The effect of nanometre-sized Au particle loading on TiO2 photocatalysed reduction of bis(2-dipyridyl)disulfide to 2-mercaptopyridine by H2O

TiO2 photocatalysed reduction of bis(2-dipyridyl)disulfide (RSSR) to 2-mercaptopyridine by H2O is enhanced significantly by incorporation of nanometre-sized Au particles. The rate is strongly dependent on the amount of Au loaded (x wt.%), passing through a maximum at x∽0.3, while it is almost independent of the Au particle size in the 4.3–11 nm range. Comparison of the effects of Au and Ag loading reveals that the rate constant of the Au(0.25 wt.%)/TiO2 system is greater than that of the Ag(0.24 wt.%)/TiO2 system by a factor of 2.6 and the activation energy of the former is about two-thirds that of the latter. The enhancing effect of the Au loading is discussed in terms of kinetic and molecular orbital considerations.