Synthesis and characterization of magnetically separable Fe3O4@SiO2@TiO2-Ag composite for degradation of Acid Blue 161

Synthesis and characterization of magnetically separable Fe3O4@SiO2@TiO2-Ag composite for degradation of Acid Blue 161 | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Synthesis and characterization of magnetically separable Fe3O4@SiO2@TiO2-Ag composite for degradation of Acid Blue 161 Hakan Kızıltas, Taner TEKİN, Derya BİRHAN, Derya TEKİN This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4977985/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 19 You are reading this latest preprint version Abstract Recyclable core-shell photocatalysts with high photocatalytic activity, which are used in water treatment and developed with great efforts in material chemistry, have attracted a lot of attention in recent years. Fe 3 O 4 @SiO 2 composite was synthesized by the Stöber method, and Fe 3 O 4 @SiO 2 @TiO 2 and Fe 3 O 4 @SiO 2 @TiO 2 -Ag composites were successfully synthesized by the sol-gel method. For the characterization of the composites, besides SEM-EDS, TEM, XRD, FTIR, UV-Vis, XPS, and VSM devices were used for magnetization measurement and then the photocatalytic activity on Acid Blue 161 dyestuff was tested. Acid Blue 161 dyestuff was used to examine the photocatalytic degradation of composites. The Fe 3 O 4 @SiO 2 @TiO 2 composite doped with Ag particles showed better photocatalytic activity than the commercially used Degussa P25 due to the suppression of the recombination of electron-hole pairs. Compared with other composites, the Fe 3 O 4 @SiO 2 @TiO 2 -Ag composite exhibited high photocatalytic activity by removing 100% of the dye under UV radiation. The synthesized Fe 3 O 4 @SiO 2 @TiO 2 -Ag composite photocatalyst is a cost-effective photocatalytic system due to its wide application area, high efficiency, and recyclability. Physical sciences/Engineering/Chemical engineering Earth and environmental sciences/Environmental sciences/Environmental chemistry Core-shell structure Ag particles photocatalytic activity Acid Blue 161 magnetic separation Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1. Introduction Environmental pollution and energy shortages, which have emerged with the rapid industrialization that has occurred throughout the world in recent years, are among the factors that hinder the progress of society and economic development [ 1 ]. Therefore, in order to ensure the continuous development of society and the economy, it is necessary to control pollution and create a clean environment and renewable [ 2 ]. Photocatalysis technique based on semiconductors used in wastewater treatment is accepted as the most effective method due to its simple use, sustainable energy production, high efficiency, low cost, and no secondary pollution [ 3 ]. In particular, the development of photocatalysts with excellent activity under visible and UV light is an area of research that attracts attention due to its wide application in energy storage, hydrogen production, and environmental purification. Photocatalysis has made significant contributions to water purification over the past three decades [ 4 , 5 ]. Titanium dioxide (TiO 2 ) is a very commonly used semiconductor photocatalyst [ 6 ]. Among many photocatalysts, TiO 2 has been favored because of its low cost, chemical stability, high efficiency/cost ratio, non-toxicity, and high antibacterial and photocatalytic activity [ 7 ]. Although nano-sized catalysts have efficient photocatalytic activity, they are too small to be recycled. To overcome this problem, some researchers have used magnetic nanoparticles to charge TiO 2 as a catalyst [ 8 ]. However, the biggest disadvantage of TiO 2 is that it causes various problems in the removal of organic pollutants in wastewater. Due to the wide band gap of 3.2 eV for TiO 2 , it only causes TiO 2 to be activated by ultraviolet (UV) light of less than 387 nm, thus limiting the photocatalytic activity under visible light. Researchers use organic dyes to make TiO 2 absorb and sensitize visible light [ 9 – 11 ]. Also, another factor limiting the catalytic activity is the high recombination of electron-hole pairs of TiO 2 . Therefore, various studies have been carried out to increase the activity of TiO 2 -based photocatalysts under UV light [ 4 – 12 ]. To overcome the above-mentioned problems, magnetic core-shell systems have been developed that allow the catalyst to be easily separated from the solution and the TiO 2 layer to absorb contaminants [ 13 ]. As a result of the studies, magnetic separation has been found to be a suitable method for recycling. The superior magnetic properties of iron oxides are used to obtain magnetic compounds (Fe 2 O 3 @TiO 2 , Fe 3 O 4 @TiO 2 ) created by TiO 2 and iron, and a promising photocatalyst for dye removal is synthesized [ 14 ]. The researchers noted that with the direct deposition of TiO 2 onto Fe 3 O 4 particles, electron-hole recombination will decrease, and photo dissolution will cause [ 15 , 16 ]. The SiO 2 layer between Fe 3 O 4 and TiO 2 is used to prevent Fe 3 O 4 from turning into antiferromagnetic α-Fe 2 O 3 during high-temperature annealing, to form anatase TiO 2 , and to increase the thermal stability of the core-shell structure [ 17 ]. Core-shell structures are double-phase material that has an inner core structure and an outer shell made of different components. These materials have been of interest because they can exhibit unique properties arising from their geometry and design [ 18 ]. These structures have many advantages such as selective, robust, low-cost, long-term stability, large surface area, and high antibacterial, and photocatalytic activities [ 19 ]. In this study, Fe 3 O 4 @SiO 2 structure was synthesized using the Stöber method since it is easy to control particle size. In fact, the Stöber method is the least complicated method that has easy control from SiO 2 thickness and to produce an excellent product shape. Fe 3 O 4 @SiO 2 @TiO 2 structure and Ag deposition were synthesized by the multi-step method. The composites were first analyzed by Transmission electron microscopy (TEM), Scanning electron microscopy (SEM-EDS), X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), UV-Vis absorption spectrometer, Vibrating sample magnetometry (VSM), and X-ray photoelectron spectroscopy (XPS) has been extensively analyzed. 2. Experimental section 2.1. Materials Iron (III) chloride hexahydrate (FeCl 3 .6H 2 O), sodium acetate (C 2 H 3 NaO 2 , Sigma Aldrich, 99%), ethylene glycol (C 2 H 6 O 2 , Sigma Aldrich, 98%), ethanol (C 2 H 5 OH), polyethylene glycol (PEG, Sigma Aldrich, Mr 7000–9000), tetraethyl orthosilicate (TEOS, Sigma Aldrich, 99%), ammonium hydroxide (NH 4 OH, Sigma Aldrich, 25%), titanium butoxide (Ti(C 4 H 9 O) 4 ), Polyvinylpyrrolidone (C 6 H 9 NO) n , Sigma Aldrich, Wt 40,000), silver nitrate (AgNO 3 , Sigma Aldrich, 99%), sodium hydroxide (NaOH, Sigma Aldrich, 99%) and distilled water are used. Acid Blue 161 (C 20 H 13 N 2 O 5 SNaCrx, Sigma Aldrich 40%) dye was used for photocatalytic experiments. 2.2. Synthesis of Fe 3 O 4 Magnetic Fe 3 O 4 particles were prepared by a solvothermal method [ 20 ]. Briefly, 5.6 g FeCl 3 .6H 2 O was dissolved in 80 mL of appropriate ethylene glycol (EG) under ultrasonic stirring. To the homogeneous yellow solution obtained, 14.4 g of sodium acetate and 4 g of polyethylene glycol (PEG) were added and stirring was continued for 15 min. After forming a homogeneous dispersion, the mixture was transferred into a Teflon-lined stainless steel autoclave reactor and heated at 200°C for 12 h. After the reaction for 12 h, the autoclave was naturally cooled to room temperature. Fe 3 O 4 particles, which were removed from the solution medium with the help of an external magnet, were washed 6 times with distilled water and ethanol and dried at 60°C for 3 h. 2.3. Synthesis of Fe 3 O 4 @SiO 2 Fe 3 O 4 @SiO 2 particles were synthesized with the help of the Stöber method. 0.1 g of obtained Fe 3 O 4 particles was mixed under ultrasonication for 15 min in a solution of 80 mL of ethanol and 20 mL of deionized water. Subsequently, 5 mL of concentrated NH 4 OH was added to the solution medium and mixed for 5 min and 1 mL of TEOS was added dropwise into the solution medium with vigorous stirring. After mixing the solution under 45% amplitude for 3 h, the product obtained was separated with an external magnet, washed 6 times with deionized water and ethanol, and dried at 60°C for 3 h and calcined for 2 h at 200°C. 2.4. Synthesis of Fe 3 O 4 @SiO 2 @TiO 2 1 g of Fe 3 O 4 @SiO 2 particles were added in 56 mL of ethanol and 3.5 mL of titanium butoxide solution and mixed under ultrasonication for 15 min. The obtained solution was then placed in a 200 mL Teflon autoclave reactor. 