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PMMA magnetic–photoluminescent bifunctional composite nanoribbons
Optical Materials 35 (2013) 526–530
Contents lists available at SciVerse ScienceDirect
Optical Materials journal homepage: www.elsevier.com/locate/optmat
Electrospinning fabrication and properties of Fe3O4/Eu(BA)3phen/PMMA magnetic–photoluminescent bifunctional composite nanoribbons Ma Qianli, Yu Wensheng, Dong Xiangting ⇑, Wang Jinxian, Liu Guixia, Xu Jia Key Laboratory of Applied Chemistry and Nanotechnology at Universities of Jilin Province, Changchun University of Science and Technology, Changchun 130022, China
a r t i c l e
i n f o
Article history: Received 13 May 2012 Received in revised form 6 October 2012 Accepted 8 October 2012 Available online 1 November 2012 Keywords: Electrospinning Nanoribbon Fluorescence property Ferroferric oxide
a b s t r a c t A new type of magnetic–photoluminescent bifunctional Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons was successfully prepared. The average width of the composite nanoribbons was ca. 19.05 ± 1.83 lm, and the thickness was ca. 786 nm. Fluorescence emission peaks of Eu3+ were observed in the Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons. The factors effecting fluorescence intensity were researched via adding different ratios of Eu(BA)3phen to PMMA and Fe3O4 nanoparticles to PMMA. The fluorescent spectra demonstrated that the optimum weight percentage of Eu(BA)3phen to PMMA was 10% due to the concentration quenching effect. Saturation magnetization of the composite nanoribbons was enhanced through introduction of more Fe3O4 nanoparticles, but the fluorescence intensity of the composite nanoribbons was decrease. Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction Electrospinning is a fascinating technique to process viscous solutions or melts into continuous fibers with diameters ranging from micrometer to submicron or nanometer. This method not only attracts extensive academic investigations; but also is applied in many areas such as filtration [1], optical and chemical sensors [2], biological scaffolds [3], electrode materials [4] and nanocables [5–7]. Nanoribbon is a kind of nanomaterial of special morphology. It has attracted increasing interests of scientists owing to its anisotropy, large width–thickness ratio, unique optical, electrical and magnetic properties. Europium complexes have excellent luminescent properties owing to the antenna effect of ligands and the f–f electron transition of Eu3+ ions, resulting in important applications in laser [8], phosphor [9], chemosensors and bioimaging probes [10]. However, rare earth complexes usually do not have good thermal and mechanical stabilities and processing properties, which restrict the use of these complexes to promising extensive photophysical applications and practical uses. To overcome these shortcomings, europium complexes must usually be incorporated into organic, inorganic, or organic/inorganic hybrid matrixes, such as zeolites or mesoporous materials, sol–gel silica, or organically modified silicates and polymers [11,12]. Magnetic nanomaterials have attracted a lot of interest of scientists recently owing to their potential applications, such as biomacromolecules separation, catalyst separation, drug/gene delivery and release, and magnetic resonance imaging [13–15]. ⇑ Corresponding author. Tel.: +86 0431 85582574; fax: +86 0431 85383815. E-mail address: [email protected] (X. Dong). 0925-3467/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.optmat.2012.10.004
Magnetic–photoluminescent nanomaterials have been applied in medical diagnostics and optical imaging, etc. At present, some preparations of Fe3O4@RE complex core–shell structure nanoparticles can be found in Refs. [16–18]. However, fabrication of bifunctional magnetic–photoluminescent composite nanoribbons has not been reported in the literatures. In this paper, we employ electrospinning technique to prepare Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons with magnetic– photoluminescent bifunction. Herein, both the magnetic nanoparticles and luminescent powders are nontoxic. PMMA used as the ribbon template is a kind of stable and biocompatible material. And then we studied the factors effecting fluorescence intensity and saturation magnetization. Some new meaningful results are obtained. 2. Experimental 2.1. Materials Methylmethacrylate (MMA), benzoylperoxide (BPO), Eu2O3, benzoic acid (BA), phenanthroline (phen), FeCl36H2O, FeSO47H2O, NH4NO3, polyethyleneglycol (PEG, Mw 20,000), ammonia, anhydrous ethanol, CHCl3, DMF and deionized water were used. All the reagents are of analytical grade. The purity of Eu2O3 is 99.99%. Deionized water are homemade. 2.2. Preparation of Fe3O4 nanoparticles Fe3O4 nanoparticles were obtained via a facile coprecipitation synthetic method, and PEG was used as the protective agents to prevent the particles from aggregation. One typical synthetic procedure was as follows: 5.4060 g of FeCl36H2O, 2.7800 g of
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FeSO47H2O, 4.04 g of NH4NO3 and 1.9 g of PEG 20000 were added into 100 ml of deionized water to form uniform solution under vigorous stirring at 50 °C. To prevent the oxidation of Fe2+, the reactive mixture was kept under argon atmosphere. After the mixture had been bubbled with argon for 30 min, 0.1 mol/L of NH3H2O was added dropwise into the mixture to adjust the pH value above 11. Then the system was continuously bubbled with argon for 20 min at 50 °C, and a black precipitate was formed. The precipitates were collected from the solution by magnetic separation, washed with deionized water for three times, and then dried in an electric vacuum oven for 12 h at 60 °C.
