Hydrophobicity Promoted Efficient Hydroxyl Radical Generation in Visible-Light-Driven Photocatalytic Oxidation

Hydroxyl radical (^•OH) with strong oxidation capability is one of the most important reactive oxygen species. The generation of ^•OH from superoxide radicals (^•O₂ ^-) is an important process in visible-light-driven photocatalysis, but the conversion generally suffers from slow reaction kinetics. Here, a hydrophobicity promoted efficient ^•OH generation in a visible-light-driven semiconductor-mediated photodegradation reaction is reported. Hydrophobic TiO₂ that is synthesized by modifying the TiO₂ surface with a thin polydimethylsiloxane (PDMS) layer and rhodamine B (RhB) are used as model semiconductors and dye molecules, respectively. The surface hydrophobicity resulted in the formation of a solid-liquid-air triphase interface microenvironment, which increased the local concentration of O₂. In the meanwhile, the saturated adsorption quantity of RhB on hydrophobic TiO₂ is improved by five-fold than that on untreated TiO₂. These advantages increased the density of the conduction band photoelectrons and ^•O₂ ^- generation, and stimulated the conversion of ^•O₂ ^- to ^•OH. This consequently not only increased the kinetics of the photocatalytic reaction by an order of magnitude, but also altered the oxidation route from conventional decolorization to mineralization. This study highlights the importance of surface wettability modulation in boosting ^•OH generation in visible-light-driven photocatalysis.