DOI:
10.1039/C4RA09076D
(Paper)
RSC Adv., 2014,
4, 56057-56062
One-pot gradient solvothermal synthesis of the Ag/Au–Fe3O4 composite nanoparticles and their applications
Received
22nd August 2014
, Accepted 13th October 2014
First published on 13th October 2014
Abstract
Herein, we report for the first time a simple and reliable one-pot methodology for the facile synthesis of the Ag/Au–Fe3O4 composite NPs. The as-prepared Ag/Au–Fe3O4 composite NPs have good crystallinity and saturation magnetization (38.021 emu g−1), resulting in their magnetic recycling. They have good catalytic activity and stability during the reduction of 4-nitrophenol in the presence of NaBH4. These Ag/Au–Fe3O4 composite NPs also have good antibacterial effect for Escherichia coli O1634. Excellent SERS was also shown for the detection of 2-nitroaniline using these Ag/Au–Fe3O4 composite NPs. The nanostructure makes the Ag/Au–Fe3O4 composite NPs stable and has a high-enhancement effect for Raman detection.
Introduction
In recent years, due to their special properties and functionality, magnetic composite nanoparticles (NPs) played a more and more important role in the fields of high technology such as information storage,1,2 color imaging,3 microwave absorption,4 medical diagnosis.5 Magnetic Fe3O4 NPs modified with a variety of functional modalities have been widely used in the fields such as molecular biology, cell separation and classification, targeted drug therapy. To date, a variety of synthesizing methods for magnetic composite Fe3O4 NPs have been developed such as chemical co-precipitation,6 inverse microemulsion,7 ultrasound irradiation,8 laser pyrolysis,9 thermal decomposition10–12 and solvothermal method.13 The nanosized Fe3O4@graphene yolk–shell nanoparticles were prepared by a hydrothermal method, which can be used for controlled anticancer drug delivery with magnetic and pH-sensitive properties.14 The Ag/Au–Fe3O4 composite NPs inherit from the three components excellent stability, solvent compatibility, low toxicity, catalytic activity, antibacterial property and magnetic separability, all of which would greatly enhance their potential application.15–24 For example, Au NPs have been found to play an important role in several catalytic processes, including low-temperature CO oxidation, reductive catalysis of chlorinated or nitrogenated hydrocarbons, and organic synthesis.25–33 Similarly, composites containing Ag NPs have good antibacterial properties and excellent surface enhanced Raman scattering (SERS).21–24,34–36 Thus, considerable effort has been devoted to developing Ag/Au–Fe3O4 composite NPs, which enables full use of their functions.
Up to now, many methods have been developed for the synthesis of Ag/Au–Fe3O4 composite NPs.34,37 Shen et al. prepared multifunctional Fe3O4@Ag/SiO2/Au core–shell microspheres that displayed long-range plasmon transfer of Ag to Au, leading to an enhanced Raman scattering.34 Wang et al. synthesized Fe3O4/Ag/Au composites for immunoassay based on surface plasmon resonance biosensor.36 The Fe3O4/Ag/Au composites have the advantages of three components of Fe3O4, Ag and Au NPs. However, all of these methods include multiple steps, which are often accompanied by some disadvantages, such as low efficiency, tedious processing steps, and use of a hazardous Fe precursor. It has been an important challenge to synthesize Ag/Au–Fe3O4 composite NPs with uniform stability and high surface activity by a simple method.
In this study, we use a simple and reliable one-pot methodology for the facile synthesis of the Ag/Au–Fe3O4 composite NPs. The as-prepared Ag/Au–Fe3O4 composite NPs have good crystallinity and saturation magnetization (38.021 emu g−1), resulting in good magnetic recycling. They show good catalytic activity during the reduction of 4-nitrophenol (4-NP) in the presence of NaBH4. The as-prepared Ag/Au–Fe3O4 composite NPs have excellent SERS for 2-nitroaniline (2-NA) solution. These Ag/Au–Fe3O4 composite NPs have good antibacterial effect for Escherichia coli O1634. These excellent properties endow the as-prepared Ag/Au–Fe3O4 composite NPs with various potential applications, such as magnetic hyperthermia, surface plasmon resonance biosensor.
