3. Result and discussion
3.1. Effect of pH on adsorption
pH value plays an important role in the adsorption process due
to the adsorption of different ions on TiO2 surfaces. As said by
Morterra (1988), the pH of solution affects the distribution of
active sites on the surface of titanium dioxide nanoparticles.
The surface charge is neutral at the isoelectric point (IEP),
which is at pH 6.8 for TiO2 nanoparticles (Zhang et al.,
2009). In general, when the pH of the solution is higher than
the isoelectric point of the adsorbent, the negative charge on
the surface provides electrostatic attractions that are favorable
for adsorbing cations such as thallium. In this experiment, the
effect of the pH on the retention of thallium on the TiO2 was
studied in the range of 4–12 and operated according to the recommended
procedure.
Fig. 2 shows the results of the effect of pH on the recoveries
of thallium(I) ions by nanoparticles, which indicates that the
adsorption percentage of the thallium sharply increases to
the maximum as the pH increases to 9 and keep constant with
the further increase of pH. Hence, in the following experiments
the sample pH was adjusted to 9.
3.2. Elution of the adsorbed Tl(I) ions
It is found from Fig. 2 that the adsorption of thallium at
pH < 4 could be negligible. Thus, various concentration of
HCl were considered for the elution of retained Tl(I) from
the microcolumn. Fig. 3 shows the effect of HCl concentration
on the recovery of the adsorbed Tl(I). It can be seen that 1.0 M
HCl is enough to recover the Tl(I) quantitatively. Therefore, we
applied 1.0 M HCl to recover the Tl(I) from microcolumn in
this research. Then the effect of elution volume on the recovery
of Tl(I) by keeping the HCl concentration equal to 1.0 M was
studied. It was found that quantitative recoveries (>95%)
could be achieved by 1.0 mL of 1.0 M HCl as the eluent.