Magnetic Core/Shell Fe3O4/Au and Fe3O4/Au/Ag Nanoparticles with ...
Supporting Information
Magnetic Core/Shell Fe3O4/Au and Fe3O4/Au/Ag Nanoparticles with Tunable Plasmonic Properties Zhichuan Xu, Yanglong Hou, Shouheng Sun* Department of Chemistry, Brown University, Providence, Rhode Island 02912
[email protected] 1. Experimental Section 1.1 Synthesis of 10 nm Fe3O4 nanoparticles (i) Iron-oleate was prepared according to the reported method (Ref. 11 in article). 4 mmol of iron-oleate was dissolved in a mixture of oleylamine and oleic acid (volume ratio 3:1) at 120°C for 1 h. Then the dark solution was heated up to 200°C for 2 h. During the heating, nitrogen gas was gently blown through the reaction system to remove the trace hydrate vapor. After that, the solution was further heated up to 300°C and kept at this temperature for 2 h. The Fe3O4 nanoparticles were precipitated by adding ethanol into the solution and washed with hexane and ethanol for several times. The as-prepared Fe3O4 nanoparticles were dispersed in hexane. 1.2 Synthesis of Au coated Fe3O4 nanoparticles (ii) In a typical coating experiment, 2.5 mmol of HAuCl4 · 3H2O was dissolved in 10 ml chloroform and 1 mmol oleylamine. Another 10 ml chloroform solution containing 40 mg 10 nm Fe3O4 nanoparticles and 2 mmol oleylamine was prepared. Under stirring, the HAuCl4 solution was added dropwise into the Fe3O4 nanoparticle solution. After 20 h, the Au coated Fe3O4 nanoparticles were precipitated by adding ethanol and washed by hexane and ethanol for several times. The Au coated Fe3O4 nanoparticles were capped with oleylamine and dispersed in hexane. In a high concentration, the core/shell nanoparticles could form a magnetic fluid as shown in Figure S1.
Figure S1. Photograph of a hexane solution of Au coated Fe3O4 nanoparticles in the (a) absence and (b) presence of a magnet.
1.3 Preparation of water-soluble Au coated Fe3O4 nanoparticles (iii) The Au coated Fe3O4 nanoparticles were further washed with a mixture of hexane and ethanol (volume ratio 1:1) for several times to remove the excess oleylamine from the surface of the core/shell nanoparticles. The core/shell nanoparticles then were dried under vacuum and added into an aqueous solution containing 0.1 M CTAB and 0.1 mM sodium citrate. After 10 min sonication, the core/shell nanoparticles dissolved completely and formed a light pink solution. S1
Figure S2 shows the TEM images and photograph of 10 nm bare Fe3O4 nanoparticles (i), the diluted core/shell nanoparticles in hexane (ii) and water-soluble core/shell nanoparticles (iii).
Figure S2. TEM images (left) and photograph (right) of the diluted hexane solution of bare Fe3O4 nanoparticles (i), the diluted core/shell nanoparticles in hexane (ii) and water-soluble core/shell nanoparticles (iii).
