Photocatalytic‐Mediated Self‐Cleaning of Natural and Artificial Fibers Under Daylight Irradiation at Ambient Temperature

Abstract

This chapter presents up-to-date work addressing the modification of textile surfaces by transparent thin TiO 2 coatings to attain self-cleaning properties under solar irradiation. The pretreatment of natural textiles like cotton or polyester textiles like polyester is achieved by Rf-plasma or UVC irradiation increasing the number of surface bonding/chelating or complexing sites. This shows the potential of these pretreatments for commercial applications. The details of the procedures followed are described. A second alternative to bind TiO 2 is through chemically inert spacers introducing the condensation of TiO 2 and some reactive groups on the textile surface. TiO 2 coating involves the optimization of the colloid preparation, powder suspension, or combinations of both depositing the smaller colloidal particles first followed by deposition of the bigger TiO 2 powder particles. In latter case, the photooxidative mechanism leading to discoloration stains and semitransparent oil-like stains will be described due to the activation induced by the UV component of the solar irradiation. X-ray photoelectron spectroscopy (XPS) evidence is presented for the Ti 2p 3/2 peak shift during stain discoloration indicative of Ti 4+ /Ti 3+ reduction during the photocatalysis. For cotton and polyester/polyamide/Nylon the self-cleaning kinetics of stain discoloration and stain mineralization leading to CO 2 is investigated. The TiO 2 surface stable coating remains active after reuse indicative of the stability of the TiO 2 film deposited on the textile surface. The characterization of TiO 2 surface layers is addressed using a variety of surface techniques. The identification of the TiO 2 rutile crystallographic phases on polyamide and of anatase on Nylon reveals the structure-forming role of the textile on the TiO 2 microstructure even at temperatures <160 °C. The design, preparation, and characterization of RF-plasma and UVC pretreated polyethylene (PE) sputtered PE–TiO 2 transparent non-scattering films. These films are shown to be active in the discoloration of the dye methylene blue (MB) under light irradiation. Photo switching from hydrophobic to a hydrophilic PE–TiO 2 surface was observed under light within 60 minutes. The hydrophilic to hydrophobic back-transformation in the dark required 24 hours and proceeded with a rate 8.7 × 10 −3 min −1 . RF-plasma pretreated PE samples for 15 minutes were subsequently sputtered by TiO 2 for 8 minutes discoloring the dye MB within 120 minutes. Low-intensity UV light (366 nm) reaching the TiO 2 bandgap-induced the discoloration of the MB dye within 420 minutes. By Fourier transform infrared spectroscopy (ATR–FTIR), a systematic shift of ν s (CH 2 ) and the ν s (CC) vibration–rotational peaks were observed during the dye MB discoloration. Evidence is presented for the concomitant increase of the roughness, hydrophilicity, and bond fluidity during MB discoloration.