Article pubs.acs.org/Langmuir
Noncontact Synergistic Effect between Au Nanoparticles and the Fe2O3 Spindle Inside a Mesoporous Silica Shell as Studied by the Fenton-like Reaction Zhe Chen,† Yu Liang,† Jing Hao,‡ and Zhi-Min Cui*,‡ †
School of Environment and Chemical Engineering, North China Electric Power University, Beijing 102206, PR China Laboratory of Bio-Inspired Smart Interfacial Science and Technology of Ministry of Education, School of Chemistry and Environment, Beihang University, Beijing 100191, PR China
‡
S Supporting Information *
ABSTRACT: An Au-Fe2O3@mesoporous SiO2 nanoreactor with a multiyolks/shell structure was synthesized through a multistep method. In this nanoreactor, the spindle Fe2O3 and Au nanoparticles were inside the same mesoporous SiO2 shell as the yolks but in a noncontact manner. The noncontact synergistic effect between Au nanoparticles and the Fe2O3 spindle was studied with a Fenton-like reaction. The catalytic activity of the AuFe2O3@mesoporous SiO2 nanoreactor to the Fenton-like reaction for the degradation of organic dyes was dramatically enhanced by the noncontact synergistic effect.
1. INTRODUCTION The yolk/shell-structured materials with a void space between the cores and the outer shell are attracting more and more research interest for their potential applications in energy storage, drug delivery, catalysis, gas sensing, and biomedicine.1−5 The void space between the cores and the outer shells provided a microenvironment for the catalytic reaction, and thus one of the most important applications for the yolk/shellstructured material is as a nanoreactor for catalysis.6−9 When the yolk/shell-structured materials with noble metal nanoparticles inside the shell were used as the nanoreactor, they showed dramatically high catalytic activities in several important reactions, including but not limited to the reduction of nitrophenol, the oxidation of aerobic alcohol, the hydrogenation of olefin, the Fenton-like reaction, the Suzuki crosscoupling reaction, and so forth.10−15 In addition, the long-term stability of the catalyst was also enhanced by the yolk/shell structure because the specific architecture could suppress the aggregation of small noble metal nanocatalysts.16 For the construction of yolk/shell-structured materials, many methods such as the selective etching of the sacrificial template, calcination to remove the interlayer, soft templating, the Kirkendall effect, galvanic replacement, and Ostwald ripening have been developed.17−20 On the basis of the types of cores and shells, the yolk/shellstructured materials can be classified into subcategories including (i) single yolk/shell, (ii) multiyolks/single shell, (iii) single core/multishells, (iv) multiyolks/shells, and (v) multishells.17 Among them, the multiyolks/single shell © XXXX American Chemical Society
structure exhibits unique and tunable optical, magnetic, electrical, and catalytic properties resulting from the collective interaction between the cores of the same or different materials.21−24 For the catalytic application, the multiyolks/ single shell structure normally provides better catalytic performance than does the single-yolk/shell structure with the same core material because multiple core particles provided more available surface area and more active sites.25,26 For example, Pd nanoparticles@mesoporous silica and a Pd/ nitrogen-doped carbon@mesoporous silica nanoreactor with multiyolks/shell structure developed in our group exhibited extremely high activity to the Suzuki cross-coupling reaction.27,28 Until now, many multiyolks/single shell nanostructures have been reported; among them, the multiyolks were mostly noble metal nanoparticles whereas the outer shell was normally metal oxides, carbon, or silica with a hollow structure.5,23,28 More than one kind of core material inside the hollow mesoporous shell is promising in catalysis because one core material can act as a catalyst and the others can act as a cocatalyst. However, the synthesis of this type of multiyolks/ single shell structure was still challenging, and the synergistic effect between the cores was not fully studied. A synergistic effect arising between two or more agents that produces an effect greater than the sum of their individual effects commonly exists in chemistry and materials science. In catalysis, the Received: September 1, 2016 Revised: November 4, 2016 Published: November 8, 2016 A
