## 3 Results and Discussion
### Adsorption Studies  
The applicative evaluation of the obtained composite was performed testing its properties as an adsorbent for aliphatic and aromatic amines in water. The analytes were chosen in order to cover a broad range of chemical properties such as polarity and basicity. In this case, we wanted to take advantage of the electrostatic exchange interaction between the analytes in the form of hydrochloride  
Figure 4: Magnification of a SC@Fe\({}_{3}\)O\({}_{4}\) microcrystal (scale: 1 \(\upmu\)m and 300 nm). amines and sulfonic groups on the surface of the composite. In Scheme 3, the ionic exchange mechanism is reported, in which the acid proton of a sulfonic group is substituted from an ammonium cation. Furthermore, the magnetic susceptibility of the material allowed a rapid and simple recovery (Figure 5). The adsorption trends are reported in Figure 6.  
Figure 5: Separation of the magnetic composite after adsorption. Figure 6: Graphical depiction of the adsorption performances of the composite with various aliphatic and aromatic amines. At this point, it is necessary to provide a more rigorous explanation to justify the different results obtained with aliphatic and aromatic amines by evaluating their chemical nature. The fundamental core of our procedure is based on the cationic exchange between the SO\({}_{3}\)H groups and the salified amines; therefore, delocalization and inductive effects become relevant in modifying the cation local charge density and the subsequent interaction strength. In particular, some electronic effects can be invoked. When amines are in their hydrochloride form, an ionic couple between the ammonium ion and its counter anion (CI\({}^{-}\)) is established. In this sense, the strength of the electrostatic interaction depends on the delocalization of the positive charge possessed by ammonium ion: the greater the substitution degree of the amine, the more the positive charge will be stabilized. A better stabilization leads the cations to interact less with their counter ions, which form hydrogen bonds with the hydroxyl groups of the cellulose backbone [70]. Therefore, the cations become free to take part in the exchange interactions with the -SO\({}_{3}\)H groups on the composite's surface. As result, the efficiency of the overall extraction of the amine from the aqueous system is improved. For these reasons, aliphatic tertiary and secondary amines as \(N\),_N_-disisopropylplethylamine and piperidine gave the best results. Nonetheless, the hard-soft acid-base theory (HSAB) helps us explain the differences for the recovery percentages obtained for the aliphatic and aromatic species. In particular, the sulfate group exhibits a borderline behavior [71; 72], while aliphatic ammonium ions are harder than the aromatic ones. Subsequently, the latter have a minor interaction with sulfate groups, providing a lower adsorption than aliphatic cations. In fact, the presence of one or two aliphatic substituents with the aromatic one on amine group, such as for N-methylaniline and \(N\),_N_-dimethylaniline, partially reduces the effect due to the aromatic ring, while not increasing the adsorption up to levels of the aliphatic amines. Furthermore, steric effects too can not be excluded as reported by [PERSON] et al. [73]. For the case of 4-methoxybenzylamine, a -CH\({}_{2}\) group separates the ammonium system from the aromatic moiety: this feature precludes the resonance stabilization, making the cation harder than the other aromatic amines. Nonetheless, its recovery percentage is worse than the data reported for N-methylaniline and \(N\),_N_-diethylaniline and very different from the results obtained for the other aliphatic analytes. Steric hindrance can also contribute to explain why the percentages obtained for 2-ethylhexylamine are slightly better than the adsorption of 1,5-dimethylhexylamine, even if electronic effects should privilege the latter.