*3.1. As Prepared Coatings*

SEM and EDX were used to analyze the topography and dopant concentration (as atomic percent of total metals) in the as-prepared doped coatings. Ag-TiO2 and Mo-TiO2 surfaces showed small submicron sized particles which were characterized by EDX as silver rich phases, suggesting that the dopant separated from the matrix TiO2. The silver content was 0.50 ± 0.05 at% in T2 and 30.0 ± 3.1 at% in T3. The Mo content in U2 was 7.0 ± 0.8 at %. The structure of coatings was analysed using XRD (Figure 2). The as-deposited TiO2 coating (T1), showed an anatase structure. Ag-TiO2 coatings showed strong silver peaks. The heat treated TiO2 and Mo-TiO2 (U1 and U2) showed anatase and rutile peaks as well as monoclinic ȕ-TiO2 which were very strong in the case of the doped coating.

**Figure 2.** Microstructure of coatings as evaluated using XRD, (**a**) as deposited TiO2 and Ag-TiO2 coatings (T1–T3 ); and (**b**) TiO2 and Mo-TiO2 coatings after heat treatment (U1 and U2) (S—substrate, An—anatase, Ru—rutile).

Figure 3 shows the photocatalytic activity for the as-prepared coatings and compares these values with those obtained for Pilkington Activ™ as a standard commercial product. As can be seen, all coatings showed high photocatalytic activity. In the case of T3, a change was also observed in the colour of the solution. This was thought to have been caused by leaching of silver from the surface. SEM analysis of the coating was performed before and after immersion in water for 2 h and showed the presence of microparticles on the surface which EDX confirmed to be silver (Figure 4). The silver microparticles in the as deposited coating were embedded in the matrix. Immersion in water resulted in the silver particles to protrude from the surface and EDX showed a reduction in the silver content, confirming that silver was indeed diffusing out of the coating.

**Figure 3.** Photocatalytic activity of the as-deposited coatings and comparison with a commercially available photocatalytic surface (Pilkington Activ™).

**Figure 4.** SEM micrographs of T3, (**a**) as deposited coating; and (**b**) after being under water for 2 h.

Mechanical resistance of the coatings was analyzed using scratch testing. Figure 5 shows the scratch tracks of the coatings after production, as observed using the SEM. Coatings T1–T3 and MC showed excellent adhesion to the stainless steel substrate and no flaking was observed around the scratch tracks. Slight flaking was observed in U1 and U2, which was localized to the area immediately next to the scratch track. This may have been caused by the lack of a Ti adhesion layer in these coatings or due to the stresses applied to the coating during annealing. Given the destructive nature of the scratch test and the high load levels used in this test, all coatings were deemed to show sufficient mechanical resistance for use on food and drinks processing surfaces.

(**a**) (**b**) (**c**) (**d**) (**e**) (**f**)

**Figure 5.** Progressive load scratch tracks of (**a**) T1; (**b**) T2; (**c**) T3; (**d**) U1; (**e**) U2 and (**f**) MC.