DOI: 10.1021/acs.langmuir.6b03235 Langmuir XXXX, XXX, XXX−XXX
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centrifugation and washed with water four times to get the AuFe2O3@C composite. 2.5. Mesoporous SiO2 Coating. The Au-Fe2O3@C composite in the last step was dispersed in the solution containing 80 mL of H2O, 60 mL of ethanol, 0.28 g of CTAB, and 1.14 mL of NH3·H2O. After ultrasonication for 20 min, 400 μL of TEOS was added, and the mixture was vigorously stirred at room temperature for 6 h. The precipitate was harvested after centrifugation and washed with distilled water three times and with ethanol three times and then dried at 80 °C for 6 h to get the Fe2O3@C@SiO2 composite. The Fe2O3@C@SiO2 product was calcined directly in a muffle furnace at 400 °C, and the final product was planet−satellites such as Au-Fe2O3@mesoporous SiO2. 2.6. Preparation of Fe2O3@Mesoporous SiO2 and Au@ Mesoporous SiO2. In the control experiment, Fe2O3@mesoporous SiO2 was produced according to our previous report.34 The Au@ mesoporous SiO2 composite was obtained by acid etching. Typically, 200 mg of the Au-Fe2O3@mesoporous SiO2 composite was dispersed in 20 mL of an HCl (2 M) aqueous solution and stirred for 24 h. Then the solid was collected by centrifugation and washed with DI water four times. Finally, the product was dried at 80 °C overnight. 2.7. Characterization. The products were characterized by scanning electron microscopy (SEM, JEOL-6701) and transmission electron microscopy (TEM, JEOL 1010/2010). The powder XRD pattern was recorded on a Shimadzu XRD-7000 (Cu Kα radiation). Nitrogen adsorption−desorption isotherms were obtained on a Quantachrome Autosorb AS-1. A plasma atom emission spectrometer (ICPE-9000) was employed to reveal the precise chemical composition of the Au-Fe2O3@SiO2 composite. The UV−vis spectrophotometer used was a Shimadzu UV-2500. 2.8. Catalytic Properties Testing. In a typical run, the reaction suspension was prepared by adding a given amount of catalyst with equivalent Fe2O3 (10.0 mg of Fe2O3, 13.0 mg of Fe2O3@mesoporous SiO2, or 13.0 mg of Au-Fe2O3@mesoporous SiO2) to a 50 mL beaker containing 20 mL of an MB solution (50 ppm). Prior to reaction, the suspension was sonicated for 5 min and magnetically stirred in the dark for 60 min to establish the adsorption/desorption equilibrium. A Fenton-like reaction was initiated by adding a known concentration of H2O2 (1.2 mL, 30 wt %) to the solution. Samples were taken at a given time interval during the reaction. The sample was separated quickly by centrifugation, and 150 μL of the sample was diluted to 3 mL for further UV−vis detection. The catalyst was recovered from the solution by centrifugation and washed with water three times for the next run of the Fenton-like reaction.
synergistic effect between a catalyst and a cocatalyst always generates a more active catalyst.29,30 Several kinds of structures of catalysts such as doping, alloy, supported, and core/shell have been developed to facilitate the synergistic effect.30−33 In the above-mentioned structures, the catalyst and cocatalyst are in close contact with each other, resulting in a more active catalyst because of the change in surface energy, electronic structure, or oxidation state caused by the contact. The nature of the synergistic effect if the catalyst and cocatalyst do not contact each other was not clear because it was hard to produce the specific structure where the catalyst and cocatalyst were not in contact. The multiyolks/shell-structured materials give us opportunities to study the noncontact synergistic effect because the catalyst and cocatalyst could be confined in the same space in a noncontact manner in the yolk/shell structure. Herein, a multiyolks/single shell-structured Au-Fe2O3@ mesoporous SiO2 nanoreactor was synthesized through a multistep method. In this nanoreactor composite, two kinds of yolk materials, the spindle Fe2O3 and small Au nanoparticles, were inside the hollow mesoporous silica shell as yolks in a noncontact manner. The spindle Fe2O3 yolk was in the central space of the hollow mesoporous silica shell as a planet, and small Au nanaoparticles were on the inner wall of the mesoporous silica shell as satellites surrounded the planet but were not on the Fe2O3 spindle. The noncontact synergistic effect between the Fe2O3 spindle and Au nanoparticles in the Fenton-like reaction for the degradation of organic dyes was further studied.
