Photocatalytic activity of electrophoretically deposited TiO2 and ZnO nanoparticles on fog harvesting meshes

TiO2 and ZnO are photocatalysts that degrade organic chemicals into smaller hydrocarbons in the presence of UV irradiation. Metal meshes have been previously used to harvest fog droplets from air streams. By merging these two observations, we hypothesize that TiO2/ZnO-coated metal meshes installed in the path of a fog-laden wind carrying contaminants, such as volatile organic compounds (VOCs), will degrade these VOCs providing pollution abatement. Stainless steel meshes are coated with a uniform, homogeneous and durable film of TiO2 or ZnO nanoparticles using electrophoretic deposition (EPD) in a phosphate ester solution. The TiO2-coated metal meshes are first activated with UV irradiation and then exposed to a fog-stream in a fog-tunnel, where the fog is pre-seeded with a VOC surrogate, methylene blue (MB), of known concentration. UV-Vis spectroscopy measurements of the water harvested determine the extent of MB degradation. The mechanism by which the phosphate ester develops an electrical charge on a nanoparticle surface leads to a conformal coating over the steel mesh. Maximum MB (0.05 mM) degradation of 36% is observed. Similar photocatalytic degradation of MB by TiO2 and ZnO coated meshes is also observed under direct UV irradiation from sunlight, confirming that the method is viable for outdoor installations.