Advanced molecular interaction in Cu2+-alginate beads with high M/G ratio for the intercalation of Li+ and Mg2+ ions

Abstract

Molecular interactions in Cu2+-alginate beads blended at high and low mannuronate-to-guluronate residue ratios, hereafter denoted as H-Alg and L-Alg, respectively, during the intercalation of Li+ and Mg2+ were analyzed using X-ray absorption spectroscopy. Cu2+ ions are slightly deoxidized from Cu(II) to Cu(I) after the intercalation, but their oxidation state remains as Cu(II). The lengths of Cu - O bonds are elongated and coordination numbers are more decreased in flexible conformation of H-Alg, compared with structured conformation of L-Alg after intercalation of Li+ and Mg2+. These results suggest that the flexible conformation can facilitate metal intercalation by rearranging the alginate G junctions as forming a coordinate structure in alginate G junctions. Moreover, the higher adsorption capacity for Mg2+ in HAlg corroborates its advanced molecular interaction in flexible conformation. Overall, this study helps elucidate the localized molecular interactions in alginate beads that are cross-linked noncovalently with divalent cations. (C) 2019 Elsevier B.V. All rights reserved.