# Novel Polymer Sorbents with Imprinted Task-Specific Ionic Liquids for Metal Removal
## 3 Results and Discussion
### Sorption Studies  
#### 3.2.1 Effect of pH  
The pH of the solution is one of the most important parameters influencing adsorption and removal of metal ions from the aqueous feed solution. The percent of metals removal as a function of pH were plotted for all tested metals and illustrated in Figure 5a-d. The presented experimental data show that, regardless of the tested sorbents and the type of metal ions adsorbed, the sorption almost does not occur when the pH is lower than 2. The sorption from solution with pH of 3 is much higher, but only for Cd(II) sorption onto VBC-K3.10 and VBBr-K3.10 as well as for the Cd(II) and Cu(II) sorption onto VBBr-K4.10, VBC-Ox3.10, VBC-Ox4.10, VBBr-Ox3.10, and VBBr-Ox4.10, in which the removal is higher than 50%. Moreover, for the Cd(II) sorption onto VBC-K3.10, VBBr-K3.10, VBBr-K4.10, VBC-Ox3.10, VBC-Ox4.10, VBBr-Ox3.10, and VBBr-Ox4.10, the further increase in the pH value does not significantly affect the sorption efficiency. The most efficient metal ion removal from pH above 4 may be attributed to the fact that the positive species (M\({}^{+2}\)) is the most abundant at this condition and can be attracted by an interaction with the negative  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **T\({}_{onset}\)\({}^{o}\)C** & **Hp\({}^{**}\), J/g** & **Tp\({}^{**}\), \({}^{o}\)C** & **Ref.** \\ \hline VBC & 382.3 & 23.1 & 83.9 \\ VBC-K3.10 & 185.4 & 12.4 & 88.3 \\ VBC-K4.10 & 159.7 & 26.3 & 100.9 \\ VBC-Ox3.10 & 193.8 & 26.1 & 93.2 \\ VBC-Ox4.10 & 179.4 & 27.6 & 90.2 \\ VBBr & 336.4 & 10.1 & 80.0 \\ VBBr-K3.10 & 158.2 & 36.6 & 88.0 \\ VBBr-K4.10 & 182.1 & 45.6 & 90.2 \\ VBBr-Ox3.10 & 195.5 & 16.1 & 77.2 \\ VBBr-Ox4.10 & 191.8 & 25.2 & 85.3 \\ Lewatit TP 207 & 80 & & [36] \\ Amberlyst 15 & 150 & & [37] \\ \hline \hline \end{tabular}  
* \(T_{onset}\)—temperature of decomposition of polymers determined from TG measurements. Hp\({}^{**}\)—heat of solvent evaporation determined from DSC thermograms. Tp\({}^{**}\)—the temperature at the maximum of heat evaporation peak determined from DSC thermograms.  
\end{table}
Table 2: Thermal properties of sorbents (and for comparison commercial resins).  
Figure 4: Thermogravimetric curves unmodified and modified VBC and VBBr with K3.10 and K4.10.  
zeta potential surface, which is in agreement with the electro-kinetic profile of the sorbents (see Figure S2). From the zeta potential measurements, a positive potential below a pH of 3.0-3.8 was indicated, which changed to a value negative above the isoelectric point.  
The sorption results also indicate that the effectiveness of the process depends on the type and the structure of the functional group. For Zn(II) and Cu(II), VBBr-Ox4.10 is much more efficient than other considered materials, while for Cd(II) the VBC-K3.10, resin has been found to be highly effective.  
The dependence of the removal efficiency on the pH of the aqueous phase probably is a result of the competitive adsorption effect of the H\({}^{+}\) ions. This effect and speciation analysis [38] point to sorption of cationic species of Zn(II), Cu(II), and Cd(II) through interactions with the ketone group (through the lone pair of the donor carbonyl oxygen atom interaction) [39] or with the oxime group, which can bind a metal cation via oxygen and nitrogen atoms [40]. To further explore the interactions between metals cations and the appropriate groups, XPS measurement was employed. It was shown that, in the case of the ketone sorbents and the O1s emission, a new low-energy feature at 531.0 eV appeared with the simultaneously decrease in 532.3 eV. The growth of the new feature also resulted in the growth of C 1s emissions at 284.8 and a decrease at 286.4 eV. For VBC and VBBr modified by the oxime derivatives, the appearance of new emission was also observed for N 1s (399.4 eV), and growth emission at 402.26 eV. Both signals were consistent with the presence of -H- and the quaternary N, in the resin structure.