Photoelectrocatalytic degradation of rhodamine B on TiO2 photonic crystals

As the inverse-opal structure facilitates the separation of electron–hole pairs and electron transfer, it may generate many radical species with strong oxidation capability. When a low bias voltage was applied on the TiO2 electrodes with inverse-opal structure, they exhibited more excellent photoelectrochemical properties and photoelectrocatalytic activity than TiO2 film under simulated solar light irradiation. When different types of active species scavengers were added, the different performances of TiO2 photonic crystals in rhodamine B degradation showed that besides ˙OH and holes, which were the main active species in the photocatalysis, O2˙− played a vital role in the photoelectrocatalytic degradation process. Furthermore, the stronger signal of ˙OH-trapping photoluminescence and the variation in the concentration of nitroblue tetrazolium reflected that more ˙OH and O2˙− could be generated in the photoelectrocatalysis than that in the photocatalysis, and O2˙− was partially obtained from the cathode surface. At last, the roles active species played in the photoelectrocatalytic and photocatalytic processes were compared, and the possible degradation mechanisms of TiO2 photonic crystals in photoelectrocatalytic and photocatalytic systems were put forward, which could provide a good insight into the mechanism of photoelectrocatalytic degradation on TiO2 photonic crystals.