Antifungal Coatings Based on Ca(OH)₂ Mixed with ZnO/TiO₂ Nanomaterials for Protection of Limestone Monuments

Abstract

The presence and deteriorating action of microbial biofilms on historic stone buildings have received considerable attention in the past few years. Among microorganisms, fungi are one of the most damaging groups. In the present work, antimicrobial surfaces were prepared using suspensions of Ca(OH)2 particles, mixed with ZnO or TiO2 nanoparticles. The antimicrobial surfaces were evaluated for their antifungal activity both in the dark and under simulated natural photoperiod cycles, using Penicillium oxalicum and Aspergillus niger as model organisms, and two limestone lithotypes commonly used in construction and as materials for the restoration of historic buildings. Both Ca(OH)2-ZnO and Ca(OH)2-TiO2 materials displayed antifungal activity: ZnO-based systems had the best antifungal properties, being effective both in the dark and under illumination. In contrast, TiO2-based coatings showed antifungal activity only under photoperiod conditions. Controls with coatings consisting of only Ca(OH)2 were readily colonized by both fungi. The antifungal activity was monitored by direct observation with microscope, X-ray diffraction (XRD), and scanning electron microscopy (SEM), and was found to be different for the two lithotypes, suggesting that the mineral grain distribution and porosity played a role in the activity. XRD was used to investigate the formation of biominerals as indicator of the fungal attack of the limestone materials, while SEM illustrated the influence of porosity of both the limestone material and the coatings on the fungal penetration into the limestone. The coated nanosystems based on Ca(OH)2-50%ZnO and pure zincite nanoparticulate films have promising performance on low porosity limestone, showing good antifungal properties against P. oxalicum and A. niger under simulated photoperiod conditions.

TiO2‐Oligoaldaramide nanocomposites as efficient core‐shell systems for wood preservation

“…In particular, TiO 2 nanocomposites (NCs), if properly irradiated, show antimicrobial properties which can be exploited to avoid fungal attacks on wooden surfaces. In fact, the photocatalytic efficiency of TiO 2 nanoparticles (NPs) was observed against attacks of bacteria, mold, and fungi …”

Polymer Nanocomposites in Building, Construction

“…At a higher titania content (10% w/v), photocatalytic action decreases (34). Antifungal coatings for monument protection were obtained by using Ca (OH) 2 and nano ZnO/TiO 2 (35).…”

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

“…More recently, a hydrophobic transparent nanocomposite based on SiO 2 -TiO 2 with self-cleaning properties has been proposed, capable of removing existing biofilms on marble [9]. In another study the preparation and characterisation of antimicrobial surfaces made by combining Ca(OH) 2 suspensions with titania or zinc oxide nanoparticles for the conservation of limestone monuments has been reported [10].…”

“…In one study zinc oxide nanoparticles have been proposed for application on oil paintings to inhibit the growth of mould [29]. For stone conservation purposes, as already mentioned, Gómez-Ortíz et al [10] developed Ca(OH) 2 -ZnO and Ca(OH) 2 -TiO 2 materials. The ZnO-based systems showed to have the best antifungal properties, being effective both in the dark and under illumination.…”