DFT study on the chemical sensing properties of B24N24 nanocage toward formaldehyde.

It has been previously shown that the toxic formaldehyde gas (H2CO) cannot be detected by pristine BC2N, carbon, and BN nanotubes, BC3 nanosheet and graphene. Herein, density functional theory calculations were employed to investigate the electronic and structural behavior of a pristine B24N24 nanocluster toward H2CO molecules. It was found that [4,6] BN bonds of the nanocluster are the most favorable sites for the H2CO adsorption, compared to the [4,8], and [6,8] ones. When an H2CO molecule is adsorbed on a [4,6] BN bond, an energy of about 16.40kcal/mol is released and the HOMO-LUMO gap of the cluster is decreased from 6.45 to 2.98eV. Thus, the electrical conductivity of the cluster is significantly increased, indicating that it can produce an electronic noise at the presence of H2CO molecules. Increasing the number of adsorbed H2CO molecules, the electrical conductivity more increases. The recovery time for the H2CO from the surface of B24N24 is calculated to be very short (∼1.02s). Also, the UV-vis spectrum shows that the λmax of the B24N24 shows a large redshift upon the adsorption process and transfers from the UV to the visible region.

Adsorption of carbon monoxide on the pristine, B- and Al-doped C3N nanosheets.

The potential application of the intrinsic and extrinsic (8,0) zigzag single-walled C3N nansheets as chemical sensor for CO molecules has been investigated using density functional theory calculations. The calculation shows that the pristine sheet is a semiconductor with a HOMO-LUMO gap (Eg) of about 2.19 eV. The pristine and B-doped sheets can weakly adsorb a CO molecule with the adsorption energies of -4.8 and -4.6 kcal mol(-1), and their electronic properties are not sensitive to this molecule. By replacing a C atom with an Al atom, localized impurity states are induced under the conduction level of the sheet. The binding interaction between the CO molecule and the Al-doped sheet becomes much stronger (Ead = -17.8 kcal mol(-1)). After the adsorption of CO on the Al-dope sheet, the Eg of the sheet is significantly decreased from 1.07 to 0.73 eV. This leads to a sizable increase in the resistance of the tube. Thus, the Al-doped sheet can show the presence of CO molecules by an electronic signal because of the change in its resistance and conductivity.