| Summary: | Fe _3 O _4 @C nanoparticles were successfully synthesized by an in situ solid-phase method using FeSO _4 , FeS _2 , and PVP K30 as the starting materials under the nitrogen atmosphere. In addition, the mechanism of the synthetic of Fe _3 O _4 @C nanoparticles was studied through in situ characterizations. The results showed that the pyrolysis of PVP K30 participated in the solid-phase reaction and resulted in the formation of carbon shells and a reduction in particle size. The structure of the Fe _3 O _4 @C nanoparticles was core–shell with the average particle size of ∼30 nm and the thickness of the carbon shell of ∼2 nm. Besides, the Raman spectrum revealed that the carbon shell mostly existed in the form of amorphous carbon. The surface area and the pore volume of the Fe _3 O _4 @C nanoparticles were estimated to be 37.74 m ^2 g ^−1 and 0.227 cm ^3 g ^−1 . Magnetization hysteresis curve exhibited the values of coercivity and remanence and saturation magnetization are found to be approximately 0.16 kOe, 12.8 emu g ^−1 , and 77 emu g ^−1 , respectively.
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