Mechanistic Study of Codoped Titania with Nonmetal and Metal Ions: A Case of C + Mo Codoped TiO₂

To study the mechanism of metal- and nonmetal-ion-doped TiO₂, TiO₂ codoped with carbon and molybdenum prepared by a hydrothermal method following calcination post-treatment is chosen as the study object. The prepared samples are characterized by X-ray diffractmeter, Raman spectroscopy, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller measurement. It is found that the doped carbon exists in the form of deposited carbonaceous species on the surface of TiO₂, and molybdenum substitutes for titanium in the lattice and exists as the Mo⁶⁺ state. All the prepared samples have comparable large surface areas. The photocatalytic activities are tested by degradation of rhodamine-B and acetone under visible light irradiation. The results show that the codoped sample has the best performance in the degradation of both RhB and acetone. Briefly, the enhanced photocatalytic activity of codoped TiO₂ is the synergistic effect of C and Mo. Mo substitutes in the Ti site in the lattice for the formation of the doping energy level, and C exists as carbonaceous species on the surface of the TiO₂, which can absorb visible light. The synergetic effects of C and Mo not only enhance the adsorption of visible light but also promote the separation of photogenerated electrons and holes, which consequently contribute to the best photodegradation efficiency of organic pollutants under visible-light irradiation. UV–vis diffuse reflectance spectra and photoluminescence spectra of the prepared samples and fluorescence of terephthalic acid for the detection of hydroxide radical are employed to verify the proposed mechanism