or biphasic (with water) system even under nominally visible light (using a >420 nm cutoff filter) irradiation. Interestingly, for example, in a biphasic system of benzyl alcohol and water and using only benzaldehyde as a photocatalyst, H2O2 concentrations exceeding those reported for most semiconductor-mediated light-driven H2O production systems can be achieved. Interestingly, as we found that benzaldehyde-mediated photocatalysis of H2O2 productions proceeds also using alternative electron donors such as ethanol, these results definitely pave the way for a more general use of benzaldehyde in visible light-driven photocatalysis. On the other hand, our findings also shed some critical light on a number of research reports on photocatalytic H2O2 production in which benzyl alcohol has been employed as electron donor. Since the auto-photocatalytic pathway initiated by the light absorption by benzaldehyde formed during photocatalysis under such conditions cannot be neglected in many cases, the interpretations of photocatalytic performance of various photocatalysts are likely contentious and distorted in such reports. Therefore, we conclude that the use of benzyl alcohol as a model electron donor in photocatalytic studies should be definitely discouraged. More generally, similar effects cannot be a priori ruled out also in case of other substrates and other photocatalytic reactions. In order to exclude the possibility that a heterogeneous photocatalytic reaction is significantly influenced by photoactivity of a reaction intermediate, a simple check protocol is mandatory that consists in filtering off the heterogeneous photocatalyst in the course of reaction and checking how much the rate of the reaction is changed by the absence of the heterogeneous photocatalyst.