Table 1 Compositions of the precursor solutions. Samples
S1 S2 S3 S4 S5 S6 S7 S8
Compositions Fe3O4 (g)
Eu(BA)3phen (g)
PMMA (g)
DMF (g)
CHCl3 (g)
0.25 0.25 0.25 0.25 0.25 0.125 0.5 0
0.005 0.025 0.050 0.075 0.100 0.050 0.050 0.050
0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6
9 9 9 9 9 9 9 9
2.3. Synthesis of rare earth organic complexes
2.4. Preparation of PMMA About 100 mL of methylmethacrylate and 0.1 g of benzoylperoxide were mixed in a 250 mL three-necked flask with a backflow device and stirred vigorously at 90–95 °C. Then stopped heating when the viscosity of the mixture solution liked glycerol, and cooled naturally to room temperature. The obtained gelatinous solution was then loaded into test tubes, the influx height was 5–7 cm. After that, the tubes were put in an electric vacuum oven for 48 h at 50 °C, the gelatinous solution was then solidified. At last, the temperature in the oven was raised to 110 °C for 2 h to terminate the reaction. 2.5. Fabrication of magnetic–luminescent composite nanoribbons via electrospinning In the preparation of precursor solutions, Fe3O4 nanoparticles were added in the mixture solution of DMF and CHCl3, then dispersed ultrasonically for 20 min, then PMMA and Eu(BA)3phen were dissolved into the above solution under stirring for 12 h. The dosage of these materials was shown in Table 1. During the electrospinning process, the precursor solution was loaded into a plastic syringe with a spinneret. A flat iron net was used as a collector and put about 12 cm away from the spinneret, and the spinneret was settled vertically. A positive direct current (DC) voltage of about 6 kV was applied between the spinneret and the collector to generate a stable continuous PMMA-based composite nanoribbon. 2.6. Characterization The as-prepared Fe3O4 nanoparticles and Fe3O4/Eu(BA)3phen/ PMMA composite nanoribbons were identified by a X-ray powder diffractometer (XRD, Bruker, D8 FOCUS) with Cu Ka radiation. The operation voltage and current were kept at 40 kV and 20 mA, respectively. The morphology and internal structure of Fe3O4/ Eu(BA)3phen/PMMA composite nanoribbons were observed by a field emission scanning electron microscope (FESEM, XL-30) and a transmission electron microscope (TEM, JEM-2010), respectively. The fluorescent properties of Eu(BA)3phen/PMMA nanoribbons and
Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons were investigated by Hitachi Fluorescence spectrophotometer F-7000. Then, the magnetic performance of Fe3O4 nanoparticles and Fe3O4/ Eu(BA)3phen/PMMA composite nanoribbons were measured by a vibrating sample magnetometer (VSM, MPMS SQUID XL). 3. Results and discussion 3.1. Characterizations of the structure and morphology The phase compositions of the Fe3O4 nanoparticles, Eu(BA)3phen complex and composite nanoribbons (S7) were identified by means of XRD analysis, as shown in Fig. 1. It can be seen that XRD pattern of Fe3O4 nanoparticles were conformed to the cubic structure of Fe3O4 (PDF 74-0748), and no characteristic peaks were observed for other impurities such as Fe2O3 and FeO(OH). From the XRD pattern of Eu(BA)3phen complex we can see that the XRD pattern is consisted of no any diffraction peaks, which means the Eu(BA)3phen is an amorphous structure. The XRD analysis result of Fe3O4/ Eu(BA)3phen/PMMA composite nanoribbons demonstrates that the composite nanoribbons contain Fe3O4 nanoparticles. Fig. 2a illustrates a FESEM image of the as-prepared Fe3O4 nanoparticles. The size distribution of the as-prepared nanoparticles was almost uniform, and the diameter of the nanoparticles was 8–10 nm. Fig. 2b and c shows FESEM images of Eu(BA)3phen/PMMA nanoribbons (S8) and Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons (S7) respectively. Fig. 3a and b demonstrates the histograms of widths of Eu(BA)3phen/PMMA composite nanoribbons and Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons. As revealed in Figs. 2b and 3a, the average width of Eu(BA)3phen/PMMA nanoribbons was 8.56 ± 0.75 lm under the confidence level of 95%, and thickness was about 735 nm. As seen from Figs. 2c and 3b, after Fe3O4 /Eu(BA)3 phen/PMMA
(311)
composite nanoribbons (220)
(400)
(511) (440) (422)
Intensity (a.u.)
Eu(BA)3phen powder was synthesized according to the traditional method as described in Ref. [19]. 0.88 g of Eu2O3 was dissolved in 5 ml of concentrated nitric acid and then crystallized by evaporation of excess nitric acid, and Eu(NO3)36H2O was acquired. Eu(NO3)3 ethanol solution was prepared by adding 10 ml of anhydrous ethanol into the above Eu(NO3)36H2O. 1.832 g of benzoic acid (BA) and 0.991 g of phenanthroline (phen) were dissolved in 100 ml of ethanol. The Eu(NO3)3 solution was then added into the solution of BA and phen with magnetic agitation for 3 h at 60 °C. The precipitate was collected by filtration and dried for 12 h at 60 °C.
