Size Regime Dependent Catalysis by Gold Nanoparticles for the Reduction of Eosin

Abstract

In this work we have addressed the gold particle catalyzed eosin reduction in the presence of NaBH4. The catalytic activity of the gold nanoparticles is different for different size regimes (size domain dependent) of the particles. It has been shown that the kinetics of the catalytic rate has a bearing with the particle size (viz., surface area, mass, etc.). The kinetics of catalytic reduction revealed that for the same surface area of different particles, the catalytic rate does not increase proportionately with the decrease in size over the whole range of average diameter from 10 to 46 nm. The rate decreases first with the increase in particle size, and above 15 nm, it increases. Moreover, if the mass effect is also taken into account, that is, catalytic rate is determined in terms of per unit mass per unit surface area, then the resulting catalytic rate falls with the rise in particle size over the whole range of size studied. However, the rate was different for the two regimes. Photochemically prepared seed in conjunction with noniterative growth method was used for producing the catalyst particles of desired size. The small seed particles were produced by the UV irradiation of Au(III) ions present in aqueous Triton X-100 medium. The particles have been characterized by UV−visible spectrophotometric and TEM studies. Almost spherical and nearly monodispersed gold nanoparticles were obtained by this method.