Study of the synthesis of chitosan derivatives containing benzo-21-crown-7 and their adsorption properties for metal ions

Three new chitosan crown ethers, N-Schiff base-type chitosan crown others (1, 111), and N-secondary amino type chitosan crown ether (H) were prepared, N-Schiff base-type chitosan crown ethers (I, III) were synthesized by the reaction of 4'-formly-benzo-21-crown-7 with chitosan or crosslinked chitosan. N-Secondary amino type chitosan-crown ether (11) was prepared through the reaction of N-Schiff base type chitosan crown ether (1) with sodium brohydride. Their structures were characterized by elemental analysis, infrared spectra analysis, X-ray diffraction analysis, and solid-state C-13 NMR analysis. In the infrared spectra, characteristic peaks of C=N stretch vibration appeared at 1636 cm(-1) for I and 1652 cm(-1) for II; characteristic peaks of N-H stretch vibration appeared at 1570 cm(-1) in II. The X-ray diffraction analysis showed that the peaks at 2theta = 10degrees and 28degrees disappeared in chitosan derivatives I and III, respectively; the peak at 2theta = 10degrees disappeared and the peak at 2theta = 28degrees decreased in chitosan-crown ether II; and the peak at 2theta = 20degrees decreased in all chitosan derivatives. In the solid-state C-13 NMR, characteristic aromatic carbon appeared at 129 ppm in all chitosan derivatives, and the characteristic peaks of carbon in C=N groups appeared at 151 ppm in chitosan crown ethers I and III. The adsorption and selectivity properties of I, II, and III for Pd2+, Au3+, Pt4+, Ag+, Cu2+, and Hg2+ were studied, Experimental results showed these adsorbents not only had good adsorption capacities for noble metal ions Pd2+, Au3+, Pt4+, and Ag+, but also high selectivity for the adsorption of Pd2+ with the coexistence of Cu2+ and Hg2+. Chitosan-crown ether II only adsorbs Hg2+ and does not adsorbs Cu2+ in an aqueous system containing Pd2+, Cu2+, and Hg2+. (C) 2002 John Wiley Sons, Inc.