- Email: [email protected]
Preparation and characterization of Fe3O4-CNTs magnetic nanocomposites for potential application in functional magnetic printing ink
Composites Part B 89 (2016) 295e302
Contents lists available at ScienceDirect
Composites Part B journal homepage: www.elsevier.com/locate/compositesb
Preparation and characterization of Fe3O4-CNTs magnetic nanocomposites for potential application in functional magnetic printing ink Xing Zhou a, b, Changqing Fang a, b, *, Yan Li a, Ningli An b, Wanqing Lei b a b
School of Mechanical and Precision Instrument Engineering, Xi'an University of Technology, Xi'an 710048, PR China Faculty of Printing, Packaging Engineering and Digital Media Technology, Xi'an University of Technology, Xi'an 710048, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 17 March 2015 Received in revised form 21 September 2015 Accepted 20 November 2015 Available online 12 January 2016
This paper presents the synthesis of magnetic carbon nanotube, Fe3O4-CNTs nanocomposites, in which Fe3O4 nanoparticles were grafted to multi-walled carbon nanotube (CNTs) by the in situ hydrothermal method. The prepared Fe3O4-CNTs nanocomposites were characterized by Fourier transform infrared spectroscopy (FT-IR), Raman, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and vibrating sample magetiometer (VSM). It was found that the Fe3O4 nanoparticles with the size of 20e50 nm had been attached to the CNTs strongly and the nanocomposites exhibited high magnetic saturation value, namely a high magnetic attachment force. Moreover, the nanocomposites were used to prepare magnetic printing ink via physical blending process. The ink film was detected by SEM and VSM, demonstrating that the magnetic ink which holds significant magnetic attachment force and drying smooth film is suitable for the printing industry. © 2016 Elsevier Ltd. All rights reserved.
Keywords: A. Polymer-matrix composites (PMCs) A. Nano-structures B. Magnetic properties B. Microstructures
1. Introduction As one of the most important anti-counterfeit materials, magnetic printing inks have been drawing wide attention and applied to vital fields for checking authenticity, such as identity card, check, paper currency, ticket, etc. which due to their efficient information storage, legibility, efficient anti-counterfeit, and low cost [1]. Actually, magnetic inks using letterpress and lithographic printing methods for document processing have been employed for several decades [2]. To study and develop magnetic printing inks, it is essential to have a deep understanding about the composition of the ink. Commonly, inks are composed of four types of ingredients: colorant, vehicle or binder, solvent and additives. The colorant is a pigment (or dye), which presents ink with color, even with some special properties to obtain special-effect inks, such as electrically conductive printing ink, magnetic printing ink, metallic printing ink, fluorescent ink, luminous ink, etc. The vehicles or binders have multiple functions in the ink, dispersing and binding the pigments,
* Corresponding author. School of Mechanical and Precision Instrument Engineering, Xi’an University of Technology, Xi’an 710048, PR China. Tel.: þ86 29 82312038; fax: þ86 29 82312512. E-mail address: [email protected] (C. Fang). http://dx.doi.org/10.1016/j.compositesb.2015.11.041 1359-8368/© 2016 Elsevier Ltd. All rights reserved.
modifying the rheological and mechanical properties, and presenting some other special properties. Solvent is to dissolve the vehicles or binders and adjust the viscosity of the ink. And additives are used to enhance the properties of ink [3]. As for magnetic printing ink, the magnetism stems from the colorants, which are commonly soft ferrites including black iron oxide (Fe3O4), brown iron oxide (g-Fe2O3), iron oxide containing cobalt (CoeFe2O3), chromium hemitrioxide (CrO2), etc [4]. These materials have been widely used in magnetic printing inks, especially the Fe3O4, of which particles are mainly acicular crystal with the size below 1 mm, making the particles are easily arranged under a magnetic field so that to acquire a high magnetism. Nevertheless, the Fe3O4 shows excellent adsorption behavior for oil in inks and inferior transfer printing performance, which may cause problems for presswork in printing process. It is said that the nanosized Fe3O4 could significantly solve these problems. Meanwhile, the nanosized particles are advantageous for use on printing substrate (mainly papers) due to the limited penetration of the magnetic particles into the substrate [5]. However, what depressed is that the sizes of Fe3O4 nanoparticles are most about 70 nm, which may cause aggregation and precipitation in the magnetic ink [6,7]. To solve the problems caused by the Fe3O4 as colorant, it is essential to develop efficient
296
X. Zhou et al. / Composites Part B 89 (2016) 295e302
ways to achieve a stable magnetic pigment in nanosized. Recently, various approaches have been explored to prepare stable magnetic Fe3O4 nanoparticles. Peng et al. [8] prepared monodispersed magnetic Fe3O4 nanoparticles with the size about 3e50 nm via a facial and repeatable method on the basis of the high-temperature pyrolysis of metal fatty acid in non-water solvent. Lemine et al. [9] acquired magnetic Fe3O4 nanoparticles in the size of about 8 nm through solegel method. Among these approaches, one main strategy is to synthesize Fe3O4 nanoparticles covered with some kind of organic/inorganic membrane [10,11], which can effectively decrease the interaction among the nanoparticles and increase the stability of magnetic pigment. On the basis of the decoration methods and conducted by the recent novel attractive carbon nanotubes (CNTs) [12,13], we assumed that the decoration of CNTs with magnetic nanoparticles (Fe3O4 in this research) is extremely promising for application as perfect magnetic colorant [14]. Actually, the combination of CNTs and Fe3O4 has been studied in lithium ion batteries [15,16], which improved or imparted new optical, magnetic and electrochemical properties for the composites. Nonetheless, no research about Fe3O4-CNTs composite has been studied in printing inks. We consider that the Fe3O4-CNTs composite can disperse homogeneously in water and water-based polymer [17], signifying a potential used in water-based ink and potential value for environmental protection. Therefore, we reported a facile and effective chemical approach to prepare the magnetic Fe3O4-CNTs nanocomposite with good appearance and magnetism. Then, the nanocomposite was used as the pigment to prepare ink and the performances and process of the nanocomposite and ink were discussed. 2. Experiment 2.1. Materials Multi-walled carbon nanotubes (CNTs) were purchased from Beijing BOYU GAOKE New Materials Co., Ltd. China. The diameter is in 20e40 nm and length is about 10e30 mm. Nitric acid (HNO3, 65e68 wt%) was purchased from Sichuan XILONG Chemical Reagent Co., Ltd. China. Ethylene glycol (EG) was purchased from Tianjin FUCHEN Chemical Reagent Factory China. FeCl3$6H2O, NaAc, ethidene diamine (EDA), Ethyleneglycol monobutyl ether (EGME), and Paraffin liquid were purchased from Tianjin TIANLI Chemical Reagent Co., Ltd. China. Ethanol absolute was purchased from Tianjin FUYU Fine Chemical Reagent Co., Ltd. China. Waterborne polyurethane dispersion (WPU) and the pigment were prepared by the previous work of our group [18,19]. Polysiloxane used as antifoaming agents in preparing ink was purchased from Jinan DUOWEIQIAO Chemical Co., Ltd. China. Apart from the CNTs, all the reagents are of analytical grade and used without any further purification. 2.2. Purification of CNTs The commercial CNTs was purified by ultrasonically dispersing it in mixture of deionized water and HNO3 for 30 min, and then the mixture of CNTs and HNO3 (5 mol/L) was stirred at 60 C for 12 h in a reflux unit. Afterwards, the solution was diluted and rinsed by deionized water under a centrifuge (Cence H1850, XiangYi, Hunan, China) with the 6000 r/min for several times until the pH value detected by PHS-3C Digital Display Acidity Meter (Hangzhou LEICI Analytic Factory China.) with an E-201-9 pH Combination Electrode from Shanghai Ruosull Science and Technology Co., Ltd. China reaches neutral, and then dried in vacuum at 60 C and grinded with an agate mortar. The acidifying CNTs were calcined at 400 C for 3 h to obtain pure CNTs for further use.
