Metal cation sorption ability of immobilized and reticulated chondroitin sulfate or fucoidan through a sol-gel crosslinking scheme

An immobilization scheme, via glycidyloxypropyl-trimethoxysilane sol-gel crosslinking, of chondroitin sulfate (CS) or fucoidan (Fd), inspired by the biological silicate bridge found in CS, is presented here. It revealed to constitute a simple and effective way of producing biopolymer-silicate composites without compromising the carboxylate- and sulfate- groups of the biopolymers, those which play a determinant role in the binding to metal cations. In the case of the Fd composite, the immobilization process resulted in the ∼4-fold enhancement of the negatively charged sorption sites, probably due to unfolding effects induced by the synthesis conditions. Textural analysis of the composites showed a microporous, low surface area (6–12 m2/g), microstructure which did not prevent the observation of relevant sorption features for metal cations, especially for Pb(II) and Cd(II). Rate constants (1–14 g/mg min−1) and affinity constants (79–370 L/mg) in the same order of magnitude of chitosan-based sorbents were determined, whereas capacities (2–24 mg/g) were smaller than the generality of those same sorbents. Globally, the sorption of metal cations by the Fd composite was superior to that by the CS composite. Furthermore, high stability of the sorbents and acceptable reproducibility of the synthesis was observed. Overall, the developed scheme of immobilization of CS and Fd appears capable of providing an effective way for integrating these biopolymers into metal cation-related applications such as biosorption, sensing or separation.

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