As(III) Sequestration by Iron Nanoparticles: Study of Solid-Phase Redox Transformations with X-ray Photoelectron Spectroscopy

Abstract

Nanoscale zerovalent iron (nZVI) has shown a high efficacy for removing arsenite (As(III)), a groundwater contaminant of great concern, yet the chemical transformations of As(III) enabled by nZVI during the sequestration process are not well understood. Using high-resolution X-ray photoelectron spectroscopy (HR-XPS), arsenic in multiple valence states was observed for nZVI particles reacted with aqueous As(III), which establishes that nZVI is capable of inducing As(III) oxidation and reduction, a unique attribute imparted by the core−shell nature of nZVI particles. Time-dependent analysis shows that As(III) oxidation was a facile and reversible reaction taking place at the surface of the iron oxide shell, whereas As(III) reduction occurred at a slower rate and led to gradual diffusion and accumulation of reduced arsenic at a subsurface layer near the Fe(0) core. Long-term (146 days) exposure of the arsenic-laden nZVI in an aqueous environment caused progressive depletion of the Fe(0) cores; however, arsenic was retained in the native oxide shell without leaching into the aqueous phase. The speciation of arsenic in the nanoparticles is strongly dependent on the loading of nZVI. While a large proportion of the arsenic was bound in a reduced state in the presence of ample nZVI, nZVIlimiting conditions resulted in rapid depletion of the Fe(0) cores and enclosure of arsenic within the oxide formation. These results show that the mechanism of nZVI-mediated arsenite removal is substantially different from that of conventional iron oxide-based adsorbents. Encapsulation of arsenic into the bulk of the solid phase suggests nZVI a potentially more capacious and robust sequestration agent for arsenic abatement.

Efficiency of Pb(II) and Mo(VI) Removal by Kaolinite Impregnated with Zero-Valent Iron Particles

“…Figure 3c and 3d show Fe 0 particles, where the dimensions do not exceed 5 μm, although it should be noticed that the particle size was not unimodal. As reported earlier, the physical parameters of Fe 0 particles such as size, dimension, and crystallinity can influence the rate of iron oxidation (Yan et al 2012). …”

Green synthesis, characterization of biomaterial-supported zero-valent iron nanoparticles for contaminated water treatment

“…Goethite has more affinity towards contaminates (Zhang et al 2014). Thus zero-valent iron core and iron hydroxides have the shells which provide a characteristic core-shell structure to ZVIN with unique redox properties (Yan et al 2012;Ritu et al 2011). Because of attractive qualities like electron donating property during the oxidation of Fe 2+ to Fe 3+ and existence of various mineral forms of iron, the ZVIN have been found to be more important in the adsorption and removal of environmental pollutants (Chicgoua et al 2012;Kumar et al 2014).…”

A new insight on the core–shell structure of zerovalent iron nanoparticles and its application for Pb(II) sequestration

“…Yet due to the high Pb(II) concentration in the wastewater from lead-acid batteries industry, the appropriate adsorbent needs to have high adsorption capacity. Recent studies have indicated that nZVI, an ideal adsorbent with strong reducing power, has many advantages with respect to treating waters polluted by heavy metals, such as high removal capacity and easy solid-liquid separation [5][6][7][8][9][10][11]. These inherent merits of nZVI make it perfect to remove Pb(II) from wastewater.…”