The swelling of EDTA-modified chitosan–silica hybrid materials
was compared to the swelling of pure EDTA–silica gel and –chitosan
(Supplementary information, Fig. S2). It was observed that there was
no pronounced swelling in the case of hybrid materials, indicating
that silica gel incorporated in the chitosan thereby increased the
rigidity of the structure. Finally, the leaching of silicon at different
pH was measured by ICP–OES (Fig. 2). It was noted that only the
material with the highest silicon content showed higher Si(II) leaching
than EDTA–silica gel. However, at pH 5 its leaching was still
below 1% (m/m), indicating the stability of the hybrid adsorbents.