14 mL of distilled water, which did not mix with the solution, was placed in a beaker in the reactor and kept in the oven at 150°C for 12 h. After the autoclave was cooled at room temperature, the product obtained was separated with an external magnet washed 6 times with deionized water and ethanol, and dried at 60°C for 3 h. Then, the particles were calcined at 500°C for 2 h. 2.5. Synthesis of Fe 3 O 4 @SiO 2 @TiO 2 -Ag Synthesis of Fe 3 O 4 @SiO 2 @TiO 2 -Ag nanoparticles takes place in two stages: Preparation of Tollen’s reagent and Ag addition of Fe 3 O 4 @SiO 2 @TiO 2 nanoparticles. To prepare 500 mL 5.10 − 3 M Tollen’s reagent; The reactions are performed as shown below by adding 25 mL of 0.1 M NaOH solution dropwise into 25 mL of 0.1 M AgNO 3 solution under 1000 rpm mixing [ 21 ]. AgNO 3 + NaOH \(\:\to\:\) AgOH + NHO 3 (1) 2AgOH AgO + HO (2) 2AgOH \(\:\to\:\) Ag 2 O + H 2 O (2) The reaction is carried out as shown below by adding a 25% NH 4 OH solution until the precipitated particles disappear into the resulting solution. Ag 2 O + 4NH 3 + H 2 O \(\:\to\:\) 2Ag(NH 3 ) +2 + 2OH − (3) Then, the obtained solution is completed to 500 mL, and 5.10 − 3 M Tollen’s reagent is obtained. In the second stage, 0.4 g Fe 3 O 4 @SiO 2 @TiO 2 composite was mixed in 100 mL of Tollen's reagent under ultrasonication for 15 min to obtain a homogeneous solution [ 22 ]. On the other hand, after dissolving 0.6 g of PVP in 90 mL of ethanol, the Fe 3 O 4 @SiO 2 @TiO 2 solution was refluxed at 70°C for 4 h. After the solution was cooled at room temperature, the product obtained was separated with an external magnet washed 6 times with deionized water and ethanol, and dried at 60°C for 3 h. Then, the particles were calcined at 500°C for 2 h. 2.6. Determination of photocatalytic activities of the composites The produced composite particle form was used to evaluate the photocatalytic degradation of Acid Blue 161 dyestuff. Dyestuff experiments were carried out in a batch reactor with the outer part isolated against the light. The temperature of the solution was kept constant at 25°C with a water circulator. Pen-Ray UV Lamp (Cole-Parmer, 257 nm, 44W m − 2 ) was used as a UV source. The saturated oxygen concentration was provided with air pumped into the reaction medium at a constant flow rate. The photocatalytic experiments were carried out using 100 mg of the produced particles photocatalysts in the presence of 400 mL of dye solution (20 mg L − 1 ). Before the degradation experiments, the composite photocatalysts produced were added to the dye solution and mixed for 30 min in the dark to stabilize. Dye concentrations at different times were determined using a UV spectrophotometer (Optizen α spectrophotometer). Measurement of the Acid Blue 161 concentration was carried out at 602.5 nm. 2.7. Characterization The size, morphology, and elemental analysis of the synthesized composite photocatalysts were investigated using Transmission Electron Microscopy (TEM, Hitachi-HT7700), Scanning Electron Microscopy (SEM, Zeiss -Sigma 300), and Energy Dispersive X-ray Spectroscopy (EDS). FTIR spectra of composites were obtained using Fourier Transform Infrared Spectroscopy (FTIR, Vertex-80v). The crystalline structures of the samples were investigated by X-ray diffraction (XRD, PANalytical-Empyrean) analysis using Cu-Kα radiation (λ = 0.15418 nm). The magnetic properties of the samples were investigated using a Vibrating Sample Magnetometer (VSM, Lake Shore, 7407) at room temperature. XPS analysis and UV-Vis absorption spectrometer measurements were carried out using (XPS, Specs-Flex) and (UV, Shimadzu-UV3600 Plus). 3. Result and Discussion TEM analysis results of the synthesized Fe 3 O 4 , Fe 3 O 4 @SiO 2 , Fe 3 O 4 @SiO 2 @TiO 2 , and Fe 3 O 4 @SiO 2 @TiO 2 -Ag composites and the diameter distribution analysis of the particles were investigated respectively and shown in Fig. 1 . As shown in Fig. 1 a, Fe 3 O 4 particles consisting of a few small Fe 3 O 4 particles were found to be spherical, and the diameter of the spherical particles was between 150 and 250 nm, with an average spherical diameter of about 210 nm. The synthesized Fe 3 O 4 particles are uniformly dispersed, spherical in shape, uniform in shape, and almost the same size. The fact that the surface of the particles is not completely smooth indicates that the Fe 3 O 4 particles are formed in smaller diameters [ 23 ]. As shown in Fig. 1 b, it is clearly seen that Fe 3 O 4 @SiO 2 particles have a core-shell structure. The black spheres show the magnetic cores and the gray color surrounding the core shows the silica shell. Since SiO 2 is an amorphous structure, it formed a thin flat layer on the surface of Fe 3 O 4 . As a result of the particle size distribution analysis, it was determined that the Fe 3 O 4 @SiO 2 composite had a diameter ranging from 160 to 260 nm and its average diameter was 220 nm. Fe 3 O 4 @SiO 2 particles were coated with a TiO 2 layer using the sol-gel method. The Fe 3 O 4 @SiO 2 @TiO 2 particles seen in Fig. 1 c have a distinguishable three-layer monodisperse structure consisting of a Fe 3 O 4 core, a SiO 2 interlayer, and a TiO 2 outer layer. Since TiO 2 forms a homogeneous coating on the silica surface, no net deposition of composite particles is observed. As a result of the particle size distribution analysis, it was determined that the Fe 3 O 4 @SiO 2 @TiO 2 composite had diameters ranging from 185 to 285 nm and its average diameter was 240 nm. As shown in Fig. 1 d, the synthesized Fe 3 O 4 @SiO 2 @TiO 2 -Ag composites show a heterogeneous distribution as in the Fe 3 O 4 @SiO 2 @TiO 2 composites. The core-shell Fe 3 O 4 @SiO 2 @TiO 2 -Ag composite appears to show superior magnetization, indicating its suitability for recovery and magnetic separation. As a result of the particle size distribution analysis, it was determined that the Fe 3 O 4 @SiO 2 @TiO 2 -Ag composite had diameters ranging from 190 to 300 nm and its average diameter was around 255 nm. The results of SEM and EDS analysis of Fe 3 O 4 , Fe 3 O 4 @SiO 2 , Fe 3 O 4 @SiO 2 @TiO 2 , and Fe 3 O 4 @SiO 2 @TiO 2 -Ag composites are shown in Fig. 2 . As shown in Fig. 2 a, the obtained Fe 3 O 4 particles have an average diameter of 210 nm. Fe 3 O 4 particles were prepared by the reduction of Fe (III) salts [ 24 ]. The synthesized Fe 3 O 4 particles showed good distribution and completed their formation globally. EDS analysis proved the presence of iron and oxygen in Fe 3 O 4 particles. As shown in Fig. 2 b, Fe 3 O 4 particles synthesized using the Stöber method were easily coated with silica. The coated SiO 2 shell can effectively prevent the chemical degradation of Fe 3 O 4 particles. This allows the synthesized photocatalyst to be used repeatedly in more than one reaction cycle [ 25 ]. The thickness of the SiO 2 shell is very important, and the high layer thickness significantly reduces the magnetic properties and recovery of the catalyst from the wastewater. In addition, a thin layer decreases the photocatalytic activity of composites while increasing particle agglomeration [ 26 ]. The obtained Fe 3 O 4 @SiO 2 particles have an average diameter of 220 nm. EDS analysis proved the presence of iron, silicon, and oxygen in Fe 3 O 4 @SiO 2 particles. The coating of the TiO 2 layer on Fe 3 O 4 @SiO 2 composites was performed by the sol-gel process and then amorphous TiO 2 was transformed into the crystalline phase through calcination at 500°C for 2 h. As shown in Fig. 2 c, the synthesized Fe 3 O 4 @SiO 2 @TiO 2 composite shows a homogeneous distribution similar to Fe 3 O 4 particles and Fe 3 O 4 @SiO 2 composite. When the SEM images are compared, it is seen that the smooth surfaces of Fe 3 O 4 and Fe 3 O 4 @SiO 2 composites become a thick crystalline layer after being coated with a TiO 2 layer [ 27 ]. The obtained Fe 3 O 4 @SiO 2 @TiO 2 particles have an average diameter of 240 nm. EDS analysis proved the presence of iron, silicon, titanium, and oxygen in Fe 3 O 4 @SiO 2 @TiO 2 particles. In order to deposit Ag particles on the surface of Fe 3 O 4 @SiO 2 @TiO 2 composite and to obtain Fe 3 O 4 @SiO 2 @TiO 2 -Ag core/shell structure, a sol-gel method was used as both reductant and stabilizer in the presence of PVP. As shown in Fig. 2 d, the synthesized Fe 3 O 4 @SiO 2 @TiO 2 -Ag composite shows a homogeneous distribution such as Fe 3 O 4 @SiO 2 @TiO 2 . As the Ag nanoparticles combined with the Fe 3 O 4 @SiO 2 @TiO 2 composite, there was an increase in the diameter of the composite. The obtained Fe 3 O 4 @SiO 2 @TiO 2 -Ag particles have an average diameter of 255 nm. EDS analysis proved the presence of iron, silicon, titanium, silver, and oxygen in Fe 3 O 4 @SiO 2 @TiO 2 particles. In order to characterize the phase purity, crystallinity, and composition of the prepared samples, X-ray diffraction patterns of the samples were obtained. Figure 3 shows the XRD patterns of Fe 3 O 4 and SiO 2 particles, Fe 3 O 4 @SiO 2 , Fe 3 O 4 @SiO 2 @TiO 2 , and Fe 3 O 4 @SiO 2 @TiO 2 -Ag composite. Figure 3 a shows the XRD graph of Fe 3 O 4 particles and all diffraction peaks are compatible with (JCPDS card No. 19–0629). Accordingly, Fe 3 O 4 particles have a face-centered cubic structure of magnetite. The relative intensity and position of the diffraction peaks of Fe 3 O 4 particles shown in Fig. 3 a diffraction peaks corresponding to planes (111), (220), (311), (400), (422), (511), and (440) demonstrated in harmony with planes of the standard Fe 3 O 4 diffraction data card (JCPDS: 19–0629) [ 28 ]. As shown in Fig. 3 b-c, the XRD pattern of Fe 3 O 4 @SiO 2 particles showed almost the same property as pure Fe 3 O 4 . However, the large peak at 2θ = 22° indicates that the coated SiO 2 shell is amorphous. The peak width seen in Fig. 3 c at X-ray diffraction 2θ = 20° and 30° is generally related to amorphous silica peaks [ 29 ]. Compared to Figs. 3 a and c, Fe 3 O 4 @SiO 2 @TiO 2 shows new diffraction peaks. The diffraction peaks of TiO 2 belong to the anatase phase and are fully compatible with (JCPDS card No: 21-1272) [ 16 ]. Fe 3 O 4 core coated with SiO 2 and TiO 2 showed no obvious change. Only the intensity of the Fe 3 O 4 peaks weakened (Fig. 3 d). As shown in Fig. 3 e, Fe 3 O 4 @SiO 2 @TiO 2 -Ag composite gives peaks compatible with (JCPDS card No: 19–0629) of Fe 3 O 4 and (JCPDS card No: 21-1272) of TiO 2 . Apart from the Fe 3 O 4 and TiO 2 characteristic peaks, 2θ = 37.90°, 44.10°, 64.30° and 77.20° diffraction peaks can be easily indexed to Ag, and the face-centered cubic structure of Ag is compatible with the (JCPDS card No: 04-0783), and indicating that crystallized Ag nanoparticles have been deposited on the outer shells. As shown in Fig. 4 , FTIR spectrums were used to characterize the composition and bond structure of the Fe 3 O 4 , Fe 3 O 4 @SiO 2 , Fe 3 O 4 @SiO 2 @TiO 