Theoretical insights about the possibility of removing Pb2+ and Hg2+ metal ions using adsorptive processes and matrices of carboxymethyl diethylaminoethyl cellulose and cellulose nitrate biopolymers

In this work, computer simulations based on the density functional theory (DFT) were used to investigate the interaction of heavy metals mercury (Hg2+) and lead (Pb2+) with the cellulose-derived adsorptive matrices, carboxymethyl diethylaminoethyl cellulose (CM-DEAEC) and cellulose nitrate (NC). Molecular Electrostatic Potential, Frontier Molecular Orbital (FMO) and reactivity indexes (RI) analyses were performed and allowed identifying the possible sites of interaction, that were in the functional groups –OH and –COO− for CM-DEAEC and in the functional groups –OH and –NO2 for NC. The structural analyzes have proven that the interactions occur because the bond lengths between the metal ions and the matrices are close and the vibrational frequencies changed after complexation. The adsorption, binding and Gibbs energies showed that the CM-DEAEC matrix is that best interacts with the Pb2+ and Hg2+ ions. The NBO results allowed the identification of the ligand and antiligant orbitals involved in the adsorption process and corroborated with the values of the structural and energetic parameters. The results found in the study show that the theoretical data provide subsidies for a possible experimental approach and future applications for effluent treatments.