The present research includes solar-light-driven photocatalytic cycles based on the photoreductions of Fe(III), Cr(VI), and Cr( III) compounds with EDTA, oxalate and other ligands. Molecular oxygen is needed to close the photocatalytic cycles in which the metal species plays a role of photocatalyst; it affects the reaction mechanism and rate. The photoinduced electron transfer was also investigated in the presence of some external electron donors, such as EDTA, aliphatic alcohols, phenol, and its halogen derivatives, oxalate, nitrate( III), sulfate( IV). The results apply to the removal of such hazardous environmental pollutants as chromate( VI) or phenol derivatives and such recalcitrant pollutants as EDTA.