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Graphene oxide (GO) membranes have attracted a great deal of attention due to their special two-dimensional (2D) structure and excellent ion sieving properties. However, GO membranes for high valence metal ion rejection still suffer from the limitation of low water permeance and low stability in wastewater treatment. In this study, we reported a kind of 2,4-diamino-6-(4-fluorophenyl)pyrimidine cross-linking graphene oxide (F-GO) membrane with larger interlayer spacing and F-functioned channels, which exhibited an excellent water permeance of ∼219.7 L m−2 h−1 bar−1, which was 5.1 times higher than that of pristine GO membranes, while still maintained 99.9% ion rejection for wastewater treatment. Furthermore, the long-term stability of the F-GO membrane in nanofiltration performance was also experimentally obtained. Overall, our research demonstrates a simple way for achieving high permeances for the effective removal of high valence ions using GO-based membranes, and they may serve as the next promising materials for wastewater treatment. [ABSTRACT FROM AUTHOR]

We show the experimental achievement of dry GO membranes with interlayer spacings in the range from 7.09 Å to 8.72 Å, tuned and fixed by salts. We found that the interlayer spacings were dominated by the anions or the groups with negative charges in between the GO membranes. Density functional theory (DFT) calculations reveal that the highly efficient tuning of the interlayer spacing in dry GO membranes is due to ion‐π interactions on the graphene sheets, together with the steric effects of anions in between the GO sheets. The findings are helpful for extending their potential applications including chemical sensors, nanomaterial devices preparation, chemical catalysis and synthesis, and gas separation. [ABSTRACT FROM AUTHOR]

The effect of cationic concentration on controlling the interlayer spacings of graphene oxide (GO) membranes is systemically studied. It was found that a higher concentration leads to narrower interlayer spacings, and thus, ions in salt solutions were effectively rejected. This provides a new avenue for ion separation using graphene-based membranes. [ABSTRACT FROM AUTHOR]

Graphene-oxide (GO) membrane with notable ions sieving properties has attracted significant attention for many applications. However, because of the water swelling of GO membrane, the rejection of monovalent metal cations is generally low. In this work, we developed a fast and facile method to fabricate a kind of reduced GO membranes using the thermal treatment method at 160 °C for only one minute, which denoted as fast reduced GO membrane (FRGO). Surprising, the FRGO membrane represents high ion sieving ability and ultrahigh water/ions selectivity, compared with other reduced GO membranes with similar average interlayer spacings, and even superior to most of GO-based membranes reported in literature. Building on these findings, we provide a new light on fabricating of energy- and environment-related high desalination performance of GO-based membranes as well as a new insight into the transport mechanism within 2D laminar nanochannels. [ABSTRACT FROM AUTHOR]

• K+ can precisely control the interlayer spacings of GO membranes. • The controlled GO membranes showed highly efficiency for ions rejection. • The separation factor of controlled GO membranes for mono-/multi-valent ions is high. Ion sieving is of great importance in a variety of applications, including water purification, bio-medical engineering, resource utilization and environment protection. Despite previous efforts, the separation efficiency for mono-/multi valent ions is still far from satisfactory. Here, we use high concentration of KCl solution to control the interlayer spacings of graphene oxide (GO) membranes. Then, these KCl-controlled GO membranes can precisely sieve mono-/multi-valentions, especially for Na+/Mg2+ separation. The excellent performance of the membranes can be attributed to the narrower interlayer spacings of KCl-controlled GO membranes. [ABSTRACT FROM AUTHOR]