Design of multifunctional SiO2–TiO2 composite coating materials for outdoor sandstone conservation

This research was aimed to develop a novel multifunctional SiO2–TiO2 composite coating for application in the field of outdoor sandstone conservation. The SiO2–TiO2 composite coating derived from the sol–gel reaction of tetraethoxysilan (TEOS) and tetrabutyl orthotitanate (TBOT). Hydroxyl-terminated polydimethylsiloxane (PDMS-OH) and poly(ethylene oxide)-poly(phenylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO, F127) surfactant were added to the SiO2–TiO2 based materials. The contact angle analysis, scanning electron microscopy measurement, stain resistant test, salt crystallization test and outdoor exposure test were conducted to investigate the effectiveness and durability of this composite coating. Results showed that SiO2–TiO2 composite materials created a hydrophobic, crack-free coating with self-cleaning and antibacterial properties on the decayed sandstone surface, allowing their use for practical outdoor sandstone conservation applications.