FTIR, UV-VIS, and DFT Approach to Study the Structural, Optical and Thermal Properties of Chitosan Biopolymer

Abstract

This study investigates the structural, optical, and thermal properties of chitosan (CS) biopolymer using experimental and computational approaches. Fourier Transform Infrared Spectroscopy (FTIR) confirmed the presence of two key functional groups–hydroxyl (OH) and amine (NH/NH₂)–which play a crucial role in CS interactions. X-ray Diffraction (XRD) analysis revealed a mixed-phase structure, comprising both crystalline and amorphous regions. Various crystallographic parameters, including full width at half maximum (FWHM), degree of crystallinity, lattice strain, dislocation density, inter-band crystallinity, and stacking faults, indicated an increase in crystallinity with greater CS film thickness. Optical characterization using Tauc plots showed a decrease in bandgap energy from 5.54 to 5.12 eV with increasing film thickness. Urbach energy analysis allowed for the estimation of steepness parameters and electron-phonon interaction energy (E_e–ph), which exhibited a reduction from 11.398 to 10.315 eV. Computational studies were performed using Density Functional Theory (DFT) at the B3LYP/6-311++G(d,p) level via the Gaussian 09 program to determine electronic and thermal properties. Additionally, thermal properties such as entropy, heat capacity, and enthalpy were evaluated using the Materials Studio software. Monte Carlo simulations were employed to estimate the adsorption energy of CS on Fe, Al, and Cu surfaces, revealing that Fe exhibited the most stable and strong coordination with CS due to its unique coordination geometry. These findings provide valuable insights into the structural and functional characteristics of CS films, contributing to their potential applications in various fields.