2.3. Synthesis of Fe3O4-CNTs nanocomposites The Fe3O4-CNTs nanocomposites were prepared by the in situ hydrothermal method in a Teflon-lined stainless-steel autoclave (50 mL capacity) in just one step. Firstly, a mass of 0.04 g purified CNTs were dispersed into a 100 mL beaker filling with 30 mL EG with ultrasonic agitation for 30 min. During the ultrasonic agitation, the beaker was covered by a piece of PE film. Secondly, 0.6 g grinded FeCl3$6H2O, 1.8 g NaAc and 6 mL EDA were added into the dried Teflon-lined stainless-steel autoclave. Thirdly, the dispersed CNTs were transferred slowly into the autoclave and stirred by a glass rod. Then, the autoclave was kept at 200 C for 4 h in an oven. Finally, the mixture was magnetically separated and then alternately washed with deionized water and ethyl alcohol for several times until no possible impurities can be found in the liquid supernatant. The obtained product was dried at 50 C in an oven for 24 h for future use. The synthesis process was shown in Fig. 1. As a comparison, Fe3O4 nanoparticles were prepared through the same process without CNTs. The proportion of the components except for magnetic particles was shown in Table 1. 2.4. Preparation of magnetic printing ink The magnetic printing ink was prepared by the physical blending process with the electric stirrer (FLUKO R30, Shanghai, China) in four-blade type agitator and high shear dispersing emulsifier (FLUKO FM200, Shanghai, China) in standard dispersing tool (18G). First of all, waterborne polyurethane dispersion used as binder was added into a 250 mL beaker, following by addition of 5 mL ethanol absolute, deionized water and the pigment. After half an hour stirring with the speed of 500 rpm, the Fe3O4-CNTs nanocomposite was added into the beaker for about 3 h stirring. And then, a partial polysiloxane was used to eliminate the foam caused by stirring. The ink system was transferred to the high shear dispersing emulsifier with the speed of about 7000 rpm for 1 h to produce the ink emulsion. Finally, EMGE and Paraffin liquid were mixed with the emulsion under the 500 rpm stir. The ink film was obtained by casting the emulsion onto Teflon surfaces, a slow evaporation of the solvent at room temperature for 2 days and then at 50 C in a vacuum drying oven for 24 h to allow the complete removal of solvent. Then, the ink film with Teflon was stored in a desiccator to avoid moisture. 2.5. Characterization of Fe3O4-CNTs nanocomposite and ink film Fourier transform infrared spectroscopy (FT-IR) was used to identify the structure of the CNTs, purified CNTs and Fe3O4-CNTs nanocomposites. The infrared spectra were obtained using a Fourier transform IR spectrophotometer (SHIMADIU FTIR-8400S (CE)) and recorded in the transmission mode at room temperature by averaging 20 scans at a resolution of 16.0 cm1. The spectra were analyzed in the frequency range of 4000e400 cm1. Raman experiments were performed on LabRAM HR 800 (HORIBA JOBIN YVON) using 633 nm excitation line from a HeeNe laser with the power about 0.5 mW under a microscope objective lens of 50WLD. The wavenumber range was 100e3500 cm1, the temperature was kept at 25 C and the samples were pressed smoothly on a clean glass slide. An X-ray diffractometer (XRD) instrument (XRD-7000, SHIMADZU LIMITED, Japan) was used to analyze the crystal structures of the Fe3O4-CNTs nanocomposites with monochromatic Cu Ka radiation (1.540598 nm). A scanning of 2q angles between 10 and 70 under the scan speed of 8.0000 deg/min was carried out. Transmission electron microscopy (TEM) was performed to investigate the microstructures of purified CNTs and Fe3O4-CNTs nanocomposites using a JEM-3010 microscope with the
X. Zhou et al. / Composites Part B 89 (2016) 295e302
297
Fig. 1. The purification process by HNO3 and decorating process with Fe3O4 nanoparticles for CNTs.
Table 1 Components of magnetic printing ink except for magnetic particles. Components
WPU
Polysiloxane
EGME
Paraffin
Pigment
The content (wt %)
65
0.5
8
1
24.5
Gatan894 CCD camera working at accelerating voltage of 300 kV with Energy Dispersive X-ray spectrometers (EDS) (Oxford INCA) under an accelerating voltage of 20 kV. The morphology of the Fe3O4-CNTs nanocomposite and ink film was analyzed with a Field Emission Scanning Electron Microscope (FE-SEM, SU8000) using an acceleration voltage of 1 kV with Energy Dispersive X-ray spectrometers (EDS) under an accelerating voltage of 20 kV. The experiments of magnetic properties of the CNTs, Fe3O4-CNTs and ink film were carried out using a vibrating sample magnetometer (VSM, VersaLab, Quantum Design, USA) with a frequency of 40 Hz under the temperature of 300 K. 3. Results and discussion 3.1. Structure of CNTs and Fe3O4-CNTs nanocomposite The structure of Fe3O4-CNTs nanocomposite was analyzed by FT-IR spectroscopy, as shown in Fig. 2. It can be observed that the
Fig. 2. FTIR spectra purified CNTs and Fe3O4-CNTs nanocomposite, respectively.
FT-IR spectra of the purified CNTs contain the only one band at 3386 cm1 assigned to the eOH stretching and bending modes in the functional groups, while the bands of Fe3O4-CNTs nanocomposite were diverse. It is noted that the band of nanocomposite at 486 cm1 assigned to the FeeO stretching and bending modes [20,21], indicating the formation of Fe3O4-CNTs nanocomposite. In addition, the bands at 3475 cm1, 1639 cm1, 1095 cm1 and 760 cm1 were ascribed to the stretching and bending modes of eOH, C]O, CeO and C]O (COO) in the functional groups of the nanocomposite. These abundant functional groups in the Fe3O4CNTs nanocomposite were beneficial for the dispersion in waterborne binder to prepare water-based ink. Raman spectra shown in Fig. 3 provide further evidence for the formation of Fe3O4-CNTs nanocomposite with the appearance of characteristic peaks of both Fe3O4 and CNTs in Fe3O4-CNTs nanocomposite spectrum. As depicted in pure CNTs Raman spectrum, the peaks, assigned to G mode (1578 cm1) and D mode (1327 cm1) respectively, are strong, and the same as to the secondary Raman signal of G0 mode (2656 cm1, the first overtone of D mode). Meanwhile, the radial breathing mode (RBM) at 230 cm1, which is the unique mode of CNTs [22], can be observed in a weak appearance in the spectrum. The ratio of ID/IG, which presents the degree of functionalization for CNTs, is ca. 1.16 and ca. 1.09 for CNTs and Fe3O4-CNTs nanocomposite, respectively. The different ratios of
Fig. 3. Raman spectra of CNTs, Fe3O4 nanocrystals, and Fe3O4-CNTs nanocomposite, respectively.
