Linen fiber template-assisted preparation of TiO2 nanotubes: palladium nanoparticle coating and electrochemical applications

TiO₂ nanotubes were fabricated from TiF₄ precursors within the pore channels of the linen fiber templates, resulting in crystalline fabricated titanate nanotubes (f-TNTs) upon removal by calcination at 500–600 °C. The f-TNTs were formed by the aggregation of TiO₂ nanoparticles (NPs) with a diameter of 80 nm; the wall thickness and size of the f-TNTs can be controlled by adjusting the concentration of the TiF₄ precursor, time, temperature, and the size of the linen fibers respectively. After that, palladium (Pd⁽⁰⁾) NPs were coated on the surface of the f-TNTs (Pd/f-TNTs) by the chemical reduction method, using NaBH₄ as a reducing agent. The size of the Pd⁽⁰⁾ NPs is about 10–13 nm. The Pd/f-TNT nanocomposite is systematically characterized by X-ray diffraction, high-resolution transmission electron microscopy, and field emission scanning electron microscopy. The Pd/f-TNT nanocomposite-modified glassy carbon electrodes exhibited excellent electrocatalytic activity as well as amperometric determination of hydrazine, ascorbic acid, and dopamine; these electrochemical applications were carried out by cyclic voltammetry.     

Enhanced field emission from multiwall carbon nanotube films by secondary growth

We have studied nickel, gold, and ferritin coatings on catalytically grown multiwall carbon nanotubes as well as the generation of secondary nanotubes by resubmitting the decorated nanotubes to the chemical vapor deposition process. Nickel layers sputtered on nanotubes show a stronger interaction with the nanotube walls than gold coatings. At ambient temperature this results in a metal film that is more homogeneous for Ni than for Au. Surface mass transport at elevated temperatures leads to a transformation of the coating to nanoscale clusters on the nanotube surface. The resulting Au clusters are spherelike with a very small contact area with the nanotube whereas the Ni clusters are stretched along the tube axis and have a large contact area. Secondary nanotubes were established by growing nanotubes directly on the walls of primary nanotubes. Thin Ni layers or ferritin served as catalysts. We compared the field emission properties of samples with and without secondary nanotubes. The presence of secondary nanotubes enhances the field emission substantially.     

Dispersion of single-walled carbon nanotubes in aqueous solution with a thermo-responsive pentablock terpolymer

Single-walled carbon nanotubes (SWNTs) were dispersed in pure water with a thermo-responsive amphiphilic PNIPAM₁₅₀-F108-PNIPAM₁₅₀ pentablock terpolymer in comparison with its precursor PEO₁₃₆-PPO₄₅-PEO₁₃₆ (F108) triblock copolymer. The stability, dispersibility, and thermo-responsive behaviors of the polymer/SWNT hybrids were characterized by UV–vis–NIR spectroscopy, thermal gravimetric analysis, viscosity measurement, Raman spectroscopy, and high-resolution transmission electron microscopy. The pentablock/SWNT hybrids showed superior ability in stabilization over F108/SWNT hybrids, and no sign of sedimentation was found at room temperature for 6 weeks or even 2 months of storage. The pentablock terpolymer can efficiently disperse SWNTs into individual tubes or small bundles with average diameter of about 5 nm, and their chains were helically wrapped onto the nanotube surface, whereas the larger bundles of the nanotubes with sizes of 15–25 nm were observed in F108/SWNT hybrids. Moreover, the pentablock/SWNT hybrids switched reversibly between the well-exfoliated and the aggregated states when cyclically increasing and decreasing temperature.     