(533)
Eu(BA)3 phen
Fe3O4 nanoparticles
PDF#74-0748 (Fe3O4) 20
30
40
50
60
70
80
2-Theta (degree) Fig. 1. XRD patterns of Fe3O4 nanoparticles, Eu(BA)3phen complex and Fe3O4/ Eu(BA)3phen/PMMA composite nanoribbons.
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a
c
b
d
e
Intensity (a.u.)
C
O Au
Fe
Fe 0
1
Eu 2
3
4
5
6
7
8
Binding Energy (keV) Fig. 2. FESEM images of (a) Fe3O4 nanoparticles, (b) Eu(BA)3phen/PMMA nanoribbons (S8) and (c) Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons (S7); TEM image of (d) Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons (S7, the arrow marks indicate some of the agglomerations of Fe3O4 nanoparticles, the inset shows the high magnification TEM image Fe3O4 nanoparticles in Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons) and EDS spectrum of (e) Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons (S7).
adding Fe3O4 nanoparticles into the polymer matrix, the average width increased to 19.05 ± 1.83 lm and thickness was about 786 nm. The increase of the average width and thickness may cause by the high conductivity of Fe3O4 nanoparticles. When Fe3O4 nanoparticles were added into the precursor and electrospun, the existence of Fe3O4 nanoparticles would enhance the repulsion force between positive charges in the nanoribbon, so the Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons were wider. The TEM image of Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons (S7) was presented in Fig. 2d. It is obviously seen from the TEM image that the Fe3O4 nanoparticles were successfully dispersed in the composite nanoribbons and a slightly agglomeration phenomenon which caused by the large surface energy of the nano-sized Fe3O4 particles [20] can be observed. The inset of Fig. 2d indicates the morphology and size of the Fe3O4 nanoparticles in the composite nanoribbons is the same as the Fe3O4 nanoparticles indicated in Fig. 2a. The energy dispersive spectrum (EDS) shown in Fig. 2e revealed that the
composite nanoribbons were consisted of C, O, Fe and Eu elements. The Au peak in the spectrum came from gold conductive film plated on the surface of the sample for SEM observation. 3.2. Fluorescent properties of Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons The fluorescent properties of the Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons containing different amounts of Eu(BA)3phen were investigated. In order to perform the contrast experiments, the mass ratios of Fe3O4 to PMMA were fixed as 1:2 from samples S1 to S5. Fig. 4a shows the excitation spectra of various samples determined at room temperature. A broad excitation band extending from 200 to 350 nm was observed when monitoring wavelength was 617 nm. The peak at 275 nm assigned to the p?p electron transition of the ligands could be also identified. The excitation intensity was increased at the beginning
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1600 1400 1200 1000 800 600 400 200 0 1(S1) 5(S2) 10(S3) 15(S4) 20(S5)
a
15
ag e(
10
5
200
250
300
350
400
450
Pe r
ce nt
Percentage (%)
20
Intensity (a.u.)
em=617nm 275nm
)
a
%
25
500
Wavelength (nm) 0 7.0
7.5
8.0
8.5
9.0
9.5
10.0
1400
10.5 ex=275nm
b
Width (nm)
617nm
30
1200
Intensity (a.u.)
6.5
1000 800
b
592nm
25
600 400
)
%
ag e(
0 1(S1) 5(S2) 10(S3) 15(S4) 20(S5)
ce nt
15 500 520 540 560 580 600 620 640 660 680 700
10
Pe r
Percentage (%)
200 20
Wavelength (nm) 5
Fig. 4. Excitation spectra (a) and emission spectra (b) of Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons containing different mass percentage of Eu(BA)3phen complex.
0 15
16
17
18
19
20
21
22
23
24
25
Width (nm) Fig. 3. Histograms of widths of Eu(BA)3phen/PMMA composite nanoribbons (a) and Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons (b).