Experimental
Chemicals
Ferric chloride hexahydrate (FeCl3·6H2O), sodium acetate (NaAc), trisodium citrate, sodium hydroxide (NaOH), 1,2-propylene glycol (PG), HAuCl4, silver nitrate (AgNO3), polyvinyl pyrrolidone (PVP), NaBH4, 4-nitrophenol (4-NP) and 2-nitroaniline (2-NA) were of analytical grade and purchased from Sinopharm Chemical Reagent Beijing Co., Ltd. All chemicals were used as received without any further purification.
Synthesis of the Ag/Au–Fe3O4 composite NPs by one-pot methodology
The Ag/Au–Fe3O4 composite NPs were prepared by a gradient solvothermal method. Firstly, 0.5 g FeCl3·6H2O were completely dissolved in 5 mL PG as recorded solution A. Then, 0.9 g NaAc and 0.15 g trisodium citrate were dissolved in 10 mL PG as recorded solution B. Secondly, solution A and solution B were mixed together under magnetic stirring, and their pH was adjusted to proper value. Third, 1.5 mL of the above solution and 13.5 mL PG were mixed together under magnetic stirring. Finally, 0.2 mL 0.5% PVP aqueous solution, 0.4 mL 2.0% HAuCl4 solution and 0.4 mL 1.0% AgNO3 solution were added into the abovementioned solution. The solution was sealed in a Teflon lined stainless steel autoclave. The reactor was maintained 150 °C for 1 h and then the temperature rose up to 200 °C and was maintained for 6 h. The heating rate from 150 °C to 200 °C was 1.67 °C min−1. After cooled to room temperature, the black products were separated magnetically. The obtained sediments were washed with ethanol and deionized water three times to eliminate organic and inorganic impurities and then dried at ambient temperature.
Application of the Ag/Au–Fe3O4 composite NPs for catalytic reduction of 4-NP
The reduction of 4-NP by the Ag/Au–Fe3O4 composite NPs in the presence of NaBH4 was carried out to examine the catalytic activity and recyclability of the Ag/Au–Fe3O4 composite NPs. Firstly, 4-NP and the Ag/Au–Fe3O4 composite NPs were dispersed in deionised water to form aqueous suspension and their concentrations were 18 mmol L−1 and 1 mg mL−1, respectively. Secondly, 34.0 mg NaBH4 were added into 6 mL deionised water and stirred uniformly at room temperature. Thirdly, 1 mL 4-NP solution and 1 mL the Ag/Au–Fe3O4 composite NPs were added into the abovementioned solution. The color of the mixture gradually changed from yellow to colorless. During the reaction, a quantitative portion of the mixture was taken at regular intervals and analysed by UV/Vis spectroscopy. After the reaction, the catalysts were magnetically recycled. As described above, catalysts were reused for the reduction of 4-NP time after time.
Application of the Ag/Au–Fe3O4 composite NPs for SERS of 2-NA
In order to examine SERS of the Ag/Au–Fe3O4 composite NPs, 2-NA solution was used for assay. Firstly, the Ag/Au–Fe3O4 composite NPs were dispersed in deionised water to form an aqueous suspension and its concentration was 1 mg mL−1. Every time 200 μL Ag/Au–Fe3O4 composite NPs suspension was placed on a glass slide, then dried at ambient temperature and set aside. Secondly, 2-NA was dispersed in deionised water to form aqueous solutions and their concentrations were 5 × 10−4, 5 × 10−5, 5 × 10−6 and 5 × 10−7 mol L−1. Thirdly, 25 μL different concentration solutions were placed on the glass slide and then SERS was tested. Finally, different carriers were also tested such as Au–Fe3O4 composite NPs, Ag–Fe3O4 composite NPs and glass slides.
