Transition of Growth Mode Controlled by the Density of Nuclei in Photocatalytic Synthesis of Ag Nanoparticles

Using the aqueous solution of AgNO3, the growth behavior of Ag nanoparticles synthesized by photocatalytic method is studied by controlling the chemical activity of TiO2 film. It is found that the Ag nanoparticles can grow up with two distinct growth modes, which correspond to the isotropic and anisotropic growth, respectively. When the concentration of AgNO3 is low, Ostwald ripening (OR) dominates the growth of Ag nanoparticles. If the concentration of AgNO3 exceeds a critical level, oriented attachment (OA) determines the Ag nanoparticles growing up into Ag nanoplates. The in-situ extinction spectra suggest that the Ag nuclei have the very similar features in the stage of nucleation before the growth of Ag nanoparticles is dominated by OR or OA mechanism. The transition of growth behavior is determined by the concentration of AgNO3 in the solution, or the local density of Ag primary nuclei. On the basis of experimental results and theoretical analysis, a physical model is suggested for the growth of Ag nanoparticles in the photocatalytic synthesis.