Abstract. Synthesis of Fe 3 O 4 /a-SiO 2 nanoparticle has been conducted based on natural materials by using the co-precipitation method. The used silica was a-SiO 2 collected from silica sand from Bancar Tuban, Indonesia. The Fe 3 O 4 collected from iron sand's Lumajang, Indonesia. The samples was set for Fe 3 O 4 : a-SiO 2 : PEG composition of 1 : 2 : 1. The process was maintained by melting the PEG 4000 and following by adding a-SiO 2 and Fe 3 O 4 . The samples were characterized by using X-Ray Diffractometry (XRD), Transmission Electron Microscopy (TEM), and Fourier Transform Infra-Red (FTIR) spectroscopy. The analysis of the XRD data showed that additional silica into Fe 3 O 4 tended to change the diffraction pattern that represents the existent of both Fe 3 O 4 and silica. The SEM images presented that the samples formed in nanometric size with core-shell structure. Furthermore, the FTIR spectra showed that Si-O-Fe bound appeared at 555-568 cm -1 . Thus, this work was able to produce the Fe 3 O 4 /aSiO 2 nanocomposites by using co-precipitation method in a core-shell structure.

This article reports the results synthesis of crystalline (Fe3O4@c-SiO2) and amorphous (Fe3O4@a-SiO2) nanoparticles from natural resources (iron sand and silica sand). The synthesis of Fe3O4 and SiO2 nanoparticles used co-precipitation and hydrothermalcoprecipitation methods with polyethylene glycol (PEG) 4000 as a template. The XRD data analysis presented that the amorphous SiO2 particles were successfully produced using hydrothermal and co-precipitation methods. The XRD data analysis also presented that the crystalline phases were formed in quartz and tridymite phases after calcination process of the amorphous phase. SEM images exhibited that the amorphous phase had different particle size and morphology from the crystalline phase. FTIR spectra presented some absorption peaks of new functional groups indicating the existence of Si-O-Si (silanol), Fe-O, C-N, and Fe-O-Si as new functional groups.