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

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 Angstrom). Interactions with smaller size TiO2 particles (less than or equal to10 Angstrom) with CdS instead led to enhancements in emission with an increase in quantum yield from 2.3% to 8.8%. Picosecond laser ash photolysis experiments have been carried out to elucidate the interparticle electron transfer processes in the CdS/TiO2 reverse micellar system.