Cadmium Immobilization on Fe Oxyhydroxides Enhanced by DOM Using Single-Molecule Determinations

Area of Science:

• Environmental Chemistry
• Geochemistry
• Materials Science

Background:

• Dissolved organic matter (DOM) influences heavy metal behavior in the environment.
• Cadmium (Cd) immobilization on iron oxyhydroxides is enhanced by DOM, but specific molecular contributions are poorly understood.
• Lack of in situ methods hinders detailed analysis of Cd-DOM-mineral interactions.

Purpose of the Study:

• To investigate the molecular mechanisms of Cd immobilization on goethite (an iron oxyhydroxide) using model organic molecules.
• To quantify the contribution of different functional groups in organic molecules to Cd adsorption and binding.
• To elucidate the role of organic molecule adsorption in forming new Cd-binding configurations.

Main Methods:

• Batch adsorption experiments.
• Solid-state characterization techniques.
• Theoretical calculations.
• Single-molecule force spectroscopy (SMFS) coupled with K-means analysis.

Main Results:

• Organic small molecules significantly increase Cd adsorption on goethite.
• Carboxyl groups demonstrated the most substantial enhancement in Cd adsorption (81.7%).
• Adsorption of organic molecules promoted the formation of new Cd-O(C) and Cd-O(Fe/C) bonds, dominating Cd binding configurations (75%-80%).

Conclusions:

• Organic molecule adsorption is the primary mechanism for enhanced Cd immobilization on goethite.
• New Cd-O(C) and Cd-O(Fe/C) bonds are key to understanding DOM-mediated Cd immobilization.
• Findings provide crucial insights into Cd behavior and a theoretical basis for pollution control in aquatic and soil environments.