Titanium dioxide (Titania or TiO₂) is well known for its photocatalytic properties and its ability to remove organic contaminants under illumination by ultraviolet (UV) light. It is also known to switch its surface wetting characteristics from being hydrophilic to superhydrophilic under exposure to UV light in air, however, less is known about photoinduced switching of the hydrophilicity of TiO₂ surfaces immersed in an oil medium. In this work, we study the kinetics of photoinduced wetting of water drops on layer-by-layer (LBL) assembled TiO₂ nanoparticle surfaces immersed in an oil environment using in-situ contact angle measurements. We develop a model, based on integrating the Langmuir-Hinshelwood adsorption isotherm with the Cassie-Baxter analysis of the effective contact angle of a drop sitting on a composite surface to relate the evolution in the measured contact angle to photocatalytically induced changes on the surface of nanoporous titania. Our model can be used to predict and control wetting kinetics in drop coalescence applications. We also show that immersed oil-water separation membranes which have been fouled by low surface tension contaminants can be rapidly recovered in-situ using this underwater photocatalytic reaction without the need for backwashing or harsh chemical reagents.