Doped TiO₂ nanophotocatalysts for leather surface finishing with self-cleaning properties

TiO₂ nanoparticles (TiO₂NPs) doped with N and Fe, exhibiting improved photocatalytic activity in the visible light region, were prepared and then applied onto leather surfaces. Diffuse reflectance spectra measurements evidenced the shifting of the absorption peak toward visible region and the enlargement of absorption band (the so-called “tail” of the band). Absorbance spectra for a 20 ppm methylene blue (MB) solution, in the presence of 0.1% (wt%) doped TiO₂NPs after 1 h under visible light irradiation, showed the high efficiency of the doping. Doped TiO₂NPs were embedded in composites material based on acrylic binder, nitrocellulose lacquer, and pigmented paste and were used for leather surface finishing. Self-cleaning properties were confirmed by spectrophotometrical measurements and CIELab color coordinates recording for the degradation of MB spots applied to the treated leather surface exposed to UVA (λ = 365 nm) and visible light irradiation. Leather treated with Fe–N co-doped TiO₂NPs presents the highest activity for MB spot degradation under visible light irradiation. The photographic images of MB dye spots and ball pen ink lines indicate a complete degradation after 30 h of exposure to visible light. Water contact angle measurements in dynamic conditions evidenced the photo-induced hydrophilicity process on functionalized leather surface, supporting the degradation phenomena through water and oxidative species generation.