Nonsacrificial Template Synthesis of Magnetic-Based YolkâShell

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Non-sacrificial template synthesis of magnetic-based yolk-shell nanostructures for the removal of acetaminophen in Fenton-like systems Quoc Cuong Do, Do-Gun Kim, and Seok-Oh Ko ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b07658 • Publication Date (Web): 03 Aug 2017 Downloaded from http://pubs.acs.org on August 7, 2017

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ACS Applied Materials & Interfaces

Non-sacrificial template synthesis of magnetic-based yolk-shell nanostructures for the removal of acetaminophen in Fenton-like systems Quoc Cuong Do, Do-Gun Kim, and Seok-Oh Ko* Department of Civil Engineering, Kyung Hee University, 1732 Deokyoung-daero, Yongin-si, Gyeonggi-do 17104, Republic of Korea. (E-mail: [email protected]; [email protected]; [email protected])

KEYWORDS: acetaminophen, magnetite, copper, yolk-shell structure, catalytic oxidation. 1 ACS Paragon Plus Environment


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ABSTRACT Recently, yolk-shell structured materials with active metal cores have received considerable attention in heterogeneous Fenton-like systems, which have excellent catalytic performance. In this study, we initially attempted the non-sacrificial template synthesis of yolk-shell structured nanoparticles with magnetite cores encapsulated in a mesoporous silica shell (Fe3O4@SiO2) via a modified sol-gel process, and then evaluated their catalytic activity for acetaminophen degradation in Fenton-like systems. Secondly, copper nanoparticles were decorated on the surface of the Fe3O4@SiO2 microspheres (Fe3O4@SiO2@Cu) in order to enhance the catalytic activity. The morphological, structural, and physicochemical properties of the prepared materials were characterized via X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, field emission transmission electron microscopy, nitrogen adsorption-desorption isotherms, specific surface area, zeta potential, magnetic properties, and Fourier transform infrared spectroscopy. The results demonstrated a successful fabrication of the targeted materials. The yolk-shell structured materials possess a spherical morphology with an active core, protective shell, and hollow void. The Fe3O4@SiO2 and Fe3O4@SiO2@Cu variants showed significantly higher acetaminophen removal rates compared to their counterparts, i.e., the Fe3O4 and Fe3O4@Cu core-shell structures. Fe3O4@SiO2@Cu showed that the copper nanoparticles were firmly immobilized on the mesoporous silica shell, dramatically improving the catalytic performance. Both the yolk-shell structured Fe3O4@SiO2 and Fe3O4@SiO2@Cu exhibited good separation and satisfactory regeneration properties, which could be recycled six times without any obvious decline in catalytic activity. Overall, the results of this study suggested that Fe3O4@SiO2 and Fe3O4@SiO2@Cu yolk-shell nanostructures could be promising

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catalysts for heterogeneous Fenton-like system, by which the removal of emerging contaminants can greatly be improved. 1. INTRODUCTION Acetaminophen (Paracetamol), a well-known pharmaceutically active compound, is extensively used as an analgesic and in antipyretic drugs, and is one of the most commonly detected pharmaceutical compounds in aquatic environments.1,2 The occurrence of such pharmaceuticals in water and the resultant long-term exposure may pose a threat for both the environment and human health, even in very low concentration. These trace pharmaceuticals are considered as major emerging pollutants in bodies of water.3-7 Among various treatment technologies, advanced oxidation processes (AOPs) are frequently considered as a promising technological approach to remove refractory and toxic organic compounds. Compared with other AOPs, Fenton oxidation is favorable and often regarded as a promising approach due to its higher generation rate of hydroxyl radicals, inexpensive methodology, easy operation, and low maintenance. However, the use of homogeneous Fenton reaction methods has several disadvantages such as operating under acidic conditions, sludge production, difficulties in retaining metal salts, and post-treatment requirements.8,9 Therefore, a heterogeneous Fenton-like process in which iron-containing solids replace soluble Fe2+ has attracted increasing attention in recent times due to its other advantages. Heterogeneous catalysts could be an alternative technology to overcome the drawbacks observed in the homogeneous reaction, such as avoiding the precipitation of soluble iron salts, greater selectivity, operation at near neutral pH, easy separation from the effluent, high stability, and the possibility to modify and recycle the catalyst.9-12



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The development of more efficient and stable catalysts has received considerable attention from chemists and material scientists for both economic and environmental reasons. Recently, a composite nanocatalyst with a yolk–shell structure has been recognized as an ideal candidate for catalysis applications due to its unique properties, including its low density, large surface area, ease of interior core functionalization, good molecular loading capacity in the void space, tunable interstitial void space, and hollow outer shell.13,14 The yolk-shell nanostructures offer better properties over simple core/shell or hollow nanoparticles in various fields, including biomedical, catalysis, sensors, lithium batteries, adsorbents, dye-sensitized solar cells, and microwave absorbers, mainly because of the presence of free void space, a porous hollow shell, and available free core surface.13 Furthermore, there are many possibilities to control the yolkshell structure properties by modifying various parameters such as the movable core size, number of cores, void space, hollow shell thickness, and porosity, or through the selection of appropriate core and shell materials to achieve the desired properties. Catalyst recovery and reuse after reaction completion are the two most important features in many catalytic systems. However, separation and recovery of the nanoscale catalysts from the effluent are not easy. To overcome these disadvantages, the use of magnetic nanoparticles has appeared as a feasible solution due to their insoluble and magnetic properties, which enable facile and efficient separation of the catalysts from the reaction mixture via an external magnet, allowing for their subsequent reuse. Recently, magnetite (Fe3O4) has received particular attention due to its good catalytic activity, fantastic magnetically separable properties, low cost, ready accessibility, and environmentally benign nature.15-17 Conversely, iron oxide-based catalysts for heterogeneous Fenton-like reactions in bulk solution usually suffer from aggregation and vulnerability, which reduces their catalytic efficiency and limits their practical application. 4 ACS Paragon Plus Environment

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Therefore, using yolk-shell structures with magnetite nanoparticles encapsulated in hollow mesoporous shells in order to enhance the catalytic efficiency and recycling performance of the material. Through a simple magnetic separation using a magnetic field, the material can be easily collected, recycled, and reused for catalysis without a significant reduction of the catalytic performance. Moreover, the activity and selectivity of magnetic nanocatalysts can be manipulated by surface modification with desirable features.17 In catalytic applications for water remediation, the large void space between the core and hollow shell is suitable for confining contaminant species, which leads to an increased catalytic reaction rate. Mesoporous nanomaterials possess unique properties such as high surface area and regular pore structure, as well as a high adsorption characteristic. The presence of a mesoporous shell not only acts as a protective shield to protect the active sites from the harsh reaction conditions, but also prevents the core nanoparticles from aggregating during operation. Among various types of inorganic materials, mesoporous silica is one of the most studied materials because of its unique properties and its wide range of applications, including the biomedical, chemical, and electronics fields, which has also been reflected in the form of yolk-shell nanostructures.13 The heterogeneous Fenton-like catalysis exhibits a relatively slow reaction rate and are inactive at high pH or without collaborating with external power supplies such as UV, ultrasounds, or microwaves.18 The use of bimetallic catalysts can be a better alternative to achieve higher material activity. Recent literature has reported that copper behaves like a Fenton reagent and is less pH dependent. In other words, it plays a similar role to iron by reacting with hydrogen peroxide to produce hydroxyl radical and it can maintain a high efficiency within higher pH environments.18-20 Moreover, copper and copper-based nanomaterials have the potential to be used in a wide range of applications because of the high natural abundance, the 5 ACS Paragon Plus Environment


