In the present work, theoretical studies based on density functional theory (DFT) have performed to comprehend the interaction between the Chitosan (CS) monomer and three types of nanotubes, namely TiO2 nanotube (TiO2NT), SiO2 nanotube (SiO2NT) and Carbon nanotube (CNT). First, the geometry of nanotubes and CS monomer and various configuration of their composites have optimized. Subsequently, the adsorption energy and equilibrium distance between CS monomer and nanotubes for the energetically most favorable Structure have calculated by the DFT method. The achieved results indicate that CS monomer has a tendency to be chemisorbed onto the surface of TiO2NT (Ei = 1.41 eV) while the type of interactions for the SiO2NT (Ei = 0.24 eV) and CNT (Ei = 0.22 eV) systems are noncovalent and the CS monomer physisorbed onto the surface of these nanotubes. It was found that the interaction of CS with TiO2NT due to the shorter equilibrium distance and greater adsorption energy is stronger than other nanotubes. We have also investigated the influence of TiO2NT diameter on the adsorption feature, and the results revealed that the adsorption energy between CS and TiO2NTs reduces by increasing TiO2NTs diameter. Moreover, the electronic density of state (DOS) of the energetically most favorable composites was analyzed. The findings of the current work would be very beneficial for scientists to explore the potential applications of these nanocomposite materials in biomedical field such as drug delivery and tissue engineering.
