## 3 Results and Discussion
### Modeling of Sorption Isotherms--Influence of pH
\begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{3}{*}{**Isotherm**} & \multicolumn{3}{c}{**Suspended**} & \multicolumn{3}{c}{**TiO\({}_{2}\)-GF**} & \multicolumn{3}{c}{**TiO\({}_{2}\)/CNT-GF**} \\ \cline{2-10}  & **5** & **7** & **9** & **5** & **7** & **9** & **5** & **7** & **9** \\ \cline{2-10}  & \(K_{d}\) (mL/g) & 103.5 & 233.8 & 234.4 & 117.12 & 179.18 & 208.91 & 197.74 & 234.12 & 329.67 \\ \(R^{2}\) & 0.9965 & 0.9970 & 0.9993 & 0.9980 & 0.9930 & 0.9922 & 0.9911 & 0.9936 & 0.9940 \\ \hline \multicolumn{2}{c}{_[PERSON]_} & \multirow{3}{*}{10.0} & \multirow{3}{*}{5.0} & \multirow{3}{*}{20.0} & \multirow{3}{*}{100} & \multirow{3}{*}{5.0} & \multirow{3}{*}{10.0} & \multirow{3}{*}{50} & \multirow{3}{*}{166.7} & \multirow{3}{*}{33.3} \\ \(k_{L}\) (mL/g) & 0.015 & 0.5 & 0.5 & 0.001 & 0.074 & 0.036 & 0.004 & 0.0013 & 0.0097 \\ \(R^{2}\) & 0.9968 & 0.8665 & 0.9072 & 0.9980 & 0.9976 & 0.9990 & 0.9911 & 0.9994 & 0.9986 \\ \hline \multicolumn{2}{c}{_Freundlich_} & \multirow{3}{*}{1.2} & \multirow{3}{*}{2.6} & \multirow{3}{*}{2.7} & \multirow{3}{*}{0.99} & \multirow{3}{*}{1.3} & \multirow{3}{*}{1.2} & \multirow{3}{*}{0.99} & \multirow{3}{*}{0.97} & \multirow{3}{*}{0.98} \\ \(K_{F}\) & & & & & & & & & \\ \(n\) & 1.2 & 2.6 & 2.7 & 0.99 & 1.3 & 1.2 & 0.99 & 0.97 & 0.98 \\ \(K_{F}\) & & & & & & & & & \\ \((\text{ug}/\text{g})\text{(mL}/\text{ug})^{1/n}\) & & 174.2 & 2025.8 & 2105.7 & 116.5 & 399.9 & 382.6 & 204.2 & 208.8 & 329.7 \\ \(R^{2}\) & 0.9982 & 0.9482 & 0.9707 & 0.9984 & 0.9974 & 0.9994 & 0.9965 & 0.9975 & 0.9967 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Sorption isotherm parameters for CRZ as an influence of pH. \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline \multirow{3}{*}{**Sample**} & \multirow{3}{*}{**c\({}_{0}\), mg/L**} & \multicolumn{3}{c}{**First Stage**} & \multicolumn{3}{c}{**Second Stage**} & \multicolumn{3}{c}{**Third Stage**} \\ \cline{3-10}  & \(k_{\text{p1}}\) & \(k_{\text{p2}}\) & \(k_{\text{p3}}\) & \(k_{\text{p3}}\) & \(k_{\text{p2}}\) & \(k_{\text{p3}}\) & \multirow{3}{*}{\(K_{\text{p3}}\)} & \multirow{3}{*}{\(K_{\text{p3}}\)} & \multirow{3}{*}{\(K_{\text{p2}}\)} & \multirow{3}{*}{\(K_{\text{p3}}\)} \\  & \(\text{ug}/\text{g}\text{ min}^{1/2}\) & & & & & & & & \(\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\The sorption coefficient \(K_{d}\) showed an increasing trend with increasing pH values for IMT and CRZ on TiO\({}_{2}\) in three forms (Figure 2). According to the literature [41,42], the zeta potential of TiO\({}_{2}\) is between 6 and 6.5, so TiO\({}_{2}\) is positively charged at pH 5; it is probably predominantly negatively charged at pH 7 and 9. The \(pK_{\text{a}}\) value of IMT nitrogen atom of piperazine is about 7.8-8.07 [27,43], which means that IMT is positively charged in acidic medium and predominantly negatively charged under alkaline conditions. At pH 5, electrostatic repulsive interactions predominated causing the least sorption, while at higher pH values, electrostatic attractive forces were promoted between neutral IMT and more negatively charged TiO\({}_{2}\). At pH 9, the sorption affinity of the pharmaceutical was highest, while at pH 7 (value close to the isoelectric point of the sorbent), agglomeration was possible on the TiO\({}_{2}\) surface resulting in lower sorption affinity [41,44]. A similar trend in sorption affinity was obtained with CRZ which has two \(pK_{\text{a}}\) values: 5.6 and 9.4. It can exist in positive, neutral, and negative forms under different pH conditions [26]. Therefore, the increase in sorption coefficient is accompanied by an increase in pH, which is due to the different species present in the medium causing repulsive forces at pH 5 or attractive forces at pH 9.