Correlation between the photocatalysed oxidation of methylene blue in solution and the reduction of resazurin in a photocatalyst activity indicator ink (Rz Paii)

<p class="MsoNormal">The initial rate of the photocatalysed oxidation of methylene blue, MB, by dissolved oxygen in solution, <i>r_i(MB)</i>, is measured for a series of titania on glass samples exhibiting a wide range of activities.  The samples used include two different types of commercial self-cleaning glass and a lab-made sol-geltitania film.  The activities of these samples are also assessed using a resazurin-based photocatalyst activity indicator ink, i.e. Rz <i>paii</i>, for which the initial rates of the photocatalysed reduction of Rz were measured, <i>r_i(Rz).</i>  A plot of <i>r_i(MB)</i>vs. <i>r_i(Rz)</i> reveals a goodstraight line, thereby demonstrating a linear correlation (for TiO₂films on glass at least) between the slow (usually hours) photocatalysed oxidation of organic materials, such as MB, and the fast (typically minutes) photocatalysed irreversible reduction of a dye, like Rz, in a <i>paii</i>.  The possible use of <i>paii </i>technology for assessing, in a simple, quick and inexpensive manner, photocatalytic films both in the laboratory and <i>in situ</i> is discussed briefly.  </p>