Preparation of Fe₃O₄ Nanoparticles and Their Application to Composite Biosorbent

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Magnetite (Fe₃O₄) nanoparticles were fabricated by hydrolyzing Fe²⁺ and Fe³⁺ ions with NaOH diffusing through a half-permeable membrane. The Fe₃O₄ nanoparticles, about 15 nm in diameter, showed ferrimagnetism with very small coercivity and remanent magnetization. The nanoparticles were combined with Sphaerotilus natans, a Gram negative bacterium used in biosorption of heavy metal ions in water, to prepare a composite biosorbent. The composite biosorbent showed excellent sorption properties to Pb²⁺ ion in a pH range between 6 and 8, and to Cr₂O₇ ^2- ion in a pH range below 4. The combination of Fe₃O₄ nanoparticles made it easy to separate the composite biosorbent from water by the use of a magnetic field and improved the sorption properties. It was also shown that the composite biosorbent was reusable after being rinsed with a dilute hydrochloric acid solution.