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 Fe3O4@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 Fe3O4 nanoparticles and the superior adsorption capacity of EPS of Klebsiella sp. J1. The physical and chemical properties of Fe3O4@EPS were analyzed comprehensively. Fe3O4@EPS exhibited the well-defined core-shell structure (size 50 nm) with high magnetic (79.01 emu g(-1)). Batch adsorption experiments revealed that Fe3O4@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 Fe3O4@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 Mg2+ and K+, and physical electrostatic sorption. The repeated adsorption-desorption experiments showed a good recycle performance of Fe3O4@EPS. This study has great importance for demonstrating magnetic Fe3O4@EPS as potential adsorbent to remove Ag+ from contaminated aquatic systems.