Nonlinear thermo-optical properties of two-layered spherical system of gold nanoparticle core and water vapor shell during initial stage of shell expansion

Nonlinear thermo-optical properties of two-layered spherical system of gold nanoparticle core and water vapor shell, created under laser heating of nanoparticle in water, were theoretically investigated. Vapor shell expansion leads to decreasing up to one to two orders of magnitude in comparison with initial values of scattering and extinction of the radiation with wavelengths 532 and 633 nm by system while shell radius is increased up to value of about two radii of nanoparticle. Subsequent increasing of shell radius more than two radii of nanoparticle leads to rise of scattering and extinction properties of system over initial values. The significant decrease of radiation scattering and extinction by system of nanoparticle-vapor shell can be used for experimental detection of the energy threshold of vapor shell formation and investigation of the first stages of its expansion

Differences in catalytic properties between mesoporous and nanoparticulate platinum

Conventional Pt/Al2O3 catalysts prepared by wet-impregnation are composed of Pt nanoparticles exposing convex and facetted surfaces deposited on high-surface area ?-Al2O3 supports. A hexagonal phase mesoporous Pt material (denoted H1-Pt) prepared by chemical reduction in the aqueous domains of a lyotropic liquid crystalline template exposes however mainly a concave surface with expected different catalytic properties. A series of Pt/Al2O3 catalysts were prepared using H1-Pt, Pt-black or wet-impregnated Pt, and the samples were characterized by SEM-EDX and TEM, and finally evaluated for CO oxidation. The H1-Pt/Al2O3 catalyst showed an ignition profile for CO oxidation at lower temperatures and thus appeared less sensitive to CO poisoning than the two other types of samples. This difference may be related to the differences in surface curvature