2. EXPERIMENTAL SECTION 2.1. Materials and Reagents. Ferric chloride (FeCl3·6H2O), sodium dihydrogen phosphate (NaH2PO4·2H2O), glucose (C6H12O6), ethanol, tin(II) chloride dehydrate (SnCl2·2H2O), chloroauric acid (HAuCl4·2H2O), ammonium hydroxide (NH3·H2O, 25 wt %), methylene blue (MB), and sodium formate (HCOONa·2H2O) were purchased from Sinopharm Chemical Reagent Co., Ltd. Cetyltrimethylammonium bromide (CTAB) and tetraethyl orthosilicate (TEOS) were supplied by Alfa Aesar. Deionized (DI) water was obtained from a Milli-Q Element system. 2.2. Preparation of Spindle Fe2O3. A 75 mL aqueous solution containing 0.02 M FeCl3 and 0.45 mM NaH2PO4 was transferred to a 100 mL Teflon-lined autoclave and then held at 105 °C in an electric oven for 48 h. After the autoclave was cooled to room temperature, the spindle Fe2O3 particles were collected by centrifugation and washed with DI water. 2.3. Polymeric Carbon-Coated Fe2O3. Spindle Fe2O3 particles (200 mg) were dispersed in 10 mL of DI water by ultrasonication to form a suspension. Then, 1.0 g of glucose (C6H12O6) and 5 mL of ethanol were added to the solution with gentle stirring. The obtained suspension was transferred to a 40 mL Teflon-lined autoclave, which was then held at 190 °C in an electric oven for 12 h. The polymeric carbon-coated Fe2O3 particles (Fe2O3@C) were harvested by centrifugation, washed with DI water, and then dried at 110 °C in an oven. 2.4. Au Nanoparticle Loading. Au nanoparticles were loaded on the Fe2O3@C composite with the assistance of Sn2+. Typically, a 200 mg Fe2O3@C composite was dispersed in 20 mL of water. Then, 20 mL of an SnCl2 aqueous solution (0.15 g of SnCl2 in 20 mL of 0.02 M HCl) was added to the above solution. After 10 min of stirring, the solid was collected by centrifugation and washed with water four times. Then the solid was redispersed in 40 mL of DI water immediately by ultrasonication. A definite amount of HAuCl4 aqueous solution was added to the solution with stirring. After 10 min, 10 mL of an HCOONa solution (containing 0.2 g of HCOONa) was added and reacted for another 3 h. Finally, the solid was harvested by
3. RESULTS AND DISCUSSION The multiyolks/shell Au-Fe2O3@mesoporous SiO2 nanoreactor composite was produced in a designed multistep method as shown in Scheme 1. In the first step, the spindle Fe2O3 was synthesized according to ref 35. Then the spindle Fe2O3 was coated with polymeric carbon to form an Fe2O3@C composite through a hydrothermal method by reaction with glucose in a mixed water/ethanol solution at high temperature.36,37 In the next step, Au nanoparticles were loaded on the surface of polymeric-carbon-coated Fe2O3 with the assistance of Sn2+ ions to form an Au-Fe2O3@C composite.38 And then, the obtained Au-Fe2O3@C composite was dispersed in another water/ ethanol mixture solution containing the base (NH3·H2O), the surfactant (CTAB), and the silica source (TEOS) to react for 6 h. A mesoporous silica layer was formed on the surface of the Au-Fe2O3@C composite in this step. Finally, the obtained product was calcined at 400 °C in a muffle furnace to remove all organic materials such as the CTAB surfactant and the polymeric carbon layer to produce a planet−satellite yolks/ shell-structured Au-Fe2O3@mesoporous SiO2 nanoreactor. (The composition of the composite was 76.5 wt % Fe2O3, 33.0 wt % SiO2, and 0.5 wt % Au.) B
DOI: 10.1021/acs.langmuir.6b03235 Langmuir XXXX, XXX, XXX−XXX
