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Preparation and characterization of magnetic hollow PMMA nanospheres via in situ emulsion polymerization
Colloids and Surfaces A: Physicochem. Eng. Aspects 363 (2010) 71–77
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Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa
Preparation and characterization of magnetic hollow PMMA nanospheres via in situ emulsion polymerization Chunlei Wang a , Juntao Yan a , Xuejun Cui a,∗ , Dengli Cong b , Hongyan Wang a,∗ a b
College of Chemistry, Jilin University, Qianjin Street 2699, Changchun 130012, China School of Pharmaceutical Sciences, Jilin University, Changchun 130012, China
a r t i c l e
i n f o
Article history: Received 12 January 2010 Received in revised form 31 March 2010 Accepted 12 April 2010 Available online 18 April 2010 Keywords: Magnetic hollow nanospheres PMMA In situ emulsion polymerization
a b s t r a c t Magnetic hollow polymethyl methacrylate (PMMA) nanospheres were successfully obtained by etching the template of CaCO3 in the core–shell Fe3 O4 @CaCO3 @PMMA nanospheres, which were synthesized via in situ emulsion polymerization in the presence of oleic acid-modified Fe3 O4 @CaCO3 composite nanoparticles. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements demonstrated that the core–shell Fe3 O4 @CaCO3 @PMMA nanospheres were uniform and possessed narrow size distributions. And a perfect spherical profile of magnetic hollow PMMA nanospheres could be also observed by TEM. Both the Fourier transform infrared (FTIR) spectrometry, high resolution TEM (HRTEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) provided the sufficient evidences for the presence of Fe3 O4 in the magnetic hollow PMMA nanospheres. Thermogravimetric analysis (TGA) investigated the composition of the resulting composite nanospheres. Moreover, the magnetic testing experiment could give us a direct proof of the presence of Fe3 O4 in magnetic hollow PMMA nanospheres. And the magnetic hollow PMMA nanospheres had a promising future in controlled drug delivery and targeted drug applications. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Magnetic nanoparticles have widespread applications in magnetic bioseparation, drug delivery, magnetic resonance imaging contrast enhancement and targeted drug, due to its excellent properties of superparamagnetism, high saturation magnetization, high magnetic susceptibility, biocompatibility and low toxicity [1–5]. Therefore, more and more researchers have focused on the fascinating feature of targeting [6–9]. However, owing to bare magnetic nanoparticles are liable to aggregation, and rapid biodegradation when they are exposed to a biological system, coupled with a limited carrying capacity, so that it is necessary to combine magnetic nanoparticles with other carriers to achieve targeted delivery efficiently [10–13]. Various inorganic or polymeric materials have been reported as carriers of magnetic materials [14,15]. The polymeric carriers that possessed functional groups can regulate the carrier properties for the desired applications [16,17], hence, inorganic core/organic shell hybrid composite exhibits its remarkable priority over other composites, which can perfectly combine their own unique properties of both magnetic material and polymeric materials.
∗ Corresponding authors. Tel.: +86 431 85168470; fax: +86 431 85168470. E-mail addresses: cui [email protected] (X. Cui), wang [email protected] (H. Wang). 0927-7757/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2010.04.016
Hollow structure materials have gained increasing attention for their various emerging applications in the medicine, immobilizing enzyme, controlled release for drugs, dyes and perfumes, catalysis and many other fields [18–20]. Several methods for synthesizing hollow structure materials have been reported, including polymerization [21], layer-by-layer self-assembly [22], and template method [23–28], etc. Among these methods, the template method is known to be one of the most effective approaches to achieve hollow nanostructures. Successful examples on synthesizing hollow materials are the use of these templates, such as inorganic nanoparticles [23–25], emulsion droplets [26], vesicular solution [27] and organic polymeric sphere [28]. There are many reports about nano-silicon dioxide [25] and gold nanoparticles [23,24] used as templates to prepare hollow nanostructures due to their considerable stability in the process of preparation, however, the very strong corrosive hydrofluoric acid (HF) is needed for etching the templates to achieve the hollow nanostructures. As is known to all, calcium carbonate (CaCO3 ) is the cheapest commercially available inorganic particles. Moreover, CaCO3 could be easily etched by weak acid and its decomposition is nontoxic and friendly to environment. Up to date, there has been numerous reports in terms of two major aspects, one is to prevent the agglomeration of CaCO3 by encapsulating polymers [29], the other is to enhance the mechanical properties of rubber or plastics by filling the CaCO3 [30,31]. In contrast, there are only a few studies concerning the synthesis of hollow materials using CaCO3 as templates [32,33]. Zhou et al.