2 , and Fe 3 O 4 @SiO 2 @TiO 2 -Ag composites. As shown in Fig. 4 , Fe 3 O 4 @SiO 2 @TiO 2 composites have more signals than Fe 3 O 4 . The three bands at 580, 630, 1630, and 3405 cm − 1 show the FTIR spectrum of pure Fe 3 O 4 nanoparticles. The 580 cm − 1 and 630 cm − 1 bands corresponds to the Fe‒O vibration [ 30 ]. The bands at 1630 and 3405 cm − 1 are associated with the presence of hydroxyl bands and correspond to OH bending and OH stretching, respectively. Symmetric vibration in the 800 cm − 1 band and asymmetric vibration at 1080 cm − 1 correspond to Si‒O‒Si. The 940–960 cm − 1 band is caused by the Si‒O‒Ti vibration and the 500–900 cm − 1 band originates from the Ti‒O‒Ti vibration [ 31 ]. O-H vibration in 1630 cm − 1 and 3370 cm − 1 bands proves the presence of water. This provides an advantage for the photocatalytic activity of the synthesized photocatalysts. The vibration of Fe 3 O 4 @SiO 2 @TiO 2 -Ag composites is similar to the vibrations in all bands of Fe 3 O 4 @SiO 2 @TiO 2 composites [ 13 ]. As with most literature studies, there are no peaks belonging to Ag nanoparticles. UV-Vis absorption spectrometer measurements shown in Fig. 5 a were used to determine the bandgap energy of synthesized Fe 3 O 4 , Fe 3 O 4 @SiO 2 , Fe 3 O 4 @SiO 2 @TiO 2 , and Fe 3 O 4 @SiO 2 @TiO 2 -Ag composites. According to the theory of bandgap, the optical band gap of composites can be defined using Tauc’s Equation: αhʋ = A (hʋ - E g ) n (4) where a is the absorption coefficient (cm − 1 ), hʋ is the photon energy (eV), A is a characteristic constant, E g is the energy bandgap (eV) and n is a parameter identifying the electronic transition type ( n = 0.5 or 2 for direct and indirect transitions, respectively). According to the Tauc equation, drawing (αhυ) 0.5 - (hυ) creates a straight line in a certain region. As shown in Fig. 5 b-c-d, the E g values of composites can be estimated by extrapolating the straight-line fit of the graphical representation of (hʋα) 0.5 versus hʋ to hʋ-axis . The E g value for Fe 3 O 4 particles energy was determined as 1.3 eV. In literature studies, E g values obtained for Fe 3 O 4 particles range from 1.16 to 2.2 eV [ 32 ]. Coating the SiO 2 semiconductor on the surface of the Fe 3 O 4 particle, whose E g value is determined as 1.3 eV, is estimated to will increase the forbidden energy bandgap due to the band theory [ 33 ]. The band gap of the Fe 3 O 4 @SiO 2 composite was determined as 1.68 eV. As it is known, TiO 2 is a semiconductor and the E g value was determined as 3.2 eV in studies in the literature [ 34 ]. With the coating of Fe 3 O 4 @SiO 2 composite with TiO 2 , it is estimated that the forbidden band gap will increase according to the band theory [ 33 ]. The E g value for the combined energy of Fe 3 O 4 @SiO 2 @TiO 2 was determined as 2.1 eV. It is estimated that coating the Ag conductor on the surface of the Fe 3 O 4 @SiO 2 @TiO 2 composite, whose E g value is determined as 2.1 eV, will reduce the band gap of the forbidden energy according to the band theory. Therefore, the value for the combined energy of Fe 3 O 4 @SiO 2 @TiO 2 -Ag was determined as 2.0 eV. In order to better understand the surface composition and bonding medium of the Fe 3 O 4 @ SiO 2 @TiO 2 -Ag composite, XPS analysis was performed and compared with the Fe 3 O 4 @ SiO 2 @TiO 2 composite. The peaks in the general XPS spectrum of Fe 3 O 4 @SiO 2 @TiO 2 -Ag composite belong to Ag, C, Ti, and O elements. The peak of element C is estimated to consist of a carbon-based contaminant. Figure 6 shows all the spectra scanned in the range of 0-1200 eV. The peaks seen in the spectrum belong to Ti, C, Fe, Si, O, and Ag elements. In Fig. 6 b, the XPS spectrum of the high-resolution Ti2p peak is given. As shown in Fig. 6 , it can be seen that the peaks of Ti2p 1/2 and Ti2p 3/2 correspond to two binding energies centered at 461 eV and 466.7 eV indicating the main valence of Ti [ 35 , 36 ]. Ti2p peaks of Fe 3 O 4 @SiO 2 @TiO 2 -Ag composite show no shift when compared with the peaks of Fe 3 O 4 @SiO 2 @TiO 2 composite, confirming that the TiO 2 layer structure remains intact throughout the preparation process. According to the XPS results, it is likely that the intensity of the Ti2p peak will decrease as the TiO 2 surface is coated with Ag nanoparticles. Figure 6 shows the XPS spectrum of the Fe 3 O 4 @SiO 2 @TiO 2 -Ag composite in the Ag3d region. The peaks showing the formation of Ag nanoparticles and corresponding to Ag 3s 3/2 and 3p 5/2 have 720 eV and 610 eV binding energy, respectively. This binding energy shows that silver has a metallic structure. Magnetic measurements of the samples were carried out at 300 K using a vibrating sample magnetometer (VSM). The measured magnetization curves for Fe 3 O 4 nanoparticles, Fe 3 O 4 @SiO 2 , Fe 3 O 4 @SiO 2 @TiO 2 , and Fe 3 O 4 @SiO 2 @TiO 2 -Ag composites were compared in Fig. 7 . As seen in Fig. 7 , saturation magnetization values for Fe 3 O 4 nanoparticles, Fe 3 O 4 @SiO 2 , Fe 3 O 4 @SiO 2 @TiO 2 , and Fe 3 O 4 @SiO 2 @TiO 2 -Ag composites at + 8000 Oe are 81, 64, 44 and 25 emu g − 1 , respectively. The non-magnetic SiO 2 and TiO 2 shells surrounding the magnetic core caused the magnetic properties of Fe 3 O 4 nanoparticles to decrease. Despite the decrease in magnetic saturation, the photocatalyst was easily removed from the solution with an external magnet. As shown in Fig. 8 , the photocatalyst of Acid Blue 161 was investigated to remove pollutants from wastewater and investigate the photocatalytic activity of Magnetic Fe 3 O 4 nanoparticles, TiO 2 (Degussa, P25), Fe 3 O 4 @SiO 2 , Fe 3 O 4 @SiO 2 @TiO 2 , and Fe 3 O 4 @SiO 2 @TiO 2 -Ag photocatalysts. Photocatalytic degradation experiments were carried out in the dark for 0–15 min and under UV light for 15–120 min. The experiments were achieved in the dark environment for the first 15 min and there was no significant change in Acid Blue 161 dye concentration. For 120 min, Fe 3 O 4 particles removed 4.36% of the dye. Due to the semiconductor feature of SiO 2 , the Fe 3 O 4 @SiO 2 composite removed 11.53% of the dye by showing better photocatalytic activity than the Fe 3 O 4 particle [ 37 ]. The decomposition rates of TiO 2 (Degussa P25) nanoparticles are 84%. In the Fe 3 O 4 @SiO 2 @TiO 2 composite, the SiO 2 interlayer between the iron oxide core and the TiO 2 shell reduces electronic interactions at the point of contact, thereby increasing photocatalytic activity and the decomposition rate of dye is 100% [ 38 ]. Fe 3 O 4 @SiO 2 @TiO 2 -Ag composite removed 100% of the dye in a shorter time than the Fe 3 O 4 @SiO 2 @TiO 2 composite. Since the Ag particles increased the specific surface area of the core-shell structure, the Fe 3 O 4 @SiO 2 @TiO 2 -Ag composite showed superior photocatalytic activity. The photocatalytic activity of the composites in the degradation of the acid blue 161 dyestuffs follows the order: Fe 3 O 4 @SiO 2 @TiO 2 -Ag > Fe 3 O 4 @SiO 2 @TiO 2 > Degussa P25 (TiO 2 ) > Fe 3 O 4 @SiO 2 > Fe 3 O 4 . 4. Conclusions In this study, Fe 3 O 4 particles were successfully synthesized by the solvothermal reaction. Fe 3 O 4 @SiO 2 composite was obtained by the Stöber method, and Fe 3 O 4 @SiO 2 @TiO 2 and Fe 3 O 4 @SiO 2 @TiO 2 -Ag composites were successfully synthesized by the sol-gel method. To determine the structural properties of synthesized composites, SEM-EDS TEM, XRD, FTIR, VSM and XPS analyses were performed, and UV-Vis analyses were used to examine the optical properties of synthesized composites. According to the TEM and SEM analysis results, it was determined that Fe 3 O 4 , Fe 3 O 4 @SiO 2 , Fe 3 O 4 @SiO 2 @TiO 2 , and Fe 3 O 4 @SiO 2 @TiO 2 -Ag composites were spherical and their average diameters were 210, 220, 240 and 255 nm. Crystal structures of Fe 3 O 4 , Fe 3 O 4 @SiO 2 , Fe 3 O 4 @SiO 2 @TiO 2 , and Fe 3 O 4 @SiO 2 @TiO 2 -Ag composites were examined by XRD analysis and it was found that Ag nanoparticles deposited in the outer shell were crystalline. Also, according to the results of the analysis, the synthesized photocatalysts showed good compatibility with standard diffraction data cards. The bond structures and bandgap energies of composites were examined by FTIR and UV-Vis analysis respectively. According to the results of the analysis, it has been understood that there is no vibration peak belonging to Ag and increases photocatalytic activity due to the harmony of the core-shell structure with each other. The band gap energies of Fe 3 O 4 , Fe 3 O 4 @SiO 2 , Fe 3 O 4 @SiO 2 @TiO 2 , and Fe 3 O 4 @SiO 2 @TiO 2 -Ag composites were determined as 1.3, 1.68, 2.1 and 2.0 eV, respectively. According to XPS results, it was determined that Fe 3 O 4 @ SiO 2 @TiO 2 -Ag composite was compatible with Fe 3 O 4 @SiO 2 @TiO 2 composite and TiO 2 preserved its layer form during Ag doping process. Acid Blue 161 dyestuff was used to examine the photocatalytic degradation of composites. Compared with other composites, the Fe 3 O 4 @SiO 2 @TiO 2 -Ag composite exhibited high photocatalytic activity by removing 100% of the dye under UV radiation. Declarations Author Contribution H.K. contributed to the concept, wrote the paper, and supervised the work. T.T. performed the parametric analysis. H.K., D.T. and D.B performed fabrication and measurements, and revised the manuscript. Data Availability The datasets generated and analyzed during the present study are not publicly available, as all the data are presented in the article and therefore there is no need to include the raw data, but they can be provided from the corresponding author upon reasonable request. References Zhao, Z. Y., Zuo, J., Fan, L. L. & Zillante, G. Impacts of renewable energy regulations on the structure of power generation in China–a critical analysis. Renew. Energy . 