Magnetic resonance study of chitosan bio-membranes with proton conductivity properties

This work reports results from impedance spectroscopy, nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) of chitosan bio-membranes, containing acetic acid and either with or without glycerol. Ionic conductivity value of 2.9×10−5 S/cm was obtained at room temperature for samples prepared with 5 wt% of acetic acid. Activation energies extracted from the conductivity data are in the range of 0.67 to 0.86 eV (65 to 83 kJ/mol). Proton (1H) line shapes and spin-lattice relaxation times were measured as a function of temperature. The NMR results show that the proton mobility of the membranes prepared with glycerol is higher than those prepared without glycerol. EPR experiments were carried out in samples doped with copper perchlorate. Analysis of the spin Hamiltonian parameters indicate that the Cu2+ ions are located in axially distorted sites, with the cooper ion coordinated to nitrogen and oxygen atoms. The in-plane metal-ligand σ-bonding was evaluated using the EPR data to obtain information about the Cu2+ ligand bond nature for the chitosan bio-membranes.

► Chitosan-based membranes with or without glycerol were prepared and studied. ► NMR and σ studies show that the addition of glycerol increases the ionic mobility. ► EPR experiments reveal that the Cu2+ ions are located in axially distorted sites. ► Spin Hamiltonian parameters indicates that the Cu2+ ions are coordinated to N and O. ► In-plane copper 3d orbital and ligand orbitals is moderately covalent.