Computational insights into nitrosamine adsorption on graphene for water remediation: A multiscale DFT, MD, and QTAIM study

Nitrosamines are persistent water contaminants of concern because of their carcinogenic potential. This study employed a multiscale computational approach to investigate the adsorption of N-nitrosodimethylamine (NDMA), N-nitrosopyrrolidine (NPYR), N-nitrosodiethylamine (NDEA), and N-nitrosomorpholine (NMOR) on pristine graphene. Conformer searches using GFN1-xTB were followed by DFT calculations at the ωB97M-D4/def2-SVP level with implicit aqueous solvation to evaluate adsorption energetics and electronic perturbations. Monte Carlo and molecular dynamics simulations in explicit water were additionally used to assess adsorption stability, diffusion behavior, and interfacial interactions. All four nitrosamines adsorbed spontaneously through physisorption dominated by dispersion, van der Waals, and π-related interactions. NMOR exhibited the strongest affinity, with a DFT adsorption energy of -20.62 kcal mol⁻¹ and the lowest surface-diffusion tendency. QTAIM and NCI analyses confirmed the closed-shell, noncovalent character of adsorption, whereas CM5 analysis indicated only localized charge redistribution. The small variations in the HOMO-LUMO gap and related electronic descriptors indicate weak perturbation of the finite graphene cluster. These findings clarify the molecular basis of nitrosamine adsorption and support further investigation of graphene-based materials for water remediation.