Normally, a dye on the surface of a photocatalyst would be oxidised like any other organic material. However, other more easily oxidised ingredients within the ink allow the dye to be chemically reduced instead. The end result is that, instead of being destroyed, the dye within the ink is transformed and simply changes colour.
Normal “invisible ink”
“In our UV activated, oxygen sensitive ink, titania nanoparticles upon exposure to a short burst of UV light are able to oxidize an organic in the ink and simultaneously reduce a dye that is also present” Dr. Andrew Mills tells Nanowerk. “This redox dye is highly colored in its original (oxidized) form) but colorless in its reduced form. Most importantly, the latter is also oxygen sensitive. So that upon UV activation the highly colored ink bleaches and is oxygen sensitive, only regaining its color upon exposure to air.” Prof. Andrew Mills, Queens University Belfast
Colour Change Ink tra