Novel Electrospun Dual-Layered Composite Nanofibrous Membrane

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Novel Electrospun Dual-Layered Composite Nanofibrous Membrane Endowed with Electricity−Magnetism Bifunctionality at One Layer and Photoluminescence at the Other Layer Zijiao Wang, Qianli Ma, Xiangting Dong,* Dan Li, Xue Xi, Wensheng Yu, Jinxian Wang, and Guixia Liu Key Laboratory of Applied Chemistry and Nanotechnology at Universities of Jilin Province, Changchun University of Science and Technology, Changchun 130022, China ABSTRACT: Dual-layered composite nanofibrous membrane equipped with electrical conduction, magnetism and photoluminescence trifunctionality is constructed via electrospinning. The composite membrane consists of a polyaniline (PANI)/Fe3O4 nanoparticles (NPs)/polyacrylonitrile (PAN) tuned electricalmagnetic bifunctional nanofibrous layer at one side and a Eu(TTA)3(TPPO)2/polyvinylpyrrolidone (PVP) photoluminescent nanofibrous layer at the other side, and the two layers are tightly combined face-to-face together into the novel dual-layered composite membrane with trifunctionality. The electric conductivity and magnetism of electrical−magnetic bifunctionality can be respectively tunable via modulating the respective PANI and Fe3O4 NPs contents, and the highest electric conductivity approaches the order of 1 × 10−2 S cm−1. Predominant red emission at 615 nm can be obviously observed in the photoluminescent layer under 366 nm excitation. Moreover, the luminescent intensity of photoluminescent layer is almost unaffected by the electrical−magnetic bifunctional layer because of the fact that the photoluminescent materials have been successfully isolated from dark-colored PANI and Fe3O4 NPs. The novel dual-layered composite nanofibrous membrane with trifunctionality has potentials in many fields. Furthermore, the design philosophy and fabrication method for the dual-layered multifunctional membrane provide a new and facile strategy toward other membranes with multifunctionality. KEYWORDS: electrospinning, dual-layered membranes, photoluminescence, electrical conduction, magnetism

1. INTRODUCTION With the growing demand for integrated devices, singlefunctional materials have become hardly able to meet the needs of modern science and technology. Therefore, scientists have gradually drawn more and more interests on multifunctional composite materials owing to their wider application fields.1−3 By using multifunctional materials, system size can be effectively reduced because different functions are integrated in one piece of material. Usually, the structural integration of various nano, micro, or bulky materials with diverse properties is the key tech to realize multifunctionality. Typical strategies to combine various components together include two ways, one is that a shell is coated on a core4,5 and the other is that different active parts are sealed into the host materials.6,7 Multifunctional conjugation meets a big challenge that each component is hard to retain its intrinsic properties but suffers the interferences by other different components, which still urgently needs to be resolved. Rare-earth (RE) complexes show unique properties such as chemical, electronic and optical performances for the existence of f−f electron transition in RE ions. Therefore, RE organic complexes have extensive applications on luminescence devices,8,9 displays,10 biolabeling,11 optical imaging,12 phototherapy, etc.13 Fe3O4 nanoparticles (NPs) are commonly used © XXXX American Chemical Society

magnetic material because of their excellent magnetism and biocompatibility.14 Recently, some types of nanomaterials possessing photoluminescent-magnetic bifunctionality have been reported, which benefit many technical areas such as magnetic resonanece, cell separation, drug targeting, and biological imaging.15−17 As the popular conducting polymers, polyaniline (PANI) has been widely researched and applied in many areas like secondary batteries, electromagnectic interference (EMI) shielding, and catalysts because of its light weight, low cost, tunable conductivity, and environmental stability.18,19 By now, trifunctional Eu(BA)3phen/PANI/Fe3O4/PVP hollow nanofibers fabricated by electrospinning process are emerged in the literature.20 In view from previous work by us and other researchers, as for the luminescent-electrical-magnetic trifunctional materials, the luminescent intensity of RE compounds will greatly decline if the RE compounds directly contact with deepcolored materials like Fe2O3, Fe3O4, and PANI.21,22 Therefore, it is urgently needed to find a new way of effectively isolating luminescence materials from Fe2O3, Fe3O4 and PANI. Received: July 12, 2016 Accepted: September 9, 2016

