The characteristics of organic matter influence its interfacial interactions with MnO₂ and catalytic oxidation...

The influence of dissolved organic matter (DOM) properties on its interfacial interactions with MnO₂ and on catalytic oxidation processes was studied by Time-Resolved Dynamic Light Scattering (TR-DLS) and Atomic Force Microscopy (AFM) under varied solution conditions. Four DOM fractions of different characteristics (e.g., SUVA, hydrophobic character, structural properties) were selected. Bared-MnO₂ nanoparticles readily aggregated in NaCl and CaCl₂ solutions. Classic DLVO Theory successfully described critical coagulation concentrations and aggregation behaviors. In NaCl solution, DOM adsorbed on MnO₂ nanoparticles and provided electrosteric stabilization. The two DOM fractions of higher hydrophobic (HPO) character were more efficient in decreasing the aggregation rates. Enhanced MnO₂ aggregation was observed at high Ca²⁺ concentrations due to charge screening and cation bridging between carboxyl groups in DOM structures. The addition of oxidant (H₂O₂) induced a high aggregation of bared-MnO₂ nanoparticles, possibly due to the release of Mn²⁺ (i.e., complexation mechanisms) and generation of reactive species (O₂^-, HO₂^-, and H). Contrasted with their hydrophilic (HPI) counterparts, HPO isolates adsorbed on MnO₂ significantly decreased the catalytic oxidation processes between H₂O₂/MnO₂; suggesting a more efficient and stronger DOM coating. Interfacial forces measured by AFM, showed weaker interactions between HPI isolates and MnO₂; suggesting unfavorable polar interactions. Conversely, the high adhesion forces between MnO₂/HPO isolate would indicate stronger bonds and hydrophobic interactions. This study provided a nanoscale understanding of the impact of DOM characteristics on: a) performance of the MnO₂ coated ceramic membranes in water treatment, and b) biogeochemical cycle of Mn-oxides in the environmental.