Composites of Fe3O4/SiO2 from Natural Material Synthesized by Co-Precipitation Method

Synthesis of Fe3O4/a-SiO2 nanoparticle has been conducted based on natural materials by using the co-precipitation method. The used silica was a-SiO2 collected from silica sand from Bancar Tuban, Indonesia. The Fe3O4 collected from iron sand’s Lumajang, Indonesia. The samples was set for Fe3O4 : a-SiO2: PEG composition of 1 : 2 : 1. The process was maintained by melting the PEG 4000 and following by adding a-SiO2 and Fe3O4. 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 Fe3O4 tended to change the diffraction pattern that represents the existent of both Fe3O4 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 Fe3O4/a-SiO2 nanocomposites by using co-precipitation method in a core-shell structure.


Introduction
Indonesia is a country with abundant natural resources. Some of the natural resources extracted from minerals are quartz sand and iron sand. Most of the content of quartz sand is silica (SiO 2 ) with the purity of 70%. Quartz sand has a characteristic of its yellowish white color (Bancar area, Tuban-East Java, Indonesia) [1], its density of 2.50-2.70 g/cm 3 , and having melting point of around 1715 °C [2]. Based on the previous research, the iron sand from Lumajang had a noticeably high level of Ferrous that could easily produce magnetic nanoparticles with high purity [3,4]. The latest reports show that Indonesia has a large number of iron minerals that consist of the main iron ore (17%), iron ore (8%) and laterite iron ore (75%) [4].
There are many applications of nanocomposites in industrial and health sectors especially the use of this material for small particles from micro to nanometric size. Thus, we need to advanced and the right technology to process it. It needs a special treatment in the process of obtaining the nanometric 2

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The 4th International Conference on Advanced Materials Science and Technology IOP Publishing IOP Conf. Series: Materials Science and Engineering 202 (2017) 012057 doi:10.1088/1757-899X/202/1/012057 materials. A lot of methods were used to get the nanocomposites with the best result including the coprecipitation method, sol-gel, etc. [2,5-8]. Nanocomposite material is a combination of two or more composing materials with a different characteristic material (matrix and filler). In this research, the magnetic particle (Fe 3 O 4 ) was combined with silica because it has multiple advantages including the ability of its pure materials to synthesize in large scale and the large capacity of cation exchange. Silica comes from a natural or synthetic material and usually is in the form of crystalline or amorphous solid [1,6,9]. Silica is a metal oxide compound that is widely available in nature, but its existence is not in the free state. It is bounded to another compound physically and chemically. This material is used in many industries and medical field because of its unique nature and morphology such as the large surface area and pore volume, and the ability to absorb various substances like water, oil, and radioactive material. In general, Silica has hydrophobic or hydrophilic properties based on its structure and morphology [10].
In composite materials, the component did not undergo a chemical change. Fe 3 O 4 /SiO 2 nanocomposite is a composite material because its constituent materials have nanometric size and exist without any new compound formed. Another work reported that the Fe 3 O 4 /SiO 2 nanocomposites were succesfully prepared by using the co-precipitation method with FeCl 3 and silica solution as the basic material [11]. In this work, we were interested to develop synthesis method of Fe 3 O 4 /SiO 2 nanocomposites by exploring the abundant natural material via a co-precipitation method. This method can be utilized to prepare an inorganic compound based on the precipitation process of substances. The advantage of this method is having a relatively low temperature in a short process [12,13]. Interestingly, the method can prepare the Fe 3 O 4 /SiO 2 nanoparticle that was illustrated to form a composite formation, where the Fe 3 O 4 ferromagnetic particle is covered inside the hollow of SiO 2 particle [11,14].

Materials
The equipment used in this research were a beaker glass, measuring glass/graduated cylinder, magnetic stirrer, filter paper, digital scales, spatula, pH meter, pipette, spatula, funnel, crucible, mortal and pestle permanent magnet, cardboard and a 60-watt lamp. The material used in this study were Bancar-Tuban sand, Lumajang iron sand, NaOH, HCl 2M, NH 4 OH, PEG 4000, and distilled water (DI). The manipulation variables were the a-SiO 2 mass and the PEG mass. The Control Variable was the mass of Fe 3 O 4 . The response variable was the phase of Fe 3 O 4 /a-SiO 2 nanocomposites.

Experiment
The step taken to synthesize the nanocomposites of Fe 3 O 4 /a-SiO 2 was melting the PEG via the stirrer at a temperature of 60 o C. It was then added with a-SiO 2 powder while it was being stirred continuously until evenly combined, after that it was added with Fe 3 O 4 powder and it was stirred for another 3 minutes, so that it formed precipitate. Those steps were repeated for 3 times with different compositions. The precipitate was then dried and thus formed Fe 3 O 4 /a-SiO 2 powder. This product was then characterized by using XRD to determine the occurrence of the composite on both Fe 3 O 4 and a-SiO 2 . Furthermore, it was also characterized by using FTIR to determine the functional group possessed by the sample of Fe 3 O 4 /a-SiO 2 . The size and distribution of the particles were characterized by using SEM/TEM. Therefore, undergoing a composite process did not change the structure of Fe 3 O 4 particle . In sample #1, the wide peak on 2 24 o showed the existence of amorphous peak silica form. This peak intensity will increase along with the addition of silica, where the position of polymer form is very influential in the composite [15]. The higher the variation of silicate addition into Fe 3 O 4 the more declined the diffraction peak pattern of Fe 3 O 4 [11, 16,17].

Data of FTIR Characterization of Fe 3 O 4 /a-SiO 2 Composites
After a test by using XRD, the Fe 3 O 4 /a-SiO 2 nanoparticles was characterized by using FTIR to determine the functional groups of the Fe 3 O 4 /a-SiO 2 sample. The functional groups corresponding to Fe 3 O 4 @SiO 2 (Sample #1) therein are depicted in Table 1.   TEM characterization aimed for knowing the morphological structure of Fe 3 O 4 /a-SiO 2 nanocomposites that formed as a Fe 3 O 4 @a-SiO 2 core shell. Here is the result of TEM test of the Fe 3 O 4 @a-SiO 2 core shell (Figure 2c). It appears that the Fe 3 O 4 particles are black-colored and coated with SiO 2 particle shown by a lighter cloud around it. Fe 3 O 4 @a-SiO 2 particle has a round-shaped property and agglomerated with other particles. The size of the Fe 3 O 4 @a-SiO2 particle was about ~25 nm and the thickness is ~9 nm. Thus, the Fe 3 O 4 /a-SiO 2 nanocomposites have successfully formed a Fe 3 O 4 @a-SiO 2 core shell [14,18]. There were significant different shape and size of the composite particles of Fe 3 O 4 @ a-SiO 2 amorphous (#sample 1) and Fe 3 O 4 @ c-SiO2 (crystal), as shown in Figure  2 (a) and Figure 2 (b); composite particle size of Fe3O4/a-SiO 2 was greater than the particle size of the Fe 3 O 4 @c-SiO 2 composite.

Conclusion
Based on the data analysis, we can conclude that Fe 3 O 4 /a-SiO 2 nanocompositeS can be fabricated by using PEG as the binder of Fe3O4 and a-SiO2 particleS, where Fe 3 O 4 , a-SiO 2 can be easily synthesized by using the co-precipitation method. The Characteristic of Fe 3 O 4 /a-SiO 2 based on XRD crystal structure and functional group of FTIR analysis shows that the Fe 3 O 4 /a-SiO 2 nanocomposites have formed a sharp peak of diffraction pattern and a distinct of functional group of Si-O-Fe on wavenumbers of 555-568 cm -1 .