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Fig. 1. Schematic showing the synthesis of magnetic hollow PMMA nanospheres via in situ emulsion polymerization.
[20] have achieved porous magnetic hollow silica nanospheres with CaCO3 /Fe3 O4 composite particles template by sol–gel method. But no work has yet been performed that magnetic hollow polymer nanospheres were achieved via in situ emulsion polymerization with Fe3 O4 @CaCO3 composite nanoparticles template. Herein we develop a facile method to prepare the core–shell Fe3 O4 @CaCO3 @PMMA nanospheres via in situ emulsion polymerization in the presence of oleic acid-modified Fe3 O4 @CaCO3 composite nanoparticles, and obtain the magnetic hollow PMMA nanospheres by etching the template of CaCO3 . The resultant magnetic hollow PMMA nanospheres not only possessed magnetic property, but also hollow space in the PMMA nanospheres, both of which will make it possible for our following potential applications in the fields of controlled release, drug delivery, targeted drug
and so on. And the resultant magnetic hollow PMMA nanospheres were characterized by means of FTIR, XRD, TEM, DLS, TGA and so on. 2. Experimental 2.1. Materials Methyl methacrylate (MMA, 99%, Aldrich) was used without purification. Ammonium persulfate (APS, Beijing Chemical Reagent Company, China) was of reagent grade. Sodium dodecylbenzene sulfonate (SDBS, Shanghai Chemical Reagents Company, China) used as the surfactants without further purification are of reagent grade. Oleic acid (OA, Tianjin Guangfu Chemical Reagents Company, China) was analytical reagent. Calcium oxide (CaO), acetic acid (HAc) and ammonia (NH4 OH, Beijing Chemical Reagent Company, China) was of reagent grade. Ferric chloride hexahydrate (FeCl3 ·6H2 O) and ferrous chloride tetrahydrate (FeCl2 ·4H2 O) were purchased from Tianjin Guangfu Chemical Reagents Company, China. And the water used was distilled followed by deionization. 2.2. Synthesis The core–shell Fe3 O4 @CaCO3 @PMMA nanospheres were successfully synthesized via in situ emulsion polymerization in the presence of OA-modified Fe3 O4 @CaCO3 composite nanoparticles.
Fig. 2. IR spectrum of: (a) pure PMMA; (b) magnetic hollow PMMA nanospheres; (c) core–shell Fe3 O4 @CaCO3 @PMMA composite nanospheres; (d) OA-modified Fe3 O4 @CaCO3 composite nanoparticles; (e) the Fe3 O4 @CaCO3 @PMMA composites after calcined at 550 ◦ C for 6 h.
Fig. 3. XRD patterns of: (a) Fe3 O4 @CaCO3 @PMMA composite nanospheres; (b) magnetic hollow PMMA nanospheres.
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Fig. 4. TEM images of: (a) citrate modified Fe3 O4 nanoparticles; (b) OA-modified Fe3 O4 @CaCO3 composite nanoparticles; (c) HRTEM image of a single Fe3 O4 @CaCO3 nanoparticle; inset (d) and (e) are FFT patterns of the corresponding HRTEM image.
