Sol-Gel Coatings for Subaquatic Self-Cleaning Windows

Abstract

Self-cleaning windows are well known for their ability to function with airborne pollutants, but there is a growing industry for semi-permanent subaquatic optical devices, where the performance of such windows should be considered. Here sol-gel technology is explored as a means of producing self-cleaning, subaquatic, sapphire windows. We demonstrate removal of marine bacteria and, in the worst-case contamination scenario, dead North Sea crude oil (API 35). This greasy contaminant was smeared across the windows to effectively reduce optical transmission strength to just 54%. The titania-based sol-gel-coated windows can restore transmission to within 10% of the clean value in less than one day, unlike standard sapphire windows, which lose 68% transmission following contamination and aquatic submergence over the same duration. A range of theories to enhance the self-cleaning performance of the sol-gel coating were explored, but none of the tested variables were able to provide any enhancement for subaquatic performance.

Sol–Gel Method Applied to Crystalline Materials

“…This issue collects four contributions, starting with the paper of A.I.M. Greer et co-workers [1] that studied TiO 2 in the anatase polymorph synthesized by sol-gel method as an effective self-cleaning agent under subaquatic conditions. It is known that TiO 2 in the anatase polymorph is a semi-conductor with a band gap energy of 3.2 eV, able to degrade pollutants in air.…”