Bio-Nanocomposites Based on Layered Double Hydroxides

A new family of functional hybrid nanocomposites based on the intercalation of naturally occurring anionic biopolymers including alginic acid, pectin, κ-carrageenan, ι-carrageenan, and xanthan gum in Zn2Al(OH)6Cl·nH2O layered double hydroxide (LDH), have been synthesized. The “coprecipitation” or “co-organized assembly” method has been successfully employed for the intercalation of such polysaccharides within the Zn2Al LDH. However, the “reconstruction” procedure from the calcined LDH in the presence of the anionic polysaccharides only resulted in a partial intercalation of the organic guest. Particular effort was devoted to the study of ι-carrageenan−Zn2Al systems. An essential feature of the prepared biopolymer−Zn2Al nanocomposites is that the anionic exchange capacity of the pristine LDH is turned into a cationic exchange capacity due to negatively charged groups in the polysaccharide structure that do not interact with the positively charged LDH layers. In agreement with the fact that most of the studied biopolymers interact strongly with calcium ions producing homogeneous gels, the prepared biopolymer−Zn2Al nanocomposites were operative as active phases of sensors for the recognition of calcium ions. Hence, the biopolymer−Zn2Al nanocomposites have been incorporated in carbon paste or PVC matrixes for the development of potentiometric sensors. These devices were applied to calcium determination by direct potentiometry and the best responses were obtained for the sensors based on alginate−LDH and ι-carrageenan−LDH nanocomposites.