Photoinduced wetting kinetics of water on immersed nanoporous titania surfaces with application to oil-water separation

Abstract

We study the self-cleaning ability of titania surfaces in oil-water environments for fouling recovery in oil-water separation applications. A number of previous studies have shown that meshes and porous structures can be used to separate oil/water mixtures through careful control of surface energy and preferential wettability, however these structured surfaces are prone to fouling by oil and dirt. The photocatalytic and hydrophilic nature of titania coatings can be exploited to ensure preferential wetting of water over oil under ultraviolet (UV) irradiation and this provides a mechanism for recovery of fouling. Titania nanoporous surfaces were prepared by depositing TiO2 nanoparticles onto flat substrates using Layer-by-Layer (LBL) assembly, and were then impregnated with oil to simulate typical fouling conditions experienced in oil-water separation applications. The resulting hydrophobic surfaces were irradiated with UV light in an oil-water environment to photocatalytically decompose the organic pollutants and restore hydrophilicity. The kinetics of this conversion from hydrophobicity to hydrophilicity were studied in situ under various UV intensities using goniometric measurements and a simple adsorption-photocatalysis model is proposed to describe the observed data.