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particles had a uniform size and a relatively rough surface as shown in Figure 1a. The spindle Fe2O3 has a length of about 200 nm and a width of about 50 nm. After the hydrothermal reaction with glucose, an even polymeric carbon layer was coated on the outside of the Fe2O3 spindles (Figure 1b). The surface of the Fe2O3@C composite was smoother than the bare spindle Fe2O3, and the TEM image showed that a thin, clean polymeric carbon layer was visible on the outside of the spindle Fe2O3 crystals. The polymeric carbon layer was quite even, with a thickness of about 10 nm. Then Au nanoparticles were loaded onto the surface of the Fe2O3@C composite to form the AuFe2O3@C composite. Small Au nanoparticles were apparent in the TEM image of the Au-Fe2O3@C composite (Figure 1c). The HRTEM image showed the lattice plane of Au nanoparticles, which proved that metallic Au was deposited on the surface of the Fe2O3@C composite. The polymeric carbon layer separated the Au nanoparticles from the inner Fe2O3 spindle. The Au-Fe2O3@C composite were further coated with another mesoporous SiO2 layer in the presence of surfactant CTAB. A TEM image showed that after the coating of mesoporous SiO2, the coating layer on the outside of the Fe2O3 spindles became thicker (Figure 1d). There was no apparent contrast between the outer mesoporous SiO2 layer and the inner polymeric carbon layer in the TEM image. However, the Au nanoparticles located on the surface of polymeric carbon become a significant identification for the outer mesoporous SiO2 layer and the inner polymeric carbon layer. The thickness of the polymeric carbon layer inside the Au nanoparticles was about 10 nm, which agrees well with the thickness of the carbon layer of the Fe2O3@C composite. The silica layer outside the Au nanoparticles had a thickness of about 30 nm. After calcination, the polymeric carbon layer between the Fe2O3 yolk and mesoporous silica shell was removed to form the void space (Figure 1e and Figure S1). The TEM image in Figure 1e shows that the Fe2O3 spindle yolk resided almost in the central space of the hollow spindle shell, leaving a void space between the Fe2O3 yolk and the silica shell, whereas small Au nanoparticles were located on the inside wall of the mesoporous silica shell. The position of the Au-Fe2O3 yolks was like that of the planet−satellites. The spindle Fe2O3 yolk was in the central space of the hollow mesoporous silica shell as a planet, and small Au nanoparticles were on the inner wall of the mesoporous silica shell as satellites surrounding the planet but not on the surface of spindle Fe2O3. The inset TEM image in Figure 1e shows visible mesoporous pores of the SiO2 shell. The thickness of the SiO2 shell was measured to be about 30 nm, which agreed well with the thickness of the silica layer of the Au-Fe2O3@C@SiO2 composite. No Au nanoparticles on the surface of the inner Fe2O3 spindle were observed in the inset of Figure 1e, demonstrating that Au nanoparticles and the Fe2O3 spindle were not in contact inside the shell. The X-ray diffraction (XRD) pattern of the spindle Fe2O3 and Au-Fe2O3@ meoporous SiO2 nanoreactor showed that they had the same crystal structure, which belongs to the α-Fe2O3 (Figure 1f). The location of the Au nanoparticles and Fe2O3 spindle in the mesoporous silica shell was further characterized by element mapping (Figure 2). The TEM image shows a separate Au-Fe2O3@mesoporous SiO2 composite particle with a broken shell (Figure 2a). The Fe2O3 spindle was in the center of the hollow mesoporous SiO2 shell, and the void space between the Fe2O3 spindle and the mesoporous SiO2 shell was apparent in the TEM image. The Au nanoparticles were
Scheme 1. Synthesis Procedure of a Planet−Satellites Yolks/ Shell-Structured Au-Fe2O3@Mesoporous SiO2 Nanoreactora
a Steps 1−4 denote the encapsulation of polymeric carbon by a hydrothermal reaction with glucose, the loading of Au nanoparticles, the encapsulation of mesoporous silica by the reaction with surfactant CTAB and silica source TEOS in a water/ethanol solution, and calcination to remove organic materials, respectively.
