5 years ago

Fast Electron Transfer and •OH Formation: Key Features for High Activity in Visible-Light-Driven Ozonation with C3N4 Catalysts

Fast Electron Transfer and •OH Formation: Key Features for High Activity in Visible-Light-Driven Ozonation with C3N4 Catalysts
Angelika Brückner, Hongbin Cao, Jiadong Xiao, Yongbing Xie, Jin Yang, Jabor Rabeah
Photocatalytic ozonation of wastewater pollutants by sunlight is a highly attractive technology close to real application. Understanding this process on the atomic scale and under realistic working conditions is challenging but vital for the rational design of catalysts and photocatalytic decontamination systems. Here we study two highly active C3N4 photocatalysts (bulk C3N4 and a nanosheet-structured C3N4) under simultaneous visible-light irradiation and O3 bubbling in water by in situ EPR spectroscopy coupled with an online spin-trapping technique. The photoexcitation of electrons to the conduction band (CB-e), their further trapping by dissolved O2 and O3, and the evolution of reactive oxygen species (ROS) have been semiquantitatively visualized. A dual role of O3 in boosting the CB-e to OH conversion is confirmed: (i) an inlet 2.1 mol % O3/O2 gas mixture can trap about 2–3 times more CB-e upon aqueous C3N4 suspension than pure O2 and further produce OH by a robust O3-mediated one-electron-reduction pathway (O3O3 → HO3OH); (ii) O3 can readily take CB-e back from O2 to form O3, thus blocking the inefficient H2O2-mediated three-electron-reduction route (O2O2 → HO2 → H2O2OH) but further strengthening the O3-mediated pathway. In the presence of 2.1 mol % O3/O2, the OH yield increases by 17 and 5 times, and consequently, the mineralization rate constant of oxalic acid increases by 84 and 41 times over bulk C3N4 and NS C3N4, respectively. This work presents an attractive opportunity to boost the yield of ROS species (OH) for water purification by visible-light-driven photocatalysis and provides a powerful tool to monitor complex photocatalytic reactions under practical conditions.

Publisher URL: http://dx.doi.org/10.1021/acscatal.7b02180

DOI: 10.1021/acscatal.7b02180

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