Preparation and photocatalytic activity of hierarchically 3D ordered macro/mesoporous titania inverse opal films

• Novel macro/mesoporous titania inverse opal (TiO2-IO) films were prepared.
• PEG 2000 modified TiO2-IO films show superior photocatalytic activity.
• The optimal PEG 2000 content was determined.The mechanism of mesopores formation and photocatalysis improvement are discussed.
• The mechanism of mesopores formation and photocatalysis improvement are discussed.

Hierarchically ordered macro/mesoporous titania inverse opal (TiO2-IO) films were prepared using a polyethyl glycol (PEG)-associated sol–gel method. Macroporous templates were obtained using the self-assembly of monodispersed polystyrene (PS) microspheres into opal structures, which were subsequently infiltrated with titanium alkoxide precursors containing PEG 2000 as the mesopore directing agent. After the PS and PEG 2000 were removed by calcination, TiO2-IO hierarchical structures with macro/mesopores were formed. SEM and TEM images show that the novel films were of 3D ordered macroporous structure, composed of titanium dioxide frameworks and several hundred nanometers spherical air voids arranged in an fcc close-packing array, and the ordered framework possessed numerous mesopores. The hierarchically ordered macro/mesoporous TiO2-IO films prepared displayed enhanced photocatalytic activity in the decolorization of rhodamine B (RhB) in a solid state photocatalytic process. The PEG 2000 content has a significant influence on the photocatalytic activity and the optimal PEG 2000 content was determined. The sample prepared with 2.1 wt.% PEG 2000 showed the highest photocatalytic activity with a rate constant (k) = 0.1346 min−1, which is a six fold increase on that found with TiO2-IO in the absence of PEG 2000 (k = 0.0225 min−1). However, an excessive amount of PEG 2000 results in the destruction of the macroporous structure and a loss of photocatalytic activity. The enhanced photocatalytic activity was attributed to the incorporation of mesopores into the macroporous skeleton via decomposition of PEG 2000 in the film. This increases the accessible surface area of the film, improves mass transport and reduces the length of the mesopore channels.

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