Synthesis, Characterization, and Catalytic Applications of CoreâShell

Article pubs.acs.org/JPCC

Synthesis, Characterization, and Catalytic Applications of Core−Shell Magnetic Carbonaceous Nanocomposites Changzi Jin,*,†,‡ Yanjie Wang,‡ Hailian Tang,‡ Haisheng Wei,‡ Xin Liu,†,‡ and Junhu Wang*,†,‡ †

Mössbauer Effect Data Center and ‡Laboratory of Catalysts and New Materials for Aerospace, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457 Zhongshan Road, Dalian 116023, China S Supporting Information *

ABSTRACT: Magnetic resorcinol/formaldehyde resin (RF) and silica/RF nanocomposites with well-defined core−shell architecture and tunable structural parameters had been prepared via the extended Stöber method. The carbon counterparts with similar structure and morphology can be obtained by thermaltreating the polymer precursors under N2 atmosphere. The prepared materials were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, Mössbauer spectroscopy, N2 physical adsorption/desorption, and thermogravimetric analysis. The catalytic applications of the synthesized magnetic nanocomposites were also explored. It has been shown that the magnetite core was oxidized to γ-Fe2O3 during polymer coating process and further reduced to original Fe3O4 phase during carbonization. In addition, the iron oxide core can react with the shell when carbonization temperature reaches 700 °C. The structural stability of magnetic silica/RF is superior to magnetic RF because of the existence of an inner silica shell. Through a simple deposition−precipitate method, active platinum nanoparticles can be loaded in high dispersity onto the surface of the nanocomposites. The constructed magnetic catalysts are very active in hydrogenation of nitroarenes to corresponding amines and can be separated facilely with an external magnetic field.

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approaches.17,18,28 However, the core−shell products from these methods are always accompanied by aggregation of particles, and it is usually difficult to adjust the structural parameters of products through controlling synthesis conditions. Therefore, developing novel strategy to prepare welldispersed and tunable core−shell magnetic carbon composites is still a challenge. The Stöber method is the most facile approach for the preparation of silica colloidal spheres and core@silica shell composites.29−31 Undoubtedly, the uniform and discrete core− shell Fe3O4@SiO2 had been prepared through this method.5,15,32−34 Considering the structural similarity between resorcinol/formaldehyde resin (RF) and silica gel, Liu et al. extended successfully the Stöber process to the preparation of monodispersed RF polymer and carbon spheres,35 which simultaneously provided a new opportunity for the synthesis of RF and carbon coated nanocomposites. Subsequently, a series of uniform core−shell architectures with high quality had been prepared successfully, including SiO2@RF, Ag@RF, TiO2@RF, Fe2O3@RF, as well as Fe3O4@RF and their carbon derivates.36−40 In a comparison with previous Fe3O4@carbon nanocomposites, the core−shell magnetic carbonaceous

INTRODUCTION In recent years, magnetic materials have attracted more and more attention owing to their unique properties and promising applications in catalysis, biomedicine, adsorption, and so on.1−7 Conventional magnetic nano/microspheres are usually unstable and easy to aggregate due to their small particle size and high surface energy. Therefore, coating magnetic nano/microspheres with other materials to construct core−shell hybrid composites is an effective strategy to increase the stability and functional groups.8−10 Magnetite (Fe3O4) is a kind of very popular magnetic material for its strong magnetic response, biocompatibility, and low toxicity.11−13 Many efforts have been paid to the fabrication of Fe3O4-based magnetic nanocomposites. To date, the core−shell magnetic composites of Fe3O4 encapsulated in silica, carbon, and metal oxides have been prepared successfully.5,9,10,14−19 Among them, carbonaceous materials as the shells have aroused much interest because of their outstanding intrinsic properties, such as large surface area, acid and base resistance, highly thermal stability (inert gas atmosphere), and abundant functional groups.9,16−18,20−22 Previously, several synthesis routes have been developed to fabricate core−shell structure of polymer and carbon coated magnetite, including the well-known “green chemistry” of glucose hydrothermal process,9,22−25 the solvothermal process from organic iron compound (ferrocene) and hydrogen peroxide,26,27 the template method, and some other synthesis © 2014 American Chemical Society

