Preparation and photocatalytic activity of TiO2 photonic crystals modified by bimetallic Ag–Pt nanostructures†

Aiming to achieve a better understanding of the interactions between photonic crystals (PCs) built of semiconductor TiO₂ and metallic nanostructures (MNSs), we studied the effect of combining the slow photon effects (SFE) occurring in the PC structure and electron trapping taking place in MNSs on the photocatalytic decomposition of a model pollutant – rhodamine B (RhB). PCs of small (203 nm), medium (316 nm) and large (493 nm) pore size were prepared with the use of the sol–gel method supported by the self-assembly of polystyrene (PS) microspheres that served as a template. Silver, platinum, and bimetallic silver–platinum nanostructures (AgNSs, PtNSs and AgPtNSs) were generated on the surface of TiO₂ PCs by photoreduction of appropriate ions under UV illumination. It was found that an increase of the pore size of PCs only changes slightly the position of the semiconductor band gap (BG), while it particularly affects the photonic band gap (PBG), shifting it towards longer wavelengths. The modification of PCs with metallic nanostructures increases the intensity of the PBG. Moreover, the phenomenon of overlapping of the PBG edge with the semiconductor BG and the applied illumination range (known as the slow photon effect (SPE) combined with the electron trapping that is the result of modification of PCs with mono- and bi-metallic nanostructures) leads to an increase in the photocatalytic activity of PCs.