Development of a novel conservation treatment of stone monuments with bioactive nanocomposites

Abstract

In this study a conservation treatment of stone monuments meant for consolidation, protection, and inhibition of biofilm formation is proposed. The method is developed as a part of a systematic investigation aimed at producing nanocomposite coatings able to exert a marked biological activity over a long period of time thanks to their peculiar structure. Zinc oxide nanoparticles, synthesised by means of simple and reproducible electrochemical procedures, are embedded in commercially available and commonly used consolidant/water repellent matrices to obtain nanostructured materials. Products based on tetraethoxysilane and/or polysiloxanes were tested. In a first step the nanomaterials were applied on stone samples and studied with scanning electron microscopy and spectrophotocolorimetry. Then, in situ experimentation was undertaken by applying nanocomposite coatings on the exterior of a 12th-century church in the south of Italy. The performances of the ZnO-nanoparticles based composite coating were compared with a previously investigated copper nanoparticles based material, successfully tested and monitored in situ for more than two years. Finally, preliminary tests on the inhibitory effect on the growth of the fungus Aspergillus niger were also carried out. The results showed that in case of zinc oxide a tenfold higher concentration of nanoparticles as compared with Cu-NPs can be utilized in the matrices without affecting the colour of the stone substrate, which means that the new material should be able to exert a long-lasting biocide activity. Laboratory and in situ tests of the developed innovative nanomaterials yielded very promising, though preliminary, results in terms of chromatic changes, morphological characteristics and bioactivity. Constant monitoring of the coatings will be continued in order to obtain all necessary information on their long term behaviour and inhibition of biological colonisation.

ZnO Nanostructures with Antibacterial Properties Prepared by a Green Electrochemical-Thermal Approach

“…Semiconductor metal oxide nanostructures, and specifically ZnO ones, have received a great amount of interest in many areas due to their unique physical, chemical and optical properties [1]. Moreover, ZnO nanomaterials are well-known antimicrobial agents [2], which can be employed in several fields where pathogen spreading should be inhibited [3][4][5]. Besides the many physical [6][7][8] and chemical [9][10][11] methods for the production of such materials, scientific research has recently focused on green and simple electrochemical approaches [12,13].…”

Inorganic Nanomaterials for Restoration of Cultural Heritage: Synthesis Approaches towards Nanoconsolidants for Stone and Wall Paintings

“…Optimization of the penetration depth and homogeneous application of nanoconsolidants remain some of the most important requirements, together with avoiding modification of the breathability of the substrate and flaking of the surface or detachment, among others. At the same time, chromatic changes caused by either nanolime concentrations or by the inclusion of NPs in the silica matrices have been reduced but not overcome . Moreover, the solvents and surfactants are potentially hazardous for living organisms and the environment.…”

“…Electrochemically synthesized zinc oxide (ZnO) NPs, incorporated in commercial consolidant/water repellent TEOS‐based products, form a material that is expected to display long‐term biocide activity. Nevertheless, chromatic changes, although reduced, still remain as the main issue for application of this nanocomposite …”

New nanomaterials for applications in conservation and restoration of stony materials: A review

“…Thus, I.D. Van der Werf et al (147) demonstrated that higher ZnO nanoparticles loadings could be achieved without affecting the color of the stone substrates. Recently, Ditaranto et al (148) developed bioactive nanocomposite systems composed by a water repellent/ consolidant product and zinc oxide nanoparticles in various %w/w concentrations for the protection of stone heritage.…”