Original photochemical synthesis of Ag nanoparticles mediated by potato starch

In this contribution, we report an original photochemical method and its mechanism, in which Ag nanoparticles (AgNPs) are formed in the presence of starch. AgNO3/potato starch aqueous suspensions are irradiated (254 nm, 8 W) at room temperature and the Ag+/starch ratio can be varied to tune the size of AgNPs. The evolution of the AgNPs plasmon resonance band during the reaction is monitored by UV–Vis spectroscopy and evidences that AgNPs are formed in a two-stage process combining nucleation and growth, with the nucleation being controlled by the amount of added starch. Moreover, infrared and Raman spectra indicates that starch undergoes oxidation simultaneously to Ag+ reduction, even though starch alone is not capable of reducing Ag+ at an appreciable rate and UV irradiation is essential to produce sizeable amounts of AgNPs. Transmission electron microscopy reveals that AgNPs are nearly spherical with diameters ranging between 13 and 8 nm. The AgNPs/starch suspensions exhibit hydrodynamic diameters between 150 and 200 nm and zeta potentials very close to zero. Since AgNPs/starch suspensions are very stable over time, the colloidal stability is ensured by the steric hindrance imposed by starch rather than electrostatic repulsion.