Ion rejection performances of functionalized porous graphene nanomembranes for wastewater purification: A molecular dynamics simulation study

Performances of small- and large-pore, porous graphene nanomembranes (PGNMs) (pristine and functionalized by amide, sulfonic acid, thiourea, and carbamate functional groups) for purification of heavy metal ions and nitrate-contaminated wastewater were determined using molecular dynamics (MD) simulation. At the operational conditions of the simulated membrane (150 and 0.1 MPa pressure on the left and right piston sides at 300 K), higher water flow rates were obtained in the functionalized PGNMs possessing large pores, as opposed to the non-functionalized and small-pore ones. Amide-functionalized PGNM provided the highest flow rate (380 and 330 molecules/ns for large and small pores, respectively). Cu²⁺ and As³⁺ ions were rejected at a level of 100% in the small-pore PGNMs, while the rejection level of the NO₃^- ions was about 95%. For large-pore PGNMs, As³⁺ ions were rejected at a level of 100%, while a few Cu²⁺ and NO₃^- ions could pass through the pores with no discernible dependence on the graphene surface chemistry. A radial distribution function (RDF) analysis revealed two hydration radii for all ions interacting with the surrounding water clusters. Overall, graphene surface chemistry modification did not significantly affect the ion rejection performance.