Theoretical study of glyphosate adsorption potential on methylcellulose and cellulose xanthate matrices compared to activated carbon: role of biopolymers in the adsorption process

This study provides theoretical insights into the potential use of cellulose derivatives, such as methylcellulose (ME) and cellulose xanthate (CX), to remove glyphosate (GLY) contaminants via adsorption. The mechanism of adsorption in ME and CX is compared with that of activated carbon. To this end, theoretical calculations based on density functional theory (DFT) were used to determine the frontier molecular orbitals (FMOs); molecular electrostatic potential (MEP); and energetic, structural, and topological parameters. The analyses of FMOs and MEP indicated two possible interaction sites. The structural parameters showed that the herbicide interacts with the ME and CX matrices, and the bond lengths of the interaction ranging from 1.58 to 3.09 angstrom, depending on the nature of the interaction. The vibrational frequencies of the bonds involved in the interaction changed after adsorption, thus confirming the existence of the interaction. The analysis of the quantum theory of atoms in molecules (QTAIM) allowed the characterization of interactions through topological parameters and showed that the most effective interactions presented a higher number of electrostatic interactions. The determined energies of the electronic interaction and the enthalpy were negative, indicating that the interaction occurred. Finally, the calculations for the glyphosate adsorption process on activated carbon (AC) showed that the terminal group -COOH presented the best energy values for interaction with GLY, followed by activated carbon with the group -OH, and finally, the activated carbon containing only aromatic rings. The results showed that the derivatives of cellulose CX and ME are promising alternatives to remove glyphosate contaminants from water.