The in situ emulsion polymerization was conducted under nitrogen atmosphere in a 250 ml four-neck flask fitted with reflux condenser, mechanical stirrer, dropping funnels and inlet for nitrogen gas and heated in the water bath. The overall schematic procedure used to synthesize the magnetic hollow PMMA nanospheres was illustrated in Fig. 1, and the detailed procedure of preparation was described as followed. 2.2.1. Synthesis of OA-modified Fe3 O4 @CaCO3 composite nanoparticles Firstly, CaO was digested into Ca(OH)2 slurry, 125 ml of 0.2 M Ca(OH)2 slurry was then charged into the 250 ml four-necked flask fitted with a mechanical overhead stirrer, coupled with a condenser, the obtained mixture was stirred with a speed of 300 rpm in a ice-water bath. Secondly, 10 ml of citrate-stabilized water-based magnetic fluid (2 wt%), which was successfully obtained by means of the approach reported in the references [7,34], was introduced into the above mixture. After fully mixed, the mixed gas of carbon dioxide and nitrogen (the volume ratio of CO2 to N2 was 1:2) was charged into the slurry at a rate of 80 l/h with a vigorous agitate. When the pH value of the solution reached 7.0, the mixed gas was terminated and the Fe3 O4 @CaCO3 composite nanoparticles were obtained. At the same time, the resultant composite nanoparticles
were heated to 75 ◦ C in a water bath, and the 4 wt% oleic acid that relative to the composite nanoparticles was added dropwise into the flask under continuous stirring for 1 h, after which the superfluous oleic acid was washed with alcohol aqueous solution for several times, then the OA-modified Fe3 O4 @CaCO3 composite nanoparticles with a strong hydrophobic feature were achieved, which significantly ameliorated the compatibility between inorganic particles and monomer. And the aqueous suspension of OA-modified Fe3 O4 @CaCO3 composite nanoparticles was adjusted to 8 wt% for further use. 2.2.2. Synthesis of magnetic hollow PMMA nanospheres First, 65 ml deionized water and 0.1 g SDBS were added into the flask. After complete dissolution of SDBS in deionized water, 15 ml OA-modified Fe3 O4 @CaCO3 composite nanoparticles aqueous suspension were introduced into the flask at room temperature with a vigorous stirring to achieve a fully dispersion phase. 1/5 of monomer (the total amount of MMA was 5 ml) was charged into the above mixture, and the flask was heated to 80 ◦ C gradually in a water bath with a stirring rate of 300 rpm. Then, 1/4 ammonium persulfate (APS) aqueous solution (0.1 g APS dissolved in 20 ml deionized water) was added into the flask, simultaneously, the stirrer speed was turned down to 250 rpm so as to
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Fig. 5. TEM images of: (a) and (b) Fe3 O4 @CaCO3 @PMMA composite nanospheres; (c) magnetic hollow PMMA nanospheres; (d) the EDS spectrum of magnetic hollow PMMA nanospheres.
achieve expected core–shell structure. When examining reflux of the flask wall was decreased, the remaining MMA and APS aqueous solution were added dropwise lasting for 0.5 h by the respective dropping funnels, the polymerization was maintained for 3 h. And the resultant product was purified by centrifugationredispersion cycles for three times in order to remove the above liquid containing homopolymer of MMA, and the obtained precipitation was dried at 60 ◦ C in vacuum for 10 h to achieve core–shell Fe3 O4 @CaCO3 @PMMA nanospheres. Then the resultant core–shell nanospheres were immersed into acetic acid (HAc) aqueous (the volume ratio of HAc to H2 O was 1:15) for 20 h to etch the template of CaCO3 , and the latex was washed three times by deionized water, centrifuged to achieve the magnetic hollow PMMA nanospheres. 2.3. Measurements X-ray diffraction (XRD) data were collected on a Rigaku D/MAX 2550 diffractometer with Cu K␣ radiation. Fourier transform infrared (FTIR) spectra of KBr powder-pressed pellets were recorded on a Nicolet Instruments Research Series 5PC Fourier Transform Infrared spectrometer. The particle sizes and their distribution of composite nanospheres were measured by dynamic light scattering (DLS) with a Malven zetasizer 3000 HSA particle sizer. Transmission electron microscopy (TEM) micrographs were performed on a JEM-2010 transmission microscope at an accelerating voltage of 200 kV, and sample preparation for TEM observation was performed by dropping a dilute suspension of the nanoparticles on the amorphous carbon-coated copper grids and drying at room temperature, then coating a layer of amorphous carbon film on the sample to protect it. Thermogravimetric analysis (TGA) was performed with a Pyris 1TGA (PerkinElmer) under the nitrogen atmosphere at a heating rate of 10 ◦ C/min from 25 to 650 ◦ C.