Figure 1 shows the TEM images of the products obtained in each manufacturing step. The as-synthesized spindle Fe2O3
Figure 1. TEM image of the spindle Fe2O3 (a), Fe2O3@C composite (b), Au-Fe Fe2O3@C composite (c), Au- Fe2O3@C@SiO2 composite (d), and Au-Fe2O3@mesoprous SiO2 nanoreactor (e). The inset in c is the HRTEM image of Au nanoparticles, and the inset in e is the TEM image with a higher magnification of the Fe2O3@mesoprous SiO2 nanoreactor, which shows the mesopores of the mesoporous silica shell. (f) XRD pattern of the mesoporous SiO2 shell, spindle Fe2O3, and Au-Fe2O3@mesoporous SiO2 nanoreactor. C
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The noncontact synergistic effect between Au nanoparticles and the Fe2O3 spindle inside the mesoporous SiO2 shell was studied via a Fenton-like reaction for the degradation of methylene blue (MB), an organic dye, at room temperature. At −60 min, the Au-Fe2O3@mesoporous SiO2 was dispersed in the MB solution as a catalyst under ultrasonication, and the mixture were stirred in the dark for 60 min to establish adsorption−desorption equilibrium. No acid or base was added to the above reaction solution to adjust the pH value. At 0 min, a definite amount of H2O2 was added to the above solution, and the Fenton-like reaction was started immediately. As shown in Figure 4, bare spindle Fe2O3 showed relatively low activity and about 10% of the MB was decolored in 120 min (Figure 4a). Compared to bare spindle Fe2O3, the yolk/shell-structured Fe2O3@mesoporous SiO2 (SEM and TEM images of Fe2O3@ mesoporous SiO2 in Figure S2) showed enhanced catalytic activity for the Fenton-like reaction. More than 40% of the MB was decolored by the yolks/shell-structured Fe2O3@mesoporous SiO2 nanoreactor in 120 min (Figure 4b). The enhanced activity was caused by the nanoreactor feature of the yolk/shellstructured Fe2O3@mesoporous SiO2, which agrees with our previous report.34 What is more important is that the catalytic activity of the multiyolks/shell-structured Au-Fe2O3@mesoporous SiO2 composite was even much greater than that of the yolk/shell-structured Fe2O3@mesoporous SiO2 nanoreactor. More than 90% of the MB was decolored in 60 min by the AuFe2O3@mesoporous SiO2 nanoreactor whereas almost full decoloration was achieved in 120 min (Figure 4d). Similar to the references, the kinetic data for the MB degradation in Figure 4 is close to a first-order rate equation.40 The rate constant κ was calculated to be 0.014, 0.11, 0.012, and 1.99 h−1 for the bare Fe2O3 spindle, Fe2O3@mesoporous SiO2 nanoreactor, Au@mesoporous SiO2 nanoreactor, and Au-Fe2O3@ mesoporous SiO2 nanoreactor, respectively. The degradation rate constant of the Au-Fe2O3@mesoporous SiO2 nanoreactor was dramatically higher than that of the other catalyst. In addition, the Au-Fe2O3@mesoporous SiO2 nanoreactor could be easily recovered by centrifugation and reused for the next run of reaction. No obvious decrease in activity was observed for the five reaction runs (Figure 4e). The dramatically enhanced activity of the Au-Fe2O3@ mesoporous SiO2 composite is surely related to their multiyolks/shell structure, especially with the specific structure of the inside yolks. Similar to our previous report, the MB molecules were adsorbed by the mesoporous shell from the bulk solution and were enriched in the void space of the nanoreactor, resulting