In Situ Hydroxylation of a Single-Atom Iron Catalyst for Preferential 1 O 2 Production from H 2 O 2

In Fenton or Fenton-like reactions, ·OH obtained by the reductive activation of H 2 O 2 is regarded as the major reactive oxygen species (ROS); however, the generation of other ROS like O 2 · – and 1 O 2 cannot be negligible. Since the degradation capability of a certain ROS would be varied to distinctive pollutants, the regulation of ROS production from H 2 O 2 activation should be applicable for a more targeted pollutant degradation. Herein, a series of carbon nitride (C 3 N 4 )-supported Fe catalysts with the state of Fe ranging among single-atom, oxide-cluster, and nanoparticle catalysts were fabricated and their activities in photo-Fenton reactions were evaluated. It was uncovered that the single-atom catalyst favored the generation of O 2 ·– and 1 O 2 via the oxidative activation of H 2 O 2 and the selectivity of 1 O 2 toward ·OH dynamically increased with the proceeding of H 2 O 2 activation, while the catalysts with an abundance of oxide clusters exhibited a significantly higher conversion of H 2 O 2 to ·OH. In situ FT-IR studies demonstrated that during the H 2 O 2 activation, the single-atom catalyst underwent a more significant surface hydroxylation than the oxide-cluster catalyst. Such a result was further consolidated by the theoretical calculation that the adsorption energy of surface hydroxyl was remarkably higher on the single-atom catalyst. Thereafter, distinctive from the easy desorption of hydroxyl during the reduction of H 2 O 2 to ·OH in oxide-cluster catalysts, the in situ surface hydroxylation on the single-atom catalyst alters the adsorption mode of H 2 O 2 to a H-bonded structure, which steers the selectivity of ROS generation to a more favored oxidative transformation of H 2 O 2 to O 2 ·– / 1 O 2 . This work uncovers the decisive role of surface hydroxyl in regulating ROS generation in a heterogeneous Fenton reaction.