Multiple approach to test nano TiO2 photo-activity

• The photocatalytic efficiency of different TiO2/SiO2 nano structured coatings was tested.
• The self-cleaning activity of functionalized textile was related to the amount of radicals detected by two different techniques.
• The results of an innovative electrochemical technique compared to a more traditional spin-trapping method were discussed.
• A discrimination between techniques more sensitive to surface interaction mechanism or to diffused radicals driven photo-reactivity was done.

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.

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