Figure 1.
(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.
Figure 2.
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 (sp2) and diverse oxygen functional groups during the mild annealing process.
Figure 3.
FTIR spectra of GO membranes after low-temperature annealing for 0 to 8 days, showing the relative changes of oxygen functionalities.
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.
Figure 4.
Formation energies and reaction barriers for proposed evolution paths (a–c) of oxygen containing functional groups on GO, calculated by DFT based calculations.
Figure 5.
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.
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.
Figure 6.
(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 versus 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.