Micelle-clay Complex Research Articles

Determination of release of organic cations from micelle–clay complexes and their re-adsorption in sand/clay columns

Release of organic cations from cationic micelle–clay complexes in slow release herbicide formulations or in column-filters for water purification may pose a problem. In this study we determined the release of octadecyltrimethylammonium (ODTMA) or benzyldimethylhexadecylammonium (BDMHDA) from micelle–clay complexes, and devised a method to retain the released cations by using a column filled with sand/clay mixtures. The adsorption of 5 mM ODTMA or BDMHDA on montmorillonite added at 5 g/l clay was complete. The release was examined at different times and complex concentrations. The percents of release of ODTMA after 24 h were 13.2, 3.8 and 0 for 0.1, 1 and 5 g/L, respectively, whereas for BDMHDA the corresponding values were 31.2, 19.4 and 7.2. Measurements of dissolved organic carbon (DOC) yielded the amount of the released organic cation from micelle–clay complexes in column-filters for water purification after adding a layer (13 cm) of quartz mixed with clay (150:1 w/w ratio) at the bottom of the column. The amount of the released organic cation from columns including the micelle–clay complexes was less (or equal within the experimental error) than the amount released from those including quartz alone or a quartz–clay mixture. Hence, the carbon analysis showed that in the ppm range all the released cations (ODTMA or BDTMA) were retained by the column-filter. The water passing through a 25 cm column filled with quartz mixed with micelle–clay was also passed sequentially through three columns filled with quartz–clay (150:1) and was concentrated 1000-fold. Measurements by GC-MS showed no traces of the organic cations. The conclusion is that the released organic cations from micelle–clay complexes can be completely retained by adding quartz–clay layers.

Water Purification from Organic Pollutants by Optimized Micelle−Clay Systems

Removal of anionic pollutants (imazaquin, sulfentrazone, sulfosulfuron) and neutral pollutants (alachlor, acetochlor, chlorotoluron, bromacil) from water by micelles preadsorbed on montmorillonite was studied. Micelles of octadecyltrimethylammonium and benzyldimethylhexadecylammonium (BDMHDA) were used. The micelle-clay systems (1% w/w) removed 87-99% of the pollutants from their water solutions containing 1-33 mg/L of herbicide. The nature of the headgroup of the organic cation, which forms the micelles, is critical. Desorption of imazaquin and acetochlor from 0.3% (w/w) suspension of BDMHDA-clay complex after 24 h was around 7% in the range of adsorbed amounts from 0.6 to 15.3 mg/g. These results indicate rather slow rates and small extents of release of pollutants from micelle-clay complexes. Column filters (25 cm) made of a mixture of quartz sand and BDMHDA micelle-clay complex at 100:1 w/w ratio removed at least 99% of above pollutants from initial solutions containing 10 mg/L; 99.5 and 97% of sulfosulfuron and alachlor were removed from their initial solutions containing 200 and 5 microg/L, respectively. These data indicate that micelle-clay complexes are very efficient for water purification from organic contaminants.

Sulfosulfuron incorporated in micelles adsorbed on montmorillonite for slow release formulations.

Slow release formulations of the anionic herbicide sulfosulfuron (SFS) were prepared by incorporating it in micelles of an organic cation octadecyltrimethylammonium, which adsorb on the clay-mineral montmorillonite. The fraction of SFS adsorbed on the micelle-clay complex reached 98%, whereas for monomer-clay complexes, its adsorption was insignificant. Fluorescence studies showed surface contact between the micelles and the clay surface. The rate of SFS release from the micelle-clay formulations in aqueous suspensions was slow (<1%, 72 h). Spraying SFS formulations on a thin soil layer in a funnel, followed by irrigations (50 mm), resulted in complete elution of SFS from the commercial formulation (dispersible granular) versus 4% from the micelle-clay formulation. A plant bioassay in Rehovot soil showed that these respective formulations yielded 23 and 65% of shoot growth inhibition of foxtail. Consequently, the slow release micelle-clay formulations of SFS yield significantly reduced leaching and enhanced biological activity, thus providing environmental and agricultural advantages.