36 (1), 24–30. https://doi.org/10.1016/j.renene.2010.05.015 (2011). Chen, Z. & Fu, M. L. Recyclable magnetic Fe 3 O 4 @SiO 2 /β-NaYF4:Yb 3+ ,Tm3+/TiO2 composites with NIR enhanced photocatalytic activity. Mater. Res. Bull. 107 , 194–203. https://doi.org/10.1016/j.materresbull.2018.07.016 (2018). Kannan, K., Radhika, D., Gnanasangeetha, D., Krishna, L. S. & Gurushankar, K. Y3 + and Sm3 + co-doped mixed metal oxide nanocomposite: Structural, electrochemical, photocatalytic, and antibacterial properties. Appl. Surf. Sci. 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Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composites\u003c/p\u003e","description":"","filename":"Picture1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4977985/v1/0a0618950bf95b892c8261c0.jpg"},{"id":70688400,"identity":"5efaa555-3637-485c-a12f-b513fc061117","added_by":"auto","created_at":"2024-12-05 15:56:47","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":137293,"visible":true,"origin":"","legend":"\u003cp\u003eSEM-EDS images of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e, and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composites\u003c/p\u003e","description":"","filename":"Picture2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4977985/v1/bdbce0ef06c90bf47bbd27b6.jpg"},{"id":70688876,"identity":"7736a120-38f9-499d-818f-54cde9140b42","added_by":"auto","created_at":"2024-12-05 16:04:47","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":41467,"visible":true,"origin":"","legend":"\u003cp\u003eXRD diagram of (a) SiO\u003csub\u003e2\u003c/sub\u003e, (b) Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, (c) Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e, (d) Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e and (e) Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composites\u003c/p\u003e","description":"","filename":"Picture3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4977985/v1/57b25d1f0c53270a2df136c3.jpg"},{"id":70688877,"identity":"93933ed4-3cf4-4a7e-85d3-be65cfc7cdd3","added_by":"auto","created_at":"2024-12-05 16:04:47","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":37070,"visible":true,"origin":"","legend":"\u003cp\u003eFTIR spectrum of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e, and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composite\u003c/p\u003e","description":"","filename":"Picture4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4977985/v1/ebdfcb276d8323b22611974c.jpg"},{"id":70689719,"identity":"5880139b-9130-49a8-a5a8-4a8cf3913f58","added_by":"auto","created_at":"2024-12-05 16:12:47","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":52077,"visible":true,"origin":"","legend":"\u003cp\u003e(a) UV-Vis absorption spectra of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composites, (b-I) Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, (c-II) Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e, (d-III) Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e and (e-IV) Tauc plot of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composites\u003c/p\u003e","description":"","filename":"Picture5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4977985/v1/0238f61516a110604ea02cfd.jpg"},{"id":70688403,"identity":"a2525419-8028-435d-9b3d-146982735ab7","added_by":"auto","created_at":"2024-12-05 15:56:47","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":21955,"visible":true,"origin":"","legend":"\u003cp\u003eXPS spectrum of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composite\u003c/p\u003e","description":"","filename":"Picture6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4977985/v1/176ad5e9b388676c0a286bab.jpg"},{"id":70689720,"identity":"a5e6e6ee-a149-44dc-952c-bcff050154fc","added_by":"auto","created_at":"2024-12-05 16:12:47","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":27126,"visible":true,"origin":"","legend":"\u003cp\u003eVSM magnetization curves of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composite\u003c/p\u003e","description":"","filename":"Picture7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4977985/v1/c14579d15a28437834c23173.jpg"},{"id":70688880,"identity":"761ff6f1-405c-4ce4-893d-3aec06ae5446","added_by":"auto","created_at":"2024-12-05 16:04:47","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":27538,"visible":true,"origin":"","legend":"\u003cp\u003eDegradation graph of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e, TiO\u003csub\u003e2\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composites on Acid Blue 161\u003c/p\u003e","description":"","filename":"Picture8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-4977985/v1/9fbb69ed3d75ce07a292e6d1.jpg"},{"id":70690084,"identity":"8a88f76d-bfd8-47e0-9b3e-f1875db50d7e","added_by":"auto","created_at":"2024-12-05 16:20:48","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1294604,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4977985/v1/10f33bbf-e6ec-4b8e-aef1-b10147e210cb.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Synthesis and characterization of magnetically separable Fe3O4@SiO2@TiO2-Ag composite for degradation of Acid Blue 161","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eEnvironmental pollution and energy shortages, which have emerged with the rapid industrialization that has occurred throughout the world in recent years, are among the factors that hinder the progress of society and economic development [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Therefore, in order to ensure the continuous development of society and the economy, it is necessary to control pollution and create a clean environment and renewable [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Photocatalysis technique based on semiconductors used in wastewater treatment is accepted as the most effective method due to its simple use, sustainable energy production, high efficiency, low cost, and no secondary pollution [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. In particular, the development of photocatalysts with excellent activity under visible and UV light is an area of research that attracts attention due to its wide application in energy storage, hydrogen production, and environmental purification. Photocatalysis has made significant contributions to water purification over the past three decades [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Titanium dioxide (TiO\u003csub\u003e2\u003c/sub\u003e) is a very commonly used semiconductor photocatalyst [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Among many photocatalysts, TiO\u003csub\u003e2\u003c/sub\u003e has been favored because of its low cost, chemical stability, high efficiency/cost ratio, non-toxicity, and high antibacterial and photocatalytic activity [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Although nano-sized catalysts have efficient photocatalytic activity, they are too small to be recycled. To overcome this problem, some researchers have used magnetic nanoparticles to charge TiO\u003csub\u003e2\u003c/sub\u003e as a catalyst [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. However, the biggest disadvantage of TiO\u003csub\u003e2\u003c/sub\u003e is that it causes various problems in the removal of organic pollutants in wastewater. Due to the wide band gap of 3.2 eV for TiO\u003csub\u003e2\u003c/sub\u003e, it only causes TiO\u003csub\u003e2\u003c/sub\u003e to be activated by ultraviolet (UV) light of less than 387 nm, thus limiting the photocatalytic activity under visible light. Researchers use organic dyes to make TiO\u003csub\u003e2\u003c/sub\u003e absorb and sensitize visible light [\u003cspan additionalcitationids=\"CR10\" citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. Also, another factor limiting the catalytic activity is the high recombination of electron-hole pairs of TiO\u003csub\u003e2\u003c/sub\u003e. Therefore, various studies have been carried out to increase the activity of TiO\u003csub\u003e2\u003c/sub\u003e-based photocatalysts under UV light [\u003cspan additionalcitationids=\"CR5 CR6 CR7 CR8 CR9 CR10 CR11\" citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. To overcome the above-mentioned problems, magnetic core-shell systems have been developed that allow the catalyst to be easily separated from the solution and the TiO\u003csub\u003e2\u003c/sub\u003e layer to absorb contaminants [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. As a result of the studies, magnetic separation has been found to be a suitable method for recycling. The superior magnetic properties of iron oxides are used to obtain magnetic compounds (Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e) created by TiO\u003csub\u003e2\u003c/sub\u003e and iron, and a promising photocatalyst for dye removal is synthesized [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. The researchers noted that with the direct deposition of TiO\u003csub\u003e2\u003c/sub\u003e onto Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles, electron-hole recombination will decrease, and photo dissolution will cause [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. The SiO\u003csub\u003e2\u003c/sub\u003e layer between Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and TiO\u003csub\u003e2\u003c/sub\u003e is used to prevent Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e from turning into antiferromagnetic α-Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e during high-temperature annealing, to form anatase TiO\u003csub\u003e2\u003c/sub\u003e, and to increase the thermal stability of the core-shell structure [\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Core-shell structures are double-phase material that has an inner core structure and an outer shell made of different components. These materials have been of interest because they can exhibit unique properties arising from their geometry and design [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. These structures have many advantages such as selective, robust, low-cost, long-term stability, large surface area, and high antibacterial, and photocatalytic activities [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eIn this study, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e structure was synthesized using the St\u0026ouml;ber method since it is easy to control particle size. In fact, the St\u0026ouml;ber method is the least complicated method that has easy control from SiO\u003csub\u003e2\u003c/sub\u003e thickness and to produce an excellent product shape. Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e structure and Ag deposition were synthesized by the multi-step method. The composites were first analyzed by Transmission electron microscopy (TEM), Scanning electron microscopy (SEM-EDS), X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), UV-Vis absorption spectrometer, Vibrating sample magnetometry (VSM), and X-ray photoelectron spectroscopy (XPS) has been extensively analyzed.\u003c/p\u003e"},{"header":"2. Experimental section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Materials\u003c/h2\u003e \u003cp\u003eIron (III) chloride hexahydrate (FeCl\u003csub\u003e3\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO), sodium acetate (C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e3\u003c/sub\u003eNaO\u003csub\u003e2\u003c/sub\u003e, Sigma Aldrich, 99%), ethylene glycol (C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e6\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, Sigma Aldrich, 98%), ethanol (C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e5\u003c/sub\u003eOH), polyethylene glycol (PEG, Sigma Aldrich, Mr 7000\u0026ndash;9000), tetraethyl orthosilicate (TEOS, Sigma Aldrich, 99%), ammonium hydroxide (NH\u003csub\u003e4\u003c/sub\u003eOH, Sigma Aldrich, 25%), titanium butoxide (Ti(C\u003csub\u003e4\u003c/sub\u003eH\u003csub\u003e9\u003c/sub\u003eO)\u003csub\u003e4\u003c/sub\u003e),\u003c/p\u003e \u003cp\u003ePolyvinylpyrrolidone (C\u003csub\u003e6\u003c/sub\u003eH\u003csub\u003e9\u003c/sub\u003eNO)\u003csub\u003en\u003c/sub\u003e, Sigma Aldrich, Wt 40,000), silver nitrate (AgNO\u003csub\u003e3\u003c/sub\u003e, Sigma Aldrich, 99%), sodium hydroxide (NaOH, Sigma Aldrich, 99%) and distilled water are used. Acid Blue 161 (C\u003csub\u003e20\u003c/sub\u003eH\u003csub\u003e13\u003c/sub\u003eN\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003eSNaCrx, Sigma Aldrich 40%) dye was used for photocatalytic experiments.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Synthesis of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e\u003c/h2\u003e \u003cp\u003eMagnetic Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles were prepared by a solvothermal method [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. Briefly, 5.6 g FeCl\u003csub\u003e3\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO was dissolved in 80 mL of appropriate ethylene glycol (EG) under ultrasonic stirring. To the homogeneous yellow solution obtained, 14.4 g of sodium acetate and 4 g of polyethylene glycol (PEG) were added and stirring was continued for 15 min. After forming a homogeneous dispersion, the mixture was transferred into a Teflon-lined stainless steel autoclave reactor and heated at 200\u0026deg;C for 12 h. After the reaction for 12 h, the autoclave was naturally cooled to room temperature. Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles, which were removed from the solution medium with the help of an external magnet, were washed 6 times with distilled water and ethanol and dried at 60\u0026deg;C for 3 h.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Synthesis of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e\u003c/h2\u003e \u003cp\u003eFe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e particles were synthesized with the help of the St\u0026ouml;ber method. 0.1 g of obtained Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles was mixed under ultrasonication for 15 min in a solution of 80 mL of ethanol and 20 mL of deionized water. Subsequently, 5 mL of concentrated NH\u003csub\u003e4\u003c/sub\u003eOH was added to the solution medium and mixed for 5 min and 1 mL of TEOS was added dropwise into the solution medium with vigorous stirring. After mixing the solution under 45% amplitude for 3 h, the product obtained was separated with an external magnet, washed 6 times with deionized water and ethanol, and dried at 60\u0026deg;C for 3 h and calcined for 2 h at 200\u0026deg;C.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003e2.4. Synthesis of Fe\u003c/b\u003e\u003csub\u003e\u003cb\u003e3\u003c/b\u003e\u003c/sub\u003e\u003cb\u003eO\u003c/b\u003e\u003csub\u003e\u003cb\u003e4\u003c/b\u003e\u003c/sub\u003e\u003cb\u003e@SiO\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003cb\u003e@TiO\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003c/h2\u003e \u003cp\u003e1 g of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e particles were added in 56 mL of ethanol and 3.5 mL of titanium butoxide solution and mixed under ultrasonication for 15 min. The obtained solution was then placed in a 200 mL Teflon autoclave reactor. 14 mL of distilled water, which did not mix with the solution, was placed in a beaker in the reactor and kept in the oven at 150\u0026deg;C for 12 h. After the autoclave was cooled at room temperature, the product obtained was separated with an external magnet washed 6 times with deionized water and ethanol, and dried at 60\u0026deg;C for 3 h. Then, the particles were calcined at 500\u0026deg;C for 2 h.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003e2.5. Synthesis of Fe\u003c/b\u003e\u003csub\u003e\u003cb\u003e3\u003c/b\u003e\u003c/sub\u003e\u003cb\u003eO\u003c/b\u003e\u003csub\u003e\u003cb\u003e4\u003c/b\u003e\u003c/sub\u003e\u003cb\u003e@SiO\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003cb\u003e@TiO\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003cb\u003e-Ag\u003c/b\u003e\u003c/h2\u003e \u003cp\u003eSynthesis of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag nanoparticles takes place in two stages: Preparation of Tollen\u0026rsquo;s reagent and Ag addition of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e nanoparticles.\u003c/p\u003e \u003cp\u003eTo prepare 500 mL 5.10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e M Tollen\u0026rsquo;s reagent; The reactions are performed as shown below by adding 25 mL of 0.1 M NaOH solution dropwise into 25 mL of 0.1 M AgNO\u003csub\u003e3\u003c/sub\u003e solution under 1000 rpm mixing [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eAgNO\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;NaOH \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\to\\:\\)\u003c/span\u003e\u003c/span\u003eAgOH\u0026thinsp;+\u0026thinsp;NHO\u003csub\u003e3\u003c/sub\u003e (1)\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003e2AgOH AgO + HO (2)\u003c/h3\u003e\n\u003cdiv class=\"Heading\"\u003e2AgOH \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\to\\:\\)\u003c/span\u003e\u003c/span\u003eAg\u003csub\u003e2\u003c/sub\u003eO\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO (2)\u003c/div\u003e \u003cp\u003eThe reaction is carried out as shown below by adding a 25% NH\u003csub\u003e4\u003c/sub\u003eOH solution until the precipitated particles disappear into the resulting solution.\u003c/p\u003e \u003cp\u003eAg\u003csub\u003e2\u003c/sub\u003eO\u0026thinsp;+\u0026thinsp;4NH\u003csub\u003e3\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\to\\:\\)\u003c/span\u003e\u003c/span\u003e2Ag(NH\u003csub\u003e3\u003c/sub\u003e)\u003csup\u003e+2\u003c/sup\u003e + 2OH\u003csup\u003e\u0026minus;\u003c/sup\u003e (3)\u003c/p\u003e \u003cp\u003eThen, the obtained solution is completed to 500 mL, and 5.10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e M Tollen\u0026rsquo;s reagent is obtained. In the second stage, 0.4 g Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e composite was mixed in 100 mL of Tollen's reagent under ultrasonication for 15 min to obtain a homogeneous solution [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. On the other hand, after dissolving 0.6 g of PVP in 90 mL of ethanol, the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e solution was refluxed at 70\u0026deg;C for 4 h. After the solution was cooled at room temperature, the product obtained was separated with an external magnet washed 6 times with deionized water and ethanol, and dried at 60\u0026deg;C for 3 h. Then, the particles were calcined at 500\u0026deg;C for 2 h.\u003c/p\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e2.6. Determination of photocatalytic activities of the composites\u003c/h2\u003e \u003cp\u003eThe produced composite particle form was used to evaluate the photocatalytic degradation of Acid Blue 161 dyestuff. Dyestuff experiments were carried out in a batch reactor with the outer part isolated against the light. The temperature of the solution was kept constant at 25\u0026deg;C with a water circulator. Pen-Ray UV Lamp (Cole-Parmer, 257 nm, 44W m\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e) was used as a UV source. The saturated oxygen concentration was provided with air pumped into the reaction medium at a constant flow rate. The photocatalytic experiments were carried out using 100 mg of the produced particles photocatalysts in the presence of 400 mL of dye solution (20 mg L\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). Before the degradation experiments, the composite photocatalysts produced were added to the dye solution and mixed for 30 min in the dark to stabilize. Dye concentrations at different times were determined using a UV spectrophotometer (Optizen α spectrophotometer). Measurement of the Acid Blue 161 concentration was carried out at 602.5 nm.