Crosslinking polymer based on amino chitosan for the adsorption of phenoxycarboxylic acids: Kinetics, isotherm, and thermodynamics.

In this work, new crosslinking polymer adsorbents were synthesized based on amino chitosan. Crosslinked amino chitosan (CNCS) was characterized by porous structure, high specific surface area (23.49 m/g), and multiple amino groups. The multiple amino groups can bring more positive charge and make the crosslinking reaction more efficient. CNCS exhibited a superior adsorption capacity for phenoxycarboxylic acids to other crosslinked chitosan adsorbents and enable rapid adsorption of phenoxycarboxylic acids. The maximum adsorption capacity for 2-(2,4-dichlorophenoxy)propionic acid (2,4-DP) of 374 mg/g and 2,4-dichlorophenoxyacetic acid (2,4-D) of 309 mg/g was achieved (adsorbent dosage: 500 mg/L, pH: 3). The adsorption isotherm of 2,4-D could be represented by Freundlich model due to the high R (0.975-0.999). Adsorption kinetics could be better represented by the pseudo-second order model. CNCS also showed good reusability for adsorbing 2,4-D, with removal efficiency remaining above 94 % even after the fifth cycle. The study also discussed the thermodynamics and adsorption mechanism of 2,4-D onto CNCS. In addition, CNCS can remove 86.3 % of 2-chlorophenoxyacetic acid (2-CPA), 95.3 % of 4-CPA, 96 % of 2,4-D, and 95.1 % of 2,4-DP from solution containing multiple phenoxycarboxylic acids, and the adsorption efficiency could reached to 94.4 % (adsorbent dosage: 1000 mg/L).