Dual-Bandgap Effect of Photonic Crystals on TiO2 Photocatalytic Activity in Ultraviolet and Visible Light Regions

Abstract

Photonic crystals (PCs) have promising characteristic to raise the light harvest of materials. PCs with one photonic band gap (PBG) were usually used to enhance the light harvest of materials. In this research work, we used PCs with dual PBGs to increase the light harvest. SiO2 PCs with dual PBGs were constructed through depositing a SiO2 PCs layer on another SiO2 PCs layer by vertical deposition method. Then the bi-layer structured SiO2 PCs were composited with nanocrystalline TiO2 film which was sensitized by CdS quantum dots (QDs) (Q-T), to produce photocatalyst for photodegradation of gaseous acetaldehyde. By adjusting the PBGs of the bi-layer SiO2 PCs, namely one PBG matching with the absorption edge of TiO2 and another PBG matching with the absorbing range of CdS QDs, the photocatalytic activity of the composite film under white light irradiation was increased to 2.11 times of that of the control photocatalyst (the Q-T film coated on a disordered porous SiO2 film). When Q-T film was coupled with a monolayer SiO2 PCs, which has single PBG centered at TiO2’s electronic band gap (EBG) of 380 nm, its photocatalytic activity was increased by 1.34 times. When coupled with a monolayer SiO2 PC with the PBG centering at the EBG of CdS QDs (465 nm), the photo-catalytic activity of the Q-T film was increased by 1.54 times. Because the SiO2 PCs with dual-PBGs can simultaneously enhance the light harvest in ultraviolet and visible light region, the Q-T film coupled with dual-PBGs SiO2 PCs showed the highest activity.