## 3 Results and Discussion
### Characterization of the Tested Adsorbents
The thermogravimetric profile of A/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) beads in oxidizing atmosphere (Figure S1c) was similar to that obtained under inert conditions, with a more intense decay in the weight sample at approximately 200 \({}^{\circ}\)C. Finally, TGA/DTG curves of A/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)/f-CNT composite (Figure S1d) showed a dramatically decreasing in the weight of sample at \(\sim\)250 \({}^{\circ}\)C, remaining a weight content of 7.37% at the final temperature, attributed to the iron oxides amount present in the composite. SEM micrographs of the synthesized materials are shown in Figure 4a-e. A TEM micrograph of f-CNT material is shown in Figure S2 (Supplementary Material). The SEM images showed the roughness of the surface of alginate beads (Figure 4a). For carbon nanotubes, the cylindrical form of f-CNTs could be appreciated with a diameter from 20 to 50 nm and a length of 50-100 nm (Figure 4b, Figure S2). \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) nanoparticles are of spherical shape, showing many aggregations due to the drying before SEM analysis (Figure 4c). The elemental composition of \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) obtained by EDX analysis was as follows: %C of 19.96, %O of 25.15, %Na of 7.92 and %Fe of 46.97%, confirming the coating of the particles with sodium citrates. The nanoparticles showed a larger size than that determined by XRD; this is due to the aggregation of nanoparticles because of van der Waals forces and magnetic repulsions [46]. For A/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) beads (Figure 4d), their external surface appeared very rough with a uniform dispersion of \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) nanoparticles. Finally, in the case of A/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)/f-CNT (Figure 4e), the surface is very rough and heterogeneous, observing areas with larger aggregations than those observed in A/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) beads. The coupling of f-CNTs with \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) nanoparticles in the alginate matrix lead to improve the mechanical properties of the composite and to have aggregations in the beads [47]. The magnetization curves of \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\), A/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) and A/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)/f-CNTs materials are shown in Figure 5. The superposition of the curves indicated that \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) nanoparticles maintained their magnetic properties when they were encapsulated in the beads. According to the shape of the obtained curves, the materials have a magnetic memory with superparamagnetic behavior. The magnetization saturation values, determined at 295 K, resulted in 42.63, 29.06 and 27.16 emu g \({}^{-1}\) for \(\gamma\)- Fe\({}_{2}\)O\({}_{3}\), A/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) and A/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)/f-CNT, respectively. Figure 4: SEM micrographs of (**a**) alginate, (**b**) f-CNT, (**c**) \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) particles, (**d**) A/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) and (**e**) A/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)/f-CNT beads. The magnetization saturation of A/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)/f-CNT beads was slightly lower than that of A/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) beads, but it stills enough to be efficiently separated from the aqueous medium. From these magnetization measurements, the mass fractions of \(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) nanoparticles in A/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\) and A/\(\gamma\)-Fe\({}_{2}\)O\({}_{3}\)/f-CNT beads were estimated to be 65 and 60%, respectively. These results revealed that the synthesized magnetic beads are excellent materials for wastewater treatment in large-scale applications because they can be easily separated from water using a magnetic field.