Hydration/expansion and cation charge compensation modulate the Brønsted basicity of distorted clay water.
Hydration/expansion and cation charge compensation modulate the Brønsted basicity of distorted clay water.
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水合/膨胀和阳离子电荷补偿调节扭曲粘土水的布朗斯台德碱度。
DOI：
10.1021/la0602113
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发表时间：
2006
期刊：
影响因子：
--
通讯作者：
J. Stucki
中科院分区：
文献类型：
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作者：
J. Cervini;R. Larson;J. Stucki
这封信地址如何铁的氧化还原循环和可交换的阳离子的水合性质的影响，在2：1页硅酸盐的吸附水的布朗斯台德碱度。探针五氯乙烷经历容易脱氯化氢为四氯乙烯，归因于结构Fe（III）还原为Fe（II）后近表面水合水分子的布朗斯台德碱度增加。在Na（+）-或K（+）-饱和的厄普顿蒙脱石存在下研究了该脱氯化氢过程[（Na0.82（Si7.84 Al0.16）（Al3.10 Fe（3+）0.3 Mg0.66）O20（OH）4]或铁质蒙皂石[（Na0.87 Si7.38 Al0.62）（Al1.08）Fe（3+）2.67 Fe（2+）0.01 Mg0.23）O20（OH）4]。铁氧化还原循环对五氯乙烷脱氯化氢的影响进行了研究，使用还原或还原和再氧化的蒙脱石样品饱和Na+（完全膨胀粘土）或K+（完全塌陷粘土）。在粘土布朗斯台德碱度的变化后，Na+ -为- K+交换阳离子电荷补偿或层间水化/膨胀所施加的可交换阳离子的性质解释。K+固定和粘土含水量之间的反比关系以及五氯乙烷转化的趋势表明，在布朗斯台德碱度的增加，从粘土亲水性的增加和扭曲的粘土水的局部活性的变化的结果。钾的固定导致部分坍塌的蒙脱石承载低量的结构Fe（II）具有类似的反应性，完全膨胀的蒙脱石（Na+形式）承载较高量的结构Fe（II）。特别是，高达80%的五氯乙烷转化为四氯乙烷的K+ -饱和，再氧化的厄普顿解释，因为K+的固定导致不可逆的膨胀和不完全的再氧化结构的Fe（II），这有助于稳定附近的网站轴承Fe（II）的电荷密度。然而，较高的五氯乙烷转化率的厄普顿蒙脱石铁质蒙皂石，表明电荷分散，而不是网站的特异性，主要是粘土的反应性。因此，粘土层间水合/膨胀所施加的性质的可交换的阳离子改变水的解离和质子交换的Fe（II）-Fe（III）层状硅酸盐易受铁氧化还原循环。
This letter addresses how iron redox cycling and the hydration properties of the exchangeable cation influence the Brønsted basicity of adsorbed water in 2:1 phyllosilicates. The probe pentachloroethane undergoes facile dehydrochlorination to tetrachloroethene, attributed to increases in the Brønsted basicity of near-surface hydrating water molecules following the reduction of structural Fe(III) to Fe(II). This dehydrochlorination process is studied in the presence of Na(+)- or K(+)-saturated Upton montmorillonite [(Na0.82 (Si7.84 Al0.16)(Al3.10 Fe(3+)0.3 Mg0.66) O20 (OH)4] or ferruginous smectite [(Na0.87 Si7.38 Al0.62)(Al1.08) Fe(3+)2.67 Fe(2+)0.01 Mg0.23) O20 (OH)4]. The effect of iron redox cycling on pentachloroethane dehydrochlorination is studied using reduced or reduced and reoxidized smectite samples saturated with Na+ (fully expanded clay) or K+ (fully collapsed clay). Variations in the clay Brønsted basicity following Na+ -for- K+ exchange are explained by cationic charge compensation or interlayer hydration/expansion imposed by the nature of the exchangeable cation. Inverse relations between K+ fixation and clay water content as well as trends in pentachloroethane transformation indicate that increases in the Brønsted basicity result from increases in the clay hydrophilicity and shifts in the local activity of distorted clay water. Potassium fixation causes partially collapsed smectites bearing low amounts of structural Fe(II) to have a similar reactivity to that of fully expanded smectites (Na+ form) bearing higher amounts of structural Fe(II). In particular, the conversion of up to 80% of the pentachloroethane to tetrachloroethane by K+ -saturated, reoxidized Upton was explained because the fixation of K+ causes nonreversible expansion and incomplete reoxidation of structural Fe(II), which contributes to the stabilization of charge density near sites bearing Fe(II). Higher pentachloroethane conversions by Upton montmorillonite over ferruginous smectite, however, suggest that charge dispersion rather than site specificity contributes predominantly to clay reactivity. Thus, clay interlayer hydration/expansion imposed by the nature of the exchangeable cation alters water dissociation and proton exchange in Fe(II)-Fe(III) phyllosilicates susceptible to iron redox cycling.