title: Configurations of the bentonite-sorbed myristylpyridinium cation and their influences on the uptake of organic compounds.
abstract: Variations in the configuration of a sorbed myristylpyridinium (MP+) surfactant cation with a loading level in bentonite were examined by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR); the attractive force from the clay basal surfaces to the sorbed MP+ and water molecule in the interlayers was estimated by thermogravimetric analysis (TG-DTG). At low loading levels (i.e., < CEC), MP+ sorbed mainly by cation exchange to clay basal surfaces to form tightly-adhered "organic films" (i.e., flat-layer). With increasing MP+ loading, sorbed MP+ gradually changed into a less confined "phase-like medium" (i.e., paraffin-type structures) via London attraction forces. Attractive forces between the mineral basal surfaces and the sorbed MP+ varied with the interlayer spacing and the stacking of MP+. Sorption of phenol and naphthalene to the resultant MP(+)--clay was a function of the configuration of MP+ aggregates on clay surfaces. At low MP+ densities, the sorbed MP+ film acted as an effective adsorbent for organic compounds. The carbon-normalized solute distribution coefficients (K(sf)) were exceptionally large and increased with MP+ densities up to approximately 340 (phenol) and approximattely 15000 mL g(-1) (naphthalene). At high MP+ loadings, the MP+ aggregates transformed into a partition-like medium, and the K(sf) values decreased sharply and leveled off. Nonetheless, because of the enhanced MP+ packing density within the clay interlayer, the solute K(sf) with a confined sorbed MP+ phase exceeded the corresponding aqueous micelle-water partition coefficients (k(mc)).
authors.affiliation: Department of Environmental Science, Zhejiang University, Hangzhou, Zhejiang 310028, China.
authors.forename: Baoliang
authors.initials: B
authors.lastname: Chen
authors.forename: Lizhong
authors.initials: L
authors.lastname: Zhu
authors.forename: Jiangxi
authors.initials: J
authors.lastname: Zhu
authors.forename: Baoshan
authors.initials: B
authors.lastname: Xing
mesh_terms: D000327:Adsorption; D000538:Aluminum Silicates; D001546:Bentonite / Q000737:chemistry*; D002412:Cations; D000077215:Clay; D008823:Micelles; D009930:Organic Chemicals / Q000302:isolation & purification; D011726:Pyridinium Compounds / Q000737:chemistry*; D012995:Solubility; D017550:Spectroscopy, Fourier Transform Infrared; D013501:Surface-Active Agents / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000302:isolation & purification*; D014961:X-Ray Diffraction
chemical_list: D000538:Aluminum Silicates; D002412:Cations; D008823:Micelles; D009930:Organic Chemicals; D011726:Pyridinium Compounds; D013501:Surface-Active Agents; D014874:Water Pollutants, Chemical; D001546:Bentonite; D000077215:Clay