Preparation of Gold Nanoparticles using Poly (amidoamine) dendrimers as Stabilizer and Their Catalytic Reduction of 4-Nitrophenol

Abstract

Gold nanoparticles are prepared in aqueous solutions by using poly (amidoamine) (PAMAM) dendrimers (generation 3.0, 3.5, 5.0 and 5.5) with various terminal groups such as methyl ester, amino, carboxyl, or sugar residue, and their mean particle sizes are 2-6 nm in diameter depending on the dendrimer/Au⁺³ ratio as well as the generation of PAMAM dendrimers. Studies of reduction reaction of 4-nitrophenol by gold nanoparticles with NaBH₄ reveal that the rate constant depends on the concentration of the dendrimers added as well as the generation of the dendrimers. Furthermore, the effect on the rate constants for PAMAM (generation 5.0 and 5.5) with various terminal groups follows the order : carboxyl ≥ amino > sugar residue > methyl ester. These results are attributed to the dendrimer-gold nanocomposite structures, depending on whether the gold nanoparticles are formed inside or outside the dendrimers.