Authors: Qingru Zeng Bohan Liao Bo Yang Hongxiao Tang Nandong Xue
Publish Date: 2006/03/31
Volume: 42, Issue: 5, Pages: 457-463
Abstract
The modification of bentonite clays by cetyltrimethylammonium bromide CTMAB surfactant via cationexchange produces materials “organoclays” with an increased capacity for sorbing organic compounds such as pesticides The sorption from solutions of two nonionic pesticides methylparathion 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 bulklike 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
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