## 3 Results and Discussion
The observed diffraction peaks at 2\(\theta\) = 39.9\({}^{\circ}\), 46.4\({}^{\circ}\), and 67.7\({}^{\circ}\) in the Fe\({}_{3}\)O\({}_{4}\)@C-Pt sample correspond to the (111), (200), and (220) crystallographic planes of face-centered cubic (FCC) Pt, respectively, which match well with metallic platinum (Pt, JCPDS No. 87-0640) [42]. The remaining characteristic XRD peaks of the Fe\({}_{3}\)O\({}_{4}\)@C-Pt sample aligned perfectly with those of Fe\({}_{3}\)O\({}_{4}\)@C, and no impurity-related diffraction signals were detected, confirming the successful incorporation of Pt nanoparticles into the Fe\({}_{3}\)O\({}_{4}\)@C matrix. The absence of carbon-related diffraction peaks in the XRD patterns suggests low crystallinity of carbon in the samples, consistent with amorphous or poorly graphitized carbon structures. Raman spectroscopy, a powerful tool for probing carbonaceous materials, was employed to further investigate the crystallinity and carbon speciation. As shown in Figure 3, both Fe\({}_{3}\)O\({}_{4}\)@C and Fe\({}_{3}\)O\({}_{4}\)@C-Pt exhibited two prominent Raman bands at 1365 cm\({}^{-1}\) (D-band) and 1592 cm\({}^{-1}\) (G-band). The broad D band at 1365 cm\({}^{-1}\) corresponds to disordered carbon structures at the edges of graphite sheets of a carbonaceous material,  
Figure 1: FT-IR spectra of Precursor, Fe\({}_{3}\)O\({}_{4}\)@C, and Fe\({}_{3}\)O\({}_{4}\)@C–Pt. Figure 2: (**a**) XRD patterns of the precursors and samples obtained at different calcination temperatures. (**b**) XRD patterns of Fe\({}_{3}\)O\({}_{4}\)@Cand Fe\({}_{3}\)O\({}_{4}\)@C–Pt. which is related to the existence of amorphous carbon. (e.g., edge defects or amorphous domains), while the sharp G band at 1592 cm\({}^{-1}\) arose from the in-plane stretching vibrations of \(sp^{2}\)-hybridized ordered graphitic carbon. The intensity ratio of the D band to the G band (\(I_{D}/I_{G}\)) quantifies the degree of graphitization. For Fe\({}_{3}\)O\({}_{4}\)@C, the \(I_{D}/I_{G}\) ratio was 0.77, whereas Fe\({}_{3}\)O\({}_{4}\)@C-Pt exhibited a slightly higher value of 0.82. Notably, the G band dominated over the D band in both samples, indicating the presence of partially graphitized carbon layers on the surface of Fe\({}_{3}\)O\({}_{4}\)@C-Pt and Fe\({}_{3}\)O\({}_{4}\)@C [43]. This enhanced graphitic ordering facilitates electron transfer between carbon and platinum nanoparticles, which is critical for improving catalytic activity in nitroarene hydrogenation [44]. Therefore, not only was the existence of carbon in the samples confirmed in the Raman spectroscopy, but direct evidence for the structural evolution from disordered carbon to graphitic domains was also provided by the Raman spectroscopy during synthetic experiment. To determine the chemical composition of the Fe\({}_{3}\)O\({}_{4}\)@C nanospheres, TGA of Fe\({}_{3}\)O\({}_{4}\)@C in air (ambient to 1000 \({}^{\circ}\)C at 10 \({}^{\circ}\)C/min; Figure S1) was performed to reveal 47.2% Fe\({}_{3}\)O\({}_{4}\) and 46.6% carbon contents. To elucidate the microstructure and morphology of each of the samples, transmission electron microscopy (TEM) was performed on Fe\({}_{3}\)O\({}_{4}\)@C and Fe\({}_{3}\)O\({}_{4}\)@C-Pt. Figure 4a-c displays TEM images of Fe\({}_{3}\)O\({}_{4}\)@C, while Figure 4e-g corresponds to Fe\({}_{3}\)O\({}_{4}\)@C-Pt. Both samples exhibited a uniform spherical morphology with a thin carbon shell (\(\sim\)2 nm for Fe\({}_{3}\)O\({}_{4}\)@C and \(\sim\)3 nm for Fe\({}_{3}\)O\({}_{4}\)@C-Pt) encapsulating the surface (Figure 4c,g). The particle size distributions (Figure 4d,h) revealed average diameters of 40-50 nm for Fe\({}_{3}\)O\({}_{4}\)@C and 50-60 nm for Fe\({}_{3}\)O\({}_{4}\)@C-Pt (The curve represents the frequency distribution curve). Notably, the Fe\({}_{3}\)O\({}_{4}\)@C-Pt sample showed distinct Pt nanoparticles (\(\sim\)2 nm) on its carbon surface, marked by red circles in Figure 4f.