and then decreased with adding more Eu(BA)3phen. The highest value occurred when the mass ratio of Eu(BA)3phen to PMMA was 10% (S3). As shown in Fig. 4b, characteristic emission peaks of Eu3+ were observed under excitation of 275 nm and ascribed to the transitions of 5D0 ? 7F1 (592 nm), 5D0 ? 7F2 (617 nm) of Eu3+, and the 5D0 ? 7F2 hypersensitive transition at 617 nm is the predominant emission peak. A comparison among S1–S5 also demonstrates that S3 had the strongest emission intensity. The results indicated that the composite nanoribbons containing 10% Eu(BA)3phen had the strongest fluorescence intensity. Therefore, the quenching concentration of Eu(BA)3phen was 10%. Meanwhile, the effect on fluorescence intensity via introduction of different amounts of Fe3O4 nanoparticles into the composite ribbons was studied. The mass percentage of Eu(BA)3phen to PMMA were fixed as 10% in samples S3, S6–S8. As presented in Fig. 5, both excitation and emission intensity of the composite nanoribbons were decreased with the increase of the amount of Fe3O4 nanoparticles introduced into the composite nanoribbons. This phenomenon may result from the light absorption of Fe3O4 nanoparticles which mixed into the composite nanoribbons [21]. 3.3. Magnetic properties of Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons The typical hysteresis loops for Fe3O4 nanoparticles and Fe3O4/ Eu(BA)3phen/PMMA composite nanoribbons containing various mass ratios of Fe3O4 nanoparticles were shown in Fig. 6. The
saturation magnetization of Fe3O4 nanoparticles was found to be 51.40 emu/g which was relatively low compared with its bulk value of 92 emu/g [22]. This behavior originates from the nano-sized effect, because for the fine magnetic particles, the surface layer has a number of defects, and thus does not contribute to magnetization. It was found from Fig. 6 and Table 2 that saturation magnetization of the composite nanoribbons was decreased with the decrease of Fe3O4 nanoparticles, indicating that the magnetic properties of the composite nanoribbons can be tuned via addition of various amounts of Fe3O4 nanoparticles. Besides, the composite nanoribbons demonstrated superparamagnetic performance owing to Fe3O4 nanoparticles introduced into the composite nanoribbons. The particle size of Fe3O4 nanoparticles was 8–10 nm, which belong to superparamagnetic materials. The coercivity of superparamagnetic materials was almost negligible at room temperature [23]. 4. Conclusions Magnetic–photoluminescent bifunctional Fe3O4/Eu(BA)3phen/ PMMA composite nanoribbons were successfully prepared by electrospinning. The average width of the composite nanoribbons was ca. 19.05 ± 1.83 lm, and the thickness was ca. 786 nm. Fluorescence emission peaks of Eu3+ were observed in the Fe3O4/ Eu(BA)3phen/PMMA composite nanoribbons. The optimum weight percentage of Eu(BA)3phen to PMMA was 10% due to the concentration quenching effect. The luminescent intensity of the composite nanoribbons was decreased when more Fe3O4 nanoparticles were added. The saturated magnetization of the composite nanoribbons was increased with the increase of the quantities of Fe3O4 nanoparticles. Besides, the design conception
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a
4500 275nm
Fe3O4:PMMA=1:1 (S7)
4000
Intensity (a.u.)
Fe3O4:PMMA=1:2 (S3)
3500
Fe3O4:PMMA=1:4 (S6)
Samples
Saturation magnetization (Ms/emu/g)
3000
Fe3O4 free
Fe3O4 nanoparticles Fe3O4: PMMA = 1:1 (S7) Fe3O4: PMMA = 1:2 (S3) Fe3O4: PMMA = 1:4 (S6)
51.40 21.74 17.50 9.92
(S8)
ex=617nm
2500 2000 1500 1000 500 0 200
250
300
350
400
450
500
Wavelength (nm)
Intensity (a.u.)
b
Table 2 Saturation magnetization of Fe3O4 nanoparticles and Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons.
5000 4500
Fe3O4:PMMA=1:1 (S7)
4000
Fe3O4:PMMA=1:2 (S3)
Acknowledgments
617nm
This work was financially supported by the National Natural Science Foundation of China (NSFC 50972020, 51072026), Ph.D. Programs Foundation of the Ministry of Education of China (20102216110002, 20112216120003), the Science and Technology Development Planning Project of Jilin Province (Grant Nos. 20070 402, 20060504), Key Research Project of Science and Technology of Ministry of Education of China (Grant No. 207026).
Fe3O4:PMMA=1:4 (S6)
3500
Fe3O4 free
3000
(S8)
ex=275nm
2500 2000
592nm
1500
color of the nanoribbons can be changed by introducing other fluorescent materials into them. The fluorescent and saturation magnetic intensities of the composite nanoribbons can also be tuned by adding different concentration of fluorescent material and Fe3O4 nanoparticles into them, respectively. The new high-performance magnetic–photoluminescent bifunctional Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons have potential applications in many fields.
1000
References
500 0 500
525
550
575
600
625
650
675
700
Wavelength (nm) Fig. 5. Excitation spectra (a) and emission spectra (b) of Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons containing different mass ratios of Fe3O4 nanoparticles.
-1
M (emu· g )
60 50
a: Fe3 O4 nanoparticles
40
b: Fe3 O4 :PMMA=1:1 (S7)
30
c: Fe3 O4 :PMMA=1:2 (S3)
20
d: Fe3 O4 :PMMA=1:4 (S6)
a
b c d
10 0 -10 -20 -30 -40 -50 -60 -10000
-5000
0
5000
10000
H (Oe) Fig. 6. Hysteresis loops of the (a) Fe3O4 nanoparticles and Fe3O4/Eu(BA)3phen/ PMMA composite nanoribbons containing different mass ratios of Fe3O4:PMMA as (b) 1:1, (c) 1:2 and (d) 1:4.
