Adsorption of Dimethyl Phthalate and Its Isomers on Nitrogen-Doped Activated Carbon: A DFT Study

Dimethyl phthalate (DMP) is an environmental contaminant known for its endocrine-disrupting properties, and its removal poses a critical environmental challenge. In this paper, we present a theoretical study of the adsorption of the DMP molecule and its isomers on pristine and nitrogen-doped graphitic surfaces, which represent the pore walls of nanoporous activated carbon, using density functional theory (DFT) calculations. Detailed wavefunction analyses were performed to elucidate the nature of adsorption on the AC surfaces. Our results reveal that nitrogen doping improves phthalate adsorption in the following order: AC-Pristine < AC-NH2 < AC-Graphitic-N < AC-Graphitic-2N. This enhancement arises from changes in charge distribution that introduce electrostatic interactions between the COOCH3 groups of the molecules and nitrogen-doped atoms on the AC surface. This study provides mechanistic insights into DMP adsorption on nitrogen-doped AC and offers rational guidelines for designing efficient carbon-based adsorbents for the removal of phthalate esters from contaminated water and the environment.