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low cost of copper, and the multiple synthesis methods available for copper-based nanomaterials.21,22 However, there is a piece of evidence that copper-based Fenton systems usually require excess chemicals and work efficiently only under a strictly anaerobic condition.23 Consequently, the use of bimetallic catalysts could offer substantial advantages for heterogeneous Fenton-like processes. In this respect, iron-copper bimetallic catalyst systems have attracted considerable interest due to their higher catalytic activity and stability for the oxidative decomposition of organic contaminants, as compared with monometallic catalysts.24,25 Therefore, integrating copper into an iron-containing material in order to obtain a highly active bimetallic catalyst has become more attractive in the area of heterogeneous Fenton-like catalysis. However, to the best of our knowledge, a combination of copper nanoparticles and a magnetite silica yolk-shell structure to form a bimetallic yolk-shell structured catalyst have not been reported. The common methodology for the synthesis of yolk-shell nanostructures is based on a sacrificial template approach, where the cores or shells are employed as the template and partially removed to form the interior void. However, from the viewpoints of being environmentally friendly and economic, non-sacrificial template approaches are more attractive due to the simplicity of the synthesis procedure and the reduced chemical waste production, which are relatively recent developments that still present significant challenges.26,27 In addition, research has shown that most studies on yolk-shell nanostructures are focused on material synthesis prior to catalytic application testing.28 Therefore, the purpose of this study is to propose a simple and non-sacrificial template approach for the synthesis of a magnetic-based yolk-shell nanostructured catalyst with new properties and applications that not only shows excellent activity and selectivity, but also attains the simplicity of catalyst separation and recovery. In this 6 ACS Paragon Plus Environment

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work, a yolk-shell structure, composed of active magnetite core, protective mesoporous silica shell, and void between them (Fe3O4@SiO2), and that decorated by copper nanoparticles (Fe3O4@SiO2@Cu) were prepared. The morphological, structural, and physicochemical properties of the prepared materials were characterized to verify the success of the synthesis procedures. Heterogeneous Fenton-like reactions catalyzed by the prepared materials for the oxidative degradation of acetaminophen were performed in batch experiments to evaluate the catalytic reactivity. The recyclability of the yolk-shell structures was also investigated to evaluate the long-term stability during the reactions.

2. MATERIALS AND METHODS 2.1. Materials preparation 2.1.1. Chemicals and materials Anhydrous ethanol (C2H6O, M=46.07 g/mol), Iron (III) chloride hexahydrate (FeCl3.6H2O, M=270.30 g/mol), anhydrous trisodium citrate (Na3C6H5O7, M=258.06 g/mol), ethylene glycol (C2H6O2, M=62.07 g/mol), sodium acetate (C2H3NaO2, M=82.03 g/mol), copper acetate monohydrate (C4H8CuO5, M=199.65 g/mol), hydrazine hydrate (H6N2O, M=50.06 g/mol), ethyl alcohol (C2H6O, M=46.07 g/mol), concentrated ammonia aqueous solution (NH5O, M=35.04 g/mol), CTAB – hexadecyltrimethylammonium bromide (C19H42BrN, M=364.45 g/mol), TEOS tetraethyl orthosilicate (SiC8H20O4, M=208.33 g/mol), sulfuric acid (H2SO4, M=98.08 g/mol), and acetaminophen (C8H9NO2, M=151.16 g/mol) were supplied by Sigma-Aldrich Inc., USA and Samchun Pure Chemical Co., Korea.



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2.1.2. Synthesis of hollow mesoporous silica spheres (HMSS) Hollow mesoporous silica spheres (HMSS) were synthesized via a modified surfactantassembly sol-gel process in a Stӧber solution containing CTAB, TEOS, ammonia, and ethanol according to the method reported previously.29 The typical preparation process was described by the following procedure. In the first step, 1.60 g of CTAB was dissolved in a solution containing deionized water, ethanol, and concentrated ammonia solution (28-30 wt%). The solution was maintained at 30 oC, and TEOS was added dropwise under vigorous stirring with the molar ratios of TEOS:CTAB:NH5O:C2H6O:H2O = 1.00:0.09:1.49:118.70:634.48. After being stirred at 30 oC for 24 h, a white product was collected via centrifugation using a VS-5000N centrifugal machine (Vision Scientific Co., Korea), which was washed several times with ethanol. To continue the process, the product was dispersed into deionized water to prepare the HMSS via a spontaneous self-transformation approach. In particular, after dispersing in deionized water, the mixture was incubated at 70 oC for 48 h, then cooled to room temperature, collected via centrifugation, and washed with ethanol. To remove the pore-generating template (CTAB), the as-synthesized materials were transferred to an ethanol solution with continual stirring at 60 oC for 3 h; the process was repeated twice to ensure all CTAB was removed. Finally, the HMSS products were separated by the centrifugal machine, washed with ethanol, and dried at 60 oC for 24 h. 2.1.3. Magnetite nanoparticles preparation In this work, magnetite nanoparticles (Fe3O4) were synthesized by a solvothermal reaction at 200 oC by the reduction of FeCl3 with ethylene glycol in the presence of sodium acetate and trisodium citrate.30 At first, FeCl3.6H2O, tri-sodium citrate, and sodium acetate were dissolved in 100 mL of ethylene glycol with magnetic stirring for 30 min. Then, the resultant yellow solution


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was transferred and sealed into a 200 mL Teflon-lined stainless-steel autoclave, which was heated up to 200 oC in the Vulcan 3-550 furnace (Neytech, USA) with a ramping rate of 5 o

C/min and maintained for 10 h to complete the reaction. Afterward, the autoclave was allowed

to cool to room temperature, and the black products were collected by magnetic separation and then washed with ethanol and deionized water several times. Finally, the products were freeze dried under a vacuum for 12 h using an OPR-FDB-5503 freeze dryer (Operon Co., Korea). 2.1.4. Yolk-shell structured Fe3O4@SiO2 preparation The obtained Fe3O4 nanoparticles above were used to prepare Fe3O4@SiO2 yolk-shell structures by spontaneous self-transformation through a modified versatile Stӧber sol-gel method,29,31 which does not require any sacrificial templates. Typically, 0.20 g Fe3O4 nanoparticles were dispersed in a solution containing deionized water, ethanol, concentrated ammonia aqueous solution, and CTAB. Then, TEOS was added dropwise to the solution under vigorous

stirring

with

molar

ratios

of

TEOS:Fe3O4:CTAB:NH5O:C2H6O:H2O

=

1.00:0.01:0.09:1.49:118.70:634.48. After being stirred for 24 h at 30 oC, the suspension was collected via a magnet and washed with ethanol and deionized water. The products were dispersed and incubated in deionized water at 70 oC for 48 h, and the yolk-shell structure was formed via a self-transformation approach. Subsequently, the products were collected by centrifugation and washed with ethanol. The pore-generating template (CTAB) was removed through a solvent extraction process.29 Briefly, the as-synthesized materials were transferred to an ethanol solution with continual stirring at 60 oC for 3 h, the process was also repeated twice to ensure all CTAB was removed. Finally, the yolk-shell products were separated using a magnet, washed with ethanol, and dried at 60 oC for 24 h.



