V2O5 nanowires exhibit an intrinsic catalytic activity towards classical peroxidase substrates such as 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 3,3,5,5,-tetramethylbenzdine (TMB) in the presence of H2O2. These V2O5 nanowires show an optimum reactivity at a pH of 4.0 and the catalytic activity is dependent on the concentration. The Michaelis-Menten kinetics of the ABTS oxidation over these nanowires reveals a behavior similar to that of their natural vanadium-dependent haloperoxidase (V-HPO) counterparts. The V2O5 nanowires mediate the oxidation of ABTS in the presence of H2O2 with a turnover frequency (k(cat)) of 2.5 x 10(3) s(-1). The K-M values of the V2O5 nanowires for ABTS oxidation (0.4 mu M) and for H2O2 (2.9 mu M) at a pH of 4.0 are significantly smaller than those reported for horseradish peroxidases (HRP) and V-HPO indicating a higher affinity of the substrates for the V2O5 nanowire surface. Based on the kinetic parameters and similarity with vanadium-based complexes a mechanism is proposed where an intermediate metastable peroxo complex is formed as the first catalytic step. The nanostructured vanadium-based material can be re-used up to 10 times and retains its catalytic activity in a wide range of organic solvents (up to 90%) making it a promising mimic of peroxidase catalysts.

V2O5 Nanowires with an Intrinsic Peroxidase-Like Activity

The color of colloidal dispersions of gold particles in a fluid, typically water, varies from red to blue, depending upon the shape and size of particles. The color and optical properties of gold nanoparticles originate from localized surface plasmons, and are sensitive to their local dielectric environment. Unlike nanospheres, the optical properties, hydrodynamic behavior as well as phase behavior of nanorods are influenced by their shape anisotropy. Thus, rods have an additional absorption peak, possess very different dynamics (affects sedimentation) and their concentrated dispersions form liquid crystalline phases. In this review, we focus on presenting the essential shape dependent optics, as well as the hydrodynamics and phase behavior of rod-like gold nanoparticles. We reveal our methodology for making less polydisperse nanorods sols by using an optimized seed-mediated synthesis (controlled chemistry), followed by shape separation by centrifugation (based on our hydrodynamics arguments). We elucidate the role of Brownian motion in determining colloidal stability and sedimentation behavior, and describe patterns formed by drying mediated assembly on glass slides and TEM grids. We outline early studies (before 1930) of gold sols that are not only instructive in learning about synthesis and physical properties of gold nanoparticles, but show how the study of colloidal gold established many key principles in colloidal science.

Colloidal dispersion of gold nanorods: Historical background, optical properties, seed-mediated synthesis, shape separation and self-assembly

Silver vanadium oxide (SVO) and V2O5 nanowires have been hydrothermally synthesized. The as-made nanowires are over 30 µm long and 10–20 nm in diameter. The nanowires have a layered structure with a d-spacing of 1.07 nm. The nanowires can be fabricated into free-standing and flexible sheets by suction filtration. The electrical conductivity of the SVO nanowires is 0.5 S/cm, compared to 0.08 S/cm for the V2O5 nanowires. The Li ion diffusion coefficient in the SVO nanowires was 7 times higher than that in the V2O5 nanowires. An electrochromic device was fabricated from the SVO nanowires that displayed a color-switching time of 0.2 s from the bleached state (green) to the colored state (red-brown) and 60% transmittance contrast.

Fabrication of silver vanadium oxide and V2O5 nanowires for electrochromics.

We demonstrate a method for embossing titania sol−gel precursor with poly(methyl methacrylate) (PMMA) molds to make thin films of titania that have dense arrays of 35−65 nm diameter pores, whose features are 1 order of magnitude smaller than those previously demonstrated for sol−gel molding. We show that the high modulus of PMMA is necessary to preserve small features with high aspect ratios on the mold for nanopatterning. The molds are prepared by thermally infiltrating PMMA into anodic alumina templates, whose pore dimensions and depths are adjustable by varying anodization conditions. The difficulties associated with mold release from a master are avoided by wet etching the template. These titania films, and others made with other semiconductors, could be useful for photovoltaic, photocatalytic, and sensing applications where nanostructuring of surfaces with controlled dimensions are essential.

/pdf/nanostructuring-titania-by-embossing-with-polymer-molds-made-3c4i5tu8ou.pdf

Nanostructuring titania by embossing with polymer molds made from anodic alumina templates.

At volume fractions larger than 85%, aqueous suspensions of lath-like goethite (alpha-FeOOH) nanorods form a lyotropic nematic phase In this article, we first discuss the nematic ordering within statistical-physics models of the isotropic/nematic phase transition We then describe the influence of a magnetic field on the nematic phase Because the nanorods bear permanent magnetic moments, the nematic suspensions have dipolar order and very low Frederiks thresholds Moreover, the nematic phase aligns parallel to a small magnetic field but realigns perpendicular to a high field because of a competition between the permanent moments of the nanorods and their negative anisotropy of magnetic susceptibility This magneto-optical study of the nematic phase is completely consistent with that of the isotropic phase of the same suspensions published in Part I (this issue, p 291) Besides, we demonstrate the field-induced biaxiality of a nematic single domain aligned perpendicular to the field We also describe here preliminary experiments where an ac electric field is applied to the nematic phase Both field amplitude and frequency were found to control the alignment direction and homeotropic-to-planar alignment transitions were observed From this data, simple models were used to estimate some physical constants of the nematic phase

Physical properties of aqueous suspensions of goethite (alpha-FeOOH) nanorods. Part II: In the nematic phase.

Weak anchoring of liquid crystals on solid substrates is usually dominated by the surface memory. We show that the memory can be removed by surface passivation by silane molecules. We realize planar, azimuthally degenerated, and memory-free anchorings without pretilt.

Planar degenerated anchoring of liquid crystals obtained by surface memory passivation

Electrooptic Effects in the Nematic and Isotropic Phases of Aqueous V2O5 Suspensions

Recent works reported planar and conical azimuthally degenerated nematic anchorings. Here we predict an additional ``anticonical'' degenerated anchoring. Its energy presents two minima, parallel and perpendicular to the substrate plane, separated by a conical energy barrier. We realize this bistable anchoring on a grafted polymer brush and we observe temperature-driven transitions between the conical, planar, and anticonical degenerated anchorings. Under electric field we break the anticonical anchoring and switch between its bistable states.

Anticonical anchoring and surface transitions in a nematic liquid crystal.

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Planar degenerated anchoring of liquid crystals obtained by surface memory passivation

Electrooptic Effects in the Nematic and Isotropic Phases of Aqueous V2O5 Suspensions

Anticonical anchoring and surface transitions in a nematic liquid crystal.