Detection of NO2 by hexa-peri-hexabenzocoronene nanographene: A DFT study

It has been previously indicated that pristine graphene cannot detect NO2 gas. Nanographene is a segment of graphene whose end atoms are saturated with hydrogen atoms and its properties are different from those of graphene. Herein, we investigated the reactivity, electronic sensitivity, and structural properties of hexa-peri-hexabenzocoronene (HBC) nanographene toward NO2 gas using density functional theory calculations. It was found that the central and peripheral rings of HBC are aromatic but the middle rings are non-aromatic, following Clar's sextet rule of aromaticity. The NO2 molecule prefers to be adsorbed on the central ring with a nitro configuration, releasing an energy of about 13.2 kJ/mol. The NO2 molecule significantly stabilizes the LUMO level of the HBC, thereby reducing the HOMO-LUMO energy gap from 3.60 to 1.35 eV. This indicates that the HBC is converted from a semiconductor to a semimetal. It was shown that the adsorption of NO2 gas by HBC can produce an electrical signal selectively in the presence of O2, H2, N2, CO2, and H2O gases. A short recovery time about 1.9 ns is predicted and the effect of density functional is investigated.