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2.1.5. Decoration of copper onto Fe3O4 and Fe3O4@SiO2 The prepared Fe3O4 nanoparticles and yolk-shell structured Fe3O4@SiO2 were decorated with copper nanoparticles using a similar procedure.32 At first, the nanoparticles were dispersed in a blue solution of copper acetate (Fe:Cu = 1:3, by molar ratio), then ultrasonically processed for 15 min. A concentrated ammonia aqueous solution (28-30 wt%) was added dropwise until pH 11 was reached, and then hydrazine hydrate was added until a brown aqueous solution appeared. Stirring for 10 min, the products (Fe3O4@Cu and Fe3O4@SiO2@Cu) were separated by magnet, washed with ethanol, and then dried at 60 oC for 24 h. 2.2. Materials characterization The morphology and structural properties of the prepared materials were characterized by a field emission scanning electron microscope (FE-SEM, Leo supra 55, Genesis 2000, EDAX, Carl Zeiss Co., Germany) equipped with a thermal field emission electron gun. Field emission transmission electron microscopy (FE-TEM, JEM-2100F, JEOL, USA) combined with energy dispersive X-Ray spectroscopy (EDS) was employed for structural and qualitative elemental composition characterization. The X-Ray diffraction (XRD) pattern was recorded with an X-Ray diffractometer (D8 advance, Bruker, USA) in order to analyze the surface elemental composition. X-ray photoelectron spectroscopy (XPS) analysis was performed using a Thermo Scientific KAlpha X-ray photoelectron spectrometer system (Thermo Scientific, USA) to provide some supportive information for the XRD results. The Brunauer-Emmett-Teller (BET) specific area and pore volume were measured via the nitrogen adsorption/desorption isotherms method using a BELSORP-max surface analyzer (MicrotracBEL Corp., Japan). A zeta potential analyzer (BI9000AT, Brookhaven Instruments Corp., USA) with dynamic light scattering was employed to


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determine point of zero charge (PZC) of the materials in aqueous suspension. Magnetism was characterized using the Lake Shore 7300 vibrating sample magnetometer (Lake Shore Cryotronics Inc., USA) at room temperature. Transmission Fourier transform infrared (FT-IR) spectra were recorded using a Spectrum One FT-IR spectrometer (Perkin-Elmer, USA) with a spectral range of 450-4000 cm-1 and a resolution of 1 cm-1. The metal components contained in the prepared materials were studied by first dissolving samples in the royal solution, then they were determined based on the total Fe and Cu concentration in the liquid phase, which was measured using a HACH DR/2500 spectrophotometer (HACH, USA) in accordance with the manufacture’s operating manual. 2.3. Catalytic activity tests Catalytic tests were performed in a four-necked flask reactor (1.0 L) equipped with a temperature controllable heating mantle (MS-DM 604, Misung Scientific Co., Korea) for the degradation of acetaminophen. Acetaminophen solution was prepared in deionized water with an initial concentration of 2.0 mg/L (600 mL), the pH was adjusted to pH 5.0 using H2SO4 (0.5 M), and temperature was maintained at 25 oC. The given amount catalyst with an equivalent Fe3O4 was added under vigorous stirring (0.2 g/L), while the required amount of hydrogen peroxide (0.9 mL, 30 wt.%) was then added to the suspension in order to initiate the Fenton-like reaction. Samplings were taken out at given time intervals, then immediately filtered through a 0.45µm syringe-driven filter, and analyzed by high performance liquid chromatography (YL9100 HPLC, Young Lin Instruments Co., Korea) using a C18 column. The mobile phase was a mixture of methanol and deionized water (2:1 v/v), and was adjusted to pH 3 by orthophosphoric acid. The HPLC was operated with a mobile phase flow rate of 0.8 mL/min, the injection volume was 25 µL, the UV detector was activated at 230 nm, and the column 11 ACS Paragon Plus Environment


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temperature was set at 25 oC. Metal leaching from the catalysts was investigated by analyzing the metal ion concentration in the treated solution using a spectrophotometer (DR/2500, HACH, USA), which was used to evaluate the stability of the materials. Adsorption experiments were also conducted to further demonstrate the relationship between catalytic performance and structure of the prepared materials in the absence of H2O2, while the other conditions were kept the same as the catalytic experiments. 2.4. Reusability tests Material recyclability is another concern for practical applications, so evaluating the longterm stability of the yolk-shell materials during the catalytic reaction is necessary. Stability tests were investigated by performing the reaction for the degradation of acetaminophen under the same conditions with six times the regeneration of catalysts. After each cycle, the material was separated by an external magnetic field, washed with ethanol, dried, and then reused for next cycle.

3. RESULTS AND DISCUSSION 3.1. Material properties


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(a)

* Fe3O4 * *

* *

Intensity (a.u)

*

Cu Fe3O4

Fe3O4@Cu

Fe3O4@SiO2@Cu Fe3O4@SiO2 HMSS 10

20

30

40

50

60

70

80

90

2-Theta (degree)

Fe 2p1/2

(b)

Fe 2p3/2

(c)

Cu 2p3/2

Cu 2p1/2

Fe3O4 Fe3O4@Cu

Fe3O4@Cu

Intensity

Intensity

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Fe3O4@SiO2@Cu

Fe3O4@SiO2@Cu

Fe3O4@SiO2 740

735

730

725

720

715

710

705

700

965

960

955

Binding energy (eV)

950

945

940

935

930

925

Binding energy (eV)

Figure 1. XRD patterns (a), XPS spectrum of Fe 2p (b), and Cu 2p (c) of the prepared materials. Figure 1a displays the XRD patterns of the prepared materials. The Fe3O4 and Fe3O4@Cu patterns revealed a relatively poor crystallinity in their structures. The additional peaks at 50.5o and 74.2o corresponding to the bare Cu were noticeably observed for the Fe3O4@Cu, and suggest the formation of Cu nanoparticles. The diffraction peak of decorated Cu at 43.3o is stronger and sharper than that of Fe3O4, which is due to the peak overlap in their patterns.33 The XRD patterns from silica-based materials have only broad peaks, referring to the amorphous structure, which is characteristic of typical products from sol-gel processing.34 The diffraction peaks of Cu in 13 ACS Paragon Plus Environment


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Fe3O4@SiO2@Cu were not clearly observed, this is probably due to the disturbance of a mesoporous silica shell and small copper particles decorated on the surface.35 However, they can be seen clearly in those XPS spectra, the XPS peaks at the binding energies of 932.8 and 952.7 eV confirm the binding of zero-valent copper (Figure 1c).18,35,36 No obvious sharp diffraction peak of Fe3O4 can be seen in the yolk-shell structures, which may be attributed to the interference of the voice structure and the thick layer of the mesoporous silica shell. The results are highly consistent with XPS data; the peaks observed in the XPS spectrum for Fe 2p at the binding energies of 710.1 and 723.7 eV are characteristic of Fe3O4,35,37 which were only found for the Fe3O4 and Fe3O4@Cu (Figure 1b). The used XRD and XPS techniques could not detect the existence of Fe3O4 in the yolk-shell structures.

