nanowires of Au, Pt, Ni Co, Fe, Ag etc., by electrodeposition techniques have been demonstrated in this article. Both potentiostatic and galvanostatic methods were employed to carry out the electrodeposition process under different potential ranges, time durations, and current densities. The electrochemical behavior of the deposited nanoparticles on various substrates was investigated by cyclic voltammetric and chronoamperometric techniques. The synthesis of mono-dispersed gold (Au) nanoparticles on indium tin oxide (ITO) coated glass, preparation of Au nanorods on nanoporous anodic alumina oxide (AAO), formation of Au nanoclusters on polypyrrole-modified glassy carbon electrode and one-step electrodeposition of nickel nanoparticle chains embedded in TiO₂ etc. have been highlighted in this article. The potential applications of synthesized nanoparticles such as the role of maghemite (Fe₂O₃) in arsenic remediation, higher electrocatalytic activity of Ag nanoclusters for the reduction of benzyl chloride, and the role of C₆₀ nanoparticle-doped carbon film in fabrication processes are also presented in this article.     

TiO2纳米线阵列膜的制备及其光催化降解气相甲醛动力学

分别以阳极氧化铝、玻璃纤维布、玻璃作载体采用溶胶-凝胶法制备TiO₂纳米线阵列膜（TiO₂/AAO）与TiO₂/玻璃、TiO₂/玻布光催化剂,用XRD、电子探针和比表面仪进行表征,并对比其光催化不同浓度气相甲醛的降解活性.结果表明：制备的TiO₂纳米线线径为26 nm,线长1.2 μm,与其他TiO₂载体相比,具有小密度、高比表面积,TiO₂/AAO光催化剂有较大反应速率常数及Langmuir吸附平衡常数,在UV下对低浓度气相甲醛有更多的活性吸附中心,这说明对低浓度气体,高比表面积催化剂有重要作用,它能更多地富集低浓度气体,提高光降解率.     

Direct growth of ultra-long platinum nanolawns on a semiconductor photocatalyst

A template- and surfactant-free process, thermally assisted photoreduction, is developed to prepare vertically grown ultra-long Pt nanowires (NWs) (about 30-40 nm in diameter, 5-6 μm in length, and up to 80 NWs/100 μm² in the wire density) on TiO₂ coated substrates, including Si wafers and carbon fibers, with the assistance of the photocatalytic ability and semiconductor characteristics of TiO₂. A remarkable aspect ratio of up to 200 can be achieved. TEM analytical results suggest that the Pt NWs are single-crystalline with a preferred 〈111〉 growth direction. The precursor adopted and the heat treatment conditions are crucial for the yield of NWs. The photoelectrons supplied by TiO₂ gives rise to the formation of nano-sized Pt nuclei from salt melt or solution. The subsequent growth of NWs is supported by the thermal electrons which also generated from TiO₂ during the post thermal treatment. The interactions between the ions and the electrons in the Pt/TiO₂ junction are discussed in this study.     

The interfacial effect of TiO2–Ag core–shell micro‐/nanowires on poly(arylene ether nitrile)

Novel TiO₂–Ag core–shell micro‐/nanowires (TiO₂ shell coating on Ag core) have been successfully prepared via a solvent–thermal method. Energy dispersive spectroscopy and X‐ray diffraction analyses revealed that the micro‐/nanowires were composed of Ag, Ti and O elements, and Ag was face‐centered cubic whereas TiO₂ was mainly amorphous. Interestingly, scanning electron microscopy (SEM) and transmission electron microscopy results showed that most of the TiO₂ bristles were perpendicular to and uniformly studded on the surface of the Ag cores. Subsequently, TiO₂–Ag/poly(arylene ether nitrile) (PEN) composite films were prepared via a solution‐casting method in order to investigate the effect of TiO₂–Ag on the PEN matrix. SEM images showed that there was good interfacial adhesion between fillers and PEN matrix owing to the special bristle‐like structure. Thermal analysis results showed that the TiO₂–Ag/PEN composite films possessed excellent thermal properties endowed by the PEN matrix. The dielectric constant of the composite films increased to 9.3 at 100 Hz when the TiO₂–Ag loading reached 40 wt%. Rheology measurements revealed that the network formed by TiO₂–Ag was sensitive to shear stress and nearly time independent. © 2013 Society of Chemical Industry     

