— In this research, first a binary n anocomposite of magnetic recyclable photocatalyst Fe 3O4/TiO 2, was synthesized by sol gel technique. Then, in order to enhance the photocatalytic activity of the synthesized nanocomposite, it was deposited by silver nanoparticles for using in degradation of organic pollutants 2, 4 -dichl orophenol (2, 4- DCP) under visible light . A range of analytical techniques including XRD, FESEM/EDX, DRS, VSM and N 2 physisorption were employed to reveal the crystal structure, morphology and property of the nanocomposites . We obtained 32% and 55% degrada tion of 2, 4-DCP under visible light after 180 min irradiation in the presence of Fe3O4/TiO 2 and Fe3O4/TiO 2/Ag respectively. Thus, the excellent visible light photocatalytic activity of Fe3O4/TiO 2/Ag sample can be attributed t o the surface plasmon resonance effect of Ag nanoparticles deposited on Fe3O4/TiO 2 nanocomposite. Keywords - Fe3O4; Ag; TiO 2 nanoparticles; Degradation; 2, 4- dichlorophenol ; I. INTRODUCTION World's population growth and drinking water scarcity has made drinki ng water supplementation, one of the fundamental problems of today's world. Therefore, water recycling will provide access to a suitable source for various uses. Recently, advanced oxidation processes (AOPs) have been proposed as a wastewater treatment solution. Among advanced oxidation processes, heterogeneous photocatalytic processes have been used as a successful method for the d ecomposition of various organic pollutants [1]. Photocatalysts are environmental cleaners that can degr ade many environmental pollutants through oxidation by using sunlight or artificial light, especially ultraviolet light. Titanium dioxide (TiO 2) is one of the photocatalysts that has been used to degrade organic pollutants. TiO 2 is an ideal photocatalyst w ith non-toxic nature, high oxidizing properties under UV radiation and low cost, which is stable under various reaction conditions and is also environment friendly [2]. There are two distinct defects in the performance of TiO 2 for the destructi on of environmental pollutants. The first is the high energy of its separation band (3.2 eV), which requires UV radiation to generate the electron -cavity pair, but UV radiation forms only about 4% of the sun's emission. In order to utilize a larger part of the radiation emitted from the sun, it is necessary to make special changes in this semiconductor system. Ag, indicating the presence of surface Plasmons resonance (SPR) at the visible light region, which has been used to develop plasmonic photocatalyst [3]. Therefore, the presence of metals such as silver at TiO 2 surface would reduce the separation band energy and expand its absorption spectrum towards the visible light region. The presence of Ag nanoparticles in semiconductors could create Schottky junctions, which decreases recombination rate of electron -cavity pair and also increases the free radicals formation rate [4]. The second defect is the recyc ling of nano -sized photocatalysts, whic h is very difficult and costly. An operational solution for photocatalyst SRPioneers © Science and Research Pioneers Institute 8th International Conference on Nanotechnology (ICN201 8), February 8 -9, 2018 , Istanbul, T urkey recycling is magnetizing TiO 2 by Fe 3O4 so that it can be separated and reused by employment of an external magnetic field [5]. This study reports the photocatalytic degradation of 2, 4-DCP under visible light over Fe3O4/TiO 2 based photocatalys t containing Ag synth esized via sol -gel method. Physico -chemical characterization of synthesized catalysts has been discussed. The effect of the Ag deposition content on photocatalytic activity has been also investigated. II. EXPERIMENTAL A. Materials FeCl 3·6H 2O (Merck No. 103943), FeSO 4·7H 2O (Merck No. 103965) were used for synthesis of Fe 3O4 nanoparticles (NPs). Tetraisopropylorthotitanat (TIP) (Merck No. 8.21895), anhydrous ethanol, ammonia, and High -purity 2, 4 -DCP, 98%, (Merck No. 803774) was used as a probe molecule for photoca talytic tests were purchased from Merck Company. Silver nitrate (AgNO 3), 99.9%, was supplied by (Merck, No.101510), Acetic acid (CH 3COOH), 99.9% (Merck No. 1.00063). All the reagents were of analytic grade and used without further purification. Double dist