Environmental photochemistry: Electron transfer from excited humic acid to TiO2 colloids and semiconductor mediated reduction of oxazine dyes by humic acid

The ability of naturally occurring Suwanee River Humic acid to sensitize a large bandgap semiconductor such as colloidal TiO₂ has been investigated by fluorescence emission. The charge injected from the humic acid sensitizer into the semiconductor was used to reduce a series of oxazine dyes viz:, N,N,N’,N’-tetraethyloxonine and Nile Blue A. The mechanism of such a sensitized reduction process was elucidated by laser flash photolysis methods. The quantum yield for such a reduction calculated from these transient absorption techniques was 0.005.