Characterization and molecular dynamic studies of chitosan–iron complexes

Chitosan–iron (Cs–Fe) complexes are prepared electrochemically in an aqueous acidic medium in one-compartment cell at different times. XRD pattern of Cs–Fe complex samples has been investigated in the range from 5° to 50° and revealed that chitosan is characterized by certain crystalline peaks at 8.73°, 11.92° and 18.96°. In addition, the crystallinity of Cs–Fe complex samples is increased with increasing the content of Fe³⁺. Ultraviolet–visible (UV–Vis) and Fourier transform-infrared (FTIR) spectroscopies have been used to investigate the optical properties of Cs–Fe complex samples. UV analysis showed that pure chitosan is characterized by absorption band at 214 nm resulted from the amide linkages and at 311 nm, as a shoulder which is attributed to intraligand n → π and π → π* transitions of the chromophoric C=O group. On the other hand, two new bands are observed in Cs–Fe complex samples at nearly 350 and 389 nm with increasing Fe³⁺ content. The optical parameters of all the samples, such as optical band gap energy (E_g), Urbach energy (E_U), dispersion energy (E_d) and oscillator energy (E_o) have been estimated. It is found that these parameters are significantly affected due to the Fe³⁺ content. FTIR spectra revealed that many of the characteristic bands of pure chitosan have been affected either in its position or its intensity due to the presence of Fe³⁺, confirming that the formation of complex between chitosan and Fe³⁺ is occurred. Dielectric relaxation spectroscopy technique has been used to investigate the dielectric properties of pure chitosan and Cs–Fe complex samples in a wide range frequency and a temperature range extended from RT to 433 K. The investigation showed that the existence of Fe³⁺ resulted in a modification in the dielectric constant (ε′) and dielectric loss (ε′′) behaviour. Dielectric loss tangent (tan δ) showed that pure chitosan is characterized by two different types of relaxations, whereas Cs–Fe complex samples are characterized by only one relaxation process.