Abstract
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.
Highlights
Heritage sites are the symbol of history
These results dismiss the hypothesis that Gd3+ may be inserted inside the TiO2 lattice. If this was the case, a distortion and volume inflation would be observed in the TiO2 lattice. It seems that gadolinium ions are impossible to enter the lattice of the TiO2 structure to replace Ti4+
Thin films of different materials composed principally of PDMS as a binder and pure/Gd-doped TiO2 NPs were applied on the Lecce stone as protective coatings
Summary
Heritage sites are the symbol of history. In addition to their intrinsic value, their conservation and maintenance provide economic benefits. Historic building materials, in particular when exposed outdoors, are subject to many phenomena such as microorganisms colonisation which cause a transformation and deterioration of art surfaces [1]. Several methodologies have been developed such as cleaning (e.g., by organic solvents, chelating agents), biocleaning, and laser methods [3,6,7,8,9]. Despite the efficiency of these methods, the use of these techniques has declined due to different problems (irreversibility, toxicity, difficulty to manipulate, high cost, etc.) [9]
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