A

DOI: 10.1021/acsami.6b08522 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces Table 1. Components of Spinning Solution I solution I

Eu(TTA)3(TPPO)2:PVP (wt %)

Eu(TTA)3(TPPO)2 (g)

PVP (g)

DMF (g)

Sa1 Sa2 Sa3 Sa4 Sa5

5 10 15 20 25

0.0500 0.1000 0.1500 0.2000 0.2500

1.0000 1.0000 1.0000 1.0000 1.0000

4.5000 4.5000 4.5000 4.5000 4.5000

Table 2. Components of Spinning Solution II solution II

PANI:PAN (wt %)

Fe3O4:PAN (mass ratio)

Fe3O4 (g)

ANI (g)

CSA (g)

APS (g)

PAN (g)

DMF (g)

Sb1 Sb2 Sb3 Sb4 Sb5 Sb6

40 50 60 70 50 50

1:1 1:1 1:1 1:1 0.5:1 2:1

0.9000 0.9000 0.9000 0.9000 0.4500 1.8000

0.3600 0.4500 0.5400 0.6300 0.4500 0.4500

0.4490 0.5612 0.6734 0.7856 0.5612 0.5612

0.8822 1.1033 1.3232 1.5437 1.1033 1.1033

0.9000 0.9000 0.9000 0.9000 0.9000 0.9000

9.0000 9.0000 9.0000 9.0000 9.0000 9.0000

under mechanical agitation at 25 °C for 2 h. APS was dispersed into the DMF (2.0000 g) as oxidant and stirred for 2 h. The suspension and the solution involved above were refrigerated to 0 °C and maintained for 1 h. Then the solution comprising APS was merged with the above suspension comprising ANI under mechanical agitation in a mixture of water and ice. Afterward, the reaction system was kept at 0 °C for 24 h. Thus, the spinning solution II was ready for electrospinning. Tables 1 and 2, respectively, give the actual components of spinning solutions I and II. The two spinning solutions were loaded into two respective plastic syringes with spinnerets, which were successfully connected to a positive high voltage direct current (DC) supply using a copper wire. An iron net as the collection device was placed at the distance of 15 cm from the spinneret and had a connection with the ground electrode of the above DC supply using a copper wire. The iron net was vertically settled and the angle between spinneret and the iron net was ca. 70°. The voltage was controlled between 13 and 14 kV. During every electrospinning process, the plastic syringe containing 4 mL of spinning solution I was first electrospun until all the spinning solution I was completely consumed, and then the other one already loaded with 4 mL of spinning solution II took place of the former to continue electrospinning process until no residual spinning solution II was left. The obtained dual-layered composite nanofibrous membrane were denoted as Sax/Sby (x= 1−5; y= 1−7) according to the corresponding spinning solutions I and II. For comparison, Eu(TTA)3(TPPO)2/Fe3O4/PANI/PVP/PAN monolayered composite nanofibrous membrane was also fabricated as contrast sample by blending equivoluminal spinning solution I (Sa4) and II (Sb2) and electrospinning at the same conditions with those for fabrication of the dual-layered composite nanofibrous membrane. This fabrication process of the monolayered composite nanofibrous membrane is basically the simplest method for the purpose of manufacturing trifunctional membrane. 2.4. Characterization. The as-prepared Fe3O4 NPs, dual-layered composite nanofibrous membrane and monolayered composite nanofibrous membrane were analyzed via using X-ray diffractometer (XRD), which was made by Bruker Corporation with the model of D8 FOCUS, and Cu Kα radiation, 40 kV of acceleration voltage and 20 mA of current were applied. The morphology of the membranes was observed by a scanning electron microscope (SEM, JSM-7610F). An X-MaxN80 energy-dispersive spectrometer (EDS) produced by Oxford Instruments and attached to the SEM was used to analyze elemental compositions. A four probes meter (RTS-4) was adopted to detect electrical conduction property. A vibrating sample magnetometer (VSM) purchased from Qunatum Design Inc. with the type of MPMS SQUID XL was applied to determine magnetism. The fluoroscence was investigated by a F-7000 fluorescence spectrophotometer manufactured by Hitachi. The excitation and emission slits were, respectively, 1.0 and 2.5 nm. The sample cell is a round groove whose diameter and depth are 1.1 cm and 2 mm, respectively. To match the sample cell, the samples