298
X. Zhou et al. / Composites Part B 89 (2016) 295e302
ID/IG suggest that the CNTs are more imperfect than Fe3O4-CNTs nanocomposite. As to Raman spectrum of Fe3O4, a strong characteristic peak at 684 cm1 can be observed. The G mode, D mode, G0 mode and characteristic peak (position a) ascribed to Fe3O4 are obvious in the Fe3O4-CNTs nanocomposite spectrum, and all of them become weak due to the low weight percent of Fe3O4 and CNTs in the nanocomposite and the chemical interactions between them [16]. The XRD patterns of the purified CNTs and Fe3O4-CNTs nanocomposite were shown in Fig. 4(a). The diffraction peaks assigned to the (002) reflection of CNTs at 2q ¼ 25.96 can be clearly seen in the purified CNTs and Fe3O4-CNTs nanocomposite. It was identified as the hexagonal graphite structure, indicating that the CNTs structure was not destroyed after the chemical precipitation of Fe3O4 [15]. Meanwhile, the intensity of the hexagonal graphite structure on CNTs was stronger than that of Fe3O4-CNTs nanocomposite, which may be ascribed to the reason that the wellcrystalline Fe3O4 grafted on the CNTs surface weakened the diffraction peak at 25.96 [23]. As shown in Fig. 4(a), the peaks at 30.3 , 35.5 , 43.32 , 57.22 and 63.04 were identified as the (220), (311), (400), (511) and (440) planes of the spinel phase of cubic Fe3O4 with O7h (F3dm) space group (JCPDS No. 65e3107), respectively [24], indicating that the resultant Fe3O4 nanoparticles in the composites are pure Fe3O4 according to the previous [15,25]. The peaks of Fe3O4-CNTs nanocomposite belongs to cubic Fe3O4 are broadened and in low intensity, implying that the crystalline size of Fe3O4 nanocrystals are quite small. Moreover, the morphology of Fe3O4 nanocrystals was shown clearly as the cubic shape in Fig. 4(b). It seemed that the particle size of these cubic Fe3O4 nanocrystals was in the range of about 20e50 nm, which can be confirmed by using Scherrer's formula on the basis of X-ray diffraction as follows [16]:
D ¼ ð0:889l=bÞcos qB Where D (nm) is the crystallite size, l (nm) is the X-ray wavelength, b (rad) is the full width at half maximum (FWHM) reflecting line broadening, qB is the Bragg angle corresponding to the maximum intensity peak, namely the peak (311) in this research. The XRD results and the morphology of the cubic Fe3O4 nanocrystals on the CNTs indicated that the Fe3O4-CNTs nanocomposite were successfully synthesized by the simple hydrothermal method. The morphology of the prepared CNTs and Fe3O4-CNTs nanocomposite were investigated by TEM and SEM, as shown in Figs. 5 and 6, respectively. It is clear that the purified CNTs, with diameter of about 50 nm as shown in Fig. 5(a), present well-graphitized walls in high purity. Fig. 5(b) and (c) illustrate the morphology of the
Fe3O4-CNTs nanocomposite, which reveal that the purified CNTs surface is uniformly coated with Fe3O4 nanoparticles with diameter less than 10 nm (the diameter can be clearly seen in the black area in Fig. 5(d)). Meanwhile, the laminar morphology and hollow structure of CNTs, which contain about 20 layers and a ~10 nm nanotube, can be clearly observed in Fig. 5(d). The Fe3O4 nanoparticles cover ca. 3e5 layers of the surface of CNTs, indicating that the nanoparticles have been well attached on the CNTs surface in this paper. The Fe3O4 nanoparticle, as shown in the corresponding high-magnification TEM image in Fig. 5(d), presents a distance between adjacent lattice planes of about 0.11 nm, which is in good agreement with the d-spacing of the (5 1 1) plane of Fe3O4 (0.14 nm) [7,26]. Furthermore, the selected area diffraction pattern of Fe3O4 nanoparticle suggests that it is crystalline, and the all diffraction rings in Fig. 5(e) could be indexed to Fe3O4 nanoparticle with cubic symmetry. These crystalline cubic Fe3O4 nanoparticle results are corresponding to the analysis of XRD and SEM results in Fig. 4. Fig. 5(f) and Table 2 suggest that the nanocomposite basically have no extra materials except for CNTs and Fe3O4, indicating the processes in this research to purify multi-walled CNTs and synthesized Fe3O4-CNTs nanocomposite are easy to obtain high purity produces. The percentage of atom of C (52.23%) and Fe (22.38%) element in Table 2 gives the information of the ratio of CNTs and Fe3O4 nanoparticles in detail, meaning the ratio of the CNTs: Fe3O4 ¼ 7: 1. What calls for special attention is that the percentage of Fe and O element listed in Table 2 is not the same with Fe3O4 (the theoretical ratio of Fe: O should be 0.75, while the actual ratio is about 0.88). The higher percentage of O could be introduced by the oxidation of CNTs. This can be demonstrated by the result of EDS experiment during the SEM experiment of the purified CNTs. The SEM images of CNTs and Fe3O4-CNTs nanocomposite in Fig. 6 show that the CNTs randomly circumvolute with an outer diameter of approximately 30e50 nm. Comparing with Fig. 6(a), Fig. 6(b) of Fe3O4-CNTs nanocomposite clearly shows that the Fe3O4 nanoparticles distributes uniformly on the surface of CNTs network, indicating that the method taken in this research is effective to obtain magnetic Fe3O4-CNTs nanocomposite. Furthermore, as shown in Fig. 6(c), additional oxygen (8.35 wt %) can be detected in the purified CNTs (the weight percentage of C element is 91.65%), indicating that the CNTs has been functionalized by nitric acid. This result is corresponding to the extra O element content in TEM detection above. In order to characterize the magnetic properties, a vibrating sample magetiometer was used to record the magnetic behavior of the CNTs, Fe3O4-CNTs nanocomposite and Fe3O4. Fig. 7 exhibits the hysteresis loops of the as-prepared samples at room temperature. It can be seen that the magnetic saturation value of the Fe3O4-CNTs
Fig. 4. (a) X-ray diffraction patterns of the normal CNTs and Fe3O4-CNTs nanocomposite, (b) SEM picture of cubic Fe3O4 nanocrystals in the Fe3O4-CNTs nanocomposite.
X. Zhou et al. / Composites Part B 89 (2016) 295e302
299
Fig. 5. TEM micrograph of (a) purified CNTs; (b) Fe3O4-CNTs nanocomposite; (c) and (d) are the corresponding high-magnification image of Fe3O4-CNTs nanocomposite in (b); (e) TEM diffraction pattern image of Fe3O4-CNTs nanocomposite; (f) EDS of Fe3O4-CNTs nanocomposite.
nanocomposite (38 emu/g, Fig. 7(b)) is much higher than that of purified CNTs (0.18 emu/g, Fig. 7(a)), while smaller than that of pure Fe3O4 (56 emu/g Fig. 7(c)) with the applied field of 10,000 Oe at room temperature. The remanence of nanocomposite is more stable than that of CNTs. Moreover, both the Fe3O4-CNTs nanocomposite and Fe3O4 presents zero remanence when the applied magnetic field is moved, implying that the nanocomposite is
superparamagnetic [7,25]. The decrease of magnetic saturation value of Fe3O4-CNTs nanocomposite compared with that of Fe3O4 may arise from the electromagnetic interference shielding property [27]. Due to the superparamagnetic and facile magnetism (38 emu/ g), it may be used as a promising vehicle for biological and functional application for it prevents the magnetic materials from aggregating and enables it to redisperse rapidly when the extra
300
X. Zhou et al. / Composites Part B 89 (2016) 295e302
Fig. 6. SEM micrograph of (a) purified CNTs; (b) Fe3O4-CNTs nanocomposite; (c) EDS of purified CNTs.
Table 2 Components of Fe3O4-CNTs nanocomposite from the EDS.
3.2. Characterization of functional magnetic printing ink
Element
Percentage of weight (wt %)
Percentage of atom (%)
CK OK Fe K Total
27.47 17.79 54.74 100.00
52.23 25.39 22.38
magnetic field is removed [20]. In addition, the magnetic saturation value of nanocomposite increases three magnitudes comparing with that of CNTs, resulting in the aggregation of nanocomposite with the aid of the eight appearance external magnet. In contrast, the purified CNTs dispersed in deionized water keep impassive in suspension for about 1 h under the magnet. This difference arises from the Fe3O4 uniformly attached to the CNTs surface. With this unique property, we assume it may be used as the additive to prepare magnetic inks with the facile magnetism in printing industry.
To observe the dispersion of Fe3O4-CNTs nanocomposite in the ink and the morphology of magnetic printing ink [28], the ink film was performed on the SEM, as shown in Fig. 8. As a comparison, the ink film with pure Fe3O4 was also observed. It can be seen that the pigment particle size is in micro scale, shown as the weak light pots in Fig. 8(a) and (b). It suggests that the addition of Fe3O4-CNTs nanocomposite does not cover the pigment, presenting a primary color of the pigment for the ink. Meanwhile, the lines shown in Fig. 8(a) and (b) indicate that the nanocomposite has been widely and uniformly dispersed in the ink. No crack is found in the micrograph, implying that the ink film is smooth and suitable for printing. Furthermore, no obvious CNTs can be observed, indicating that the Fe3O4-CNTs nanocomposite has been coated by the other components in the ink. Notably and luckily, at the edge of the ink film, some bridge-liked linkages in the ink film were founded, indicating that the nanocomposites dispersed well in the ink. As
Fig. 7. Hysteresis loops of (a) purified CNTs; (b) Fe3O4-CNTs nanocomposite; (c) Fe3O4. The inset in (a) is the photograph of magnet in an eight appearance (left); the insets in (a), (b) and (c) (all the right) are the photographs of CNTs, Fe3O4-CNTs nanocomposite and Fe3O4 dispersed in deionzed water in the presence of the external magnet.
