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.
Nanocrystalline mesoporous gamma-Al2O3 film of high thickness has been developed and characterized. The films were prepared on ordinary glass substrates by a single dip-coating method using boehmite (AlOOH) sols derived from aluminum tri-sec-butoxide in presence of cetyltrimethylammonium bromide (CTAB) as structure-directing agent. The dried films were heat-treated at 500 degrees C in air to remove the organics and strengthen the network. The GIXRD of the heat-treated (500 degrees C) film shows a broad peak in the low-angle region supporting the formation of worm-hole-like disordered mesostructures. The high-angle GIXRD, FTIR, and TEM of the films confirm the formation of gamma-Al2O3. N2 adsorption-desorption analyses showed that the heat-treated (500 degrees C) film has a BET surface area of 171 m(2) g(-1) with a pore volume of 0.188 cm(3) g(-1) and mean pore diameter 4.3 nm. Pt nanoparticles (NPs) (approximately 2.7 mol % with respect to the equivalent AlO(1.5)) were generated inside the mesopores of the heat-treated films simply by soaking H2PtCl6 solutions into it, and followed by thermal decomposition at 500 degrees C. The surface area and pore volume of the Pt-incorporated film have been reduced to 101 m(2) g(-1) and 0.119 cm(3) g(-1) respectively, confirming the inclusion of Pt NPs inside the pores. FESEM and TEM studies revealed uniform distribution of Pt NPs (2-8.5 nm; average diameter 4.9 nm) in the films. Catalytic properties of the Pt-incorporated films were investigated in two model (one inorganic and other organic) systems: reduction of hexacyanoferrate(III) ions by thiosulfate to ferrocyanide, and p-nitrophenol to p-aminophenol. In both the cases, the catalyst showed excellent activities, and the reduction reactions followed smoothly, showing isosbestic points in the UV-visible spectra. The catalyst films can be separated easily after the reactions and reused several times.
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