Effect of bismuth doping on the crystal structure and photocatalytic activity of titanium oxide

The doping of TiO₂ with metals and non-metals is considered one of the most significant approaches to improve its photocatalytic efficiency. In this study, the photodegradation of methyl orange (MO) was examined in relation to the impact of Bi-doping of TiO₂. The doped TiO₂ with various concentrations of metal was successfully synthesized by a one-step hydrothermal method and characterized using X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), and UV-vis spectroscopy. The XRD results revealed that the anatase phase, with an average crystallite size of 16.2 nm, was the main phase of TiO₂. According to the anatase texture results, it was found that the doping of TiO₂ increased the specific surface area for Bi₂O₃@TiO₂ without a change in the crystal structure or the crystal phase of TiO₂. Also, XPS analysis confirmed the formation of Ti⁴⁺ and Ti³⁺ as a result of doping with Bi. The activities of both pure TiO₂ and Bi-doped TiO₂ were tested to study their ability to decolorize MO dye in an aqueous solution. The photocatalytic degradation of MO over Bi₂O₃@TiO₂ reached 98.21%, which was much higher than the 42% achieved by pure TiO₂. Doping TiO₂ with Bi increased its visible-light absorption as Bi-doping generated a new intermediate energy level below the CB edge of the TiO₂ orbitals, causing a shift in the band gap from the UV to the visible region, thus enhancing its photocatalytic efficiency. In addition, the effects of the initial pH, initial pollutant concentration, and contact time were examined and discussed.