In addition to the published ISO tests the use of inks to rapidly screen the photocatalytic activity of self-cleaning films can be carried out [1-3], details of which are given below under further information. We can also carry out non-ISO tests such as removal of stearic acid (also for self-cleaning surfaces) [4,5], destruction of 4-chlorophenol (for powders) [6-9], or activity vs. usage and activity vs. weathering plots.
All the inks suggested (MB, Rz, DCIP) work on the same principle, namely: as usual ultrabandgap irradiation of the semiconductor photocatalyst generates conductance band electrons (e–) and valence and holes (h+). The ink contains a sacrificial electron donor, SED, such as glycerol, which reacts irreversibly and rapidly with the photogenerated holes, leaving the photogenerated electrons to reduce the indicator ink dye molecules, D, contained within the ink film. All these steps take place in the encapsulation medium of the polymer, HEC, which features in the ink formulation. Unlike all the ISO tests, the photocatalyst indicator inks are extremely rapid in response, displaying a clearly visible colour change upon dye reduction, as indicated below:
References
[1] A. Mills, J. Hepburn and M. McFarlane, ACS Appl. Mater. Interfaces, 1 (2009) 1163.
[2] A.Mills, J. Wang, S-K. Lee and M. Simonsen, Chem. Commun., 2005, 2721.
[3] A. Mills and M.McGrady, J. Photochem. Photobiol., A,193 (2008) 228.
[4] A. Mills, A. Lepre, N. Elliott, S. Bhopal, I. P. Parkin and S.A. O’Neill, J. Photochem. Photobiol., A, 160 (2003) 213.
[5] A. Mills and J. Wang, J. Photochem. Photobiol., A, 182 (2006) 181.
[6] J. Theurich, M. Lindner and D.W. Bahnemann, Langmuir, 12 (1996) 6368.
[7] A. Mills, S. Morris and R. Davies, J. Photochem. Photobiol., A, 70 (1993) 183.
[8] A. Mills and S. Morris, J. Photochem. Photobiol., A, 71 (1993) 75.
[9] C.M. Teh and A. R. Mohamed, J. Alloys Compd., 509 (2011) 1648.