Sequestration of agrochemicals from aqueous media using cross-linked chitosan-based sorbents

The sorption properties are reported for chitosan and its cross-linked forms (chitosan-glutaraldehyde; CG) with some model agrochemical sorbates [pentachlorophenol (PCP), 2,4-dichlorophenol (2,4-DCP) and 2,4-dichlorophenoxy acetic acid (2,4-D), dicamba and carbofuran]. The CG cross-linked materials were prepared at variable C:G monomer mole ratios: 1:0.5 (CG1), 1:1 (CG2), (CG3). The sorbents were characterized using diffuse reflectance infrared Fourier transform spectroscopy, thermogravimetric analysis and a dye sorption method using phenolphthalein. The sorption studies were carried out in aqueous solution at pH 9 except for dicamba and carbofuran (pH 7). The isotherm results were evaluated by the Sips, Freundlich, and Langmuir models. The Sips model provided the "best-fit" results where the sorption capacity increased as the cross-linker content of the CG materials increased. The relative uptake for chitosan and its cross-linked forms adopted the following order: PCP > 2,4-DCP > 2,4-D. In the case of dicamba and carbofuran, the former had a higher sorptive uptake. The variable uptake of the sorbates were attributed to their relative lipophilicity where the main driving force of these solid-solution systems relates to hydrophobic effects, in accordance with the tunable physicochemical properties of the chitosan sorbent materials.