Catalytic reduction of methyl viologen by sulfide ion within MCM-41

Methyl viologen in the presence of mesoporous MCM-41 and sulfide ions is found to undergo a spontaneous catalytic reduction to methyl viologen radical (MV+). Various control conditions, including passivation of the external surface and modification of the internal surface of MCM-41, suggest that the catalytic reduction occurs principally within the pores of MCM-41. The source of the sulfide ions can be either an added sulfide salt or coordinatively unsaturated surface sulfide ions of an occluded sulfide nanoparticle. The present system offers a means for the spontaneous formation of methyl viologen radicals, which might serve as a complementary measurement for electron microscopy probing of the location of sulfide nanoparticles synthesized within the pores of mesoporous materials.