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e2.7. Characterization\u003c/h2\u003e \u003cp\u003eThe size, morphology, and elemental analysis of the synthesized composite photocatalysts were investigated using Transmission Electron Microscopy (TEM, Hitachi-HT7700), Scanning Electron Microscopy (SEM, Zeiss -Sigma 300), and Energy Dispersive X-ray Spectroscopy (EDS). FTIR spectra of composites were obtained using Fourier Transform Infrared Spectroscopy (FTIR, Vertex-80v). The crystalline structures of the samples were investigated by X-ray diffraction (XRD, PANalytical-Empyrean) analysis using Cu-Kα radiation (λ\u0026thinsp;=\u0026thinsp;0.15418 nm). The magnetic properties of the samples were investigated using a Vibrating Sample Magnetometer (VSM, Lake Shore, 7407) at room temperature. XPS analysis and UV-Vis absorption spectrometer measurements were carried out using (XPS, Specs-Flex) and (UV, Shimadzu-UV3600 Plus).\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Result and Discussion","content":"\u003cp\u003eTEM analysis results of the synthesized Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e, and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composites and the diameter distribution analysis of the particles were investigated respectively and shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles consisting of a few small Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles were found to be spherical, and the diameter of the spherical particles was between 150 and 250 nm, with an average spherical diameter of about 210 nm. The synthesized Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles are uniformly dispersed, spherical in shape, uniform in shape, and almost the same size. The fact that the surface of the particles is not completely smooth indicates that the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles are formed in smaller diameters [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb, it is clearly seen that Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e particles have a core-shell structure. The black spheres show the magnetic cores and the gray color surrounding the core shows the silica shell. Since SiO\u003csub\u003e2\u003c/sub\u003e is an amorphous structure, it formed a thin flat layer on the surface of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e. As a result of the particle size distribution analysis, it was determined that the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e composite had a diameter ranging from 160 to 260 nm and its average diameter was 220 nm. Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e particles were coated with a TiO\u003csub\u003e2\u003c/sub\u003e layer using the sol-gel method. The Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e particles seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec have a distinguishable three-layer monodisperse structure consisting of a Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e core, a SiO\u003csub\u003e2\u003c/sub\u003e interlayer, and a TiO\u003csub\u003e2\u003c/sub\u003e outer layer. Since TiO\u003csub\u003e2\u003c/sub\u003e forms a homogeneous coating on the silica surface, no net deposition of composite particles is observed. As a result of the particle size distribution analysis, it was determined that the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e composite had diameters ranging from 185 to 285 nm and its average diameter was 240 nm. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed, the synthesized Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composites show a heterogeneous distribution as in the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e composites. The core-shell Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composite appears to show superior magnetization, indicating its suitability for recovery and magnetic separation. As a result of the particle size distribution analysis, it was determined that the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composite had diameters ranging from 190 to 300 nm and its average diameter was around 255 nm.\u003c/p\u003e \u003cp\u003eThe results of SEM and EDS analysis of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e, and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composites are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea, the obtained Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles have an average diameter of 210 nm. Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles were prepared by the reduction of Fe (III) salts [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. The synthesized Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles showed good distribution and completed their formation globally. EDS analysis proved the presence of iron and oxygen in Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles synthesized using the St\u0026ouml;ber method were easily coated with silica. The coated SiO\u003csub\u003e2\u003c/sub\u003e shell can effectively prevent the chemical degradation of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles. This allows the synthesized photocatalyst to be used repeatedly in more than one reaction cycle [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. The thickness of the SiO\u003csub\u003e2\u003c/sub\u003e shell is very important, and the high layer thickness significantly reduces the magnetic properties and recovery of the catalyst from the wastewater. In addition, a thin layer decreases the photocatalytic activity of composites while increasing particle agglomeration [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. The obtained Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e particles have an average diameter of 220 nm. EDS analysis proved the presence of iron, silicon, and oxygen in Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e particles. The coating of the TiO\u003csub\u003e2\u003c/sub\u003e layer on Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e composites was performed by the sol-gel process and then amorphous TiO\u003csub\u003e2\u003c/sub\u003e was transformed into the crystalline phase through calcination at 500\u0026deg;C for 2 h. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec, the synthesized Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e composite shows a homogeneous distribution similar to Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e composite. When the SEM images are compared, it is seen that the smooth surfaces of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e composites become a thick crystalline layer after being coated with a TiO\u003csub\u003e2\u003c/sub\u003e layer [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. The obtained Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e particles have an average diameter of 240 nm. EDS analysis proved the presence of iron, silicon, titanium, and oxygen in Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e particles. In order to deposit Ag particles on the surface of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e composite and to obtain Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag core/shell structure, a sol-gel method was used as both reductant and stabilizer in the presence of PVP. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed, the synthesized Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composite shows a homogeneous distribution such as Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e. As the Ag nanoparticles combined with the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e composite, there was an increase in the diameter of the composite. The obtained Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag particles have an average diameter of 255 nm. EDS analysis proved the presence of iron, silicon, titanium, silver, and oxygen in Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e particles. In order to characterize the phase purity, crystallinity, and composition of the prepared samples, X-ray diffraction patterns of the samples were obtained. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the XRD patterns of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and SiO\u003csub\u003e2\u003c/sub\u003e particles, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e, and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composite.