Probing significant light absorption enhancement of titania inverse opal films for highly exalted photocatalytic degradation of dye pollutants

The continuous titania inverse opal (TiO₂-IO) films have been prepared by sol-gel infiltration method and calcined at different temperatures. The morphologies of the TiO₂ inverse opal films remain unchanged under high temperature treatment. XRD patterns reveal an anatase crystalline phase between 550 and 900°C and a mixture of anatase and rutile phase at 1000°C. Comparing with the mesoporous TiO₂ films obtained under the same conditions, all the TiO₂ inverse opal films demonstrate a highly enhanced photocatalytic activity in photodegradation of rhodamine B (RhB) as dye pollutant model in aqueous solution. In spite of the fact that the TiO₂ inverse opal films with open macroporous structures and possible light scattering effect of the wavelengths can result in the higher photocatalytic activity in the degradation of the dye pollutant, the phenomenon of the slow photon occurring in the TiO₂ inverse opal photonic crystals can explain the extraordinary enhancement of the photocatalytic activity. In consequence, the TiO₂-IO-700, TiO₂-IO-550 and TiO₂-IO-800 films show the best photocatalytic performance mainly due to the slow photon effect at the light incident angle at 0°, 20° and 45°, respectively, a direct proof of light absorption enhancement due to the slow photon effect. The slow photon effect in TiO₂ inverse opals to enhance light absorption and further to enhance photocatalysis is very important for further potential applications in solar cells and other processes linked to the light absorption.