Influence of Ligand Size and Chelation Strength on Zerovalent Iron Nanoparticle Adsorption and Oxidation Behavior in the Presence of Water Vapor and Liquid Water
Functionalization, adsorption, ligands, nanoparticles, oxidation
The effectiveness of zerovalent iron (ZVI) nanoparticles in applications from water remediation to catalysis is intimately tied to adsorption and oxidation processes at the nanoparticle surface. Understanding water sorption and ZVI oxidation as a function of surface-sorbed organic ligand properties can provide new fundamental insights into tuning the reactivity of the nanoparticles. In this work, ZVI nanoparticles were synthesized in the presence of four different organic ligand molecules: two carboxymethyl cellulose polymers of different molecular weights and two phosphonate chelators with different known iron chelation strengths. The resulting ZVI nanoparticles were similar in size (∼100 nm), and adsorption and oxidation behavior are compared on the basis of the properties of the ligand sorbed to the surface of the ZVI nanoparticles. Adsorption and oxidation processes are studied via quartz crystal microbalance (QCM) measurements, where the change in nanoparticle mass is followed over time as the nanoparticles were exposed to varying levels of relative humidity in air or oxygenated water. A clear dependence was shown between measured change in mass and either chelation strength or polymer molecular weight. An increase in either the ligand size or the chelation strength reduced oxidation in oxygenated water. Ligand size resulted in an increase in water vapor adsorption. Reversible mass changes were observed for RH values ≤50% and as a function of ligand, suggesting water sorption, while irreversible mass changes were observed for RH values ≥50% and suggest ZVI oxidation. QCM results were further corroborated with dynamic light scattering, zeta-potential measurements, and scanning electron microscopy. Our results suggest that water adsorption on and oxidation of ZVI nanoparticles may be engineered to a suitable degree through a more thorough understanding of ligand–ZVI interactions.
A. Gankanda, N.S. Rentz, L.F. Greenlee. Influence of ligand size and chelation strength on zerovalent iron nanoparticle adsorption and oxidation behavior in the presence of water vapor and liquid water. Journal of Physical Chemistry C (2019) 123(4), 2474-2487. DOI: 10.1021/acs.jpcc.8b07850.