illed water was used for preparation of all aqueous solutions. B. Preparation of Fe 3O4 and TiO 2 NPs We synthesized Fe 3O4 nanoparticles by chemical precipitation technique according to Mentioned procedure in ref [6] and for synthes is of TiO 2, the method reported in reference [7] will be used with some modifications. Subsequently, the obtained nanoparticles identified by various analysis. C. Synthesis of binary (Fe 3O4/TiO 2) nanocomp osite (Fe 3O4/TiO 2) nanocomposites Synthesis: We mixed 0.1 g of the Fe 3O4 nanoparticles with 4 ml of titanium isopropoxide (TIP) (as a titanium source) and 70 ml of water -free ethanol and placed it in an ultrasonic bath for one hour (Solution A). Solution B prepared by mixing 3 ml of acetic acid and 90 ml of distilled water. Then solution B was added to solution A, stirred at 50 °C for 30 min. Finally, after cooling to room temperature, we separate the synthesized solid from the suspension by centrifugation. Rinsed with ethanol and dried for 12 h at 60 °C. For the final step, the obtained solid is heated under atmospheric pressure at 300 °C for one hour. D. Ag deposited on Fe3O4/TiO 2 sample The prepared Fe3O4/TiO 2 sample was deposited by Ag nanoparticles accord ing to reported procedure in re f [7]. 0.5g of Fe3O4/TiO 2 was suspended by sonication in 10 mL of deionized water to which AgNO 3 (1 mL, 100.0 mM) was added slowly; the resulting solution was stirring at 20°C for 30 min, and then Na 2CO 3 (0.5 mL, 1.0% w/v) was slowly added. The resulting slurry by filtering was separated and dried at room temperature. This nanocomposite was labelled as FTA (a), where (a) is the weight percentage of Ag in the final solid that obtained by EDX analysis. E. Characterization The XRD patterns were recorded on a Siemens, D5000 (Germany). The morphology of the prepared samples were characterized using scanning electron microscope (SEM) (Vegall -Tescan Company) equipped with an energ y dispersive X -ray (EDX). The diffuse reflectance UV–Vis spectra (DRS) of the samples were recorded by an Ava Spec -2048TEC spectrometer. The nitrogen physisorption measurements were performed with a Quantachrome Autosorb -1-MP (Micromeritics). The BET areas were determined by static nitrogen physisorption at -196 °C subsequent to out -gassing at 200 °C, until the pressure was lower than 5 mbar. All of magnetic measurements have been done by VSM system where is located in the Nano Magnetic Laboratory, in the University of Kashan, Iran, The system is made of Meghnatis Daghighe Kavir, (MDK), Company, Kashan I. R. Iran. F. Photocatalytic degradation of 2, 4-DCP In a typical run, the suspension containing 10 mg photocatalyst an d 100 mL aqueous solution of 2, 4-DCP (40 mg/L) was stirred first in the dark for 10 min to establish adsorption/desorption equilibrium. Irradiation experiments were carried out in a self -built reactor for 180min irradiation . A visible (Halogen, ECO OSRAM, 500W) lamp was used as irradiation sour ce. At certain intervals, small aliquots (2 mL) were withdrawn and filtered to remove the photocatalyst particles. These aliquots were used for monitoring the degradation progress, with Rayleigh UV -2601 UV/VIS spectrophotometer (λ max= 227nm). III. RESULT AND D ISCUSSION A. X-ray diffraction analysis Figure 1. A shows the X -ray diffraction pattern of the synthesized Fe 3O4 nanoparticles in the present study. The diffractions at 2θ = 30.2°, 35.6°, 43.5°, 54.3° , 57.4° and 63.1° are observed, which are related to the c ubic spinel structure of Fe 3O4, reported by JCPDS reference number 0629 -9, thus synthesis of magnetic nanoparticles is confirmed [8]. SRPioneers © Science and Research Pioneers Institute 8th International Conference on Nanotechnology (ICN201 8), February 8 -9, 2018 , Istanbul, T urkey FIGURE 1. XRD patterns of A) Fe 3O4, B) a) TiO 2, b) Fe3O4/TiO 2, and c) Fe 3O4/TiO 2/Ag Figure 1. B shows the XRD patterns of the pure TiO 2 and Fe3O4/TiO 2 and Fe3O4/TiO 2/Ag nanocomposites. All the observed diffractions are related to the anatase phase according to the refer ence (PDF 24 -1272) [9]. The reason for the low intensity of Fe 3O4 nanoparticles and silver atoms diffraction is that they are very small in compariso n to TiO 2, and because of the high TiO 2 crystallinity, most of the Fe 3O4 diffraction is not visible. The size of the TiO 2 crystal was calculated using first diffraction width and Scherrer's equation. Which varies between 7.11 to 10.38 nm [10]. () 0.9 / coshklD    In this equation, D (hkl) is the crystal size based on Miller's index (101), λ is the wavelength of the X -ray, β is the width of the peak at half of its height, and θ is the Bragg's angle for the desired diffraction. Also, to calculate the parameters (a = b ≠ c), 101 crystalline location of anatase phase is used from the following equation. 