Modified nano-SiO2/TiO2 hybrid fluorinated B-72 as antimicrobial and hydrophobic coatings for the conservation of ancient bricks

A transparent superhydrophobic organic–inorganic composite coating was prepared with fluorinated B72 as the base organic component and methyl-modified silica/titania (SiO2/TiO2) by hexamethyldisilazane (HMDS) as the inorganic component by a simple and gentle means to protect ancient bricks from the invasion of micro-organisms and the breakage of weathering. Contact angle, transparency, adhesion, and hardness tests were utilized to testify the content of TiO2 in the inorganic component. The modified SiO2/TiO2 and the composite coating were characterized by infrared spectroscopy (FT-IR), transmission electron microscope (TEM), and scanning electron microscope (SEM). 8% TiO2 in methyl-modified silica was proved to achieve the highest contact angle. Compared with the untreated bricks, the composite coating enhanced the performance of ancient bricks against weathering, bacteria, and algae. In detail, the inhibitory effect of the coating on Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) was studied by a bacteriostatic circle test and fluorescence staining, and the influence of the composite coating on algae was determined by comparative experiment as well. Finally, the mechanism of the coating on antibacterial and anti-algae was explored and summarized. The results demonstrated that the weathering process can be slowed by coating the bricks with silica-titania hybrid fluorinated B-72 without altering their outward appearance, thereby protecting ancient buildings without structural repairs involving cement, glues, or concrete which alter the original architect's concept.