3. Results and discussion 3.1. FTIR spectra In order to confirm the components of OA-modified composite nanoparticles, the core–shell Fe3 O4 @CaCO3 Fe3 O4 @CaCO3 @PMMA composite nanospheres and magnetic hollow PMMA nanospheres, FTIR spectrum was employed and the results were presented in Fig. 2. The curve (Fig. 2(a)) displayed the characteristic adsorption peaks of PMMA at 1731, 1386–1452, and 1140–1267 cm−1 , which were attributed to vibration adsorption of carbonyl, bending vibrations of CH3 , stretching vibrations of C–O–C, respectively. The curve (Fig. 2(d)) of OA-modified Fe3 O4 @CaCO3 composite nanoparticles not only exhibited the characteristic adsorption peaks of CaCO3 (1453 and 876 cm−1 ) and oleic acid (2860 and 2930 cm−1 ), but also the characteristic adsorption peak of Fe3 O4 (578 cm−1 ) [35], and the results suggested that Fe3 O4 existed in the OA-modified Fe3 O4 @CaCO3 composites. Based on the curve (Fig. 2(c)) of core–shell Fe3 O4 @CaCO3 @PMMA composite nanospheres, it was noted that there were the intensive specific adsorption peaks of CaCO3 at 1453 and 876 cm−1 , adsorption peak of Fe3 O4 at 578 cm−1 , and the characteristic adsorption peaks of PMMA as well, it suggested that both CaCO3 and Fe3 O4 nanoparticles existed in PMMA composites. Moreover, Fig. 2(e) was the curve of the core–shell Fe3 O4 @CaCO3 @PMMA composites after calcined at 550 ◦ C for 6 h, which was well coincident with that of Fig. 2(d), it indicated that OA-modified Fe3 O4 @CaCO3 composite nanoparticles were fully encapsulated by PMMA. In addition, comparison was made between the core–shell Fe3 O4 @CaCO3 @PMMA composite nanospheres and magnetic hollow PMMA nanospheres by the FITR spectrum, it was found that specific adsorption peak of CaCO3 at 1453 and 876 cm−1 were not
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Fig. 6. The particle size distribution of: (a) citrate modified Fe3 O4 nanoparticles; (b) OA-modified Fe3 O4 @CaCO3 composite nanoparticles; (c) core–shell Fe3 O4 @CaCO3 @PMMA composite nanospheres; (d) magnetic hollow PMMA nanospheres.
existed in Fig. 2(b), which demonstrated that CaCO3 template was thoroughly eliminated from the core–shell Fe3 O4 @CaCO3 @PMMA composite nanospheres. On the basis of the above analysis, we could find that there was the characteristic adsorption peak of Fe3 O4 at 578 cm−1 in the curves of Fig. 2(b–e), it was confirmed that Fe3 O4 was existed in the composite particles. 3.2. XRD patterns Based in Fig. 3(a), characteristic diffraction peak of [1 0 4], [1 1 0], [1 1 3], [2 0 2], [0 1 8], and [1 1 6] were observed, it could be indexed to the typical calcite structure of CaCO3 nanoparticles, however, the characteristic diffraction peak of Fe3 O4 nanoparticles were not found, and this phenomenon can be interpreted that the strong characteristic diffraction peak of CaCO3 covered up the weak diffraction peak of Fe3 O4 . In contrast, Fig. 3(b) indicated that magnetic hollow PMMA nanospheres possessed standard spinel structure of Fe3 O4 nanoparticles with characteristic diffraction peaks of [2 2 0], [3 1 1], [4 0 0], [4 2 2], [5 1 1], and [4 4 0], but the diffraction peaks of CaCO3 were not detected, which implied that the templates of CaCO3 were fully etched by acetic acid and Fe3 O4 nanoparticles were remained. Therefore, it was concluded that spinel structure of Fe3 O4 nanoparticles were not damaged during
the process of acid etching, which further provided evidence for the exist of Fe3 O4 in the hollow PMMA nanospheres as well as TEM results.
