Electrochemical sensing of heptazine graphitic C3N4 quantum dot for chemical warfare agents; a quantum chemical approach

Abstract

Despite the numerous publications describing the photocatalytic and electronic properties of heptazine-based C3N4, the systematic study on the sensing behavior of pure heptazine-C3N4 toward harmful chemical warfare agents (CWAs) is still lacking. Herein, we performed DFT calculations to investigate the adsorption behavior of C3N4 toward various harmful and toxic CWAs including formaldehyde (OCH2), thioformaldehyde (SCH2), phosgene (OCCl2), and thiophosgene (SCCl2). ωB97XD functional of DFT along with 6–31G (d, p) basis set is used for all calculations for accurate estimation of noncovalent interactions. The CWAs are physiosorbed onto the C3N4 having calculated interaction energy between −16.01 and −11.00 kcal/mol. Noncovalent interactions are further analyzed by symmetry-adapted perturbation theory (SAPT0), noncovalent interaction index (NCI), and quantum theory of atoms in molecules (QTAIM) analyses. The electronic behavior is characterized by the HOMO and LUMO energies, their energy gaps, and natural bond orbital (NBO) charge transfer. The charge transportation either donation or back donation is characterized by energy density difference (EDD) and charge decomposition analysis (CDA) analyses. The results demonstrate the trend of sensitivity of C3N4 for toxic gases is OCH2@C3N4 > SCH2@C3N4 > OCCl2@C3N4> SCCl2@C3N4. This theoretical work suggests that the C3N4 can act as a good electrochemical sensor for a variety of toxic gaseous molecules.