Electrospinning is a relatively simple, straightforward, and versatile fiber-forming technology,23−25 which provides a unique way to produce nanofibers from polymer solutions or melts.26 This method shows an extensive application in cosmetics, skin regeneration, battery, filters, light-emitting diodes and etc.27−31 In previous work, our group has successfully fabricated electricity−magnetism bifunctional film via electrospinning, which can be utilized as EMI shielding materials.32 In this work, we propose a layer-by-layer (LBL) electrospinning technique for fabricating novel luminescent−electrical−magnetic trifunctional dual-layered composite nanofibrous membrane. Of the novel composite membrane, one layer consists of the nanofibers containing PANI, Fe3O4 NPs and PAN which has tunable electrical−magnetic bifunctionality, and the other layer is formed by the template of PVP nanofibers containing RE complex that possesses photoluminescent performance. In order to highlight the excellent performance of dual-layered membrane, we also prepared the counterpart monolayered composite membrane with the same components as contrast sample. Because of its multifunctionality, the new typed dual-layered membrane demonstrates applications in drug trageting, nanodevices and EMI shielding, etc.

2. EXPERIMENTAL SECTIONS 2.1. Chemical Reagents. 2-Thenoyltrifluoroacetone (HTTA), (IS)-(+)-camphor-10 sulfonic acid (CSA), triphenylphosphine oxide (TPPO), Eu2O3 (99.99%), ammonium persulfate (APS), oleic acid (OA), ammonia, FeSO4·7H2O, aniline (ANI), FeCl3·6H2O, NH4NO3, PVP K90 (Mw ≈ 130 000), polyethylene glycol (PEG, Mw ≈ 20 000), N,N-dimethylformamide (DMF), PAN, and absolute alcohol. All of the chemicals were analytically pure. Deionized water was made by ourselves. 2.2. Syntheses of OA-Modified Fe3O4 NPs and Europium Complex. OA modified Fe3O4 NPs and Eu(TTA)3(TPPO)2 complex were used as raw materials for preparing spinning solutions, and they were synthesized according to ref 33 and 34, respectively. 2.3. Fabrication of the Eu(TTA)3(TPPO)2/PVP]/[PANI/Fe3O4/ PAN] Dual-Layered Composite Nanofibrous Membrane via Electrospinning. The first spinning solution for fabricating Eu(TTA)3(TPPO)2/PVP layer (named solution I) was prepared as following. Eu(TTA)3(TPPO)2 was added into DMF (4.5000 g) and then PVP (1.0000 g) was introduced under mechanical agitation at ambient temperature for 24 h. As for preparing the other spinning solution for synthesizing PANI/Fe3O4/PAN layer (named solution II), Fe3O4 NPs were dispersed into DMF (7.0000 g) under ultrasonic for 20 min and then PAN (0.9000 g) was added into the suspension at 60 °C for 5 h. Then CSA and ANI were dispersed into the above suspension B


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ACS Applied Materials & Interfaces were cut into 1.1 cm in diameter and directly put into the sample cell without folding. When the fluorescent layer was adopted as the test surface, the fluorescent layer faced out. On the contrary, the electrical− magnetic layer faced out when it was used as test surface.

3. RESULTS AND DISCUSSION 3.1. Phase Analyses. XRD results of the as-prepared Fe3O4 NPs, dual-layered composite nanofibrous membrane (Sa4/Sb2)

Figure 1. XRD patterns of Fe3O4 NPs, two sides of dual-layered composite nanofibrous membrane (Sa4/Sb2) and the monolayered composite nanofibrous membrane as contrast sample.