3.3. Morphology and particle size analysis Both TEM and HRTEM measurements could provide further insights into the structure of composite nanoparticles, therefore TEM and HRTEM measurements were employed in this paper. TEM images of citrate modified Fe3 O4 nanoparticles (Fig. 4(a)) and OAmodified Fe3 O4 @CaCO3 composite nanoparticles (Fig. 4(b)) were shown in Fig. 4. Seen from Fig. 4(a), Fe3 O4 nanoparticles were of spherical shape with a particle size in the range of 10–18 nm. Fig. 4(b) displayed the TEM images of OA-modified Fe3 O4 @CaCO3 composite nanoparticles, it is noted that the resultant composite nanoparticles were cubic, and possessed a particle size in the range of 55–90 nm. Moreover, vivid microstructure of resultant composite nanoparticles demonstrated that Fe3 O4 nanoparticles were successfully embedded in the CaCO3 particles, which facilitated the achievement of magnetic hollow PMMA nanospheres. In addition, based on the HRTEM image (Fig. 4(c)) of a single Fe3 O4 @CaCO3 nanoparticle and FFT patterns (Fig. 4(d and e)) of the corresponding HRTEM image, it was found that the edge area of the
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Fig. 7. TGA curves of: (a) pure PMMA; (b) magnetic hollow PMMA nanospheres; (c) Fe3 O4 @CaCO3 @PMMA composite nanospheres.
HRTEM image (Fig. 4(c)) was one dimensional lattice fringes with an interplanar spacing about 0.2811 nm, which corresponded to the (0 0 6) lattice plane of the calcite CaCO3 (0.2843 nm). And the center area of the HRTEM image was two-dimensional lattice fringes with an interplanar spacing about 0.2823 and 0.2553 nm, which corresponded to the (0 0 6) lattice plane of the calcite CaCO3 (0.2843 nm) and the (3 1 1) lattice plane of the cubic Fe3 O4 (0.2529 nm), respectively. To investigate the morphology of the core–shell Fe3 O4 @CaCO3 @PMMA nanospheres and magnetic hollow PMMA nanospheres, TEM measurement was performed, the TEM images of resultant nanospheres were showed in Fig. 5, and the EDS spectrum of magnetic hollow PMMA nanospheres as well. It was proved that the clear core–shell structure of Fe3 O4 @CaCO3 @PMMA composite nanospheres (Fig. 5(a)) was observed with a shell thickness of 10 nm, and the core–shell composite nanospheres (Fig. 5(b)) were uniform with an average diameter of 100 nm. As could be vividly seen from Fig. 5(c), the magnetic hollow PMMA nanospheres possessed a perfect spherical profile. Moreover, it was noted that Fe3 O4 nanoparticles with a diameter of 15 nm could be examined in the hollow space, which endowed hollow PMMA nanospheres with magnetic properties. Thus, the magnetic hollow PMMA nanospheres brought about potential applications in the various fields of controlled release, drug delivery, targeted drug and so on. Furthermore, EDS spectrum of magnetic hollow PMMA nanospheres (Fig. 5(d)) indicated that besides C and Cu peaks from the TEM grid, only Fe and O were observed, however, Ca peak was not detected, which further proved that CaCO3 was completely etched. In addition, the results of DLS measurement in Fig. 6 also indicated that both citrate modified Fe3 O4 nanoparticles (Fig. 6(a)), OA-modified Fe3 O4 @CaCO3 composite nanoparticles (Fig. 6(b)), the core–shell Fe3 O4 @CaCO3 @PMMA composite nanospheres (Fig. 6(c)), and magnetic hollow PMMA nanospheres (Fig. 6(d)) possessed narrow size distributions, with an average diameter of 16, 80, 110 and 115 nm, respectively, which were consistent with the results of TEM. 3.4. TGA and magnetic testing Thermogravimetric analysis was also employed to investigate the composition of the resulting composite nanospheres, and the detailed results were depicted in Fig. 7. Pure PMMA (Fig. 7(a)) showed no residual weigh due to the complete decomposition of PMMA. When incorporating the Fe3 O4 @CaCO3 nanoparticles into
Fig. 8. The photographs of magnetic testing: (a) the magnetic hollow PMMA nanospheres in aqueous solution, and (b) the directed movement under an external magnetic field.