Adsorption of Eu(III) on titanate nanotubes studied by a combination of batch and EXAFS technique

The effects of pH,contact time and natural organic ligands on radionuclide Eu(Ⅲ) adsorption and mechanism on titanate nanotubes(TNTs) are studied by a combination of batch and extended X-ray absorption fine structure(EXAFS) techniques.Macroscopic measurements show that the adsorption is ionic strength dependent at pH < 6.0,but ionic strength independent at pH > 6.0.The presence of humic acid(HA) /fulvic acid(FA) increases Eu(Ⅲ) adsorption on TNTs at low pH,but reduces Eu(Ⅲ) adsorption at high pH.The results of EXAFS analysis indicate that Eu(Ⅲ) adsorption on TNTs is dominated by outer-sphere surface complexation at pH < 6.0,whereas by inner-sphere surface complexation at pH > 6.0.At pH < 6.0,Eu(Ⅲ) consists of ～ 9 O atoms at REu?O ≈ 2.40  in the first coordination sphere,and a decrease in NEu-O with increasing pH indicates the introduction of more asymmetry in the first sphere of adsorbed Eu(Ⅲ).At long contact time or high pH values,the Eu(Ⅲ) consists of ～2 Eu at REu-Eu ≈ 3.60  and ～ 1 Ti at REu-Ti ≈ 4.40 ,indicating the formation of inner-sphere surface complexation,surface precipitation or surface polymers.Surface adsorbed HA/FA on TNTs modifies the species of adsorbed Eu(Ⅲ) as well as the local atomic structures of adsorbed Eu(Ⅲ) on HA/FA-TNT hybrids.Adsorbed Eu(Ⅲ) on HA/FA-TNT hybrids forms both ligand-bridging ternary surface complexes(Eu-HA/FA-TNTs) as well as surface complexes in which Eu(Ⅲ) remains directly bound to TNT surface hydroxyl groups(i.e.,binary Eu-TNTs or Eu-bridging ternary surface complexes(HA/FA-Eu-TNTs)).The findings in this work are important to describe Eu(Ⅲ) interaction with nanomaterials at molecular level and will help to improve the understanding of Eu(Ⅲ) physicochemical behavior in the natural environment.     

Effect of pH value on the microstructure and deNO(x) catalytic performance of titanate nanotubes loaded CeO2

The relationship between catalytic performance and pH value of post-treatment of the catalyst supports-titanate materials was investigated and discussed. Three types of titanate nanotubes (TNTs) that are acidic TNTs (TNTs-1.6, pH value at 1.6), neutral TNTs (TNTs-7), and alkaline TNTs (TNTs-12) were synthesized by hydrothermal method with the controlled washing pH value and then were used as the catalyst supports for ceria. These titanate-supported ceria catalysts showed extremely different performance for the selective catalytic reduction in NO. The pH value had a notable effect on the structure and composition of titanate nanotubes and further affected the state and redox property of cerium oxides. The structure of TNTs-1.6, TNTs-7, and TNTs-12 were identified as anatase-like structure, protonated titanate (H(2)Ti(3)O(7)), and Na-containing titanate, respectively. Indeed, the residual sodium (TNTs-12) was harmful to ceria, but the presence of water in the interlayer (TNTs-7) was beneficial to the stability of nanotube structure. Therefore, TNTs-7 doped ceria showed the best SCR activity among these tested samples.     

Synergistic effects of CdS in sodium titanate based nanostructures for hydrogen evolution

Synergistic effect of CdS decorated sodium titanate nanostructures showed enhanced H₂ production abilities. The confinement effect and synergistic effect of decorated CdS inside the sodium titanate nanotubes are investigated.     

DNA‐Directed Growth of Pd Nanocrystals on Carbon Nanotubes towards Efficient Oxygen Reduction Reactions

Unique DNA‐promoted Pd nanocrystals on carbon nanotubes (Pd/DNA–CNTs) are synthesized for the first time, in which through its regularly arranged PO₄^3? groups on the sugar–phosphate backbone, DNA directs the growth of ultrasmall Pd nanocrytals with an average size of 3.4 nm uniformly distributed on CNTs. The Pd/DNA–CNT catalyst shows much more efficient electrocatalytic activity towards oxygen reduction reaction (ORR) with a much more positive onset potential, higher catalytic current density and better stability than other Pd‐based catalysts including Pd nanocrystals on carbon nanotubes (Pd/CNTs) without the use of DNA and commercial Pd/C catalyst. In addition, the Pd/DNA–CNTs catalyst provides high methanol tolerance. The high electrocatalytic performance is mainly contributed by the ultrasmall Pd nanocrystal particles grown directed by DNA to enhance the mass transport rate and to improve the utilization of the Pd catalyst. This work may demonstrate a universal approach to fabricate other superior metal nanocrystal catalysts with DNA promotion for broad applications in energy systems and sensing devices.     

