Impacts of environmental levels of hydrogen peroxide and oxyanions on the redox activity of MnO2 particles

Despite the widespread presence of hydrogen peroxide (H₂O₂) in surface water and groundwater systems, little is known about the impact of environmental levels of H₂O₂ on the redox activity of minerals. Here we demonstrate that environmental concentrations of H₂O₂ can alter the reactivity of birnessite-type manganese oxide, an earth-abundant functional material, and decrease its oxidative activity in natural systems across a wide range of pH values (4-8). The H₂O₂-induced reductive dissolution generates Mn(II) that will re-bind to MnO₂ surfaces, thereby affecting the surface charge of MnO₂. Competition of Bisphenol A (BPA), used as a target compound here, and Mn(II) to interact with reactive surface sites may cause suppression of the oxidative ability of MnO₂. This suppressive effect becomes more effective in the presence of oxyanions such as phosphate or silicate at concentrations comparable to those encountered in natural waters. Unlike nitrate, adsorption of phosphate or silicate onto birnessite increased in the presence of Mn(II) added or generated through H₂O₂-induced reduction of MnO₂. This suggests that naturally occurring anions and H₂O₂ may have synergetic effects on the reactivity of birnessite-type manganese oxide at a range of environmentally relevant H₂O₂ amounts. As layered structure manganese oxides play a key role in the global carbon cycle as well as pollutant dynamics, the impact of environmental levels of hydrogen peroxide (H₂O₂/MnO₂ molar ratio ≤ 0.3) should be considered in environmental fate and transport models.