2 2 2 2 22/ 1/ /d h c a kl   In this equation, D, the distance between neighbouring places, is calculated by Bragg's law () / 2sinhklD To calculate a = b and c, respectively, the angles of the third (2 0 0) and first (1 0 1) diffractions of the anatase phase are used respectively [11]. Table 1 shows the unit cell parameters and volume for the a natase phase TiO 2 in the synthesized samples and confirmed the formation of pure anatase phase. TABLE 1. Phase, crystal size and lattice parameters of the prepared samples Sample Phase Crystal size (nm) a=b (Å) c (Å) Cell volume (Å3) TiO 2 Anatase 10.38 3.77 9.59 136.30 Fe3O4/TiO 2 Anatase 7.11 3.79 9.37 134.87 Fe3O4/TiO 2/Ag Anatase 8.31 3.80 9.28 134.40 B. FESEM/EDX analysis In order to investigate the surface morphology of the synthesized samples, FESEM studies were performed. The FESEM images of pure Ti O2, Fe3O4/TiO 2 and Fe3O4/TiO 2/Ag samples are shown in Figure 2. The FESEM images of Fe3O4/TiO 2/Ag sample show that TiO 2 coated the surface of Fe 3O4 nanoparticles and Ag nanoparticles deposited on Fe 3O4/TiO 2 nanocomposite. (a) (b) (c) FIGURE 2. FESEM images of a) TiO 2, b) Fe3O4/TiO 2, and c) Fe3O4/TiO 2/Ag The EDX results were used to examine the elemental composition of the pure TiO 2, Fe3O4/TiO 2 and Fe3O4/TiO 2/Ag nanocomposites (Figure 3 and Table 2). The EDX result confirms the pre sence of C , Ti, O, Fe and Ag elements in these samples. In the EDX spectra of Fe3O4/TiO 2/Ag sample, the absorption peak at 3 keV is for metallic silver and confirms the presence of silver nanoparticles in the prepared sample. Figure 4 shows elemental mappi ng images of the prepared samples. TABLE 2. Elemental chemical analysis of the prepared samples. Sample C wt% O wt% Ti wt% Fe wt% Ag wt% TiO 2 8.12 41.68 35.96 - - Fe3O4/TiO 2 6.31 40.15 41.99 1.75 - Fe3O4/TiO 2/Ag 8.73 43.84 31.16 1.94 2.09 SRPioneers © Science and Research Pioneers Institute 8th International Conference on Nanotechnology (ICN201 8), February 8 -9, 2018 , Istanbul, T urkey FIGURE 3. EDX spectra of a) TiO 2, b) Fe3O4/TiO 2, and c) Fe3O4/TiO 2/Ag (a) (b) (c) FIGURE 4. Elemental mapping of a) TiO 2, b) Fe3O4/TiO 2, and c) Fe3O4/TiO 2/Ag C. DRS analysis The di ffuse reflectance spectra of the prepared samples over the wavelength range of 200 –800 nm are shown in Figure 5. A. The DR spectrum of pure TiO 2 consists of a broad intense absorption around 400 nm, due to the charge -transfer from the valence band formed b y 2p orbitals of the oxide anions to the conduction band formed by 3d t 2g orbitals of the Ti4+ cations [12]. We calculated the band gap energy from the DR spectra according to below equation [13] for the prepared samples. 0.5( ) ( )g F R h A h E Where A is constant, F(R) is the Kubelka -Munk function and E g is the band gap. The band gap of the plasmonic photocatalyst TiO 2/Fe 3O4/Ag nanocomposite decreased slightly compared with Fe3O4/TiO 2 (Table 3). FIGURE 5. A): Diffuse reflectance spectra and B) Kubelka -Munk plots for the band gap energy calculation of a) TiO 2, b) Fe3O4/TiO 2, and c) Fe3O4/TiO 2/Ag TABLE 3. Band gap energy of the prepared samples. Sample TiO 2 Fe3O4/TiO 2 Fe3O4/TiO 2/Ag Eg (eV) 3.05 2.70 2.60 D. N2 physisorption analysis N2 adsorption -desorption isotherms are carried out (Figure 6). The sorption isotherms for all of the prepared samples correspond to the type IV isotherm according to the IUPAC classification [14]. Textural and structural parameters of the obtained samples are shown in Table 4. Specific surface areas and average pore diameter were calculated according to the BET method, pore volumes were derived from the desorption branch according to the BJH model. The BET surface area of ternary nanocomposite (Fe 3O4/TiO 2/Ag sample) is greater than the starting material (Fe 3O4/TiO 2 sample), indicating the C K