1.4 Synthesis of Fe3O4/Au and Fe3O4/Au/Ag nanoparticles from (iii) 1.4.1 Deposition of Au on core/shell nanoparticles 25 ml water dispersion of the core/shell Fe3O4/Au nanoparticles (iii) (~5 mg) was mixed with 15 ml aqueous solution containing 0.1 M CTAB, 0.5 mM HAuCl4 and 1 mM ascorbic acid under stirring. After 6 h, the nanoparticles were separated by centrifuging at 8000 rpm and washed with deionized water. This procedure deposited another ~0.5 nm Au on the surface of core/shell nanoparticles (iii), giving 1.5 nm Au coated Fe3O4 nanoparticles. To deposit an extra ~0.5 nm Au on the 1.5 nm Au coated Fe3O4 nanoparticles, the nanoparticles were re-dispersed in 25 ml 0.1 M CTAB aqueous solution and then mixed with 25 ml solution containing 0.1 M CTAB, 0.5 mM HAuCl4 and 1 mM ascorbic acid and mixture stirred for 6 h. The 2 nm Au coated nanoparticles were separated by centrifuging and washed with deionized water To deposit an extra ~0.5 nm Au on the 2 nm Au coated nanoparticles, the nanoparticles were re-dispersed into 25 ml 0.1 M CTAB solution and mixed with 30 ml solution containing 0.1 M CTAB, 0.5 mM HAuCl4 and 1 mM ascorbic acid and stirred for 6 h. The ~2.5 nm Au coated nanoparticles were separated by centrifuging and washed with deionized water. To make 3.5 nm Au coated Fe3O4 nanoparticles, the 2.5 nm Au coated Fe3O4 nanoparticles were re-dispersed with 25 ml 0.1 M CTAB solution and mixed with 40 ml solution containing 0.1 M CTAB, 0.5 mM HAuCl4 and 1 mM ascorbic acid and stirred for 6 h. 1.4.2 Deposition of Ag on core/shell nanoparticles (iii) To deposit ~1 nm Ag on the surface of core/shell nanoparticles (iii), 25 ml water dispersion core/shell Fe3O4/Au nanoparticles (~5 mg) were mixed with 15 ml aqueous solutions containing 0.1 M CTAB, 1 mM AgNO3 and 1 mM ascorbic acid under stirring and then 0.1 ml 0.01 M NaOH solution was added into the mixed solution. After 4 h, the ~ 1 nm Ag coated core/shell nanoparticles were separated by centrifuging at 8000 rpm and washed with deionized water. They were re-dispersed into 25 ml 0.1 M CTAB solution and mixed with 15 ml AgNO3 solution under stirring. Then, 0.1 ml 0.01 M NaOH was added into the solution to produce ~ 1.5 nm Ag coated nanoparticles. The ~1.5 nm Ag coated nanoparticles were centrifuged at 8000 rpm and washed with deionized water. They were further dissolved into 25 ml 0.1 M CTAB solution and mixed with 20 ml AgNO3 solution followed by adding 0.1 ml 0.01 M NaOH solution. The ~2 nm Ag
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coated nanoparticles were centrifuged at 8000 rpm and washed with deionized water. 1.5 Characterizations The TEM study was carried out on a Philips EM 420 transmission electron microscope at 120kV. The UV-vis absorption spectra were recorded by a PerkinElmer Lambda 35 UV/Vis spectrometer. The magnetic properties of samples were examined by a Lakeshore 7404 high sensitivity vibrating sample magnetometer (VSM) with fields up to 1.5 tesla at room temperature. X-ray diffraction patterns were collected on a Bruker AXS D8-Advanced diffractometer with Cu Ka radiation (λ = 1.5418 Å). 2. TEM images of the Fe3O4/Au and Fe3O4/Au/Ag nanoparticles
Figure S3. HRTEM of a single Fe3O4/Au nanoparticle (iii) showing ~1 nm coating of Au on the surface of Fe3O4 core.
Figure S4. TEM images of core/shell Fe3O4/noble-metal nanoparticles with (a) ~1 nm, (b) ~1.5 nm, (c) ~2 nm, (d) ~2.5 nm, (e) ~3.5 nm of Au, and (f) ~1 nm, (g) ~1.5 nm, (h) ~2 nm of Ag.
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3. Hysteresis loops of core/shell Fe3O4/Au nanoparticles
80
(A)
60
Moment (emu/g)
40 20
(F)
0 -20 -40 -60 -80
-15
-10
-5
0
5
10
15
H (kOe)
Figure S5. Hysteresis loops of (A) Fe3O4 nanoparticles and core/shell Fe3O4/Au nanoparticles with different Au shell thickness at (B) ~1, (C) ~1.5 (D) ~2, (E) ~2.5, and (F) ~3.5 nm.