Template assisted fabrication of TiO2 and WO3 nanotubes

Anodic aluminum oxide (AAO) templates with diameters of 200–500 nm were generated by anodizing a commercial aluminum (Al) substrate (99.7%) in 1 vol% phosphoric acid (H₃PO₄), with an applied voltage of 195 V. Titania and tungsten oxide nanotubes (NTs) were successfully grown on AAO template by the sol–gel process. Thermal gravimetric analyzer (TGA) curves showed that gel can be transfered to nanocrystalline particles after 19% weight loss of water molecule by evaporation. The results showed that the nanocrystalline TiO₂ NTs presented at 200 °C, and grains grew as temperature increased. At a temperature of 550 °C, the (101), (103), (004), (112), (200), (105), and (211) planes of anatase TiO₂ were detected clearly, whereas tungsten oxide NTs are amorphous after heat treatment at 200 °C or 300 °C. But the (110), (111), (002), (022), (222), and (004) planes of γ-WO₃ phase can be observed obviously after the heat treatment at 400 °C.     

Kinetic study of Pt nanocrystal deposition on Ag nanowires with clean surfaces via galvanic replacement

ABSTRACT: Without using any templates or surfactants, this study develops a high-yield process to prepare vertical Ag-Pt core-shell nanowires (NWs) by thermally assisted photoreduction of Ag NWs and successive galvanic replacement between Ag and Pt ions. The clean surface of Ag nanowires allows Pt ions to reduce and deposit on it and forms a compact sheath comprising Pt nanocrystals. The core-shell structural feature of the NWs thus produced has been demonstrated via transmission electron microscopy observation and Auger electron spectroscopy elemental analysis. Kinetic analysis suggests that the deposition of Pt is an interface-controlled reaction and is dominated by the oxidative dissolution of Ag atoms. The boundaries in between Pt nanocrystals may act as microchannels for the transport of Ag ions during galvanic replacement reactions.     

Effect of Ag/Al co-doping method on optically p-type ZnO nanowires synthesized by hot-walled pulsed laser deposition

Silver and aluminum-co-doped zinc oxide (SAZO) nanowires (NWs) of 1, 3, and 5 at.% were grown on sapphire substrates. Low-temperature photoluminescence (PL) was studied experimentally to investigate the p-type behavior observed by the exciton bound to a neutral acceptor (A⁰X). The A⁰X was not observed in the 1 at.% SAZO NWs by low-temperature PL because 1 at.% SAZO NWs do not have a Ag-O chemical bonding as confirmed by XPS measurement. The activation energies (E_a) of the A⁰X were calculated to be about 18.14 and 19.77 meV for 3 and 5 at.% SAZO NWs, respectively, which are lower than the activation energy of single Ag-doped NW which is about 25 meV. These results indicate that Ag/Al co-doping method is a good candidate to make optically p-type ZnO NWs.     

Electrochemical synthesis of poly(p-phenylene) and poly(p-phenylene)/TiO2 nanowires in an ionic liquid

This study shows for the first time that poly(p-phenylene) (PPP) nanowires can be easily obtained by electrochemical synthesis at room temperature. The method involves the template assisted electropolymerization of benzene in the air and water stable ionic liquid 1-hexyl-3-methylimidazolium tris(pentafluoroethyl)trifluorophosphate ([HMIm]FAP). Track-etched polycarbonate membranes (PC) with an average pore diameter of 90 nm were used as templates. Dense and highly flexible bundles of PPP nanowires with a high aspect ratio (>160) were easily obtained by this method. In addition, we present here our first results to obtain PPP/TiO₂ nanowires by the combination of a sol–gel technique with electropolymerization. HR-SEM, TEM and EDX were used for the structural characterization of the nanowires.     

Fabrication of cobalt-nickel binary nanowires in a highly ordered alumina template via AC electrodeposition

Cobalt-nickel (Co-Ni) binary alloy nanowires of different compositions were co-deposited in the nanopores of highly ordered anodic aluminum oxide (AAO) templates from a single sulfate bath using alternating current (AC) electrodeposition. AC electrodeposition was accomplished without modifying or removing the barrier layer. Field emission scanning electron microscope was used to study the morphology of templates and alloy nanowires. Energy-dispersive X-ray analysis confirmed the deposition of Co-Ni alloy nanowires in the AAO templates. Average diameter of the alloy nanowires was approximately 40 nm which is equal to the diameter of nanopore. X-ray diffraction analysis showed that the alloy nanowires consisted of both hexagonal close-packed and face-centered cubic phases. Magnetic measurements showed that the easy x-axis of magnetization is parallel to the nanowires with coercivity of approximately 706 Oe. AC electrodeposition is very simple, fast, and is useful for the homogenous deposition of various secondary nanostuctured materials into the nanopores of AAO.     

