Anisotropic gold nanoparticle doped mesoporous boehmite films and their use as reusable catalysts in electron transfer reactions.

Anisotropic Au nanoparticle (NP) doped mesoporous and oriented boehmite films of about 2 microm in thickness were prepared and used as reusable catalysts. The films were characterized by grazing incidence X-ray diffraction (GIXRD), field emission scanning electron and transmission electron microscopies, optical absorptions and surface area and pore size measurements. GIXRD of the doped films showed a preferential growth of boehmite crystallites in the (020) plane. The electron microscopy studies revealed existence of dispersed anisotropic Au NPs of approximately 15-40 nm size range and irregular Au aggregates of approximately 200-300 nm inside the mesoporous boehmite films. The optical absorption of the films showed Au-plasmon bands at 605 nm and broad absorption covering the near-infrared (NIR) region due to the anisotropic Au nanostructures. These films showed excellent catalytic activities in both the organic (p-nitrophenol to p-aminophenol by sodium borohydride) and inorganic (ferricyanide to ferrocyanide by thiosulphate) electron transfer (redox) reactions in aqueous solutions with high rate constant values. The films can be easily separated after the reaction and reused several times without any significant degradation of their original catalytic activity.