the polymerization system, the resultant Fe3 O4 @CaCO3 @PMMA composite nanospheres (Fig. 7(c)) exhibited a residual weight of about 22%, which was attributed to the presence of Fe3 O4 @CaCO3 nanoparticles. Compared with Fig. 7(c), the magnetic hollow PMMA nanospheres (Fig. 7(b)) possessed a residual weight of about 2%, which further suggested that CaCO3 nanoparticles were effectively etched from the Fe3 O4 @CaCO3 @PMMA composite nanospheres by using diluted acetic acid and Fe3 O4 nanoparticles were remained. Moreover, based on the above results, it could be concluded that magnetic content of the magnetic hollow PMMA nanospheres was about 2%. In order to further explore the magnetic properties of magnetic hollow PMMA nanospheres, the separation and redispersion process of the magnetic hollow PMMA nanospheres were conducted. As shown in Fig. 8, the magnetic hollow PMMA nanospheres in aqueous solution were brown emulsion (Fig. 8(a)), and they could do oriented movement in an external magnetic field (Fig. 8(b)), once the external magnetic field was removed, they would be redispersed into the emulsion with agitation. On the basis of the above separation and redispersion process, the magnetic nanoparticles were vividly proved to be existed in the PMMA hollow space. 4. Conclusion In summary, magnetic hollow PMMA nanospheres were successfully obtained by etching the template of CaCO3 in the core–shell Fe3 O4 @CaCO3 @PMMA nanospheres, which were synthesized via in situ emulsion polymerization in the presence of OA-modified Fe3 O4 @CaCO3 composite nanoparticles. And the resultant magnetic hollow PMMA nanospheres were characterized by means of FTIR, XRD, TEM, DLS, EDS and so on. TEM images and DLS measurements demonstrated that the obtained core–shell Fe3 O4 @CaCO3 @PMMA nanospheres were uniform and possessed narrow size distributions. Furthermore, TEM images showed that the magnetic hollow PMMA nanospheres with a shell thickness of 10 nm possessed a perfect spherical profile. Based on the results of IR, XRD, EDS and magnetic testing experiment, Fe3 O4 was proved to be existed in the magnetic hollow PMMA nanospheres, which endowed the hollow PMMA nanospheres with magnetic properties. Owing to their particular hollow structures and magnetic properties, the resultant magnetic hollow PMMA nanospheres could
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bring about potential applications in the various fields of controlled release, drug delivery, targeted drug and so on. Acknowledgements This work was supported by the Personnel Exchange Program (PPP) (No. [2008]3070) approved by China Scholarship Council (CSC) and German Academic Exchange Service (DAAD), the Specialized Research Fund for the Doctoral Program of Higher Education of