## 3 Results and Discussion
while the other two samples (Fe\({}_{3}\)O\({}_{4}\)@C-Pt and Precursor) exhibited narrower distributions of 1.3-70 nm. Notably, after supporting Pt on Fe\({}_{3}\)O\({}_{4}\)@C, the resulting Fe\({}_{3}\)O\({}_{4}\)@C-Pt demonstrated enlarged pore sizes while retaining a relatively high specific surface area (54 m\({}^{2}\)/g) and abundant mesopores (Table S1). Remarkably, the specific surface area of Fe\({}_{3}\)O\({}_{4}\)@C-Pt in this work was significantly larger than that reported in our previous study [53], providing favorable sites for catalytic processes. According to Table S1, the precursor exhibited a low specific surface area (24 m\({}^{2}\)/g). However, after calcination at 550 \({}^{\circ}\)C under N\({}_{2}\), Fe\({}_{3}\)O\({}_{4}\)@C underwent phase transformation, resulting in a sharp increase in the specific surface area accompanied by the generation of micropores. In summary, the hierarchical micro-mesoporous structure of Fe\({}_{3}\)O\({}_{4}\)@C-Pt maximized the active site exposure, facilitated substrate adsorption and transport, and thereby enhanced catalytic performance. Detailed PSD data, BET surface areas, and NLDFT-calculated pore volumes are summarized in Table S1. The Fe\({}_{3}\)O\({}_{4}\)@C-Pt composite demonstrated dual functionality through its catalytic activity and magnetic retrievability, enabling efficient recycling in reaction cycles. The magnetic properties of Fe\({}_{3}\)O\({}_{4}\)@C and Fe\({}_{3}\)O\({}_{4}\)@C-Pt were analyzed via vibrating sample  
Figure 6: (**a**) N\({}_{2}\) adsorption-desorption isotherms. (**b**) Pore diameter distribution curves of Precursor, Fe\({}_{3}\)O\({}_{4}\)@C, and Fe\({}_{3}\)O\({}_{4}\)@C–Pt, with inset in (**b**) showing pore diameter distribution from 1 to 100 nm. magnetometry (VSM). As shown in Figure 7, a saturation magnetization (_Ms_) of \(\sim\)45 emu/g for Fe\({}_{3}\)O\({}_{4}\)@C was revealed. Upon supporting Pt, Fe\({}_{3}\)O\({}_{4}\)@C-Pt exhibited a slightly reduced _M_s of 44 emu/g, which may have arisen from low Pt loading (0.57 wt. %, confirmed by ICP) or uniform Pt dispersion on the carbon surface. This observation aligns with the XRD patterns (Figure 2b) and TEM imaging (Figure 4f,g). The hydrogenation of nitrobenzene (**1a**) catalyzed by Fe\({}_{3}\)O\({}_{4}\)@C-Pt was systematically evaluated. Two critical parameters--cataly selection and reducing agents--were investigated. The initial control experiments employed toluene as the solvent and hydrazine hydrate (N\({}_{2}\)H\({}_{4}\)-H\({}_{2}\)O) as the reductant. Notably, no reaction occurred in the absence of a catalyst or with Fe\({}_{3}\)O\({}_{4}\)@C alone (Table S2, entries 1-2). Fe\({}_{3}\)O\({}_{4}\)@C-Pt exhibited significant catalytic activity, achieving >99% conversion (Table S2, entry 3). This confirms that Pt nanoparticles on Fe\({}_{3}\)O\({}_{4}\)@C serve as active sites for nitrobenzene hydrogenation. Furthermore, the reducing agent plays a crucial role. Hydrazine hydrate demonstrated superior reduction efficiency compared with H\({}_{2}\), NaBH\({}_{4}\), and ammonium formate (Table S2, entries 4-7), likely due to its moderate reducing power and environmental benignity. The solvent plays a pivotal role in organic reactions. To evaluate its impact, eight solvents were screened (Table S3, entries 1-8). Notably, water achieved a yield of >99% aniline, highlighting its advantages as a green solvent--non-toxic, sustainable, and environmentally benign--for organic transformations. Regarding the impact of temperature on the reaction, when the reaction was carried out at a low temperature, including ambient conditions, the resulting yield was low (Table S3, entries 9-10). Another notable factor that impacted the product yield was the duration of the reaction. It is evident that as the reaction time decreased, the yield also decreased; the yield of aniline was only 75% after 2 h compared with that at 3 h (Table S3, entries 1 and 11).