Figure 2. FE-SEM and TEM images of the prepared materials, respectively, Fe3O4 nanoparticles (a, f), Fe3O4@Cu composites (b, g), hollow mesoporous silica sphere (c, h), yolk-shell Fe3O4@SiO2 (d, i), and yolk-shell Fe3O4@SiO2@Cu (e, j). The surface morphology and structural characterization of the prepared materials were investigated by FE-SEM and FE-TEM, and their typical images are presented in Figure 2. FESEM and TEM images are very consistent with each other and show that the materials are well14 ACS Paragon Plus Environment

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dispersed, spherical, and uniform in morphology. A noticeable contrast between the cavity and silica shell can be seen in the silica-based materials, which clearly verified the formation of a hollow structure (Figure 2h, i, j). Differences from the HMSS, FE-TEM images of Fe3O4@SiO2 and Fe3O4@SiO2@Cu were considered as an endorsement of the yolk-shell structure (Figure 2i, j). Dispersed dark spots of iron oxides were observed in the distinct void space formed, which indicated that the hydrophilic Fe3O4 nanoparticles were successfully encapsulated by the silica shell. The surface morphology and yolk-shell structure of Fe3O4@SiO2 did not change after being decorated with Cu nanoparticles. Figure 2j reveals that Cu has been firmly grafted on the surface silica shell to form an outer thin layer, which can be distinguished by two different contrast layers of the silica shell. Furthermore, the energy dispersive X-ray spectroscopy (EDS) mapping images of all the prepared materials have qualitatively identified the presence and distribution of elements that correspond to the synthesized materials composition (Figure 3), which were also confirmed by the determination of content in the materials (Table 1). The results demonstrated a successful formation of the targeted materials.



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Figure 3. Energy dispersive X-ray spectroscopy (EDS) mapping images of HMSS (a), Fe3O4 (b), Fe3O4@Cu (c), Fe3O4@SiO2 (d), and Fe3O4@SiO2@Cu (e).


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Figure 4. Nitrogen adsorption/desorption isotherms of silica based materials (a) and non-silica based materials (b). The porous characteristics of the prepared materials were investigated by evaluating the nitrogen adsorption/desorption isotherms. As show in Figure 4, all the isotherms exhibit similar typical type IV curves according to the IUPAC nomenclature with three distinct regions, monolayer-multilayer adsorption (0.0 - 0.4 P/P0), capillary condensation (0.4 - 0.8 P/P0), and multilayer adsorption on the outer surface (0.8 - 1.0 P/P0), which reflect the characteristics of mesoporous materials.24,29,38-41 The surface characteristics of all synthesized materials are summarized in Table 1. In comparison to the specific surface area and pore volume of HMSS (590.28 m2/g, 0.54 cm3/g), these values decreased gradually from Fe3O4@SiO2 (532.15 m2/g, 0.45 cm3/g) to Fe3O4@SiO2@Cu (458.86 m2/g, 0.41 cm3/g). The main reason for such a decrease could be due to the augmentation of the samples density after encapsulating Fe3O4, which has a higher density than silica, and the copper nanoparticles decorated in the silica microspheres. It is reasonable that the specific BET surface areas and pore volumes of yolk-shell Fe3O4@SiO2 and Fe3O4@SiO2@Cu are much higher than those of Fe3O4 (129.14 m2/g, 0.13 cm3/g) and



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Fe3O4@Cu (120.13 m2/g, 0.12 cm3/g); this is not only because of the samples density, but also the inner silica shell and hollow structure. However, the mean pore size of the materials was not significantly changed, which were approximately 3.50 and 4.00 nm for the silica based and nonsilica based materials, respectively (Table 1), which further confirmed the property of mesoporous material. Interestingly, when copper decorated the surface of Fe3O4 and Fe3O4@SiO2, the specific BET surface areas and pore volumes of the new-formed materials (Fe3O4@Cu and Fe3O4@SiO2@Cu) were slightly decreased (Table 1). The reason for this is that copper nanoparticles were entrapped in and thus blocked the mesopore channels of the Fe3O4 and silica surface, which can be found in the EDS mapping images (Figure 2c, e). Table 1. Properties of the synthesized materials.

Material HMSS Fe3O4 Fe3O4@Cu Fe3O4@SiO2 Fe3O4@SiO2@Cu

BET surface area (m2/g)

Pore volume (cm3/g)*

Mean pore size (nm)

Fe content (mg/g)

Cu content (mg/g)

pHPZC

590.28 129.14 120.13 532.15 458.86

0.54 0.13 0.12 0.45 0.41

3.63 4.03 4.08 3.36 3.54

698.0 654.0 45.2 44.0

56.0 17.3

2.2 4.7 5.5 3.7 4.1

Note: “*”the pore volume was calculated at P/Po = 0.990; “-“the data were not investigated.


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Fe3O4@SiO2@Cu Fe3O4@SiO2

Transmittance (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


HMSS Fe3O4@Cu Fe3O4

3950

3450

2950

2450

1950

1450

950

450

Wave number (cm-1)

Figure 5. FTIR spectra of the prepared materials. Fourier transform infrared (FTIR) spectra of the prepared materials over the range of 450 to 3000 cm-1 are shown in Figure 5. The bands at 3425 and 1620 cm-1 correspond to the -O-H stretching vibration and H-O-H bending vibration due to the existence of surface hydroxyl groups and water, respectively.42-44 For all the magnetite based-materials, the absorption band observed at 585 cm-1 corresponds to the Fe-O-Fe stretching vibration from the magnetite phase;45 this band was found to be at much lower transmittance intensities in the Fe3O4@SiO2, and Fe3O4@SiO2@Cu spectra reflects the encapsulation of silica on the magnetite nanoparticles. For all the silica-based materials, the strong broad peak around 1085 cm-1 arises from Si-O-Si asymmetrical stretching vibration, while the weaker absorption bands at 800 cm-1 and 470 cm-1 correspond to Si-O symmetrical stretching vibration.39 The peak at 954 cm-1 may be attributed to the vibration of Si-O-Fe and/or Si-O-H bonds.46 Additionally, the absorbance bands at 2925 and 2855 cm-1 indicate the stretching vibration of the –C-H intramolecular bonds, and the band around 1480 cm-1 corresponds to -C-H bending vibration.39,44,47 These vibration bands indicated that the CTAB has remained in the prepared materials as impurities. The decreased intensity of the absorbance bands at 585 and 1390 cm-1 were noticed for the spectrum of Fe3O4@Cu in 19 ACS Paragon Plus Environment


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comparison to that of Fe3O4, thereby confirming the successful decoration of copper nanoparticles (Cu0).

