The preparation of well-defined dendrimer-encapsulated palladium and platinum nanoparticles and their catalytic evaluation in the oxidation of morin

Abstract

The preparation of dendrimer-encapsulated platinum (Pt-DENs) and palladium (Pd-DENs) nanoparticles using generation 6-hydroxyl-terminated poly(amidoamine) (PAMAM) dendrimers as a templating agent is described. These nanoparticles were characterized using UV–vis spectrophotometry, spectrofluorophotometry, Fourier transform infrared spectrometry (FTIR), and high resolution transmission electron microscopy (HRTEM). The UV–vis spectra of palladium and platinum dendrimer-encapsulated nanoparticles gave a clear proof that nanoparticles were formed. It was found from FTIR spectra that there are shifts of peaks from higher wave numbers to lower wave numbers after reduction with sodium borohydride and these confirm the encapsulation of nanoparticles inside the voids of the dendrimer. The particle diameters were found to be 1.4±0.2 and 1.6±0.2nm in diameter for palladium and platinum respectively from HRTEM. These nanoparticles were evaluated as catalysts in the oxidation of morin by hydrogen peroxide. The kinetic data was modeled to the Langmuir–Hinshelwood equation. The model allows relating apparent rate constant to the total surface area (S) of the nanoparticle. The Langmuir–Hinshelwood model also allows a direct relationship between the kinetic constant (k) and Kmorin and KH2O2. The Arrhenius and Eyring equations were used to determine thermodynamic parameters for the oxidation of morin.