Functionalization of electrochemically prepared titania nanotubes with Pt for application as catalyst for fuel cells

Titania nanotubes (TiNTs) were prepared by electrochemical anodization and were used as a support for depositing Pt. After annealing the TiNTs changed to crystalline anatase phase and were doped with carbon. The TiNTs/Pt/C was tested as electrode for electrochemical catalysis of methanol oxidation. The composite catalyst activities were measured by cyclic voltammetry in 1 M CH₃OH + 1 M H₂SO₄. The results demonstrated that TiNTs/Pt/C can greatly enhance the catalytic activity of methanol oxidation. The CO stripping led to the increase in the current peak of methanol oxidation due to activating the catalyst surface by point defect formation. Moreover, the higher ratio of the forward anodic peak current to the reverse anodic peak current indicates more effective removal of the poisonous species.     

Advances in research on structural characterisation of agricultural products using atomic force microscopy

Atomic force microscopy (AFM) has many unique features compared with other conventional microscopies, such as high magnification with high resolution, minimal sample preparation, acquiring 2D and 3D images at the same time, observing ongoing processes directly, the possibility of manipulating macromolecules, etc. As a nanotechnology tool, AFM has been used to investigate the nanostructure of materials in many fields. This mini-review focuses mainly on its latest application to characterise the macromolecular nanostructure and surface topography of agricultural products. First the fundamentals of AFM are briefly explained. Then the macromolecular nanostructure information on agricultural products from AFM images is introduced by exploring the structure-function relationship in three aspects: agricultural product processing, agricultural product ripening and storage, and genetic and environmental factors. The surface topography characterisation of agricultural products using AFM is also discussed. The results reveal that AFM could be a powerful nanotechnology tool to acquire a deeper understanding of the mechanisms of structure and quality variations of agricultural products, which could be instructive in improving processing and storage technologies, and AFM is also helpful to reveal the essential nature of a product at nanoscale.     

Influence of nanostructure on titanium corrosion resistance in fluoridated medium

ABSTRACT

Nanocrystalline titanium, mainly owing to its high corrosion resistance, mechanical strength to density ratio and biocompatibility, has a great application potential in dental implantology. However, fluoridated agents commonly used for oral hygiene could have a destructive influence on the titanium protective passive films and lead to the formation of local corrosion damages. In this work, the effect of nanostructuring on titanium corrosion resistance in the concentration of F^? which is typical for toothpastes, was evaluated by different electrochemical and surface characterisation techniques. It was found that nanostructure influences beneficially on titanium corrosion resistance in fluoride solution. Furthermore, the lower increase in nanocrystalline titanium surface roughness in corrosion solutions indicates better stability of passive film formed on its surface.

This paper is part of a thematic issue on Titanium.     

Highly branched PtCu nanodandelion with high activity for oxygen reduction reaction

A facile hydrothermal route has been developed to synthesize the highly branched Pt₅₈Cu₄₂ nanoparticles via mixing the H₂PtCl₆ and CuCl₂ with octadecylamine. The Pt₅₈Cu₄₂ after post treatment forms a dandelion flower 3-D structure. A combination of both the branched shape and PtCu composition effects in the Pt₅₈Cu₄₂-nanoparticles shows superior electrocatalytic activity and durability to commercial Pt black for oxygen reduction reaction. The mechanism for the de-alloying and reconstructing of the Pt₅₈Cu₄₂-nanoparticles in electrochemical activity and durability tests has been proposed. It is found that after the durability process, the Pt₅₈Cu₄₂ precursor alloy changes into a substantially Pt enriched PtCu alloy (Pt₇₉Cu₂₁) with a Pt skin. The Pt skin effectively prevents the further dissolution of the Cu below the near-surface to enhance its durability. What's more, the Pt skin exposed to (111) planes which have the lowest surface energy among the low-index planes further promotes the improvement of durability of the PtCu catalyst.     

Bismuth telluride nanostructures: preparation,thermoelectric properties and topological insulating effect

Bismuth telluride is known to wield unique properties for a wide range of device applications. However, as devices migrate to the nanometer scale, significant amount of studies are being conducted to keep up with the rapidly growing nanotechnological field. Bi₂Te₃ possesses distinctive properties at the nanometer level from its bulk material. Therefore, varying synthesis and characterization techniques are being employed for the realization of various Bi₂Te₃ nanostructures in the past years. A considerable number of these works have aimed at improving the thermoelectric (TE) figure-of-merit (ZT) of the Bi₂Te₃ nanostructures and drawing from their topological insulating properties. This paper reviews the various Bi₂Te₃ and Bi₂Te₃-based nanostructures realized via theoretical and experimental procedures. The study probes the preparation techniques, TE properties and the topological insulating effects of 0D, 1D, 2D and Bi₂Te₃ nanocomposites. With several applications as a topological insulator (TI), the topological insulating effect of the Bi₂Te₃ is reviewed in detail with the time reversal symmetry (TRS) and surface state spins which characterize TIs. Schematics and preparation methods for the various nanostructural dimensions are accordingly categorized.     