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Magnetic Core/Shell Fe3O4/Au and Fe3O4/Au/Ag Nanoparticles with Tunable Plasmonic Properties Zhichuan Xu, Yanglong Hou, Shouheng Sun* Department of Chemistry, Brown University, Providence, Rhode Island 02912
[email protected] 1. Experimental Section 1.1 Synthesis of 10 nm Fe3O4 nanoparticles (i) Iron-oleate was prepared according to the reported method (Ref. 11 in article). 4 mmol of iron-oleate was dissolved in a mixture of oleylamine and oleic acid (volume ratio 3:1) at 120°C for 1 h. Then the dark solution was heated up to 200°C for 2 h. During the heating, nitrogen gas was gently blown through the reaction system to remove the trace hydrate vapor. After that, the solution was further heated up to 300°C and kept at this temperature for 2 h. The Fe3O4 nanoparticles were precipitated by adding ethanol into the solution and washed with hexane and ethanol for several times. The as-prepared Fe3O4 nanoparticles were dispersed in hexane. 1.2 Synthesis of Au coated Fe3O4 nanoparticles (ii) In a typical coating experiment, 2.5 mmol of HAuCl4 · 3H2O was dissolved in 10 ml chloroform and 1 mmol oleylamine. Another 10 ml chloroform solution containing 40 mg 10 nm Fe3O4 nanoparticles and 2 mmol oleylamine was prepared. Under stirring, the HAuCl4 solution was added dropwise into the Fe3O4 nanoparticle solution. After 20 h, the Au coated Fe3O4 nanoparticles were precipitated by adding ethanol and washed by hexane and ethanol for several times. The Au coated Fe3O4 nanoparticles were capped with oleylamine and dispersed in hexane. In a high concentration, the core/shell nanoparticles could form a magnetic fluid as shown in Figure S1.
Figure S1. Photograph of a hexane solution of Au coated Fe3O4 nanoparticles in the (a) absence and (b) presence of a magnet.
1.3 Preparation of water-soluble Au coated Fe3O4 nanoparticles (iii) The Au coated Fe3O4 nanoparticles were further washed with a mixture of hexane and ethanol (volume ratio 1:1) for several times to remove the excess oleylamine from the surface of the core/shell nanoparticles. The core/shell nanoparticles then were dried under vacuum and added into an aqueous solution containing 0.1 M CTAB and 0.1 mM sodium citrate. After 10 min sonication, the core/shell nanoparticles dissolved completely and formed a light pink solution. S1
Figure S2 shows the TEM images and photograph of 10 nm bare Fe3O4 nanoparticles (i), the diluted core/shell nanoparticles in hexane (ii) and water-soluble core/shell nanoparticles (iii).
Figure S2. TEM images (left) and photograph (right) of the diluted hexane solution of bare Fe3O4 nanoparticles (i), the diluted core/shell nanoparticles in hexane (ii) and water-soluble core/shell nanoparticles (iii).
