Adsorption of Eriochrome Black T on the chitin surface: Experimental study, DFT calculations and molecular dynamics simulation

Abstract

In this study, chitinwith highmolecularweightwas extracted fromshrimp shells and characterized by XRD, FTIR, and SEM. The solid was investigated in Eriochrome black T dye (EB) adsorption in aqueous solution. Experimental results indicated high EB uptake in acidic medium with maximum adsorption capacity of 167.31 mg/g. The kinetics of adsorption followed pseudo-second-order kinetic model and equilibrium data fitted well Langmuir model suggesting a suitable chemisorption process. The thermodynamic parameters showed a spontaneous and exothermic process with favorable adsorption at a relatively low temperature. The molecular dynamics (MD) simulation confirms the chemical adsorption capability of the EB on the (110) surface of the biopolymer. Moreover, density functional theory (DFT) calculations were carried out to understand the experimental behavior. The order of the interaction energies calculated for the complexes indicates that the best and possible adsorption process can take place with the anionic H2EB− form of the dye. The deformation energies indicates that the conformational re-arrangement makes both the EB and chitin surface less stable which supported the experiment and quantum chemical analyses. This result also demonstrates the accuracy and feasibility of the MD simulation to study the adsorption mechanism.