Photocatalytic self-cleaning coatings to remove oleic acid, an organic pollutant, from cotton fabrics

Some textiles and apparel cannot be laundered, such as astronauts’ clothes on the space station, smart textiles that contain optical fiber electronic devices. Thus, self-cleaning technology can be considered as a potential technique that can be used to remove sebum, which is secreted by the human body, from such textiles and apparel. In this study, the photocatalytic self-cleaning properties of cotton fabrics coated with TiO₂ nanoparticles were evaluated for their efficacy in removing the sebum that is transferred from human skin to the fabric. Cotton fabric was treated with four different weight ratios of the TiO₂ photocatalyst, and the surface morphology, elemental composition, and thermogravimetric analysis were determined and evaluated. For the self-cleaning properties, the color changes of the photographic images and the differences in the colors were recorded and obtained using oleic acid as the pollutant and Oil Red O as the coloring agent before and after simulated sunlight irradiation. The results showed that, compared to 0 wt% coated fabric, the 20 wt% coated fabric decolorized in the shortest time, and it showed a higher initial speed in color difference. For the lower weight ratios, such as 1 wt%, much more time was required to obtain the same color difference as the 20 wt% coated fabric. It meant that increasing the weight ratio and irradiation time provided enhanced self-cleaning properties. In addition, Fourier Transform Infrared Spectroscopy (FTIR) spectra were evaluated in order to obtain a quantitative evaluation of the pollutants. Examination of the peaks of oleic acid clarified that the self-cleaning properties increased as the weight ratio and irradiation time increased. Moreover, results of the high performance liquid chromatography (HPLC) showed that besides 0 wt% coated fabric, it cannot detect the contaminant on the other samples after irradiation, which were found to concide with the results showed by FTIR. Based on this study, we found that the color changes from photographs and the colorimeter can be used as references, but they do not provide decisive evidence of degradation, especially for colorless pollutants. The FTIR spectra and liquid chromatography can be used to make decisive judgements concerning the self-cleaning properties of photocatalysis. The findings in this study identified a potential application for textiles and apparel that cannot be washed in liquid media, such as astronauts’ suits on the station, smart textiles for actuators and sensors.