Research PaperSynergistic effect of surface and bulk single-electron-trapped oxygen vacancy of TiO2 in the photocatalytic reduction of CO2

- Three different TiO2 with surface oxygen vacancy and/or bulk SETOV were fabricated.
- Coexistence of two defects exhibited an enhanced activity for CO2 photo-reduction.
- Increasing the ratio of SO/SETOV facilitates to separate the photoexcited e-h pairs.

Oxygen vacancies play an important role in many photocatalytic reaction, and have attracted enormous attention from the scientists and engineers. The surface or bulk oxygen vacancies have a different function in the photo-reaction process. Herein, three different TiO2 nanoparticles possessing surface oxygen vacancies (SO) and/or bulk single-electron-trapped oxygen vacancy (SETOV) were fabricated by dehydration or reduction of different titania precursors. The three kinds of TiO2 nanoparticles were characterized systematically by XRD, TEM, Raman, XPS, ESR, TG, UV-vis DRS, and PL techniques. The photocatalytic reduction results of CO2 indicated that both the bulk SETOVs and surface oxygen vacancies contributed to the enhancement of the light absorption, while the surface vacancies facilitated to the separation of the photo-generated charge carriers, and on the contrast, the bulk SETOVs acted as the recombination center. The co-existence of the surface and bulk oxygen vacancies exhibited a synergistic effect to improve the photoreduction efficiency of CO2 to CH4. Through adjusting the ratio of the surface and bulk oxygen vacancies and analyzing the positron lifetime and relative intensity by positron annihilation, the photoreduction efficiency of CO2 improved with the increase of the ratio of surface oxygen vacancies to bulk SETOVs.

Oxygen vacancies with different types and concentrations play important roles in many photocatalytic reaction, and attracts much attention recently. Herein, we fabricated three different TiO2 nanomaterials with surface oxygen vacancies and/ or bulk single-electron-trapped oxygen vacancy (SETOVs) successfully, and found that they exhibited different function in photocatalytic reduction of CO2. Through adjusting the ratio of the surface oxygen vacancies and bulk SETOVs, and analyzing the positron lifetime and relative intensity by positron annihilation, we found that the photo-reduction efficiency of CO2 improved with the increase of the ratio of surface oxygen vacancies.172