Highly oriented growth of titanate nanotubes (TNTs) in micro and confinement spaces on sol–gel derived amorphous TiO2 thin films under moderate hydrothermal condition

Synthesis of titanate nanotubes (TNTs) from sol–gel derived amorphous TiO₂ thin films under moderate hydrothermal condition has been reported. TNTs from film possess a tubular morphology that is the same crystalline phase as one synthesized from TiO₂ powder so far. TNTs obtained in this study are not entangled one another but oriented and isolated on the substrate. Growth of highly oriented TNTs is observed in micro grooves of amorphous TiO₂ thin film. Their orientation is also maintained with the growth of TNTs.     

Heterogeneous photocatalysis of methylene blue over titanate nanotubes: effect of adsorption

Titanate nanotubes were synthesized with hydrothermal reaction using TiO(2) and NaOH as the precursors and subsequent calcination at 400°C for 2h. The products were characterized with SEM and XRD. Adsorption and photocatalysis of methylene blue over titanate nanotubes and TiO(2) were investigated. The results indicated that titanate nanotubes exhibited a better photocatalytic degradation of methylene blue in a simultaneous adsorption and photodegradation system than that in equilibrium adsorption followed by a photodegradation system, whereas TiO(2) showed no significant differences in photocatalytic activity in the two systems. The methylene blue overall removal efficiency over TNTs in the first system even exceeded that over TiO(2). The different catalytic performances of titanate nanotubes in the two systems were tentatively attributed to different effects of adsorption of methylene blue, i.e., the promoting effect in the former and the inhibition effect in the latter. Decantation experiments showed that the titanate nanotube photocatalyst could be easily separated from the reaction medium by sedimentation. Thus titanate nanotubes with high sedimentation rates and concurrent adsorption represent a new catalyst system with a strong potential for commercial applications.     

Spontaneous reduction of metal ions on the sidewalls of carbon nanotubes

Nanotube/nanoparticle hybrid structures are prepared by forming Au and Pt nanoparticles on the sidewalls of single-walled carbon nanotubes. Reducing agent or catalyst-free electroless deposition, which purely utilizes the redox potential difference between Au3+, Pt2+, and the carbon nanotube, is the main driving force for this reaction. It is also shown that carbon nanotubes act as a template for wire-like metal structures. The successful formation of the hybrid structures is monitored by atomic force microscopy (AFM) and electrical measurements.     

Synthesis and Catalytic Studies of Uniform Os &; Os–Pd Nanoparticles Supported on MWNTs

Os and Os–Pd nanoparticles supported on multi-walled carbon nanotubes were prepared by vacuum pyrolysis at 573 K using the [Os₃CO₁₀(NCMe)₂] and [Pd(acac)₂] as precursors. The nanoparticles prepared showed a narrow size distribution (Os: 1.8 nm; Os–Pd: 4.3 nm) and were decorated evenly on the surface of the nanotubes. By controlling the metal-to-nanotube ratio, Os nanotubes were prepared using the carbon nanotubes as a template. The catalysis of Os–Pd nanoparticles towards CVD carbon nanotube synthesis was studied. Dedicated to Professor Gunther Schmid on the occasion of his 70th birthday.     

