Atmospherically Stable Nanoscale Zero-Valent Iron Particles Formed under Controlled Air Contact: Characteristics and Reactivity

Atmospherically stable NZVl (nanoscale zero-valent iron) particles were produced by modifying shell layers of Fe-H2 NZVI particles (RNIP-10DS) by using a controlled air contact method. Shell-modified NZVl particles were resistant to rapid aerial oxidation and were shown to have TCE degradation rate constants that were equivalent to 78% of those of pristine NZVI particles. Fe-H2 NZVl particles that were vigorously contacted with air (rapidly oxidized) showed a substantially compromised reactivity. Aging of shell-modified particles in water for one day resulted in a rate increase of 54%, implying that depassivation of the shell would play an important role in enhancing reactivity. Aging of shell-modified particles in air led to rate decreases by 14% and 46% in cases of one week and two months of aging, respectively. A series of instrumental analyses using transmission electron microscopy, X-ray diffractography, X-ray photoelectron spectroscopy, and X-ray absorption near-edge structure showed that the shells of modified NZVl particles primarily consisted of magnetite (Fe3O4). Analyses also implied that the new magnetite layer produced during shell modification was protective against shell passivation. Aging of shell-modified particles in water yielded another major mineral phase, goethite (alpha-FeOOH), whereas aging in air produced additional shell phases such as wustite (FeO), hematite (alpha-Fe2O3), and maghemite (gamma-Fe2O3).