One-step nanoencapsulation of essential oils and their application in hybrid coatings: A sustainable long-lasting treatment of stone materials against biodeterioration

In this study, two essential oils (EOs) with preventive proved biocidal efficacy, namely oregano and eugenol, are encapsulated in silica nanocontainer, then dispersed in multifunctional, hybrid and nanocomposite coating. The aim of this work is to reduce toxicity of restoration materials, to avoid the chemicals dispersion in the environment and to extent stone protection treatments, preventing biofouling. Composite silica nanocapsules, containing separately the two EOs, are prepared via one-step synthesis, based on oil-in-water miniemulsion polymerisation processes, and fully characterised by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N 2 physisorption (BET/BJH). Micro-Raman spectroscopy (RS) and thermal analysis (TG/DSC). In a second step, nanocomposite coatings, based on a flexible tetraethyl orthosilicate (TEOS) matrix, are synthesised dispersing TiO 2 nanoparticles and the two silica nanocapsules incorporating EOs. The coatings were applied on three different lithotypes samples of historical importance: brick, piperine and mortar. The effectiveness and compatibility of the coating formulation with the different stone substrates were assessed through a multi-analytical standard protocol. The silica nanocapsules, show monodispersed spherical shape with size ∼110 nm, a core-shell structure, a BET surface area of 600–700 m 2 /g and high loading capacity. The results on coatings characterisation show a crack-free and transparent structure. Moreover, the tests on applied coatings reveal the high hydrophobicity of the treated stone samples (static contact angle in the range ∼ 130–140° and reduction of liquid water capillary absorption 97–99 %) and unaltered permeability to water vapour (density of water vapour flow rate in the range 150–200 g/m 2 ·d), demonstrating the suitability of the nanocomposite hybrid coatings for the application in stone protection against biodeterioration. • Nanocomposite hybrid coatings have been synthesised to contrast biodeterioration of stones. • Essential oils are successfully encapsulated in mesoporous core-shell silica nanocapsules. • Nanocapsules and photocatalytic TiO 2 nanoparticles are dispersed in the hybrid polymetric matrix. • Crack-free and transparent coatings are obtained and tested on different stone substrates. • Treated stone surfaces show very high hydrophobicity and unaltered permeability to water vapour.