Structural Perturbations in the Solid–Water Interface of Redox Transformed Nontronite

Yan, Lian; Stucki, Joseph W.

doi:10.1006/jcis.2000.6794

Cited by 29 publications

(20 citation statements)

References 56 publications

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“…The electron‐depleted C is then easily attacked by a nucleophile. The surface charge density, and thus the electronegativity, of the reduced clay exceeds that of the oxidized clay, resulting in more countercations and more polarized waters of hydration near the reduced clay surface [34, 35], which is expected to increase the acidity of the water. The lower pH environment in this bulk solution would promote the dechlorination of atrazine.…”

Section: Resultsmentioning

confidence: 99%

“…This is attributed to a greater electron density at basal oxygens due to reduction of Fe(III) to Fe(II) in the structure. This increased basicity enhances the direct coupling between the basal surface and adsorbed H 2 O [34, 35]. In such an alkaline environment, atrazine is hydrolyzed by direct nucleophilic displacement of Cl by an hydroxyl (OH) [21] rather than by the stepwise protonation process described previously for an acidic environment.…”

Section: Resultsmentioning

confidence: 99%

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Fate of atrazine and alachlor in redox‐treated ferruginous smectite

Stucki

et al. 2001

Enviro Toxic and Chemistry

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The oxidation state of structural iron (Fe) in clay minerals exerts a large influence on clay surface chemistry and may affect the adsorption and degradation of pesticides in the environment. This effect, however, has been little investigated. In the present study, herbicides atrazine and alachlor were reacted with ferruginous smectite (sample SWa-1) in its oxidized, reduced (either chemically or bacterially), and reduced-reoxidized states. In some experiments the herbicide was labeled with 14C. Gas chromatography/mass spectrometry (GC-MS) was also used to detect alachlor degradation products. Compared to oxidized clays, reduction by both chemical and microbial treatments decreased the concentration of both herbicides in the surrounding solution. Reoxidized clay exhibited behavior similar to the oxidized clay. Hydrolysis-dechlorination of atrazine occurred in the presence of chemically reduced SWa-1, and GC-MS analysis of alachlor revealed at least 14 degradation products after treatment with reduced clay and only two with the oxidized clay. Interaction of atrazine and alachlor with the clay may be through a H bond with the waters of hydration surrounding interlayer cations, the extent of which should increase with increasing acidity; but under reduced conditions, the validity of this model is unclear. Reduction of structural Fe may affect pH-dependent phenomena in two ways: The increased surface charge density increases the number of hydrated interlayer cations, thereby enhancing surface acidity, and increased electron density at basal surface oxygens increases their Brønsted basicity. Atrazine could, therefore, adsorb and/or degrade through either acid or alkaline hydrolysis pathways. Increased reduction potential of the reduced clay surfaces may also promote degradation.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Fate of atrazine and alachlor in redox‐treated ferruginous smectite

Stucki

et al. 2001

Enviro Toxic and Chemistry

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“…This means that partial exfoliation does not occur and surface area may not increase significantly. water molecules adsorbed on the smectite surface and water associated with exchangeable cations in the interlayer space (Farmer, 1974;Yan and Stucki, 2000;Madejová and Komadel, 2001;Bishop et al, 2002;Frost et al, 2002;Madejová, 2003). Because the KBr pellets were heated overnight, the water content was somewhat attenuated (Pentrák et al, 2012).…”

Section: X-ray Diffractionmentioning

confidence: 96%

Nitrate Reduction by Redox-Modified Smectites Exchanged with Chitosan

Pentrák

Pentráková

Radian

et al. 2014

Clays and clay miner.

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The presence of nitrate and other redox-active anionic contaminants in terrestrial ecosystems poses a significant risk to humans and other forms of life on Earth. The purpose of the present study was to test a potential in situ system, using poly-(D) glucosamine (chitosan) adsorbed to mineral surfaces under redox-active conditions in order to degrade nitrate to lower oxidation states. Chitosan is a linear polysaccharide derived from the chitin found in the shells of shrimp and other shellfish. Five different loadings of chitosan (0, 0.075, 0.25, 0.50, and 1.0 g/L; labeled C0, C1, C2, C3, and C4, respectively) were adsorbed to ferruginous smectite (SWa-1) to form chitosan-SWa-1 composites (CSC) in the pH range 5.8À4. The CSC was then reduced by Na 2 S 2 O 4 in a citrate-bicarbonate buffered dispersion and washed free of excess salts under inert-atmosphere conditions. Upon addition of the nitrate, the solution pH remained slightly acidic, ranging from 5.5 to 4.7. Samples were analyzed for Fe(II) content, reacted with a NaNO 3 solution, and then re-analyzed for structural Fe(II) content. Supernatant solutions were analyzed for nitrate, nitrite, and ammonium. In samples C1 to C4, extensive concentrations of nitrite were observed in the supernatants with a corresponding increase in the reoxidation of structural Fe(II), proving that a coupled redox reaction had occurred between the nitrate and the structural Fe in the clay mineral. The most efficient loading, defined as the largest percentage of adsorbed nitrate reduced to nitrite, occurred in sample C1. The total amount of nitrate reduced and Fe(II) reoxidized followed the trend 0 = C0 < C2 < C3 < C4 & C1. Chitosan showed the potential to reverse the surface charge of constituent clay minerals, thereby enabling the CSC to remove nitrate anions from aqueous mineral systems via redox reactions with structural Fe(II) in clay minerals.

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“…Previous research found that surface-sensitive properties of smectites including surface charge (49,50), specific surface area (51), interlayer spacing (52), and the structure of interlayer water (29,33,53,54) are significantly modified in the reduced state. The increase of the surface charge density (49) and the decrease of the specific surface area (51) in reduced smectites resulted in a decreased accessibility of interlayer spaces and thus a lower sorption capacity in the reduced smectites for aniline (Fig.…”

Section: Interfacial Interactionsmentioning

confidence: 99%

“…Special precautions were taken to remove any possible Fe oxide mixtures or impurities in the sample (29). Assay for total iron revealed 0.45 mmol of Fe/g of clay (or 2.51% by weight) for Upton montmorillonite and 2.97 mmol of Fe/g of clay (or 17.47% by weight) for SWa-1 ferruginous smectite, as determined by the colorimetric 1,10-phenanthroline method (30).…”

Section: Clay Samplesmentioning

confidence: 99%