Application of the Ag/Au–Fe3O4 composite NPs for antibacterial effect on Escherichia coli O1634
In order to test antibacterial effect of the Ag/Au–Fe3O4 composite NPs, culture of Escherichia coli O1634 was carried out. Firstly, 5.7 g fungi medium and 7.0 g nutrient agar were dispersed in 200 mL deionised water to form aqueous solutions. Secondly, the fungi medium solution was put into a high temperature sterilizer for sterilizing it for 30 min and then cooled in a super clean bench. Thirdly, Escherichia coli O1634 was inoculated in solutions, shaken well and then evenly poured into the fungus Petri dishes. They were punched by hole puncher after waiting for fungi medium solution condensation. Subsequently, 20 μL, 1, 1.25, 2.5, 5 mg mL−1 Ag/Au–Fe3O4 composite NPs solutions were poured in the holes. After waiting for 30 min, the fungus Petri dishes were turned over and cultivated for 24 h in a 4 °C oven. Finally, antibacterial effect of the Ag/Au–Fe3O4 composite NPs for Escherichia coli O1634 was measured.
Characterization
Transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) were performed on a JEOL JEM 2010F electron microscope operating at 200 kV. Energy-dispersive X-ray (EDX) spectroscopy measurements were obtained using a Hitachi S-4800 scanning electron field emission microscope. X-ray-powder diffraction patterns were accumulated on a Japan Rigaku D/max γA X-ray diffractometer by using graphite monochromatised Cu-Kα radiation (λ = 1.5418 Å). UV/Vis spectra were obtained by using a JASCO V-570 spectrophotometer at room temperature. The magnetic hysteresis loops of the samples were recorded on a Model PPMS-9 Physics Property Measurement System. The SERS spectra for the 532 nm probes were recorded using a Renishaw inVia spectrometer equipped with a microscope and a 50× objective (numerical aperture of 0.75).
Results and discussion
The X-ray diffraction (XRD) patterns of the synthesized Fe3O4, Au–Fe3O4, Ag–Fe3O4 and Ag/Au–Fe3O4 composite NPs are shown in Fig. 1. For all NPs, three diffraction peaks at 35.6°, 57.3° and 62.7° were indexed to the (311), (511) and (440) planes of the Fe3O4 cubic inverse spinel phase. As for Au–Fe3O4 composite NPs, four extra diffraction peaks at 38.2°, 44.2°, 64.4° and 77.6° were indexed to the (111), (200), (220) and (311) planes of the Au cubic phase. As for Ag–Fe3O4 composite NPs, four extra diffraction peaks at 38.1°, 44.1°, 64.3° and 77.5° were indexed to the (111), (200), (220) and (311) planes of the Ag cubic phase, whereas for Ag/Au–Fe3O4 composite NPs, four extra diffraction peaks at 38.3°, 44.3°, 64.6° and 77.7° were indexed to the (111), (200), (220) and (311) planes of the Ag and Au cubic phase. As shown in Fig. 1, Ag/Au–Fe3O4 composite NPs show good crystallinity. Therefore, Ag/Au–Fe3O4 composite NPs were successfully prepared, which was confirmed by the XRD pattern.
 |
| Fig. 1 XRD patterns of the Fe3O4 NPs, Au–Fe3O4 composite NPs, Ag–Fe3O4 composite NPs and Ag/Au–Fe3O4 composite NPs. | |
In order to analyse the morphology of the synthesized Ag/Au–Fe3O4 composite NPs, the observations by transmission electron microscopy (TEM) were carried out. Fig. 2 shows the TEM images of the prepared Ag/Au–Fe3O4 composite NPs, together with Fe3O4 NPs, Au–Fe3O4 composite NPs and Ag–Fe3O4 composite NPs for comparison. The as-prepared Ag/Au–Fe3O4 composite NPs display a narrow size distribution. Fig. 3 shows the high resolution transmission electron microscopy (HR-TEM) images of the prepared Fe3O4 NPs, Au–Fe3O4 composite NPs, Ag–Fe3O4 composite NPs and Ag/Au–Fe3O4 composite NPs. As shown in Fig. 3d, the interplanar spacings are 0.204, 0.235, 0.253 and 0.296 nm, which are consistent with the (200) plane of the Ag cubic phase, the (111) plane of the Au cubic phase, the (311) plane and (220) plane of the Fe3O4 cubic inverse spinel phase, respectively. The existence of both Au and Ag in the Ag/Au–Fe3O4 composite NPs is confirmed by the HR-TEM images. For Fe3O4 NPs, the interplanar spacings are 0.209 and 0.296 nm, which are consistent with the (400) plane and (311) plane of the Fe3O4 cubic inverse spinel phase, respectively. Similarly, both the Au cubic phase and the Fe3O4 cubic inverse spinel phase are found in the Au–Fe3O4 composite NPs. In the HR-TEM image of Ag–Fe3O4 composite NPs, the Ag cubic phase and the Fe3O4 cubic inverse spinel phase are observed. Through the abovementioned analysis of experimental data, the preparation of the Ag/Au–Fe3O4 composite NPs is achieved by the one-pot gradient solvothermal process.
