Modified magnetic chitosan materials for heavy metal adsorption: a review

Abstract

Magnetic chitosan materials have the characteristics of both chitosan and magnetic particle nuclei, showing the characteristics of easy separation and recovery, strong adsorption capacity and high mechanical strength, and have received extensive attention in adsorption, especially in the treatment of heavy metal ions. In order to further improve its performance, many studies have modified magnetic chitosan materials. This review discusses the strategies for the preparation of magnetic chitosan using coprecipitation, crosslinking, and other methods in detail. Besides, this review mainly summarizes the application of modified magnetic chitosan materials in the removal of heavy metal ions in wastewater in recent years. Finally, this review also discusses the adsorption mechanism, and puts forward the prospect of the future development of magnetic chitosan in wastewater treatment.

Fig. 1. (a) Chemical structure and (b) SEM micrographs of chitosan, (c) typical morphology of magnetic nanocomposites. The magnetic nanoparticle is represented by a blue ball. Gray represents non-magnetic entities and matrix materials, (d) SEM micrographs of Fe₃O₄.

Fig. 2. (a and b) In situ synthesis steps of magnetic chitosan.

Fig. 3. (a) Schematic diagram of the formation mechanism of Fe₃O₄ magnetic nanoparticles, (b) the main structure of magnetic nanoparticles modified by organic materials, (c) Fe₃O₄@SiO₂-chitosan synthesis steps, (d) SEM images of the Fe₃O₄ (i and ii), Fe₃O₄@SiO₂ (iii and iv), (e) schematic diagram of the formation of magnetic chitosan nanocomposites by two-step method, (f) SEM images of Fe₃O₄-CS beads, and (g) SEM images of magnetic chitosan microspheres.

Fig. 4. Schematic diagram of magnetic chitosan synthesized by the (a) crosslinking method and (b) related crosslinking agents.

Fig. 5. Schematic diagram of magnetic chitosan synthesized by (a) spray drying and photochemical method, (b) electrostatic drop method.

Fig. 6. Effect of solution pH on sorption of Fe₃O₄-CS and Fe₃O₄-CS/EDTA toward heavy metals (a) and MB (b), (c) internal SEM images of MCMAs, (d) magnetization curve of MCMAs, (e) magnetic separation of MCMAs, (f) effect of contact time on Cu(ii) removal, and (g) FT-IR spectra of MCMAs before and after Cu(ii) adsorption.

Fig. 7. (a) Effect of graphene oxide on the Cu²⁺ adsorption capacity of MCGON adsorbent, (b) comparison between the experimental and modeled isotherm plots for the adsorption of Cu²⁺ onto the MCGON adsorbent, SEM images showing the surface morphology of the (c) chitosan and (d) chitosan-cellulose hydrogel beads, (e) adsorption capacity diagram of magnetic chitosan materials modified by different methods of Cu(ii).

Fig. 8. (a) Adsorption capacity diagram of magnetic chitosan materials modified by different methods of Pb(ii), (b and c) SEM micrographs of MCS-Sch, (d) XRD patterns of Fe₃O₄, chitosan and MCS-Sch, (e) FTIR spectra of (i) CoFe₂O₄, (ii) amine-CoFe₂O₄, (iii) chitosan, (iv) chitosan/CoFe₂O₄ and (v) TEPA modified chitosan/CoFe₂O₄, (f) adsorption kinetics of Cu(ii) and Pb(ii) on chitosan/CoFe₂O₄, and (g) adsorption kinetics of Cu(ii) and Pb(ii) on TEPA modified chitosan/CoFe₂O₄.

Fig. 9. (a) FT-IR of Pb(ii)-IMB and S. marcescens, (b) XRD spectra of Pb(ii)-IMB and Fe₃O₄, (c) desorption and adsorption of CH-MNP-CA nano-adsorbents over five runs, (d) comparison chart of removal efficiency percentage of unmodified chitosan, magnetic chitosan and MGC nanoadsorbent in adsorption of Cu²⁺ and Pb²⁺ ions, (e) FE-SEM images of guanidinylated chitosan, (f) FE-SEM images of MGC nanobiocomposite.

Fig. 10. (a) FE-SEM images of the cross-section of MCF3DG, (b and c) photographs of a lightweight and strong MCF3DG supporting weight, (d) the combined influence of the lead ion concentration and adsorbent dosage (MCF3DG) (i); the combined influence of the adsorbent dosage and contact time (ii); the combined influence of the adsorbent dosage and solution pH (iii) on lead ion removal efficiency.

Fig. 11. (a) Adsorption capacity diagram of magnetic chitosan materials modified by different methods of Cr(vi), (b) Cr(vi) adsorption–desorption behaviors on Fe(iii)-CBs, (c) adsorption kinetics of Cr(vi) ions. (d) TEM images of hollow Fe₃O₄/SiO₂/CS-TETA nanocomposites, (e) SEM images of MCPs, (f) SEM images of DMCPs, (g) ZP–pH profiles of the magnetic adsorbents, and (h) effect of pH on the adsorption capacity of Cr(vi).

Fig. 12. (a) Effect of pH on the removal of metal ions onto EDTA-M-Cs, (b) SEM micrographs for the Ch/g-HNTs@ZnγM composite, the experimental and kinetic plots of (c) V(v) and (d) Pd(ii) adsorption on Fe₃O₄-CSN, (e) effects of pH on adsorption behavior of Co(ii), and (f) adsorption-desorption recycles for the removal of Co(ii).

Fig. 13. Summary of the magnetic chitosan adsorption mechanism.

Fig. 14. (a) Effect of pH on the metal ions removal using the PVA/chitosan/a-Fe₃O₄-2 nanofibrous membrane,, (b-1) Cr 2p XPS spectra of Cr-loaded VMCP; (b-2) N 1s spectra before (i) and after adsorption (ii); (b-3) O 1s spectra before (i) and after adsorption (ii).

Fig. 15. Proposed adsorption mechanism using FFO@Sil@Chi-DTPA to capture MB and Pb(ii) simultaneously.