Adsorption of haem by magnetic chitosan microspheres: Optimal conditions, adsorption mechanisms and density...

Magnetic chitosan microspheres (Al@CTS@Fe₃O₄) were prepared for haem separation via chemical cross-linking of chitosan, Fe₃O₄ and AlCl₃·6H₂O. The properties of the Al@CTS@Fe₃O₄ microspheres were investigated through techniques including XRD, TEM, FTIR, BET analysis, SEM, TG, VSM, XPS and pHpzc analysis. The haem adsorption of Al@CTS@Fe₃O₄ was optimized via a Box-Behnken design (BBD) with three operating factors: Fe₃O₄ dose (0.5-1.3 g), AlCl₃·6H₂O concentration (0.25-1.25 mol/L) and glutaraldehyde dose (2-6 mL). The optimal haem adsorption effect was achieved with 1.1 g of Fe₃O₄, 0.75 mol/L AlCl₃·6H₂O, and 3 mL of glutaraldehyde. The adsorption kinetics and isotherms demonstrated that haem adsorption by the Al@CTS@Fe₃O₄ microspheres was best described by the pseudo-second-order model. The maximum adsorption capacity is 33.875 mg/g at pH 6. After six adsorption-desorption cycles, the removal of haem still reached 53.83 %. The surface adsorption mechanism of haem on Al@CTS@Fe₃O₄ can be attributed to electrostatic, hydrogen bonding, and n-π interactions. Thermodynamic calculations indicated that the adsorption process is spontaneous, with the microspheres preferentially accepting electrons and haem preferentially providing electrons. Consequently, the Al@CTS@Fe₃O₄ microspheres exhibit considerable potential as adsorbents for haem separation.