Fabrication and Characterization of Inverse-Opal Titania Films for Enhancement of Photocatalytic Activity

Abstract

Novel materials with a periodic structure have recently been intensively studied for various photonic and photocatalytic applications due to an efficient light harvesting ability. Here, inverse opal titania (IOT) has been investigated for possible enhancement of photocatalytic activity. The IOT films were prepared on a glass support from silica and polystyrene (PS) opals by sandwich-vacuum-assisted infiltration and co-assembly methods, respectively. The reference sample was prepared by the same method (the latter) but with PS particles of different sizes, and thus without photonic feature. The modification of preparation conditions was performed to prepare the films with a high quality and different photonic properties, i.e., photonic bandgap (PBG) and slow pho-tons’ wavelengths. The morphology and optical properties were characterized by scanning electron microscopy (SEM) and UV/vis spectroscopy, respectively. The photocatalytic activity was evaluated (also in dependence on the irradiation angle) for oxidative decomposition of acetaldehyde gas under irradiation with blue LED by measuring the rate of evolved carbon dioxide (CO2). It has been found that PBG wavelength depends on the size of particles forming opal, the void diameter of IOT, and irradiation angle, as expected from Bragg’s law. The highest activity (more than two-fold enhancement in the comparison to the reference) has been achieved for the IOT sample of 226-nm void diameter and PBG wavelengths at 403 nm, prepared from almost monodisperse PS particles of 252-nm diameter. Interestingly, significant decrease in activity (five times lower than reference) has been obtained for the IOT sample of also high quality but with 195-nm voids, and thus PBG at 375 nm (prohibited light). Accordingly, it has been proposed that the perfect tunning of photonic properties (here the blue-edge slow-photon effect) with bandgap energy of photocatalyst (e.g., absorption of anatase) results in the improved photocatalytic performance.