Assessment of nanoparticles/nanocomposites to inhibit micro-algal fouling on limestone facades

This study conducted a comparison between biocide treatments based on nanoparticles of silver, copper, ZnO, TiO2 and silver/ TiO2 nanocomposites to analyse their capability to inhibit microalgal fouling on stone buildings. Biofouling is one of the main alterations on stone facades, causes degradation of their constituent materials and interferes with their aesthetic values. The proposed treatments were tested on a limestone from the historic quarry of Estepa (Spain), widely used as construction material in the South of Spain. The applicability of the treatments was evaluated by colorimetry. The biocidal effectiveness of the nanoparticles was studied on stone surfaces by multispectral imaging, digital image analysis and optical coherence tomography. This is a low-cost and efficient protocol to validate biocidal treatments for limestone monuments, and our results demonstrate the potential of silver and ZnO nanoparticles as a protective treatment for stone facades. The results have implications for practitioners working on historic buildings.