一维CeO2纳米管载体对Pd纳米粒子团聚的抑制及催化性能的提高

用一维CeO₂纳米管替代非一维结构的商用CeO₂, 用于负载Pd而制得的催化剂在空气气氛下高温煅烧过程中Pd纳米粒子的团聚受到明显抑制, 在选择性有氧氧化苯甲醇生成苯甲醛反应中, 所制CeO₂纳米管负载的Pd催化剂表现出更高的催化活性. 可见, 一维金属氧化物材料有望用作载体以抑制贵金属纳米粒子的团聚, 从而提高其催化性能.     

An investigation of the mechanisms of electronic sensing of protein adsorption on carbon nanotube devices

It has been reported that protein adsorption on single-walled carbon nanotube field effect transistors (FETs) leads to appreciable changes in the electrical conductance of the devices, a phenomenon that can be exploited for label-free detection of biomolecules with a high potential for miniaturization. This work presents an elucidation of the electronic biosensing mechanisms with a newly developed microarray of nanotube "micromat" sensors. Chemical functionalization schemes are devised to block selected components of the devices from protein adsorption, self-assembled monolayers (SAMs) of methoxy(poly(ethylene glycol))thiol (mPEG-SH) on the metal electrodes (Au, Pd) and PEG-containing surfactants on the nanotubes. Extensive characterization reveals that electronic effects occurring at the metal-nanotube contacts due to protein adsorption constitute a more significant contribution to the electronic biosensing signal than adsorption solely along the exposed lengths of the nanotubes.     

Fabrication of a new ECL biosensor for choline by encapsulating choline oxidase into titanate nanotubes and Nafion composite film

A simple strategy for encapsulating choline oxidase (ChOD) into the titanate nanotubes (TNTs) and Nafion composite film for choline sensing was proposed. Hydrogen peroxide, as the product of the redox enzymatic reaction, could enhance the ECL of luminol. Therefore, the substrates of corresponding redox enzymes could be detected indirectly through the determination of hydrogen peroxide in the luminol ECL system. Through this approach, it was found that ChOD could be fixed firmly into the TNTs contained composite film. TNTs would not only offer excellent photocatalytic activity toward luminol-H₂O₂ ECL system, but also provide a shelter for the biomolecules, such as redox enzyme to retain its bioactivity.     

Mesoporous Bubble‐like Manganese Silicate as a Versatile Platform for Design and Synthesis of Nanostructured Catalysts

Manganese silicate in bubble‐like morphology was used as a versatile platform to prepare a new class of yolk–shell hybrids. The mesoporosity of the shell was generated from the interbubble space and the bubble structure of manganese silica was used to hold and support nanoparticles (e.g., Au, Ag, Pt, Co, Ni, Au–Pd alloy, MoO₂, Fe₃O₄, carbon nanotubes and their combinations). We also used heterogeneous catalysis reactions to demonstrate the workability of these catalysts in both liquid and gas phases.     

Polymer-Protected Bimetallic Clusters. Preparation and Application to Catalysis

Colloidal dispersions of polymer-protected Pd/Pt and Pd/Au bimetallic clusters were prepared by reduction of an alcoholic solution of PdCl₂ and H₂PtCl₆ or HAuCl₄ in the presence of poly(N-vinyl-2-pyrrolidone). The reduction can be carried out by refluxing in alcohol or by irradiation with visible light. The dispersions of the bimetallic clusters obtained are stable for months at room temperature and have from dark brown to brownish red color. Transmission electron micrographs show that the bimetallic clusters are composed of well-dispersed ultrafine particles of uniform size, about 1.5 nm for Pd-Pd and 3.4 nm for Pd-Au in diameter. The catalytic activity of the bimetallic clusters depends on the metal composition. In the case of the partial hydrogenation of 1, 3-cyclooctadiene, the activity went through a maximum when the alloy composition reached about 80% Pd and 20% Pt, or 60% Pd and 40% Au.     

