Photocatalytic dechlorination of polychlorinated biphenyls using leuco-methylene blue sensitization, broad spectrum visible lamps, or light emitting diodes.

Photocatalytic routes to dechlorinate polychlorinated biphenyls (PCBs) have considerable potential for development. This paper describes efficient dye-photocatalyzed processes which can be driven by long wavelength light sources including light-emitting diodes (LEDs), fluorescent lamps, and quite probably sunlight. The reduced form of methylene blue (MB), leuco-methylene blue (LMB), has previously been found to photoinduce dechlorination of chloroaromatics with an electron transfer from its triplet excited state. Sodium borohydride, used in this case is an efficient sacrificial reductant, which can maintain LMB as the major species in competition with air oxidation of LMB to MB. There is also evidence that it plays a further (chain reaction) role in promoting the LMB photodechlorination process as well. The generality of the photoelectron transfer from reduced members of the phenothiazine dye family is demonstrated with phenothiazine and leuco-methylene green when a wavelength (UV) is chosen to produce the highly reductive triplet. It is likely that dechlorination can be initiated by many triplet excited states with adequate reduction potential.