An Analysis of Zinc Sorption to Amorphous versus Crystalline Iron Oxides Using XAS

Trivedi, Paras; Axe, Lisa; Tyson, Trevor

doi:10.1006/jcis.2001.7971

Cited by 76 publications

(67 citation statements)

References 43 publications

(68 reference statements)

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“…For arsenate (AsO 4 Þ 3À , there are variations among types of inner-sphere complexes between the phases, including monodentate, bidentate, mononuclear and binuclear species . Finally, with Zn(II), the type of complex (octahedral or tetrahedral) appears to be dependent both on substrate and pH (Trivedi et al, 2001;Waychunas et al, 2002). These differences confirm that complexation is highly substrate (and therefore surface)-dependent, and thus suggest that large changes in the type of complexation could occur in nanoparticulate phases.…”

Section: Surface Complexation Geometrymentioning

confidence: 66%

Nanoparticulate Iron Oxide Minerals in Soils and Sediments: Unique Properties and Contaminant Scavenging Mechanisms

2005

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Nanoparticulate goethite, akaganeite, hematite, ferrihydrite and schwertmannite are important constituents of soils, sediments and mine drainage outflows. These minerals have high sorption capacities for metal and anionic contaminants such as arsenic, chromium, lead, mercury and selenium. Contaminant sequestration is accomplished mainly by surface complexation, but aggregation of particles may encapsulate sorbed surface species into the multigrain interior interfaces, with significant consequences for contaminant dispersal or remediation processes. Particularly for particle sizes on the order of 1-10 nm, the sorption capacity and surface molecular structure also may differ in important ways from bulk material. We review the factors affecting geochemical reactivity of these nanophases, focusing on the ways they may remove toxins from the environment, and include recent results of studies on nanogoethite growth, aggregation and sorption processes.

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Section: Surface Complexation Geometrymentioning

confidence: 66%

Nanoparticulate Iron Oxide Minerals in Soils and Sediments: Unique Properties and Contaminant Scavenging Mechanisms

2005

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“…The three samples corresponding to S 5 , S 20 , and S 40 in Fig. 1 were selected for EXAFS measurements.…”

Section: The Microscopic Structure Of Adsorbed Zn(ii)mentioning

confidence: 99%

“…Generally, edge-sharing adsorption is energetically more favorable than corner-sharing adsorption [20]. Consequently, the edge-sharing adsorption mode is more difficult to be desorbed than that of corner-sharing mode.…”

Section: Effect Of Linkage Mode On Adsorption Irreversibilitymentioning

confidence: 99%

“…In recent years, the EXAFS technique has been increasingly employed for providing structural and compositional information of surface complexes [19,20], which often offers critical insights into the underlying adsorption/desorption mechanisms [21][22][23]. This facilitates our understanding of commonly observed phenomena such as sorption hysteresis and slow sorption/desorption processes.…”

Section: Introductionmentioning

confidence: 99%

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EXAFS studies on adsorption irreversibility of Zn(II) on TiO2: Temperature dependence

Pan

Zhang

et al. 2008

Journal of Colloid and Interface Science

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Adsorption irreversibility of Zn(II) on TiO 2 at various temperatures was studied using a combination of classical macroscopic methods and extended X-ray absorption fine structure (EXAFS) spectroscopy. When the temperature was increased from 5 to 40 • C, the Zn(II) adsorption capacity increased by 130%, and adsorbed Zn(II) became more reversible. The standard Gibbs free energy change ( G 0 ) of the adsorption reaction at 5, 20, and 40 • C was determined to be −19.58 ± 0.30, −22.28 ± 0.10, and −25.14 ± 0.21 kJ mol −1 , respectively. And the standard enthalpy ( H 0 ) and entropy ( S 0 ) were 24.55 ± 2.91 kJ mol −1 and 159.13 ± 0.53 J mol −1 K −1 , respectively. EXAFS spectra results showed that the hydrated Zn(II) was adsorbed through fourfold coordination with an average Zn-O bond distance of 1.98 ± 0.01 Å. Two Zn-Ti atomic distances of 3.25 ± 0.02 and 3.69 ± 0.03 Å were observed, which corresponded to an edge-sharing linkage mode (strong adsorption) and a cornersharing linkage mode (weak adsorption), respectively. As the temperature increased from 5 to 40 • C, the number of strong adsorption sites (N 1 ) remained relatively constant while the number for the weak adsorption sites (N 2 ) increased by 31%. These results indicate that the net gain in adsorption capacity and the decreased adsorption irreversibility at elevated temperatures were due to the increase in available weak adsorption sites (N 2 ) or the decrease in the ratio of N 1 /N 2 . Both the macroscopic sorption/desorption equilibrium data and the molecular level evidence of this study suggest that in a given environmental system (e.g., soils or natural waters) zinc and other similar heavy metals are likely more mobile at higher temperatures.

