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 photo-catalytic activity and the efficiency of modified TiO2 nanomaterials with the purpose to identify the mostsuitable analytical method to probe photocatalysis in self-cleaning textiles. The present study sets upreliable, robust, fast and low-cost tests and compares them using TiO2/SiO2nanocomposite systems withdifferent SiO2contents. The photocatalytic activity and efficiency of these nanocomposites were bench-marked by three different experimental protocols: a recently developed electrochemical technique todetermine hydroxyl radicals (•OH) and two well-known methods, namely trapping of•OH radicals bysalicylic acid and degradation of Rhodamine B dye due to photocatalytic actions. The results suggest that the photoactivity of TiO2incorporated 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 diffusedin 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.