Novel N-F-Codoped TiO2 Inverse Opal with a Hierarchical Meso-/Macroporous Structure: Synthesis, Characterization, and Photocatalysis

We reported a new simple route to fabricate N-F-codoped titania inverse opal (IO) films with a hierarchical meso-/macroporous structure, in which the IO structure and the N-F codoping play a role as physical and chemical modifications for titania, respectively. Both modifications are simultaneously achieved via a liquid phase deposition process using a silica colloidal crystal as a template for the first time. The average size of a mesopore in the TiO2 frameworks is 3.2 nm, and that of an interpenetrating aligned macropore is adjusted in the range of 201-315 nm. The N-F-codoped TiO2 IO films exhibit 6.6-7.4 times the methylene blue visible-light photodegradation rate comparing with N-F-codoped TiO2 films without the IO structure. This high visible-light activity was mainly ascribed to a synergetic effect of the hierarchical meso-/macroporous structure and N-F codoping. Furthermore, it was found that the multiple scattering effect of the macroporous structure is more pronounced than the slow photon effect of IOs for facilitating visible-light photocatalysis in our system from the comparison with nonperiodic macroporous N-F-codoped TiO2. The repeated cycling tests revealed that samples showed stable photocatalytic activity.