TiO2–SiO2–PDMS nano-composite hydrophobic coating with self-cleaning properties for marble protection

Abstract

This research work presents the design of a transparent-hydrophobic hybrid semi-crystalline SiO2–TiO2 coating and its application in the field of monument conservation. The SiO2–TiO2 coating derived from a mixture of tetraethoxysilane (TEOS) and titanium-tetra-isopropoxide (TTIP) incorporating an organosilane, the hydroxyl-terminated polydimethylsiloxane (PDMS). The complete hydrolysis of TEOS was achieved by oxalic acid, which also controlled the gel drying. XRD, DTA–TG, FT-IR and SEM analyses evaluated the designed coating, which is transparent, crack-free with a crystallite size of 5nm. The evolution of the hydrolysis of TEOS, as well as the copolymerization of TEOS, TiO2 and PDMS as a function of time were assessed by FT-IR analysis. The effectiveness of TiO2–SiO2–PDMS nano-composite as hydrophobic coating was investigated by capillary water absorption and static contact angle measurements. The SEM analysis of the treated sample revealed a homogeneous crack-free coating on marble, while FT-IR proved that condensation and copolymerization reactions took place on the marble surface. The removal of both methylene blue stains and biofilm on treated samples support the self-cleaning properties of the designed coating. The total color differences and the decrease of the water vapor permeability range within acceptable limits. After treatment, a decrease in the water capillary coefficient and an increase in the contact angle were observed. The innovation of this synthesis pertains to the application of a hydrophobic transparent nano-composite based on SiO2–TiO2 with self-cleaning properties, without modifying the color of the marble surface and the water vapor permeability.