Received: September 2, 2014 Revised: October 10, 2014 Published: October 10, 2014 25110

dx.doi.org/10.1021/jp508853a | J. Phys. Chem. C 2014, 118, 25110−25117

The Journal of Physical Chemistry C

Article

Figure 1. Schematic illustration for synthesis of core−shell magnetic carbonaceous nanocomposites.

spheres from extended Stöber method possess discrete and well-defined morphology and tunable structure parameters. However, current research mainly focuses on the preparation of the composites, and relatively few studies are performed on their detailed characterization and catalytic applications. In this paper, we synthesized well-defined core−shell magnetic RF and SiO2/RF nanocomposites with tunable structural parameters through the extended Stöber process of resorcinol and formaldehyde polymerizing. Corresponding carbon derivates were obtained by further heat-treating the polymer precursors under N2 atmosphere. Both the magnetic cores and the shells of the composite products were investigated in detail. In addition, the synthesized magnetic nanocomposites had been loaded with active metal nanoparticles (Pt, Pd) to construct functional heterogeneous catalysts, whose catalytic properties were also investigated.

0.2 g of TEOS as silica source was added to the reaction solution before the addition of carbon sources. The magnetic carbon and silica/carbon spheres, denoted as MC and MSC, respectively, were obtained by thermaltreatment of their respective polymer precursors at 500 °C for 4 h under N2 atmosphere with heating rate of 2 °C/min. Synthesis of Magnetic Catalysts. The magnetic catalysts were prepared by deposition−precipitation method. Typically, 150 mg magnetic supports were dispersed in 50 mL of ethanol, followed by the addition of 0.1 mL of H2PtCl6 (77 mM) (or 0.06 mL of PdCl2 (225 mM)). Then the mixture was refluxed at 80 °C with stirring for 2 h, and the solid was separated with the help of magnet and washed with ethanol and water several times. Finally, the obtained magnetic Pt- (or Pd-) based catalyst was dried at 85 °C under vacuum. Characterizations. Powder X-ray diffraction (XRD) patterns were recorded in a PANalytical X’Pert PRO powder X-ray diffractometer using Cu Kα radiation. Scanning electron microscopy (SEM) images were measured on JSM-7800F field emission electron microscope. Transmission electron microscopy (TEM) images were taken on a Tecnai G2 Spirit electronic microscope with an accelerating voltage of 120 kV. N2 physical adsorption−desorption isotherm was measured on a Micromeritics ASAP 1020 apparatus. The samples were degassed at 110 °C for 5 h before the measurement. Thermogravimetric analysis (TG) was carried out on a Setaram Setsys 16/18 thermogravimetric analyzer. Fourier transform infrared (FT-IR) spectra were collected on a Bruker EQUINOX 55 spectrometer using KBr pellets. The contents of Pt in the composite catalysts were analyzed by inductively coupled plasma spectrometry (ICP) on an IRIS Intrepid II XSP instrument. The 57Fe Mössbauer spectra were recorded at room temperature with the spectrometer working in constant acceleration mode with the use of 57Co (Rh) source. All spectra were computer-fitted to a Lorentzian shape with a leastsquares fitting procedure. The isomer shifts (ISs) were given with respect to the centroid of α-Fe at room temperature. Catalytic Tests. Hydrogenation of nitroarenes to corresponding anilines was performed in Teflon-lined autoclave (50 mL capacity). Typically, 5 mL of solution of reactant (nitrobenzene or 2-nitrochlorobenzene) in ethanol (0.1 M) and 40 mg catalyst were added into the autoclave. Then, the autoclave was swept by H2 to remove the air and sealed with H2 pressure at 0.3 MPa. Subsequently, the reaction mixture was stirred at 40 °C for a period of time. The reaction products were analyzed by means of GC Agilent 6890 equipped with a HP-5 capillary column and a FID detector. The catalysts were

