(734b) Stability of Phosphonate-Functionalized Iron Nanoparticles

Greenlee, L. F., National Institute of Standards & Technology
Rentz, N. S., National Institute of Standards & Technology
Wilson, S. J., National Institute of Standards & Technology

Iron nanoparticles are of interest in fields such as water treatment and alternative energy, due to their reactive properties and low cost.  When combined with other metals, iron-metal nanoparticles can act as catalysts for a diverse set of reactions.  In solution-based nanoparticle synthesis, organic stabilizers play a critical role in the properties of the nanoparticles, including size, morphology, composition, and colloidal stability.  While polymers are often used in nanoparticle synthesis, chelator-type molecules can also be used as nanoparticle stabilizers. In this study, we characterize iron nanoparticles synthesized in water in the presence of a phosphonate chelator, amino tris(methylene phosphonic acid) (ATMP) for a range of molar ratios of ATMP to iron.  An increase in the molar ratio from 0.05 to 0.8 decreases nanoparticle size from approximately 150 nm to less than 10 nm.  Colloidal ATMP-stabilized iron nanoparticles are stable over a broad range of pH values, and zeta potential measurements were used to evaluate colloidal stability.  Diffraction analysis indicates that ATMP-stabilized iron nanoparticles may have a nano-crystallite structure, with potential regions of amorphous iron.  Characterization results of ATMP-stabilized iron nanoparticles are compared to results obtained previously for carboxymethyl cellulose (CMC)-stabilized iron nanoparticles. Quartz crystal microbalance measurements are used to evaluate the effect of surface functionalization on oxidation rate of the iron nanoparticles, and nanoparticle stability during storage is evaluated.