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea shows the XRD graph of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles and all diffraction peaks are compatible with (JCPDS card No. 19\u0026ndash;0629). Accordingly, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles have a face-centered cubic structure of magnetite. The relative intensity and position of the diffraction peaks of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea diffraction peaks corresponding to planes (111), (220), (311), (400), (422), (511), and (440) demonstrated in harmony with planes of the standard Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e diffraction data card (JCPDS: 19\u0026ndash;0629) [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb-c, the XRD pattern of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e particles showed almost the same property as pure Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e. However, the large peak at \u003cem\u003e2θ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;22\u0026deg; indicates that the coated SiO\u003csub\u003e2\u003c/sub\u003e shell is amorphous. The peak width seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec at X-ray diffraction \u003cem\u003e2θ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;20\u0026deg; and 30\u0026deg; is generally related to amorphous silica peaks [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Compared to Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea and c, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e shows new diffraction peaks. The diffraction peaks of TiO\u003csub\u003e2\u003c/sub\u003e belong to the anatase phase and are fully compatible with (JCPDS card No: 21-1272) [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e core coated with SiO\u003csub\u003e2\u003c/sub\u003e and TiO\u003csub\u003e2\u003c/sub\u003e showed no obvious change. Only the intensity of the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e peaks weakened (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed). As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ee, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composite gives peaks compatible with (JCPDS card No: 19\u0026ndash;0629) of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and (JCPDS card No: 21-1272) of TiO\u003csub\u003e2\u003c/sub\u003e. Apart from the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e and TiO\u003csub\u003e2\u003c/sub\u003e characteristic peaks, \u003cem\u003e2θ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;37.90\u0026deg;, 44.10\u0026deg;, 64.30\u0026deg; and 77.20\u0026deg; diffraction peaks can be easily indexed to Ag, and the face-centered cubic structure of Ag is compatible with the (JCPDS card No: 04-0783), and indicating that crystallized Ag nanoparticles have been deposited on the outer shells. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, FTIR spectrums were used to characterize the composition and bond structure of the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e, and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composites.\u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e composites have more signals than Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e. The three bands at 580, 630, 1630, and 3405 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e show the FTIR spectrum of pure Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanoparticles. The 580 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 630 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e bands corresponds to the Fe‒O vibration [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. The bands at 1630 and 3405 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are associated with the presence of hydroxyl bands and correspond to OH bending and OH stretching, respectively. Symmetric vibration in the 800 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e band and asymmetric vibration at 1080 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e correspond to Si‒O‒Si. The 940\u0026ndash;960 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e band is caused by the Si‒O‒Ti vibration and the 500\u0026ndash;900 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e band originates from the Ti‒O‒Ti vibration [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. O-H vibration in 1630 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 3370 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e bands proves the presence of water. This provides an advantage for the photocatalytic activity of the synthesized photocatalysts. The vibration of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composites is similar to the vibrations in all bands of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e composites [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. As with most literature studies, there are no peaks belonging to Ag nanoparticles. UV-Vis absorption spectrometer measurements shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea were used to determine the bandgap energy of synthesized Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e, and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composites.\u003c/p\u003e \u003cp\u003eAccording to the theory of bandgap, the optical band gap of composites can be defined using Tauc\u0026rsquo;s Equation:\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eαhʋ = A (hʋ - E\u003csub\u003eg\u003c/sub\u003e)\u003csup\u003en\u003c/sup\u003e (4)\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere a is the absorption coefficient (cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), \u003cem\u003ehʋ\u003c/em\u003e is the photon energy (eV), A is a characteristic constant, E\u003csub\u003eg\u003c/sub\u003e is the energy bandgap (eV) and n is a parameter identifying the electronic transition type (\u003cem\u003en\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0.5 or 2 for direct and indirect transitions, respectively). According to the Tauc equation, drawing \u003cem\u003e(αhυ)\u003c/em\u003e\u003csup\u003e\u003cem\u003e0.5\u003c/em\u003e\u003c/sup\u003e\u003cem\u003e- (hυ)\u003c/em\u003e creates a straight line in a certain region. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb-c-d, the E\u003csub\u003eg\u003c/sub\u003e values of composites can be estimated by extrapolating the straight-line fit of the graphical representation of \u003cem\u003e(hʋα)\u003c/em\u003e\u003csup\u003e0.5\u003c/sup\u003e versus \u003cem\u003ehʋ\u003c/em\u003e to \u003cem\u003ehʋ-axis\u003c/em\u003e. The E\u003csub\u003eg\u003c/sub\u003e value for Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles energy was determined as 1.3 eV. In literature studies, E\u003csub\u003eg\u003c/sub\u003e values obtained for Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles range from 1.16 to 2.2 eV [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Coating the SiO\u003csub\u003e2\u003c/sub\u003e semiconductor on the surface of the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particle, whose E\u003csub\u003eg\u003c/sub\u003e value is determined as 1.3 eV, is estimated to will increase the forbidden energy bandgap due to the band theory [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. The band gap of the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e composite was determined as 1.68 eV. As it is known, TiO\u003csub\u003e2\u003c/sub\u003e is a semiconductor and the E\u003csub\u003eg\u003c/sub\u003e value was determined as 3.2 eV in studies in the literature [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. With the coating of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e composite with TiO\u003csub\u003e2\u003c/sub\u003e, it is estimated that the forbidden band gap will increase according to the band theory [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. The E\u003csub\u003eg\u003c/sub\u003e value for the combined energy of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e was determined as 2.1 eV. It is estimated that coating the Ag conductor on the surface of the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e composite, whose E\u003csub\u003eg\u003c/sub\u003e value is determined as 2.1 eV, will reduce the band gap of the forbidden energy according to the band theory. Therefore, the value for the combined energy of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag was determined as 2.0 eV. In order to better understand the surface composition and bonding medium of the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@ SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composite, XPS analysis was performed and compared with the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@ SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e composite.\u003c/p\u003e \u003cp\u003eThe peaks in the general XPS spectrum of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composite belong to Ag, C, Ti, and O elements. The peak of element C is estimated to consist of a carbon-based contaminant. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows all the spectra scanned in the range of 0-1200 eV. The peaks seen in the spectrum belong to Ti, C, Fe, Si, O, and Ag elements. In Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003eb, the XPS spectrum of the high-resolution Ti2p peak is given. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e, it can be seen that the peaks of Ti2p\u003csub\u003e1/2\u003c/sub\u003e and Ti2p\u003csub\u003e3/2\u003c/sub\u003e correspond to two binding energies centered at 461 eV and 466.7 eV indicating the main valence of Ti [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. Ti2p peaks of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composite show no shift when compared with the peaks of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e composite, confirming that the TiO\u003csub\u003e2\u003c/sub\u003e layer structure remains intact throughout the preparation process. According to the XPS results, it is likely that the intensity of the Ti2p peak will decrease as the TiO\u003csub\u003e2\u003c/sub\u003e surface is coated with Ag nanoparticles. Figure\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows the XPS spectrum of the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composite in the Ag3d region. The peaks showing the formation of Ag nanoparticles and corresponding to Ag 3s\u003csub\u003e3/2\u003c/sub\u003e and 3p\u003csub\u003e5/2\u003c/sub\u003e have 720 eV and 610 eV binding energy, respectively. This binding energy shows that silver has a metallic structure. Magnetic measurements of the samples were carried out at 300 K using a vibrating sample magnetometer (VSM). The measured magnetization curves for Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanoparticles, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e, and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composites were compared in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eAs seen in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, saturation magnetization values for Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanoparticles, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e, and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composites at +\u0026thinsp;8000 Oe are 81, 64, 44 and 25 emu g\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively. The non-magnetic SiO\u003csub\u003e2\u003c/sub\u003e and TiO\u003csub\u003e2\u003c/sub\u003e shells surrounding the magnetic core caused the magnetic properties of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanoparticles to decrease. Despite the decrease in magnetic saturation, the photocatalyst was easily removed from the solution with an external magnet. