Influence of chain lengths and loading levels on interlayer configurations of intercalated alkylammonium and their transitions in rectorite

Simultaneous adsorption of aflatoxin B1 and zearalenone by mono- and di-alkyl cationic surfactants modified montmorillonites

Organo-montmorillonites (OMts) modified with mono- and di-alkyl cationic surfactants were prepared to remove polar mycotoxin aflatoxin B₁ (AFB₁) and weak polar, hydrophobic mycotoxin zearalenone (ZER) simultaneously. The structural and surface properties of the prepared OMts were investigated. In vitro adsorption experiments were carried out to simulate the in vivo conditions of gastrointestinal tract of animals by a batch mode. The adsorption of AFB₁ and ZER in both single and binary-contaminate systems were investigated systematically. Both OMts showed super enhanced adsorption capacities towards AFB₁ and ZER whenever in single and binary-contaminate systems compared with raw Mt, indicating the effectiveness of the prepared OMts acted as mycotoxins adsorbents. DODAC-Mt showed a higher adsorption capacity towards AFB₁ and ZER than OTAB-Mt. The equilibrium data of AFB₁ on OMts were fitted satisfactorily with Freundlich and Linear models, suggesting the co-existence of different adsorption mechanism which were proposed to be ion-dipole interactions (between surfactant cations and carbonyl groups of AFB₁) and adsorption/partition mechanisms. The adsorption isotherms of OMts to ZER matched best with Linear models, implying the adsorption/partition mechanism. For simultaneous adsorption, the adsorption process of one mycotoxin was slightly affected by the presence of the other mycotoxin due to the requirement of partial same sorption sites. In addition, the solution pH had negligible influence on the adsorption process of OMts, meaning no desorption occurred when the adsorbents pass through from stomach to intestine as animal feed.

Nature of the interlayer environment in an organoclay optimized for the sequestration of dibenzo-p-dioxin

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(+).