Photocatalytic behavior of colored mortars containing TiO 2 and iron oxide based pigments

This paper analyses the effect of adding iron based pigments to produce photocatalytic colored mortars (Ph-CM) evaluating nitrogen oxide air purification-NOx, Rhodamine B self-cleaning-RhB and formation rate of hydroxyl radicals-OH. All Ph-CM tested shifted towards lower energy values with respect to the absorption-edge of the TiO2-mortar samples without pigments. However, different UV–Visible photoactivity behavior was obtained in function of the type and content of pigment. The results indicate that even though a decrease in the photocatalytic efficiency can occur, in some cases, an interfacial electron transfer between the conduction band of iron pigment and the photocatalytic mortar could also take place, resulting in an effective inhibition of electron-hole recombination, higher formation rate of OH, and thereby higher photocatalytic activity. This electron transfer ability directly depends on the band-edge position of pigment-cement heteroestructure and the iron to pigment ratio.