Using deep eutectic solvent dissolved low-value cotton linter based efficient magnetic adsorbents for heavy metal removal.

In this study, a novel magnetic bio-adsorbent was synthesized by modifying cotton linter (CL) cellulose with deep eutectic solvents (DESs) and FeO magnetic nanoparticles. The adsorption capacity of CL, FeO/CL, FeO/CL-oxidation, and FeO/CL-DES for Cu was 11.0, 66.1, 85.7, and 93.1 mg g, 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 FeO nanoparticles increased the proportion of hydroxyl groups and thus improved the ion-exchange ability of Cu. The dissolution of DES significantly decreased fiber crystallinity and increased the number of hydroxyl group (amorphous regions increased), thus improving the chelation reaction of Cu, which was favorable for surface adsorption. In addition, we used the Langmuir and Freundlich isothermal models to simulate the adsorption behavior of FeO/CL-DES, and the results indicated that Cu 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.