Crop, Soil and Environmental Sciences, Purdue University, West Lafayette, Indiana 47907-2054, United States.
Environ Sci Technol. 2012 Sep 4;46(17):9584-91. doi: 10.1021/es300699y. Epub 2012 Aug 17.
A Na-smectite clay (Na-SWy-2) was exchanged with various amounts of dimethyldioctadecylammonium bromide (DODA-Br) up to twice the cation exchange capacity (CEC). The organoclay (DODA-SWy-2) with DODA-Br added at 2 × CEC exhibited a maximum 4.2 nm d-spacing and a 31.4% carbon content, which demonstrates DODA(+) intercalation. DODA-SWy-2 was evaluated as an archetype of commercial products used to sequester hydrophobic contaminants, and the nature of the primarily C18 alkylhydrocarbon-chain interlayer environment was emhasized. Shifts in ν(CH) and CH(2) rocking band positions in DODA-SWy-2-complex FTIR-spectra indicate that DODA C18 chains were more ordered as DODA surface coverage was increased. Differential scanning calorimetry analysis indicated a DODA-SWy-2 gel-to-liquid transition temperature much lower than the melting point of crystalline DODA-Br and similar to that of aqueous DODA-Br vesicles. This suggests that the transition was governed by C18 alkyl tail-tail interactions in the clay interlamellar region. Dibenzo-p-dioxin (DD) sorption from water by DODA-SWy-2 was compared to DD sorption by the geosorbents granular activated carbon (GAC), K-exchanged saponite, and a muck soil. The linear K(l) sorption coefficients (log K(l)) from a linear fit of the sorption isotherms were 4.37 for DODA-SWy-2, 5.55 for GAC, 3.19 for muck soil, and 2.46 for K-saponite. The DD-organic-matter-normalized sorption coefficient (K(om)) was ∼2.4 times the octanol-water partition coefficient (K(ow)). This indicates that DD has a higher affinity for the nonpolar interlayer DODA organic phase than for octanol. In contrast, the K(om) for muck soil DD sorption was 10 times less than K(ow), which reflects the higher polarity of amorphous soil organic matter relative to octanol. Enhanced DD uptake by the DODA-derived lipophilic phase in the organoclay is attributed to the low polarity, "open" C18 alkyl structure due to the physical dimensions of "v-shaped" DODA(+) molecular, and low density of the interlamellar phase (0.50 g/cm3) density of intercalated DODA(+).
钠蒙脱石（Na-SWy-2）与不同量的二甲基二辛基溴化铵（DODA-Br）交换，直到达到阳离子交换容量（CEC）的两倍。添加 2×CEC 的 DODA-Br 的有机土（DODA-SWy-2）表现出最大的 4.2nm d 间距和 31.4%的碳含量，表明 DODA（+）插层。DODA-SWy-2 被评估为用于隔离疏水性污染物的商业产品的原型，强调了主要的 C18 烷基氢链层间环境的性质。在 DODA-SWy-2 复合物的 FTIR 谱中，ν（CH）和 CH（2）摇摆带位置的移动表明，随着 DODA 表面覆盖率的增加，DODA C18 链变得更加有序。差示扫描量热分析表明，DODA-SWy-2 凝胶到液体的转变温度远低于结晶 DODA-Br 的熔点，与水溶液中的 DODA-Br 囊泡相似。这表明该转变受粘土层间区域中 C18 烷基尾-尾相互作用的控制。与地质吸附剂颗粒活性炭（GAC）、K 交换皂石和淤泥土壤相比，DODA-SWy-2 从水中吸附二苯并-p-二恶英（DD）。从吸附等温线的线性拟合中得出的线性 K（l）吸附系数（log K（l））分别为 4.37 用于 DODA-SWy-2，5.55 用于 GAC，3.19 用于淤泥土壤，2.46 用于 K-皂石。DD-有机物质归一化吸附系数（K（om））是辛醇-水分配系数（K（ow））的约 2.4 倍。这表明 DD 对非极性层间 DODA 有机相的亲和力高于辛醇。相比之下，淤泥土壤 DD 吸附的 K（om）比 K（ow）低约 10 倍，这反映了无定形土壤有机质相对于辛醇的极性较高。DODA 衍生的亲脂性相中 DD 的摄取增强归因于低极性，“开放”C18 烷基结构由于“V 形”DODA（+）分子的物理尺寸和插层相的低密度（~0.50g/cm3），“V 形”DODA（+）分子。