X. Zhou et al. / Composites Part B 89 (2016) 295e302
301
Fig. 8. SEM micrograph of magnetic printing ink: (a) 5000, (b), (c) 15,000 Fe3O4-CNTs nanocomposites; (d) Fe3O4.
comparison, the particles presented in Fig. 8(d) obviously aggregated together, indicating that the dispersion of Fe3O4-CNTs composites is better than that of pure Fe3O4. The magnetic property of the magnetic printing ink was detected by the vibrating sample magetiometer (VSM). Fig. 9 presents the hysteresis loops of the magnetic ink at room temperature. The ink film presents zero remanence when the applied magnetic field is moved, suggesting that the ink is superparamagnetic. Comparing with the magnetic force of the purified CNTs (0.18 emu/ g) and Fe3O4-CNTs nanocomposite (38 emu/g), the ink film presents a suitable magnetic force (1.58 emu/g) which is much lower than that of the nanocomposite while higher than that of the purified CNTs. The reduction of the magnetic force of the magnetic ink film
indicates that the magnetic force was affected by the other components of the ink, such as waterborne polyurethane binder and additives. This arises from the coating of the other components surrounding the Fe3O4-CNTs nanocomposite. We consider that the coating weakens the magnetic field response of the nanocomposite and reduces the magnetism of the ink. Comparing with the magnetic force (in the range of 0.6e0.6 emu/g) of the magnetic nanoparticle based inks reported by Speliotis et al. [29] and Shi et al. [12], the stronger magnetic force of ca. 1.58 emu/g (under the applied field of 10,000 Oe) for the Fe3O4-CNTs nanocomposite suggests that the magnetic ink holds the potential application in screen-printing. Furthermore, the inserted picture in Fig. 9 depicts the attraction of the magnetic ink film by the magnet, signifying magnetic attracted performance for the magnetic ink film. 4. Conclusions A facile and effective chemical approach has been carried out for synthesizing Fe3O4-CNTs nanocomposite. The FT-IR, Raman, TEM and SEM results suggest that Fe3O4 nanoparticles (particles size in the range of 20e50 nm) have been strongly and uniformly attached to the purified CNTs. According to the VSM, the Fe3O4-CNTs nanocomposite presents a property of superparamagnetic, holding a potential application in vehicle for biological and functional materials. In addition, magnetic printing ink was prepared with the Fe3O4-CNTs nanocomposite via the physical blending process. The ink film shows a smooth surface and high attachment force to the magnet, indicating that the magnetic ink hold an excellent performance for screen-printing and anti-counterfeit. Acknowledgements
Fig. 9. Hysteresis loops of magnetic ink film and the attracted film by magnet (inserted picture).
The authors acknowledge the financial supports provided by the Natural Science Foundation of China (Grant No. 51372200), Programs for New Century Excellent Talents in University of Ministry
302
X. Zhou et al. / Composites Part B 89 (2016) 295e302
of Education of China (Grant No.: NCET-12-1045), Shaanxi Programs for Science and Technology Development (Grant No. 2010K01-096), Xi'an Programs for Science and Technology Plan (Grant No. CXY1433(6)) and (Grant No. CXY1430(9)), Ph.D. Innovation fund projects of Xi'an University of Technology (Fund No. 310-252071501).
References € rlenbach: Wiley-VCH Verlag GmbH & [1] Gubin SP. Magnetic nanoparticles. Mo Co. KGaA, Weinheim; 2009. [2] Charles SW. Some application of magnetic fluids-use as an ink and in microwave system. J Magn Magn Mater 1987;65(2e3):350e8. [3] Robert T. “Green ink in all colors”dprinting ink from renewable resources. Prog Org Coat 2015;78:287e92. [4] Yurkov GY, Baranov DA, Dotsenko IP, Gubin SP. New magnetic materials based on cobalt and iron-containing nanoparicles. Compos Part B 2006;37:413e7. [5] Huang Q, Shen W, Xu Q, Tan R, Song W. Properties of polyacrylic acid-coated silver nanoparticle ink for inkjet printing conductive tracks on paper with high conductivity. Mater Chem Physic 2014;147:550e6. [6] Li YD, Liao HW, Qian YT. Hydrothermal synthesis of ultrafine a-Fe2O3 and Fe3O4 powders. Master Res Bull 1998;33:841e4. [7] Si SF, Li CH, Wang X, Yu DP, Peng Q, Li YD. Magnetic monodisperse Fe3O4 nanoparticles. Cryst Growth Des 2005;5(2):391e3. [8] Jana NR, Chen Y, Peng X. Size-and shape-controlled magnetic (Cr, Mn, Fe, Co, Ni) oxide nanocrystals via a simple and general approach. Chem Mater 2004;16:3931e5. [9] Lemine OM, Omri K, Zhang B, Mir LE, Sajieddine M, Alyamani A, et al. Sol-gel synthesis of 8 nm magnetite (Fe3O4) nanoparticles and their magnetic properties. Superlattices Microstruct 2012;52:793e9. [10] Marjanovi c N, Chiolerio A, Kus M, Ozel F, Tilki S, Ivanovi c N, et al. Magnetite nanoparticles: synthesis, thin film properties and inkjet printing of magnetic cores for inductor applications. Thin Solid Films 2014;570:38e44. [11] Zhang W, Chen X, Tang T, Mijowska E. Superstable magnetic nanoreactors with high efficiency for Suzuki-coupling reactions. Nanoscale 2014;6: 12884e9. [12] Shi D, He P, Zhao P, Guo FF, Wang F, Huth C, et al. Magnetic alignment of Ni/ Co-coated carbon nanotubes in polystyrene composites. Compos Part B 2011;42:1532e8. [13] Koo Y, Littlejohn G, Collins B, Yun Y, Shanov VN, Schulz M, et al. Synthesis and characterization of AgeTiO2eCNT nanoparticle composites with high photocatalytic activity under artificial light. Compos Part B 2014;57:105e11.
~ a A. New alignment procedure of [14] Prolongo SG, Meliton BG, Rosario GD, Uren magnetiteeCNT hybrid nanofillers on epoxy bulk resin with permanent magnets. Compos Part B 2013;46:166e72. [15] He Y, Huang L, Cai JS, Zheng XM, Sun SG. Structure and electrochemical performance of nanostructured Fe3O4/carbon nanotube composites as anodes for lithium ion batteries. Electrochim Acta 2010;55:1140e4. [16] Guo Q, Guo P, Li J, Yin H, Liu J, Xiao F, et al. Fe3O4-CNTs nanocomposites: inorganic dispersant assisted hydrothermal synthesis and application in lithium ion batteries. J Solid State Chem 2014;213:104e9. [17] Ren D, Li Z, He P. Chemistry of carbon nanotubes. Beijing: Chemical Industry Press; 2013. [18] Fang CQ, Zhou X, Yu Q, Liu SL, Guo DG, Yu RE, et al. Synthesis and characterization of low crystalline waterborne polyurethane for potential application in water-based ink binder. Prog Org Coat 2014;77:61e71. [19] Zhou X, Fang CQ, Yu Q. Synthesis of polyurethane dispersion in nanoparticles and theie properties depend on aging time. J Disper Sci Tech 2015;36: 1178e89. [20] Liu Y, Jiang W, Wang Y, Zhang XJ, Song D, Li FS. Synthesis of Fe3O4/CNTs magnetic nanocomposites at the liquid-liquid interface using oleate as surfactant and reactant. J Magn Magn Mater 2009;321:408e12. [21] Sahoo Y, Goodarzi A, Swihart MT, Ohulchanskyy TY, Kaur N, Furlani EP, et al. Aqueous ferrofluid of magnetite nanoparticles: fluorescence labeling and magnetophoretic control. J Phys Chem B 2005;109:3879e85. [22] Zhang X, Geng H. Carbon nanotube, graphene fiber and film. Beijing: Science Press; 2014. [23] Li S, Gong Y, Yang Y, He C, Hu L, Zhu L, et al. Recyclable CNTs/Fe3O4 magnetic nanocomposites as adsorbents to remove bisphenol A from water and their regeneration. Chem Engin J 2015;260:231e9. [24] Lan Q, Liu C, Yang F, Liu SY, Xu J, Sun DJ. Synthesis of bilayer oleic acid-coated Fe3O4 nanoparticles and their application in pH-responsive Pickering emulsions. J Colloid Interf Sci 2007;310:260e9. [25] Wang S, Bao H, Yang P, Chen G. Immobilization of trypsin in polyanilinecoated nano-Fe3O4/carbon nanotube composite for protein digestion. Anal Chim Acta 2008;612:182e9. [26] Jung BY, Lim HS, Sun YK, Suh KD. Synthesis of Fe3O4/C composite microspheres for a high performance lithium-ion battery anode. J Power Sources 2013;244:177e82. [27] Arjmand M, Mahmoodi M, Gelves GA, Park S, Sundararaj U. Electrical and electromagnetic interference shielding properties of flow-induced oriented carbon nanotubes in polycarbonate. Carbon 2011;49:3430e40. [28] Zhou X, Li Y, Fang C, Li S, Cheng Y, Lei W, et al. Recent advances in synthesis of waterborne polyurethane and their application in water-based ink: a review. J Mater. Sci Tech 2015;31:708e22. [29] Speliotis T, Niarchos D, Meneroud P, Magnac G, Claeyssen F, Pepin J, et al. Micro-motor with screen-printed rotor magnets. J Magn Magn Mater 2007;316:e120e3.
