Formation of Hydrogen Peroxide in Photocatalytic Reactions

To characterize the formation of H₂O₂ in photocatalytic reactions, HCHO and HCOOH have been photocatalytically decomposed by use of TiO₂ and Pd/TiO₂ under irradiation with the UV light emitted from a blacklight blue fluorescent lamp (BL) or germicidal lamp (GL). An enzymatic method has been introduced to accurately measure the H₂O₂ concentration. The photocatalyst irradiated with the UV light emitted from the GL produces H₂O ₂ from water at a larger rate and amount. Deposition of Pd on TiO₂ increases the rate and amount of the formation of H ₂O₂ from water. In the absence of the photocatalyst, no HCOOH is decomposed under irradiations with both the UV lights from the BL and GL, whereas the decomposition becomes possible in the presence of the photocatalyst. H₂O₂ is formed in parallel with the photocatalytic decomposition of HCOOH. In the presence of the photocatalyst, the concentration of the H₂O₂ formed during the decomposition of HCHO is smaller than that formed from water alone. In contrast, this relationship is reversed with the decomposition of HCOOH. This is considered due to the formation of H₂O₂ in the process of the decomposition of HCOOH to carbon dioxide and water. The rates of decomposition of HCHO and HCOOH are directly proportional to their respective rates of formation of H₂O₂, indicating that there is a close relationship between the photocatalytic activity and the capability of the photocatalyst to form H₂O₂.