A density functional study on the acidity properties of pristine and modified SiC nano-sheets

Surface acidity is an important property that is frequently used to characterize the reactivity of surfaces. NH3 is well known as a probe molecule in determining the acidity of surfaces experimentally. Here, the adsorption of an NH3 molecule at different sites of a SiC nanosheet was investigated based on density functional theory framework. It was found that NH3 can be weakly adsorbed on the surface of the pristine with the adsorption energy (Ead) of about 3.5 kcal/mol with no sensible effect on the electronic properties of the sheet. Replacing a Si or C atom with both Al and B atoms increases the Ead, indicating that the acidity of SiC sheet can be controlled by doping of B and Al atoms. Relative magnetic order of the acidity for different surfaces was found to be: AlC, a C atom was replaced with a Al, (Ead=86.4 kcal/mol)⪢⪢AlSi (Ead=39.2 kcal/mol)>BC (Ead=30.9 kcal/mol)>BSi (Ead=12.3 kcal/mol)⪢⪢pristine h-SiC (Ead=3.5 kcal/mol). Moreover, it was found that when a C atom of the sheet was doped by an Al atom, HOMO–LUMO gap of the sheet becomes highly sensitive to NH3 adsorption so that it is decreased by about 31.3% after the adsorption process. It shows that the AlC-doped sheet may be used in the detection of NH3 gas molecules.