Contents lists available at ScienceDirect
Composites Part B journal homepage: www.elsevier.com/locate/compositesb
Preparation and characterization of Fe3O4-CNTs magnetic nanocomposites for potential application in functional magnetic printing ink Xing Zhou a, b, Changqing Fang a, b, *, Yan Li a, Ningli An b, Wanqing Lei b a b
School of Mechanical and Precision Instrument Engineering, Xi'an University of Technology, Xi'an 710048, PR China Faculty of Printing, Packaging Engineering and Digital Media Technology, Xi'an University of Technology, Xi'an 710048, PR China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 17 March 2015 Received in revised form 21 September 2015 Accepted 20 November 2015 Available online 12 January 2016
This paper presents the synthesis of magnetic carbon nanotube, Fe3O4-CNTs nanocomposites, in which Fe3O4 nanoparticles were grafted to multi-walled carbon nanotube (CNTs) by the in situ hydrothermal method. The prepared Fe3O4-CNTs nanocomposites were characterized by Fourier transform infrared spectroscopy (FT-IR), Raman, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and vibrating sample magetiometer (VSM). It was found that the Fe3O4 nanoparticles with the size of 20e50 nm had been attached to the CNTs strongly and the nanocomposites exhibited high magnetic saturation value, namely a high magnetic attachment force. Moreover, the nanocomposites were used to prepare magnetic printing ink via physical blending process. The ink film was detected by SEM and VSM, demonstrating that the magnetic ink which holds significant magnetic attachment force and drying smooth film is suitable for the printing industry. © 2016 Elsevier Ltd. All rights reserved.
Keywords: A. Polymer-matrix composites (PMCs) A. Nano-structures B. Magnetic properties B. Microstructures
1. Introduction As one of the most important anti-counterfeit materials, magnetic printing inks have been drawing wide attention and applied to vital fields for checking authenticity, such as identity card, check, paper currency, ticket, etc. which due to their efficient information storage, legibility, efficient anti-counterfeit, and low cost [1]. Actually, magnetic inks using letterpress and lithographic printing methods for document processing have been employed for several decades [2]. To study and develop magnetic printing inks, it is essential to have a deep understanding about the composition of the ink. Commonly, inks are composed of four types of ingredients: colorant, vehicle or binder, solvent and additives. The colorant is a pigment (or dye), which presents ink with color, even with some special properties to obtain special-effect inks, such as electrically conductive printing ink, magnetic printing ink, metallic printing ink, fluorescent ink, luminous ink, etc. The vehicles or binders have multiple functions in the ink, dispersing and binding the pigments,
* Corresponding author. School of Mechanical and Precision Instrument Engineering, Xi’an University of Technology, Xi’an 710048, PR China. Tel.: þ86 29 82312038; fax: þ86 29 82312512. E-mail address: [email protected] (C. Fang). http://dx.doi.org/10.1016/j.compositesb.2015.11.041 1359-8368/© 2016 Elsevier Ltd. All rights reserved.
modifying the rheological and mechanical properties, and presenting some other special properties. Solvent is to dissolve the vehicles or binders and adjust the viscosity of the ink. And additives are used to enhance the properties of ink [3]. As for magnetic printing ink, the magnetism stems from the colorants, which are commonly soft ferrites including black iron oxide (Fe3O4), brown iron oxide (g-Fe2O3), iron oxide containing cobalt (CoeFe2O3), chromium hemitrioxide (CrO2), etc [4]. These materials have been widely used in magnetic printing inks, especially the Fe3O4, of which particles are mainly acicular crystal with the size below 1 mm, making the particles are easily arranged under a magnetic field so that to acquire a high magnetism. Nevertheless, the Fe3O4 shows excellent adsorption behavior for oil in inks and inferior transfer printing performance, which may cause problems for presswork in printing process. It is said that the nanosized Fe3O4 could significantly solve these problems. Meanwhile, the nanosized particles are advantageous for use on printing substrate (mainly papers) due to the limited penetration of the magnetic particles into the substrate [5]. However, what depressed is that the sizes of Fe3O4 nanoparticles are most about 70 nm, which may cause aggregation and precipitation in the magnetic ink [6,7]. To solve the problems caused by the Fe3O4 as colorant, it is essential to develop efficient
296
X. Zhou et al. / Composites Part B 89 (2016) 295e302
ways to achieve a stable magnetic pigment in nanosized. Recently, various approaches have been explored to prepare stable magnetic Fe3O4 nanoparticles. Peng et al. [8] prepared monodispersed magnetic Fe3O4 nanoparticles with the size about 3e50 nm via a facial and repeatable method on the basis of the high-temperature pyrolysis of metal fatty acid in non-water solvent. Lemine et al. [9] acquired magnetic Fe3O4 nanoparticles in the size of about 8 nm through solegel method. Among these approaches, one main strategy is to synthesize Fe3O4 nanoparticles covered with some kind of organic/inorganic membrane [10,11], which can effectively decrease the interaction among the nanoparticles and increase the stability of magnetic pigment. On the basis of the decoration methods and conducted by the recent novel attractive carbon nanotubes (CNTs) [12,13], we assumed that the decoration of CNTs with magnetic nanoparticles (Fe3O4 in this research) is extremely promising for application as perfect magnetic colorant [14]. Actually, the combination of CNTs and Fe3O4 has been studied in lithium ion batteries [15,16], which improved or imparted new optical, magnetic and electrochemical properties for the composites. Nonetheless, no research about Fe3O4-CNTs composite has been studied in printing inks. We consider that the Fe3O4-CNTs composite can disperse homogeneously in water and water-based polymer [17], signifying a potential used in water-based ink and potential value for environmental protection. Therefore, we reported a facile and effective chemical approach to prepare the magnetic Fe3O4-CNTs nanocomposite with good appearance and magnetism. Then, the nanocomposite was used as the pigment to prepare ink and the performances and process of the nanocomposite and ink were discussed. 2. Experiment 2.1. Materials Multi-walled carbon nanotubes (CNTs) were purchased from Beijing BOYU GAOKE New Materials Co., Ltd. China. The diameter is in 20e40 nm and length is about 10e30 mm. Nitric acid (HNO3, 65e68 wt%) was purchased from Sichuan XILONG Chemical Reagent Co., Ltd. China. Ethylene glycol (EG) was purchased from Tianjin FUCHEN Chemical Reagent Factory China. FeCl3$6H2O, NaAc, ethidene diamine (EDA), Ethyleneglycol monobutyl ether (EGME), and Paraffin liquid were purchased from Tianjin TIANLI Chemical Reagent Co., Ltd. China. Ethanol absolute was purchased from Tianjin FUYU Fine Chemical Reagent Co., Ltd. China. Waterborne polyurethane dispersion (WPU) and the pigment were prepared by the previous work of our group [18,19]. Polysiloxane used as antifoaming agents in preparing ink was purchased from Jinan DUOWEIQIAO Chemical Co., Ltd. China. Apart from the CNTs, all the reagents are of analytical grade and used without any further purification. 2.2. Purification of CNTs The commercial CNTs was purified by ultrasonically dispersing it in mixture of deionized water and HNO3 for 30 min, and then the mixture of CNTs and HNO3 (5 mol/L) was stirred at 60 C for 12 h in a reflux unit. Afterwards, the solution was diluted and rinsed by deionized water under a centrifuge (Cence H1850, XiangYi, Hunan, China) with the 6000 r/min for several times until the pH value detected by PHS-3C Digital Display Acidity Meter (Hangzhou LEICI Analytic Factory China.) with an E-201-9 pH Combination Electrode from Shanghai Ruosull Science and Technology Co., Ltd. China reaches neutral, and then dried in vacuum at 60 C and grinded with an agate mortar. The acidifying CNTs were calcined at 400 C for 3 h to obtain pure CNTs for further use.
