Sequestration of Metal Cations with Zerovalent Iron NanoparticlesA Study with High Resolution X-ray Photoelectron Spectroscopy (HR-XPS)

Abstract

Applications of nanoscale zerovalent iron (nZVI) for removal of metal cations in water are investigated with the result that nZVI has much larger capacity than conventional materials for the sequestration of Zn(II), Cd(II), Pb(II), Ni(II), Cu(II), and Ag(I). Characterizations with high-resolution X-ray photoelectron spectroscopy (HR-XPS) confirm that the iron nanoparticles have a core-shell structure, which leads to exceptional properties for concurrent sorption and reductive precipitation of metal ions. For metal ions such as Zn(II) and Cd(II) with standard potential E 0 very close to or more negative than that of iron (-0.41 V), the removal mechanism is sorption/ surface complex formation. For metals with E 0 greatly more positive than iron, for instance Cu(II), Ag(I), and Hg(II), the removal mechanism is predominantly reduction. Meanwhile, metals with E 0 slightly more positive than iron for example Ni(II) and Pb(II) can be immobilized at the nanoparticle surface by both sorption and reduction. The dual sorption and reduction mechanisms on top of the large surface of nanosized particles produce rapid reaction and high removal efficiency, and offer nZVI as an efficient material for treatment and immobilization of toxic heavy metals.

A radiotracer study of the adsorption behavior of aqueous Ba2+ ions on nanoparticles of zero-valent iron

“…The standard electrode potential (SEP) of Ba 2+ (=−2.91 V, 298 K) is much smaller than that of Fe 2+ (=−0.44 V, 298 K), hence a redox reaction leading to formation of Ba 0 seems to be highly unlikely. In a recent study in which HRXPS was applied, the mechanism of adsorption on iron nanoparticles was studied for a number of metal ions [12]. According to this study, ions with SEP smaller than that of Fe 2+ (as it is the case with Ba 2+ , Zn 2+ , and Cd 2+ ) did not undergo changes in their valence state upon fixation on NZVI surface.…”

“…Comparatively, less effort was devoted to studying the adsorption of metal ions on NZVI. The ions investigated so far include As(III) and As(V) [7][8][9], Pb(II) [3], Cr(VI) [10], Ni(II) [11], and other ions [12]. No reports are present on the applicability of NZVI for radioactive isotopes which are important from radioactive waste management viewpoint.…”

Simultaneous removal of cadmium and nitrate in aqueous media by nanoscale zerovalent iron (nZVI) and Au doped nZVI particles

“…Nanoscale zerovalent iron (nZVI), with Fe(0) core and iron oxide shell, has been proposed for the treatment of Cd contamination (Kharisov et al, 2012;Li and Zhang, 2007;Boparai et al, 2011). However, there is a large discrepancy in Cd removal capacity of nZVI reported (e.g.…”

Effects of nitrate on the treatment of lead contaminated groundwater by nanoscale zerovalent iron

“…Nanoscale zerovalent iron (nZVI) has been extensively considered for in situ groundwater remediation [7][8][9][10] of a wide range of groundwater pollutants including chlorinated solvents [11,12], chlorinated pesticides [13], heavy metals [14][15][16], and nitrate [17][18][19]. Pb 2+ is immobilized by nZVI mainly through sorption and coprecipitation and partly by reduction [15]. Nitrate removal by nZVI generally occurs via reduction to ammonium (Eq.…”

“…Nitrate concentrations as high as 300 mg/L have been detected in groundwater [2].nZVI is easily oxidized on exposure to water, hence the Fe(0) core is surrounded by an oxide layer [6,29]. The core-shell structure is key for Pb 2+ sequestration (partly reduction by core but mainly adsorption and co-precipitation on shell) [15,29,30], but this unique structure is destroyed during the nitrate reduction process as Fe(0) may be oxidized completely [19]. The potential effect of the damaged structure on the ability of nZVI to immobilize Pb 2+ has not been investigated to date.…”