## 3 Results and Discussion
### Dye Adsorption Evaluation  
The effect of contact time on MO adsorption over the prepared materials is given in Figure 5a. Adsorption equilibrium was achieved within less than 5 min for all materials containing UiO-66. On the contrary, equilibrium was reached at longer reaction times for pure Pal and TiO\({}_{2}\). Significant differences were also detected in the experimentally observed adsorption capacity at equilibrium (q\({}_{\text{e,exp}}\)). The q\({}_{\text{e,exp}}\) together with the removal efficiency (RE %) are given in Table 1. Both TiO\({}_{2}\) and Pal presented low q\({}_{\text{e}}\) and removal efficiency. On the contrary, the pure U and PU composite presented high adsorption capacity, with the PU sample being the most efficient (q\({}_{\text{e}}\) = 213.3 mg\(\cdot\)g\({}^{-1}\)). This suggests that the presence of Pal at low amounts in the composite was beneficial for MO adsorption. An increase in the adsorption capacity of dyes was previously shown in oxide/MOFs or clay mineral/MOF composites including UiO-66 [25; 42; 54; 55], as well as in other MOF-based composites [20; 21]. In the specific case of Pal/UiO-66 composites, formation of microporosity at the interface of the two parts was shown to increase the specific surface area that may affect adsorption efficiency [56]. A decrease in the q\({}_{\text{e}}\) and the removal efficiency was observed in the composite bearing TiO\({}_{2}\) (i.e., PUT). This was probably related to the relatively high amount of TiO\({}_{2}\) in the PUT composite that presented low q\({}_{\text{e}}\). However, the removal efficiency in these composites was not a linear combination of the individual counter parts considering their content in the composites. Taking into account the fast kinetic profile of MO adsorption, the high q\({}_{\text{e}}\), and the removal efficiency, the adsorption behavior of the PUT composite was dominated by UiO-66. Lastly, in order to verify the stability of the composites, recycling adsorption experiments using the most efficient composite were performed (Figure S1). The stability was evidenced by the small loss of adsorption efficiency after three consecutive cycles [56]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **q\({}_{\text{e,exp}}\)** & \multirow{2}{*}{**RE (\%)1**} & **q\({}_{\text{e,cal}}\)** & **k\({}_{2}\)** & **k\({}^{2}\)** & **k\({}^{2}\)** & **k** \\  & **(mg\(\cdot\)g\({}^{-1}\))** & & **(mg\(\cdot\)g\({}^{-1}\))** & **(g\(\cdot\)mg\({}^{-1}\)\(\cdot\)min\({}^{-1}\))2** ** & **(min\({}^{-1}\))3** ** \\ \hline U & 195.7 & 87.1 & 196.1 & 0.012 & 0.999 & \\ PU & 213.3 & 94.9 & 212.8 & 0.074 & 0.999 & \\ PUT & 174.7 & 77.5 & 175.4 & 0.108 & 0.999 & 0.0153 \\ TiO\({}_{2}\) & 41.3 & 18.3 & & & & 0.0043 \\ Pal & 20.9 & 9.3 & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Experimentally obtained and calculated values for q\({}_{\text{e}}\), removal efficiency (RE %), and correlation coefficient (\(R^{2}\)) for the pseudo-second-order kinetic model used to simulate the adsorption process and photocatalytic rate constant (k). Figure 4: UV/Vis absorption spectra (**a**) and plots used to estimate the bandgap energies (**b**). The pseudo-second-order kinetic model [54; 55; 57; 58; 59] was used to fit the experimental data as represented by Equation (3). \[\frac{\mathrm{t}}{\mathrm{q_{t}}}=\frac{1}{\mathrm{k_{2}q_{e}^{2}}}+\frac{ \mathrm{t}}{\mathrm{q_{e}}}, \tag{3}\]  
where \(\mathrm{q_{e}}\) is the amount of MO adsorbed at equilibrium, \(\mathrm{q_{t}}\) the MO adsorbed at time t, and \(\mathrm{k_{2}}\) is the rate constant (\(\mathrm{g\cdot mg^{-1}\cdot min^{-1}}\)) of the second-order adsorption kinetics. The fitted adsorption kinetic curves for the materials containing UiO-66 as a function of time are given in Figure 5b. The correlation coefficient \(R^{2}\) together with the calculated adsorption at equilibrium (\(\mathrm{q_{e,cal}}\)) is given in Table 1. High correlation coefficients were obtained for all materials.