Nature of the Interlayer Environment in an Organoclay Optimized for the Sequestration of Dibenzo-p-dioxin

Abstract

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 CH2 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 Kl sorption coefficients (log Kl) 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 (Kom) was ~2.4 times the octanol–water partition coefficient (Kow). This indicates that DD has a higher affinity for the nonpolar interlayer DODA organic phase than for octanol. In contrast, the Kom for muck soil DD sorption was ~10 times less than Kow, 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+.

Sequestration of 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin by activated carbon eliminates bioavailability and the suppression of immune function in mice

“…Greater reduction efficiencies were achieved using sorbent particles of smaller size . These reductions in aqueous concentrations are largely predictable because activated carbons represent high–surface area absorbents with a porous structure that is intrinsically suitable for sorption of nonpolar aromatic compounds . Over 90% of porosity of the activated carbon used in the present study is from micropores, which are pores <2 nm in diameter (Table ).…”

Activated carbons of varying pore structure eliminate the bioavailability of 2,3,7,8-tetrachlorodibenzo-p-dioxin to a mammalian (mouse) model

“…This is especially true in the case of planar hydrophobic compounds which are intrinsically suitable for hydrophobic pore-filling processes coupled with van der Waals attraction characteristic of contaminant sorption by AC [32]. The sorption capacity of ACs have been shown to be orders of magnitude greater than the primary native soil/sediment sorptive component for hydrophobic contaminants, namely amorphous organic matter [33]. Pore structure is known to play an important role in the sorption potential of all porous media across a variety of scales [34].…”

Adsorption of novel insensitive munitions compounds at clay mineral and metal oxide surfaces

“…[10] The siloxane surfaces of layer silicate clays, such as smectite, have been shown to be effective sorbents for NACs. [2,10,11] The type of exchangeable interlayer cation (e.g. K þ v. Na þ ) has also been shown to affect the uptake of NACs by layer silicate clays: cations of lower hydration energy (e.g.…”