AES characterizations (the C and O concentration distributions along the thickness) for GO membranes after annealing at 80°C for (a) 0 and (b) 9 days, respectively.

<p>The sputter rate is 35 nm/min. (c) The comparison of O/C ratio distributions along the depth within GO membranes after 0- and 9-day annealing. (d, e) C (red) and O (green) mappings of GO membranes after 0- and 9-day annealing, respectively. The mappings were performed after sputtering the GO membranes for 5 min to exclude the effect of surface O physisorption.</p

Selective Ion Transport through Functionalized Graphene Membranes Based on Delicate Ion–Graphene Interactions

Recently, graphene oxide (GO) membranes have been reported with the ability to separate different solutes in aqueous suspensions by a molecular sieving effect. On the other hand, we propose that the chemical interactions between ions and GO membranes might also take effect in selective ion transmembrane transportation. In this paper, on the basis of the permeation of Cu²⁺ and Mg²⁺ sources through hydroxyl-, carboxyl-, and amino-functionalized graphene membranes, the delicate ion–graphene interactions which might be responsible for the selective ion permeation are investigated. We demonstrate experimentally that the coordination between transition-metal cations and carboxyl functionalities and the cation−π interactions between main-group cations and sp² regions are responsible for the selective transport of small ions through graphene-based membranes, which is beyond the scope of molecular sieving effect proposed previously. Notably, by grafting amino groups onto the graphene basal planes, the permeations of Cu²⁺ and Mg²⁺ cations are both weakened. These results not only throw light upon the mechanism for the selective ion permeation through graphene-based membranes but also lay a foundation for the separation of target ions by grafting specific functionalities

Formation energies and reaction barriers for proposed evolution paths (a–c) of oxygen containing functional groups on GO, calculated by DFT based calculations.

<p>Formation energies and reaction barriers for proposed evolution paths (a–c) of oxygen containing functional groups on GO, calculated by DFT based calculations.</p

XPS spectra of GO during the mild annealing procedure at 80°C for (a) 0 day, (b) 4 days and (c) 9 days, respectively. (d) The O 1s spectra of GO after annealing for 0 to 9 days. (e) The atomic percentages of C and O after annealing for 0 to 9 days. (f) The relative ratios of C-C (<i>sp²</i>) and diverse oxygen functional groups during the mild annealing process.

<p>XPS spectra of GO during the mild annealing procedure at 80°C for (a) 0 day, (b) 4 days and (c) 9 days, respectively. (d) The O 1s spectra of GO after annealing for 0 to 9 days. (e) The atomic percentages of C and O after annealing for 0 to 9 days. (f) The relative ratios of C-C (<i>sp²</i>) and diverse oxygen functional groups during the mild annealing process.</p

Ion permeation tests.

<p>(a) Schematic drawing for the ionic transport through GO laminates. (b) Photograph of the self-made ion permeation apparatus. (c) Ionic permeation processes (drain conductivity variations <i>versus</i> time) through GO membranes after mild annealing for 0 to 9 days. (d) The changes of ion permeation rates for GO membranes annealing for various degrees.</p

FTIR spectra of GO membranes after low-temperature annealing for 0 to 8 days, showing the relative changes of oxygen functionalities.

<p>The plots in (b) show the transmittance changes of the bands assigned to C = O (∼1730 cm⁻¹) and C-OH (∼3400 cm⁻¹) during mild annealing.</p

GO membranes.

<p>(a) Schematic diagram for the diffusion and transformation of oxygen functionalities on GO during the mild annealing procedure. (b) Photographs of GO samples after annealing at 80°C for 0 and 9 days, respectively.</p