Spectroscopic, Hartree–Fock and DFT study of the molecular structure and electronic properties of functionalized chitosan and chitosan-graphene oxide for electronic applications.

Chitosan is a natural biopolymer that is classified among the most important biodegradable polysaccharides widely used in different environmental and industrial applications, such as tissue engineering, biomedical devices, electronics and supercapacitors, water filtration, and food packaging. Theoretical infrared spectra of chitosan were computed using both Hartree–Fock (HF) and Density Functional Theory (DFT) methods, with different basis sets, including 3-21g, 6-31g, 6-311g, LANL2DZ, and LANL2MB, to identify the ideal basis set that is closest to the experimental results. DFT:B3LYP/3-21g** was the best model for chitosan and was used to investigate its functionalization with various functional groups such as (OH, NH₂, COOH, CH₃, CHO, CN, SH) and graphene oxide (GO). Molecular electrostatic potential, total dipole moment, and HOMO–LUMO band gap (∆E) calculations indicated that Chitosan-GO is the most reactive and stable structure, with a ∆E of 0.3023 eV. Consequently, Chitosan–GO composite was prepared and analyzed using ATR–FTIR spectroscopy. The spectra revealed a new band at 1620 cm⁻¹, which was attributed to the COOH group of GO and was red-shifted owing to the hydrogen bonding between the GO and NH₂ of chitosan, confirming the synthesis of Chitosan–GO composite. The significant improvement in the electronic properties of Chitosan-GO based on the obtained results promotes it to be used in electronic applications such as the development of electrodes for supercapacitors. [ABSTRACT FROM AUTHOR]