Bioluminescence-induced photocatalysis on semiconducting oxide nanosheets

A novel semiconductor photocatalytic reaction system employing a photo-emitting enzyme as an internal light source is pro-posed in the present study. The system completely overturns common sense that conventional photocatalytic reactions must require irradiation from an external light source. A horseradish peroxidase (HRP) catalyzing oxidative bioluminescence reaction of luminol in the presence of H2O2 and manganate nanosheets (MNSs) with a narrow bandgap were utilized for an internal light source and semiconductor photocatalysts, respectively, and both of them coexisted in a same reactant solution. In other words, nano-sized light sources were highly dispersed in the solution, resulting in photo-excitation of MNSs over the entire solution. Photo-activated MNSs simultaneously caused oxidation and reduction, where platinum hexachloride anions (PtCl62-) were utilized as a model substance to be reacted photocatalytically. According to X-ray absorption near edge spectroscopy (XANES) of MNSs after the photocatalytic reaction, the anions were mainly transformed into solid phases of PtO2 and/or Pt(OH)(4) by reacting with holes in MNSs. In contrast, a control experiment without HRP, i.e. a dark experiment, did not leave any evidence for photocatalytic reaction of PtCl62-. The detailed mechanism and the advantages/disadvantages of the proposed unique system are explained.