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, the photocatalyst of Acid Blue 161 was investigated to remove pollutants from wastewater and investigate the photocatalytic activity of Magnetic Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e nanoparticles, TiO\u003csub\u003e2\u003c/sub\u003e (Degussa, P25), Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e, and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag photocatalysts.\u003c/p\u003e \u003cp\u003ePhotocatalytic degradation experiments were carried out in the dark for 0\u0026ndash;15 min and under UV light for 15\u0026ndash;120 min. The experiments were achieved in the dark environment for the first 15 min and there was no significant change in Acid Blue 161 dye concentration. For 120 min, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles removed 4.36% of the dye. Due to the semiconductor feature of SiO\u003csub\u003e2\u003c/sub\u003e, the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e composite removed 11.53% of the dye by showing better photocatalytic activity than the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particle [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e]. The decomposition rates of TiO\u003csub\u003e2\u003c/sub\u003e (Degussa P25) nanoparticles are 84%. In the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e composite, the SiO\u003csub\u003e2\u003c/sub\u003e interlayer between the iron oxide core and the TiO\u003csub\u003e2\u003c/sub\u003e shell reduces electronic interactions at the point of contact, thereby increasing photocatalytic activity and the decomposition rate of dye is 100% [\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composite removed 100% of the dye in a shorter time than the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e composite. Since the Ag particles increased the specific surface area of the core-shell structure, the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composite showed superior photocatalytic activity. The photocatalytic activity of the composites in the degradation of the acid blue 161 dyestuffs follows the order: Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag\u0026thinsp;\u0026gt;\u0026thinsp;Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026gt;\u0026thinsp;Degussa P25 (TiO\u003csub\u003e2\u003c/sub\u003e)\u0026thinsp;\u0026gt;\u0026thinsp;Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;\u0026gt;\u0026thinsp;Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e.\u003c/p\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eIn this study, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e particles were successfully synthesized by the solvothermal reaction. Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e composite was obtained by the St\u0026ouml;ber method, and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composites were successfully synthesized by the sol-gel method. To determine the structural properties of synthesized composites, SEM-EDS TEM, XRD, FTIR, VSM and XPS analyses were performed, and UV-Vis analyses were used to examine the optical properties of synthesized composites. According to the TEM and SEM analysis results, it was determined that Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e, and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composites were spherical and their average diameters were 210, 220, 240 and 255 nm. Crystal structures of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e, and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composites were examined by XRD analysis and it was found that Ag nanoparticles deposited in the outer shell were crystalline. Also, according to the results of the analysis, the synthesized photocatalysts showed good compatibility with standard diffraction data cards. The bond structures and bandgap energies of composites were examined by FTIR and UV-Vis analysis respectively. According to the results of the analysis, it has been understood that there is no vibration peak belonging to Ag and increases photocatalytic activity due to the harmony of the core-shell structure with each other. The band gap energies of Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e, Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e, and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composites were determined as 1.3, 1.68, 2.1 and 2.0 eV, respectively. According to XPS results, it was determined that Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@ SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composite was compatible with Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e composite and TiO\u003csub\u003e2\u003c/sub\u003e preserved its layer form during Ag doping process. Acid Blue 161 dyestuff was used to examine the photocatalytic degradation of composites. Compared with other composites, the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composite exhibited high photocatalytic activity by removing 100% of the dye under UV radiation.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eH.K. contributed to the concept, wrote the paper, and supervised the work. T.T. performed the parametric analysis. 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Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e composite was synthesized by the St\u0026ouml;ber method, and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e and Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composites were successfully synthesized by the sol-gel method. For the characterization of the composites, besides SEM-EDS, TEM, XRD, FTIR, UV-Vis, XPS, and VSM devices were used for magnetization measurement and then the photocatalytic activity on Acid Blue 161 dyestuff was tested. Acid Blue 161 dyestuff was used to examine the photocatalytic degradation of composites. The Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e composite doped with Ag particles showed better photocatalytic activity than the commercially used Degussa P25 due to the suppression of the recombination of electron-hole pairs. Compared with other composites, the Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composite exhibited high photocatalytic activity by removing 100% of the dye under UV radiation. The synthesized Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e@SiO\u003csub\u003e2\u003c/sub\u003e@TiO\u003csub\u003e2\u003c/sub\u003e-Ag composite photocatalyst is a cost-effective photocatalytic system due to its wide application area, high efficiency, and recyclability.\u003c/p\u003e","manuscriptTitle":"Synthesis and characterization of magnetically separable Fe3O4@SiO2@TiO2-Ag composite for degradation of Acid Blue 161","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-12-05 15:56:42","doi":"10.21203/rs.3.rs-4977985/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-09-30T05:24:19+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-09-29T16:36:48+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-09-28T04:24:35+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-09-27T08:34:22+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-09-26T20:22:31+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-09-26T03:23:59+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-09-25T20:31:33+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"7797414505815878641051234758856777372","date":"2024-09-19T12:46:33+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"259673368769892017051837886944009800924","date":"2024-09-19T09:10:15+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"220790957577157945420172399117600001520","date":"2024-09-19T08:57:02+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"93672721887695694711455159190079991958","date":"2024-09-19T08:11:20+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"137428184199790536879633856436854205962","date":"2024-09-19T08:10:28+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"182315943998674314735258438478074065543","date":"2024-09-19T08:08:04+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"198805932722824719962296715991105960256","date":"2024-09-19T08:06:58+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-09-19T08:01:30+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-09-19T07:46:08+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2024-09-19T07:41:47+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-09-19T05:24:05+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2024-08-26T12:35:01+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"356c0b03-c52e-40a6-945a-4746bfa1bd30","owner":[],"postedDate":"December 5th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":38341524,"name":"Physical sciences/Engineering/Chemical engineering"},{"id":38341525,"name":"Earth and environmental sciences/Environmental sciences/Environmental chemistry"}],"tags":[],"updatedAt":"2025-10-20T05:23:39+00:00","versionOfRecord":[],"versionCreatedAt":"2024-12-05 15:56:42","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4977985","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4977985","identity":"rs-4977985","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}