Effects of Iron Oxidation State and Organic Cations on Dioctahedral Smectite Hydration
Effects of Iron Oxidation State and Organic Cations on Dioctahedral Smectite Hydration
复制标题
铁氧化态和有机阳离子对二八面体蒙皂石水化的影响
DOI：
10.1346/ccmn.2000.0480216
复制
发表时间：
2000
影响因子：
2.2
通讯作者：
A. Banin
中科院分区：
文献类型：
--
作者：
J. Stucki;Jun Wu;H. Gan;P. Komadel;A. Banin
Na交换的二八面体蒙皂石中结构Fe的还原降低了在水中的溶胀性，但由于粘土夹层也在该过程中坍塌，因此对表面水化能的伴随影响是不确定的。本研究探讨了水合行为的氧化和还原的二八面体蒙脱石粘土交换极性（钠）和弱极性（有机）阳离子，以确定之前和之后的Fe还原的表面的性质，并确定粘土表面是亲水性或疏水性。用四甲基铵（TMA）、三甲基苯基铵（TMPA）或十六烷基三甲基铵（HDTMA）取代Na后，各种双八面体蒙皂石中的H2O含量均降低。在有机粘土中，H2O吸附随着阳离子复杂性的增加而降低。对于氧化的蒙脱石，那些与TMPA交换保留较少的H2O比那些与Na交换在所有压力下。这种差异的程度取决于粘土，并随着施加的压力的增加而减小。还原铁（III），铁（II）的八面体片减少钠饱和蒙脱石的膨胀，显然导致一些以前膨胀夹层崩溃。如果Na层间阳离子在还原后交换为烷基铵，但在溶胀压力测量之前，溶胀增加或保持接近恒定，表明有机阳离子破坏了与还原蒙脱石层相关的夹层的塌陷过程。减少TMPA饱和蒙脱石表面更强烈的水化，如果八面体片被还原比如果氧化。因此，结构铁的减少增加了蒙皂石基底表面的水化能，但溶胀性可能会减少或增加，这取决于不同的可交换阳离子发生的层间坍塌的程度。
Reduction of structural Fe in Na-exchanged dioctahedral smectites decreases swellability in water, but because clay interlayers also collapse in the process the concomitant effect on surface hydration energy is uncertain. This study examined the hydration behavior of oxidized and reduced dioctahedral smectite clays exchanged with polar (Na) and weakly-polar (organic) cations to determine the nature of the surface before and after Fe reduction, and to determine if clay surfaces are hydrophilic or hydrophobic. The H2O content in various dioctahedral smectites decreased if Na was replaced by tetramethylammonium (TMA), trimethylphenylammonium (TMPA), or hexadecyltrimethylammonium (HDTMA). Among the organo-clays, H2O adsorption decreased with increasing complexity of the cation. For oxidized smectites, those exchanged with TMPA retained less H2O than those exchanged with Na at all pressures. The extent of this difference depended on the clay and decreased with increasing applied pressure. Reduction of Fe(III) to Fe(II) in the octahedral sheets decreased the swelling of Na-saturated smectites, apparently causing some previously swelling interlayers to collapse. If the Na interlayer cation was exchanged to alkylammonium after reduction, but prior to swelling-pressure measurements, the swelling increased or remained near constant, suggesting that the organo-cation disrupted the collapse process of the interlayers associated with the reduced smectite layers. Reduced TMPA-saturated smectite surfaces are more strongly hydrated if the octahedral sheet is reduced than if oxidized. Thus, reduction of structural Fe increases the hydration energy of smectite basal surfaces, but swellability could decrease or increase depending on the extent of interlayer collapse occurring with different exchangeable cations.