Polyoxometalate ionic liquid between graphene oxide surfaces as a new membrane in the desalination process: a molecular dynamics study

Abstract

In this study, the performance of the positioning of polyoxometalate ionic liquid ([Keggin][emim]₃ IL) between graphene oxide (GO) plates with different concentrations (nIL-GO (n = 1–4)) were examined in the desalination process at different external pressures using molecular dynamics (MD) simulations. The use of Keggin anions with charged GO layers was also investigated in the desalination process. The potential of the mean force, average number of hydrogen bonds, self-diffusion coefficient, and angle distribution function were calculated and discussed. The results showed that although the presence of polyoxometalate ILs between the GO plates decreases water flux, they efficiently increase salt rejection. The positioning of one IL increases salt rejection to two times at lower pressure and increases it up to four times at higher pressure. Moreover, the positioning of four ILs results in almost complete salt rejection at all pressures. The use of only Keggin anions between the charged GO plates (n[Keggin]-GO⁺³ⁿ) presents more water flux and a smaller salt rejection rate than the nIL-GO systems. However, the n[Keggin]-GO⁺³ⁿ systems show a nearly complete salt rejection at high concentrations of Keggin anions. These systems also have a smaller risk of the contamination of the desalinated water by the probable escape of cations from the nanostructure to the desalinated water at very high pressures.