Binding Mechanism of 2,4‐Dichlorophenoxyacetic Acid by Organo‐Clays

Abstract

AbstractThe interaction of the herbicide 2,4‐dichlorophenoxyacetic acid (2,4‐D) with decylammonium‐montmorillonite (C10M) and decylammonium‐vermiculite (C10V) was studied by measuring 2,4‐D adsorption at different pH levels, and by preparing herbicide‐organic clay complexes which were characterized by x‐ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT‐IR). The adsorption of 2,4‐D at different pH values indicated that the undissociated form was preferentially adsorbed on C10M, whereas the anionic form was adsorbed by C10V. The adsorption of 2,4‐D was much greater for C10V than for C10M. X‐ray diffraction diffractograms and FT‐IR spectra of C10M did not show any changes after exposure to 2,4‐D, indicating adsorption on external surfaces by weak lyopbilic, aromatic ring‐alkylchain(tail), bond. The d001 values of the two C10V samples expanded after 2,4‐D exposure from 2.1 to 2.9 nm and from 2.4 to 3.3 nm, indicating interlayer adsorption of the herbicide. The FT‐IR spectrum of herbicide‐C10V complex showed the presence of a small amount of the molecular form of 2,4‐D weakly adsorbed on external surfaces by lyophilic (ring‐tail) bonding, but most of the herbicide molecules were adsorbed at the interlayer spaces by hydrogen bonds between carbonyl group (vc=0 at 1634 cm−1) of 2,4‐D and ammonium group of the interlayer organic cations. Some 2,4‐D molecules in C10V complex appeared to be dissociated as suggested by two bands at 1590 and 1330 cm−1, which corresponded to the unsymmetrical and symmetrical vibrations, respectively, of the COO− groups.