From ceria nanotubes to nanowires through electrogeneration of base

The preparation of Ce(OH)₃/CeO₂ nanostructures (NSs) through electrogeneration of base into anodic alumina membranes was studied. The effects of solvent (alcohol and/or water), Ce³⁺ partner anion nature (chloride or nitrate) and concentration, applied potential or current density in driving the morphology toward nanowires (NWs) and/or nanotubes (NTs) was described. The structural analysis performed by X-Ray Diffraction and Raman Spectroscopy allowed to evidence that the presence of Ce(IV) into the nanostructures strongly depends on the oxygen content in the growing environment.     

Nanowires embedded porous TiO2@C nanocomposite anodes for enhanced stable lithium and sodium ion battery performance

A porous carbon nanocomposite with embedded TiO₂ nanowires (NWs) was synthesized using a two-step synthetic method in which carbon matrix was obtained by carbonizing a vacuum dried gel. This unique structure in which TiO₂ nanowires uniformly distributed in and tightly bonded to the carbon matrix shortened the electron transport path and reduced the transmission resistance. Nanoporous structure ensured continuous transfer of Li⁺/Na⁺ and supplied a large specific surface area of 280.82 m² g⁻¹ to provide more active sites. Different from other existing works on TiO₂@C anode materials with TiO₂ loading higher than 60 wt%, the obtained very small amount of TiO₂ (~12 wt%) improved the electrochemical and long-cycle performance of carbon substrate with TiO₂ NWs embedded significantly, due to uniformly distributed TiO₂ NWs throughout the carbon matrix. These TiO₂@C composite anodes could deliver a specific capacity of 286 mA h g⁻¹ at 0.3 C, 197 mA h g⁻¹ at 0.15 C for lithium and sodium ion batteries, respectively. It maintained remarkably stable reversible capacities of 128 and 125 mA h g⁻¹ for lithium and sodium ion batteries at 3 C during 2500 cycles, respectively. Smaller fluctuations and smoother curves demonstrated that sodium ion storage was more stable than lithium ion storage for the TiO₂@C composite anode. In addition, the capacitive contributions of TiO₂@C in both systems are quantified by kinetics analysis.     

氧化铝模板中Ag纳米线阵列的选择性生长

利用Ag离子与Br离子之间的化学沉积作用在孔隙中充满明胶的阳极氧化铝（AAO）模板中制备了AgBr/AAO纳米介孔复合材料.材料选择性曝光后,利用原位显影液对其进行化学显影,在AAO模板中选择性得到Ag纳米线阵列.实验结果表明：Ag纳米线是连续的、致密的,且具有多晶结构,充满了曝光部分的模板孔隙.本文还对影响Ag纳米线选择性生长的因素进行了简单讨论.     

Fabrication of diameter-modulated and ultrathin porous nanowires in anodic aluminum oxide templates

Anodic aluminum oxide (AAO) membranes with modulated pore diameter were synthesized by pulse anodization in 0.3 M sulfuric acid at 1 °C. For AAO growth, a typical combination of alternating mild anodizing (MA) and hard anodizing (HA) pulses with applied potential pulses of 25 V and 35 V was applied. The control of the duration of HA pulses will provide an interesting way to tune the shape of pores and the structure of AAO channels. It was found that a non-uniform length of HA segments in cross section of AAO is usually observed when the HA pulse duration is shorter than 1.2 s. The pulse anodization performed with longer HA pulses leads to the formation of AAO templates with periodically modulated pore diameter and nearly uniform length of segments. Various diameter-modulated metallic nanowires (Au, Ag, Ni and Ag–Au) were fabricated by electrodeposition in the pores of anodic alumina membranes. A typical average nanowire diameter was about 30 nm and 48 nm for MA and HA nanowire segments, respectively. After a successful dealloying silver from Ag–Au nanowires, porous ultrathin Au nanowires were obtained.     

A novel facile synthesis and characterization of molybdenum nanowires

We describe a straightforward technique to synthesize pure Mo nanowires (NWs) from Mo₆S_yI_z (8,2 <y + z ≤ 10) NWs as precursor templates. The structural transformations occur when Mo₆S_yI_z NWs are annealed in Ar/H₂ mixture leading to the formation of pure Mo NWs with similar structures as initial morphologies. Detailed microscopic characterizations show that large diameters (>15 nm) Mo NWs are highly porous, while small diameters (<7 nm) are made of solid nanocrystalline grains. We find NW of diameter 4 nm can carry up to 30 μA current without suffering structural degradation. Moreover, NWs can be elastically deformed over several cycles without signs of plastic deformation.     

