A novel, fast-responding, indicator ink for thin film photocatalytic surfaces

A new photocatalyst indicator ink based on methylene blue (MB) is described that allows the presence and activity of a thin (15 nm) photocatalytic film to be assessed in seconds. The ink is very stable (shelf life > 6 months) and the color change (blue to colorless) striking. The ink utilizes a sacrificial electron donor, glycerol, to trap the photogenerated holes, leaving the photogenerated electrons to react with MB to produce its reduced, leuco, form (LMB). The efficacy of the MB ink is due to the presence of acid in its formulation, which curtails significantly the otherwise usual, rapid reoxidation of LMB by ambient O2.