2.3. Synthesis of Fe3O4-CNTs nanocomposites The Fe3O4-CNTs nanocomposites were prepared by the in situ hydrothermal method in a Teflon-lined stainless-steel autoclave (50 mL capacity) in just one step. Firstly, a mass of 0.04 g purified CNTs were dispersed into a 100 mL beaker filling with 30 mL EG with ultrasonic agitation for 30 min. During the ultrasonic agitation, the beaker was covered by a piece of PE film. Secondly, 0.6 g grinded FeCl3$6H2O, 1.8 g NaAc and 6 mL EDA were added into the dried Teflon-lined stainless-steel autoclave. Thirdly, the dispersed CNTs were transferred slowly into the autoclave and stirred by a glass rod. Then, the autoclave was kept at 200 C for 4 h in an oven. Finally, the mixture was magnetically separated and then alternately washed with deionized water and ethyl alcohol for several times until no possible impurities can be found in the liquid supernatant. The obtained product was dried at 50 C in an oven for 24 h for future use. The synthesis process was shown in Fig. 1. As a comparison, Fe3O4 nanoparticles were prepared through the same process without CNTs. The proportion of the components except for magnetic particles was shown in Table 1. 2.4. Preparation of magnetic printing ink The magnetic printing ink was prepared by the physical blending process with the electric stirrer (FLUKO R30, Shanghai, China) in four-blade type agitator and high shear dispersing emulsifier (FLUKO FM200, Shanghai, China) in standard dispersing tool (18G). First of all, waterborne polyurethane dispersion used as binder was added into a 250 mL beaker, following by addition of 5 mL ethanol absolute, deionized water and the pigment. After half an hour stirring with the speed of 500 rpm, the Fe3O4-CNTs nanocomposite was added into the beaker for about 3 h stirring. And then, a partial polysiloxane was used to eliminate the foam caused by stirring. The ink system was transferred to the high shear dispersing emulsifier with the speed of about 7000 rpm for 1 h to produce the ink emulsion. Finally, EMGE and Paraffin liquid were mixed with the emulsion under the 500 rpm stir. The ink film was obtained by casting the emulsion onto Teflon surfaces, a slow evaporation of the solvent at room temperature for 2 days and then at 50 C in a vacuum drying oven for 24 h to allow the complete removal of solvent. Then, the ink film with Teflon was stored in a desiccator to avoid moisture. 2.5. Characterization of Fe3O4-CNTs nanocomposite and ink film Fourier transform infrared spectroscopy (FT-IR) was used to identify the structure of the CNTs, purified CNTs and Fe3O4-CNTs nanocomposites. The infrared spectra were obtained using a Fourier transform IR spectrophotometer (SHIMADIU FTIR-8400S (CE)) and recorded in the transmission mode at room temperature by averaging 20 scans at a resolution of 16.0 cm1. The spectra were analyzed in the frequency range of 4000e400 cm1. Raman experiments were performed on LabRAM HR 800 (HORIBA JOBIN YVON) using 633 nm excitation line from a HeeNe laser with the power about 0.5 mW under a microscope objective lens of 50WLD. The wavenumber range was 100e3500 cm1, the temperature was kept at 25 C and the samples were pressed smoothly on a clean glass slide. An X-ray diffractometer (XRD) instrument (XRD-7000, SHIMADZU LIMITED, Japan) was used to analyze the crystal structures of the Fe3O4-CNTs nanocomposites with monochromatic Cu Ka radiation (1.540598 nm). A scanning of 2q angles between 10 and 70 under the scan speed of 8.0000 deg/min was carried out. Transmission electron microscopy (TEM) was performed to investigate the microstructures of purified CNTs and Fe3O4-CNTs nanocomposites using a JEM-3010 microscope with the
X. Zhou et al. / Composites Part B 89 (2016) 295e302
297
Fig. 1. The purification process by HNO3 and decorating process with Fe3O4 nanoparticles for CNTs.
Table 1 Components of magnetic printing ink except for magnetic particles. Components
WPU
Polysiloxane
EGME
Paraffin
Pigment
The content (wt %)
65
0.5
8
1
24.5
Gatan894 CCD camera working at accelerating voltage of 300 kV with Energy Dispersive X-ray spectrometers (EDS) (Oxford INCA) under an accelerating voltage of 20 kV. The morphology of the Fe3O4-CNTs nanocomposite and ink film was analyzed with a Field Emission Scanning Electron Microscope (FE-SEM, SU8000) using an acceleration voltage of 1 kV with Energy Dispersive X-ray spectrometers (EDS) under an accelerating voltage of 20 kV. The experiments of magnetic properties of the CNTs, Fe3O4-CNTs and ink film were carried out using a vibrating sample magnetometer (VSM, VersaLab, Quantum Design, USA) with a frequency of 40 Hz under the temperature of 300 K. 3. Results and discussion 3.1. Structure of CNTs and Fe3O4-CNTs nanocomposite The structure of Fe3O4-CNTs nanocomposite was analyzed by FT-IR spectroscopy, as shown in Fig. 2. It can be observed that the
Fig. 2. FTIR spectra purified CNTs and Fe3O4-CNTs nanocomposite, respectively.
FT-IR spectra of the purified CNTs contain the only one band at 3386 cm1 assigned to the eOH stretching and bending modes in the functional groups, while the bands of Fe3O4-CNTs nanocomposite were diverse. It is noted that the band of nanocomposite at 486 cm1 assigned to the FeeO stretching and bending modes [20,21], indicating the formation of Fe3O4-CNTs nanocomposite. In addition, the bands at 3475 cm1, 1639 cm1, 1095 cm1 and 760 cm1 were ascribed to the stretching and bending modes of eOH, C]O, CeO and C]O (COO) in the functional groups of the nanocomposite. These abundant functional groups in the Fe3O4CNTs nanocomposite were beneficial for the dispersion in waterborne binder to prepare water-based ink. Raman spectra shown in Fig. 3 provide further evidence for the formation of Fe3O4-CNTs nanocomposite with the appearance of characteristic peaks of both Fe3O4 and CNTs in Fe3O4-CNTs nanocomposite spectrum. As depicted in pure CNTs Raman spectrum, the peaks, assigned to G mode (1578 cm1) and D mode (1327 cm1) respectively, are strong, and the same as to the secondary Raman signal of G0 mode (2656 cm1, the first overtone of D mode). Meanwhile, the radial breathing mode (RBM) at 230 cm1, which is the unique mode of CNTs [22], can be observed in a weak appearance in the spectrum. The ratio of ID/IG, which presents the degree of functionalization for CNTs, is ca. 1.16 and ca. 1.09 for CNTs and Fe3O4-CNTs nanocomposite, respectively. The different ratios of
Fig. 3. Raman spectra of CNTs, Fe3O4 nanocrystals, and Fe3O4-CNTs nanocomposite, respectively.
