The role of physical and operational parameters in photocatalysis by N-doped TiO2 sol–gel thin films

• Better photocatalytic efficiency was achieved by annealing in air vs. N2 or ammonia.
• Photocatalytic removal was similar for variously charged molecular species.
• N-doped TiO2 showed no absorption of visible light, correlated with low CBZ removal.
• CBZ intermediates demonstrated involvement of a OH mechanism.
• N-doped TiO2 showed enhanced disinfection of P. aeruginosa under UVA, as with CBZ.

Physical and operational parameter effects on photocatalysis of micropollutants and bacteria by N-doped TiO2 sol–gel thin films were examined under a solar simulator. Samples annealed in air or N2 showed superior photocatalytic efficiency to those annealed in ammonia, even though the nitrogen concentration was higher in the latter. Similar photocatalytic removal of positively, negatively and neutral charged molecules correlated with negligible dark sorption. Nevertheless, the Langmuir–Hinshelwood (L–H) model indicated that the sorption–desorption mechanism exists when the catalyst is “active” under solar light exposure. The coated films were reusable and there was no deterioration of photocatalytic activity with any molecules, with any charge. The N-doped TiO2 films showed a shift in absorption gap toward longer wavelengths compared to the non-doped TiO2 films, although this shift did not allow absorption of visible light, correlating with the low reactivity under visible light (λ > 400 nm), and the low calculated quantum yield of the film – 0.42%. With respect to mechanisms, hydroxylated derivatives of carbamazepine (CBZ) byproducts demonstrated attack of the aromatic ring by hydroxyl radicals. N-doped film also exhibited enhanced photocatalytic disinfection capabilities for Pseudomonas aeruginosa, similar to CBZ, under exposure to UVA wavelengths.

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