Photocatalytic growth of Ag nanoparticles on TiO2 films: growth behavior and kinetics study by UV–Vis-NIR extinction spectroscopy and scanning electron microscopy

Abstract

Ag nanoparticles can easily be deposited on semiconductors through the photocatalytic growth process to yield directly attached metal nanoparticles on the material surface. However, the growth behavior and kinetics of the photocatalytic growth require further investigations to guide controlled preparation. Herein, the behavior and kinetics of photocatalytic growth Ag nanoparticles on sol–gel TiO₂ films were first explored by in situ UV–Vis-NIR extinction spectroscopy and scanning electron microscopy. The results suggested average size evolution of Ag NPs varied according to d³ ∝ t law, and Ostwald ripening mechanism dominated by the growth process of Ag NPs. The in situ UV–Vis-NIR extinction spectra highlighted the presence of a critical concentration of Ag⁺ ion at a given irradiation intensity. The critical AgNO₃ concentration C(I) gradually rose with the irradiation intensity. The values of C(I) at 1, 1.6, and 5.3 mW/cm² irradiations were approximately 400, 800, and 1600 mg/L, respectively. For Ag⁺ ion levels below the critical concentration, the growth of Ag NPs was controlled by Ag⁺ diffusion-limited growth. For Ag⁺ ion levels above the critical concentration, the growth of Ag NPs was controlled by photo-induced carrier diffusion-limited growth. Overall, the clarified kinetics of photocatalytic growth of Ag nanoparticles on sol–gel TiO₂ films would help prepare customized noble metal nanoparticles by photocatalytic growth or other similar methods like electrochemical deposition and galvanic cell replacement.