Crystallographic phase engineering of MnO2 for efficient peracetic acid activation: Unraveling the critical role of surface manganese oxidation state.

This study systematically investigates the influence of MnO2 crystallographic phase on the activation efficiency of peracetic acid (PAA). Firstly, α-, β-, γ-, and δ-MnO2 were synthesized through tailored methods. The oxidative activity of these catalysts was evaluated based on the degradation kinetics of naproxen (NAP), revealing the following catalytic activity order: α-MnO2 > δ-MnO2 > γ-MnO2 > β-MnO2. Further analysis revealed that NAP oxidation in the different crystallographic phases MnO2/PAA process mainly depends on RO• and 1O2. Comprehensive characterization and density functional theory (DFT) calculations were employed to elucidate the surface chemistry, intrinsic redox properties, structural stability, crystal features, and Mn-O bonding interactions. The results demonstrated an inverse correlation between the average oxidation state of surface manganese sites and the activation efficiency of PAA, thereby elucidating the fundamental origin of the high activity observed in specific crystalline phases of MnO2. The surface-localized chemical environment, rather than bulk characteristics, serves as the dominant factor governing the catalytic performance. Surfaces featuring lower average oxidation states exhibit enhanced reducibility of manganese species, which facilitates more rapid initiation of the catalytic reaction. These insights offer valuable guidance for the rational design of efficient and cost-effective MnO2-based catalysts for advanced water treatment applications.