and preparation method of the composite nanoribbons are of universal significance for the fabrication of other magnetic–photoluminescent composite nanoribbons. For instance, the fluorescent
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Contents lists available at SciVerse ScienceDirect
Optical Materials journal homepage: www.elsevier.com/locate/optmat
Electrospinning fabrication and properties of Fe3O4/Eu(BA)3phen/PMMA magnetic–photoluminescent bifunctional composite nanoribbons Ma Qianli, Yu Wensheng, Dong Xiangting ⇑, Wang Jinxian, Liu Guixia, Xu Jia Key Laboratory of Applied Chemistry and Nanotechnology at Universities of Jilin Province, Changchun University of Science and Technology, Changchun 130022, China
a r t i c l e
i n f o
Article history: Received 13 May 2012 Received in revised form 6 October 2012 Accepted 8 October 2012 Available online 1 November 2012 Keywords: Electrospinning Nanoribbon Fluorescence property Ferroferric oxide
a b s t r a c t A new type of magnetic–photoluminescent bifunctional Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons was successfully prepared. The average width of the composite nanoribbons was ca. 19.05 ± 1.83 lm, and the thickness was ca. 786 nm. Fluorescence emission peaks of Eu3+ were observed in the Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons. The factors effecting fluorescence intensity were researched via adding different ratios of Eu(BA)3phen to PMMA and Fe3O4 nanoparticles to PMMA. The fluorescent spectra demonstrated that the optimum weight percentage of Eu(BA)3phen to PMMA was 10% due to the concentration quenching effect. Saturation magnetization of the composite nanoribbons was enhanced through introduction of more Fe3O4 nanoparticles, but the fluorescence intensity of the composite nanoribbons was decrease. Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction Electrospinning is a fascinating technique to process viscous solutions or melts into continuous fibers with diameters ranging from micrometer to submicron or nanometer. This method not only attracts extensive academic investigations; but also is applied in many areas such as filtration [1], optical and chemical sensors [2], biological scaffolds [3], electrode materials [4] and nanocables [5–7]. Nanoribbon is a kind of nanomaterial of special morphology. It has attracted increasing interests of scientists owing to its anisotropy, large width–thickness ratio, unique optical, electrical and magnetic properties. Europium complexes have excellent luminescent properties owing to the antenna effect of ligands and the f–f electron transition of Eu3+ ions, resulting in important applications in laser [8], phosphor [9], chemosensors and bioimaging probes [10]. However, rare earth complexes usually do not have good thermal and mechanical stabilities and processing properties, which restrict the use of these complexes to promising extensive photophysical applications and practical uses. To overcome these shortcomings, europium complexes must usually be incorporated into organic, inorganic, or organic/inorganic hybrid matrixes, such as zeolites or mesoporous materials, sol–gel silica, or organically modified silicates and polymers [11,12]. Magnetic nanomaterials have attracted a lot of interest of scientists recently owing to their potential applications, such as biomacromolecules separation, catalyst separation, drug/gene delivery and release, and magnetic resonance imaging [13–15]. ⇑ Corresponding author. Tel.: +86 0431 85582574; fax: +86 0431 85383815. E-mail address: [email protected] (X. Dong). 0925-3467/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.optmat.2012.10.004
Magnetic–photoluminescent nanomaterials have been applied in medical diagnostics and optical imaging, etc. At present, some preparations of Fe3O4@RE complex core–shell structure nanoparticles can be found in Refs. [16–18]. However, fabrication of bifunctional magnetic–photoluminescent composite nanoribbons has not been reported in the literatures. In this paper, we employ electrospinning technique to prepare Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons with magnetic– photoluminescent bifunction. Herein, both the magnetic nanoparticles and luminescent powders are nontoxic. PMMA used as the ribbon template is a kind of stable and biocompatible material. And then we studied the factors effecting fluorescence intensity and saturation magnetization. Some new meaningful results are obtained. 2. Experimental 2.1. Materials Methylmethacrylate (MMA), benzoylperoxide (BPO), Eu2O3, benzoic acid (BA), phenanthroline (phen), FeCl36H2O, FeSO47H2O, NH4NO3, polyethyleneglycol (PEG, Mw 20,000), ammonia, anhydrous ethanol, CHCl3, DMF and deionized water were used. All the reagents are of analytical grade. The purity of Eu2O3 is 99.99%. Deionized water are homemade. 2.2. Preparation of Fe3O4 nanoparticles Fe3O4 nanoparticles were obtained via a facile coprecipitation synthetic method, and PEG was used as the protective agents to prevent the particles from aggregation. One typical synthetic procedure was as follows: 5.4060 g of FeCl36H2O, 2.7800 g of
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FeSO47H2O, 4.04 g of NH4NO3 and 1.9 g of PEG 20000 were added into 100 ml of deionized water to form uniform solution under vigorous stirring at 50 °C. To prevent the oxidation of Fe2+, the reactive mixture was kept under argon atmosphere. After the mixture had been bubbled with argon for 30 min, 0.1 mol/L of NH3H2O was added dropwise into the mixture to adjust the pH value above 11. Then the system was continuously bubbled with argon for 20 min at 50 °C, and a black precipitate was formed. The precipitates were collected from the solution by magnetic separation, washed with deionized water for three times, and then dried in an electric vacuum oven for 12 h at 60 °C.
