Facet-dependent activation of chlorine dioxide over Mn2O3 for benzo[a]pyrene degradation.

Benzo[a]pyrene (Bap) is a representative highly recalcitrant and extremely toxic polycyclic aromatic hydrocarbon. Although chlorine dioxide (ClO2) oxidation technology can be employed for Bap treatment, it often suffers from incomplete oxidation and the residual accumulation of highly toxic intermediate products. In this study, a series of Mn2O3 catalysts with different exposed facets are synthesized to regulate ClO2 activation pathways for deep Bap degradation. The cubic Mn2O3 exposing predominantly (001) facets possesses more oxygen vacancies and facilitates the adsorption of ClO2 species. These adsorbed ClO2 species subsequently undergo coupling disproportionation to generate singlet oxygen (1O2) and chlorine radical species (•ClO), while concurrently enabling the formation of transient high-valent MnV(O)+ species. The synergistic interaction between 1O2 and MnV(O)+ establishes a non-radical-dominated oxidation regime, leading to an efficient Bap degradation rate exceeding 97.6% and excellent stability. In contrast, Mn2O3 exposing (111) facets with fewer oxygen vacancies shows lower activity because Bap degradation proceeds mainly via hydroxyl radical (•OH)-dominated pathways. This work demonstrates that the facet engineering of Mn2O3 can be tuned to regulate the activation pathways of chlorine dioxide, providing fundamental mechanistic insight and a rational design strategy for the efficient and deep oxidation of persistent polycyclic aromatic hydrocarbons.