Evaluation of the applicability of nano-biocide treatments on limestones used in cultural heritage.

Abstract

One of the main problems in the conservation of historical buildings and archaeological sites is theone caused by biodeterioration. Biopatina, biocrust or biofouling generate aesthetical changes andinduce degradation processes within the stone matrix. In this work, three treatments based on sil-ver nanoparticles and silver/titanium dioxide nanocomposites have been studied as potential biocidesfor limestones: citrate-stabilized silver nanoparticles, silver/TiO2nanocomposites and citrate-stabilizedsilver/TiO2nanocomposites. These treatments were synthesized following a bottom-up method, using ornot a stabilizing agent (citrate), and have been characterized by UV-Visible spectrophotometry, DynamicLight Scattering and Raman spectroscopy. These treatments were applied on limestones from three differ-ent Spanish quarries located in Utrera (Seville), El Puerto de Santa María (Cadiz) and Novelda (Alicante).The aesthetical modification of limestone surfaces was studied by colorimetric techniques and the effec-tiveness of protection against biofouling formation was tested using an accelerated biofouling growthassay. The best results were obtained for the treatments based on citrate-stabilized silver nanoparti-cles. The effectiveness of the treatments depends on their penetration depth in the stone matrix andin this study, we have used Laser Induced Breakdown Spectroscopy to determine the depth profilesof nanocomposite presence in the stone matrix. Our results demonstrate that nanocomposites basedon citrate-stabilized silver nanoparticles can be useful for the treatment of historical buildings andarchaeological sites made of limestone, without producing high colour increments. Additionally, we have demonstrated the suitability of Laser Induced Breakdown Spectroscopy for the detection of silver/TiO2nanocomposites and for the generation of depth profiles.