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

Abstract

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.

Renewable Starch Carriers with Switchable Adsorption Properties

“…A monotonic increase in the change for absorbance of Phth occurs with increasing starch dosage (Figure ), in agreement with independent studies of chitosan- and cellulose-based materials. , It can be inferred that the trends in decolorization of Phth relate to the relative accessibility of the surface −OH groups of starch, in agreement with a related study of chitosan and its modified forms, and by results reported by Udoetok et al for cross-linked cellulose . The variable uptake of Phth for cross-linked chitosan and cellulose was due to variable surface accessibility of the biopolymer – OH groups due to pillaring effects upon cross-linking. , Similar trends were reported by Dehabadi et al for cross-linked starches (AP, AM, and AM50), where surface accessible −OH groups are influenced by steric and branching effects of linear versus branched polysaccharides . Phth undergoes decolorization due to complex formation with polysaccharides due to cooperative interactions such as ion-dipole and hydrophobic effects, as a result of shifts in the p K a of the dye upon complex formation as reported for β-CD/Phth …”

“…A monotonic increase in the change for absorbance of Phth occurs with increasing starch dosage (Figure 7), in agreement with independent studies of chitosan-and cellulosebased materials. 32,53 It can be inferred that the trends in decolorization of Phth relate to the relative accessibility of the surface −OH groups of starch, in agreement with a related study of chitosan and its modified forms, 57 and by results reported by Udoetok et al for cross-linked cellulose. 32 The variable uptake of Phth for cross-linked chitosan and cellulose was due to variable surface accessibility of the biopolymer − OH groups due to pillaring ef fects upon cross-linking.…”

“…32 The variable uptake of Phth for cross-linked chitosan and cellulose was due to variable surface accessibility of the biopolymer − OH groups due to pillaring ef fects upon cross-linking. 32,57 Similar trends were reported by Dehabadi et al for cross-linked starches (AP, AM, and AM50), where surface accessible −OH groups are influenced by steric and branching effects of linear versus branched polysaccharides. 41 Phth undergoes decolorization due to complex formation with polysaccharides due to cooperative interactions such as ion-dipole and hydrophobic effects, as a result of shifts in the pK a of the dye upon complex formation as reported for β-CD/Phth.…”

Surface-Modified Chitosan: An Adsorption Study of a “Tweezer-Like” Biopolymer with Fluorescein

“…This method provides insight related to the presence of accessible hydrophilic functional groups of an adsorbent and a measure of its hydrophile-lipophile balance (HLB). The swelling percentage of CS-Ac-An was 40%, in comparison to 400% for pristine chitosan [47]. This considerable drop was related to a reduction of the surface hydrophilicity after grafting of aniline and the reduction in the number of free -NH 2 groups that may undergo hydrogen bonding.…”

“…Swelling tests were performed at ambient pH (7.0) by mixing 100 mg of CS-Ac-An with 7 mL of water for 24 h. The weight of swollen CS-Ac-An samples was determined after drying to constant on a pre-weighed filter paper (W s ). The dry weight (W d ) was determined after drying the hydrated adsorbent in a vacuum oven for 12 h at 50 • C [47]. The swelling ratio was obtained according to Equation (2).…”