The effect of doping graphene with silicon on the adsorption of cadmium(II): theoretical investigations

In this research, the influence of doping graphene with silicon on the adsorption of Cd2+ was investigated using the infrared (IR), natural bond orbital (NBO) and frontier molecular orbital (FMO) computations. The thermodynamic parameters including Gibbs free energy changes (ΔGad), enthalpy variations (ΔHad) and thermodynamic constant (Kth) revealed that, the Si impurity made the cadmium adsorption more spontaneous, exothermic, irreversible, and experimentally feasible. The effect of temperature and geometrical situation of silicon impurities at three ortho, meta and para conditions were also evaluated. The results indicated that, the adsorption efficiency was higher at room temperature and doping graphene with silicon at the ortho position. The NBO results demonstrated that, the cadmium interaction with both pristine and Si-doped graphenes was chemisorption, which was due to formation of the covalent bonds with Sp 3 hybridization in all of the evaluated configurations. The applicability of the pristine and Si-doped graphenes as an electrochemical sensing material for detection of the cadmium was also assessed by the FMO parameters including, bandgap, electrophilicity, and maximum transferred charge capacity. The ortho silicon doped graphene was found to be the best recognition element for the Cd(II) as the bandgap experienced the sharpest increase from 1.82 eV to 7.74 eV in the case of this adsorbent.