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“…As foreign metal cations are introduced to the surface, the 2 C and 1 E complexes may form on mixed edge-sharing octahedra (e.g., Fe-Cu or Fe-Zn). Indeed, the edge-sharing complex of metal cations on Fe and Al oxides is the dominant surface complex at and below monolayer coverage [20,[22][23][24][25][26]. An unambiguous differentiation of the second shell metal in As(V) spectra is however quite difficult, with some indicators given only by the position of the imaginary part in the FT [26].…”

Section: Introductionmentioning

confidence: 99%

Arsenic speciation in multiple metal environments: I. Bulk-XAFS spectroscopy of model and mixed compounds

Gräfe

Tappero

Marcus

et al. 2008

Journal of Colloid and Interface Science

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X-ray absorption fine structure (XAFS) spectroscopy was employed to determine the bonding environment of As(V) in the presence of Cu(II) and Zn(II) on goethite and gibbsite. In addition, several mineral species and precipitates derived from homogeneous and heterogeneous (presence of α-Cr 2 O 3 ) super-saturations were studied. Structural parameters were determined after resolving the broad second shells in r-space by differential k-weighting (1, 2 or 3) and k-ranging (2.5-vs 3.5-12.75 Å) of the raw EXAFS functions. In precipitates, AsO 4 was incorporated in the metal-hydroxides forming clinoclase-like and koettigite-like structures in the presence of Cu(II) and Zn(II), respectively. In the presence of both Cu(II) and Zn(II), the clinoclase structure formed preferentially over the koettigite structure under homogeneous oversaturated solution conditions and in the presence of eskolaite (α-Cr 2 O 3 ). Silica promoted the formation of koettigite-like zinc-arsenate precipitates from initial As(V) and Zn(II) solution concentrations of 500 µM. On goethite and gibbsite, 750 µM As(V) formed mainly bidentate binuclear surface species in accordance with many previous findings even in the presence of equimolar Cu(II) and or Zn(II) concentrations. Copper was readily identified in the second shell environment of As(V) sorbed on gibbsite, but not on goethite. We hypothesize that this complex formed on the basis of Cu(II)'s ability to form polymeric species in solution and at the mineral-water interface in agreement with previous studies. The effects of Zn(II) on the coordination environment of As(V) on gibbsite and goethite could not be ascertained with As K-edge EXAFS spectroscopy. In addition to bidentate binuclear surface complexes, As(V) formed edge-sharing complexes with Fe, Al, and Cu atoms, which we could differentiate on the basis of the inter-atomic distances, phase shifts between wavefunctions of Fourier-filtered peaks, and differences in amplitude of the absorption envelopes. The analyses showed that of all data reduction steps, data presented in r-space and as wavefunctions of Fourier-filtered shells offer the greatest possibility for fingerprinting and inferring the influence of co-sorbing metal cations on the As(V) sorption complex. With regards to interpretations of micro-EXAFS data by abstract factor analyses and linear least-square combination fitting, analyses of As K-edge data should not be performed on the raw χ(k) data, but rather on consistently isolated second and higher-order shell features.

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An Analysis of Zinc Sorption to Amorphous versus Crystalline Iron Oxides Using XAS

Cited by 76 publications

References 43 publications

Nanoparticulate Iron Oxide Minerals in Soils and Sediments: Unique Properties and Contaminant Scavenging Mechanisms

Nanoparticulate Iron Oxide Minerals in Soils and Sediments: Unique Properties and Contaminant Scavenging Mechanisms

EXAFS studies on adsorption irreversibility of Zn(II) on TiO2: Temperature dependence

Arsenic speciation in multiple metal environments: I. Bulk-XAFS spectroscopy of model and mixed compounds

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