Figure 6. Zeta potential measurements for the prepared materials as a function of pH. The surface charges of all prepared materials under varying pH values have been investigated by measuring their zeta potentials and the results are shown in Figure 6. It can be estimated that the points of zero charge (PZC) of Fe3O4, Fe3O4@Cu, HMSS, Fe3O4@SiO2, and Fe3O4@SiO2@Cu are 4.7, 5.5, 2.2, 3.7, and 4.1, respectively (Table 1). The zeta potential values of the yolk-shell structured materials indicate that they are more positive than the pure HMSS. These values of Fe3O4@Cu are also higher than those of the bare Fe3O4, suggesting that the decoration of copper leads to the increase of pHPZC.48 A similar trend was also observed for Fe3O4@SiO2@Cu compared to Fe3O4@SiO2. This indicates that Cu-decorated materials, i.e., Fe3O4@Cu and Fe3O4@SiO2@Cu are less negatively charged than their counterparts at the investigated pH. It also suggests that Cu-decorated materials are more electrostatically attractive to negatively charged species, such as acetaminophen, which may lead to a better adsorption affinity with the anionic species. 20 ACS Paragon Plus Environment

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(a) 100

Fe3O4

75

Magnetization (emu/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fe3O4@Cu

50 25 0 -25 -50 -75 -100 -15000 -10000

-5000

0

5000

10000

15000

Applied magnetic field (Oe)

Figure 7. VSM hysteresis loops of Fe3O4 and Fe3O4@Cu (a), and the separation of Fe3O4@SiO2 and Fe3O4@SiO2@Cu in water (b). The magnetic properties of Fe3O4 and Fe3O4@Cu samples as a function of the applied field were carried out at room temperature using a vibrating sample magnetometer (VSM), and the results are reported in Figure 7. The magnetic hysteresis curves of both Fe3O4 and Fe3O4@Cu exhibit similar magnetic properties with high saturation magnetization. The magnetic saturation value of Fe3O4 was found to be as high as 76.30 emu/g. After decorating with copper nanoparticles, the magnetic saturation value slightly decreased to 72.77 emu/g. The decrease in saturation magnetization of Fe3O4@Cu can be attributed to the decrease of Fe3O4 content and the contribution of nonmagnetic Cu in the composite.24,33 Similarly, this may also explain the yolkshell structured materials Fe3O4@SiO2 and Fe3O4@SiO2@Cu after the formation of a lowdensity silica shell. Unfortunately, VSM data could not obtained because of the low density of those materials. However, they still offer good magnetic responsivity, which makes them efficiently separated from the experimental medium by an external magnetic field. As can be



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seen in Figure 7, the yolk-shell microspheres dispersed in water were rapidly transported toward the magnet bar within a short time period when an external magnetic field was applied. 3.2. Catalytic activity tests

Figure 8. Acetaminophen removal (a) in the presence of H2O2 (15.0 mM), and (b) in the absence of H2O2 (Other conditions: C0 = 2.0 mg/L, pH = 5.0, T = 25.0 oC, t = 120 min, Fe3O4 = 0.2 g/L). Table 2. Metals leaching in the effluent solutions. Without H2O2 Material HMSS Fe3O4 Fe3O4@Cu Fe3O4@SiO2 Fe3O4@SiO2@Cu

With H2O2

Total Fe (mg/L)

Total Cu (mg/L)

Total Fe (mg/L)

Total Cu (mg/L)

1.55 0.09 0.02 0.02

0.47 0.24

1.95 0.45 0.02 0.02

0.84 1.27

Note: “-“the data were not investigated The catalytic activity of all prepared materials were studied via acetaminophen degradation experiments, as shown in Figure 8. In the case of HMSS, there was no obvious degradation of 22 ACS Paragon Plus Environment

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acetaminophen observed after 120 min in either the presence or absence of H2O2, indicating that the HMSS itself plays no role in the oxidation or adsorption of acetaminophen. As can be seen from Figure 8b, the results show the poor degradation of acetaminophen in the absence of H2O2 after 120 min, indicating that the degradation is mainly due to the catalytic oxidation reaction. However, the removal of acetaminophen are different for Fe3O4 (5.9%), Fe3O4@Cu (19.2%), Fe3O4@SiO2 (10.9%), and Fe3O4@SiO2@Cu (31.7%), reflecting the different in material structures. The decoration of copper nanoparticles makes the newly formed materials have higher adsorption capacity than those of the precursor materials. In the presence of H2O2 (Figure 8a), Fe3O4, Fe3O4@Cu, and Fe3O4@SiO2 exhibited comparable degradation efficiencies of 58.8, 65.3, 67.0%, respectively, after 120 min of operation. However, the yolk-shell structured Fe3O4@SiO2 showed a faster degradation rate, by reaching a similar result after 60 min, suggesting a greater catalytic efficiency than that of either the Fe3O4 or Fe3O4@Cu. Accordingly, the structural differences in these materials are important for the observed higher catalytic activity. The newly formed materials, after decorating with copper nanoparticles, really enhanced the catalytic efficiency. This was especially true for the yolk-shell structured Fe3O4@SiO2@Cu, which exhibited a superior catalytic activity for the degradation of acetaminophen that neared completion within 20 min. After 120 min of the catalytic reaction, although leaching copper ion was detected up to 0.84 and 1.27 mg/L for the Fe3O4@Cu and Fe3O4@SiO2@Cu, respectively (Table 2), these values correspond to less than 1% total metals, and are quite low when compared to other copper-based heterogeneous catalysts reported in the literature.25,49,50 The results imply that high catalytic activity of the material can be retained after regeneration. The yolk-shell structured materials displayed a better catalytic performance than the other materials for the degradation of acetaminophen, which may have contributed to the structural 23 ACS Paragon Plus Environment


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features of the materials. For the incorporation of an active core, mesoporous silica shells favor the adsorption of reactants from bulk solution, and then rapidly diffuse through the mesoporous pores toward Fe3O4 active sites, which is beneficial for the heterogeneous reaction.51 The degradation of acetaminophen molecules continuously reduces the reactant concentration in the interior void of the yolk-shell structures, which facilitates acetaminophen molecules to continually diffuse through the silica shell. This maintains the continuity of the catalytic reaction and guarantees the conversion of the target molecules.52 The cavity of the yolk-shell structures also provides a perfect microenvironment to confine the reactants, leading to a relatively higher instantaneous concentration of reactants in the hollow space of the yolk-shell structures, where the Fe3O4 cores are more accessible to the reactants, and thus affording a driving force to accelerate the reaction rate.15,51,53 Furthermore, the results shows almost no iron leaching from the yolk-shell structures during the oxidation of acetaminophen (Table 2), suggesting the structure of the materials could protect the Fe3O4 nanoparticles against leaching into solution. One possibility may be the high stability of the Fe3O4 nanoparticles encapsulated inside the silica shell, which inhibited the release of iron into the solution. Another possibility is that leaching iron could bind to the negatively charged inner surface of the silica shell through electrostatic interaction. The decoration of copper nanoparticles makes the newly formed materials more reactive because of some notable advantages as follows. First, copper nanoparticles were immobilized and well-dispersed on the mesoporous surface of the precursor, implying that a larger amount of active sites are provided; therefore, the reactant molecules adsorbed onto active sites on the catalyst surface could be instantly decomposed. Secondly, the synergistic effects of iron and copper favor the redox cycles of Fe3+/ Fe2+ and Cu2+/Cu+, which can enhance the catalytic reaction rates of contaminant degradation by accelerating the electron transfer.24,54,55


