INTRODUCTION
At present, understanding the scientific properties of environmental pollution from different perspectives is economically very valuable. Much research has been done to find a method using photocatalysis to decompose [1–3]. Ag known to have excellent photocatalytic activity in the decomposition and purification of various contaminating components [4–7]. Silver one of royal metals, has optimum conditions for oxidation reactions. It has been used to produce a highly efficient photocatalyst with an appropriate band [8]. Besides its large magnetic anisotropy and moderate saturation magnetization, it has remarkable chemical stability and mechanical hardness [9–12]. They have excellent mechanical, chemical, and thermal properties with water resistant function [13–17].  This study describes the synthesis and characterization of nanosized silver particles using precipitation method. investigated the formation of monodispersed nanoparticles in transition. The prepared nanoparticles were compared in the same environment in terms of morphology and structure properties. 

MATERIALS AND METHODS
AgNO3 , Fe(NO3)3 9H2O, FeCl2 6H2O, lactose, tri sodium citrate, NaBH4 were purchased from Merck or Aldrich and all the chemicals were used as received without further purifications. A multiwave ultrasonic generator (Bandeline MS 73), equipped with a converter/transducer and titanium oscillator, operating at 20 kHz with a maximum power output of 150 W was used for the ultrasonic irradiation.. XRD patterns were recorded by a Philips, X-ray diffractometer using Ni-filtered CuKα radiation. SEM images were obtained using a LEO instrument model 1455VP. Prior to taking images, the samples were coated by a very thin layer of Pt (using a BAL-TEC SCD 005 sputter coater) to make the sample surface conductor and prevent charge accumulation, and obtaining a better contrast.  

Synthesis of carbon/magnetite/silver nanoparticles
For preparation of carbon nano templates, walnut shell were calcined at 350ºC. After that the black powders were dispersed in water under ultrasonic irradiation 150W, 60 min. Iron nitrate and iron chloride were added and dissolved in the solvent and under nitrogen atmosphere ammonia was added.  Then silver nitrate was added to the C@Fe3O4 dispersion. After 60 min mixing under heater-stirrer lactose and ammonia ere added for reduction of silver ions to silver metals.   A brown precipitate was then centrifuged and rinsed with distilled water. Finally obtained precipitate was dried at 85ºC and the press was done for preparation of tubular catalyst. The schematic diagram for experimental setup for nanoparticle and nanocomposite preparation used in the precipitation procedure (Fig. 1).

RESULTS AND DISCUSSION
For characterization of the phase and crystallization X-ray diffraction pattern was used (Fig. 2). The XRD pattern of Fe3O4 reveals the typical diffraction pattern of pure cubic phase (JCPDS No.: 75-0033) with Fd-3m space group which is consistent with magnetite ferrite. 
The crystalline sizes from Scherrer equation, Dc=Kλ/βCosθ, was calculated, where β is the width of the observed diffraction peak at its half maximum intensity (FWHM), K is the shape factor, which takes a value of about 0.9, and λ is the X-ray wavelength (CuKα radiation, equals to 0.154 nm).The average crystalline size for Fe3O4 and Ag nanoparticles were found to be about 10 and 15nm respectively [18-23]. 
Scanning electron microscopy was employed for estimation of morphology and particle size of the products. SEM image of Fe3O4 nanoparticle are shown in Fig. 3. The results confirm that particle size is about 20 nm . SEM image of the C@Fe3O4 nanoparticles is illustrated in Fig. 4. According to scanning electron microscopy images the average particle size is found to be around 90 nm. Figs. 5. shows SEM image of the C@Fe3O4@Ag nanoparticles, image confirms growth stage overcome to nucleation stage, nanoparticles on the star-like matrix was prepared.
Fig. 6 shows magnetic property of magnetite was studied using VSM instrument. The result indicates that, the sample exhibit super paramagnetic property. A saturation magnetization around 84 emu/g, and coercivity about zero Oe have been achieved. Magnetization curve of C@Fe3O4 that also exhibits also ferromagnetic behaviour with a coercivity of about 200 Oe and saturation magnetization of  60 emu/g (Fig. 7). VSM curve of C@Fe3O4@Ag nanocomposites after CO interaction is shown in Fig. 8.  It depicts ferromagnetic behaviour (coercivity around 250 Oe, saturation magnetization: 60 emu/g). The magnetic property of the prepared nanocomposites is an essential characteristic of a heterogeneous nanocomposite since materials with this magnetic behaviour have low tendency in inter-particles agglomeration caused by dipole-dipole interaction in comparison with ferromagnetic nanocomposites. 
UV-vis absorption spectrum of C@Fe3O4@Ag nanocomposites is illustrated in Fig. 9, a broad peak around 480nm is related to nano structures levels. Catalyst reaction of C@Fe3O4@Ag nanocomposites for conversion of carbon monoxide to carbon monoxide schematically is depicted in Fig. 10. 400 ppm of carbon monoxide gas were purged under tubular carbon/magnetite/silver nano-catalyst. Two gas sensor/detectors were applied before and after tubular nanocomposite catalyst. After transmission of gas from tube concentration of carbon monoxide reduce to under 25ppm. 

CONCLUSION
In this work, C@Fe3O4@Ag nanocomposites were prepared via a simple chemical two steps route. The crystalline structure, surface functional group, and optical properties of as-obtained samples were characterized via X-ray diffraction pattern (XRD),  FTIR spectrometry , and UV–visible absorption spectroscopy, respectively. The morphological properties of products were investigated via scanning electron microscopy (SEM). Then, the prepared C@Fe3O4@Ag nanocomposites were applied for the oxidation of carbon monoxide to carbon dioxide. The findings confirmed prepared C@Fe3O4@Ag nanocomposites can act as a good oxidation agent for the conversion of carbon monoxide to carbon dioxide.

ACKNOWLEDGEMENTS
This work has been supported financially by Arak University of Technology.

CONFLICT OF INTEREST
The authors declare that there are no conflicts of interest regarding the publication of this manuscript.