Synthesis and characterization of stable lead (II) orthophosphate nanoparticle suspensions

Abstract

There is great interest in producing nanoparticles for various applications. The objective of this work was to develop a procedure for reproducibly creating stable lead (Pb) phosphate nanoparticle aqueous suspensions. A stable 5 mg/L Pb-phosphate nanoparticle “stock” suspension was synthesized via chemical precipitation of Pb and orthophosphate in water at pH 7.5 with 4.4 mg soluble PO₄/L and 7 mg C/L dissolved inorganic carbon. The stock suspension was subsequently diluted to produce stable 0.10 mg/L Pb “challenge” water suspensions without compromising the nanoparticle size, structure, mineralogy and solubility. Specifically, the hexagonal hydroxypyromorphite nanoparticles had an average diameter of 38 nm based on transmission electron microscopy analysis and an associated Pb solubility of 0.001 mg/L. The properties of the stock suspensions were not impacted by further dilutions, and the challenge water suspensions remained stable for 24 hours. In the context of drinking water, a protocol to produce such a stable Pb nanoparticle challenge water suspension would be very useful in evaluating Pb bioavailability, identifying Pb remediation strategies, and testing filter effectiveness to remove Pb from water.

Keywords:

• Lead-phosphate particles
• nanomaterials
• hydroxypyromorphite
• drinking water

Acknowledgements

The authors would like to acknowledge Robert Janke, Dr. Regan Murray, Dr. Thomas Speth (EPA ORD), and Dr. David Wahman with EPA ORD, and Valerie Bosscher (EPA Region 5) for providing technical manuscript reviews. We would also like to acknowledge EPA ORD management, and EPA’s Safe and Sustainable Water Resources Program for their support, Michael Schock for his encouragement and laboratory analyses assistance, and Mike DeSantis for assistance with XRD analyses.

Disclaimer

The information in this article has been reviewed in accordance with the U.S. Environmental Protection Agency’s policy and approved for publication. The views expressed in this article are those of the authors and do not necessarily represent the views or the policies of EPA. Any mention of trade names, manufacturers, or products does not imply an endorsement by the U.S. Government or EPA; EPA and its employees do not endorse any commercial products, services, or enterprises. This project was supported in part by an appointment to the Research Participation Program at the Office of Research and Development, U.S. EPA, administered by the Oak Ridge Institute for Science and Education through an interagency agreement between the U.S. Department of Energy and U.S. EPA.