Self-cleaning of modified cotton textiles by TiO 2 at low temperatures under daylight irradiation

Abstract

This study shows that samples of bleached cotton (C 2) and of mercerized cotton (E) textiles can be activated by RF-plasma, MW-plasma and UV-irradiation introducing functional groups negatively charged to anchor TiO 2 on the textile surface. The preparation of the TiO 2 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 CO 2 evolved upon daylight irradiation with 50% full solar light intensity (AM 1). For base treated cotton (C 2), UV activated textile followed by TiO 2 deposition from Degussa TiO 2 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 TiO 2 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 TiO 2 crystallites for the MW-plasma (E) cotton samples at time zero and for the same after 20 machine household washings. The coating of TiO 2 on the textiles presented variable thickness of 120–300 nm. The TiO 2 cluster size and distribution from sol–gel precursors after daylight induced stain discoloration did not vary with respect to the TiO 2 cluster size before irradiation. This is the evidence the stable nature of the TiO 2 cluster deposition on the cotton surface. X-ray evidence for rutile formation on the C 2 cotton fibers was obtained. Elemental analysis revealed Ti-loadings of 1–1.5% (w/w) for the TiO 2 attached by different techniques. The self-cleaning leading to the stain discoloration was quantified to assess the photo-activity of the TiO 2 clusters prepared under different experimental conditions. This process shows promise for the total removal of stains containing persistent colored pigments on the cotton fibers.