Nanoporous graphene quantum dots constructed from nanoribbon superlattices with controllable pore morphology and size for wastewater treatment

The pollution of water bodies with toxic components possesses a dangerous impact on human health and the environment. Therefore, it is vital to find efficient materials for water treatment. Herein we construct various nanoporous graphene quantum dots from nanoribbon superlattices with tunable pore size and abundant active sites. The investigations are performed using density functional theory calculations. Depending on the type of superlattice, the pore size can be tuned from 3 angstrom to 11 angstrom and the pore morphologies are also controllable. Some of the nanoporous graphenes have edge states at the zigzag terminations that decrease the band gap and act as active sites. While others do not have edge states due to the armchair terminations and form semiconductors with an energy gap of similar to 2.7 eV Molecular electrostatic potential confirms that edge carbon atoms have high negative electronic densities and thus they are suitable for intermolecular coordination with the toxic metals. The considered 2D membranes show good capability to adsorb heavy metals, namely Cd, Pb, and Hg, with negligible deformation. Additionally, attaching chemical groups or elements, namely CN, COOH, CS2, N, O, and S, to the pores not only increases the adsorption energy but also helps control the pore size. Therefore, with the enhanced adsorption energy and tunable pore size, the constructed nanoporous graphene quantum dots are ideal candidates for 2D membranes.