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A Better Drop to Drink

Method for creating nanoparticle heavy-metal sorbents saves water--literally

Come together, Come apart: The top panel depicts the one-step ligand exchange method used to install heavy-metal chelating ligands to the surface of a superparamagnetic iron oxide nanoparticle, which allows tuning the affinity toward a variety of interesting analytes. The lower panel shows a dispersion of ligand-stabilized magnetic nanoparticles in a heavy-metal contaminated system. A short incubation allows the metal to bind to the nanoparticles and facilitates removal of the heavy-metal ions using a small rare earth magnet.

Using magnetic sorbent materials to overcome limitations posed by traditional heavy-metal remediation methods may become an important part of an advanced method to eliminate toxic heavy metals from aquatic systems and drinking water—an important Department of Energy (DOE) environmental objective. In a progressive research effort, scientists from Pacific Northwest National Laboratory (PNNL), the University of Washington, and Oregon Health & Science University produced a novel, comprehensive study showcasing a viable, relatively simple method for engineering high-performance, superparamagnetic, iron oxide nanoparticle heavy-metal sorbents using a facile ligand exchange process to bind readily available affinity ligands onto the nanoparticle surface.

Using a method to synthesize iron oxide nanoparticles with higher purity (fewer trace metal contaminants) that are highly crystalline, superparamagnetic, and impart a high active surface area (>100 m2 g-1), the nanoparticles become ideal sorbent candidates for application to a wide range of separation and sensing challenges. In this study, the researchers used ligands chosen for their chelation capabilities, including a variety of thiol-containing ligands and ethylenediamine tetraacetic acid (EDTA). Each magnetic nanoparticle sorbent was dispersed in river water spiked with seven environmentally significant heavy metals to determine how they would react to the surface.

The scientists used EMSL's microscopic testing facilities, including transmission electron microscopy and X-ray photoelectron spectroscopy analyses, to fully characterize the nanoparticles following surface modification with the selected chelating ligands. Characterization of the magnetic properties of the nanoparticles also was conducted using EMSL's vibrating sample magnetometer.

Scientific impact: This study provides necessary fundamental base knowledge to improve research into high throughput for rapid screening for exposure to radiation, as well as bioremediation efforts that either remove heavy-metal contaminants or retard their mobility. Both of these issues are longstanding DOE and Department of Defense concerns. The research also suggests a viable engineering method for synthesizing magnetic Fe3O4 nanoparticles and tailoring the surface chemistry toward specific heavy-metal contaminants of concern, including lead, mercury, cadmium, silver, copper, cobalt, and thallium.

Societal impact: Magnetically manipulating sorbent materials and tuning the affinity toward a variety of analytes potentially could provide a rapid, easy, and cost-effective water purification system. In addition, heavy-metal removal methods could be further streamlined and adapted to large-scale water remediation.

Reference: Warner CL, RS Addleman, AD Cinson, TC Droubay, MH Engelhard, MA Nash, W Yantasee, and MG Warner. 2010. “High-Performance, Superparamagnetic, Nanoparticle-Based Heavy Metal Sorbents for Removal of Contaminants from Natural Waters.” ChemSusChem 3(6):749-757. DOI: 10.1002/cssc.201000027.

Acknowledgment: The research, featured on the cover of ChemSusChem (June 21, 2010), was supported by the National Institute of Health National Institute of Allergy and Infectious Diseases, the Oregon Nanoscience and Microtechnologies Institute (ONAMI) Safer Nanomaterials and Nanomanufacturing Initiative (SNNI), and PNNL's Laboratory Directed Research and Development.

User Proposal: 30400

Released: July 28, 2010