298
X. Zhou et al. / Composites Part B 89 (2016) 295e302
ID/IG suggest that the CNTs are more imperfect than Fe3O4-CNTs nanocomposite. As to Raman spectrum of Fe3O4, a strong characteristic peak at 684 cm1 can be observed. The G mode, D mode, G0 mode and characteristic peak (position a) ascribed to Fe3O4 are obvious in the Fe3O4-CNTs nanocomposite spectrum, and all of them become weak due to the low weight percent of Fe3O4 and CNTs in the nanocomposite and the chemical interactions between them [16]. The XRD patterns of the purified CNTs and Fe3O4-CNTs nanocomposite were shown in Fig. 4(a). The diffraction peaks assigned to the (002) reflection of CNTs at 2q ¼ 25.96 can be clearly seen in the purified CNTs and Fe3O4-CNTs nanocomposite. It was identified as the hexagonal graphite structure, indicating that the CNTs structure was not destroyed after the chemical precipitation of Fe3O4 [15]. Meanwhile, the intensity of the hexagonal graphite structure on CNTs was stronger than that of Fe3O4-CNTs nanocomposite, which may be ascribed to the reason that the wellcrystalline Fe3O4 grafted on the CNTs surface weakened the diffraction peak at 25.96 [23]. As shown in Fig. 4(a), the peaks at 30.3 , 35.5 , 43.32 , 57.22 and 63.04 were identified as the (220), (311), (400), (511) and (440) planes of the spinel phase of cubic Fe3O4 with O7h (F3dm) space group (JCPDS No. 65e3107), respectively [24], indicating that the resultant Fe3O4 nanoparticles in the composites are pure Fe3O4 according to the previous [15,25]. The peaks of Fe3O4-CNTs nanocomposite belongs to cubic Fe3O4 are broadened and in low intensity, implying that the crystalline size of Fe3O4 nanocrystals are quite small. Moreover, the morphology of Fe3O4 nanocrystals was shown clearly as the cubic shape in Fig. 4(b). It seemed that the particle size of these cubic Fe3O4 nanocrystals was in the range of about 20e50 nm, which can be confirmed by using Scherrer's formula on the basis of X-ray diffraction as follows [16]:
D ¼ ð0:889l=bÞcos qB Where D (nm) is the crystallite size, l (nm) is the X-ray wavelength, b (rad) is the full width at half maximum (FWHM) reflecting line broadening, qB is the Bragg angle corresponding to the maximum intensity peak, namely the peak (311) in this research. The XRD results and the morphology of the cubic Fe3O4 nanocrystals on the CNTs indicated that the Fe3O4-CNTs nanocomposite were successfully synthesized by the simple hydrothermal method. The morphology of the prepared CNTs and Fe3O4-CNTs nanocomposite were investigated by TEM and SEM, as shown in Figs. 5 and 6, respectively. It is clear that the purified CNTs, with diameter of about 50 nm as shown in Fig. 5(a), present well-graphitized walls in high purity. Fig. 5(b) and (c) illustrate the morphology of the
Fe3O4-CNTs nanocomposite, which reveal that the purified CNTs surface is uniformly coated with Fe3O4 nanoparticles with diameter less than 10 nm (the diameter can be clearly seen in the black area in Fig. 5(d)). Meanwhile, the laminar morphology and hollow structure of CNTs, which contain about 20 layers and a ~10 nm nanotube, can be clearly observed in Fig. 5(d). The Fe3O4 nanoparticles cover ca. 3e5 layers of the surface of CNTs, indicating that the nanoparticles have been well attached on the CNTs surface in this paper. The Fe3O4 nanoparticle, as shown in the corresponding high-magnification TEM image in Fig. 5(d), presents a distance between adjacent lattice planes of about 0.11 nm, which is in good agreement with the d-spacing of the (5 1 1) plane of Fe3O4 (0.14 nm) [7,26]. Furthermore, the selected area diffraction pattern of Fe3O4 nanoparticle suggests that it is crystalline, and the all diffraction rings in Fig. 5(e) could be indexed to Fe3O4 nanoparticle with cubic symmetry. These crystalline cubic Fe3O4 nanoparticle results are corresponding to the analysis of XRD and SEM results in Fig. 4. Fig. 5(f) and Table 2 suggest that the nanocomposite basically have no extra materials except for CNTs and Fe3O4, indicating the processes in this research to purify multi-walled CNTs and synthesized Fe3O4-CNTs nanocomposite are easy to obtain high purity produces. The percentage of atom of C (52.23%) and Fe (22.38%) element in Table 2 gives the information of the ratio of CNTs and Fe3O4 nanoparticles in detail, meaning the ratio of the CNTs: Fe3O4 ¼ 7: 1. What calls for special attention is that the percentage of Fe and O element listed in Table 2 is not the same with Fe3O4 (the theoretical ratio of Fe: O should be 0.75, while the actual ratio is about 0.88). The higher percentage of O could be introduced by the oxidation of CNTs. This can be demonstrated by the result of EDS experiment during the SEM experiment of the purified CNTs. The SEM images of CNTs and Fe3O4-CNTs nanocomposite in Fig. 6 show that the CNTs randomly circumvolute with an outer diameter of approximately 30e50 nm. Comparing with Fig. 6(a), Fig. 6(b) of Fe3O4-CNTs nanocomposite clearly shows that the Fe3O4 nanoparticles distributes uniformly on the surface of CNTs network, indicating that the method taken in this research is effective to obtain magnetic Fe3O4-CNTs nanocomposite. Furthermore, as shown in Fig. 6(c), additional oxygen (8.35 wt %) can be detected in the purified CNTs (the weight percentage of C element is 91.65%), indicating that the CNTs has been functionalized by nitric acid. This result is corresponding to the extra O element content in TEM detection above. In order to characterize the magnetic properties, a vibrating sample magetiometer was used to record the magnetic behavior of the CNTs, Fe3O4-CNTs nanocomposite and Fe3O4. Fig. 7 exhibits the hysteresis loops of the as-prepared samples at room temperature. It can be seen that the magnetic saturation value of the Fe3O4-CNTs
Fig. 4. (a) X-ray diffraction patterns of the normal CNTs and Fe3O4-CNTs nanocomposite, (b) SEM picture of cubic Fe3O4 nanocrystals in the Fe3O4-CNTs nanocomposite.
X. Zhou et al. / Composites Part B 89 (2016) 295e302
299
Fig. 5. TEM micrograph of (a) purified CNTs; (b) Fe3O4-CNTs nanocomposite; (c) and (d) are the corresponding high-magnification image of Fe3O4-CNTs nanocomposite in (b); (e) TEM diffraction pattern image of Fe3O4-CNTs nanocomposite; (f) EDS of Fe3O4-CNTs nanocomposite.
nanocomposite (38 emu/g, Fig. 7(b)) is much higher than that of purified CNTs (0.18 emu/g, Fig. 7(a)), while smaller than that of pure Fe3O4 (56 emu/g Fig. 7(c)) with the applied field of 10,000 Oe at room temperature. The remanence of nanocomposite is more stable than that of CNTs. Moreover, both the Fe3O4-CNTs nanocomposite and Fe3O4 presents zero remanence when the applied magnetic field is moved, implying that the nanocomposite is
superparamagnetic [7,25]. The decrease of magnetic saturation value of Fe3O4-CNTs nanocomposite compared with that of Fe3O4 may arise from the electromagnetic interference shielding property [27]. Due to the superparamagnetic and facile magnetism (38 emu/ g), it may be used as a promising vehicle for biological and functional application for it prevents the magnetic materials from aggregating and enables it to redisperse rapidly when the extra
300
X. Zhou et al. / Composites Part B 89 (2016) 295e302
Fig. 6. SEM micrograph of (a) purified CNTs; (b) Fe3O4-CNTs nanocomposite; (c) EDS of purified CNTs.
Table 2 Components of Fe3O4-CNTs nanocomposite from the EDS.
3.2. Characterization of functional magnetic printing ink
Element
Percentage of weight (wt %)
Percentage of atom (%)
CK OK Fe K Total
27.47 17.79 54.74 100.00
52.23 25.39 22.38
magnetic field is removed [20]. In addition, the magnetic saturation value of nanocomposite increases three magnitudes comparing with that of CNTs, resulting in the aggregation of nanocomposite with the aid of the eight appearance external magnet. In contrast, the purified CNTs dispersed in deionized water keep impassive in suspension for about 1 h under the magnet. This difference arises from the Fe3O4 uniformly attached to the CNTs surface. With this unique property, we assume it may be used as the additive to prepare magnetic inks with the facile magnetism in printing industry.
To observe the dispersion of Fe3O4-CNTs nanocomposite in the ink and the morphology of magnetic printing ink [28], the ink film was performed on the SEM, as shown in Fig. 8. As a comparison, the ink film with pure Fe3O4 was also observed. It can be seen that the pigment particle size is in micro scale, shown as the weak light pots in Fig. 8(a) and (b). It suggests that the addition of Fe3O4-CNTs nanocomposite does not cover the pigment, presenting a primary color of the pigment for the ink. Meanwhile, the lines shown in Fig. 8(a) and (b) indicate that the nanocomposite has been widely and uniformly dispersed in the ink. No crack is found in the micrograph, implying that the ink film is smooth and suitable for printing. Furthermore, no obvious CNTs can be observed, indicating that the Fe3O4-CNTs nanocomposite has been coated by the other components in the ink. Notably and luckily, at the edge of the ink film, some bridge-liked linkages in the ink film were founded, indicating that the nanocomposites dispersed well in the ink. As
Fig. 7. Hysteresis loops of (a) purified CNTs; (b) Fe3O4-CNTs nanocomposite; (c) Fe3O4. The inset in (a) is the photograph of magnet in an eight appearance (left); the insets in (a), (b) and (c) (all the right) are the photographs of CNTs, Fe3O4-CNTs nanocomposite and Fe3O4 dispersed in deionzed water in the presence of the external magnet.