Table 1 Compositions of the precursor solutions. Samples
S1 S2 S3 S4 S5 S6 S7 S8
Compositions Fe3O4 (g)
Eu(BA)3phen (g)
PMMA (g)
DMF (g)
CHCl3 (g)
0.25 0.25 0.25 0.25 0.25 0.125 0.5 0
0.005 0.025 0.050 0.075 0.100 0.050 0.050 0.050
0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5
0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6
9 9 9 9 9 9 9 9
2.3. Synthesis of rare earth organic complexes
2.4. Preparation of PMMA About 100 mL of methylmethacrylate and 0.1 g of benzoylperoxide were mixed in a 250 mL three-necked flask with a backflow device and stirred vigorously at 90–95 °C. Then stopped heating when the viscosity of the mixture solution liked glycerol, and cooled naturally to room temperature. The obtained gelatinous solution was then loaded into test tubes, the influx height was 5–7 cm. After that, the tubes were put in an electric vacuum oven for 48 h at 50 °C, the gelatinous solution was then solidified. At last, the temperature in the oven was raised to 110 °C for 2 h to terminate the reaction. 2.5. Fabrication of magnetic–luminescent composite nanoribbons via electrospinning In the preparation of precursor solutions, Fe3O4 nanoparticles were added in the mixture solution of DMF and CHCl3, then dispersed ultrasonically for 20 min, then PMMA and Eu(BA)3phen were dissolved into the above solution under stirring for 12 h. The dosage of these materials was shown in Table 1. During the electrospinning process, the precursor solution was loaded into a plastic syringe with a spinneret. A flat iron net was used as a collector and put about 12 cm away from the spinneret, and the spinneret was settled vertically. A positive direct current (DC) voltage of about 6 kV was applied between the spinneret and the collector to generate a stable continuous PMMA-based composite nanoribbon. 2.6. Characterization The as-prepared Fe3O4 nanoparticles and Fe3O4/Eu(BA)3phen/ PMMA composite nanoribbons were identified by a X-ray powder diffractometer (XRD, Bruker, D8 FOCUS) with Cu Ka radiation. The operation voltage and current were kept at 40 kV and 20 mA, respectively. The morphology and internal structure of Fe3O4/ Eu(BA)3phen/PMMA composite nanoribbons were observed by a field emission scanning electron microscope (FESEM, XL-30) and a transmission electron microscope (TEM, JEM-2010), respectively. The fluorescent properties of Eu(BA)3phen/PMMA nanoribbons and
Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons were investigated by Hitachi Fluorescence spectrophotometer F-7000. Then, the magnetic performance of Fe3O4 nanoparticles and Fe3O4/ Eu(BA)3phen/PMMA composite nanoribbons were measured by a vibrating sample magnetometer (VSM, MPMS SQUID XL). 3. Results and discussion 3.1. Characterizations of the structure and morphology The phase compositions of the Fe3O4 nanoparticles, Eu(BA)3phen complex and composite nanoribbons (S7) were identified by means of XRD analysis, as shown in Fig. 1. It can be seen that XRD pattern of Fe3O4 nanoparticles were conformed to the cubic structure of Fe3O4 (PDF 74-0748), and no characteristic peaks were observed for other impurities such as Fe2O3 and FeO(OH). From the XRD pattern of Eu(BA)3phen complex we can see that the XRD pattern is consisted of no any diffraction peaks, which means the Eu(BA)3phen is an amorphous structure. The XRD analysis result of Fe3O4/ Eu(BA)3phen/PMMA composite nanoribbons demonstrates that the composite nanoribbons contain Fe3O4 nanoparticles. Fig. 2a illustrates a FESEM image of the as-prepared Fe3O4 nanoparticles. The size distribution of the as-prepared nanoparticles was almost uniform, and the diameter of the nanoparticles was 8–10 nm. Fig. 2b and c shows FESEM images of Eu(BA)3phen/PMMA nanoribbons (S8) and Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons (S7) respectively. Fig. 3a and b demonstrates the histograms of widths of Eu(BA)3phen/PMMA composite nanoribbons and Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons. As revealed in Figs. 2b and 3a, the average width of Eu(BA)3phen/PMMA nanoribbons was 8.56 ± 0.75 lm under the confidence level of 95%, and thickness was about 735 nm. As seen from Figs. 2c and 3b, after Fe3O4 /Eu(BA)3 phen/PMMA
(311)
composite nanoribbons (220)
(400)
(511) (440) (422)
Intensity (a.u.)
Eu(BA)3phen powder was synthesized according to the traditional method as described in Ref. [19]. 0.88 g of Eu2O3 was dissolved in 5 ml of concentrated nitric acid and then crystallized by evaporation of excess nitric acid, and Eu(NO3)36H2O was acquired. Eu(NO3)3 ethanol solution was prepared by adding 10 ml of anhydrous ethanol into the above Eu(NO3)36H2O. 1.832 g of benzoic acid (BA) and 0.991 g of phenanthroline (phen) were dissolved in 100 ml of ethanol. The Eu(NO3)3 solution was then added into the solution of BA and phen with magnetic agitation for 3 h at 60 °C. The precipitate was collected by filtration and dried for 12 h at 60 °C.
