UV-induced synthesis, characterization and formation mechanism of silver nanoparticles in alkalic carboxymethylated chitosan solution

The silver nanoparticles (AgNPs) were synthesized in an alkalic aqueous solution of silver nitrate (AgNO(3))/carboxymethylated chitosan (CMCTS) with ultraviolet (UV) light irradiation. CMCTS, a water-soluble and biocompatible chitosan derivative, served simultaneously as a reducing agent for silver cation and a stabilizing agent for AgNPs in this method. UV-vis spectra and transmission electron microscopy (TEM) images analyses showed that the pH of AgNO(3)/CMCTS aqueous solutions, the concentrations of AgNO(3) and CMCTS can affect on the size, amount of synthesized AgNPs. Further by polarized optical microscopy it was found that the CMCTS with a high molecular weight leads to a branch-like AgNPs/CMCTS composite morphology. The diameter range of the AgNPs was 2-8 nm and they can be dispersed stably in the alkalic CMCTS solution for more than 6 months. XRD pattern indicated that the AgNPs has cubic crystal structure. The spectra of laser photolysis of AgNO(3)/CMCTS aqueous solutions identified the early reduction processes of silver cations ( Ag(+)) by hydrated electron (e(aq)(-)) formed by photoionization of CMCTS. The rate constant of corresponding reduction reaction was 5.0 x 10(9) M(-1) s(-1).