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However, as is similar with most of Fenton-like catalysts of nano-sized metal oxides, the leaching of copper species under the reaction conditions is a major drawback of this approach, which needs to be addressed somehow despite the very low concentration of copper detected. 3.3. Reusability tests

1.00

2nd

1st

4th

3rd

6th

5th

Fe3O4@SiO2 0.80

C/Co

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fe3O4@SiO2@Cu

0.60

0.40

0.20

0.00 0

30

60

90 120 0

30

60

90 120 0

30

60

90 120 0

30

60

90 120 0

30

60

90 120 0

30

60

90

120

Time (min)

Figure 9. Stability test of Fe3O4@SiO2 (0.4 g/L) and Fe3O4@SiO2@Cu (0.2 g/L) with the degradation of acetaminophen (Other conditions: C0 = 2.0 mg/L, H2O2 = 15.0 mM, pH = 5.0, T = 25.0 oC, t = 120 min). The recycled Fe3O4@SiO2 and Fe3O4@SiO2@Cu exhibited excellent catalytic performance after six cycles (Figure 9) and outstanding structural stability (Figure 10). No obvious loss of the catalytic reactivity for either material was observed for acetaminophen degradation, and the removal efficiency was quite similar during the six cycles, indicating that the materials are very stable during the reaction. This was further confirmed by FT-IR analysis of the two studied materials under three different conditions, i.e., the original samples, and after one and six cycles of the regeneration (Figure 11). Almost no change was observed for all the spectra of Fe3O4@SiO2 and Fe3O4@SiO2@Cu, even after six cycles of regeneration. In addition, the 25 ACS Paragon Plus Environment


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materials were easily separated after the catalytic reaction by simple application of an external magnetic field due to magnetic nature of the magnetite-containing yolk-shell structures (Figure 7b).

Figure 10. FE-TEM images of Fe3O4@SiO2 (a, b) and Fe3O4@SiO2@Cu (c, d) after one and six cycles of the regeneration, respectively.


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(a)

(b)

Fe3O4@SiO2 - after 6 cycles

Fe3O4@SiO2@Cu- after 6 cycles Fe3O4@SiO2@Cu- after 1 cycle

Fe3O4@SiO2 - after 1 cycle

Transmittance (%)

Transmittance (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Fe3O4@SiO2 - pristine

3950

3450

2950

2450

1950

1450

950

450

Fe3O4@SiO2@Cu- pristine

3950

3450

2950

Wave number (cm-1)

2450

1950

1450

950

450

Wave number (cm-1)

Figure 11. FT-IR spectra of Fe3O4@SiO2 (a), and Fe3O4@SiO2@Cu (b) before and after regenerations.

4. CONCLUSION Efforts to remove acetaminophen have been considered as an urgent request due to it is an emerging persistent organic pollutant which has potential significant impacts on human health and the environment. In this work, yolk-shell structured Fe3O4@SiO2 were successfully prepared via non-sacrificial template approach, which contains active core, a protective shell, and a hollow void with superparamagnetic properties at room temperature. They were employed as catalysts in Fenton-like reactions for acetaminophen degradation from aqueous solution. The Fe3O4@SiO2 was effectively used as an efficient and good reusable catalyst in a Fenton-like system. The mesoporous silica shell not only enhances the degradation rate by enriching the reactant molecules around the active core, but also protects the active core from leaching. The copper nanoparticles were firmly immobilized on the silica shell, and Fe3O4@SiO2@Cu dramatically enhanced the catalytic performance and sustainability for repeated runs. A 2.0 mg/L of 27 ACS Paragon Plus Environment


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acetaminophen was almost completely degraded by Fe3O4@SiO2@Cu in 20 min, while only a 67.0% reduction was achieved by Fe3O4@SiO2 after 120 min under the same experiment conditions. The decoration of copper onto the yolk-shell Fe3O4@SiO2 was demonstrated to be an effective and promising approach for a great improvement of the catalytic activity of the monometallic yolk-shell structure. In addition, both the yolk-shell structured Fe3O4@SiO2 and Fe3O4@SiO2@Cu exhibited good separation and satisfactory regeneration properties, which could be recycled six times without any obvious decline in catalytic activity. The simple procedures for both catalyst preparation and recovery, as well as the excellent catalytic reactivity and recycling efficiency of the yolk-shell structured Fe3O4@SiO2 and Fe3O4@SiO2@Cu, demonstrate a potential application for the removal of persistent pharmaceuticals from aquatic environments. Further study on the reaction mechanism, affecting factors, co-existing pollutants, and material modification are being investigated.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Phone: +82-31-201-2999; Fax: +82-31-202-8854 Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS 28 ACS Paragon Plus Environment

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This work was partially supported by a National Research Foundation of Korea (NRF) grant (NRF-2016R1A2B4015385) and the Korea Ministry of Environment (MOE) as “GAIA (GeoAdvanced Innovative Action) Project (#2015000550004).

REFERENCES

(1) de Luna, M. D. G.; Briones, R. M.; Su, C.-C.; Lu, M.-C. Kinetics of Acetaminophen Degradation by Fenton Oxidation in a Fluidized-bed Reactor. Chemosphere 2013, 90, 1444-1448. (2) Zhang, H.; Cao, B.; Liu, W.; Lin, K.; Feng, J. Oxidative Removal of Acetaminophen using Zero Valent Aluminum-acid System: Efficacy, Influencing Factors, and Reaction Mechanism. J. Environ. Sci. 2012, 24, 314-319. (3) Villota, N.; Lomas, J. M.; Camarero, L. M. Study of the Paracetamol Degradation Pathway that Generates Color and Turbidity in Oxidized Wastewaters by Photo-Fenton Technology. J. Photochem. Photobiol. A 2016, 329, 113-119. (4) Rivera-Utrilla, J.; Sánchez-Polo, M.; Ferro-García, M. Á.; Prados-Joya, G.; Ocampo-Pérez, R. Pharmaceuticals as Emerging Contaminants and their Removal from Water. A Review. Chemosphere 2013, 93, 1268-1287. (5) Barceló, D. Emerging Pollutants in Water Analysis. TrAC Trends in Anal. Chem. 2003, 22, 14-16. (6) Kümmerer, K. The Presence of Pharmaceuticals in the Environment due to Human Use – Present Knowledge and Future Challenges. J. Environ. Manage. 2009, 90, 2354-2366. (7) Petrie, B.; Barden, R.; Kasprzyk-Hordern, B. A Review on Emerging Contaminants in Wastewaters and the Environment: Current Knowledge, Understudied Areas and Recommendations for Future Monitoring. Water Res. 2015, 72, 3-27. (8) Xavier, S.; Gandhimathi, R.; Nidheesh, P. V.; Ramesh, S. T. Comparison of Homogeneous and Heterogeneous Fenton Processes for the Removal of Reactive Dye Magenta MB from Aqueous Solution. Desalin.Water Treat. 2015, 53, 109-118. (9) Ling, Y.; Long, M.; Hu, P.; Chen, Y.; Huang, J. Magnetically Separable Core–shell Structural γ-Fe2O3@Cu/Al-MCM-41 Nanocomposite and its Performance in Heterogeneous Fenton Catalysis. J. Hazard. Mater. 2014, 264, 195-202.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 33

