Surfactant-modified clay minerals, organoclays, are well-studied and used commercially for removing contaminants from water. Nevertheless, dry organoclay properties are typically used to understand and predict contaminant sorption. In this work, the effects of water saturation on two properties important to contaminant sorption were examined: organoclay interlayer space and surfactant alkyl tail conformational ordering. Montmorillonite was modified to 0.25–3.0 CEC using three surfactants: hexadecyltrimethylammonium (HDTMA), hexadecylpyridinium (HDPy), and hexadecyltrimethylphosphonium (HDTMP). At low surfactant-loadings (< 1 CEC and < 15% f_OC), water saturation expanded the maximum organoclay interlayer by 4–8 Å, depending on the surfactant and its loading but had little effect on surfactant tail conformational ordering. At low surfactant loadings, water saturation likely promotes contaminant sorption relative to expectations based on dry organoclay properties, particularly for larger contaminants, due to a relaxation of the physical constraints of the interlayer. At higher surfactant loadings, HDTMA and HDTMP organoclays showed relatively small effects of water saturation, but effects were significant for HDPy organoclays. The maximum interlayer space of the HDPy organoclay at 20.7% f_OC expanded 3-fold (+22.3 Å) upon hydration, which is attributed to a substantial rearrangement of the pyridinium headgroup. All HDPy organoclays with f_OC > 20% experienced a notable increase in the alkyl tail conformational ordering upon hydration, becoming fully solid-like, even as negligible interlayer expansion occurred at the highest loadings. At high HDPy-loading water saturation would likely restrict sorption of contaminants relative to what might be expected based on dry properties, due to the energetic barrier of cavity formation in the more solid-like interlayer phase. This work provides evidence from three types of organoclays that water-saturated organoclay properties can differ substantially from those of dry organoclays. Characterization of organoclays under water-saturated conditions that are relevant to contaminant sorption will facilitate our understanding and improvement of organoclay performance.

表面活性剂改性的粘土矿物、有机粘土经过充分研究并在商业上用于去除水中的污染物。然而，干燥的有机粘土特性通常用于理解和预测污染物的吸附。在这项工作中，研究了水饱和度对污染物吸附的两个重要特性的影响：有机粘土层间空间和表面活性剂烷基尾部构象排序。使用三种表面活性剂将蒙脱石改性为 0.25–3.0 CEC：十六烷基三甲基铵 (HDTMA)、十六烷基吡啶鎓 (HDPy) 和十六烷基三甲基鏻 (HDTMP)。在低表面活性剂负载量（< 1 CEC 和 < 15% f _OC）下，水饱和度使最大有机粘土夹层扩大 4-8 Å，具体取决于表面活性剂及其负载量，但对表面活性剂尾部构象排序影响不大。在低表面活性剂负载量下，相对于基于干燥有机粘土特性的预期，水饱和可能促进污染物吸附，特别是对于较大的污染物，这是由于中间层的物理约束的放松。在较高的表面活性剂负载量下，HDTMA 和 HDTMP 有机粘土对水饱和度的影响相对较小，但对 HDPy 有机粘土的影响显着。HDPy 有机粘土在 20.7% f _OC时的最大层间空间在水合时膨胀了 3 倍 (+22.3 Å)，这归因于吡啶鎓头基的大幅重排。所有f _OC  > 20% 的 HDPy 有机粘土在水合时烷基尾部构象排序显着增加，变得完全固体状，即使在最高负载量下发生的层间膨胀可以忽略不计。在高 HDPy 负载水饱和度下，由于在更像固体的夹层相中形成空腔的能量势垒，相对于基于干燥特性的预期，水饱和度可能会限制污染物的吸附。这项工作提供了三种类型有机粘土的证据，表明水饱和有机粘土的性能与干燥有机粘土的性能有很大不同。在水饱和条件下与污染物吸附相关的有机粘土的表征将有助于我们理解和改进有机粘土的性能。