and the counterpart monolayered composite nanofibrous membrane are revealed in Figure 1. XRD patterns reveal that the Fe3O4 NPs are readily indexed to cubic-phase of Fe3O4 (PDF#88−0866), and impure phases (e.g., Fe2O3 and FeO(OH)) are not detected. The XRD patterns of the two sides of dual-layered composite nanofibrous membrane are obviously different. When the electrical-magnetic layer faces the detector of X-ray diffractometer, characteristic diffraction peaks of Fe3O4 can be detected. By contrast, no diffraction peaks of Fe3O4 can be observed when fluorescent layer faces toward the detector. These results indicate that Fe3O4 NPs only exist in the electricalmagnetic layer, but not in the fluorescent layer. As for the counterpart monolayered composite nanofibrous membrane, diffraction peaks of Fe3O4 can be detected, indicating that Fe3O4 NPs disperse in the whole monolayered composite nanofibrous membrane. The broad diffraction peaks ranged from 15 to 25° in the samples, showing the existence of amorphous substances. 3.2. Morphology and Structure. The SEM images, EDS spectra, and histograms of diameter distribution of the nanofibers in the membrane are demonstrated in Figure 2. The cross section of the dual-layered membrane can be clearly seen from SEM image with low magnification, as shown in Figure 2a. One can identify that the membrane is composed of two layers with different thicknesses. The thicker electrical−magnetic layer is ca. 159.31 μm in thickness, in which PAN is the template. The thickness of the thinner luminescent layer whose template is PVP is about 64.93 μm. Figure 2c, e shows the SEM images of the electrical−magnetic layer and the luminescent layer at high magnification, respectively. It can be seen that the two layers are composed of crossed nanofibers. Figure 2d, f demonstrates the histograms of the diameter distribution of the nanofibers in each layer. The average diameters are 1.2 ± 0.03 μm and 400 ± 1 nm under the confidence level of 95% for the nanofibers in

Figure 2. (a) SEM images of cross-section, (c) electrical-magnetic layer, (e) luminescent layer, and (b) EDS spectrum of dual-layered composite nanofibrous membrane; the histograms of (d) diameter distribution of nanofibers in electrical-magnetic layer and (f) luminescent layer; SEM images of (g) cross-section and (i) nanofibers, (h) EDS spectrum and (j) the histogram of diameter of monolayered composite nanofibrous membrane.

electrical−magnetic and luminescent layer, respectively. Figure 2b depicts the energy-dispersive spectrum. The dual-layered composite nanofibrous membrane is comprised of elements Fe, Eu, P, S, C, O, and Pt, in which Pt is used as conductive coating layer for SEM observation. At the same time, the morphology of monolayered composite nanofibrous membrane is also observed. The cross section of the monolayered composite nanofibrous membrane shows an unstratified structure and is ca. 215.79 μm in thickness, as shown in Figure 2g. Elemental C, O, Fe, Eu, P, S, and Pt are also observed from the energy dispersive spectrum in Figure 2h. Figure 2i shows the SEM image of the nanofibers in the C


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Figure 4. Schematic diagrams of the structure of (a) dual-layered composite nanofibrous membrane and (b) monolayered composite nanofibrous membrane.

spherical Fe3O4 NPs exist in the nanofibers in electrical− magnetic layer, and the two layers are tightly combined together to form the dual-layered composite membrane. While as illustrated in Figure 4b, the monolayered composite nanofibrous membrane has the same color and components on both sides. All the components, including Eu(TTA)3(TPPO)2, Fe3O4 NPs, PANI, and the templates PVP and PAN, uniformly exist in the whole membrane. 3.3. Electrically Conductive Analysis. The electrical properties of the two layers of the dual-layered composite nanofibrous membrane were investigated. For the testing samples, the mass percentage of Eu(TTA)3(TPPO)2 to PVP and the mass ratio of Fe3O4 to PAN are respectively settled at 20% and 1:1, and the mass percentages of PANI to PAN are changed from 40, 50, 60, to 70%. The electrical conductivities of the dual-layered composite nanofibrous membrane (electrical− magnetic layer) and the monolayered composite nanofibrous membrane are listed in Table 3. All those conductivities were tested for 3 times and the final data were the average results. It has been known that charge transport capacity provided by connective electrical network is a critical factor to the conductivity of PANI.35,36 Therefore, it is evidently seen that with the dosage of PANI increasing, higher conductivity can be achieved, and darker color electrical-magnetic layer possesses. As for the luminescent layer, the electrical conductivity value cannot be obtained by using four probes meter which is used to characterize conductors, meaning that the luminescent layer is insulated. The schematic diagram of the color gradient with different percentage of PANI to PAN is shown in Figure 5. Because PANI is dark green, it is reasonable that the green color of the electrical−magnetic layer becomes darker when more PANI is introduced. It is found from Table 3 that as the dosage of PANI increasing, the conductivity of electrical-magnetic layer enhances dramatically, meaning that the conductive property of the dual-layered composite nanofibrous membrane is able to be readily tuned. The conductivity of electrical-magnetic layer of the