 |
| Fig. 2 TEM images of (a) Fe3O4 NPs, (b) Au–Fe3O4 composite NPs, (c) Ag–Fe3O4 composite NPs and (d) Ag/Au–Fe3O4 composite NPs. | |
 |
| Fig. 3 HR-TEM images of (a) Fe3O4 NPs, (b) Au–Fe3O4 composite NPs, (c) Ag–Fe3O4 composite NPs and (d) Ag/Au–Fe3O4 composite NPs. | |
Typical energy dispersive X-ray spectra (EDS) of the Au–Fe3O4 composite NPs, the Ag–Fe3O4 composite NPs and Ag/Au–Fe3O4 composite NPs are shown in Fig. 4. In Fig. 4a, it indicates the existence of Au, Fe and O in the Au–Fe3O4 composite NPs. The amount of Au NPs in the Au–Fe3O4 composite NPs is tested by EDS, which is 16.90%. Fig. 4b shows the existence of Ag, Fe and O in the Ag–Fe3O4 composite NPs. Similarly, the amount of Ag NPs in the Ag–Fe3O4 composite NPs is 25.37%. As shown in Fig. 4c, the amount of Au and Ag NPs in the Ag/Au–Fe3O4 composite NPs is 7.20% and 23.25%, respectively. Therefore, the existence of Au and Ag in the Ag/Au–Fe3O4 composite NPs was also confirmed by the EDS.
 |
| Fig. 4 EDX spectrum of (a) Au–Fe3O4 composite NPs, (b) Ag–Fe3O4 composite NPs and (c) Ag/Au–Fe3O4 composite NPs. | |
As shown in Fig. 5, the magnetic properties of the synthesized Fe3O4 NPs, Au–Fe3O4 composite NPs, Ag–Fe3O4 composite NPs and Ag/Au–Fe3O4 composite NPs were measured by vibrating sample magnetometer (VSM) at room temperature. The magnetization of the synthesized Fe3O4 NPs, Au–Fe3O4 composite NPs, Ag–Fe3O4 composite NPs and Ag/Au–Fe3O4 composite NPs, which were recorded at 2 T are 58.558, 37.571, 49.150 and 38.021 emu g−1, respectively. Due to the good saturation magnetization, the Au–Fe3O4 composite NPs can be quickly magnetically recycled.
