Local structure of iron oxide sensitizing Nb2O5 photocatalysts

We here couple Nb2O5 with Fe2O3 to form visible-light active heterojunctions. The formed heterojunctions are responsive to visible light, and more importantly, photoactive for the mineralization of refractory organic compounds upon exposure to visible light. The sensitizer, Fe2O3, is found to govern the photocatalytic activity of the heterojunction. Therefore, the local structure of the sensitizer is investigated in-depth with X-ray absorption spectroscopy, including X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). Results show that the local structure of Fe2O3 is generally insensitive to the Fe2O3 loading amount, as confirmed by EXAFS. The lengths of the Fe-O coordination and Fe-Fe coordination in the heterojunctions are 1.93 and 2.92 angstrom, respectively, which are shorter than those in bulk Fe2O3. At a Fe2O3 loading amount that is higher than the optimum value, trace amounts of isolated Fe2O3 and bulk Fe2O3 are likely formed at the heterojunction. This is unfavorable for electron-hole separation, and hence, detrimental to the photocatalytic activity. (C) 2019 Elsevier B.V. All rights reserved.