Role of Ag Loading on the Concentration of Surface-Reaching Photoexcited Holes in TiO<sub>2</sub> Nanoparticles
Cong Fu, Lingfang Liu, Guofeng Zhao
Abstract
The effect of noble metal cocatalyst loading on the concentration of surface-reaching photoexcited charges on semiconductors is an interesting and important issue in photocatalysis. Herein, through in situ diffuse-reflectance infrared spectroscopy (DRIFTS), an adsorbate (methanol) surface elementary reaction kinetic analysis method has been exploited to track the concentration of surface-reaching photoholes in a series of Ag/TiO 2 nanoparticles with varied Ag loading. The photocatalytic oxidation of adsorbed methanol species on the Ag/TiO 2 surface proceeds via first-order reaction kinetics. Thus, the measured reaction rate constants directly reflect the concentration of surface-reaching photoholes under light irradiation. By determining the specific reaction rate constants for methanol oxidation on the Ag/TiO 2 surface, we discover that the concentration of surface-reaching photoholes under light irradiation exhibits a volcano-shaped dependence on the Ag loading. Under the optimized Ag loading, it could be found that the concentration of surface-reaching photoholes on Ag/TiO 2 surface is nearly 1.5 times greater than that of the pristine TiO 2 surface. These results provide, for the first time, unambiguous experimental evidence for the significance of modification with suitable noble metal cocatalysts on regulation of surface-reaching photoexcited charges in semiconductor-based photocatalysis.