Turn on the light: Diffusio-osmosis induced by photocatalytic reactions

“Turn on the light; diffusio-osmosis induced by photocatalytic reactions” aims to decrease mass transfer limitation in the boundary layer of a photocatalytic system by diffusio-osmosis. Upon illumination of the photocatalyst, a reaction occurs where organic compounds are converted into minerals. A boundary layer arises if the reaction is much faster than transport to and from the wall, creating mass transfer limitations. Diffusio-osmosis is a surface-induced flow created by a concentration gradient parallel to the surface. The magnitude of the diffusio-osmosis depends on the concentration gradient and a compound-surface specific interaction potential. Here, the concentration gradient is created by the photocatalytic reaction at the surface. The system of interest is the degradation of organic compounds over titanium dioxide in a microreactor. The organic compounds of interest are formic acid, acetic acid, oxalic acid, methylene blue, potassium formate, sodium formate, and lithium formate. The diffusio-osmotic flow is determined by measuring the reaction rates of these compounds over titanium dioxide and combining this with the theoretical information about the interaction potential between compound and surface. The thesis concludes that the magnitude of the diffusio-osmotic flow induced by the degradation of organic compounds over titanium dioxide is lower compared to the diffusive rate of the compounds to and from the surface. For the system researched it is thus not possible to reduce mass transfer limitations in the boundary layer by diffusio-osmosis. An numerical study is performed to determine under which conditions diffusio-osmosis could reduce mass transfer limitations, also when the byproducts of the reaction are taken into account.