Pure and Nb-doped TiO₂ crystalline thin films with different molar ratios of niobium were produced by sol–gel process using the dip-coating method. The results of X-ray diffractometry analysis using Rietveld refinement confirmed the presence of the anatase phase and the partial substitution of Ti⁴⁺ by Nb⁵⁺ in the [TiO₆] octahedra, since changes in the lattice parameters, crystalline strain and crystallite size were observed. The occupation of niobium atoms at the Ti⁴⁺ sites and an increase in the oxygen content were also determined. Atomic force microscopy analyses showed a uniform and homogeneous surface morphology and high-resolution transmission microscopy showed agglomerated nanoparticles. Nanoindentation and ellipsometry techniques evidenced that the insertion of Nb in the TiO₂ matrix caused an increase in density and hardness (~ 18%) values and a reduction in the root mean square (RMS) values (30 and 75% of reduction for 3% and 1% Nb/TiO₂). Nb-doped TiO₂ thin films showed better performance in the photodegradation of methylene blue, reaching a degradation rate of 44% after 4 h of testing, against 26% for pure TiO₂ thin film. The reaction rate was almost twice as high for the doped thin film, with a half-life time of 285 min versus 529 min for pure TiO₂ film.

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