Removal of Cr(VI) from aqueous solution using amino-modified Fe3O4-SiO2-chitosan magnetic microspheres with high acid resistance and adsorption capacity

A novel, bioadsorbent material of polyethylenimine-modified magnetic chitosan microspheres enwrapping magnetic silica nanoparticles (Fe3O4-SiO2-CTS-PEI) was prepared under relatively mild conditions. The characterization results indicated that the adsorbent exhibited high acid resistance and magnetic responsiveness. The Fe3O4 loss of the adsorbent was measured as 0.09% after immersion in pH 2.0 water for 24 h, and the saturated magnetization was 11.7 emu/g. The introduction of PEI obviously improved the adsorption capacity of Cr(VI) onto the adsorbent by approximately 2.5 times. The adsorption isotherms and kinetics preferably fit the Langmuir model and the pseudo-second-order model. The maximum adsorption capacity was determined as 236.4 mg/g at 25 degrees C, which was much improved compared to other magnetic chitosan materials, and the equilibrium was reached within 60 to 120 min. The obtained thermodynamic parameters revealed the spontaneous and endothermic nature of the adsorption process. Furthermore, the Cr(VI)-adsorbed adsorbent could be effectively regenerated using a 0.1 mol/L NaOH solution, and the adsorbent showed a good reusability. Due to the properties of good acid resistance, strong magnetic responsiveness, high adsorption capacity, and relatively rapid adsorption rate, the Fe3O4-SiO2-CTS-PEI microspheres have a potential use in Cr(VI) removal from acidic wastewater. (C) 2015 Wiley Periodicals, Inc.