Biopolymer-clay nanocomposites based on chitosan intercalated in montmorillonite

The objective of this work is the intercalation of the cationic biopolymer chitosan in Na+-montmorillonite, providing compact and robust three-dimensional nanocomposites with interesting functional properties. CHN chemical analysis, X-ray diffraction, Fourier transform infrared spectroscopy, scanning transmission electron microscopy, energy-dispersion X-ray analysis, and thermal analysis have been employed in the characterization of the nanocomposites, confirming the adsorption in mono- or bilayers of chitosan chains depending on the relative amount of chitosan with respect to the cationic exchange capacity of the clay. The first chitosan layer is adsorbed through a cationic exchange procedure, while the second layer is adsorbed in the acetate salt form. Because the deintercalation of the biopolymer is very difficult, the -NH3+Ac- species belonging to the chitosan second layer act as anionic exchange sites and, in this way, such nanocomposites become suitable systems for the detection of anions. These materials have been successfully used in the development of bulk-modified electrodes exhibiting numerous advantages as easy surface renewal, ruggedness, and long-time stability. The resulting sensors are applied in the potentiometric determination of several anions, showing a higher selectivity toward monovalent anions. This selectivity behavior could be explained by the special arrangement of the polymer as a nanostructured bidimensional system.