Synthesis of crosslinked chitosan‐crown ethers and evaluation of these products as adsorbents for metal ions

Two new crosslinked‐crown ethers (CCTS‐N=CH‐B‐15‐C‐5 and CCTS‐N=CH‐B‐18‐C‐6) were synthesized by the reaction of crosslinked chitosan (CCTS‐NH 2 ) with 4`‐formyl benzo‐15‐crown‐5 and 4`‐formyl benzo‐18‐crown‐6. Their structures were confirmed with elemental analysis, infrared spectra analysis, solid‐state 13 C NMR analysis, X‐ray diffraction analysis, and differential scanning calorimetry thermogram analysis. In the infrared spectra of CCTS‐N=CH‐B‐15‐C‐5 and CCTS‐N=CH‐B‐18‐C‐6, the characteristic peak of C=N stretch vibration appeared at 1650 cm −1 . The X‐ray diffraction analysis showed that the peak at 2θ = 20° decreased greatly in CCTS‐N=CH‐B‐15‐C‐5 and CCTS‐N=CH‐B‐18‐C‐6. In the 13 C NMR spectra of CCTS‐N=CH‐B‐15‐C‐5 and CCTS‐N=CH‐B‐18‐C‐6, the characteristic peak of aromatic carbon appeared at 128‐ppm, the characteristic peak of carbon in the C=N group appeared at 151 ppm. The adsorption and selectivity properties of CCTS‐N=CH‐B‐15‐C‐5 and CCTS‐N=CH‐B‐18‐C‐6 for Ag + , Pd 2+ , Pb 2+ , Cd 2+ , and Cr 3+ were studied. The experimental results showed that the two crosslinked chitosan‐crown ethers have not only good adsorption capacities for Ag + and Pd 2+ , but also high selectivity for the adsorption of Ag + or Pd 2+ with the coexistence of Pb 2+ and Cr 3+ . The selectivity coefficients of CCTS‐N=CH‐B‐15‐C‐5 and CCTS‐N=CH‐B‐18‐C‐6 were $K_{{\rm Pd}^{2+}/{\rm Pb}^{2+}} = 9.9, K_{{\rm Ag}^{+}/{\rm Pb}^{2+}} = 9.8, K_{{\rm Pd}^{2+}/{\rm Cr}^{3+}} = \infty, K_{{\rm Pd}^{2+}/{\rm Pb}^{2+}} = 11.5, K_{{\rm Ag}^{+}/{\rm Pb}^{2+}} = 7.1, K_{{\rm Pd}^{2+}/{\rm Cr}^{3+}} = \infty,$ respectively. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 501–506, 1998