Intraparticle Reduction of Arsenite (As(III)) by Nanoscale Zerovalent Iron (nZVI) Investigated with In Situ X-ray Absorption Spectroscopy

Abstract

While a high efficiency of contaminant removal by nanoscale zerovalent iron (nZVI) has often been reported for several contaminants of great concern, including aqueous arsenic species, the transformations and translocation of contaminants at and within the nanoparticles are not clearly understood. By analysis using in situ time-dependent X-ray absorption spectroscopy (XAS) of the arsenic core level for nZVI in anoxic As(III) solutions, we have observed that As(III) species underwent two stages of transformation upon adsorption at the nZVI surface. The first stage corresponds to breaking of As-O bonds at the particle surface, and the second stage involves further reduction and diffusion of arsenic across the thin oxide layer enclosing the nanoparticles, which results in arsenic forming an intermetallic phase with the Fe(0) core. Extended X-ray absorption fine-structure (EXAFS) data from experiments conducted at different iron/arsenic ratios indicate that the reduced arsenic species tend to be enriched at the surface of the Fe(0) core region and had limited mobility into the interior of the metal core within the experimental time frame (up to 22 h). Therefore, there was an accumulation of partially reduced arsenic at the Fe(0)/oxide interface when a relatively large arsenic content was present in the solid phase. These results illuminate the role of intraparticle diffusion and reduction in affecting the chemical state and spatial distribution of arsenic in nZVI materials.

Bimetallic nickel–iron nanoparticles for groundwater decontamination: Effect of groundwater constituents on surface deactivation

“…High resolution X-ray photoelectron spectroscopy (HR-XPS) analysis was performed on a PHI 5000 Versa Probe system using a monochromated AlKa radiation. Sample preparation follows the procedure we described previously (Yan et al, 2012). High-resolution scans were acquired at a 45 takeoff angle and 150 eV pass energy.…”

Synthesis and characterization of robust zero valent iron/mesoporous carbon composites and their applications in arsenic removal

“…Therefore many research groups use ZVI to remove arsenic from waters. [3,[10][11][12] Adsorption of As(III) was rapid on ferric hydroxide formed via Fe(0) surface oxidation by dissolved oxygen.…”

Simultaneous determination of arsenic and cadmium by hydride generation atomic fluorescence spectrometry using magnetic zero-valent iron nanoparticles for separation and pre-concentration

“…The SEM images of the nZVI before and after adsorption indicated a transformation from porous ( Fig.2A) to agglomerated structure (Fig.2B). As shown in Fig.2C, the broad XRD peak located at 2θ angle between 44º and 45º proved the small size of nZVI and was assigned to be the forming a core-shell structure with zero-valent iron (ZVI) as its nuclei and Fe oxyhydroxide as its coating [27][28]. In this core-shell structure, the Fe oxyhydroxide shell offers strong adsorption capability [29], which may be the mechanism that As and Cd were effectively adsorbed.…”