Size regime dependent catalysis by gold nanoparticles for the reduction ofeosin

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 part icles, It has been shown that the kinetics of the catalytic rate has a bear ing with the particle size (viz., surface area. mass, etc.). The kinetics o f catalytic reduction revealed that for the same surface area of different particles, the catalytic rate does not increase proportionately with the de crease in size over the whole range of average diameter from 10 to 46 nm. T he 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, th at is, catalytic rate is determined in terms of per unit mass per unit surf ace 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 non iterative growth method was used for producing the catalyst particles of de sired 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 be en characterized by UV-visible spectrophotometric and TEM studies. Almost s pherical and nearly monodispersed gold nanoparticles were obtained by this method.