(533)
Eu(BA)3 phen
Fe3O4 nanoparticles
PDF#74-0748 (Fe3O4) 20
30
40
50
60
70
80
2-Theta (degree) Fig. 1. XRD patterns of Fe3O4 nanoparticles, Eu(BA)3phen complex and Fe3O4/ Eu(BA)3phen/PMMA composite nanoribbons.
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a
c
b
d
e
Intensity (a.u.)
C
O Au
Fe
Fe 0
1
Eu 2
3
4
5
6
7
8
Binding Energy (keV) Fig. 2. FESEM images of (a) Fe3O4 nanoparticles, (b) Eu(BA)3phen/PMMA nanoribbons (S8) and (c) Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons (S7); TEM image of (d) Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons (S7, the arrow marks indicate some of the agglomerations of Fe3O4 nanoparticles, the inset shows the high magnification TEM image Fe3O4 nanoparticles in Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons) and EDS spectrum of (e) Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons (S7).
adding Fe3O4 nanoparticles into the polymer matrix, the average width increased to 19.05 ± 1.83 lm and thickness was about 786 nm. The increase of the average width and thickness may cause by the high conductivity of Fe3O4 nanoparticles. When Fe3O4 nanoparticles were added into the precursor and electrospun, the existence of Fe3O4 nanoparticles would enhance the repulsion force between positive charges in the nanoribbon, so the Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons were wider. The TEM image of Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons (S7) was presented in Fig. 2d. It is obviously seen from the TEM image that the Fe3O4 nanoparticles were successfully dispersed in the composite nanoribbons and a slightly agglomeration phenomenon which caused by the large surface energy of the nano-sized Fe3O4 particles [20] can be observed. The inset of Fig. 2d indicates the morphology and size of the Fe3O4 nanoparticles in the composite nanoribbons is the same as the Fe3O4 nanoparticles indicated in Fig. 2a. The energy dispersive spectrum (EDS) shown in Fig. 2e revealed that the
composite nanoribbons were consisted of C, O, Fe and Eu elements. The Au peak in the spectrum came from gold conductive film plated on the surface of the sample for SEM observation. 3.2. Fluorescent properties of Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons The fluorescent properties of the Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons containing different amounts of Eu(BA)3phen were investigated. In order to perform the contrast experiments, the mass ratios of Fe3O4 to PMMA were fixed as 1:2 from samples S1 to S5. Fig. 4a shows the excitation spectra of various samples determined at room temperature. A broad excitation band extending from 200 to 350 nm was observed when monitoring wavelength was 617 nm. The peak at 275 nm assigned to the p?p electron transition of the ligands could be also identified. The excitation intensity was increased at the beginning
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1600 1400 1200 1000 800 600 400 200 0 1(S1) 5(S2) 10(S3) 15(S4) 20(S5)
a
15
ag e(
10
5
200
250
300
350
400
450
Pe r
ce nt
Percentage (%)
20
Intensity (a.u.)
em=617nm 275nm
)
a
%
25
500
Wavelength (nm) 0 7.0
7.5
8.0
8.5
9.0
9.5
10.0
1400
10.5 ex=275nm
b
Width (nm)
617nm
30
1200
Intensity (a.u.)
6.5
1000 800
b
592nm
25
600 400
)
%
ag e(
0 1(S1) 5(S2) 10(S3) 15(S4) 20(S5)
ce nt
15 500 520 540 560 580 600 620 640 660 680 700
10
Pe r
Percentage (%)
200 20
Wavelength (nm) 5
Fig. 4. Excitation spectra (a) and emission spectra (b) of Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons containing different mass percentage of Eu(BA)3phen complex.
0 15
16
17
18
19
20
21
22
23
24
25
Width (nm) Fig. 3. Histograms of widths of Eu(BA)3phen/PMMA composite nanoribbons (a) and Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons (b).
