## 3 Results and Discussion
### Solid-Phase Extraction of Dyes
However, the high values of the correlation coefficients make it possible to judge in favor of the applicability of both the pseudo-first- and pseudo-second-order models for describing the chemical stage of the sorption process, as well as for the possibility of considering intermolecular interactions in the analyzed systems. Figure 9: Dependence of the degree of extraction on the contact time (**a**—SY, **b**—TAR, **c**—Orange II, **d**—Methyl Orange). The adsorption of organic dyes by MOFs can occur for various reasons:  
1. The adsorption of the dye may be due to the electrostatic interaction between MOF and the adsorbate. The neutrality of the studied sorbent means the absence of any active functional groups but does not exclude the occurrence of an electrostatic charge on the surfaces of the sorbent and sorbate. For example, well-vacuum-dried copper terephthalate, placed in a glass storage vessel, easily covers the walls of this vessel, spreading in a relatively thin layer, which we repeatedly observed. 2. A sufficiently high oxygen content in the MOF composition allows for the formation of hydrogen bonds with dye molecules. 3. The formation of \(\pi\)-\(\pi\) stacking between the benzene rings of the sorbent and sorbate is possible. Cation and anion \(\pi\) interactions are possible. 4. Similar examples of interactions between sorbents of similar classes and organic dyes are quite often discussed in the works [35; 36]. The sorbent can be used repeatedly. For this, a study was made of the number of working cycles (Figure 10). The results show that the extraction of the dyes from the aqueous solutions was quantitative over four cycles. The average values of extraction with the standard deviations of the dyes for four cycles were as follows: SY--79.3 \(\pm\) 3.1%; TAR--89.1 \(\pm\) 2.3%; Orange II--92.1 \(\pm\) 3.2%; Methyl Orange--85.4 \(\pm\) 1.0%. These results suggest that the sorbent was mechanically stable and had excellent recyclability. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Dye**} & \multirow{2}{*}{\(\mathbf{T}_{\text{c}}\,^{\circ}\mathbf{C}\)} & \multirow{2}{*}{\(\boldsymbol{q_{e}}\)} & \multicolumn{2}{c}{**Pseudokinetics of the First Order**} & \multicolumn{2}{c}{**Pseudokinetics of the Second Order**} \\ \cline{5-8}  & & & \(\mathbf{k_{1}}\) & \(\mathbf{R^{2}}\) & \(\mathbf{k_{2}\times 10^{3}}\) & \(\mathbf{R^{2}}\) \\ \hline \multirow{4}{*}{SY} & 5 & 34.6 & 0.554 & 0.965 & 0.696 & 0.886 \\ \cline{2-8}  & 20 & 33.3 & 0.600 & 0.946 & 0.622 & 0.873 \\ \cline{2-8}  & 35 & 32.2 & 0.624 & 0.935 & 0.603 & 0.800 \\ \hline \multirow{4}{*}{TAR} & 5 & 37.0 & 0.965 & 0.987 & 2.435 & 0.983 \\ \cline{2-8}  & 20 & 36.2 & 0.700 & 0.992 & 0.848 & 0.972 \\ \cline{2-8}  & 35 & 36.1 & 0.554 & 0.989 & 0.698 & 0.978 \\ \hline \multirow{4}{*}{Orange II} & 5 & 38.6 & 0.624 & 0.865 & 0.584 & 0.917 \\ \cline{2-8}  & 20 & 38.2 & 0.600 & 0.883 & 0.548 & 0.890 \\ \cline{2-8}  & 35 & 37.5 & 0.509 & 0.879 & 0.508 & 0.767 \\ \hline \multirow{4}{*}{Methyl Orange} & 5 & 34.6 & 0.674 & 0.994 & 1.044 & 0.968 \\ \cline{2-8}  & 20 & 34.3 & 0.445 & 0.889 & 0.607 & 0.855 \\ \cline{1-1} \cline{2-8}  & 35 & 34.0 & 0.383 & 0.902 & 0.558 & 0.849 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Estimated kinetic parameters.