Enhanced permeability of rGO/S-GO layered membranes with tunable inter-structure for effective rejection of salts and dyes

Abstract

In this work, a novel rGO/S-GO laminated membrane was prepared by a pressure-assembly stacked method, followed with a thermal deoxygenation process. The neighboring interlayer spacing (d) between the composite layers are tunable due to the incorporation of S-GO. The nano-filtration performances of the rGO/S-GO laminated membranes were evaluated at a low-pressure condition. Molecule dynamics (MD) simulation was used to further investigate the size distribution of spacing between GO, rGO and S-GO sheets. The results of filtration experiments indicated that the obtained rGO/S-GO membrane showed a satisfied rejection performance for the removal of dyes and salts with a pressure of two bar. The rejection rates of MB, CR, RB and MO were 99.5%, 99.9%, 97.3% and 98.6%, while the rejection rates of Na2SO4, MgSO4, MgCl2 and NaCl were 86.3%, 40.9%, 35.7% and 60.5%, respectively. Compared to the pristine rGO membrane, the water permeation of rGO/S-GO laminated membrane was significantly improved from ∼0.98 to ∼3.78 L/(m2·h·bar) due to the enlarged ‘gateway’ for transport of water molecules. The results of classical MD simulation showed that the neighboring layer spacing of rGO, GO and S-GO was ∼8.4, ∼10.2, and ∼14.3 Å, respectively. Their neighboring layer spacing was dependent on the chemical functional groups on the edges of GO sheets. It was further confirmed that the introduction of chemical groups on the GO caused the expansion of the interlayer ‘gap’ between neighboring sheets, which was responsible for the enhanced permeability. These findings would contribute to the development of GO-based nanofiltration membranes with high permeability and understanding the transport mechanism of water molecule.