## 3 Results
### Kinetics of Removal of Cr (III) Ions Using OP  
Figure 1 shows the removal of Cr (III) using WTOP, where it is observed that the adsorption capacity increases with respect to pH in such a way that there is 38.67, 45.24, and 53.15 mg/g at pH 0.91, 1.78, and 2.72, respectively. A decrease in adsorption could also be observed when increasing the amount of mass present in the Cr (III) solution, which suggests that, despite increasing the presence of available active sites, these are more dispersed on the surface of WTOP, which makes it difficult to capture Cr ions because they do not have the necessary force to remove the ion from the solution. In contrast, when the active sites are closer to the surface, they can generate a significant force that removes the Cr (III) ions more easily, as they may not have the same energy, it is necessary to have more than one active site to remove Cr from the solution. In Table S1, the values of each parameter of the different adsorption kinetic models are shown considering the criterion of the deterministic coefficient (R\({}^{2}\)) and the normalized standard deviation (Aq). The best fit is provided by the Elovich model, and this model infers that the active sites of the bioadsorbent are heterogeneous and therefore exhibit different activation energies and cause a better adsorption, confirming what was observed in the variation of mass present in the Cr (III) solution where the removal of these ions is also affected by the environment of the solution. At a pH of 0.91 there is a removal percentage of 24.4% which increased as the pH increased (at 1.78 there is 59.3% removal) 67.2% being the maximum removal percentage at a pH of 2.72. Figure 2 shows the removal behavior of Cr (III) with MTOP, which is similar to that obtained with WTOP, where an increase in the adsorption capacity is found with the increase in pH, obtaining values of 23.61, 29.97, and 43.17 mg/g at pH 0.91, 1.78, and 2.72, respectively. This indicates that the applied treatment causes a significant change in the adsorption of Cr (III) since a decrease in the adsorption capacity of 38.44, 33.75, and 22.53% is observed at pH of 0.91, 1.78, and 2.72, respectively, in comparison with the values obtained with WTOP. Based on the parameters of the kinetic models obtained in Table S2, the best fit is also obtained with the Elovich model, which suggests that the nature of the active sites was not significantly altered by the treatment. The removal percentages of Cr (III) obtained with WTOP were 37.9%, 46.2%, and 52.1% at a pH of 0.91, 1.78, and 2.72 respectively, when comparing these values with those obtained with the MTOP treatment, \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{2}{c}{\(-\)**AG, kJ/mol**} \\ \hline pH & 0.91 & 1.78 & 2.72 \\ WTOP & 22.49 & 23.24 & 22.85 \\ MTOP & 23.58 & 23.31 & 23.02 \\ OPTmA & 22.68 & 22.18 & 23.38 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: \(\Delta\)G adsorption of Cr (III) with OP. Figure 1: WTOP adsorption capacity at different pH: (**a**) 0.91, (**b**) 1.78 and (**c**) 2.72.  
it is inferred that the treatment influences directly in the removal percentage because at pH 0.91, 1.78, and 2.72 there was a relationship of 1.55, 1.28, and 1.14 times more removal with WTOP compared to MTOP. On the other hand, in the adsorption of Cr (III) with OPTmW (Figure 3) at pH 0.91, 1.78, and 2.72, a removal capacity of 15.81, 22.05, and 30.34 mg/g, respectively, was obtained, the behavior exhibited was similar to that of the other two treatments. Comparing the adsorption capacity values obtained between OPTmW and WTOP, decreases of 50.05, 51.23 and 42.91% are observed at pH of 0.91, 1.78 and 2.72, respectively, which indicates that the combination of both treatments does not increase the Cr (III) adsorption capacity, and unlike what is expected, there is no synergistic effect. Table S3 shows the parameters of the different adsorption models obtained, where it can be seen that the best fit is presented with the Elovich model as with the two previous treatments.