2D CuBDC and IRMOF-1 as reverse osmosis membranes for seawater desalination: a molecular dynamics study

Abstract

In this study, molecular dynamics simulation is conducted to evaluate the performance of CuBDC and IRMOF-1 metal–organic frameworks (MOFs) as 2D membranes in the reverse osmosis (RO) desalination process. Both 2D MOF membranes possess the same 1,4-benzenedicarboxylate linkers but different metal nodes, which correspond to different molecular structures. The performance of the 2D membranes is assessed in terms of their water flux and ion rejection rate. The effects of different metal nodes and membrane structures on the interactions between the 2D membranes and salt ions are investigated and explained according to the radial distribution function, interaction energy, and ion density distribution. Our results indicate that the pore entrance of both MOF membranes exhibit higher affinity towards Cl- ions than Na+ ions. Furthermore, complete ion rejection is achieved for both MOF membranes at half the thickness of their physical counterparts (CuBDC: ∼50 Å and IRMOF-1: 40 Å). The lower water flux in the CuBDC membrane is also determined to be caused by the low water density within it. Overall, MD simulation is particularly useful for studying 2D MOF membranes in RO since it is capable of accurately modeling nanoscale structures. Of the two 2D MOF membranes tested, the IRMOF-1 membrane displays the higher water flux due to its more porous structure.