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 S10, the SEM image of AO-Fc
after uranium extraction (Figure S10a) and uranium elution (Figure S10b)
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 before uranium adsorption of adsorbent (AO-Fc)
(Figure 8). 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 confirming the presence of uranium on AO-Fc
(Figure 8a). As shown in Figure S11a, 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 from Figure S11b, 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. Further, the uranium-loaded adsorbent was analyzed by FTIR
and the results were compared (Figure 8b), the uranium-loaded spectra
showed 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-Fc54,55.