Photocatalytic Generation of H₂O₂ Via a Hydrogen-Abstraction Pathway by Bi_2.15WO₆ under Visible Light

Photocatalytic technology is a popular research area for converting solar energy into environmentally friendly chemicals and is considered the greenest approach for producing H₂O₂. However, the corresponding reactive oxygen species (ROS) and pathway involved in the photocatalytic generation of H₂O₂ by the Bi_2.15WO₆-glucose system are still not clear. Quenching experiments have established that neither ^•OH nor h⁺ contribute to the formation of H₂O₂, and show that the formed surface superoxo (≡Bi-OO^•) and peroxo (≡Bi-OOH) species are the predominant ROS in H₂O₂ generation. In addition, various characterizations indicate the enhanced electron-transfer on the surface of Bi_2.15WO₆ with increasing contents of glucose via the ligand-to-metal charge transfer pathway, confirming H-transfer from glucose to ≡Bi-OO^• or ≡Bi-OOH. The increased production of H₂O₂ with decreasing bond dissociation energy (BDE_O-H) values of various phenolic compounds again supports the H-transfer mechanism from phenolic compounds to ≡Bi-OO^• and then to ≡Bi-OOH. DFT calculations further reveal that on the Bi_2.15WO₆ surface, oxygen is sequentially reduced to ≡Bi-OO^• and ≡Bi-OOH, while H-transfer from H₂O or glucose to ≡Bi-OO^• and ≡Bi-OOH, resulting in the production of H₂O₂. The lower energy barrier of H-transfer from adsorbed glucose (0.636 eV) than that from H₂O (1.157 eV) indicates that H-transfer is more favorable from adsorbed glucose. This work gives new insight into the photocatalytic generation of H₂O₂ by Bi_2.15WO₆ in the presence of glucose/phenolic compounds via the H-abstraction pathway.