## 3 Results and Discussion
As corroborated by previous studies (Table S3, entries 12-14), heterogeneous noble-metal Pt catalysts similarly demonstrate exceptional nitrobenzene hydrogenation performance [54, 55, 56]. It can be inferred that the optimal reaction conditions were determined: hydrazine hydrate as the reducing agent, water as the solvent, maintaining a temperature of 70 \({}^{\circ}\)C, and a reaction time of 3 h.  
Based on the aforementioned results, the Fe\({}_{3}\)O\({}_{4}\)@C-Pt catalyst was further employed to expand the substrate scope to 20 substituted nitroarenes. As shown in Table 1, all substrates were transformed into the corresponding aromatic amines with high activity, achieving yields exceeding 93%. The experimental findings revealed that the product yields were significantly influenced by the electronic effects of functional groups on the nitroarenes. Specifically, the nitrobenzene derivatives bearing electron-donating groups (-CH\({}_{3}\), -OCH\({}_{3}\), -NH\({}_{2}\), and -SO\({}_{3}\)H) as well as two biphenyl derivatives were efficiently  
Figure 7: Magnetic hysteresis curves of Fe\({}_{3}\)O\({}_{4}\)@C–Pt (red line) and Fe\({}_{3}\)O\({}_{4}\)@C (blue line). reduced to the target anilines with high yields (Table 1, entries 1-9, **2a-2i**, and 18-19, **2r-2s**) [57]. Furthermore, the nitroarenes bearing electron-withdrawing carbonyl groups (-CHO, -COCH\({}_{3}\), and -COOH) demonstrated consistently high yields (\(\geq\)94%) (Table 1, entries 10-12, **2j-2l**) [58]. \begin{table}
\begin{tabular}{c c c c c} \hline Entry & Substrate & Product (2a–2s) & Time (  
Halogenated nitroarenes (-F, -Cl, -Br, and -I) were successfully reduced to halogen substituted anilines with minimal by-products (Table 1, entries 13-17, **2m-2q**) [59,60]. However, 4-iodonitrobenzene (Table 1, entry 15, **2o**) displayed slower reaction kinetics and a reduced yield compared with other halogenated substrates, likely due to dehalogenation during hydrogenation. Finally, the reduction of a heterocyclic nitro compound, 3-nitropyridine, under Fe\({}_{3}\)O\({}_{4}\)@C-Pt catalysis afforded 3-aminopyridine with a yield of 94%  
\begin{table}
\begin{tabular}{c c c c c} \hline  & & & & \\  & & & & \\  & & & &  
after 9 h (Table 1, entry 20, **2t**) [61]. The \({}^{1}\)H NMR spectra of all products (**2a-2t**) are provided in the Supplementary Materials (Figures S1-S20). To further elucidate the \({}^{1}\)H NMR spectra of the catalytic hydrogenation products in the Supplementary Materials, this section employs the \({}^{1}\)H NMR data of aniline as an illustrative example. The aromatic proton signals in the \({}^{1}\)H NMR spectrum of aniline (generated via catalytic hydrogenation of nitrobenzene) were observed in the \(\delta\) 6.61-7.12 ppm range, consistent with the deshielding effect induced by the strong electron-donating nature of the amino group (-NH\({}_{2}\)) on the benzene ring. Specifically, the doublet at \(\delta\) 6.61 (\(J\) = 7.5 Hz, 2H) corresponded to the para-hydrogens of the benzene ring, arising from coupling with the two adjacent ortho-hydrogens. The triplet at \(\delta\) 6.73 (\(J\) = 7.7 Hz, 1H) was attributed to the meta-hydrogen, which was split by coupling with two neighboring ortho-hydrogens. The triplet at \(\delta\) 7.12 (\(J\) = 7.9 Hz, 2H) was assigned to the ortho-hydrogens, which were split by coupling with one meta-hydrogen and one para-hydrogen. Additionally, the singlet at \(\delta\) 3.51 (integrating to 2H) corresponded to the exchangeable protons of the amino group (-NH\({}_{2}\)). This sharp singlet, rather than a broad peak, may reflect rapid proton exchange under the measurement conditions (e.g., in chloroform-\(d\)), which suppresses the peak broadening typically associated with amine protons. The observed splitting patterns, chemical shifts, and integration ratios collectively confirmed the structure of aniline, with the electron-donating amino group modulating both the shielding effects and spin-spin coupling interactions across the aromatic system.