Self-Cleaning cotton textiles surfaces modified by photoactive SiO2/TiO2 coating

The photocatalytic activity of TiO2–SiO2-coated cotton textiles was investigated through the self-cleaning of red wine stains. It was shown that a TiO2–SiO2 species could be produced at temperatures of 100 °C with acceptable photo-activity on non-heat resistant materials. The most suitable Ti-content of the coating was found to be 5.8% and for SiO2, the content was 3.9% (w/w). The discoloration of red wine led to CO2 evolution that was more efficient for TiO2–SiO2-coated cotton for samples than of TiO2-coated ones. The reasons for these results are discussed. The textile surface did not show any change after several consecutive light-induced discoloration cycles of a red wine stain. By high-resolution transmission electron microscopy (HRTEM), the TiO2–SiO2 layer thickness on the cotton fibers was detected to 20–30 nm. The TiO2 and SiO2 were both observed to have particle sizes between 4 and 8 nm. Further electron microscopy work coupled with energy dispersive spectroscopy (EDS) showed that the Ti-particles were always surrounded by amorphous SiO2 and never alone by themselves. Infrared spectroscopy revealed that no modification of the cotton could be detected after photo-discoloration processes with TiO2–SiO2, taking a wine stain as model compound. The mixed TiO2 and SiO2 colloids lead during the dip-coating and subsequent thermal treatment on cotton to an organized structure of highly dispersed TiO2 particles always surrounded by amorphous silica.