The co-adsorption of sulfate and metal ions on Al-doped graphene: a first principles study

The co-adsorption of sulfate and metal ions on intrinsic and Al-doped graphene is investigated through first principles calculations. When SO₄^2- ions exist only, both of intrinsic and Al-doped graphene can form stable adsorption configurations with SO₄^2-. However, the presence of Cu²⁺/Ca²⁺/Zn²⁺/Mg²⁺ ions attenuates the interaction between intrinsic graphene and SO₄^2-, resulting in weak physical adsorption between them, while Al-doped graphene can still constitute co-adsorption chemically with both SO₄^2- and Cu²⁺/Ca²⁺/Zn²⁺/Mg²⁺ ions simultaneously. The sensitivity of Al-doped graphene towards co-adsorbed ions is in the order of SO₄^2--Cu²⁺ > SO₄^2--Zn²⁺ > SO₄^2--Ca²⁺ > SO₄^2--Mg²⁺. The research indicates Al-doped graphene could be a promising material for sensing sulfate ions under the presence of various metal ions.

All of the calculations were carried out by using a first principles method based on density functional theory (DFT). The generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) functional was selected to describe electron exchange-correlation energy. The double numerical plus polarization (DNP) was employed as the basis set. The conductor-like screening model (COSMO) was implemented to simulate the aqueous solvent effect.