Probing the tunneling of electrons from SnO2 to ZnO in dye sensitization of composite SnO2/ZnO by use of generated H2O2 via reduction of O2

A composite system of SnO2/ZnO semiconductors was found to generate a higher H2O2 yield than individual oxide semiconductors when they were sensitized with various dyes. The optimum quantum yields for H2O2 generation were found to be 6.00 x 10(-2), 4.05 x 10(-2) and 3.33 x 10(-2), respectively, for Eosin Y, Rose Bengal and Rhodamine 6G. Under similar conditions, Eosin Y showed quantum yields of 2.03 x 10(-2) and 2.34 x 10-(3), respectively, for ZnO and SnO2 particles. With the higher yield of H2O2 for the composite system, the possibility of electron transfer from the low band position semiconductor to the high band position semiconductor is demonstrated and is attributed to the transfer of injected high-energy electrons from the excited dye molecules on SnO2 to ZnO particles.