Evaluation of water desalination performances of functionalized nanoporous graphene membranes by molecular dynamics simulation

Nanoporous graphene membrane (NPGM) is a promising candidate for water desalination due to its unique features, such as chemical stability, high resistance to chlorine and fouling, excellent mechanical strength, and tunable permeability. In this work, the water desalination performances of small- and large-pore, pristine and functionalized NPGMs, with the latter containing amide, sulfonic acid, thiourea, and carbamate functional groups, were evaluated by molecular dynamics (MD) simulation. Our results indicate that pore functionalization leads to a decrease in water flow rate through the membrane. Among functionalized NPGMs, large-pore, amide-functionalized NPGM exhibited the highest water flow rate. In terms of ion rejection performance, pore functionalization resulted in partial Na⁺ and Cl⁻ ion rejection by both small- and large-pore NPGMs. For small-pore, functionalized NPGMs, the rejection of Na⁺ and Cl⁻ ions were higher than 98%. Comparing between the ion rejection performances of large-pore, functionalized NPGMs, the following order of Na⁺ ion rejection rates were observed: carbamate > sulfonic acid > thiourea > amide. The carbamate functionalization of large-pore NPGM led to about 21% and 18% Na⁺ and Cl⁻ rejection, respectively. This observation is in good correlation with the smallest effective pore diameter in the carbamate-functionalized NPGM and the largest ion-carbamate interaction energies.