 |
| Fig. 5 Magnetic hysteresis curve at room temperature of the Fe3O4 NPs, Au–Fe3O4 composite NPs, Ag–Fe3O4 composite NPs and Ag/Au–Fe3O4 composite NPs. | |
The catalytic performance of the Ag/Au–Fe3O4 composite NPs was investigated using the reduction of 4-NP to 4-aminophenol (4-AP) in the presence of NaBH4 as a model reaction. Fig. 6 showed the typical UV/Visible absorption spectra of 4-NP catalyzed by the Fe3O4 NPs, Ag–Fe3O4 composite NPs and Ag/Au–Fe3O4 composite NPs. After adding the Ag/Au–Fe3O4 composite NPs, the peak intensity at 400 nm decreased with concomitant increase in peaks of 4-AP at 230 and 300 nm, as shown in Fig. 6c. The disappearance of the peak at 400 nm indicated the accomplishment of the reaction within 10 min, and the color of the mixture gradually changed from yellow to colorless. Fe3O4 NPs didn't have any catalytic performance within 2 h, as shown in Fig. 6a. The same amount of 4-AP was catalyzed by the Ag–Fe3O4 composite NPs in Fig. 6b. The reduction of 4-NP catalyzed by the Ag–Fe3O4 composite NPs needed 30 min. The Ag/Au–Fe3O4 composite NPs have more excellent catalytic performance than Ag–Fe3O4 composite NPs. Compared with the previously reported methods,38,39 Ag/Au–Fe3O4 composite NPs show better catalytic performance. Because the reusability of the catalyst is an important issue for practical applications, the reusability of the Ag/Au–Fe3O4 composite NPs was further investigated. The Ag/Au–Fe3O4 composite NPs were recycled by a magnet. As shown in the Fig. 6d, it was noted that the Ag/Au–Fe3O4 composite NPs showed a complete conversion under each cycle. Our Ag/Au–Fe3O4 composite NPs can be reused for six cycles, which suggests that the Ag/Au–Fe3O4 composite NPs are not deactivated during the catalytic cycle processes. Through the abovementioned analysis of experimental data, the synthesized Ag/Au–Fe3O4 composite NPs have excellent catalytic activity for the reduction of 4-NP.
 |
| Fig. 6 UV/Vis absorption spectra of 4-NP catalyzed by (a) Fe3O4 NPs, (b) Ag–Fe3O4 composite NPs and (c) Ag/Au–Fe3O4 composite NPs; (d) catalytically recyclable reduction of 4-NP by the Ag/Au–Fe3O4 composite NPs in the presence of NaBH4. | |
In order to illustrate multifunctional properties of the synthesized Ag/Au–Fe3O4 composite NPs, SERS spectra of different amounts of 2-NA on the composite NPs were carried out as shown in Fig. 7a. With the increase of 2-NA solution concentration, SERS effect of the synthesized Ag/Au–Fe3O4 composite NPs was more significant. The linear range of solution concentration was 5 × 10−4 to 5 × 10−7 mol L−1. Similarly, SERS spectra of 2-NA on the Ag/Au–Fe3O4 composite NPs, Ag–Fe3O4 composite NPs, Au–Fe3O4 composite NPs and glass were carried out, as shown in Fig. 7b. The Ag/Au–Fe3O4 composite NPs have more SERS effect than both Au–Fe3O4 composite NPs and Ag–Fe3O4 composite NPs. Therefore, the synthesized Ag/Au–Fe3O4 composite NPs have excellent SERS effect for 2-NA solution.
 |
| Fig. 7 (a) SERS spectra of different amounts (5 × 10−4 to 5 × 10−7 mol L−1) of 2-NA on the Ag/Au–Fe3O4 composite NPs; (b) SERS spectra of 2-NA on the Ag/Au–Fe3O4 composite NPs, Ag–Fe3O4 composite NPs, Au–Fe3O4 composite NPs and glass. | |
In order to further illustrate multifunctional properties of the synthesized Ag/Au–Fe3O4 composite NPs, antibacterial effect by the different concentrations composite NPs for Escherichia coli O1634 were carried out, as shown in Fig. 8. The Ag/Au–Fe3O4 composite NPs had clear bacteriostatic ring for Escherichia coli O1634. The average size of antibacterial effect of the composite NPs for Escherichia coli O1634 is as shown in Table 1. Although the concentrations of Ag/Au–Fe3O4 composite NPs were 1.0, 1.25, 2.5 and 5 mg L−1, the average sizes of antibacterial effect of the composite NPs for Escherichia coli O1634 were 6.9, 8.6, 9.1 and 9.5 mm. Therefore, the synthesized Ag/Au–Fe3O4 composite NPs have excellent antibacterial effect for Escherichia coli O1634.