Layer-by-layer assembled multilayer films of titanate nanotubes, Ag- or Au-loaded nanotubes, and nanotubes/nanosheets with polycations

Aqueous suspensions of hydrothermally synthesized titanate nanotubes and poly(diallyldimethylammonium chloride) (PDDA) have been employed to fabricate multilayer films on various substrates in a layer-by-layer fashion. Atomic force microscopy displays the dense coverage of the substrate surface by the nanotubes. UV-vis absorption spectroscopy confirms the consecutive growth of PDDA/nanotube layer pairs. Single crystalline Ag and Au nanoparticles with narrow size distribution spatially correlating with the nanotubes have been obtained by treating the nanotubes with AgNO(3) or HAuCl(4) aqueous solution followed by chemical reduction. The noble metal nanoparticles show a strong surface plasmon absorption band. A multilayer film construction of the noble-metal-loaded nanotubes has also been achieved. This process has been further extended to the heteroassembly of nanotubes/nanosheets in different layer sequences.     

Alkali metal intercalated titanate nanotubes: A vibrational spectroscopy study

Alkali metal (Li⁺, Na⁺, K⁺) intercalated titanate nanotubes have been studied by vibrational spectroscopy (Raman and FT-infrared), X-ray diffraction, and electron microscopy. The vibrational spectroscopic data shown that the most affected vibrational mode is that related to Ti-O bond whose oxygen is not shared among the TiO₆ units of the framework structure. A correlation between vibrational frequency shifts and intercalated metal was found, thus showing that vibrational spectroscopy is very useful for probing metal intercalated titanate nanotubes. Our results provide good evidences that the structure of titanate layers in titanate nanotube, a subject of long debate in the literature, is similar to trititanates (like Na₂Ti₃O₇).     

Effects of pore structure and surface chemical characteristics on the adsorption of organic vapors on titanate nanotubes

Effects of pore structure and surface chemical characteristics of titanate nanotubes (TNTs) on their adsorptive removal of organic vapors were investigated. TNTs were prepared via a hydrothermal treatment of TiO₂ powders in a 10 M NaOH solution at 150?°C for 24?h, and subsequently washed with HCl aqueous solution of different concentrations. Effects of acid washing process (or the sodium content) on the microstructures and surface chemical characteristics of TNTs were characterized with nitrogen adsorption-desorption isotherms, FTIR, and water vapor adsorption isotherms. For the adsorption experiments, gravimetric techniques were employed to determine the adsorption capacities of TNTs for four organic vapors with similar heats of vaporization (i.e., comparable heats of adsorption) but varying dipole moments and structures, including n-hexane, cyclohexane, toluene, and methyl ethyl ketone (MEK), at isothermal conditions of 20 and 25?°C. The experimental data were correlated by well-known vapor phase models including BET and GAB models. Isosteric heats of adsorption were calculated and heat curves were established. Equilibrium isotherms of organic vapors on TNTs were type II, characterizing vapor condensation to form multilayers. The specific surface area (and pore volume) and hydrophilicity of TNTs were the dominating factors for the determination of their organic vapors adsorption capacity. The GAB isotherm equation fitted the experimental data more closely than the BET equation. The heats of adsorption showed that the adsorption of organic vapors on TNTs was primarily due to physical forces and adsorbates with larger polarity might induce a stronger interaction with TNTs.     

光稳定二氧化钛纳米管负载钯催化剂光降解甲基橙过程中的活性物种(英文)

采用光沉积法制备了光稳定二氧化钛纳米管负载钯催化剂.通过X射线衍射、紫外-可见漫反射光谱、透射电子显微镜(TEM)、氮气吸附-脱附、X射线光电子能谱(XPS)、光致发光光谱和光电流等表征手段研究了催化剂的结构和性质.TEM表明二氧化钛纳米管经光照后仍然保持良好的管状结构;XPS结果表明大部分Pd以零价形式存在.以甲基橙溶液作为模拟废液研究了催化剂在紫外光及模拟日光条件下的光催化活性.当Pd的负载量为0.3 wt%时,催化剂的光催化活性最高并且优于P25的光催化活性.另外,通过在光降解过程中加入不同的捕获剂研究了不同氧化活性组分的作用.结果表明,光生空穴(hrb+)在光催化降解过程中起主要作用.