Elucidating the adsorption mechanisms of anionic dyes on chitosan (110) surface in aqueous medium by quantum chemical and molecular dynamics

This work reports the molecular dynamic (MD) simulation modeling of the adsorption mechanisms of anionic dyes; tartrazine (TRZ), sunset yellow (SSY), and brilliant blue (BRB) on the chitosan (Chit) (110) surface. Quantum chemical descriptors calculations suggested a strong inclination of chitosan to donate electrons indi-cating that it can be readily protonated in its nitrogen atoms in an acidic medium, which act as potential interaction sites for the anionic dyes. Simulation results indicated that the adsorption process was performed with a parallel orientation of the dyes on the chitosan (110) surface. The adsorption energies were -8459.71, -5278.01, and -2486.50 kcal/mol for TRZ, SSY, and BRB, respectively. Therefore, the studied biopolymer indicated the highest adsorption ability for TRZ dye (Ead (TRZ-Chit) >Ead (SSY-Chit) > Ead (BRB-Chit)). The adsorption energy analysis showed that the removal of the studied molecules was an exothermic chemisorption process, which could be governed by steric parameters according to the findings obtained with the MD and quantum chemical descriptors. The radial distribution function (RDF) further confirmed the interactions, wherein the bonding distances between dyes and the chitosan surface were lower than 3.5 angstrom. The obtained dynamic descriptors results revealed appropriate fitting with experimental data.

Automated summary

This study utilized molecular dynamic simulation to investigate the adsorption mechanisms of anionic dyes on the chitosan surface, revealing that chitosan exhibited the highest adsorption ability for the tartrazine dye. The adsorption process was found to be an exothermic chemisorption process.