(10) Cuzzola, A.; Bernini, M.; Salvadori, P. A Preliminary Study on Iron Species as Heterogeneous Catalysts for the Degradation of Linear Alkylbenzene Sulphonic Acids by H2O2. Appl. Catal. B Environ. 2002, 36, 231-237. (11) Dhakshinamoorthy, A.; Navalon, S.; Alvaro, M.; Garcia, H. Metal Nanoparticles as Heterogeneous Fenton Catalysts. ChemSusChem. 2012, 5, 46-64. (12) Polshettiwar, V.; Luque, R.; Fihri, A.; Zhu, H.; Bouhrara, M.; Basset, J.-M. Magnetically Recoverable Nanocatalysts. Chem. Rev. 2011, 111, 3036-3075. (13) Purbia, R.; Paria, S. Yolk/shell Nanoparticles: Classifications, Synthesis, Properties, and Applications. Nanoscale 2015, 7, 19789-19873. (14) Yue, Q.; Zhang, Y.; Wang, C.; Wang, X.; Sun, Z.; Hou, X.-F.; Zhao, D.; Deng, Y., Magnetic Yolk-shell Mesoporous Silica Microspheres with Supported Au Nanoparticles as Recyclable High-performance Nanocatalysts. J. Mater. Chem. A 2015, 3, 4586-4594. (15) Zeng, T.; Zhang, X.; Wang, S.; Ma, Y.; Niu, H.; Cai, Y. Assembly of a Nanoreactor System with Confined Magnetite Core and Shell for Enhanced Fenton-Like Catalysis. Chem. Eur. J. 2014, 20, 6474-6481. (16) Costa, R. C. C.; Moura, F. C. C.; Ardisson, J. D.; Fabris, J. D.; Lago, R. M. Highly Active Heterogeneous Fenton-like Systems Based on Fe0/Fe3O4 Composites Prepared by Controlled Reduction of Iron Oxides. Appl. Catal. B Environ. 2008, 83, 131-139. (17) Rathore, P. S.; Patidar, R.; Shripathi, T.; Thakore, S. Magnetically Separable Core-shell Iron oxide@nickel Nanoparticles as High-performance Recyclable Catalysts for Chemoselective Reduction of Nitroaromatics. Catal. Sci. Technol. 2015, 5, 286-295. (18) Xia, M.; Long, M.; Yang, Y.; Chen, C.; Cai, W.; Zhou, B. A Highly Active Bimetallic Oxides Catalyst Supported on Al-containing MCM-41 for Fenton Oxidation of Phenol Solution. Appl. Catal. B Environ. 2011, 110, 118-125. (19) Lam, F. L. Y.; Hu, X. pH-Insensitive Bimetallic Catalyst for the Abatement of Dye Pollutants by Photo-Fenton Oxidation. Ind. Eng. Chem. Res. 2013, 52, 6639-6646. (20) Parvulescu, V. I.; Granger, P. Current Heterogeneous Catalytic Processes for Environmental Remediation of Air, Water, and Soil. In New and Future Developments in Catalysis; Suib, S. L., Eds., Elsevier: Amsterdam 2013; pp 487-534. (21) Gawande, M. B.; Goswami, A.; Felpin, F.-X.; Asefa, T.; Huang, X.; Silva, R.; Zou, X.; Zboril, R.; Varma, R. S. Cu and Cu-Based Nanoparticles: Synthesis and Applications in Catalysis. Chem. Rev. 2016, 116, 3722-3811. (22) Zhang, L.; Xu, D.; Hu, C.; Shi, Y. Framework Cu-doped AlPO4 as an Effective Fentonlike Catalyst for Bisphenol A Degradation. Appl. Catal. B Environ. 2017, 207, 9-16. (23) Bokare, A. D.; Choi, W. Review of Iron-free Fenton-like Systems for Activating H2O2 in Advanced Oxidation Processes. J. Hazard. Mater. 2014, 275, 121-135. (24) Wang, Y.; Zhao, H.; Zhao, G. Iron-copper Bimetallic Nanoparticles Embedded within Ordered Mesoporous Carbon as Effective and Stable Heterogeneous Fenton Catalyst for the Degradation of Organic Contaminants. Appl. Catal. B Environ. 2015, 164, 396-406.


Page 31 of 33

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(25) Han, Z.; Dong, Y.; Dong, S. Copper–iron Bimetal Modified PAN Fiber Complexes as Novel Heterogeneous Fenton Catalysts for Degradation of Organic Dye under Visible Light Irradiation. J. Hazard. Mater. 2011, 189, 241-248. (26) Han, J.; Chen, R.; Wang, M.; Lu, S.; Guo, R. Core-shell to Yolk-shell Nanostructure Transformation by a Novel Sacrificial Template-free Strategy. Chem. Commun. 2013, 49, 1156611568. (27) Lee, J.; Kim, S. M.; Lee, I. S. Functionalization of Hollow Nanoparticles for Nanoreactor Applications. Nano Today 2014, 9, 631-667. (28) Li, Z.; Li, M.; Bian, Z.; Kathiraser, Y.; Kawi, S. Design of Highly Stable and Selective Core/yolk–shell Nanocatalysts: A review. Appl. Catal. B Environ. 2016, 188, 324-341. (29) Teng, Z.; Su, X.; Zheng, Y.; Sun, J.; Chen, G.; Tian, C.; Wang, J.; Li, H.; Zhao, Y.; Lu, G. Mesoporous Silica Hollow Spheres with Ordered Radial Mesochannels by a Spontaneous SelfTransformation Approach. Chem. Mater. 2013, 25, 98-105. (30) Liu, J.; Sun, Z.; Deng, Y.; Zou, Y.; Li, C.; Guo, X.; Xiong, L.; Gao, Y.; Li, F.; Zhao, D. Highly Water-Dispersible Biocompatible Magnetite Particles with Low Cytotoxicity Stabilized by Citrate Groups. Angew. Chem. Int. Ed. 2009, 48, 5875-5879. (31) Liu, J.; Cheng, J.; Che, R.; Xu, J.; Liu, M.; Liu, Z. Synthesis and Microwave Absorption Properties of Yolk–Shell Microspheres with Magnetic Iron Oxide Cores and Hierarchical Copper Silicate Shells. ACS Appl. Mater. Interfaces 2013, 5, 2503-2509. (32) Ji, J.; Zeng, P.; Ji, S.; Yang, W.; Liu, H.; Li, Y. Catalytic Activity of Core–shell Structured Cu/Fe3O4@SiO2 Microsphere Catalysts. Catal. Today 2010, 158, 305-309. (33) Tang, M.; Zhang, S.; Li, X.; Pang, X.; Qiu, H. Fabrication of Magnetically Recyclable Fe3O4@Cu Nanocomposites with High Catalytic Performance for the Reduction of Organic Dyes and 4-nitrophenol. Mater. Chem. Phys. 2014, 148, 639-647. (34) Corma, A. From Microporous to Mesoporous Molecular Sieve Materials and Their Use in Catalysis. Chem. Rev. 1997, 97, 2373-2420. (35) Wang, J.; Liu, C.; Hussain, I.; Li, C.; Li, J.; Sun, X.; Shen, J.; Han, W.; Wang, L. Ironcopper Bimetallic Nanoparticles Supported on Hollow Mesoporous Silica Spheres: the Effect of Fe/Cu Ratio on Heterogeneous Fenton Degradation of a Dye. RSC Adv. 2016, 6, 54623-54635. (36) Wang, Z.-Z.; Zhai, S.-R.; Zhai, B.; An, Q.-D. One-Step Green Synthesis of Multifunctional Fe3O4/Cu Nanocomposites toward Efficient Reduction of Organic Dyes. Eur. J. Inorg. Chem. 2015, 2015, 1692-1699. (37) Wang, T.; Yang, W.; Song, T.; Li, C.; Zhang, L.; Wang, H.; Chai, L. Cu Doped Fe3O4 Magnetic Adsorbent for Arsenic: Synthesis, Property, and Sorption Application. RSC Adv. 2015, 5, 50011-50018. (38) Cui, Z.-M.; Chen, Z.; Cao, C.-Y.; Jiang, L.; Song, W.-G. A Yolk-shell Structured Fe2O3@mesoporous SiO2 Nanoreactor for Enhanced Activity as a Fenton Catalyst in Total Oxidation of Dyes. Chem. Commun. 2013, 49, 2332-2334.