N K O K TiK TiK TiL keV010002000300040005000 0 5 10 C K N K O K TiK TiK TiL FeK FeK FeL keV0100020003000400050006000 0 5 10 (a) (b) (c) SRPioneers © Science and Research Pioneers Institute 8th International Conference on Nanotechnology (ICN201 8), February 8 -9, 2018 , Istanbul, T urkey deposition of Ag nanoparticles o n the surface of Fe3O4/TiO 2 nanocomposite. TABLE 4. Textural and structural parameters of the prepared sample. Sample SBET (m2/g) Average pore diameter (nm) Pore volume (cm3/g) TiO 2 91.01 7.15 0.17 Fe3O4/TiO 2 124.87 4.83 0.25 Fe3O4/TiO 2/Ag 159.43 5.17 0.19 Relative Pressure (p/p°)0.0 0.20.30.40.50.60.70.80.91.0Quantity Adsorbed (cm³/g STP ) 00102030405060708090100110T7-07-e1 - AdsorptionIsotherm Linear PlotT7-07-e1 - Desorption 0.1 Relative Pressure (p/p°)0.00.10.20.30.40.50.60.70.80.91.0Quantity Adsorbed (cm³/g STP ) 0020406080100120140160T5-05-E2 - AdsorptionIsotherm Linear Plot T5-05-E2 - Desorption (a) (b) Relative Pressure (p/p°)0.00.10.20.30.40.50.60.70.80.91.0Quantity Adsorbed (cm³/g STP ) 0020406080100120140T8-08-E5 - AdsorptionIsotherm Linear Plot T8-08-E5 - Desorption (c) FIGURE 6. N 2 adsorption –desorption isotherms for a) TiO 2, b) Fe3O4/TiO 2, and c) Fe 3O4/TiO 2/Ag E. Magnetic properties of the nanocomposites In order to evaluate the magnetic response of the magnetic nanocomposites to an external field, the saturation magnetization (Ms) of the samples were measured [15]. The Ms value of the Fe 3O4 nanoparticles is significantly higher than the Fe 3O4/TiO 2 and Fe3O4/TiO 2/Ag nanocomposites, which is because the Fe3O4 nanoparticles are coated with a layer of anatase TiO 2 in the Fe 3O4/TiO 2 and Fe 3O4/TiO 2/Ag samples. The small decrease in the Ms value of the Fe 3O4/TiO 2/Ag sample compared to that of the Fe 3O4/TiO 2 sample (Figure 7) can be attributed to the slight increase of mass and size due to the adherence of Ag nanoparticles on to the surface of the magnetic composites. FIGURE 7. Comparison of hysteresis curves of A) Fe 3O4 and B) (a) Fe 3O4/TiO 2 and (b) Fe 3O4/TiO 2/Ag F. Photocatalytic performance of the prepared samples To evaluate the photocatalytic activity of the synthesized samples a set of experiments for 2, 4-DCP deg radation with an initial concentration of 40 mg L-1 under visible light at room temperature was carried out in aqueous suspension using TiO 2, Fe3O4/TiO 2 and Fe3O4/TiO 2/Ag catalysts, and the experimental results are shown in Figure 8. The experimental resu lts demonstrated that among the prepared samples, the Fe 3O4/TiO 2/Ag catalyst showed t he highest efficiency of the 2, 4-DCP degradation under visible light ( 55% degradation obtained after 180 min irradiation).the results show that the photocatalytic activit y of pure TiO 2 is lower than that of Fe3O4/TiO 2 and Fe3O4/TiO 2/Ag samples . It implies that the Ag promotes the charge pair separation efficiency for TiO 2 catalysts. The electron transfer from the TiO 2 conduction band to Ag particles at the interface is thermodynamically possible because the Fermi level of TiO 2 is higher than that of Ag metal. This results in the formation of a Schottky barrier at metal semiconductor contact region and improves the photocatalytic activity of TiO 2. SRPioneers © Science and Research Pioneers Institute 8th International Conference on Nanotechnology (ICN201 8), February 8 -9, 2018 , Istanbul, T urkey FIGURE 8. Photocataly tic oxidation of 2, 4 -DCP in the presence of the prepared samples under visible light (Initial concentration of 2, 4 -DCP, 40 mg /L; volume, 100 mL; catalyst dosage, 10 mg, 180 min irradiation ). IV. CONCLUSION Pure TiO 2 and nanocomposites of Fe3O4/TiO 2 and Fe3O4/TiO 2/Ag were synthesized by the sol -gel method for degradation of 2, 4-dichlorophenol. The obtained photocatalysts identified by different analysis techniques such as XRD, DRS, N 2 physisorption, VSM and FESEM/EDX. Among all samples, Fe3O4/TiO 2/Ag cataly st exhibited the highest photocatalytic activity by 55% degradation under visible light after 1 80 min irradiation. The high photocatalytic activity can be attributed to both the high the photocatalyst specific surface areas and the plasmon resonance of sil ver nanoparticles. ACKNOWLEDGEMENTS The authors wish to acknowledge the financial support of University of Tehran for supporting of this research .