Self-cleaning of modified cotton textiles by TiO2 at low temperatures under daylight irradiation

This study shows that samples of bleached cotton (C2) and of mercerized cotton (E) textiles can be activated by RF-plasma, MW-plasma and UV-irradiation introducing functional groups negatively charged to anchor TiO2 on the textile surface. The preparation of the TiO2 colloids and the cotton surface functionalization are described in a detailed way. The photo-discoloration and mineralization of stains of red wine, coffee, make up and grease were monitored following the CO2 evolved upon daylight irradiation with 50% full solar light intensity (AM 1). For base treated cotton (C2), UV activated textile followed by TiO2 deposition from Degussa TiO2 P25 was the most active sample during the discoloration of wine and coffee stains under daylight irradiation. In the case of the mercerized cotton samples (E), MW-plasma activation of the textile surface followed by TiO2 deposition from a titanium tetra-isopropoxide (TTIP) colloid showed the most favorable discoloration kinetics. The images obtained by electron microscopy (TEM) and by (HRTEM) show 5-7 nm TiO2 crystallites for the MW-plasma (E) cotton samples at time zero and for the same after 20 machine household washings. The coating of TiO2 on the textiles presented variable thickness of 120-300 nm. The TiO2 cluster size and distribution from sol-gel precursors after daylight induced stain discoloration did not vary with respect to the TiO2 cluster size before irradiation. This is the evidence the stable nature of the TiO2 cluster deposition on the cotton surface. X-ray evidence for rutile formation on the C2 cotton fibers was obtained. Elemental analysis revealed Ti-loadings of 1-1.5% (w/w) for the TiO2 attached by different techniques. The self-cleaning leading to the stain discoloration was quantified to assess the photo-activity of the TiO2 clusters prepared under different experimental conditions. This process shows promise for the total removal of stains containing persistent colored pigments on the cotton fibers.