Photocatalytic activity under visible light of Ni:TiO₂-NiTiO₃ synthesized through a modified sol-gel method

One of the most challenging goals in materials science is to shift the absorption band of TiO₂ toward the visible region of the electromagnetic spectrum. This is a fundamental strategy to improve its photocatalytic performance. In this paper, we present a simple methodology based on the sol-gel method, which allows the displacement of the band edge of TiO₂, accompanied by the appearance of additional absorption bands in the optical spectrum. In our methodology, TiO₂ was synthesized and doped with 5% and 10% w/w nickel. The resulting material was dried at 100 °C and subjected to thermal treatment at 500 °C for 1 h each. The obtained material was characterized by scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry, diffuse reflectance, X-ray diffraction, Raman spectroscopy, and XPS. Our results indicate that Ni doping of TiO₂ was successfully carried out, while NiTiO₃ appears from the first drying stage at 100 °C and undergoes the transition from the amorphous to the crystalline phase during the sintering process at 500 °C. Furthermore, all the materials studied showed high catalytic activity under UV irradiation. In particular, the nickel-doped thermally treated materials also exhibited good catalytic performance under visible light, even better than the amorphous phases obtained under UV irradiation.