Due to the ongoing threat of degradation of artefacts and monuments, the conservation of cultural heritage items has been gaining prominence on the global scale. Thus, finding suitable approaches that can preserve these materials while keeping their natural aspect of is crucial. In particular, preventive conservation is an approach that aims to control deterioration before it happens in order to decrease the need for the intervention. Several techniques have been developed in this context. Notably, the application of coatings made of metal oxide nanomaterials dispersed in polymer matrix can be effectively address stone heritage deterioration issues. In particular, metal oxide nanomaterials (TiO₂, ZnO, CuO, and MgO) with self-cleaning and antimicrobial activity have been considered as possible cultural heritage conservative materials. Metal oxide nanomaterials have been used to strengthen heritage items in several studies. This review seeks to update the knowledge of different kinds of metal oxide nanomaterials, especially nanoparticles and nanocomposites, that have been employed in the preservation and consolidation of heritage items over the last 10 years. Notably, the transport of nanomaterials in diverse environments is undoubtedly not well understood. Therefore, controlling their effects on various neighbouring non-target organisms and ecological processes is crucial.

Nowadays, durable protective coatings receive more attention in the field of conservation for several reasons (they are cost effective, time consuming, more resistance, etc.). Hence, this study was focused on producing a multi-functional, durable coating to protect different stone materials, especially, Lecce stone, bricks, and marble. For this purpose, ZrO₂-doped-ZnO-PDMS nanocomposites (PDMS, polydimethylsiloxane used as the binder) were synthesized by in situ reaction (doped nanoparticles were inserted into the polymer matrix during the synthesis of PDMS) and the performances of resulting coatings were examined by handling different experimental analyses. In particular, the study aimed to evaluate the durability properties of the coating along with the self-cleaning effect. As a result, the durability of the nanocomposite coating with respect to the well-known PDMS coating was assessed after exposure to two different ageing cycles: solar ageing (300 W, 1000 h) and humid chamber ageing (RH > 80%, T = 22 ± 3 °C, desiccator, 2 years). All the results were in good agreement with each other providing that newly prepared nanocomposite coating can be used as a durable protective coating for different stone materials.

The development of nanocomposite materials with multifunctional protective features is an urgent need in many fields. However, few works have studied the durability of these materials. Even though TiO₂ nanoparticles have been extensively applied for self-cleaning effect, it displays a weak activity under visible light. Hence, in this study, pure and Gd-doped TiO₂ nanoparticles (molar ratios of doping ions/Ti are 0.1 and 1) were synthesised, characterised, and then mixed with polydimethylsiloxane (PDMS), used as a binder, in order to produce a homogenised thin film on a very porous stone substrate. To our knowledge, Gd-doped TiO₂/PDMS protective coatings are studied for the first time for application on historic structures. The protective coatings developed in this work are intended to reduce the surface wettability of the stone and protect the historic stones from dye pollution and microorganism colonisation. Moreover, in this study, the durability of the developed nanocomposite was deeply studied to evaluate the stability of the coatings. Results confirmed that samples treated with the lowest concentrations of Gd ions (0.1 mol%) showed acceptable chromatic variations, a good repellent feature, acceptable water vapour permeability, good durability, the highest self-cleaning activity, and good inhibitory behaviour against microbial colonisation.

The main objective of this research is to determine the optimal application conditions of a newly synthesized multifunctional coating containing Ag-doped TiO₂ nanoparticles when used as a possible protective agent for sandstone. Firstly, Ag-TiO₂ nanoparticles with anatase structure, spherical shape and controllable sizes were prepared using the sol–gel method and characterized. The biocidal activity of Ag-doped TiO₂ NPs was studied by comparing its performance to pure TiO₂ NPs against two representative Gram-positive and Gram-negative bacterial strains, under both visible irradiation and in the dark; then, the antimicrobial efficiency of two different concentrations of Ag-TiO₂ nanoparticles (0.1–1 mol%) was evaluated against two phototrophic strains commonly isolated from deteriorated surfaces. Results showed that the photoactivation and photokilling activity of TiO₂ were highly improved by doping with Ag. Next, prepared nanopowders were dispersed in a binder with different powder/PDMS ratios: (0.1, 0.2, 0.5 and 1% w/v TiO₂) and then applied in different amounts (2, 3 and 6 g/m²) on Serena stone specimens. Results revealed that the application of 2 g/m² nanocomposite at powder/binder ratios equal to 1% w/v TiO₂ provided a fine hydrophobic character for the stone material with acceptable chromatic variations.