Direct measurement of picosecond interfacial electron transfer from photoexcited TiO2 powder to an adsorbed molecule in the opaque suspension

The excited state dynamics and interfacial electron transfer of an optically scattering TiO2 powder suspension in alkaline water (pH = 10) with and without methyl viologen (MV2+) as an electron acceptor was examined by means of femtosecond diffuse reflectance absorption spectroscopy using a femtosecond white-light continuum as a probe pulse. The spectral analysis of broad transient absorption bands directly proved plural trapping sites of electrons with different electronic structure and surface electron transfer from photoexcited TiO2 particles to adsorbed MV2+ molecules in the few picoseconds to nanosecond timescale.