## 3 Results and Discussion
### Characterization of the Tested Adsorbents
Finally, the loss of mass of 8% corresponded to the decomposition of CaCO\({}_{3}\) which begins at 600 \({}^{\circ}\)C. Beyond 700 \({}^{\circ}\)C, only quicklime remained as the residue of the decomposition of CaCO\({}_{3}\), representing 14.75% of the initial mass of alginate. Thus, the total weight loss for alginate is 85.24%. One endothermic peak at 70\({}^{\circ}\)C and two exothermic peaks at 483\({}^{\circ}\)C and 533 \({}^{\circ}\)C were observed. The three peaks can be attributed to the dehydration of alginate, degradation of alginate and formation of CaCO\({}_{3}\), respectively. For \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\), the TGA/TDA (Figure 3b) curve suggested a weight loss of 8.16% at temperatures ranging from 30 to 240 \({}^{\circ}\)C, and 12.53% at temperatures from 240 to 475 \({}^{\circ}\)C. These mass losses could be ascribed to two endothermic peaks (at 89.27 and 305.4 \({}^{\circ}\)C) related to the evaporation of the water adsorbed on the surface of \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) and to the degradation of organic matter resulting from the presence of citrate ions, respectively. The third loss in weight (16.08%) at 593.67 \({}^{\circ}\)C was attributed to the transition of \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) to hematite, \(\alpha\)-Fe\({}_{2}\)O\({}_{3}\)[45]. The total loss in mass for \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) was of 36.77%. Above 845 \({}^{\circ}\)C, a \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) mass weight of 63.22% remained. Likewise, the total weight loss of the f-CNT (Figure 3c) was only of 8.53%, with an endothermic peak at 85 \({}^{\circ}\)C. In the case of A/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) (Figure 3d), three losses in mass (9, 27.77 and 14.76%) were observed at 30-758 \({}^{\circ}\)C. These losses of mass are due to the loss of water, the thermal degradation of the alginate and citrates, the formation of CaCO\({}_{3}\) and the transition of \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) to \(\alpha\)-Fe\({}_{2}\)O\({}_{3}\), respectively. The presence of alginate in A/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) decreased the thermal stability of \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\), leading to a total weight loss of 51.53%. The residue corresponded to metal oxides and quicklime. The results showed that A/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) is stable at temperatures above 758 \({}^{\circ}\)C and that the material contains \(48\pm 1\) wt% of inorganic matter and \(51\pm 1\) wt% of organic matter, indicating that the mass ratio between inorganic and organic matter in A/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) is approximately of 1.0. In the case of A/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)/f-CNT (Figure 3e), the weight loss is higher than that observed in the other materials. Four losses in mass were observed; the first (10.13%) corresponded to the dehydration of the beads; the second (11.29%) and the third (66.52%) attributed to the degradation of the organic matter and the fourth (3.35%) was due to the degradation of CaCO\({}_{3}\) and the transition of \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) towards \(\alpha\)-Fe\({}_{2}\)O\({}_{3}\). The organic matter content was of 91.29%, while the inorganic matter was of 8.43%. These mass losses corresponded to one exothermic peak at 202 \({}^{\circ}\)C and two endothermic peaks at 89 \({}^{\circ}\)C and 725 \({}^{\circ}\)C.  
TGA/DTG profiles of \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) particles, f-CNT, A/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) beads and A/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)/f-CNT under air atmosphere were obtained (Figure S1a-d in Supplementary Material). For \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\), similar TG profile was observed (Figure S1a), with weight losses at the same temperatures that those detected under inert atmosphere. A great change was obtained for the TGA/DTG profile of f-CNT (Figure S1b), observing that practically the total mass of sample was burned off at 900 \({}^{\circ}\)C under air.