Redox shuttle enhances nonthermal femtosecond two-photon self-doping of rGO-TiO_{2-: X} photocatalysts under visible light

Self-doped TiO₂ has attracted intense attention in photocatalysis due to its improved solar absorption and superior activities. Here we propose an efficient femtosecond two-photon photosynthetic doping method to synthesize visible-active rGO-TiO_2-x photocatalysts based on a redox shuttle mechanism. By employing ethanol molecules as the hole scavenger and GO/rGO nanosheets as the electron acceptor and transporter, the charge separation of photogenerated electron-hole pairs is substantially enhanced, suppressing the charge recombination. Consequently, oxygen vacancies and Ti³⁺ states are facilely introduced into the TiO₂ lattice, resulting in a significantly reduced bandgap (1.62 eV). Meanwhile, benefitting from the nonthermal characteristics of a femtosecond laser in contrast to a conventional long-pulse laser, the average nanoparticle size, shape and lattice structures could be well maintained during the preparation process. The resultant rGO-TiO_2-x nanocomposites exhibit superior photodegradation of methylene blue and bisphenol A under visible light. The proposed doping strategy presents a new and highly effective approach to tune the optical and electronic properties of semiconductor nanocrystals for environmental remediation and energy conversion.