Unveiling the highly disordered NbO6 units as electron-transfer sites in Nb2O5 photocatalysis with N-hydroxyphthalimide under visible light irradiation

Abstract

Although different NbOx units are present in Nb2O5-based catalysts, the correlations between these structures and activity remain unclear, which considerably hinders the further development of Nb2O5 photocatalysis. Herein, we utilized N-hydroxyphthalimide (NHPI) as the probe molecule to distinguish the role of different NbOx units in the activation of C–H bond under visible light irradiation. With the addition of NHPI, Nb2O5 catalysts with highly disordered NbO6 units exhibited higher activities than that with slightly disordered NbO6 units (419–495 vs. 82 μmol·g−1·h−1) in photocatalytic selective oxidation of ethylbenzene. Revealed by Raman spectra, electron paramagnetic resonance spectra, and transmission-electron-microscopy images, highly disordered NbO6 units were confirmed to act as the active sites for the transfer of photogenerated electrons from NHPI, promoting the generation of phthalimide-N-oxyl (PINO) radicals for the enhanced conversion of ethylbenzene under visible light irradiation. This study provides guidance on the role of local NbOx units in Nb2O5 photocatalysis.