Development of a Multifunctional Coating for the Protection of Built Heritage

The preservation of stone materials in architectural heritage is often challenged by biodeterioration and environmental degradation. Essential oils represent a promising green alternative to conventional biocides, thanks to their natural antimicrobial properties. However, their high volatility and potential to alter surface appearance limit their direct application. In this work, a multifunctional protective coating was developed based on the encapsulation of Origanum compactum essential oil into MCM-41 mesoporous silica, designed to ensure gradual release and prolonged activity while minimizing chromatic alteration. The MCM-41 and oregano essential oil composite material was embedded in a hybrid hydrogel matrix composed of tetrathyl orthosilicate (TEOS), methyltriethoxysilane (MTES), and chitosan. This formulation was applied on three representative stone substrates (white marble, green marble, and concrete) to evaluate its properties and effectiveness. The coating demonstrated a substantial increase in surface hydrophobicity, while maintaining water vapor permeability below the reduction threshold considered acceptable in conservation practice. Colorimetric analysis showed a ΔE value equal to 3, confirming no perceptible visual alteration. Additionally, microbiological testing against Aspergillus niger and Penicillium chrysogenum confirmed the antimicrobial effectiveness of the coating over a 60-day period, with significantly reduced fungal colonization compared to untreated surfaces. The results support the proposed system as a sustainable and compatible solution for the conservation of built heritage, combining hydrophobic protection, breathability, and long-term antimicrobial action. Future developments will explore its applicability to other substrates and essential oils.