A comprehensive DFT study of magnetic cellulose nanocomposite for adsorptive removal of venlafaxine and its transformation products from wastewater

The global rise in antidepressant consumption underscores the urgent need for effective systems to detect, capture, and treat bioactive pharmaceutical pollutants in aquatic environments. Venlafaxine (VEN), a widely prescribed antidepressant, and its transformation products (TPs), are frequently detected in wastewater, raising significant environmental concerns due to their persistence. Magnetite cellulose nanocomposites (MCNC) offer promising adsorptive capabilities due to their unique physicochemical properties and surface functionalities. Since adsorbents are not universally effective for all pollutants, understanding their compatibility with specific contaminants is essential before experimental application. This multiscale density functional theory (DFT) study, employing B3LYP and dispersion-corrected B3LYP-D3(BJ) functionals, elucidates the adsorption mechanisms of VEN and TPs onto cellulose nanocrystals (CNC) and MCNC surfaces, providing critical insights into their electronic and energetic interactions. Our investigation highlights that accurate adsorption free energies, which are crucial for predicting spontaneous and exothermic processes, necessitate the inclusion of both solvation and dispersion corrections. This is because gas-phase calculations significantly overestimate interaction energies. In contrast, Frontier Molecular Orbital (FMO) analysis revealed that CNC facilitates stable, physical adsorption. Meanwhile, MCNC exhibited substantially reduced energy gaps, indicative of enhanced electrophilicity and reactivity due to the Fe 3 O 4 functionalization. Molecular electrostatic potential (MEP) mapping highlighted the Fe 3 O 4 surface oxygen atoms as critical nucleophilic centers that engage in robust electrostatic and Lewis acid-base interactions with electron-deficient VEN and TPs. Non-covalent interaction (NCI) and Quantum Theory of Atoms in Molecules (QTAIM) analyses confirmed the predominance of diverse closed-shell interactions, including hydrogen bonding (e.g., O–H···O/N, Fe–H···C), π-π stacking, van der Waals, hydrophobic, and dipole-dipole forces, with a notable partial covalent character. The MCNC consistently exhibited the highest adsorption capacity, which was attributed to the synergistic interactions between its components and the availability of multiple binding sites. These findings demonstrate the potential of MCNC as an efficient adsorbent for VEN and its metabolites. These mechanistic insights provide a robust theoretical foundation for designing and optimizing advanced materials to mitigate antidepressant pollution, which requires future experimental validation to corroborate computational predictions. • The DFT study explores adsorption mechanisms of venlafaxine and its TPs on magnetic cellulose nanocomposites. • It is found that with Fe 3 O 4 functionalization, the reactivity and pollutant adsorption efficiency increases. • Solvation and dispersion corrections are crucial for accurate adsorption energies. • VEN and its metabolites adsorbs on MCNC better than CNC. • Our findings provide a theoretical basis for designing advanced adsorbents.