3.4 Adsorbent stability and interaction with uranyl ions
The morphology of the adsorbent after uranium extraction/elution was
analyzed by using SEM analysis. From Figure 10, we see the SEM images
after uranium extraction (Figure 10a) and uranium elution (Figure 10b)
confirmed that seawater exposed AO-Fc maintained the integrity of
structure after reuse of several cycles for a long time of seawater
exposure. The detailed chemical composition of the uranium-loaded
adsorbent (AO-Fc-U) adsorbent was analyzed by XPS and FTIR analysis and
the results were compared with the adsorbent before uranium adsorption
(AO-Fc) (Figure 11). The uranium-loaded adsorbent (AO-Fc-U) showed two
peaks at 390.9 eV and 380.1 eV assigned to U 4f5/2 and U
4f7/2 confirmed the presence of uranium on AO-Fc (Figure
11a). As shown in Figure 11b, two types of Nitrogen peaks were observed
at 400.05 eV and 398.4 eV assigned to N-H and C=N respectively. And also
in accordance with Figure 11c, the binding energy of both N-H and C=N
shifted to higher binding energy at 400.9 eV and 399.1 eV. The positive
shift in N-H and C=N groups confined the coordination of nitrogen and
uranium ions. To further analysis the uranium-loaded adsorbent was
analyzed by FTIR. Compared with the results (Figure 11d), the uranium
loaded spectra showed the shifts at various peaks or increase peak
intensity. What is more, in the FTIR spectrum of AO-Fc, two new peaks
were observed at 937 cm-1 and 1161
cm-1 confirming the presence of uranium on
AO-Fc50,51.