Single-pot synthesis: Plant mediated gold nanoparticles catalyzed reduction of methylene blue in presence of stannous chloride

Gold nanoparticles of about 20 nm in diameter and having lambda(max) at 542 nm is prepared by addition of HAuCl4 solution to green tea leaves extract at room temperature. The synthetic route does not involve any toxic chemicals or organic solvent and it is totally aqueous phase synthesis; so it is a green approach. The synthesized nanoparticles were used as a catalyst for the reduction of methylene blue dye in the presence of Sn(II) in aqueous and micellar media and the rate of reduction is determined by measuring the decrease in absorbance of the dye at 663 nm spectrophotometrically. The rate of reduction follows the order Rate(SDS) > Rate(CTAB) > Rate(water). The activation energy as determined using Arrhenius equation for the reaction catalyzed by gold nanoparticles is 38.42 kJ mol(-1) and the slow reaction rate of uncatalyzed reaction has been manifested through larger activation energy of about 88.13 kJ mol(-1). (C) 2010 Elsevier B.V. All rights reserved.