Dual Biocide Behaviour of Quaternary Ammonium Functionalized Mesoporous Silica Nanoparticles Loaded with Thymus Essential Oil for Stone Conservation

Mesoporous silica nanoparticles (MSNs) functionalized with silane quaternary ammonium compounds (SiQACs) were synthesized and utilized as carriers for thymus essential oil (TO), a green bio-antifouling agent. The synthesis of MSNs functionalized with SiQACs was carried out in a single step, with clear advantages in terms of simplicity of the process, high yield (94%) and saving of reagents and solvents for the MSN purification. After loading with TO, this innovative dual-action antifouling system was able to integrate the intrinsic biocidal properties of SiQACs with the release of TO from MSN pores, resulting in an engineered material with prolonged efficacy. The antifouling compounds incorporated into the nanoparticles accounted for 42% of the total weight. The biocidal performance was evaluated by monitoring the growth inhibition of Chlorella sorokiniana, a microalga commonly associated with stone biodeterioration. Additionally, these nanoparticles were embedded in a commercial silane-based protective coating and applied to tuff stone samples to assess their ability to mitigate biofilm formation over extended periods. Results demonstrated the system’s high potential for durable protection against microbial colonization and biofilm growth on stone surfaces.