DFT Investigation of Electronic Modulation and Site Specific CFC-11 Sensing on Difuran Functionalized Heptazine Based g-C 3 N 4

Abstract

The Montreal Protocol has significantly reduced chlorofluorocarbon (CFC) use, yet ongoing inadvertent releases and unregulated emissions necessitate advanced sensing technologies. This study employs DFT-TDDFT methods to investigate difuran-functionalized s-heptazine graphitic carbon nitride (Hz-df) as a sensor for CFC-11, a major ozone-depleting compound. Structural optimizations reveal that difuran functionalization enhances the electronic properties of pristine s-heptazine (Hz), as evidenced by charge density difference (CDD) and transition density matrix (TDM) analyses, indicating improved charge delocalization and excitation. CFC-11's interaction with Hz-df was examined at three adsorption sites: Site-A, Site-B, and Site-C. BSSE-corrected interaction energy calculations showed Site A had the strongest interaction, followed closely by Site B, with Site C exhibiting weaker interaction. Natural bond orbital (NBO) analysis corroborated these findings, showing similar and greater charge transfer at Sites A and B compared to Site C. Non-covalent interactions were confirmed by 2D/3D reduced density gradient (RDG) isosurfaces and molecular electrostatic potential (MEP) mapping, with Sites A and B demonstrating pronounced interactions. Quantum theory of atoms in molecules (QTAIM) further validated these interactions via bond critical point (BCP) analysis. Electronic structure analyses, including density of states (DOS), revealed site-specific perturbations. UV-Vis spectra indicated distinct optical properties and absorption wavelengths (λmax) for all three complexes, highlighting the surface's potential as an optical sensor. Kinetic analysis of desorption behavior suggested a slower recovery at Site A, indicating stronger gas retention. Site B offered a practical balance between sensitivity and reversibility, while Site C exhibited the fastest recovery. Overall, this theoretical study underscores Hz-df's effectiveness in detecting CFC-11. Sites A and B are favored for strong interaction at low concentrations, while Site C is more responsive at higher concentrations where rapid detection is crucial. These findings support Hz-df-based sensors for real-time monitoring of CFC-11 emissions, providing an eco-friendly approach to protect the ozone layer and mitigate greenhouse effects.