title: Sulfometuron incorporation in cationic micelles adsorbed on montmorillonite.
abstract: The aim of this study was to understand the interactions between alkylammonium cations present as monomers and micelles and a clay mineral, montmorillonite, to develop slow release formulations of anionic herbicides, such as sulfometuron (SFM) whose leaching in soils is an environmental and economic problem. In the proposed formulation the herbicide is incorporated in positively charged micelles of quaternary amine cations, which in turn adsorb on the negatively charged clay. The adsorption of hexadecyltrimethylammonium (HDTMA) and octadecyltrimethylammonium (ODTMA) on montmorillonite was studied above and below their critical micelle concentrations (CMC). At concentrations above the CMC, the loading exceeded the clay's cation exchange capacity (CEC) and indicated higher affinity of the cation with the longer alkyl chain. An adsorption model could adequately simulate adsorption at concentrations below the CMC, and yield fair predictions for the effect of ionic strength. The model indicated that above the CMC adsorbed micelles contributed significantly to the amount of ODTMA adsorbed. Evidence for adsorption of ODTMA micelles on montmorillonite was provided by X-ray diffraction, freeze-fracture electron microscopy, and dialysis bag measurements. SFM was not adsorbed directly on the clay mineral, and adsorbed at low levels, when the organic cation was adsorbed as monomers. In contrast, a large fraction of SFM adsorbed on the clay mineral when incorporated in micelles that adsorbed on the clay.
authors: Seagram Center for Soil and Water Sciences and Department of Field Crops, Vegetables and Genetics, Faculty of Agricultural, Food and Environmental Sciences, Hebrew University of Jerusalem, Rehovot 76100, Israel.
authors: Yael Golda
authors: YG
authors: Mishael
authors: Tomas
authors: T
authors: Undabeytia
authors: Giora
authors: G
authors: Rytwo
authors: Brigitte
authors: B
authors: Papahadjopoulos-Sternberg
authors: Baruch
authors: B
authors: Rubin
authors: Shlomo
authors: S
authors: Nir
mesh_terms: D000327:Adsorption; D001546:Bentonite / Q000737:chemistry*; D002412:Cations; D004787:Environmental Pollution / Q000517:prevention & control; D005614:Freeze Fracturing; D006540:Herbicides / Q000737:chemistry*; D008823:Micelles; D008854:Microscopy, Electron; D009994:Osmolar Concentration; D000644:Quaternary Ammonium Compounds / Q000737:chemistry; D012989:Soil Pollutants; D013453:Sulfonylurea Compounds / Q000737:chemistry*
chemical_list: D002412:Cations; D006540:Herbicides; D008823:Micelles; D000644:Quaternary Ammonium Compounds; D012989:Soil Pollutants; D013453:Sulfonylurea Compounds; D001546:Bentonite; C013912:decyltrimethylammonium; C042031:sulfometuron methyl