P R China (No. 20090061120078/3M2102261412) and the Special Fund for Basic Scientific Research of Central Colleges, Jilin University (No. 421031481412). References [1] H.H. Yang, S.Q. Zhang, X.L. Chen, Z.X. Zhuang, Magnetite-containing spherical silica nanoparticles for biocatalysis and bioseparations, Anal. Chem. 76 (2004) 1316–1321. [2] K. Woo, J. Hong, S. Choi, H.W. Lee, J.P. Ahn, C.S. Kim, Easy synthesis and magnetic properties of iron oxide nanoparticles, Chem. Mater. 16 (2004) 2814– 2818. [3] L. Levy, Y. Sahoo, K.S. Kim, E.J. Bergey, P.N. Prasad, Nanochemistry: synthesis and characterization of multifunctional nanoclinics for biological applications, Chem. Mater. 14 (2002) 3715–3721. [4] T. Fried, G. Shemer, G. Markovich, Ordered two-dimensional arrays of ferrite nanoparticles, Adv. Mater. 13 (2001) 1158–1161. [5] D.K. Kim, Y. Zhang, W. Voit, K.V. Rao, M. Muhammed, Synthesis and characterization of surfactant-coated superparamagnetic monodispersed iron oxide nanoparticles, J. Magn. Magn. Mater. 225 (2001) 30–36. [6] J. Kim, J.E. Lee, J. Lee, Y. Jang, S.W. Kim, K. An, J.H. Yu, T. Hyeon, Generalized fabrication of multifunctional nanoparticle assemblies on silica spheres, Angew. Chem. Int. Ed. 45 (2006) 4789–4793. [7] Y.S. Han, D. Radziuk, D. Shchukin, H. Moehwald, Sonochemical synthesis of magnetic protein container for targeted delivery, Macromol. Rapid Commun. 29 (2008) 1203–1207. [8] B. Zebli, A.S. Susha, G.B. Sukhorukov, A.L. Rogach, W.J. Parak, Magnetic targeting and cellular uptake of polymer microcapsules simultaneously functionalized with magnetic and luminescent nanocrystals, Langmuir 21 (2005) 4262– 4265. [9] N. Nasongkla, E. Bey, J. Ren, H. Ai, C. Khemtong, J.S. Guthi, S.F. Chin, A.D. Sherry, D.A. Boothman, J. Gao, Multifunctional polymeric micelles as cancer-targeted, MRI-ultrasensitive drug delivery systems, Nano Lett. 6 (2006) 2427–2430. [10] I.J. Brucea, J. Taylorb, M. Toddb, M.J. Daviesb, E. Borionib, C. Sangregorioa, T. Sen, Synthesis, characterisation and application of silica-magnetite nanocomposites, J. Magn. Magn. Mater. 284 (2004) 145–160. [11] X.Q. Liu, Z.Y. Ma, J.M. Xing, H.Z. Liu, Preparation and characterization of aminosilane modified superparamagnetic silica nanospheres, J. Magn. Magn. Mater. 270 (2004) 1–6. [12] P.A. Dresco, V.S. Zaitsev, R.J. Gambino, B. Chu, Preparation and properties of magnetite and polymer magnetite nanoparticles, Langmuir 15 (1999) 1945–1951. [13] S.H. Sun, H. Zeng, Size-controlled synthesis of magnetite nanoparticles, J. Am. Chem. Soc. 124 (2002) 8204–8205. [14] J.L. Arias, V. Gallardo, S.A. Gómez-Lopera, R.C. Plaza, A.V. Delgadoa, Synthesis and characterization of poly(ethyl-2-cyanoacrylate) nanoparticles with a magnetic core, J. Control. Release 77 (2001) 309–321.
