Synthesis of TiO2 thin films with highly efficient surfaces using a sol–gel technique

Three different strong acid catalysts were used in a simple sol–gel synthesis to produce TiO2 thin films with increased homogeneity and enhanced photocatalytic activity on their mesoporous surfaces. Various techniques were used to characterize the samples, including UV–visible spectrophotometry, X-ray diffraction, micro-Raman spectrometry, photobleaching, scanning electron microscopy, transmission electron microscopy and high-resolution transmission electron microscopy. The band gaps varied from 3.73 to 3.75 eV and the transmittance was >80%. An anatase phase was obtained in all the samples and the crystal size varied from 20 to 45 nm as a function of the annealing temperature. The increase in the efficiency of the surface of the TiO2 thin films was evaluated by photodegradation of methylene blue in water. The results showed that the acid catalysts used in the synthesis had an important effect on the morphology and photocatalytic activity of the thin films, resulting in more efficient surfaces. Synthesis with hydrofluoric acid produced thin films with a homogenous mesoporous structure and improved the photodegradation of the methylene blue dye to 92% in 2.5 h.