## 3 Results and Discussion  
### Hybrid Polymer Formation  
To obtain novel HIXs with high CuO content, we used two carboxyl cation exchangers (Table 1), which show the highest ion exchange capacity (almost 11.0 meq/g) among mass-produced ion exchangers. These resins contained the same functional groups and in a comparable amount, but they differed in the structure and chemical composition of the polymeric skeleton. The matrix of the macroreticular cation exchanger was obtained by polymerizing a methacrylic acid with divinylbenzene (DVB) as a cross-linking agent, whereas the matrix of the gel-like cation exchanger was obtained by polymerizing an acrylic acid with DVB (the precise producer data concerning the cross-linking degree value are not known). The acrylic resins are slightly more strongly acidic (more dissociated, pK\({}_{4}\) 4.8) than the methacrylic acid products (less dissociated, pK\({}_{4}\) 5.7) [58]. Reaction equations illustrate the transformations to which both cation exchangers were subjected to dope CuO Equations (1)-(5):  
\[[\mathrm{P}]-\mathrm{COOH}+\mathrm{NaOH}\ \rightarrow[\mathrm{P}]- \mathrm{COONa}+\mathrm{H}_{2}\mathrm{O} \tag{1}\]  
\[2[\mathrm{P}]-\mathrm{COONa}+\mathrm{CuSO}_{4}\ \rightarrow([\mathrm{P}]- \mathrm{COO})_{2}\mathrm{Cu}+\mathrm{Na}_{2}\mathrm{SO}_{4} \tag{2}\]  
\[([\mathrm{P}]-\mathrm{COO})_{2}\mathrm{Cu}\ \ \mathrm{excess}\mathrm{NaOH}\ \{2[\mathrm{P}]- \mathrm{COONa}\}\#\mathrm{CuO} \tag{3}\]  
\[\{2[\mathrm{P}]-\mathrm{COONa}\}\#\mathrm{CuO}+\mathrm{CuSO}_{4}\ \rightarrow([\mathrm{P}]- \mathrm{COO})_{2}\mathrm{Cu}\#\mathrm{CuO}+\mathrm{Na}_{2}\mathrm{SO}_{4} \tag{4}\]  
\[[\mathrm{P}]-\mathrm{COONa}\#\mathrm{CuO}+\mathrm{CH}_{3}\mathrm{COOH}\ \rightarrow[\mathrm{P}]- \mathrm{COOH}\#\mathrm{CuO}+\mathrm{CH}_{3}\mathrm{COONa} \tag{5}\]  
[P]--polymeric skeleton of cation exchanger. Three types of materials were synthesized: with the functional groups in the Na\({}^{+}\) form (M/Na#CuO, G/Na#CuO), with the functional groups in the Cu\({}^{2+}\) form (M/Cu#CuO, G/Cu#CuO), and with the functional groups in the H\({}^{+}\) form (M/H#CuO, G/H#CuO). As the functional groups of both host materials occurred in the H\({}^{+}\) form (M/H, G/H), consequently, they cannot remove Cu\({}^{2+}\) ions from solutions of mineral acid salts (because the acid produced lowers the pH and prevents further ion exchange); firstly, they had to be converted into the Na\({}^{+}\) form. For this purpose, 1 M NaOH was used, initially in the batch method and then in the column, as the reaction (Equation (1)) was running with a thermal effect and with a large increase in the volume of the bed (H\({}^{+}\rightarrow\) Na\({}^{+}\) swelling-in-water 80-100%). The functional groups in the Na\({}^{+}\) form could already be converted into the Cu\({}^{2+}\) form by passing 0.1 M CuSO\({}_{4}\) solution through the resin bed in column (Equation (2)). Then, the resin was shaken with an excess of NaOH solution in batch condition to precipitate CuO in its matrix (Equation (3)). To obtain HIX with a simpler elementary composition, the functional groups were converted into the Cu\({}^{2+}\) form (Equation (4)). The aim of transformation of M/Na#CuO and G/Na#CuO to M/H#CuO and G/H#CuO (Equation (5)) was to obtain HIXs that would not alkalize the reaction environment, as high pH makes many sorption and catalytic processes inefficient. To perform such gentle transformation effectively, i.e., to prevent the dissolution of the deposit in acidic medium, 0.05 M CH\({}_{3}\)COOH (pH \(\sim\) 3.9) was used, considering that the degree of ionization of the -COOH groups in resins corresponds to that of acetic acid. Therefore, CH\({}_{3}\)COOH solution was passed through the M/Na#CuO or G/Na#CuO bed in the column until traces of Cu\({}^{2+}\) appeared in the effluent. In the case of M/Na#CuO, this was done at pH \(\sim\) 6.0, and in the case of G/Na#CuO at pH \(\sim\) 4.7.