Titania Enhanced Photocatalysis and Dye Giant Absorption in Nanoporous 1D Bragg Microcavities

Light trapping effects are known to boost the photocatalytic degradation of organic molecules in 3D photonic structures of anatase titania (a-TiO₂) with an inverse opal configuration. In the present work, we show that photocatalytic activity can also be enhanced in a-TiO₂ thin films if they are incorporated within a nanoporous 1D optical resonant microcavity. We have designed and manufactured multilayer systems that, presenting a high open porosity to enable a straightforward diffusion of photodegradable molecules, provide light confinement effects at wavelengths around the absorption edge of photoactive a-TiO₂. In brief, we have observed that a nanoporous 1D Bragg microcavity prepared by electron beam evaporation at oblique angles comprising a central defect layer of nanoporous a-TiO₂ boosts the photocatalytic degradation of nitrobenzene and methyl orange dye solutions. The multilayer structure of the microcavity was designed to ensure the appearance of optical resonances at the a-TiO₂ layer location and wavelengths around the absorption onset of this semiconductor. In this porous 1D Bragg microcavity, the diffusion constraints of molecules through the capping layers covering the a-TiO₂ are effectively compensated by an increase in the photocatalytic activity due to the light confinement phenomena. We also report that the absorption coefficient of methyl orange dye solution infiltrated within the pore structure of the microcavity is exalted at the wavelengths of the corresponding optical resonances. This effect gives rise to a small but non-negligible visible light photodegradation of dye molecules. The possibilities of tailoring the design of 1D photonic systems to boost the photocatalytic activity of a-TiO₂ are discussed.