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EXPERIMENTAL SECTION Chemicals. Ferric chloride hexahydrate (FeCl3·6H2O), sodium acetate (NaAc), ethanol, ethylene glycol, tetraethylorthosilicate (TEOS), resorcinol, and ammonia (25−28%) were purchased from Tianjin Kermel Chemical Company. Sodium citrate dihydrate and formaldehyde solution (37−40%) were purchased from Tianjin Damao Chemical Company. Dihydrogen hexachloroplatinate (H2PtCl6·6H2O, 99.9%) and palladium chloride (PdCl2) were obtained from AldrichSigma. All the chemicals were of analytical grade and used as received without purification. Synthesis of Magnetite Cores. The magnetite cores were synthesized by solvothermal reaction according to our previous report.33 Synthesis of Magnetic RF (Carbon) and SiO2/RF (Carbon) Nanocomposites. The core−shell magnetic RF and silica/RF nanocomposites, denoted as MRF and MSRF, respectively, were synthesized through an extended Stöber method. For the MRF spheres, 140 mg of magnetite particles were dispersed in 60 mL of water and ethanol (volume ratio = 2:1), followed by addition of 0.3 mL ammonia, 0.2 g of resorcinol, and 0.3 g of formaldehyde solution (mass ratio = 1:1.5). The obtained mixture was mechanically stirred at 30 °C for 24 h, and then was transferred into Teflon-lined stainlesssteel autoclave and heated at 100 °C for another 24 h. The product was collected by an external magnet and further airdried at 60 °C. The MSRF composite spheres were prepared through a similar process to that of MRF except with a little difference. The volume ratio of water and ethanol was changed to 1:3, and more ammonia (1.0 mL) was needed. In addition, 25111



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Figure 2. SEM (up) and TEM (down) images of (a, e) MRF, (b, f) MSRF, (c, g) MC, and (d, h) MSC.

Figure 3. TEM images of MRF (up) and MSRF (down) synthesized with the amount of resorcinol at (a, d) 0.1 g, (b, e) 0.2 g, and (c, f) 0.3 g.

which are well-dispersed in the water/ethanol solution.11 With the catalysis effect of ammonia, the carbonous reactants of resorcinol and formaldehyde polymerized cover directly the magnetic particles and form the core−shell magnetic polymers without using other assisted surfactants.38,39 In addition, because of the similar synthetic conditions but different reaction rate of Stöber silica gels and RF polymers,36,41 magnetic silica/RF nanocomposites with double layered core− shell structure can be prepared by introducing simultaneously the respective reactants precursors into the synthesis system. Figure 2 presents the SEM and TEM images of the prepared materials. It can be found that both MRF and MSRF exhibit

magnetically recovered and thoroughly washed with ethanol for recycle tests.

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RESULTS AND DISCUSSION Controlled Synthesis of the Core−Shell Magnetic Nanocomposites. The facile preparation process for the core−shell magnetic nanocomposites was illustrated by Figure 1. In general, in order to obtain the products with uniform core−shell structure, highly dispersed core matters in the synthesis system are necessary. Herein, the citrate groups capped magnetite particles with particle size of ∼200 nm were utilized as magnetic cores (Supporting Information Figure S1), 25112



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uniform spheric morphology and well-defined core−shell structure. Compared to MRF, MSRF possesses obvious double layer shells composed of silica and RF polymer. Timedependent products from MSRF preparation possess different shell character (Supporting Information Figure S2), which demonstrate one-pot formation of silica and RF polymer but at different speed.36,41 The RF polymer shell of MRF and MSRF can be converted into carbon by heat-treating the composites under nitrogen atmosphere. The MC and MSC composites possess similar morphology and structure as their respective polymer precursors, which indicate that the core−shell structure did not change during the carbonization process. After treating with NaOH solution, the MSC transformed a yolk−shell magnetic carbon (Supporting Information Figure S3), which further confirmed the double layered core−shell structure with inner silica shell and outer RF (carbon) shell of MSRF and MSC. In addition, due to the controllable character of Stöber method, the RF polymer shell’s thickness of the MRF and MSRF materials can be tuned easily by varying the concentration of carbonous reactants.40 As Figure 3 shows, the thickness of RF shell for the MRF and MSRF can be tuned from 20 to 100 nm by changing the dosage of resorcinol from 0.1 to 0.3 g. As to MSRF, the thickness of inner silica shell is also tunable through changing the concentration of silica source (Supporting Information Figure S4). Characterization of the Core−Shell Magnetic Nanocomposites. Figure 4 presents the XRD patterns of the

Figure 5. Room-temperature 57Fe Mössbauer spectra of (a) MRF, (b) MSRF, (c) MC, (d) MSC.

