Photovoltage and Photocatalyzed Growth in Citrate-Stabilized Colloidal Silver Nanocrystals

The photocatalyzed reduction of aqueous silver ions, by citrate adsorbed on silver nanocrystals, is studied on Formvar/carbon TEM grids and in photoelectrochemical cells. The reaction is characterized by transmission electron microscopy (TEM) monitoring of individual particles throughout the growth process. The photoinitiated growth on the silver particles is uniform and is not dependent upon the laser polarization. The potential of silver particle working electrodes is shown to shift negatively under irradiation in solutions of citrate. Adding silver ions to this system quenches the charging of the particle working electrode through charge transfer to the silver ions. The reaction is hypothesized to result from photoelectron transfer from adsorbed citrate to the silver nanoparticle. Nanocrystal growth occurs when this “stored” charge reduces silver ions in solution. Comments are offered on the photo-reformulation of colloidal nanocrystals into prisms reported in the literature.