Coupling homogeneous and heterogeneous catalysis for the efficient and selective activation of H2O2

Abstract

In this work, we exploited the synergy between homogeneous and heterogeneous catalysis for the efficient and selective activation of H₂O₂. The homogeneous catalyst contained a very trace amount of Fe²⁺ (0.26 ppm), which is lower than the international effluent discharge standard for Fe (0.50 ppm). The heterogeneous catalyst was composed of holey graphitic carbon nitride (g-C₃N₄) nanosheets carrying highly dispersed single atoms (Mn, Ni, or Cu). Mechanistic studies revealed that the strong interaction between single metal sites and H₂O₂ forms two adsorption configurations (HOO– and H(O–O)–), which trigger the generation of different reactive oxygen species (ROS). The heterogeneous Mn–C₃N₄ catalyst provided single Mn–N₃ sites that activated H₂O₂ to produce O₂ by forming HOO–Mn–N₃, while the adjacent Fe²⁺ quickly reduced the generated O₂ to ˙O₂⁻, which can efficiently remove organic pollutants and inactivate Escherichia coli under neutral conditions. The single-atom Mn–C₃N₄, in addition, provided photoactive electrons that drive the efficient cycling of the homogeneous Fe²⁺/Fe³⁺ catalyst (which is the rate-determining step) under very trace Fe²⁺ input. By coupling homogeneous and heterogeneous catalysis, an excellent and advanced oxidation process with potential for large-scale application is reported in this work; the findings also shed light on the theoretical aspects of the efficient and selective activation of H₂O₂ at the atomic level.