MRF and MSRF exhibit the only Fe3+ oxidation state, which indicate that the magnetic cores in them are not Fe3O4 but γFe2O3 phase.33,42 The carbonized samples MC and MSC also give the similar Fe3O4 spectra as initial magnetic core. These results show that the magnetic cores can be partially oxidized during the RF coating process. After carbonization, the oxidized magnetic cores return to the Fe3O4 phase again, which may be due to the reduction of the RF polymer shell or some emitted reductive gases such as CO, H2 during carbonization.43 Figure 6 shows the N2 physical adsorption/desorption isotherms of the magnetic composites. MRF and MSRF are absolute nonporous and exhibit very small surface areas of 11 and 10 m2/g, respectively. After the thermal treatment under N2 atmosphere, the nonporous RF polymer transformed to porous carbon. It is observed that both MC and MSC exhibit isotherms of type-I, which indicate their microporous structure. By comparison with the polymer precursors, MC and MSC possess large surface areas of 276 and 221 m2/g, respectively. MSC has lower surface areas than MC which is due to the existence of nonporous silica inner shell. Thermogravimetric analysis can provide quantitative information for RF content in magnetic composites. As Figure 7 has shown, in air atmosphere, MRF and MSRF display final weight loss of 74% and 53%, respectively. Without considering the initial around 10% weight loss below 120 °C in all cases, which is due to the removal of adsorbed water, the weight fractions of RF polymer in MRF and MSRF are about 64% and 43%, respectively. The weight loss in nitrogen was different (Figure 7c,d). MRF and MSRF were heated in N2 atmosphere to 800 °C, leading to the total weight loss of 37% and 55%, respectively. It is strange that MRF displays a significant weight loss at ∼700 °C, which indicates that there might be some other reactions besides the carbonization of RF polymer. In order to explore what happened during this process, additional MC and MSC carbonized at 700 °C (denoted as MC-700 and MSC-700) were prepared and investigated. Figure 8 presents the XRD patterns and Mössbauer spectra of MC-700 and MSC-700. Obviously, both MC-700 and MSC700 display different XRD patterns from the samples carbonized at 500 °C. For MC-700, the diffraction peaks of Fe3O4 became very weak, and some new diffraction peaks appeared, which indicates other species were formed, including

Figure 4. XRD patterns of (a) magnetite core, (b) MRF, (c) MSRF, (d) MC, (e) MSC.

prepared materials. Both initial magnetic core and carbon composites (MC and MSC) exhibit typical patterns of Fe3O4 phase. By comparison, the diffraction peaks for MRF and MSRF shift toward high angles (Supporting Information Figure S5), which are closer to the maghemite (γ-Fe2O3) phase. In spite of this, it is not easy to distinguish clearly the XRD patterns of Fe3O4 and γ-Fe2O3 because of their similarity. Herein, Mössbauer spectroscopy was employed to clarify the phase state of magnetic iron oxide cores in the prepared materials. Figure 5 shows the room-temperature 57 Fe Mössbauer spectra of different magnetic composites, and the corresponding hyperfine parameters are summarized in Table 1. According to our previous report, the two sextet spectra for initial magnetic core confirm its Fe3O4 phase (Supporting Information Figure S6).33 However, the Mössbauer spectra of 25113



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Table 1. Mössbauer Hyperfine Parameters of Different Magnetic Compositesa sample MRF MSRF MC MSC MC-700

MSC-700

a

IS (mm/s)

QS (mm/s)

2Γ (mm/s)

B (T)

A (%)

phase assignment

0.35 0.33 0.33 0.32 0.57 0.32 0.62 0.30 0 0.19 0.43 0.66 0.28 1.16

−0.01 0 −0.02 −0.01 0 −0.02 −0.01 −0.02 0.01 0.02 0.04 −0.03 −0.02 2.85

0.95 0.59 1.02 0.64 0.77 0.46 0.64 0.35 0.28 0.41 0.74 0.51 0.28 0.33

43 47 42 46 44 48 45 48 33 21 47 46 49

44 56 44 56 51 49 67 33 65 30 5 26 13 61

γ-Fe2O3 γ-Fe2O3 Fe3O4 Fe3O4 Fe Fe3C Fe3O4 Fe3O4 Fe2SiO4

IS, isomer shift relative to α-Fe; QS, quadrupole splitting; 2Γ, line width; B, magnetic field; A, relative subspectrum area.

