Super-strong interactions between multivalent anions and graphene

Based on the density functional theory (DFT) calculations, we showed that the interactions between different valence anions (PO₄^3-, CH₃PO₄^2-, (CH₃)₂PO₄^-) and graphene significantly increased as the valence of anion increased from negative monovalence to negative trivalence. The adsorption energy of (CH₃)₂PO₄^- on the electron-rich graphene flake (C₈₄H₂₄) is -8.3 kcal/mol. The adsorption energy of CH₃PO₄^2- on the electron-rich graphene flake (C₈₄H₂₄) is -48.0 kcal/mol, which is about six times that of (CH₃)₂PO₄^- adsorption on electron-rich graphene flake (C₈₄H₂₄) and is even much larger than that of CO₃^2- adsorption on electron-deficient aromatic ring C₆F₆ (-28.4 kcal/mol). The adsorption energy of PO₄^3- on the electron-rich graphene flake (C₈₄H₂₄) is -159.2 kcal/mol, which is about 20 times that of (CH₃)₂PO₄^- adsorption on the graphene flake (C₈₄H₂₄). The super-strong adsorption energy is mainly attributed to the orbital interactions between multivalent anions and graphene. This work provides new insights for understanding the interaction between multivalent anions and π -electron-rich carbon-based nanomaterials and is helpful for the design of graphene-based DNA biosensor.