4-Year In-Situ Assessment of a Photocatalytic TiO2/SiO2 Antifouling Treatment for Historic Mortar in a Coastal City

This manuscript presents a 4 years in-situ evaluation of TiO2/SiO2-based product applied to a mortar seating belonging to the bleachers of the Cadiz Roman Theatre, affected by biofouling and organic deposits. Antifouling performance was studied by colorimetric measurements and ATP analyses. Surface sampling was performed for biofouling identification, being remarkable the presence of filamentous fungi and cyanobacteria. Additionally, antifouling performance was checked during a 4 years in-situ monitoring study. SEM observations, carried out 4 years after the product application, demonstrate that the TiO2 integration in a SiO2 matrix produces a durable coating which allows for prolongation of the antifouling performance over time. According to the results obtained, 4 years after the application of the treatment, the treated area still maintains its antifouling efficacy, exhibiting a 40% reduction in organic deposit and 61% inhibition of biological growth compared to the untreated area. The results of this study show that the application of the SiO2/TiO2-based product may potentially reduce the costs of cleaning and maintenance works. At the same time, it is considered that the antifouling efficacy is more pronounced during the first two years and could be taken into account in the maintenance and re-application actions.