Mid-term evaluation of the antifouling properties of ionic liquids based coatings applied on limestone and marble probes in marine environment

Underwater cultural heritage (UCH) faces numerous threats that endanger its conservation. The deterioration of submerged stones artifacts starts for a concurrence of physical-chemical events such abrasion, deposition, oxidation, and reduction, as well as biological factors such as microorganisms, and later on, macroorganisms colonization. Due to environmental conditions, in situ protection of UCH poses serious issues and the current methods suggested by the 2001 UNESCO convention result inefficient for the long-time conservation of archaeological sites. One of the main problems is biodeterioration due to microbes present in the underwater environment. During my PhD research activities, within the framework of the CRIMAC-UNALTERABLE project, investigations were carried out in order to test anti-biofouling ecofriendly coatings to protect the underwater stone cultural heritage. Therefore, a coating based on a mixture of surfactant ionic liquids (IL), which gave excellent results in the protection of terrestrial CH was chosen. The activities were initially aimed at characterizing the physical properties of IL-treated Carrara marble and limestone probe surfaces in association with various silica consolidants and their persistency in water environments through UV-daylight weathering and washing tests. Finally, the antifouling behavior was evaluated after exposure of treated and untreated in coastal marine environment for 1 year. Each tested condition was sampled at increasing time intervals (24 hours, 1, 6, and 12 months). Biodeterioration processes and antifouling activity of the IL based coatings were studied at each time point by microscopic analysis (stereo-microscopy, CLSM and SEM) and DNA metabarcoding. Seawater and sediments samples were also studied to monitoring the dynamics of the surrounding environment that affected surface biofouling processes. The use of coatings based on ionic liquid technology combined with current commercial silica-based consolidants has demonstrated an effective increase in durability of coatings applied to marble surfaces exposed in a marine environment by slowing down surface biofouling. However, the two-step applied coating results in less durability on more porous limestone surfaces, while the monolayer coating homogeneously penetrates below the first layer of the stone surface interfering with the foulers' interaction to the surface and decreasing their biodeteriorating action.