Chitosan/bentonite nanocomposite: Preliminary studies of its potentiometric response to nitrate ions in water

The scope of this work is to obtain and characterize a nanobiocomposite as Ion Selective Electrodes (ISE) for nitrate ion determination in water. This nanocomposite is based upon the intercalation of chitosan, a cationic biopolymer, in bentonite. Chitosan (CS)/bentonite nanocomposites were prepared by ionic exchange. The amino groups in the CS can be protonated in acidic solution and they can replace the interlayer cation on the clay surface. Nitrate (II) was added at the end of the preparation process for blocking the cationic exchange sites and enhance the potentiometric response to nitrate. Chitosan/bentonite films were obtained by solvent cast method. X-Ray Diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS) and Fourier-Transformed-Infrared Spectroscopy (FTIR) were used to characterize the nanocomposites. These studies confirm that the chitosan was intercalated into the bentonite interlayer spacing due to the electrostatic attraction between NH₃⁺ groups and the negatively charge bentonite surface. These measurements confirm that there exist possibilities to reverse the ion exchange of this nanocomposite. Potentiometric measurements were performed using an Ag/AgCl reference electrode and an ISE with chitosan/bentonite membranes deposited on a graphite-epoxy electrode as a working electrode. A linear fitting was performed between 2×10^-4M and 8×10^-1M of concentration with a near Nernstian slope of -54.6 mV/dec. The selectivity towards some interfering ions was calculated according to the Separate Solution Method (SSM).