Figure 3. Digital photos of the dual-layered composite nanofibrous membrane: (a) a folded membrane, (b) electrical-magnetic layer, (c) luminescent layer, (d) the emission light under 366 nm excitation in darkness, and (e) monolayered composite nanofibrous membrane.

monolayered composite nanofibrous membrane. As seen from Figure 2j, the average diameter of these nanofibers is 280 ± 1 nm. The physical photos of the membranes are presented in Figure 3a−e. As seen from Figure 3a, there is an obvious difference between the two layers of the membrane. The electrical− magnetic layer is blackish green (Figure 3b) because of the existence of PANI and Fe3O4 NPs, whereas the luminescent layer is white (Figure 3c). One can see that the product possesses a unique and interesting two-layered structure: its two sides reveal different color because of the different compositions. The picture of Figure 3d shows the red light emitted from the luminescent layer under 366 nm UV illumination in darkness. As shown in Figure 3e, the counterpart monolayered composite nanofibrous membrane is blackish green, but the color is lighter than the electrical−magnetic layer of the dual-layered composite nanofibrous membrane, which is because the white Eu(TTA)3(TPPO)2 is mixed into dark-colored PANI and Fe3O4 NPs, leading to overall lighter color. Figure 4 depicts the schematic diagrams of the structures for the dual-layered composite nanofibrous membrane and monolayered composite nanofibrous membrane. As revealed in Figure 4a, in macroscopic view, the dual-layered membrane has different colors on each side. At the microscopic level, the membrane consists of two kinds of nanofibers with different compositions. Eu(TTA)3(TPPO)2 powders appear in the nanofibers in luminescent layer, whereas the PANI molecular chain and D


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Table 3. Electrical Conductivities of Electrical−Magnetic Layer of the Membranes with Different Mass Percentages of PANI and Fe3O4 NPs and Monolayered Composite Nanofibrous Membrane conductivity (S cm−1) samples

variables

Sa4/Sb1

PANI:PAN = 40% Fe3O4:PAN = 1:1

Sa4/Sb2


Sa4/Sb3


Sa4/Sb4


Sa4/Sb5

PANI:PAN = 50% Fe3O4:PAN = 0.5:1

Sa4/Sb6


contrast sample


measurements

average data

5.62 × 10−4 7.34 × 10−4 5.43 × 10−4 4.62 × 10−3 3.38 × 10−3 3.37 × 10−3 7.98 × 10−3 8.81 × 10−3 1.06 × 10−2 1.75 × 10−2 2.34 × 10−2 1.49 × 10−2 4.31 × 10−3 4.50 × 10−3 3.32 × 10−3 2.79 × 10−3 3.87 × 10−3 2.54 × 10−3 6.21 × 10−3 1.35 × 10−3 9.44 × 10−4

6.13 × 10−4

3.79 × 10−3

8.92 × 10−3

1.86 × 10−2

4.04 × 10−3

3.07 × 10−3

2.83 × 10−3

Figure 5. Schematic diagrams of the dual-layered composite nanofibrous membrane containing different mass percentages of PANI.

Table 4. Saturation Magnetization of Fe3O4 NPs, DualLayered Composite Nanofibrous Membranes at Different Fe3O4 NP Mass Ratios and the Monolayered Composite Nanofibrous Membrane As Contrast Sample samples

saturation magnetization (Ms) (emu g−1)

Fe3O4 NPs contrast sample (Fe3O4:PAN = 1:1) Sa4/Sb5 (Fe3O4:PAN = 0.5:1) Sa4/Sb3 (Fe3O4:PAN = 1:1) Sa4/Sb6 (Fe3O4:PAN = 2:1)