in a higher reactant concentration in the void space. The difference was that small Au nanoparticles surrounding the spindle Fe2O3 core were introduced into the hollow mesoporous silica shell in the multiyolks/shellstructured Au-Fe2O3@mesoporous SiO2 composite. To clarify the role the Au nanoparticles, the spindle Fe2O3 core was removed by acid etching to produce the Au@mesoporous SiO2 composite (Figure S3). The Au@mesoporous SiO2 composite was further employed as a catalyst for the Fenton-like reaction under the same condition. The results showed that the adsorption of MB in Au@mesoporous SiO2 was almost the same as for the Au-Fe2O3@mesoporous SiO2 composite 0 min before the reaction. However, the Fenton-like activity of the Au@mesoporous SiO2 composite was much lower. The MB concentration was decreased slightly during the 120 min reaction time, indicating that Au nanoparticles inside the mesoporous silica shell alone were not active in the Fenton-like
Figure 2. TEM image of a separate planet−satellite Au-Fe2O3@ mesoporous SiO2 composite (a) and the corresponding element mapping of the same sample: (b) Si, (c) Au, and (d) Fe.
observed on the inner wall of the mesoporous SiO2 shell from the TEM image. Their corresponding element mapping showed that Si and Au had almost the same outline whereas the outline of Fe was smaller (Figure 2b−d). These features demonstrated that in the Au-Fe2O3@mesoporous SiO2 composite Au nanoparticles are not deposited on the Fe2O3 spindle but surround it in the noncontact location. The N2 adsorption−desorption isotherm of the planet− satellite yolks/shell-structured Au-Fe2O3@mesoporous SiO2 nanoreactor exhibited a typical type IV isotherm. The remarkably sharp capillary condensation step between 0.2 and 0.4 P/P0 indicates that the sample possessed a narrow size distribution (Figure 3).39 The pore size distribution calculated
Figure 3. Nitrogen adsorption−desorption isotherm and nonlocal density functional theory (NLDFT) pore size distribution (inset) of the planet−satellite yolks/shell-structured Au-Fe2O3@mesoporous SiO2 nanoreactor.
by nonlocal density functional theory (NLDFT) showed one intensive peak at 1.5 nm, which suggests that the pore size of the mesoporous silica shell was about 1.5 nm. Moreover, the calculated BET surface area of the Au-Fe2O3@mesoporous SiO2 nanoreactor was 498.6 m2/g. This large number was attributed to the mesoporous silica shell, which might play an important role in the catalytic reaction when the nanoreactor was employed as a catalyst. D
DOI: 10.1021/acs.langmuir.6b03235 Langmuir XXXX, XXX, XXX−XXX
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Figure 4. Fenton-like degradation of MB in the dark as a function of time using (a) bare spindle Fe2O3, (b) an Fe2O3@mesoporous SiO2 nanoreactor, (c) an Au@mesoporous SiO2 composite, and (d) an Au-Fe2O3@mesoporous SiO2 nanoreactor as catalysts. The Au@mesoporous SiO2 composite was obtained by etching the spindle Fe2O3 core of the Au-Fe2O3@mesoporous SiO2 nanoreactor. Reaction conditions: 0.5 g·L−1 equivalent Fe2O3, 50 mg·L−1 MB, 18 g·L−1 H2O2, room temperature. Ci denotes the initial concentration of MB. The reaction was started at 0 min. (e) Cycling performance of the multiyolks/shell-structured Au-Fe2O3@mesoporous SiO2 nanoreactor with respect to the Fenton-like degradation of MB (reaction time 60 min).
