Evaluation of catalytic activity of Ag and Au dendrimer-encapsulated nanoparticles in the reduction of 4-nitrophenol

Abstract

Langmuir–Hinshelwood parameters were determined with the use of gold and silver dendrimer-encapsulated nanoparticles (Au-DENs and Ag-DENs) as catalysts. Dendrimers were used as templating and stabilizing agents to ensure that there is no aggregation of metal nanoparticles. The synthesis of DENs using amine terminated generation 4 poly(amido)amine dendrimer (G4-PAMAM-NH2) was successfully demonstrated. These synthesized DENs were characterized using UV–visible spectrophotometry (UV–vis), electron dispersion X-ray analysis (EDX), and Fourier transformed infrared spectrophotometry (FTIR). High resolution transmission electron microscopy (HRTEM) was used to determine the average particle sizes, and the average particle sizes were found to be 1.23±0.13 and 1.17±0.13nm for Au- and Ag-DENs, respectively. Comparison of catalytic activity between the two metal nanoparticles was done in terms of thermodynamic parameters obtained from Langmuir–Hinshelwood fits at 298K. 4-Nitrophenol (NP) reduction by sodium borohydride (NaBH4) in the presence of the synthesized DENs as homogeneous catalysts was used by virtue of being a model reaction. Effect of diffusion barrier in all kinetic runs was addressed by calculations of the second Damköhler number and by the application of the second Fick's law of diffusion. The Langmuir–Hinshelwood model proved to be an efficient model for thermodynamic comparison of the two metal nanoparticles.