Amino-functionalized magnetic chitosan beads to enhance immobilization of potassium copper hexacyanoferrate for selective Cs+ removal and facile recovery

Abstract

Potassium copper hexacyanoferrate (KCuHCF)-incorporated magnetic chitosan beads (HMC) were synthesized for both selective Cs⁺ removal in aqueous solutions and facile recovery of the spent adsorbent. To disperse and immobilize large amounts of the KCuHCF, methyl acrylate and diethylenetriamine were sequentially grafted onto the one-step synthesized magnetic chitosan beads. The additional introduction of amino functionality led to the enriched Cu²⁺ ions on the bead surface to incorporate KCuHCF into the grafting matrix. Consequently, the HMC exhibited a high Cs⁺ capacity calculated to be 136.47 mg g^-1 from the Langmuir model, and the equilibrium was established within 4 h. Moreover, the HMC exhibited excellent stability in a wide pH range from 4 to 11 and an outstanding Cs⁺ selectivity (>97%) in seawater (1.11 mg L^-1 Cs⁺). From a practical point of view, the HMC was stable during five successive adsorption cycles and easily recovered by magnets, enabling continuous operation to decontaminate a large volume of wastewater.

Fig. 1. Schematic representation for the HMC synthesis.

Fig. 2. SEM images of (a) and (b) the MC, and (c) and (d) the HMC.

Fig. 3. (a) TGA profiles of the MC and HMC. (b) Magnetization curves of the MC and HMC depends on field (Oe), and images of the HMC before and after separation by magnets (inset).

Fig. 4. (a) XRD patterns of the MC and HMC and (b) FT-IR spectra of beads in each synthesis step.

Fig. 5. XPS N 1s spectra of the (a) MC and (b) HMC.

Fig. 6. (a) Effect of adsorbent dose on removal efficiency (%) and adsorbed amounts (mg g⁻¹). (b) Effect of pH of solution on Cs⁺ adsorption in DI water.

Fig. 7. (a) The Cs⁺ adsorption isotherm curve and (b) adsorption kinetics and plot of t/Q_tvs. t for the HMC.

Fig. 8. (a) Images of cyclic Cs⁺ adsorption and magnetic separation of the HMC. (b) Removal efficiency (%) of the HMC in seawater (1–5 cycles).

Fig. 9. (a) Full range XPS spectrum of the HMC after Cs⁺ adsorption, and (b) the K 2p and (c) Cs 3d XPS spectra. (d) XRD patterns before and after Cs⁺ adsorption of the HMC.