Mechanisms of Enhanced Electrocatalytic Activity for Oxygen Reduction Reaction on High-Index Platinum n(111)-(111) Surfaces.

Oxygen reduction reactions (ORRs) on high-index planes of Pt n(111)-(111) were studied by density functional theory (DFT). The stepped surfaces, where n = 2, 3, and 4, showed that O2, O, and OH exhibited higher binding energies along the step compared to the terrace plane. The Pt atoms along the step can become distorted through the binding of the O and OH, where the shift in position of the Pt atoms is the largest along the stepped sites, hence forming stronger bonds with O atoms. One of the two O atoms produced from the bond dissociation of O2 will push the other one down a step with lower binding energies, consequently reducing the energy required for the protonation reaction (O + H(+) → OH, and OH + H(+) → H2O). The quicker recovery back to the clean Pt surface would therefore improve the catalytic properties of Pt nanoparticles, especially those with exposure to high-indexed facets.

Crystal plane-dependent gas-sensing properties of zinc oxide nanostructures: experimental and theoretical studies.

The sensitivity of a metal oxide gas sensor is strongly dependent on the nature of the crystal surface exposed to the gas species. In this study, two types of zinc oxide (ZnO) nanostructures: nanoplates and nanorods with exposed (0001) and (10̄10) crystal surfaces, respectively, were synthesized through facile solvothermal methods. The gas-sensing results show that sensitivity of the ZnO nanoplates toward ethanol is two times higher than that of the ZnO nanorods, at an optimum operating temperature of 300 °C. This could be attributed to the higher surface area and the exposed (0001) crystal surfaces. DFT (Density Functional Theory) simulations were carried out to study the adsorption of ethanol on the ZnO crystal planes such as (0001), (10̄10), and (11̄20) with adsorbed O(-) ions. The results reveal that the exposed (0001) planes of the ZnO nanoplates promote better ethanol adsorption by interacting with the surface oxygen p (O2p) orbitals and stretching the O-H bond to lower the adsorption energy, leading to the sensitivity enhancement of the nanoplates. These findings will be useful for the fabrication of metal oxide nanostructures with specifically exposed crystal surfaces for improved gas-sensing and/or catalytic performance.

Deposition of gold nanoparticles on ß-FeOOH nanorods for detecting melamine in aqueous solution.

This study demonstrates a facile but efficient approach to deposit metallic (gold) nanoparticles on ß-FeOOH nanorods to obtain Au/ß-FeOOH nanocomposites without the assistance of any polymers or surfactants at ambient conditions. In this method, a strong reducing agent (NaBH(4)) can be used to extensively produce Au nanoparticles, converting ß-FeOOH into Fe(3)O(4) and depositing gold particles onto magnetic Fe(3)O(4) simultaneously. The microstructure, composition, and chemical properties of the obtained nanocomposites are characterized by various advanced techniques, including transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and UV-vis spectroscopy. Moreover, the Au/ß-FeOOH nanocomposite can be used to detect trace melamine using UV spectrum in the ultraviolet wavelength range (190-260 nm), in which the nanocomposites show a higher sensitivity toward melamine due to the promotion of symmetry-forbidden bands (n→π(*)) of melamine molecules and also avoid the disturbance of commercial products containing solid colloids or food colorings that distort visual spectrum during the detection of chemical sensing. The deposition mechanisms and their sensing detection toward melamine are discussed.

Molecular dynamics study on Au/Fe3O4 nanocomposites and their surface function toward amino acids.

The deposition of gold nanoparticles on the magnetite (Fe(3)O(4)) surface is demonstrated through a molecular dynamics method. The simulated results show that an intermediate layer composed by such as a surfactant, polymer, or silica plays a key role in the formation of core/shell Fe(3)O(4)/Au nanostructures. The functional groups of the intermediate layer are crucial factors in depositing gold onto the Fe(3)O(4) surface via nonbonding interactions, in which the van der Waals and columbic forces will determine the strength of interaction toward the gold and iron oxide. Such interactions can affect the stability of the metal-coated nanocomposites and hence the functional properties. The nanocomposite is further investigated on the surface adsorption of amino acids (e.g., cysteine), which may be useful for functional exploration in biomedical applications.