TIME-RESOLVED OPTICAL STUDY ON THE CHARGE-CARRIER DYNAMICS IN A TIO2 AGI SANDWICH COLLOID/

Preparation of a sandwich colloid involving TiO2 and AgI (hexagonal) p articles in alkaline aqueous solution is described. Time-resolved opti cal absorption experiments are reported that involve pulsed laser exci tation at 355 Mn (TiO2 bandgap) and at 410 MI (AgI bandgap). Charge ca rrier dynamics was probed directly by transient absorption measurement s in the near-infrared and by reaction with methyl viologen (MV(2+)). Reduction of MV(2+) was observed to occur over a period of 100-200 mu s. MV(+) so produced reduced AgI to silver. By contrast, MV(2+) reduct ion upon bandgap excitation of neat alkaline TiO2 colloid was complete within 1 mu s. These observations signal a prolonged electron-hole se paration in the case of the AgI/TiO2 sol and indicate the formation of sandwich particles.