Sorption of methyl-parathion and carbaryl by an organo-bentonite

Abstract

The modification of bentonite clays by cetyltrimethylammonium bromide (CTMAB) surfactant via cation-exchange produces materials ("organo-clays") with an increased capacity for sorbing organic compounds such as pesticides. The sorption from solutions of two nonionic pesticides, methyl-parathion and carbaryl, by an organobentonite has been investigated. The pesticides are partitioned into the surfactant. The distribution coefficients, K ss , show a strong dependence on surfactant loading of the bentonite. The surfactant configuration at the clay surface has a marked influence on the effective volume and density of the bound surfactant. At low surfactant loadings, the K ss values increased, reached a maximum, and then decreased as the extent of loading increased. At low loading levels, the surfactant appears to form a monolayer (organic film) that effectively adsorbs the pesticides, resulting in very high K ss values. At high loadings, the sorbed surfactant appears to form a bulk-like medium that behaves essentially as a distribution phase. As a result, the K ss values decreased appreciably, and became less dependent on the CTMAB loading. Moreover, when the surfactant concentration in water was greater than the critical micelle concentration, the surfactant uptake on the clay reaches a plateau and an increasing fraction of the micelles remain in solution, together with the pesticides which bound to them. The competition for the pesticides between the aqueous micelles and the sorbed surfactant leads to a decrease in distribution coefficients.

Effect of CPC, Brij-35, and SDBS Surfactants on the Adsorption and Movement of Carbofuran in Indian Soils

“…There exist highly significant correlations between K F * and K D * constants and clay + silt content of the soils in the presence of all the three surfactants. It could be ascribed to the fact that the molecules of the cationic surfactant are adsorbed on the clay fraction of the soil Zeng et al, 2006;Rodriguez-Cruz et al, 2006), whereas the molecules of the non-ionic and anionic surfactant are adsorbed to the fine silt content of the soils (Rodriguez-Cruz et al, 2005;Hardy et al, 1999;Marques et al, 2002). Highly significant correlations with CEC at 1 × CMC and 2 × CMC of CPC also indicate an increase in the number of exchangeable sites on the soil surfaces owing to increase in the organic carbon content of the soils.…”

A review on the adsorption of diuron, carbaryl, and alachlor using natural and activated clays

“…Zeng et al (2006) modified bentonite clays using CTAB surfactant to increase its capacity for adsorbing organic compounds such as nonionic pesticides, including carbaryl. The pesticides were partitioned into the surfactant and the distribution coefficients K ss were measured.…”

“…For instance, considerably more carbaryl is sorbed to the Ca 2+ exchanged clay than in the case of Mg 2+ and Mg 2+ has the largest enthalpy of hydration of all the cations studied (Fernandes de Oliveira et al, 2005). Zeng et al (2006) modified bentonite clays using CTAB surfactant to increase its capacity for adsorbing organic compounds such as nonionic pesticides, including carbaryl. The pesticides were partitioned into the surfactant and the distribution coefficients K ss were measured.…”

Twofold role of calcined hydrotalcites in the degradation of methyl parathion pesticide

“…Studies concerning the surface modification of cationic clays and hydrotalcites with organic ions, as pesticide sorbents, have been reviewed by Cornejo et al [ 5 ]. For instance, MP undergoes degradation when it is sorbed on a bentonite (cationic clay) [ 6 – 8 ]. Moreover, the bentonite sorption capacity may be increased if the clay is exchanged with cetyltrimethylammonium bromide (CTAB).…”