A combined molecular dynamic simulation, DFT calculations, and experimental study of the eriochrome black T dye adsorption onto chitosan in aqueous solutions

This study aims to evaluate and understand the adsorption of eriochrome black T (EB) by chitosan extracted from local shrimp shells under different experimental conditions. Chitosan samples were characterized by XRD, SEM, and FTIR. Experimental results indicate that the process was pH-dependent with a high adsorption capacity in acidic medium. The adsorption was rapid and kinetic data were suitably correlated to the pseudo-secondorder kinetic model. EB molecules were adsorbed on monolayer according to the Langmuir model with an adsorption capacity of 162.3mg/g. On the other hand, it should be noted that calculated quantumchemical parameters support the experimentally obtained results. The interaction energies calculated for (molecule/chitosan) complexes were in the order of H2EB− > HEB2− (O38) > HEB2− (O48) > EB > H3EB > EB3−, which means that the best and possible adsorption process can take placewith H2EB− form. The molecular dynamics (MD) approachwas performed to illuminate the nature of the relationship between the EB and the chitosan (110) surface. Itwas found that the chitosan (110) surface adsorbs EB molecule in a nearby parallel orientation. The higher negative adsorption energy determined for the H2EB− implies that the adsorption mechanism is the typical chemisorption.