Photocatalytic Degradation Enhancement in Pickering Emulsions Stabilized by Solid Particles of Bare TiO₂

Pickering emulsions provide a new way to enhance the efficiency of photocatalytic degradation of water-insoluble pollutants. Indeed, the semiconductor solid particles dually act as the photocatalyst and stabilizer of the emulsion droplets whose size dramatically affects the photocatalytic reaction. The present work aims at the validation of this concept by using bare TiO₂ without any surface modification. Nanostructured TiO₂ has been prepared by a simple sol-gel process and characterized by X-ray diffraction, specific surface area analysis, scanning electron microscopy, and diffuse reflectance spectroscopy. The emulsions were prepared by using 1-methylnaphthalene (1-MN) as a model organic contaminant scarcely soluble in water and bare TiO₂ as the photocatalyst/stabilizer. The emulsions have been characterized by electrical conductivity, optical microscopy, and light-scattering analyses. The photocatalytic degradation of 1-MN was 50 times faster in stable Pickering emulsions with respect to the case of biphasic liquid systems containing TiO₂. This finding allows us to propose Pickering emulsions stabilized by TiO₂ nanoparticles as an effective and novel way to intensify the photocatalytic degradation of water-insoluble organic pollutants.