PHOTOCHEMISTRY OF IRON-OXIDE COLLOIDS

The photochemistry of two aqueous colloids of iron oxides (hematite and amorphous), have been investigated by laser flash photolysis and steady-state techniques. Excited ruthenium tris-bipyridine, *Ru(bpy)//3**2** plus , is quenched by the amorphous colloid provided polyacrylic acid (PAA) used to stabilize the colloid and promote adsorption of Ru(bpy)//3**2** plus onto the oxide surface. No net chemical change takes place. The quenching effect is most marked at pH 7. Generation of reduced methyl viologen, MV** plus . , by irradiation of the PAA-MV**2** plus complex causes a dissolution of the pure oxide by e** minus transfer from MV** plus . to the colloid. The measured rate of this reaction is a factor of 10 less than that calculated for a diffusion-controlled process.