Enhanced Ion Sieving of Graphene Oxide Membranes via Surface Amine Functionalization

Abstract

Membranes based on two-dimensional (2D) nanomaterials have shown great potential to alleviate the worldwide freshwater crisis due to their outstanding performance of freshwater extraction from saline water via ion rejection. However, it is still very challenging to achieve high selectivity and high permeance of water desalination through precise d-spacing control of 2D nanomaterial membranes within subnanometer. Here, we developed functionalized graphene oxide membranes (FGOMs) with nitrogen groups such as amine groups and polarized nitrogen atoms to enhance metal ion sieving by one-step controlled plasma processing. The nitrogen functionalities can produce strong electrostatic interactions with metal ions and result in a mono/divalent cation selectivity of FGOMs up to 90 and 28.3 in single and binary solution, which is over 10-fold than that of graphene oxide membranes (GOMs). First-principles calculation confirms that the ionic selectivity of FGOMs is induced by the difference of binding energies between metal ions and polarized nitrogen atoms. Besides, the ultrathin FGOMs with a thickness of 50 nm can possess a high water flux of up to 120 mol m–2 h–1 without sacrificing rejection rates of nearly 99.0% on NaCl solution, showing an ultrahigh water/salt selectivity of around 4.31 × 103. Such facile and efficient plasma processing not only endows the GOMs with a promising future sustainable water purification, including ion separation and water desalination, but also provides a new strategy to functionalize 2D nanomaterial membranes for specific purposes.

Stable Two‐dimensional Nanoconfined Ionic Liquids with Highly Efficient Ionic Conductivity

“…However, a series of material limitations have seriously hampered the development of the current energy which can accommodate more ions to enhance the flux. [30][31][32][33][34] Ease of fabrication and functionalization further promotes the applications of 2D nanochannels. [35][36][37][38][39][40] Moreover, the effect of nanomaterials on ILs is controversial and likely depends on different confinement scales.…”

“…In comparison with the nanomaterials above, 2D nanochannels generated by nanosheets are promising candidates for QLSE supporters because of the extended interlayer space created by the layer‐to‐layer repulsive interactions or intercalated compounds, which can accommodate more ions to enhance the flux. [ 30–34 ] Ease of fabrication and functionalization further promotes the applications of 2D nanochannels. [ 35–40 ] Moreover, the effect of nanomaterials on ILs is controversial and likely depends on different confinement scales.…”

Microscopically tuning the graphene oxide framework for membrane separations: a review

“…Lei and co-workers developed an ultrathin functionalized GO membrane of 50 nm thickness with enriched nitrogen functional groups by simultaneously introducing nitrogen functional groups to enhance metal ion sieving by one-step controlled plasma processing (Fig 8b). 79 The selectivity of such GO-based membranes for mono/divalent cation was synthesised to be 10-fold higher than that of pristine GOMs. An ultrahigh water/salt selectivity of approximately 4.31 × 10 3 was also achieved when applying K + , Na + , Ca 2+ , and Mg 2+ ions to evaluate the permeation rates.…”

Angstrom-scale ion channels towards single-ion selectivity

“…In another illustration by Wang et al, the ion selectivity of the PET membrane decreases by one order of magnitude as the pore size increases to 1 nm. 77 As 2D ion channels/membranes are fabricated by selfassembly of various 2D material nanosheets into lamellar membranes, the interlayer spaces (d) and functional groups of the membranes are varied with the variations of materials (i.e., graphene, 157,160,161 GO, 102,107,143,148,[162][163][164] Mxene, 104,165-167 BN, 105,168 and MoS 2 103) and fabrication procedures, resulting in different metal ion sieving properties of these 2D ion channel membranes. The ion permeation rates decrease exponentially with the decreasing d, as well as the channel cut-off diameter.…”