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(39) Yang, R.; Liu, Y.; Yan, X.; Liu, S.; Zheng, H. An Effective Method for the Synthesis of Yolk-shell Magnetic Mesoporous Carbon-surface Molecularly Imprinted Microspheres. J. Mater. Chem. A 2016, 4, 9807-9815. (40) Angı, A.; Sanlı, D.; Erkey, C.; Birer, Ö. Catalytic Activity of Copper (II) Oxide Prepared via Ultrasound Assisted Fenton-like Reaction. Ultrason. Sonochem. 2014, 21, 854-859. (41) Zhao, W.; Chen, H.; Li, Y.; Li, L.; Lang, M.; Shi, J. Uniform Rattle-type Hollow Magnetic Mesoporous Spheres as Drug Delivery Carriers and their Sustained-Release Property. Adv. Funct. Mater. 2008, 18, 2780-2788. (42) Patil, R. M.; Shete, P. B.; Thorat, N. D.; Otari, S. V.; Barick, K. C.; Prasad, A.; Ningthoujam, R. S.; Tiwale, B. M.; Pawar, S. H. Non-aqueous to Aqueous Phase Transfer of Oleic Acid Coated Iron Oxide Nanoparticles for Hyperthermia Application. RSC Adv. 2014, 4, 4515-4522. (43) Yang, S.; Zeng, T.; Li, Y.; Liu, J.; Chen, Q.; Zhou, J.; Ye, Y.; Tang, B., Preparation of Graphene Oxide Decorated Fe3O4@SiO2 Nanocomposites with Superior Adsorption Capacity and SERS Detection for Organic Dyes. J. Nanomater. 2015, 2015, 8. (44) van der Meer, J.; Bardez-Giboire, I.; Mercier, C.; Revel, B.; Davidson, A.; Denoyel, R. Mechanism of Metal Oxide Nanoparticle Loading in SBA-15 by the Double Solvent Technique. J. Phys. Chem. C 2010, 114, 3507-3515. (45) Raja, K.; Verma, S.; Karmakar, S.; Kar, S.; Das, S. J.; Bartwal, K. S. Synthesis and Characterization of Magnetite Nanocrystals. Cryst. Res. Technol. 2011, 46, 497-500. (46) Rohilla, S.; Kumar, S.; Aghamkar, P.; Sunder, S.; Agarwal, A. Investigations on Structural and Magnetic Properties of Cobalt Ferrite/silica Nanocomposites Prepared by the Coprecipitation Method. J. Magn. Magn. Mater. 2011, 323, 897-902. (47) Díaz-Visurraga, J.; Daza, C.; Pozo, C.; Becerra, A.; von Plessing, C.; García, A. Study on Antibacterial Alginate-stabilized Copper Nanoparticles by FT-IR and 2D-IR Correlation Spectroscopy. Int. J. Nanomed. 2012, 7, 3597-3612. (48) Chai, L.; Wang, Y.; Zhao, N.; Yang, W.; You, X. Sulfate-doped Fe3O4/Al2O3 Nanoparticles as a Novel Adsorbent for Fluoride Removal from Drinking Water. Water Res. 2013, 47, 4040-4049. (49) Pires, C. A.; Santos, A. C. C. d.; Jordão, E. Oxidation of Phenol in Aqueous Solution with Copper Oxide Catalysts Supported on γ-Al2O3, Pillared Clay and TiO2: Comparision of the Performance and Costs Associated with Each Catalyst. Braz. J. Chem. Eng. 2015, 32, 837-848. (50) Bhargava, S.; Jani, H.; Tardio, J.; Akolekar, D.; Hoang, M. Catalytic Wet Oxidation of Ferulic Acid (A Model Lignin Compound) Using Heterogeneous Copper Catalysts. Ind. Eng. Chem. Res. 2007, 46, 8652-8656. (51) Chen, Z.; Cui, Z.-M.; Niu, F.; Jiang, L.; Song, W.-G. Pd Nanoparticles in Silica Hollow Spheres with Mesoporous Walls: a Nanoreactor with Extremely High Activity. Chem. Commun. 2010, 46, 6524-6526. (52) Liu, C.; Li, J.; Qi, J.; Wang, J.; Luo, R.; Shen, J.; Sun, X.; Han, W.; Wang, L. Yolk–Shell Fe0@SiO2 Nanoparticles as Nanoreactors for Fenton-like Catalytic Reaction. ACS Appl. Mater. Interfaces 2014, 6, 13167-13173. 32 ACS Paragon Plus Environment

Page 33 of 33

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(53) Shi, W.; Du, D.; Shen, B.; Cui, C.; Lu, L.; Wang, L.; Zhang, J. Synthesis of Yolk–Shell Structured Fe3O4@void@CdS Nanoparticles: A General and Effective Structure Design for Photo-Fenton Reaction. ACS Appl. Mater. Interfaces 2016, 8, 20831-20838. (54) Kang, H.-Y.; Wang, H. P. Preparation of Magnetic Recoverable Nanosize Cu–Fe2O3/Fe Photocatalysts. Environ. Sci. Technol. 2013, 47, 7380-7387. (55) Albuquerque, A. S.; Tolentino, M. V. C.; Ardisson, J. D.; Moura, F. C. C.; de Mendonça, R.; Macedo, W. A. A. Nanostructured Ferrites: Structural Analysis and Catalytic Activity. Ceram. Int. 2012, 38, 2225-2231.

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Nonsacrificial Template Synthesis of Magnetic-Based YolkâShell

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Nonsacrificial Template Synthesis of Magnetic-Based YolkâShell