Computational analysis of C9N4 monolayer as a novel adsorbent for toxic gases

A novel C 9 N 4 nanosheet has been investigated for its potential use as an electrochemical sensor for gaseous pollutants including CO, NO, CO 2, HF, and COCl 2. The sensing ability of C 9 N 4 is explored theoretically at the ωB97XD/6-311G (d, p) level of theory. The results showed the physisorption of all analytes on the C 9 N 4 surface. The highest interaction energy of −21.96 kcal/mol was observed in COCl 2 @C 9 N 4. The order of interaction energy was COCl 2 @C 9 N 4 > NO@C 9 N 4  > HF@C 9 N 4  > CO 2 @C 9 N 4  > CO@C 9 N 4. The Electronic properties of the complexes were examined using EDD (Electron Density Difference), NBO (natural bond orbital), FMO (frontier molecular orbital), and DOS (density of state) analysis. According to NBO analysis, CO 2 @C 9 N 4 exhibited the maximum amount of charge transfer (−0.026 e − ), whereas COCl 2 @C 9 N 4 exhibited the minimum amount of charge transfer. The adsorption of COCl 2 onto the surface of C 9 N 4 resulted in change in the energy gap with a value of −3.12 eV compared to −3.15 eV for C 9 N 4. These findings highlighted the potential of C 9 N 4 as a promising electrochemical sensor for COCl 2. The transfer of charges takes place from the analytes to the C 9 N 4, except in HF, where no charge transfer took place. This divergence could be attributed to the strongly bonded electrons between the fluorine and hydrogen atoms of HF. QTAIM and NCI analysis were performed to determine the nature of non-covalent interactions. At 298K, a recovery time of 1.25 × 10 4  s was calculated for the desorption of COCl 2 from the surfaces of C 9 N 4. It was observed that C 9 N 4 shows the highest sensitivity toward COCl 2 among all selected analytes.