and QS of 1.16 and 2.85 mm/s, respectively, which can be typically classified as Fe2SiO4.44 These results are in accordance with XRD analysis. In core−shell MRF, the RF shell is in contact with the magnetic core (γ-Fe2O3). So the γ-Fe2O3 core is not only facile to be reduced but also tends to react with RF shell to form carbide at high temperature. In addition, the formation of graphite is due to the graphitization of RF polymer catalyzed by Fe3+.39 This is why the MRF has sudden weight loss at ∼700 °C in nitrogen flow (Figure 7c). In contrast, the magnetic core of MSRF is isolated from the outer RF shell by nonporous silica inner shell. As a result, the deep reduction of the core and its reaction with RF shell are prohibited. Instead, when the carbonization temperature is as high as 700 °C, the silica shell reacted with magnetic core, and product Fe2SiO4 was formed. Without the catalysis effect from the magnetic iron oxide core, graphitization of RF polymer cannot occur at 700 °C. Therefore, the iron, carbide, and graphite do not appear in MSC-700. Figure 9 provides the TEM images of MC-700 and MSC700. It can be found that the core−shell architecture of MC700 was seriously damaged, which is due to the graphitization of RF shell and the reactions between the shell and magnetic core. As Figure 9b has shown, the magnetic cores of MSC-700 are no longer solid spheres and became a near hollow structure. At the same time, its inner silica shell also became unclear. These phenomena were caused by the reaction between magnetic core and silica shell. However, the outer carbon shell of MSC-700 remains intact, as well as its whole morphology, which implies that the structural stability of MSRF is superior to MRF. Catalytic Application of the Core−Shell Magnetic Nanocomposites. The prepared core−shell magnetic nanocomposites can be used as catalyst supports for catalytic applications. Through the deposition−precipitation process,9 active platinum nanoparticles can be loaded onto the magnetic composites.9 Figure 10 presents the TEM images of the obtained catalysts Pt/MSRF and Pt/MSC. It can be seen that both samples remain the well-defined core−shell architecture of supports with very tiny Pt nanoparticles (about 2 nm in size) decorating at the outer surface. The MSRF possesses a relatively high density of Pt nanoparticles to MSC, indicating the different Pt loading amounts of the two catalysts. The ICP analysis has shown that the Pt contents of Pt/MSRF and Pt/ MSC are 0.65% and 0.25%, respectively, which is in accordance

Figure 6. N2 physical adsorption/desorption isotherms of (a) MRF, (b) MSRF, (c) MC, (d) MSC.

Figure 7. TG curves of MRF (a, c) and MSRF (b, d) under air (real line) and nitrogen (broken line) atmosphere.

iron, iron carbide (Fe3C), and graphite. As to MSC-700, in addition to the Fe3O4, the diffraction peaks of Fe2SiO4 were observed. Mössbauer spectra (Figure 8, Table 1) further confirm the phase composition of MC-700 and MSC-700. The magnetic core of MC-700 is composed principally of iron and iron carbide. The very weak sextet is assigned to small amounts of magnetite. The doublet subspectrum in MSC-700 give IS 25114



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Figure 8. XRD patterns (left) and Mössbauer spectra (right) of (a) MC-700 and (b) MSC-700.

with TEM images. We attributed the higher Pt loading amount on MSRF to the more functional groups of its RF polymer shell (Supporting Information Figure S7), which is a benefit to the interaction between Pt nanoparticles and the support. A similar phenomenon can also be found for MRF and MC system (Table 2). For the small Pt particle size and high dispersion, the XRD patterns of Pt/MSRF and Pt/MSC do not exhibit the Ptcharacter diffraction peaks (Supporting Information Figure S8). The catalytic performances of obtained Pt-based catalysts were investigated by hydrogenation of nitroarenes to amines, and corresponding results are exhibited in Table 2. It can be found that both Pt/MSRF and Pt/MF are very active in hydrogenation of nitroarenes, with almost 100% conversion of reactants and TOF values more than 4000 h−1. In contrast, carbon-based Pt/MSC and Pt/MC show slightly lower activity, giving the TOF value in hydrogenation of nitrobenzene of 2341 and 3170 h−1, respectively. The higher activity of Pt/MSRF and Pt/MF may be related to the large amounts of functional groups that exist in RF polymer. The blank supports without Pt loading are absolutely inactive in hydrogenation of nitrobenzene, which means that both the RF (carbon) shell and iron oxide core have no catalytic contribution in this reaction. However, because of the existence of the magnetic core, the catalysts can be facilely separated from the reaction system with the help of a magnet (Figure 11). In addition, the recycling test of Pt/MSRF catalyst for the hydrogenation of nitrobenzene was also performed, and the result is shown in Figure 11. It can be seen that the excellent catalytic property of fresh Pt/MSRF was

Figure 9. TEM images of (a) MC-700 and (b) MSC-700.

