Xu Liheng, Zhu Lizhong
Department of Environmental Science, Zhejiang University, Hangzhou 310028, China.
J Colloid Interface Sci. 2009 Mar 1;331(1):8-14. doi: 10.1016/j.jcis.2008.11.030. Epub 2008 Nov 20.
Illuminating the factors that influence the organic carbon content normalized sorption coefficient (K(oc)) of organoclays towards hydrophobic organic compounds (HOCs) is meaningful for predicting and optimizing the sorption capacity of organoclay. In this paper, the structures and sorption characteristics towards HOCs of organobentonites synthesized with octadecyltrimethylammonium chloride (OTMAC) and dioctadecyldimethylammonium chloride (DODMAC) were studied in order to further account for the variation of K(oc). The conformations of bentonite-sorbed OTMA(+) and DODMA(+) transformed from disorder to order as surfactant loading increasing. The packing densities of DODMA(+) aggregates were higher than those of OTMA(+) aggregates at low surfactant loadings. At high surfactant loading region (1.0-1.4CEC for OTMA-Bent and 0.5-0.7CEC for DODMA-Bent), similar paraffin-type bilayer arrangements were adopted by sorbed OTMA(+) and DODMA(+), and their packing densities were close under the same f(oc) in dry state organobentonites. It was found that loading forms of surfactant onto bentonite had important effect on the structure of organobentonite in water-saturated state, and further to influence the sorption characteristics of organobentonite towards HOCs. When the loading exceeded 0.8CEC, OTMAC in salt molecule form appeared in the clay interlayer via hydrophobic interaction. The strong hydration of surfactant ammonium heads and the counterions (Cl(-)) in aqueous system interfered the hydrophobic interaction of the OTMA(+) clusters and destroyed the close packing in clay galleries. As a result, the sorption capacity of organobentonite towards HOCs was sharply reduced.
阐明影响有机粘土对疏水性有机化合物（HOCs）的有机碳含量归一化吸附系数（K(oc)）的因素，对于预测和优化有机粘土的吸附能力具有重要意义。本文研究了用十八烷基三甲基氯化铵（OTMAC）和二甲基二（十八烷基）氯化铵（DODMAC）合成的有机膨润土的结构及其对HOCs的吸附特性，以进一步解释K(oc)的变化。随着表面活性剂负载量的增加，膨润土吸附的OTMA(+)和DODMA(+)的构象从无序转变为有序。在低表面活性剂负载量下，DODMA(+)聚集体的堆积密度高于OTMA(+)聚集体。在高表面活性剂负载区域（OTMA-膨润土为1.0 - 1.4CEC，DODMA-膨润土为0.5 - 0.7CEC），吸附的OTMA(+)和DODMA(+)采用相似的石蜡型双层排列，并且在干态有机膨润土中相同f(oc)下它们的堆积密度相近。研究发现，表面活性剂在膨润土上的负载形式对水饱和状态下有机膨润土的结构有重要影响，进而影响有机膨润土对HOCs的吸附特性。当负载量超过0.8CEC时，盐分子形式的OTMAC通过疏水作用出现在粘土夹层中。表面活性剂铵头基和水体系中抗衡离子（Cl(-)）的强水合作用干扰了OTMA(+)簇的疏水作用，破坏了粘土层间的紧密堆积。结果，有机膨润土对HOCs的吸附能力急剧降低。
