Effect of diffusional film on formation of hydrogen peroxide in photocatalytic reactions

We recently found that photocatalytic reactions produce H₂O ₂ at a concentration level of ppm (parts per million) from water. For some reason, however, other researchers have paid little attention to the formation of H₂O₂ in this reaction. Of course, one of the reasons is due to low sensitivities of the conventional methods employed to measure the H₂O₂ concentration. However, we suppose that there is another reason which makes it difficult to measure it. To elucidate this reason, therefore, an effect of linear liquid velocity on the photocatalytic formation of H₂O₂ from water is experimentally investigated, and an explanation for the experimental result is made using a mathematical model that takes into consideration the formation and decomposition of H₂O₂ and its diffusion through a film in the neighborhood of the photocatalyst surface into a bulk liquid. This effect is also discussed on the formation of H₂O₂ from an aqueous solution of formic acid. As a result, it is concluded that the diffusion film is responsible for the reduction in the H₂O₂ concentration.