Effect of Ag nanoparticle size on the photoelectrochemical properties of Ag decorated TiO2 nanotube arrays

Silver (Ag) nanoparticle decorated titanium dioxide nanotube arrays (TiO2 NTAs) were fabricated using a two-step method based on an electrochemical anodization procedure followed by a photochemical reduction process. UV-visible diffuse reflectance spectroscopy and photoluminescence emission spectroscopy demonstrated that the Ag decorating significantly enhanced the light absorption of TiO2 NTAs in the visible spectral range and improved the separation of photo-induced charge carriers in the TiO2 NTAs. The photoelectrochemical properties of prepared samples were investigated by the transient photocurrent measurement and the potential dependence of photocurrent under visible light irradiation. The results show that the photoelectrochemical behavior of Ag decorated TiO2 NTAs is dependent on the size of the Ag particles. The maximum photoconversion efficiency of Ag decorated TiO2 NTAs is about 3.3 times greater than that of bare TiO2 NTAs. Electrochemical impedance spectroscopy measurements of the subject materials revealed that the photoelectron lifetime of Ag decorated TiO2 NTAs increases as the Ag nanoparticle's size decreases. We propose that the enhanced photoelectrochemical properties of Ag decorated TiO2 NTAs results from different ratios of light absorption to scattering caused by the localized surface plasmon resonance of the various sizes of Ag nanoparticles. The tunable photoelectrochemical properties of Ag decorated TiO2 NTAs are expected to have promising applications in photoelectrochemical solar cells and other light-harvesting devices. (C) 2012 Elsevier B. V. All rights reserved.