Essential role of atomic H* in activating hydrogen peroxide to produce singlet oxygen for emerging organic contaminants degradation

Atomic H* has been reported to be thermodynamically feasible for activating hydrogen peroxide (H2O2) to produce radicals, while the nonradical pathway and the contributions of metal sites and atomic H* in H2O2 activation need further exploration. In this study, a TiO2 @MnO2 catalyst was synthesized via a facile hydrothermal method and surprisingly found to produce atomic H* over Mn sites in water without external energy input (e.g., light and electricity). Atomic H* plays an essential role in the activation of H2O2 via a nonradical pathway, which induces the removal of tiamulin up to 80.4-91.7% in 20 min at a wide pH range of 4.0-11.0. Density function theory calculations prove that atomic H* owns a much lower total energy barrier (Delta Gtotal = 0.68 eV) for the decomposition of H2O2 to generate superoxide and singlet oxygen than Mn sites (Delta Gtotal = 2.90 eV). This study is a re-visit to the mechanism of activating H2O2 via atomic H* for efficient degradation of emerging organic contaminants.