Photocatalysts and EOs could they ever be friends? A coating for stone materials

This study presents the formulation of a hybrid protective coating for stone materials, designed to provide both photocatalytic and antimicrobial properties by leveraging the synergistic combination of titanium dioxide (TiO 2 ) photocatalytic nanoparticles with mesoporous silica (SiO 2 ) MCM-41 nanocontainers loaded with Origanum compactum essential oil (EO). The ordered mesoporous SiO 2 , enriched with TiO 2 nanoparticles, serves as carried for the EO, while a hybrid hydrogel composed of chitosan and a mixture of silicon alkoxides (MTES and TEOS) is used to formulate the protective coating. The coating was applied to stone mock-ups, and its performance was evaluated in terms of hydrophobicity, water permeability, colorimetric changes, and antimicrobial efficacy. The results demonstrated that the coating effectively combined photocatalytic, antimicrobial, and self-cleaning functionalities, offering a sustainable and high-performance solution for the preservation of heritage materials while minimizing environmental impact and risks to operators.