Novel microporous B6N6 covalent organic framework (COF) as an electrochemical sensor for the ultra-selective detection of nitroaniline isomers; a DFT outcome

The density functional theory (DFT) simulations are performed to study the sensitivity and selectivity of a novel (star shape) boron nitride two-dimensional covalent organic framework (B6N6) towards adsorption of toxic nitroaniline isomers. The binding energies of nitroaniline isomers onto the B6N6 material have been evaluated with hybrid B3LYP functional along with third order Grimme dispersion (D3) method in order to accurately account for dispersion effects. Noncovalent interaction index (NCI) and quantum theory of atoms in molecules (QTAIM) illustrate that weak van der Waals forces are the main contributor in stabilizing the reported complexes. The BSSE corrected binding energies of oNA, mNA and pNA on B6N6 are -15.42, -14.73 and -14.34 kcal/mol, respectively. These results reveal that the sensitivity and selectivity of B6N6 decreases in the order of oNA > mNA > pNA. The effect of aromaticity of nitro-aniline isomers in stabilizing the complexes is studied through the ring critical point (RCP) based on Bader atoms in molecule analysis. The sensitivity of B6N6 for nitroaniline isomers is further justified by the electronic properties. For example, the density of states (DOS) reveal that the new occupied energies states appear between original HOMO and LUMO orbitals of pristine B6N6 upon complexation with nitroaniline isomers. The newly generated occupied orbitals are closer to the Fermi energy level which increase the conductivity of B6N6, thus the significant amount of NBO charge transfer is noticed. The amounts of charge transfer in oNA@B6N6, mNA@B6N6 and pNA@B6N6complexes are 0.05, 0.09 and 0.05 e−, respectively. The percentage contribution of orbitals in charge transfer is estimated by the orbital composition analysis. Finally, the effect of increasing concentration of nitroaniline molecules on the sensing properties of B6N6 is also studied, which shows that the binding energies are less negative per molecule by increasing the number of nitroaniline units. The findings of this study reveal that the B6N6 star like COF material shows excellent sensing abilities for the toxic molecules. In summary, B6N6 material is a valuable addition with ultrahigh sensitivity as well as selectivity for future electrochemical sensor devices.