Synthesis of Iron Nanoparticles from Spartina alterniflora for Cadmium Immobilization in Coastal Wetland Sediments

A green synthesis method for iron nanoparticles was developed using the leaf extract of the invasive plant <i>Spartina alterniflora</i> (Sa-FeNPs), targeting the remediation of cadmium (Cd) in coastal sediments. The obtained Sa-FeNPs, characterized as amorphous Fe-O-C composites, significantly reduced the amount of bioavailable Cd. Specifically, Sa-FeNPs achieved a 34.63-38.39% decrease in the weak-acid-extractable fraction at a 7% application rate. The primary mechanisms underlying the adsorption and complexation of Cd are the large specific surface area of the Sa-FeNPs, their rich functional groups (-OH, -COOH, C=C, C-O), iron redox reactions, and total organic carbon (TOC) conversion. This study offers an environmentally friendly and low-cost remediation strategy for the utilization of excessive <i>S. alterniflora</i> biomass resources and controlling Cd pollution in coastal wetlands.