MnO₂ Structural Polymorph-Mediated Interaction with Dissolved Organic Matter: Underlying Protection and...

Area of Science:

• Environmental Chemistry
• Geochemistry
• Material Science

Background:

• Manganese dioxide (MnO2) is crucial for dissolved organic matter (DOM) cycling.
• The diverse solid-phase speciation of MnO2 complicates understanding DOM-mineral interactions.

Purpose of the Study:

• Investigate the adsorption, protection, and transformation of DOM by various MnO2 polymorphs.
• Determine the influence of MnO2 phase structure and properties on DOM fate.

Main Methods:

• Comparative analysis of DOM interactions with different MnO2 polymorphs (α-, β-, δ-MnO2).
• Assessment of DOM adsorption capacity based on specific surface area.
• Evaluation of DOM protection and transformation mechanisms, including reactive oxygen species (ROS) generation and redox reactions.

Main Results:

• Higher specific surface area of MnO2 correlated with increased DOM adsorption.
• δ-MnO2 provided superior DOM protection via physical entrapment within its layered structure.
• α- and δ-MnO2 generated reactive oxygen species (ROS), transforming DOM into smaller molecules or inorganic carbon.
• β-MnO2 showed minimal ROS production, instead oxidizing DOM via Mn4+ redox, yielding mid- to high-molecular-weight compounds.

Conclusions:

• MnO2 crystal structure is a key regulator of DOM protection.
• The abundance of Mn4+ and ROS dictates DOM transformation pathways.
• Findings offer critical insights into the environmental fate of DOM influenced by MnO2.