Theoretical Study of the Interaction between Graphitic Carbon Nitride and 2,6-Dichloro-1,4-benzoquinone Pollutants: Environmental Applications

Halobenzoquinones (HBQs) are an emerging class of disinfection byproducts of growing environmental concern due to their high toxicity and persistence in aquatic systems. In this work, we investigate the adsorption behavior of 2,6-dichloro-1,4-benzoquinone (DCBQ) on two phases of graphitic carbon nitride─triazine-based (t-g-C3N4) and tri-s-triazine-based (h-g-C3N4)─combining Grand Canonical Monte Carlo (GCMC) simulations with first-principles density functional theory (DFT) calculations. GCMC was employed to identify the most probable adsorption configurations and competitive water coadsorption under realistic aqueous conditions. The results reveal that h-g-C3N4 exhibits a significantly higher adsorption capacity and stronger affinity toward DCBQ compared to t-g-C3N4, even at high water ratios, highlighting its superior selectivity for pollutant capture. DFT calculations were then applied to refine the structural, energetic, and electronic properties of the selected configurations. Both g-C3N4 phases exhibit physisorption-driven interactions with DCBQ, accompanied by band gap modulation and the emergence of molecular states near the Fermi level. Noncovalent interaction (NCI) and reduced density gradient (RDG) analyses further demonstrate that adsorption is governed primarily by dispersion forces and π–π interactions. Additionally, isolated dimer calculations show that DCBQ molecules can stabilize one another through favorable noncovalent contacts, supporting the cooperative adsorption behavior observed in GCMC simulations. Overall, our results provide a comprehensive multiscale description of DCBQ adsorption on g-C3N4 and reveal that h-g-C3N4 is a promising candidate material for the selective capture of halobenzoquinones in aqueous media. This study advances the understanding of pollutant–surface interactions and contributes to the development of nanostructured adsorbents for water purification applications.