Encapsulation of environmentally-friendly biocides in silica nanosystems for multifunctional coatings

In cultural heritage field, significant research efforts have been recently made to improve the efficacy of anti-vegetative treatments and to reduce the environmental impact caused by biocides high concentration. According to the pro-ecological approach, this work reports a novel approach based on the encapsulation/incorporation of environmentally-friendly biocides in different silica nanosystems in order to control the development of biological patinas on outdoor cultural heritage. Two different green biocides have been selected and tested in silica nanosystems: the zosteric acid sodium salt (ZS), a natural antifoulant compound produced by Zostera marina (eelgrass), and the usnic acid (UA), a secondary metabolite produced by some saxicolous lichens. ZS was previously successfully encapsulated but never entrapped in mesoporous silica; instead, UA is, for the first time, encapsulated and in situ entrapped into the silica nanosystems in order to control the release over time. Both silica nanosystems have been characterized as far as their dimensions and superficial properties and loading capability. The antifouling activity was assessed against microorganisms from biopatinas colonising the Aurelian Walls in Rome. Our results have shown that the two nanosystems have complementary properties, thus it is possible to tune the antifouling efficiency by combining the two in different proportions.