Interparticle electron transfer between size-quantized CdS and TiO2 semiconductor nanoclusters

Abstract

Photoinduced electron transfer in a size-quantized CdS/TiO₂ composite system has been investigated using emission and transient absorption spectroscopy. Quantum-sized CdS and TiO₂ particles were synthesized in reverse micelles using di-octyl sulfosuccinate (Aerosol-OT, AOT) as the surfactant stabilizer. The particle sizes of CdS and TiO₂ were controlled by varying water-to-surfactant molar ratio, w_o = [H₂O]/[AOT], with values of 1, 2.5, 5 and 10. The blue-shift in the absorption onset confirmed size-quantization of these semiconductor particles. Electron transfer from photoexcited CdS to TiO₂ was found to depend on the particle size of TiO₂, where charge transfer was observed only when TiO₂ particles were sufficiently large (>12 Å). Interactions with smaller size TiO₂ particles (⩽10 Å) with CdS instead led to enhancements in emission with an increase in quantum yield from 2.3% to 8.8%. Picosecond laser flash photolysis experiments have been carried out to elucidate the interparticle electron transfer processes in the CdS/TiO₂ reverse micellar system.