In this study, a novel magnetic bio-adsorbent was synthesized by modifying cotton linter (CL) cellulose with deep eutectic solvents (DESs) and Fe3O4 magnetic nanoparticles. The adsorption capacity of CL, Fe3O4/CL, Fe3O4/CL-oxidation, and Fe3O4/CL-DES for Cu2+ was 11.0, 66.1, 85.7, and 93.1 mg g-1, respectively, under the optimal adsorption conditions of an initial pH value of 6.0, stirring rate of 300 rpm, and a temperature of 30 °C. The presence of Fe3O4 nanoparticles increased the proportion of hydroxyl groups and thus improved the ion-exchange ability of Cu2+. The dissolution of DES significantly decreased fiber crystallinity and increased the number of hydroxyl group (amorphous regions increased), thus improving the chelation reaction of Cu2+, which was favorable for surface adsorption. In addition, we used the Langmuir and Freundlich isothermal models to simulate the adsorption behavior of Fe3O4/CL-DES, and the results indicated that Cu2+ follows a Freundlich isotherm model of multilayer adsorption. The fitting of the adsorption kinetics model indicated that the adsorption process involves multiple adsorption mechanisms and can be described by a quasi-second-order model. These results provide a potential method for the preparation of high-efficiency adsorbents from low-value cotton linter, which has broad application prospects in wastewater treatment.
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