Effective Removal of Congo Red from Water using Chitosan@UiO‐67 Hydrogel Spheres: Synthesis, Characterization and Adsorption Mechanisms

A chitosan-coated UiO-67 composite hydrogel was prepared by using the gelation property of chitosan in a sodium hydroxide solution. The composite hydrogel has excellent strength and swelling properties. The abundant pore-size structure on the surface of the composite hydrogel promotes the entry of CR pollutant macromolecules into the interior of the hydrogel. The adsorption properties of composite hydrogels were better than those of chitosan and UiO-67 monomer for CR. The composite hydrogel showed the highest adsorption capacity for CR at room temperature. The composite hydrogel still has good adsorption performance after four times of repeated use. It has a good application prospect for treating CR pollutants.

Abstract

A hydrogel (Chitosan@UiO-67) adsorbent was prepared by a green and simple method for the adsorption of Congo red. SEM, FT-IR, TGA, BET, and XRD were used to characterize CS@UiO-67 hydrogel. The effects of temperature, initial CR concentration, contact time, pH, and adsorbent dose on the adsorption properties of CS@UiO-67 hydrogel were studied in batch adsorption experiments. FT-IR analysis showed that the hydroxyl group of chitosan had covalent coordination with Zr, which enhanced the stability of chitosan after complexation with UiO-67. As for the adsorption experiment, the maximum adsorption capacity of the adsorbent calculated by the Langmuir model was 1001.2 mg ⋅ g⁻¹ at room temperature (301 K). Kinetic analysis showed that the adsorption of congo red on CS@UiO-67 hydrogel conformed to the pseudo-second-order model. The adsorption process accorded with the Langmuir model by isotherm analysis. Thermodynamic analysis showed that the adsorption process was spontaneous and exothermic. The adsorption of CR on CS@UiO-67 hydrogel spheres was mainly attributed to electrostatic attraction, hydrogen bonds, and π-π bonds. After four cycles of regeneration, the material removal rate can still reach about 65 %. The new adsorbent has good application prospects.

Zum Volltext