 |
| Fig. 8 Antibacterial effect on the (a) 5.0 mg L−1, (b) 2.5 mg L−1, (c) 1.25 mg L−1, (d) 1.0 mg L−1 Ag/Au–Fe3O4 composite NPs for Escherichia coli O1634. | |
Table 1 The average size of antibacterial effect of the Ag/Au–Fe3O4 composite NPs for Escherichia coli O1634
Number |
The concentrations of Ag/Au–Fe3O4 composite NPs (mg mL−1) |
The average size (mm) |
a |
5.0 |
9.5 |
b |
2.5 |
9.1 |
c |
1.25 |
8.6 |
d |
1.0 |
6.9 |
Conclusions
In summary, we have successfully synthesized the Ag/Au–Fe3O4 composite NPs by one-pot method, which is based on a gradient solvothermal route. The as-prepared Ag/Au–Fe3O4 composite NPs have good crystallinity and saturation magnetization (38.021 emu g−1), resulting in their magnetic recycling. They have good catalytic activity during the reduction of 4-NP in the presence of NaBH4. The as-prepared Ag/Au–Fe3O4 composite NPs have excellent SERS for 2-NA solution. These Ag/Au–Fe3O4 composite NPs have good antibacterial effect for Escherichia coli O1634. This work might successfully synthesize similar composite structure by one-pot method on a large-scale and broaden practical applications of this kind of composite nanostructured materials.
Acknowledgements
The supports of the National Natural Science Foundation of China (project no. 61171049, 51273122, 61178035 and 81171454) and the Research Fund for the Distinguished Young Scholars of Sichuan University (2011SCU04B21) are acknowledged with gratitude.
Notes and references
- A. Chakraborty, J. Magn. Magn. Mater., 1999, 204, 57 CrossRef CAS.
- Y. Wang, L. Zhang, X. Gao, L. Mao, Y. Hu and X. Lou, Small, 2014, 10, 2815 CrossRef CAS PubMed.
- F. Ziolo, Developer composition containing superparamagnetic polymers, US Pat., 4474866, 02-10-1984.
- J. Liu, J. Cheng, R. Che, J. Xu, M. Liu and Z. Liu, ACS Appl. Mater. Interfaces, 2013, 5, 2503 CAS.
- L. Josephson, C. H. Tung, A. Moore and R. Weissleder, Bioconjugate Chem., 1999, 10, 186 CrossRef CAS PubMed.
- N. Li, G. Huang, X. Shen, H. Xiao and S. Fu, J. Mater. Chem. C, 2013, 1, 4879 RSC.
- S. Mann, H. C. Sparks and R. G. Board, Advances in microbial physiology, Elsevier, Amsterdam, 1990, pp. 125–181 Search PubMed.
- J. Safari and Z. Zarnegar, RSC Adv., 2013, 3, 17962 RSC.
- S. Veintemillas-Verdaguer, O. Bomatí-Miguel and M. P. Morales, Scr. Mater., 2002, 47, 589 CrossRef CAS.
- S. Capone, M. G. Manera, A. Taurino, P. Siciliano, R. Rella, S. Luby, M. Benkovicova, P. Siffalovic and E. Majkova, Langmuir, 2014, 30, 1190 CrossRef CAS PubMed.
- J. Park, E. Lee, N. M. Hwang, M. Kang, S. C. Kim, Y. Hwang, J. G. Park, H. J. Noh, J. Y. Kim, J. H. Park and T. Hyeon, Angew. Chem., Int. Ed., 2005, 44, 2872 CrossRef CAS PubMed.
- J. Park, K. An, Y. Hwang, J. G. Park, H. J. Noh, J. Y. Kim, J. H. Park, N. M. Hwang and T. Hyeon, Nat. Mater., 2004, 3, 891 CrossRef CAS PubMed.
- S. B. Cho, J. S. Noh, S. J. Park, D. Y. Lim and S. H. Choi, J. Mater. Sci., 2007, 42, 4877 CrossRef CAS.
- S. Li, J. Zheng, D. Chen, Y. Wu, W. Zhang, F. Zheng, J. Cao, H. Ma and Y. Liu, Nanoscale, 2013, 5, 11718 RSC.
- E. D. Smolensky, M. C. Neary, Y. Zhou, T. S. Berquo and V. C. Pierre, Chem. Commun., 2011, 47, 2149 RSC.
- M. A. Nash, P. Yager, A. S. Hoffman and P. S. Stayton, Bioconjugate Chem., 2010, 21, 2197 CrossRef CAS PubMed.
