Photo-enhanced Gd-TiO2/PDMS nanocomposites for stone preservation

The protection of stone artifacts from different defacements (chemical, physical and biological agents) is an essential event due to their historical value. Hence, many research groups have focused on developing nanocomposite materials with multifunctional protective features to protect building stones, especially with high porosity and to reduce the high cost of maintenance of these materials. TiO2 nanoparticles have been extensively used for self-cleaning applications, particularly, cleaning and preventing colonization of heritage building material surfaces. However, this semiconductor displays a weak activity under visible light, which can be properly enhanced by doping with Lanthanide ions. In addition, their inert colours make it possible to elaborate transparent thin films. The present research work focused to develop photo enhanced nanocomposite coatings: pure and Gd doped TiO2 nanoparticles with different doping amounts were mixed with Polydimethylsiloxane (PDMS) used as a binder. Moreover, newly prepared coatings were applied on a very porous stone substrate (Lecce stone) in order to investigate the self-cleaning properties and the protecting ability towards the historic stones from dye pollution and micro-organisms colonization. For this purpose, different analyses and tests have been performed on the coated stone specimens such as chromatic measurements, static contact angle measurements, water capillary absorption test, permeability to water vapour, pencil hardness test, scanning electron microscope combined with energy-dispersive X-ray spectroscopy (SEM-EDS), optical microscope analyses, self-cleaning test and biological experiments. In addition, the durability of the coatings was studied to evaluate the stability of the elaborated nanocomposites. Results showed that PDMS mixed with 0.1 mol% Gd-TiO2 materials can be considered as a promising and durable candidate to protect highly porous heritage building surfaces.