1.4 Synthesis of Fe3O4/Au and Fe3O4/Au/Ag nanoparticles from (iii) 1.4.1 Deposition of Au on core/shell nanoparticles 25 ml water dispersion of the core/shell Fe3O4/Au nanoparticles (iii) (~5 mg) was mixed with 15 ml aqueous solution containing 0.1 M CTAB, 0.5 mM HAuCl4 and 1 mM ascorbic acid under stirring. After 6 h, the nanoparticles were separated by centrifuging at 8000 rpm and washed with deionized water. This procedure deposited another ~0.5 nm Au on the surface of core/shell nanoparticles (iii), giving 1.5 nm Au coated Fe3O4 nanoparticles. To deposit an extra ~0.5 nm Au on the 1.5 nm Au coated Fe3O4 nanoparticles, the nanoparticles were re-dispersed in 25 ml 0.1 M CTAB aqueous solution and then mixed with 25 ml solution containing 0.1 M CTAB, 0.5 mM HAuCl4 and 1 mM ascorbic acid and mixture stirred for 6 h. The 2 nm Au coated nanoparticles were separated by centrifuging and washed with deionized water To deposit an extra ~0.5 nm Au on the 2 nm Au coated nanoparticles, the nanoparticles were re-dispersed into 25 ml 0.1 M CTAB solution and mixed with 30 ml solution containing 0.1 M CTAB, 0.5 mM HAuCl4 and 1 mM ascorbic acid and stirred for 6 h. The ~2.5 nm Au coated nanoparticles were separated by centrifuging and washed with deionized water. To make 3.5 nm Au coated Fe3O4 nanoparticles, the 2.5 nm Au coated Fe3O4 nanoparticles were re-dispersed with 25 ml 0.1 M CTAB solution and mixed with 40 ml solution containing 0.1 M CTAB, 0.5 mM HAuCl4 and 1 mM ascorbic acid and stirred for 6 h. 1.4.2 Deposition of Ag on core/shell nanoparticles (iii) To deposit ~1 nm Ag on the surface of core/shell nanoparticles (iii), 25 ml water dispersion core/shell Fe3O4/Au nanoparticles (~5 mg) were mixed with 15 ml aqueous solutions containing 0.1 M CTAB, 1 mM AgNO3 and 1 mM ascorbic acid under stirring and then 0.1 ml 0.01 M NaOH solution was added into the mixed solution. After 4 h, the ~ 1 nm Ag coated core/shell nanoparticles were separated by centrifuging at 8000 rpm and washed with deionized water. They were re-dispersed into 25 ml 0.1 M CTAB solution and mixed with 15 ml AgNO3 solution under stirring. Then, 0.1 ml 0.01 M NaOH was added into the solution to produce ~ 1.5 nm Ag coated nanoparticles. The ~1.5 nm Ag coated nanoparticles were centrifuged at 8000 rpm and washed with deionized water. They were further dissolved into 25 ml 0.1 M CTAB solution and mixed with 20 ml AgNO3 solution followed by adding 0.1 ml 0.01 M NaOH solution. The ~2 nm Ag
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coated nanoparticles were centrifuged at 8000 rpm and washed with deionized water. 1.5 Characterizations The TEM study was carried out on a Philips EM 420 transmission electron microscope at 120kV. The UV-vis absorption spectra were recorded by a PerkinElmer Lambda 35 UV/Vis spectrometer. The magnetic properties of samples were examined by a Lakeshore 7404 high sensitivity vibrating sample magnetometer (VSM) with fields up to 1.5 tesla at room temperature. X-ray diffraction patterns were collected on a Bruker AXS D8-Advanced diffractometer with Cu Ka radiation (λ = 1.5418 Å). 2. TEM images of the Fe3O4/Au and Fe3O4/Au/Ag nanoparticles
Figure S3. HRTEM of a single Fe3O4/Au nanoparticle (iii) showing ~1 nm coating of Au on the surface of Fe3O4 core.
Figure S4. TEM images of core/shell Fe3O4/noble-metal nanoparticles with (a) ~1 nm, (b) ~1.5 nm, (c) ~2 nm, (d) ~2.5 nm, (e) ~3.5 nm of Au, and (f) ~1 nm, (g) ~1.5 nm, (h) ~2 nm of Ag.
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3. Hysteresis loops of core/shell Fe3O4/Au nanoparticles
80
(A)
60
Moment (emu/g)
40 20
(F)
0 -20 -40 -60 -80
-15
-10
-5
0
5
10
15
H (kOe)
Figure S5. Hysteresis loops of (A) Fe3O4 nanoparticles and core/shell Fe3O4/Au nanoparticles with different Au shell thickness at (B) ~1, (C) ~1.5 (D) ~2, (E) ~2.5, and (F) ~3.5 nm.
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