- W. Liang, W. Yi, Y. Li, Z. Zhang, M. Yang, C. Hu and A. Chen, Mater. Lett., 2010, 64, 2616 CrossRef CAS PubMed.
- X. Lian, J. Jin, J. Tian and H. Zhao, ACS Appl. Mater. Interfaces, 2010, 2, 2261 CAS.
- J. S. Beveridge, M. B. Buck, J. F. Bondi, R. Misra, P. Schiffer, R. E. Schaak and M. E. Williams, Angew. Chem., Int. Ed., 2011, 50, 1 CrossRef PubMed.
- X. Meng, B. Li, X. Ren, L. Tan, Z. Huang and F. Tang, J. Mater. Chem. A, 2013, 1, 10513 CAS.
- T. J. Wood, G. A. Hurst, W. C. E. Schofield, R. L. Thompson, G. Oswald, J. S. O. Evans, G. J. Sharples, C. Pearson, M. C. Petty and J. P. S. Badyal, J. Mater. Chem., 2012, 22, 3859 RSC.
- J. Liu, Z. Zhao, H. Feng and F. Cui, J. Mater. Chem., 2012, 22, 13891 RSC.
- P. Gong, H. Li, X. He, K. Wang, J. Hu, W. Tan, S. Zhang and X. Yang, Nanotechnology, 2007, 18, 1 Search PubMed.
- B. Chudasama, A. K. Vala, N. Andhariya, R. V. Upadhyay and R. V. Mehta, Nano Res., 2009, 2, 955 CrossRef CAS.
- I. X. Green, W. Tang, M. Neurock and J. T. Yates Jr, Science, 2011, 333, 736 CrossRef CAS PubMed.
- A. Wittstock, V. Zielasek, J. Biener, C. M. Friend and M. Bäumer, Science, 2010, 327, 319 CrossRef CAS PubMed.
- D. I. Enache, J. K. Edwards, P. Landon, B. Solsona-Espriu, A. F. Carley, A. A. Herzing, M. Watanabe, C. J. Kiely, D. W. Knight and G. J. Hutchings, Science, 2006, 311, 362 CrossRef CAS PubMed.
- M. Haruta, N. Yamada, T. Kobayashi and S. J. Iijima, Catalysis, 1989, 115, 301 CrossRef CAS.
- A. Orlov, D. A. Jefferson, N. Macleod and R. M. Lambert, Catal. Lett., 2004, 92, 41 CrossRef CAS.
- S. Praharaj, S. Nath, S. K. Ghosh, S. Kundu and T. Pal, Langmuir, 2004, 20, 9889 CrossRef CAS PubMed.
- J. Zeng, Q. Zhang, J. Chen and Y. Xia, Nano Lett., 2010, 10, 30 CrossRef CAS PubMed.
- J. Gong and C. B. Mullins, Acc. Chem. Res., 2009, 42, 1063 CrossRef CAS PubMed.
- G. J. Hutchings, Top. Catal., 2008, 48, 55 CrossRef CAS.
- J. Shen, Y. Zhu, X. Yang, J. Zong and C. Li, Langmuir, 2013, 29, 690 CrossRef CAS PubMed.
- M. Fan, F. J. Lai, H. L. Chou, W. T. Lu, B. J. Hwang and A. G. Brolo, Chem. Sci., 2013, 4, 509 RSC.
- J. Wang, D. Song, H. Zhang, J. Zhang, Y. Jin, H. Zhang, H. Zhou and Y. Sun, Colloids Surf., B, 2013, 102, 165 CrossRef CAS PubMed.
- Z. Xu, Y. Hou and S. Sun, J. Am. Chem. Soc., 2007, 129, 8698 CrossRef CAS PubMed.
- L. Li, E. S. G. Choo, X. Tang, J. Ding and J. Xue, Acta Mater., 2010, 58, 3825 CrossRef CAS PubMed.
- Q. An, M. Yu, Y. Zhang, W. Ma, J. Guo and C. Wang, J. Phys. Chem. C, 2012, 116, 22432 CAS.
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