Ordered CoFe2O4 nanowire arrays with preferred crystal orientation and magnetic anisotropy

CoFe₂O₄ nanowire arrays were fabricated by electrodeposition of Fe²⁺ and Co²⁺ into anodic aluminum oxide (AAO) templates and further oxidization. The phase structure of the nanowires is cubic spinel-type, and the XRD result exhibits perfect preferred crystallite orientation along the nanowire axes. Compared with CoFe₂O₄ nanowire arrays synthesized by other methods, the magnetic hysteresis loops demonstrate that the arrays of nanowires exhibit uniaxial magnetic anisotropy with easy magnetization direction along the nanowire axes owing to the large shape anisotropy. This approach provides a facile technology to fabricate oxide nanowires with uniaxial magnetic anisotropy.     

Inactivation of Escherichia coli using UV/Ag?TiO2/O3‐mediated advanced oxidation: application to ballast water disinfection

BACKGROUND: Ballast water discharge from ships is regarded as one of the four major risk factors that threaten global marine environmental safety, and ballast water treatment is vital to prevent the introduction of potentially invasive species. The UV/Ag? TiO₂/O₃ process has been investigated for its potential use for ballast water treatment using Escherichia coli (E. coli) as an indicator bacterium. Inactivation curves were obtained, and the occurrence of oxidants was studied. RESULTS: Compared with individual unit processes with ozone or UV/Ag? TiO₂, the inactivation of E. coli by the combined UV/Ag? TiO₂/O₃ process was enhanced, and the inactivation efficiency was improved with increasing ultraviolet intensity and ozone dose. The initial total residual oxidant (TRO) concentration was positively correlated with ozone dose, and resulted in faster decay rate for lower initial concentration. Persistence of TRO resulted in a cumulative bacteria mortality in the effluent. CONCLUSION: The UV/Ag? TiO₂/O₃ process was found to be efficient for E. coli inactivation in simulated ballast water. Copyright © 2011 Society of Chemical Industry     

Mechanism of formation of urchin-like ZnO

Thin films composed of ZnO nanowires (NWs) hierarchically organized with an urchin-like 3D morphology were obtained by combining the electrochemical deposition and sphere lithography methods. Deposited on a transparent conductive oxide substrate (TCO), a monolayer of carboxylate modified polystyrene spheres organized with a hexagonal closed-packed structure played the role of a template. The spheres were activated in a solution of zinc chloride by the formation of bonds between the carboxylate terminals and the Zn²⁺ ions and were used as a template for the electrodeposition of vertically aligned ZnO NWs around them. Without this treatment, ZnO NWs were deposited only on the TCO substrate between the PS spheres. To reach a density of nanowires high enough to obtain the urchin morphology, the concentration of ZnCl₂ had to be at least equal to 2 M. It was also found, as soon as small grains of ZnO started to be electrodeposited on the polystyrene spheres that the spheres were no longer close packed. The space created between them increased with the increase in the number of small ZnO grains and the increase in their length, allowing the further growth of the nanowires between the spheres. As a result the initial round shape of the spheres was modified and the urchin-like ZnO exhibited an ellipsoidal shape.     

Magnetization reversal of Co/Pd multilayers on nanoporous templates

By making use of an e-beam deposition system, the [Co(2 Å)/Pd(10 Å)]₁₅ multilayers were prepared on a Si(100) substrate and anodized aluminum oxide [AAO] templates with average pore diameters of around 185, 95, and 40 nm. The mechanism of magnetization reversal of the Co/Pd multilayers was investigated. Wall motion was observed on the Co/Pd multilayers grown on the Si substrate. A combination of wall motion and domain rotation was found in the sample grown on the AAO template with a 185-nm pore diameter. For the samples grown on the AAO templates with pore diameters of around 95 and 40 nm, the reversal mechanism was dominated by domain rotation. The rotational reversal was mainly contributed from the underlying nanoporous AAO templates that provided an additional pinning effect.PACS: 75.30.Gw, magnetic anisotropy; 78.67.Rb, nanoporous materials; 75.60.Jk, magnetization reversal mechanisms.