Applied Catalysis B: Environmental 150–151 (2014) 411–420 Contents lists available at ScienceDirect Applied Catalysis B: Environmental jo ur nal ho me p age: www.elsevier.com/locate/apcatb Probing significant light absorption enhancement of titania inverse opal films for highly exalted photocatalytic degradation of dye pollutants Min Wu a,b , Jing Liu a , Jun Jin a , Chao Wang a , Shaozhuan Huang a , Zhao Deng a , Yu Li a,∗∗ , Bao-Lian Su a,b,c,∗ a Laboratory of Living Materials at the State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, 122 Luoshi Road, 430070 Wuhan, Hubei, China b Laboratory of Inorganic Materials Chemistry (CMI), University of Namur, 61 rue de Bruxelles, B-5500 Namur, Belgium c Department of Chemistry and Clare Hall College, University of Cambridge, Lensfield Road, Cambridge, UK a r t i c l e i n f o Article history: Received 20 October 2013 Received in revised form 16 December 2013 Accepted 19 December 2013 Available online 27 December 2013 Keywords: TiO2 Inverse opal Photonic crystal Slow photon Photocatalytic activity a b s t r a c t The continuous titania inverse opal (TiO 2 -IO) films have been prepared by sol–gel infiltration method and calcined at different temperatures. The morphologies of the TiO 2 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 TiO 2 films obtained under the same conditions, all the TiO 2 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 TiO 2 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 TiO 2 inverse opal photonic crystals can explain the extraordinary enhancement of the photocatalytic activity. In consequence, the TiO 2 -IO-700, TiO 2 -IO-550 and TiO 2 -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 TiO 2 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. © 2013 Elsevier B.V. All rights reserved. 1. Introduction During the last decades, TiO 2 has been expected to be the most promising photocatalyst in environmental applications, such as the photodegradation of organic pollutants and the purifica- tion of water and air [1–3]. To achieve high photodegradation efficiency of the pollutants, various methods have been carried out to improve the activity of TiO 2 by controlling the morpholo- gies [4], doping anions and cations [5], modification of surface with metals and graphene [6–8] and exposing high surface energy facets [9,10]. TiO 2 aerosol [11–13], meso/nanoporous TiO 2 [14–16] and photonic materials [17–20] have also been used for efficient ∗ Corresponding author. Tel.: +86 27 87855322/+32 81 724531; fax: +86 27 87879468/+32 81 725414. ∗∗ Corresponding author. Tel.: +86 27 87855322; fax: +86 27 87879468. E-mail addresses: yu.li@whut.edu.cn (Y. Li), bao-lian.su@unamur.be, bao-lian.su@fundp.ac.be (B.-L. Su). photodegradation of organic pollutants due to the good mass trans- port and high surface area. For the photocatalytic process, it is well known that when a pho- ton with energy of h matches or exceeds the band gap energy (E g ) of the semiconductor, an electron is excited from the valence band to the conduction band, leaving a hole behind. These charge carri- ers migrate to the surface and react with the chemicals adsorbed on the surface to decompose these chemicals. Generally, the pho- tocatalytic activity of a semiconductor is mainly determined by three factors: the light absorption properties; the light excited charges (electron–hole pairs) transport rate and the electron–hole recombination rates on the surface [1–3]. As mentioned above, a lot of works have been reported on accelerating the electron–hole separation and transport to enhance the photocatalytic activity [21–24]. Most of the previous works on light absorption focused on broadening the absorption of TiO 2 to visible light [25–28]. Another possible way to reinforce the light absorption property, however less explored, is the increase of the path length of light to improve the photocatalytic efficiency, a structure effect other than 0926-3373/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apcatb.2013.12.037