DFT study on radon adsorption by graphene oxide quantum dots from optically radioactive environment, using three organic functional groups: a new approach to wastewater treatment

In this work, we investigated the ²²²Rn capture capacity of silica (SiO₂), carboxyl (COOH) and carbonyl functionalized graphene oxide quantum dots (GQDs) using density functional theory. Optimization and calculations of all properties of the systems were achieved using Gaussian 09. Analysis of the frontier orbitals revealed full participation of C and O atoms for successful ²²²Rn adsorption. The largest charge transfer was attributed to COOH groups, with HOMO-LUMO gap of 9.46 eV. Based on the natural bond orbital (NBO) calculations, presence of highest value of orbital energy indicated that the adsorption process includes all the core and valence natural atomic orbitals (NAOs). Results from IR, Raman and UV–Vis analysis revealed well adsorption of radon in the UV and IR regions corresponding to characteristic adsorption by covalent compounds. Although all the systems were found worthy for ²²²Rn adsorption; out of the three functional groups, it was found that the carboxyl groups demonstrated versatile binding capacity than silica and carbonyl groups, hence provided better radon adsorption. Finally, results obtained from this research are essential for ensuring clean water for domestic use.