Deposition of polydopamine onto magnetic chitosan microspheres for efficient adsorption of Congo red and easy recycling

To achieve effective adsorptive removal of Congo red (CR) from wastewater, magnetic chitosan microspheres CTS-Fe 3 O 4 were initially synthesized through emulsion crosslinking, followed by the preparation of polydopamine-coated microspheres PDA-CTS-Fe 3 O 4 via deposition of polydopamine (PDA) onto CTS-Fe 3 O 4. The physicochemical properties of synthesized microspheres were systematically characterized. The influence of adsorbent dosage, contact time, pH, ionic strength, and temperature was investigated, and the results demonstrated that PDA-CTS-Fe 3 O 4 (679.99 mg·g −1 ) exhibited superior adsorption performance compared with CTS-Fe 3 O 4 (595.21 mg·g −1 ) towards CR. The adsorption processes of both microspheres adhered to the pseudo-first-order kinetic model and Langmuir isotherm model, and were determined to be spontaneous and endothermic. The adsorption energy between PDA-CTS-Fe 3 O 4 and CR was higher than that between CTS-Fe 3 O 4 and CR, and the enhanced adsorption capacity of CR onto PDA-CTS-Fe 3 O 4 was attributed to the synergistic effect of π-π stacking interaction, hydrogen bonding, and electrostatic attractive force.