Transient FTIR Measurements at Nanoseconds Resolution: Correlating between Faceting and Photocatalytic Activity in BiOCl

Transient IR measurements of photo-excited bismuth oxychloride (BiOCl) were performed by a step-scan technique at a resolution of 2.5 nanoseconds. Six types of faceted BiOCl particles, which differed also in their average size, were used. Following excitation, an increase in the intensity of the Bi-O signal, which lasted for 70-130 nanoseconds was observed. A negative correlation between the characteristics of the transient signal (duration of signal and intensity) versus the photocatalytic activity toward the reduction of Cr(VI) was found. In parallel, a positive correlation was found between the duration of the transient signal and the specific surface area of the various types of particles. The increased transient intensity is explained in terms of formation of deep traps, most likely at the surface of the particles. The results demonstrate that transient vibrational spectroscopy may serve as an important tool for studying photocatalytic materials.