自组装法制备微/纳米结构苯胺低聚物的研究进展

介绍了一类新颖的可溶电活性材料——微/纳米结构苯胺低聚物。阐述了苯胺低聚物纳米纤维、微球、纳米片等微/纳米结构的自组装制备方法。从嵌段共聚物组装、软模板合成以及重结晶/沉积这三大自组装手段概述了国内外自组装法制备微纳米结构苯胺低聚物及其相关性质的研究进展,分析了各种自组装手段的优缺点。指出微/纳米结构苯胺低聚物今后的研究方向为：寻找组装过程简单、形貌易控的制备方法,提高目标产物的光电性能以及在保证苯胺低聚物电导性的同时提高低聚物的稳定性。     

Recent research situation in tin dioxide nanomaterials: synthesis,microstructures, and properties

This review article summarizes the new research in solid-state physical chemistry understanding of the microstructure characteristics of semiconductor tin oxide thin films made in the last years in our group. The work mainly focuses on the fabrication technology of semiconductor tin oxides thin films by using pulsed laser deposition (PLD) as well as the application of this technology on new micro- and nanostructured materials. It is an interdisciplinary work that integrates the areas of physics, chemistry and materials science.     

The growth of ordered ZnAl2O4 nanostructures using AAO as a reactive template

The use of anodic aluminum oxide (AAO) as a reactive template in the fabrication of ordered arrays of spinel ZnAl₂O₄ nanostructures is demonstrated. This involves the growth of monocrystalline Zn nanowires into an AAO template using a pulse dc electrodeposition technique followed by a heat treatment in air at 800 °C. The formation of ZnAl₂O₄ nanotubes in the solid-state reaction is driven by the Kirkendall effect. In addition, the formation of such ZnAl₂O₄ nanostructure arrays requires that the molar ratio of ZnO to Al₂O₃ be less than unity. This corresponds to a ratio of pore radius to half inter-pore separation of 0.63 which serves as a guide to the initial template geometry required for the formation of an array of discrete nanotubes.     

A simple one-step fabrication of micrometer-scale hierarchical TiO2 hollow spheres

Hierarchical TiO₂ hollow spheres had been prepared based on bubble templates by a simple one-step hydrothermal method. The diameter of hollow spheres was about 700 nm and the shell thickness of them was 69 nm. They were composed of similar spindle- or needle-like building units. Furthermore, hydrothermal time had an important influence on the morphology and crystallinity of hollow spheres. Moreover, the UV-Vis diffuse reflectance spectra of TiO₂ hollow spheres heated at 150 °C for 10 h showed the strongest absorption in the UV-Vis region and the Raman spectrum demonstrated the anatase sample. Additionally, a possible formation mechanism of TiO₂ hollow spheres was proposed. So this novel and simple method would provide a development direction to fabricate all kinds of inorganic hollow spheres by one-step procedure.     

Mild and facile synthesis of Ag2S nanowire precursor using mercaptoacetic acid as a reductant/stabilizer and its subsequent conversion to Ag2S or CdS nanowires

Silver sulfide nanowire precursor was prepared at room temperature by simple mixing of mercaptoacetic acid (MAA) and silver nitrate solutions for 10–20 min duration. The MAA concentration in the chemical reaction bath was varied from 1 to 10 mM to afford nanowire precursors ranging in length from 800 nm to 42 μm and diameters ranging from 53 to 210 nm. The chemical identity of the precursor was established as a Ag⁺–⁻SCH₂COOH complex by a variety of spectroscopic probes. It could be converted into crystalline Ag₂S nanowires (with no alteration in nanowire dimensions) by a thermal anneal at ∼300 °C. Reverse cation exchange of the Ag₂S nanowire precursor in a Cd²⁺-containing medium afforded CdS nanowires (with some alterations in morphology) whose chemical identity was confirmed by Raman spectroscopy and photoluminescence. Finally the dual role of MAA as a capping agent and reducing agent in the formation of the Ag₂S nanowire precursor complex is briefly discussed.