Dual-Path Oxidation of Phenolic Organic Contaminants Triggered by the β-MnO2/Bisulfite System

Manganese dioxide (MnO2) is often used to treat pollutants in water owing to its high oxidative activity. Bisulfite (BS) as an activator can promote the degradation efficiency of MnO2. However, the mechanism of different crystalline MnO2 in the presence of BS is still controversial. The oxidation performance of the tunnel type (α-MnO2, β-MnO2) and the two-dimensional lamellar type (δ-MnO2) in the presence of BS was investigated. β-MnO2/BS exhibited the highest oxidative activity under optimal conditions. The bisphenol A (BPA) oxidation kinetic constant of β-MnO2/BS (0.737 min–1) was 6 and 2.3 times higher than that of δ-MnO2/BS and α-MnO2/BS, respectively. The mineralization efficiency of BPA reached 80.05% within 15 min, owing to the high content of Mn(IV) in β-MnO2. BS could rapidly reduce β-MnO2 to produce a high concentration of Mn(III). Soluble Mn(III) directly participates in the BPA oxidation, and the surface Mn(III) can react with the surface adsorbed oxygen molecules (Oad) to generate superoxide radicals (O2•–) to promote the deep mineralization of target contaminants. Moreover, the β-MnO2/BS system can efficiently oxidate various phenolic organic pollutants even in natural water. This research can provide new insights for better understanding of the oxidation process of different crystalline-phase MnO2/BS.