Time dependent synthesis of gold nanoparticles using chitosan as reducing agent: A spectroscopic approach

Abstract

The present study attempted synthesis of gold nanoparticle using chitosan from shrimp waste and evaluated the kinetics
of gold nanoparticle (AuNPs) formation. Two different forms of chitosan (high molecular weight and medium molecular
weight forms) were used for the preparation of AuNPs. The formation of nanoparticles was studied using UV-VIS spectra
obtained at different time intervals during synthesis. The typical UV-VIS spectrum of non-aggregated spherical AuNPs
at 520 nm was obtained for both chitosan forms and the maximum absorbance was higher for the sample prepared with
medium molecular weight chitosan. The results clearly indicated that the characteristic surface plasmonic resonance (SPR)
peak became recognisable at 5 min of heating for the sample with high molecular weight chitosan and 3 min of heating
for medium molecular weight chitosan. This indicated that, the lower the molecular weight, the faster the formation of
nanoparticles. The wavelength (λ) of absorption maxima was selected and normalised with respect to the absorption maxima
at 15 min. The sigmoidal shape of kinetic curve implied the autocatalytic character of AuNP formation. The data from the
samples were fitted with two step Finke-Watzky kinetics model and the kinetics constants were derived. The rate constant
of the nucleation reaction was found higher for the medium molecular weight chitosan.
Keywords: AuNPs, Chitosan, Gold nanoparticles, Molecular weight, Rate constant