30.7 4.1 3.5 4.6 8.4

amounts of Fe3O4 NPs are also tested when other parameters are fixed. The results given in Table 3 illustrate that the existence of Fe3O4 NPs only has a little influence on the conductivity of duallayered composite nanofibrous membrane. 3.4. Magnetism. The hysteresis loops of Fe3O4 NPs, duallayered composite nanofibrous membranes with different mass ratio of Fe3O4 NPs and the contrast sample monolayered composite nanofibrous membrane are revealed in Figure 6, and their saturation magnetizations are summarized in Table 4. As seen from Table 4, along with incorporating more Fe3O4 NPs, the saturation magnetization of dual-layered composite nanofibrous membrane is enhanced from 3.5 to 8.4 emu g−1, implying that the composite membranes possess tunable magnetism. Dual-layered membrane (Sa4/Sb2) has close magnetic property to monolayered composite nanofibrous membrane, which is

Figure 6. Hysteresis loops of the Fe3O4 NPs, dual-layered composite nanofibrous membranes at different Fe3O4 mass ratio and monolayered composite nanofibrous membrane as contrast sample.

dual-layered membrane (Sa4/Sb2) is slightly higher than that of the monolayered membrane for the reason that such insulating materials like Eu(TTA)3(TPPO)2, Fe3O4 NPs, PAN, and PVP are all dispersed in the monolayered composite nanofibrous membrane, resulting in a hindering in the formation of the continuous conducting network. Besides, to research the effect of Fe3O4 NPs on the electrical conductivity, the conductivities of membranes with different E


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Figure 7. Schematic diagrams of the dual-layered composite nanofibrous membrane with various mass ratios of Fe3O4 to PAN.

Figure 8. (a) Excitation and (b−d) emission spectra of dual-layered composite nanofibrous membrane doped with different contents of Eu(TTA)3(TPPO)2 (a, b) at the PANI percentage of 50% and Fe3O4 ratio of 1:1, (c) PANI and (d) Fe3O4 NPs at the Eu(TTA)3(TPPO)2 percentage of 20%.

Figure 9. Illustrations of excitation and emission light of dual-layered composite nanofibrous membrane at (a) various percentages of PANI and (b) various ratios of Fe3O4.

F


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introduced into polymer matrix.37,38 Thus, 20% of Eu(TTA) 3(TPPO) was picked for fabricating dual-layered composite nanofibrous membrane in the following study. On the other hand, the luminescent property of dual-layered composite nanofibrous membranes is also explored via modulating the contents of PANI and Fe3O4 NPs. As shown in Figure 8c, d, it is amazing to find that no significant decrease of emission intensity of luminescent layers in the dual-layered composite membranes is observed when the contents of Fe3O4 and PANI are varied. As seen from the schematic diagrams in Figure 9, owing to the unique dual-layered structure, the electrical−magnetic layer has little impact on the luminescent property of the luminescent layer, despite the varied contents of PANI and Fe3O4 NPs in the electrical-magnetic layer (possessing tunable electrical-magnetic bifunctionality). The new findings can be explained that the new-typed dual-layered composite nanofibrous membrane realizes the isolation of electricalmagnetic layer from luminescent layer, leading to almost no impact between the two layers. Besides, to further demonstrate the advantage of the unique structure of the dual-layered membrane, the fluorescent performance of the luminescent layer and electrical−magnetic layer of dual-layered membrane are respectively investigated by comparing with those of the monolayered composite nanofibrous membrane. As shown in Figure 10, one can see that no emission can be detected in the electrical-magnetic layer because the excitation light cannot pass through the electrical-magnetic layer and excite the Eu(TTA)3(TPPO)2 in the fluorescent layer, and simultaneously, indicating that Eu(TTA)3(TPPO)2 does not mix into the electrical-magnetic layer. Thus, a conclusion can be safely drawn that the dual-layered membrane has different fluorescent properties in the two layers. Compared with the luminescent layer of dual-layered composite nanofibrous membrane, monolayered composite nanofibrous membrane exhibits very weak emissions of Eu3+. Figure 11 is the schematic diagrams revealing the comparison of photoluminescent property between dual-layered membrane (luminescent layer) and monolayered membrane. As for the monolayered composite nanofibrous membrane, Eu(TTA)3(TPPO)2 directly contacts with deep-colored PANI and Fe3O4 NPs which strongly absorb and weaken excitation and emission light, leading to a severe decrease in luminescent intensity.39 On the other hand, many studies have proved that elemental Fe can cause fluorescence quenching of RE luminescent compounds, which also results in the decrease in luminescent intensity.40,41 On the contrary, because the luminescent layer and electrical-magnetic layer are separated in dual-layered composite nanofibrous membrane, the luminescent property of the luminescent layer is almost unaffected by electrical-magnetic layer. This result fully demonstrates that dual-layered composite nanofibrous membrane possesses better fluorescence properties. Judging from the above analysis of electricity, magnetism and luminescence, we can reasonably arrive at the conclusion that the dual-layered nanofibrous membrane possesses better performances than its counterpart monolayered membrane.

