Photocatalytic Activity of Multi-Doped TiO2 Nanoparticles for Degradation of Rhodamine B

Titanium dioxide (TiO2), as a chemically stable, nontoxic, highly efficient, and relatively inexpensive photocatalyst, has been widely used for water and air purification since many environmental pollutants can be degraded by oxidation and reduction processes on TiO2 surface. Under irradiation with light of sufficient energy to span TiO2's band gap, the electron (e-) can be promoted into the conduction band (CB), leaving a hole (h+) in the valence band (VB). Then, electrons and holes can initiate redox reactions on the surface of TiO2. Finally, pollutants can be degraded into CO2 and H2O. However, the application of TiO2 is limited by its UV activation requirement because of its large band gap (3.2 or 3.0 eV in the anatase or rutile crystalline phase, respectively). Therefore, efforts have been directed towards shifting the optical sensitivity of TiO2 from UV to the visible light region for the efficient use of solar energy, which is composed of only about 2-3% UV light. A lot of work has been done on the shift of TiO2's optical response by doping transition metal ions (Ru3+, V4+, Mo5+, Os3+, and Re5+) or nonmetal atoms (C, S, N, F). It is of great interest to investigate the synergetic effects of multiple dopants on the optical shift, crystallinity, surface areas, and activity of TiO2. We have successfully synthesized visible-light-active multi-doped TiO2 photocatalysts through a facile sol-gel process. catalysts were characterized by N2 desorption-adsorption, X-ray diffraction (XRD), UV-vis spectroscopy, and X-ray photoelectron spectroscopy (XPS). The photocatalytic reactivity of these multi-doped TiO2 catalysts were investigated and detailed information were provided regarding the catalyst structure and reaction mechanisms.