Figure 10. TEM images of (a) Pt/MSRF and (b) Pt/MSC.

Table 2. Catalytic Performance of Various Magnetic Catalysts for Hydrogenation of Nitroarenes substrate nitrobenzene

nitrochlorobenzene

a

catalysts

Pt (wt %)

time (min)

conversion (%)

selectivity (%)

TOFa (h−1)

Pt/MSRF Pt/MSC Pt/MRF Pt/MC MSRF MSC MRF MC Pt/MSRF Pt/MSC

0.65 0.25 0.73 0.12 0 0 0 0 0.65 0.25

30 30 30 30 30 30 30 30 30 30

100 96.4 100 28.1

95.1 93.5 89.2 29.4

4502 2341 4008 3170

99.9 84.9

70 75.4

4502 1755

TOF values were calculated on the basis of total Pt contents using the molar amounts of converted reactants after initial 5 min of reaction. 25115



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separated. All these results indicate that the prepared core− shell magnetic carbonaceous composites have bright prospects in catalytic applications.

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ASSOCIATED CONTENT

S Supporting Information *

TEM images of magnetite core, yolk−shell magnetic carbon, MSRF prepared at different time scale and with thicker inner silica shell, Pt/MSRF after four reaction cycles and Pd/MSRF. Partial enlarged of XRD patterns of various magnetic materials, XRD patterns of Pt/MSRF and Pt/MSC. Mössbauer spectrum of magnetite core. FT-IR spectra of MSRF and MSC. This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Authors Figure 11. Recycling results of Pt/MSRF in hydrogenation of nitrobenzene (left) and its convenient separation with the help of external magnet (right). For recycling tests, the dosages of catalysts were decreased to 0.02 g, and the reaction time was 10 min; other conditions remained unchanged.

*E-mail: [email protected]. Phone: +86-411-84379159. Fax: +86-411-84685940. *E-mail: [email protected].

not retained during recycle test. An obvious decline of catalytic property began at the second cycle, and the third cycle only gave the conversion and selectivity of 29% and 21%, respectively. According to the ICP analysis, even after four reaction cycles, the Pt/MSRF catalyst still contains the Pt content of 0.61%, which is very close to the fresh one and indicates that very few Pt active sites were lost during the reaction. However, TEM image shows that the Pt nanoparticles tend to aggregate with each other after reaction (Supporting Information Figure S9), which may be one of the causes for decreased activity. In addition, after calcination at 200 °C under air, the catalytic performance of deactivated catalyst had been improved to a certain degree, which implied that the active sites covered by some organic species also lead to the deactivation of the catalyst.45 Anyway, the prepared magnetic nanocomposites are significant, especially for catalysis. Through a simple deposition−precipitation route, they can be loaded with active Pt nanoparticles to construct magnetic composite catalysts, as well as other active metallic nanoparticles, for example Pd (Supporting Information Figure S10), demonstrating the universality of the core−shell magnetic nanocomposites as catalyst supports. The constructed Pt-based catalysts are very active in hydrogenation of nitroarenes. The defective reusability of the catalysts might be improved by modification of the nanocomposite supports or use of other catalyst preparation process. Corresponding studies are in progress.

ACKNOWLEDGMENTS We are grateful to the National Natural Science Foundation of China (No. 21403220, 11079036, 11205160).

Notes

The authors declare no competing financial interest.

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CONCLUSION In summary, we prepared the well-defined core−shell magnetic RF polymer (MRF) and RF/silica (MSRF) composites with tunable structural parameters through the extended Stöber method. After thermal-treatment in N2 flow, the nonporous RF polymer shell of the composites converted to porous carbon, accompanied by the reduction of the magnetic core. The MSRF has superior structural stability to MRF for the existence of inner silica shell. It was demonstrated that the composites can be loaded with platinum nanoparticles in high dispersity and the constructed Pt-based catalysts exhibited high activity in hydrogenation of nitroarenes and can be magnetically 25116



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Synthesis, Characterization, and Catalytic Applications of CoreâShell

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