Table 3
The most important XPS results reside in the shifts of the binding
energy (BE) of the key elements (oxygen, silicon and aluminum)(Table 3) providing evidence of the occurrence of metal
interaction with the host surface. For oxygen, the BE value decreased
from 532.55 eV down to 531.00 eV and 527.00 eV upon Cu and Ag
incorporation in NaMt samples, respectively. Similar sequence was
noticed in H20@CT, but with much weaker BE decrease from 533.00 eV down
to 531.65 eV and 531.74 eV after Cu and Ag incorporation. This suggests
weaker metal retention in this organic composite. Such a BE weakening
indicates lower electron binding to their parent-atom due to an
attraction by next-neighboring species, and can be explained in terms of
Lewis-Acid-Base (LAB) interaction between lattice oxygen and MNPs. This
indicates weaker interaction with CuNPs as compared to AgNPs in both
materials, and weaker retention strength of both metals in H20@CT.
BE decay was also noticed for Si and Al atoms from 1383.20 to 103 and
1411.29 to 75, respectively, suggesting additional MNP interactions with
the aluminosilicate surface (Fig. 2.b) . The presence of a C1s
signal in clay samples may be due to CaCO3, as supported
by the XRD pattern of bentonite with 113, 202 and 018 plane families
between 40-45 degrees. XPS data, more particularly for cellulose-based
samples (Fig. S12 ) showed no significant BE shift for C atom,
indicating that carbon interaction with MNP, if any, is negligible.