Ruthenium bipyridyl complex-sensitized dechlorination of CCl4 in aqueous micellar solutions under visible light

The sensitized dechlorination of CCl4 in water was successfully demonstrated in the presence of nonionic surfactants (Brij-35) and ruthenium bipyridyl complexes [RuII(bpy)3] under visible light illumination (λ > 420 nm). The ruthenium complex plays the role of a visible light sensitizer for this reductive conversion process, which is excited by absorbing visible light and subsequently transfers an electron to CCl4. The photoinduced electron transfers from the excited sensitizer to CCl4 take place only in the presence of the surfactant, which concentrates both reactants within a micelle. The ruthenium sensitizer should be oxidized after transferring an electron to CCl4, but immediately regenerated by abstracting an electron from surrounding surfactant molecules. As a result, the ruthenium sensitizer acts as a photocatalyst with producing chlorides far above the stoichiometric concentration of the added sensitizer. The dechlorination rate was significantly reduced in the presence of dissolved oxygen, because the excited sensitizer is quenched by O2. With increasing each concentration of the surfactant, sensitizer, or CCl4, the corresponding CCl4 dechlorination rate progressively increased, to reach a saturation at the concentration of 4.0 g/L (surfactant), 5 μM (sensitizer), or 30 mM (CCl4), respectively. The visible light activity was strongly dependent on the kind of surfactants as well.