Determination of the Oxide Layer Thickness in Core−Shell Zerovalent Iron Nanoparticles

Abstract

Zerovalent iron (nZVI) nanoparticles have long been used in the electronic and chemical industries due to their magnetic and catalytic properties. Increasingly, applications of nZVI have also been reported in environmental engineering because of their ability to degrade a wide variety of toxic pollutants in soil and water. It is generally assumed that nZVI has a core-shell morphology with zerovalent iron as the core and iron oxide/hydroxide in the shell. This study presents a detailed characterization of the nZVI shell thickness using three independent methods. High-resolution transmission electron microscopy analysis provides direct evidence of the core-shell structure and indicates that the shell thickness of fresh nZVI was predominantly in the range of 2-4 nm. The shell thickness was also determined from high-resolution X-ray photoelectron spectroscopy (HR-XPS) analysis through comparison of the relative integrated intensities of metallic and oxidized iron with a geometric correction applied to account for the curved overlayer. The XPS analysis yielded an average shell thickness in the range of 2.3-2.8 nm. Finally, complete oxidation reaction of the nZVI particles by Cu(II) was used as an indication of the zerovalent iron content of the particles, and these observations further correlate the chemical reactivity of the particles and their shell thicknesses. The three methods yielded remarkably similar results, providing a reliable determination of the shell thickness, which fills an essential gap in our knowledge about the nZVI structure. The methods presented in this work can also be applied to the study of the aging process of nZVI and may also prove useful for the measurement and characterization of other metallic nanoparticles.

Oxidative Stress Induced in Microorganisms by Zero-valent Iron Nanoparticles

“…Generally, nZVI particles are very reactive and their surface properties change rapidly over time depending on environmental conditions. To protect nZVI particles from rapid oxidation (65), the particle core, which consists of zero-valent iron, is covered by a protective shell (28,65,74). Besides different organic molecules (82), the shell can be formed by Fe 2+ and Fe 3+ oxides as a result of oxidation.…”

Enhanced removal of dissolved aniline from water under combined system of nano zero-valent iron and Pseudomonas putida

“…Many researches have suggested toxic nature of nZVI to bacterial communities under anaerobic conditions (Martin et al 2008;Kim et al 2011;Honghai et al 2008;Nassar and Ringsred 2012). But in presence of oxygen an outer shell of FeO(OH) layer have been reported to be formed on nZVI surface and due to the formation of the outer shell layer of FeO(OH) bacterial growth promotion and biofilm generation have been reported in case of several bacterial community (Otte et al 2013;Jang et al 2014;Yang et al 2013).…”

Conjunctive effect of CMC–zero-valent iron nanoparticles and FYM in the remediation of chromium-contaminated soils

“…Nowadays, use of Fe 0 nanoparticles is becoming an increasingly popular method for treatment of hazardous and toxic wastes and for remediation of contaminated soil and ground water (Li and Zhang 2006;Lien et al 2006). Fe 0 nanoparticles provide a high surface-to-volume ratio, which promotes mass transfer to and from the solid surface resulting in high potential for contaminant removal and degradation (Martin et al 2008). Mixing Fe 0 and sand (yielding Fe 0 /sand filters) at suitable proportions has been proposed as a promising option for safe drinking water production (Chicgoua Noubactep et al 2010).…”