Synthesis of Core–Shell Magnetic Nanocomposite Fe3O4@ Microbial Extracellular Polymeric Substances for Simultaneous Redox Sorption and Recovery of Silver Ions as Silver Nanoparticles

Microbial extracellular polymeric substance (EPS) is a complex high molecular weight compound secreted from many organisms. In this work, magnetic nanocomposite Fe 3 O 4 @EPS of Klebsiella sp. J1 were first synthesized for silver ions (Ag + ) wastewater remediation, which synergistically combined the advantages of the easy separation property of magnetic Fe 3 O 4 nanoparticles and the superior adsorption capacity of EPS of Klebsiella sp. J1. The physical and chemical properties of Fe 3 O 4 @EPS were analyzed comprehensively. Fe 3 O 4 @EPS exhibited the well-defined core–shell structure (size 50 nm) with high magnetic (79.01 emu g –1 ). Batch adsorption experiments revealed that Fe 3 O 4 @EPS achieved high Ag + adsorption capacity (48 mg g –1 ), which was also much higher than many reported adsorbents. The optimal solution pH for Ag + adsorption was around 6.0, with the sorption process followed pseudo-second-order kinetics. Ag + adsorption on Fe 3 O 4 @EPS was mainly attributed to the reduction of Ag + to silver nanoparticles (AgNPs) by benzenoid amine (−NH−), accompanied by the chelation between Ag + and hydroxyl groups, ion exchange between Ag + and Mg 2+ and K +, and physical electrostatic sorption. The repeated adsorption–desorption experiments showed a good recycle performance of Fe 3 O 4 @EPS. This study has great importance for demonstrating magnetic Fe 3 O 4 @EPS as potential adsorbent to remove Ag + from contaminated aquatic systems.