Using ZnO nanoparticles in fungal inhibition and self-protection of exposed marble columns in historic sites

The marble columns at many historic sites represent one of the most important and fundamental architectural elements in a building. They are almost always subject to serious damage, whether in the base, middle, or crowns of columns by fungal infection. In most cases, the microbial deterioration affects the physical and mechanical properties of historic marble columns, which have in turn been affected by other damaging factors (e.g., weathering from the elements or mechanical damage), leading to their partial or total collapse. In this current study, researchers are turning to new technologies in order to find the ideal solution to inhibit fungal growth, and, in turn achieve the total protection of exposed historic marble columns. The photocatalytic inorganic nanoparticles of ZnO have been employed for the purpose of long-term protection of exposed marble columns by inhibiting microbial-fungal attack and forming a protective surface layer. ZnO nanoparticles were dispersed in laboratory synthesized acrylic polymer to create a combined biocidal and consolidating coating to be applied on historic marble columns substrate. The synthesized nanocomposite coating was characterized and applied to marble samples collected from various archeological sites in Egypt. The protecting effect of synthesized nanocoating against fungal attack by Aspergillus niger and Penicillium sp., in addition to RH/Temperature, UV aging, and mechanical deterioration, was studied. The consolidating action of the obtained mixtures was evaluated through microscopic examination and capillary water absorption. Further, colorimetric measurements have been performed to evaluate the optical appearance of the columns. ZnO nanocomposites displayed better performance when compared to the pure synthesized acrylic polymer. The coated ZnO nanoparticles enhanced the durability of stone surface to resist the fungal attack when subjected to inoculums containing Aspergillus niger and Penicillium sp. and improved the resistance to UV aging, relative humidity, and thermal effect compared to the samples coated with the acrylic polymer without ZnO nanoparticles. Self-protection properties were confirmed without any obvious color changes on marble surfaces.