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

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 center dot 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 pi-pi bonds. After four cycles of regeneration, the material removal rate can still reach about 65 %. The new adsorbent has good application prospects.