Carbon Nitride as a Platform for Sulphur-Containing Pollutant Sensing: A Density Functional Theory Study on Sulphur Mustard and Minoxidil

Background: Carbon nitride (C6N8) holds promise as a two-dimensional nanomaterial for chemical sensing because of its advantageous electronic properties, high surface area, and structural stability. Method: The suitability of C6N8 for the adsorptive sensing of sulphur mustard (C4H8Cl2S) and minoxidil (C9H15N5O) was investigated using density functional theory calculations at the B3LYP/6-31G(d,p) level. The sensing mechanism and adsorption behavior were explored through interaction energy calculations and frontier molecular orbital, density of states, natural bond orbital (NBO), molecular electrostatic potential mapping, electron localization function (ELF), quantum theory of atoms in molecules (QTAIM), and noncovalent interaction (NCI) analyses. Results: The calculated adsorption energies of sulphur mustard and minoxidil (−30.39 and −85.34 kJ mol−1, respectively) indicated favorable adsorption, with minoxidil exhibiting stronger interactions with the C6N8 surface. Upon the adsorption of sulphur mustard and minoxidil, the bandgap of C6N8 decreased from 4.206 to 4.007 and 3.067 eV, respectively. Charge transfer between the adsorbates and sensing surface, together with hydrogen bonding, van der Waals interactions, and steric effects, was confirmed by NBO, NCI, ELF, and QTAIM analyses. Conclusion: C6N8 exhibits excellent sensitivity toward both analytes and can serve as a promising sensing platform for the detection of hazardous sulphur-containing pollutants and pharmaceutical contaminants. The results provide valuable theoretical insights for the development of advanced nanosensor technologies.