Density Functional Theory Calculations of Tetragonal Graphene Nanobowls for Toxic Heavy Metal Ion Removal from Wastewater

The removal of heavy metal ions (HMIs) from polluted environments is crucial for safeguarding public health and improving water quality. This study investigates the HMI adsorption capabilities of a tetragonal graphene nanobowl (TGNB), an sp2-hybridized carbon-based nanomaterial, in wastewater. The negative cohesive energy of -6.75 eV and real vibrational frequencies confirm that the TGNB structure is stable and can occur naturally. The nanobowl exhibited an energy gap of 1.148 eV, revealing its semiconducting nature. Using density functional theory calculations, the adsorption behavior of TGNB for Ni(ii) and As(iii) ions was explored in an aqueous medium. The optimized TGNB structure showed adsorption energies of -3.07 eV for Ni(ii) and -13.10 eV for As(iii), causing significant structural deformation. The interaction of HMIs with TGNB resulted in substantial changes in the energy gap and work function, suggesting its applicability in HMI detection and monitoring in wastewater. The negative entropy change confirms the thermodynamic stability of all the complexes. Strong, partially covalent, as well as van der Waals interactions were observed between TGNB and HMIs. The adsorption process was exothermic and spontaneous, with strong interactions confirmed for most complexes. These findings demonstrate the potential of TGNB as an efficient stable nanomaterial for HMI detection and removal from wastewater.