Solid-State, Planar Photoelectrocatalytic Devices Using a Nanosized TiO₂ Layer

Solid-state planar photoelectrocatalytic devices using a nanosized Ti02 layer have been fabricated and used in the photodegradation of gaseous formaldehyde (HCHO). It is discovered for the first time that in the photocatalytic degradation of HCHO over TiO2 film, besides a well-known process of exciton dissociation expressed as TiO2* --> e(-) + h+ (process A), there exists an HCHO-involved process of exciton dissociation expressed as TiO2 + HCHO* --> TiO2(-) + HCHO+ (process B); these two processes have comparable contributions to the electron photogeneration. A biased photocatalytic device is unable to photodegrade HCHO under the nitrogen condition, but under the air condition, a positive synergic effect of bias on the photodegradation of HCHO over the planar photoelectrocatalytic device has been observed, mainly attributed to it that the horizontal electric field can displace electrons generated via process B away from their counterparts, effectively suppressing hole-electron recombination on TiO2 surface and thereby leading to the enhanced formation of O2- species. The current research points out that the planar photoelectrocatalytic device can provide the in-depth investigations on the mechanisms of the photocatalytic degradation over nanosized semiconductor oxide films, and also have potential application in decomposing and mineralizing organic gas-phase pollutants.