X. Zhou et al. / Composites Part B 89 (2016) 295e302
301
Fig. 8. SEM micrograph of magnetic printing ink: (a) 5000, (b), (c) 15,000 Fe3O4-CNTs nanocomposites; (d) Fe3O4.
comparison, the particles presented in Fig. 8(d) obviously aggregated together, indicating that the dispersion of Fe3O4-CNTs composites is better than that of pure Fe3O4. The magnetic property of the magnetic printing ink was detected by the vibrating sample magetiometer (VSM). Fig. 9 presents the hysteresis loops of the magnetic ink at room temperature. The ink film presents zero remanence when the applied magnetic field is moved, suggesting that the ink is superparamagnetic. Comparing with the magnetic force of the purified CNTs (0.18 emu/ g) and Fe3O4-CNTs nanocomposite (38 emu/g), the ink film presents a suitable magnetic force (1.58 emu/g) which is much lower than that of the nanocomposite while higher than that of the purified CNTs. The reduction of the magnetic force of the magnetic ink film
indicates that the magnetic force was affected by the other components of the ink, such as waterborne polyurethane binder and additives. This arises from the coating of the other components surrounding the Fe3O4-CNTs nanocomposite. We consider that the coating weakens the magnetic field response of the nanocomposite and reduces the magnetism of the ink. Comparing with the magnetic force (in the range of 0.6e0.6 emu/g) of the magnetic nanoparticle based inks reported by Speliotis et al. [29] and Shi et al. [12], the stronger magnetic force of ca. 1.58 emu/g (under the applied field of 10,000 Oe) for the Fe3O4-CNTs nanocomposite suggests that the magnetic ink holds the potential application in screen-printing. Furthermore, the inserted picture in Fig. 9 depicts the attraction of the magnetic ink film by the magnet, signifying magnetic attracted performance for the magnetic ink film. 4. Conclusions A facile and effective chemical approach has been carried out for synthesizing Fe3O4-CNTs nanocomposite. The FT-IR, Raman, TEM and SEM results suggest that Fe3O4 nanoparticles (particles size in the range of 20e50 nm) have been strongly and uniformly attached to the purified CNTs. According to the VSM, the Fe3O4-CNTs nanocomposite presents a property of superparamagnetic, holding a potential application in vehicle for biological and functional materials. In addition, magnetic printing ink was prepared with the Fe3O4-CNTs nanocomposite via the physical blending process. The ink film shows a smooth surface and high attachment force to the magnet, indicating that the magnetic ink hold an excellent performance for screen-printing and anti-counterfeit. Acknowledgements
Fig. 9. Hysteresis loops of magnetic ink film and the attracted film by magnet (inserted picture).
The authors acknowledge the financial supports provided by the Natural Science Foundation of China (Grant No. 51372200), Programs for New Century Excellent Talents in University of Ministry
302
X. Zhou et al. / Composites Part B 89 (2016) 295e302
of Education of China (Grant No.: NCET-12-1045), Shaanxi Programs for Science and Technology Development (Grant No. 2010K01-096), Xi'an Programs for Science and Technology Plan (Grant No. CXY1433(6)) and (Grant No. CXY1430(9)), Ph.D. Innovation fund projects of Xi'an University of Technology (Fund No. 310-252071501).
References € rlenbach: Wiley-VCH Verlag GmbH & [1] Gubin SP. Magnetic nanoparticles. Mo Co. KGaA, Weinheim; 2009. [2] Charles SW. Some application of magnetic fluids-use as an ink and in microwave system. J Magn Magn Mater 1987;65(2e3):350e8. [3] Robert T. “Green ink in all colors”dprinting ink from renewable resources. Prog Org Coat 2015;78:287e92. [4] Yurkov GY, Baranov DA, Dotsenko IP, Gubin SP. New magnetic materials based on cobalt and iron-containing nanoparicles. Compos Part B 2006;37:413e7. [5] Huang Q, Shen W, Xu Q, Tan R, Song W. Properties of polyacrylic acid-coated silver nanoparticle ink for inkjet printing conductive tracks on paper with high conductivity. Mater Chem Physic 2014;147:550e6. [6] Li YD, Liao HW, Qian YT. Hydrothermal synthesis of ultrafine a-Fe2O3 and Fe3O4 powders. Master Res Bull 1998;33:841e4. [7] Si SF, Li CH, Wang X, Yu DP, Peng Q, Li YD. Magnetic monodisperse Fe3O4 nanoparticles. Cryst Growth Des 2005;5(2):391e3. [8] Jana NR, Chen Y, Peng X. Size-and shape-controlled magnetic (Cr, Mn, Fe, Co, Ni) oxide nanocrystals via a simple and general approach. Chem Mater 2004;16:3931e5. [9] Lemine OM, Omri K, Zhang B, Mir LE, Sajieddine M, Alyamani A, et al. Sol-gel synthesis of 8 nm magnetite (Fe3O4) nanoparticles and their magnetic properties. Superlattices Microstruct 2012;52:793e9. [10] Marjanovi c N, Chiolerio A, Kus M, Ozel F, Tilki S, Ivanovi c N, et al. Magnetite nanoparticles: synthesis, thin film properties and inkjet printing of magnetic cores for inductor applications. Thin Solid Films 2014;570:38e44. [11] Zhang W, Chen X, Tang T, Mijowska E. Superstable magnetic nanoreactors with high efficiency for Suzuki-coupling reactions. Nanoscale 2014;6: 12884e9. [12] Shi D, He P, Zhao P, Guo FF, Wang F, Huth C, et al. Magnetic alignment of Ni/ Co-coated carbon nanotubes in polystyrene composites. Compos Part B 2011;42:1532e8. [13] Koo Y, Littlejohn G, Collins B, Yun Y, Shanov VN, Schulz M, et al. Synthesis and characterization of AgeTiO2eCNT nanoparticle composites with high photocatalytic activity under artificial light. Compos Part B 2014;57:105e11.
~ a A. New alignment procedure of [14] Prolongo SG, Meliton BG, Rosario GD, Uren magnetiteeCNT hybrid nanofillers on epoxy bulk resin with permanent magnets. Compos Part B 2013;46:166e72. [15] He Y, Huang L, Cai JS, Zheng XM, Sun SG. Structure and electrochemical performance of nanostructured Fe3O4/carbon nanotube composites as anodes for lithium ion batteries. Electrochim Acta 2010;55:1140e4. [16] Guo Q, Guo P, Li J, Yin H, Liu J, Xiao F, et al. Fe3O4-CNTs nanocomposites: inorganic dispersant assisted hydrothermal synthesis and application in lithium ion batteries. J Solid State Chem 2014;213:104e9. [17] Ren D, Li Z, He P. Chemistry of carbon nanotubes. Beijing: Chemical Industry Press; 2013. [18] Fang CQ, Zhou X, Yu Q, Liu SL, Guo DG, Yu RE, et al. Synthesis and characterization of low crystalline waterborne polyurethane for potential application in water-based ink binder. Prog Org Coat 2014;77:61e71. [19] Zhou X, Fang CQ, Yu Q. Synthesis of polyurethane dispersion in nanoparticles and theie properties depend on aging time. J Disper Sci Tech 2015;36: 1178e89. [20] Liu Y, Jiang W, Wang Y, Zhang XJ, Song D, Li FS. Synthesis of Fe3O4/CNTs magnetic nanocomposites at the liquid-liquid interface using oleate as surfactant and reactant. J Magn Magn Mater 2009;321:408e12. [21] Sahoo Y, Goodarzi A, Swihart MT, Ohulchanskyy TY, Kaur N, Furlani EP, et al. Aqueous ferrofluid of magnetite nanoparticles: fluorescence labeling and magnetophoretic control. J Phys Chem B 2005;109:3879e85. [22] Zhang X, Geng H. Carbon nanotube, graphene fiber and film. Beijing: Science Press; 2014. [23] Li S, Gong Y, Yang Y, He C, Hu L, Zhu L, et al. Recyclable CNTs/Fe3O4 magnetic nanocomposites as adsorbents to remove bisphenol A from water and their regeneration. Chem Engin J 2015;260:231e9. [24] Lan Q, Liu C, Yang F, Liu SY, Xu J, Sun DJ. Synthesis of bilayer oleic acid-coated Fe3O4 nanoparticles and their application in pH-responsive Pickering emulsions. J Colloid Interf Sci 2007;310:260e9. [25] Wang S, Bao H, Yang P, Chen G. Immobilization of trypsin in polyanilinecoated nano-Fe3O4/carbon nanotube composite for protein digestion. Anal Chim Acta 2008;612:182e9. [26] Jung BY, Lim HS, Sun YK, Suh KD. Synthesis of Fe3O4/C composite microspheres for a high performance lithium-ion battery anode. J Power Sources 2013;244:177e82. [27] Arjmand M, Mahmoodi M, Gelves GA, Park S, Sundararaj U. Electrical and electromagnetic interference shielding properties of flow-induced oriented carbon nanotubes in polycarbonate. Carbon 2011;49:3430e40. [28] Zhou X, Li Y, Fang C, Li S, Cheng Y, Lei W, et al. Recent advances in synthesis of waterborne polyurethane and their application in water-based ink: a review. J Mater. Sci Tech 2015;31:708e22. [29] Speliotis T, Niarchos D, Meneroud P, Magnac G, Claeyssen F, Pepin J, et al. Micro-motor with screen-printed rotor magnets. J Magn Magn Mater 2007;316:e120e3.