Adsorption of chlorine oxyanions, as water disinfectant by-products, on graphene flakes: A quantum chemical investigation

Abstract

Chlorine oxyanions namely: hypochlorite ClO-, chlorite ClO2-, chlorate ClO3-, and perchlorate ClO4-, are considered to be harmful for public health since they are disinfectant by-products and are usually found in the disinfection process of drinking water treatment plants (DWTPs). The removal of these oxyanions is, therefore, an important demand. In the current work, the adsorption of chlorine oxyanions on some graphene flakes (Gr) such as coronene (C24H12), circumcoronene (C54H18), and circumcircumcoronene (C96H24), has been theoretically investigated. Favorable adequate (anion-π) interaction between the chlorine oxyanions and the electron-rich graphene flakes have been elucidated, where the stabilization largely originates from attractive electrostatic and dispersion effects. The exponential increase in the attractive electrostatic and dispersion components of the adsorption energies is found to be, in part, a consequence of a charge transfer contribution from the oxygen lone pairs of electrons of oxyanions (donors) to the low-lying π*-orbitals of graphene flakes (acceptors). This finding means that the favorable anion−π interaction between a chlorine oxyanion and a graphene surface is not purely non-covalent.