Synthesis and application of monodisperse silver and gold nanoparticles as catalysts for kinetic investigations of model reactions

Abstract:A hyperbranched polymers, dendrimers, synthesized for the first time by Tomalia and available in market in the form of poly-amidoamine (PAMAM) and poly-propylene imine (PPI) dendrimers are used as templates in the synthesis of metal nanoparticles to prevent agglomeration. Here, we study the synthesis of generation five amino-terminated poly(amidoamine) dendrimer encapsulated silver and gold nanoparticles. To avoid the intra-dendrimer stabilization, a spectrophotometric titration of the silver and gold ions into the dendrimer was performed. The results lead to the determination of the loading capacity of the dendrimers. The influence of temperature was evaluated by performing the titration at different temperatures. The colloidal metal nanoparticles were purified by dialyzing overnight against de-ionized water. The synthesis process of the silver and gold nanoparticles was monitored using UV-vis spectroscopy. The interaction of metal ions and tertiary amine group was assessed using a FTIR spectroscopy. TEM and EDX analysis were performed to obtain the distribution and average size of the metal nanoparticles, and to evaluate the purity of colloidal metal nanoparticles, respectively. The concentration of the metal nanoparticles in solution was determined by AAS. The specific surface area of silver and gold nanoparticles were estimated by self-assembled monolayer approach using the UV-photometric analysis to quantify the absorbed and unabsorbed organothiol. The catalytic activities of silver and gold nanoparticles were evaluated using the oxidation reaction of two different dyes, methylene blue and morin, as benchmark reactions. Hydrogen peroxide was used as an oxidizing agent and its stability during the catalytic process was assured by maintaining the pH constant using carbonate buffer. The Langmuir-Hinshelwood mechanism was applied to evaluate the catalytic performance of encapsulated silver and gold nanoparticles. This mechanism requires the adsorption of the reactants onto the catalyst surface prior to the start of the reaction. The catalytic process and the kinetic data set recorded were performed using UV-vis spectroscopy. The stability of the encapsulated metal nanoparticles during the reaction was evaluated by a three cycle runs using a dialysis bag.M.Sc. (Chemistry