Removal of Heavy Metal Ions from Water Using Functionalized Carbon Nanosheet: A Density-Functional Theory Study

Abstract

Background: Currently, a clean environment and human health have been regarded as the most important challenges of humankind; therefore, the ability of carbon-based nanomaterials as a new type of adsorbents in the removal of various pollutants from aqueous solutions has caused the widespread attention of research groups. Objectives: Carbon nanosheet (CNS) and its amine-functionalized derivatives were considered to remove heavy metal ions (HMIs) (zinc(II) ion [Zn2+]/cadmium(II) ion [Cd2+]/mercury(II) ion [Hg2+]) from water. Methods: This theoretical study in the framework of density-functional theory (DFT) was performed to gain insight into the HMIs (Zn2+/Cd2+/Hg2+) adsorption and removal by CNS and {(NH2)n-CNS (n = 1 - 2)}. The calculation level was hybrid DFT methods, such as wB97XD/lanl2dz. Results: Based on DFT calculations, more negative chemical potential value (-1.827 eV), high global softness (0.964 eV), low highest occupied molecular orbital (NH2)2-CNS lowest unoccupied molecular orbital-HMI gap, and more negative adsorption energy (range: -75 to -93 kJ mol-1) in (NH2)2-CNS demonstrated that this compound as a suitable adsorbent removed HMIs (Zn2+/Cd2+/Hg2+) from water than other nanosheets. The HMIs adsorption was confirmed by the natural bond orbital and quantum theory of atoms in molecules. Conclusions: The CNS and amine-functionalized structures have a good ability for HMIs (Zn2+/Cd2+/Hg2+) removal due to high chemical potential, electrophilicity, and adsorption energy.