## 4 Conclusions  
In this work, we studied the possibility of using coproducts of plant origin as adsorbent systems for environmental pollutants. These materials are the starch-enriched and deproteinized barley seeds BS-HVL and BC-HVL. There are several reasons for using these materials. First, they may be used for the development of natural materials for specific applications in water depollution. The majority of organic flocculants, coagulants and adsorbents used in the field of water treatment are obtained from synthetic (petroleum) resources. The seeds we modified are abundant and cheap products, made from renewable, biodegradable and biocompatible agricultural raw materials. The second reason is in line with the development of sustainable chemistry. The BS-HVL and BC-HVL that were used are deproteinized fractions enriched with starch, a polysaccharide which presents very interesting modification chemistry. To simplify the optimization process, the effect of pH was first studied by a one-variable-at-a-time method, after which the influences of other parameters, such as sonication time, initial dye concentrations and adsorbent dosage were examined. The optimal conditions were pH 7, a dose of 0.05 g of BC-HVL or BS-HVL, a sonication time of 90 min, and initial concentrations of 50 mg L\({}^{-1}\) for X-PR and MGC, respectively, which resulted in high removal percentages (91% for X-PR and 98% for MGC). In addition, the adsorption capacities were 71.6 mg g\({}^{-1}\) and 44.8 mg g\({}^{-1}\) for X-PR and 44.8 mg g\({}^{-1}\) and 121.5 mg g\({}^{-1}\) for MGC. The adsorption equilibrium study showed that both Langmuir and Freundlich models had adequate competence for the description and evaluation of the adsorption process. The kinetic study was performed at different time intervals. The results indicated that the adsorption processes can be fitted and predicted by the pseudo-second-order model with an adsorption capacity of 61.7 mg g\({}^{-1}\) and 41.7 mg g\({}^{-1}\) for X-PR and 54 mg g\({}^{-1}\) and 41.8 mg g\({}^{-1}\) for MGC. In a difficult economic context, characterized by increased competition on the polysaccharide market, cereal producers are wondering about the possibilities of novel applications for the products and wastes from this sector of activity.  
Conceptualization, F.E.M., F.C. and J.C.G.E.d.S.; methodology, F.E.M.; investigation, C.B., H.E.F., F.E.M., and M.H.Z.; resources, J.C.G.E.d.S.; data curation, F.E.M.; writing--original draft preparation, F.E.M.; writing--review and editing, F.C.; supervision, F.C., J.B., M.P.L. and J.C.G.E.d.S.; project administration, J.C.G.E.d.S. All authors have read and agreed to the published version of the manuscript.  
This work was completed in the Faculty of Sciences of the University of Porto, within the framework of program Erasmus (Key Action 1, MOBILE+3). \"Fundacao para a Ciencia e Tecnologia\" (FCT, Portugal) is acknowledged for the project UIDB/00081/2020.  
Not applicable.  
The authors declare no conflict of interest.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multicolumn{2}{c}{**BS-HVL**} & \multicolumn{2}{c}{**BC-HVL**} \\ \cline{2-5}  & **X-PR** & **MGC** & **X-PR** & **MGC** \\ \hline \(\Delta\)H\({}^{\circ}\) **(k) mol\({}^{-1}\))** & 23.55 & 12.757 & 21.179 & 13.386 \\ \(\Delta\)S\({}^{\circ}\) **(J mol\({}^{-1}\) K\({}^{-1}\))** & 90.797 & 46.074 & 103.734 & 74.759 \\  & T = 294 K & \(-\)27.034 & \(-\)13.533 & \(-\)30.477 & \(-\)21.966 \\ \(\Delta\)G\({}^{\circ}\) **(k) mol\({}^{-1}\))** & T = 303 K & \(-\)27.942 & \(-\)13.948 & \(-\)31.410 & \(-\)22.639 \\  & T = 323 K & \(-\)29.758 & \(-\)14.869 & \(-\)33.485 & \(-\)24.134 \\  & T = 343 K & \(-\)30.666 & \(-\)15.791 & \(-\)35.560 & \(-\)25.629 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Thermodynamic parameters for the adsorption of X-PR and MGC onto BS-HVL and BC-HVL (m\({}_{\text{ad}}\) = 50 mg; C\({}_{0}\) = 50 mg L\({}^{-1}\); pH = 7 \(\pm\) 0.3 and stirring speed 150 rpm).