Figure 10. Emission spectra of luminescent layer and electricalmagnetic layer in dual-layered composite nanofibrous membrane (Sa4/ Sb2) and monolayered composite nanofibrous membrane as contrast sample.

Figure 11. Illustrations of excitation and emission light of (a) duallayered composite nanofibrous membrane and (b) monolayered composite nanofibrous membrane.

because they have the same theoretical Fe3O4 contents. The schematic diagrams of the dual-layered composite nanofibrous membrane containing different mass ratios of Fe3O4 to PAN are depicted in Figure 7. The color in the electrical−magnetic layer of the dual-layered composite nanofibrous membrane is changed from yellowish-green to dark green with the increase of Fe3O4 contents. This is because black Fe3O4 NPs darken the color of the electrical−magnetic layer. 3.5. Fluorescent Performance. A series of dual-layered composite nanofibrous membranes doped with various contents of Eu(TTA)3(TPPO)2 are fabricated to study the fluorescent performance of the dual-layered composite nanofibrous membrane when the contents of PANI to PAN is 50% and Fe3O4 to PAN is settled to 1:1. Figure 8a, b demonstrates the excitation and emission spectra in the luminescent layer of duallayered composite nanofibrous membrane, in which the Eu(TTA)3(TPPO)2 content is varied from 5% to 25% (samples Sax/Sb2, x = 1−5). As illustrated in Figure 8a, there is a wide band from 200 to 400 nm in excitation spectra monitored at 615 nm. π → π* electron transition of ligands at 366 nm can be determined as well. According to the emission spectra in Figure 8b, under 366 nm excitation, strong characteristic emission peaks of Eu3+ are located at 580, 592, 615 nm. These peaks are respectively attributed to 5D0 → 7F0, 5D0 → 7F1, 5D0 → 7F2 energy level transitions, and the red light emission at 615 nm assigned to 5D0 → 7F2 hypersensitive transition is dominant. With the increase in Eu(TTA)3(TPPO)2 concentration, fluorescent intensity gradually increases first and then decreases. The sample containing 20% of Eu(TTA)3(TPPO)2 has the highest intensity. The decrease of fluorescent intensity as the content of Eu(TTA)3(TPPO)2 exceeds 20% is attributed to fluorescence quenching due to the fact that too many rare earth complexes are

4. CONCLUSIONS In summary, a new-typed trifunctional dual-layered composite nanofibrous membrane endowed with luminescence at one layer, magnetism and electrical conduction at the other layer has successfully been fabricated for the first time via electrospinning technology by means of modulating spinning solutions one by one during electrospinning process. The thicknesses of G


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luminescent layer and electrical-magnetic layer are 64.93 and 159.31 μm, respectively. The electrically conductive performance and magnetism of the dual-layered composite nanofibrous membrane are modulated through varying the contents of PANI and Fe3O4 NPs. Furthermore, it is very gratifying to see that the dual-layered composite nanofibrous membrane shows excellent luminescent property without significant impact by the PANI and Fe3O4 NPs. This novel dual-layered composite nanofibrous membrane may have applications in the fields of EMI shielding materials, nanodevices, and full-color display. Moreover, the design philosophy and fabrication method are significant to new-typed multifunctional materials.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Tel.: +86-043185582575. Fax: +86-0431-85383815. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (NSFC 51573023, 50972020, 51072026), the Science and Technology Development Planning Project of Jilin Province (Grants 20130101001JC, 20070402).

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Novel Electrospun Dual-Layered Composite Nanofibrous Membrane

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