Self-cleaning modified TiO2-cotton pretreated by UVC-light (185 nm) and RF-plasma in vacuum and also under atmospheric pressure

Two new innovative findings presented in this study are: (a) TiO2-cotton fabrics obtained by pretreatment with UVC-light (185nm) at atmospheric pressure introduced functionalities into the cotton surface enabling the chelation/binding of TiO2. This was possible since the molar absorption coefficient of O-2 and N-2 is very low at 185 nm and (b) the radiofrequency (RF-plasma) pretreatment of cotton surface lead to the formation active binding sites on the cotton at atmospheric pressure. This unexpected RF effect was due to the drastic localized heating of the cotton leading to intermolecular H-bond breaking between the cellulose surface-OH groups of adjacent molecules with the formation of functionalized groups in the cellulose fibers. The discoloration kinetics of the wine stain on the TiO2-cotton pretreated by RF at atmospheric pressure for 10 min was the most favorable. The red wine stains discoloration under Suntest simulated light was monitored by diffuse reflectance spectroscopy (DRS) and by the CO2 evolution during the stain mineralization. By X-ray photoelectron spectroscopy (XPS) it was possible to monitor the decrease of the C, N, S-species on the textile topmost layers during the discoloration process. The XPS Ti 2p(3/2) peak shifts indicating Ti4+/Ti3+ oxido-reduction taking place during the photocatalysis. X-ray diffraction showed the formation of the anatase phase on the cotton. By X-ray fluorescence the loading of TiO2 before and after the discoloration process was found to be similar to 0.8%. High-resolution electron microscopy (HRTEM) shows transparent TiO2 anatase 8-18 nm coating the cotton with layers similar to 31 nm (+/- 10%). These 3-4 TiO2 layers on the cotton did not affect the touch or handling properties of the cotton enabling the potential commercial use of the TiO2-cotton fabrics. (C) 2009 Elsevier B.V. All rights reserved.