The contribution of aliphatic-rich plant biopolymer to sorption of hydrophobic organic compounds is significantly important because of their preservation and accumulation in the soil environment, but sorption mechanism is still not fully understood. In this study, sorption of 1-naphthol by plant cuticular fractions was examined to better understand the contributions of respective fraction. Toward this end, cuticular materials were isolated from the fruits of tomato by chemical method. The tomato cuticle sheet consisted of waxes （6.5 wt%）, cuticular monomer （69.5 wt%）, and polysaccharide （24.0 wt%）. Isotherms of 1-naphthol to the cuticular fractions were nonlinear （N value （0.82 - 0.90）） at the whole tested concentration ranges. The K∞/Kow ratios for bulk cuticle （TC1）, dewaxed cuticle （TC2）, cutin （TC4）, and desugared cuticle （TC5） were larger than unity, suggested that tomato bulk cuticle and cutin are much powerful sorption medium. Sorption capability of cutin （TC4） was 2.4 times higher than the nonsaponifiable fraction （TC3）. The 1-naphthol interactions with tomato cuticular materials were governed by both hydrophobic-type interactions and polar （H-bonding） interactions. Removal of the wax and polysaccharide materials from the bulk tomato cuticle caused a significant increase in the sorption ability of the cuticular material. There was a linear negative trend between K∞ values and the amount of polysaccharides or fraction＇s polarities （（N＋O）/C）; while a linear positive relationship between K∞ values and the content ofcutin monomer （linear R^2 = 0.993） was observed for present in the cuticular fractions. Predominant sorbent of the hydrophobic organic compounds （HOCs） in the plant cuticular fraction was the cutin monomer, contributing to 91.7% of the total sorption of tomato bulk cuticle.
To further elucidate interaction of nitroaromatic compounds with mineral surface, the sorption of m-dinitrobenzene （m-DNB） and nitrobenzene to original bentonite in aqueous solution containing different electrolytes （i.e., KCl, NH4Cl, CaCl2 and Tetramethylammonium bromide （TMAB）） was studied. The sorption of m-DNB was greatly enhanced with the presence of KCl and NH4Cl, while little influence was observed with CaCl2 and TMAB, following the order of KCl 〉 NH4Cl 〉〉 TMAB, CaCl2, or DI water. For nitrobenzene, sorption enhancement only occurred at high nitrobenzene concentrations in the presence of KCl, and the solute equilibrium concentration at inflexion point was lowered with increasing KCl concentration. These sorption enhancements were significantly promoted with the increase of electrolyte concentration. The salting-out effect is insufficient to account for the sorption enhancement by original bentonite with increasing KCI or NH4Cl concentration. X-ray diffraction patterns of bentonite suspensions indicated that the sorption enhancement of m-DNB was attributed to the intercalation of K^＋ or NH4^＋ into bentonite interlayer and then dehydration with m-DNB to form inner-sphere complexes, which caused previously expanded bentonite interlayers to collapse in aqueous suspension, thus further enhanced the interaction of phenyl with siloxane surface. In comparison, the sorption enhancement of NB is attributed to the formation of outer-sphere complexes with K^＋ at high solute-loadings （〉 20（0-400 mg/kg）. The sorption of m-DNB to initially modified TMA^＋-bentonite and K^＋-bentonite was almost the same as respective sorption to original bentonite in solution containing TMA^＋ and K^＋.
CHEN Baoliang, HUANG Wenhai Department of Environmental Science, Zhejiang University, Hangzhou 310028, Zhejiang, China.
A series of carbonaceous biosorbents was prepared by pyrolyzing pine needles, a model biomass, at various temperatures (100–700°C) under an oxygen-limited condition for 6 h. The elemental compositions and the specific surface areas (BET-N2) of the biosorbents were analyzed. Sorption properties of 4-nitrotoluene to the biosorbents and their mechanisms were investigated, and then correlated with the structures of the biosorbents. The result shows that with the increase of the pyrolytic temperature, the aromaticity of the carbonaceous biosorbents increases dramatically and the polarity (the (N+O)/C atomic ratio) decreases sharply. Correspondingly, conformations of the organic matter in the biosorbents transform gradually from a “soft-state” to a “hard-state” and the specific surface areas of the resultant biosorbents extend rapidly. The sorption isotherms fit well with the Freundlich equation. The regression parameters (i.e., N and IgK f) are linearly related to the aromaticity indices (the H/C atomic ratio). Contributions of adsorption and partition to total sorption of the carbonaceous biosorbents are quantified. The adsorption of the carbonaceous biosorbents increases quickly with the increase of the pyrolytic temperature. The saturated adsorption amounts (Q max) increase linearly with the increase of the specific surface areas (SA) of the biosorbents. For the carbonaceous biosorbents with hard-state carbon, the calculated normalized-Q max values by SA are comparable to the theoretical estimation (2.45 μmol/m2). In comparison, for the carbonaceous sorbents with soft-state carbon, the calculated normalized-Q max values by SA are much higher than the theoretical estimation. The partition coefficients (K om) increase with the decrease of the polarity of the biosorbents, reaching a maximum, and then decrease sharply with further decreasing the polarity, suggesting that partition mechanism be dominated by the compatibility and accessibility of the sorbent medium with organic pollutant. These observations w