reaction (Figure 4c). Therefore, the enhanced activity of the Au-Fe2O3@mesoporous SiO2 composite was not attributed to the spindle Fe2O3 or the Au nanoparticles alone but to the collective interaction between the spindle Fe2O3 and the Au nanoparticles inside the mesoporous SiO2 shell. There was a noncontact synergistic effect between the Fe2O3 spindle and Au nanoparticles inside the mesoporous SiO2 shell to bring about much higher catalytic activity of the Au-Fe2O3@mesoporous SiO2 composite. When the Au nanoparticles were directly loaded onto the surface of metal oxides, a synergistic effect always emerged to produce better catalytic performance.41−43 However, the synergistic effect induced by the noncontact location of metal oxides and Au nanoparticles (such as the planet−satellites-like location in this report) was rarely reported. The hypothetical mechanism of the synergistic effect was that H2O2 was decomposed to ·OH radicals on the surface of the spindle Fe2O3 core and then the ·OH radicals degraded the MB molecules in the hollow space of the yolks/shell-structured nanoreactor. The existence of Au nanoparticles may resist the recombination of the ·OH radicals to keep them at high concentration. Thus, the synergistic effect between the Fe2O3 planet and Au satellites plus the yolk/mesoporous shell structure endow the Au-Fe2O3@mesoporous SiO2 composite with a much higher activity in the Fenton-like reaction.
metal oxides and Au nanoparticles inside the mesoporous SiO2 shell played the key role in the higher activity of the AuFe2O3@mesoporous SiO2 nanoreactor. The detailed and more accurate mechanism of the noncontact synergistic effect between planet−satellites such as Au-Fe2O3 yolks in the multiyolks/shell-structured Au-Fe2O3@mesoporous SiO2 nanoreactor in the Fenton-like reaction will be studied in the future.
4. CONCLUSIONS A multiyolks/shell-structured Au-Fe2O3@mesoporous SiO2 nanoreactor was fabricated through a multistep method. In the Au-Fe2O3@mesoporous SiO2 nanoreactor, Au nanoparticles and the Fe2O3 spindle were inside the same mesoporous SiO2 shell as yolks with a structure in which Au nanoparticles surrounded the Fe2O3 spindle but were not on it. The synergistic effect between the noncontact Au nanoparticles and the Fe2O3 spindle was further studied via the Fenton-like reaction as a model reaction. When used as a catalyst for the Fenton-like reaction leading to the degradation of MB, the multiyolks/shell-structured Au-Fe2O3@mesoporous SiO2 nanoreactor had much higher activity with respect to not only the Fe2O3@mesoporous SiO2 nanoreactor but also the Au nanoparticles@mesoporous SiO2 composite. The noncontact synergistic effect induced by the planet−satellite location of
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.langmuir.6b03235. SEM image of the multiyolks/shell-structured AuFe2O3@mesoporous SiO2 nanoreactor, SEM and TEM images of the yolk/shell-structured Fe2O3@mesoporous SiO2 nanoreactor, and TEM image of the Au@ mesoporous SiO2 composite (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Zhi-Min Cui: 0000-0002-5959-374X The authors declare no competing financial interest.
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ACKNOWLEDGMENTS We are grateful for financial support from the National Basic Research Program of China (MOST 2013CB933004 and 2014CB931802), the National Natural Science Foundation of China (NSFC 51302008 and 51502089), and the Fundamental Research Funds for the Central Universities (2016MS03).
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REFERENCES
(1) Li, G. D.; Tang, Z. Y. Noble metal nanoparticle@metal oxide core/yolk-shell nanostructures as catalysts: recent progress and perspective. Nanoscale 2014, 6, 3995−4011. (2) Park, J. C.; Song, H. Metal@Silica Yolk-Shell Nanostructures as Versatile Bifunctional Nanocatalysts. Nano Res. 2011, 4, 33−49.
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DOI: 10.1021/acs.langmuir.6b03235 Langmuir XXXX, XXX, XXX−XXX
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DOI: 10.1021/acs.langmuir.6b03235 Langmuir XXXX, XXX, XXX−XXX
