Multiple approach to test nano TiO₂ photo-activity

One of the most important applications of nanostructured TiO₂ is the manufacture of self-cleaning textiles. It is believed that the self-cleaning properties originate from the photocatalysis of water by nanostructured TiO₂, but the mechanisms acting on textiles, and particularly the phenomena occurring at the interface, are not fully understood yet. A comparative study is proposed here to investigate the photocatalytic activity and the efficiency of modified TiO₂ nanomaterials with the purpose to identify the most suitable analytical method to probe photocatalysis in self-cleaning textiles. The present study sets up reliable, robust, fast and low-cost tests and compares them using TiO₂/SiO₂ nanocomposite systems with different SiO₂ contents. The photocatalytic activity and efficiency of these nanocomposites were benchmarked by three different experimental protocols: a recently developed electrochemical technique to determine hydroxyl radicals (OH) and two well-known methods, namely trapping of OH radicals by salicylic acid and degradation of Rhodamine B dye due to photocatalytic actions. The results suggest that the photoactivity of TiO₂ incorporated in textiles is mainly related to a direct reactivity of the surface oxidizing carriers toward the organic target molecule. The salicylic acid and Rhodamine B test provide mutually consistent results drawing similar trends of the photocatalytic performance. The electrochemical method turns to be a valid alternative when photocatalytic reactivity is driven by OH radicals diffused in a liquid medium. For self-cleaning textile applications, the salicylic acid test provides a more reliable quantitative prediction of the photocatalytic activity, while the Rhodamine B test represents a robust qualitative indicator.