and then decreased with adding more Eu(BA)3phen. The highest value occurred when the mass ratio of Eu(BA)3phen to PMMA was 10% (S3). As shown in Fig. 4b, characteristic emission peaks of Eu3+ were observed under excitation of 275 nm and ascribed to the transitions of 5D0 ? 7F1 (592 nm), 5D0 ? 7F2 (617 nm) of Eu3+, and the 5D0 ? 7F2 hypersensitive transition at 617 nm is the predominant emission peak. A comparison among S1–S5 also demonstrates that S3 had the strongest emission intensity. The results indicated that the composite nanoribbons containing 10% Eu(BA)3phen had the strongest fluorescence intensity. Therefore, the quenching concentration of Eu(BA)3phen was 10%. Meanwhile, the effect on fluorescence intensity via introduction of different amounts of Fe3O4 nanoparticles into the composite ribbons was studied. The mass percentage of Eu(BA)3phen to PMMA were fixed as 10% in samples S3, S6–S8. As presented in Fig. 5, both excitation and emission intensity of the composite nanoribbons were decreased with the increase of the amount of Fe3O4 nanoparticles introduced into the composite nanoribbons. This phenomenon may result from the light absorption of Fe3O4 nanoparticles which mixed into the composite nanoribbons [21]. 3.3. Magnetic properties of Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons The typical hysteresis loops for Fe3O4 nanoparticles and Fe3O4/ Eu(BA)3phen/PMMA composite nanoribbons containing various mass ratios of Fe3O4 nanoparticles were shown in Fig. 6. The
saturation magnetization of Fe3O4 nanoparticles was found to be 51.40 emu/g which was relatively low compared with its bulk value of 92 emu/g [22]. This behavior originates from the nano-sized effect, because for the fine magnetic particles, the surface layer has a number of defects, and thus does not contribute to magnetization. It was found from Fig. 6 and Table 2 that saturation magnetization of the composite nanoribbons was decreased with the decrease of Fe3O4 nanoparticles, indicating that the magnetic properties of the composite nanoribbons can be tuned via addition of various amounts of Fe3O4 nanoparticles. Besides, the composite nanoribbons demonstrated superparamagnetic performance owing to Fe3O4 nanoparticles introduced into the composite nanoribbons. The particle size of Fe3O4 nanoparticles was 8–10 nm, which belong to superparamagnetic materials. The coercivity of superparamagnetic materials was almost negligible at room temperature [23]. 4. Conclusions Magnetic–photoluminescent bifunctional Fe3O4/Eu(BA)3phen/ PMMA composite nanoribbons were successfully prepared by electrospinning. The average width of the composite nanoribbons was ca. 19.05 ± 1.83 lm, and the thickness was ca. 786 nm. Fluorescence emission peaks of Eu3+ were observed in the Fe3O4/ Eu(BA)3phen/PMMA composite nanoribbons. The optimum weight percentage of Eu(BA)3phen to PMMA was 10% due to the concentration quenching effect. The luminescent intensity of the composite nanoribbons was decreased when more Fe3O4 nanoparticles were added. The saturated magnetization of the composite nanoribbons was increased with the increase of the quantities of Fe3O4 nanoparticles. Besides, the design conception
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a
4500 275nm
Fe3O4:PMMA=1:1 (S7)
4000
Intensity (a.u.)
Fe3O4:PMMA=1:2 (S3)
3500
Fe3O4:PMMA=1:4 (S6)
Samples
Saturation magnetization (Ms/emu/g)
3000
Fe3O4 free
Fe3O4 nanoparticles Fe3O4: PMMA = 1:1 (S7) Fe3O4: PMMA = 1:2 (S3) Fe3O4: PMMA = 1:4 (S6)
51.40 21.74 17.50 9.92
(S8)
ex=617nm
2500 2000 1500 1000 500 0 200
250
300
350
400
450
500
Wavelength (nm)
Intensity (a.u.)
b
Table 2 Saturation magnetization of Fe3O4 nanoparticles and Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons.
5000 4500
Fe3O4:PMMA=1:1 (S7)
4000
Fe3O4:PMMA=1:2 (S3)
Acknowledgments
617nm
This work was financially supported by the National Natural Science Foundation of China (NSFC 50972020, 51072026), Ph.D. Programs Foundation of the Ministry of Education of China (20102216110002, 20112216120003), the Science and Technology Development Planning Project of Jilin Province (Grant Nos. 20070 402, 20060504), Key Research Project of Science and Technology of Ministry of Education of China (Grant No. 207026).
Fe3O4:PMMA=1:4 (S6)
3500
Fe3O4 free
3000
(S8)
ex=275nm
2500 2000
592nm
1500
color of the nanoribbons can be changed by introducing other fluorescent materials into them. The fluorescent and saturation magnetic intensities of the composite nanoribbons can also be tuned by adding different concentration of fluorescent material and Fe3O4 nanoparticles into them, respectively. The new high-performance magnetic–photoluminescent bifunctional Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons have potential applications in many fields.
1000
References
500 0 500
525
550
575
600
625
650
675
700
Wavelength (nm) Fig. 5. Excitation spectra (a) and emission spectra (b) of Fe3O4/Eu(BA)3phen/PMMA composite nanoribbons containing different mass ratios of Fe3O4 nanoparticles.
-1
M (emu· g )
60 50
a: Fe3 O4 nanoparticles
40
b: Fe3 O4 :PMMA=1:1 (S7)
30
c: Fe3 O4 :PMMA=1:2 (S3)
20
d: Fe3 O4 :PMMA=1:4 (S6)
a
b c d
10 0 -10 -20 -30 -40 -50 -60 -10000
-5000
0
5000
10000
H (Oe) Fig. 6. Hysteresis loops of the (a) Fe3O4 nanoparticles and Fe3O4/Eu(BA)3phen/ PMMA composite nanoribbons containing different mass ratios of Fe3O4:PMMA as (b) 1:1, (c) 1:2 and (d) 1:4.
and preparation method of the composite nanoribbons are of universal significance for the fabrication of other magnetic–photoluminescent composite nanoribbons. For instance, the fluorescent
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