77
[15] J.D. Qiu, H.P. Peng, R.P. Liang, Ferrocene-modified Fe3 O4 @SiO2 magnetic nanoparticles as building blocks for construction of reagentless enzyme-based biosensors, Electrochem. Commun. 9 (2007) 2734–2738. [16] Y. Wu, J. Guo, W.L. Yang, C.C. Wang, S.K. Fu, Preparation and characterization of chitosan-poly(acrylic acid) polymer magnetic microspheres, Polymer 47 (2006) 5287–5294. [17] Z.Q. Shi, Y.F. Zhou, D.Y. Yan, Preparation of poly(b-hydroxybutyrate) and poly(lactide) hollow spheres with controlled wall thickness, Polymer 47 (2006) 8073–8079. [18] Z.Z. Li, L.X. Wen, L. Shao, J.F. Chen, Fabrication of porous hollow silica nanoparticles and their applications in drug release control, J. Control. Release 98 (2004) 245–254. [19] Y. Satoa, Y. Kawashimab, H. Takeuchib, H. Yamamoto, In vitro evaluation of floating and drug releasing behaviors of hollow microspheres (microballoons) prepared by the emulsion solvent diffusion method, Eur. J. Pharm. Biopharm. 57 (2004) 235–243. [20] J. Zhou, W. Wu, D. Caruntu, M.H. Yu, A. Martin, J.F. Chen, C.J. O’Connor, W.L. Zhou, Synthesis of porous magnetic hollow silica nanospheres for nanomedicine application, J. Phys. Chem. C 111 (2007) 17473–17477. [21] J. Jang, H. Ha, Fabrication of hollow polystyrene nanospheres in microemulsion polymerization using triblock copolymers, Langmuir 18 (2002) 5613–5618. [22] E. Donath, G.B. Sukhorukov, F. Caruso, S.A. Davis, H. Möhwald, Novel hollow polymer shells by colloid-templated assembly of polyelectrolytes, Angew. Chem. Int. Ed. 37 (1998) 2201–2205. [23] S.M. Marinakos, J.P. Novak, L.C. Brousseau III, A.B. House, E.M. Edeki, J.C. Feldhaus, D.L. Feldheim, Gold particles as templates for the synthesis of hollow polymer capsules. control of capsule dimensions and guest encapsulation, J. Am. Chem. Soc. 121 (1999) 8518–8522. [24] S.M. Marinakos, D.A. Shultz, D.L. Feldheim, Gold nanoparticles as templates for the synthesis of hollow nanometer-sized conductive polymer capsules, Adv. Mater. 11 (1999) 34–37. [25] H.T. Pu, F.J. Jiang, Z.L. Yang, Preparation and properties of soft magnetic particles based on Fe3 O4 and hollow polystyrene microsphere composite, Mater. Chem. Phys. 100 (2006) 10–14. [26] S. Schacht, Q. Huo, G. Voigt-Martin, G.D. Stucky, F. Schuth, Oil–water interface templating of mesoporous macroscale structures, Science 273 (1996) 768–771. [27] C.A. McKelvey, E.W. Kaler, J.A. Zasadzinski, B. Coldren, H.T. Jung, Templating hollow polymeric spheres from catanionic equilibrium vesicles: synthesis and characterization, Langmuir 16 (2000) 8285–8290. [28] K.J.C. van Bommel, A. Friggeri, S. Shinkai, Organic templates for the generation of inorganic materials, Angew. Chem. Int. Ed. 42 (2003) 980–999. [29] Y. Sheng, J.Z. Zhao, B. Zhou, X.F. Ding, Y.H. Deng, Z.C. Wang, In situ preparation of CaCO3 /polystyrene composite nanoparticles, Mater. Lett. 60 (2006) 3248–3250. [30] J. Yu, J. Yu, Z.X. Guo, Y.F. Gao, Preparation of CaCO3 /polystyrene inorganic/organic composite nanoparticles, Macromol. Rapid Commun. 22 (2001) 1261–1264. [31] X.K. Ma, B. Zhou, Y.H. Deng, Y. Sheng, C.Y. Wang, Y. Pan, Z.Z. Wang, Study on CaCO3 /PMMA nanocomposite microspheres by soapless emulsion polymerization, Colloid Surf. A 312 (2008) 190–194. [32] S.C. Zhang, X.G. Li, Synthesis and characterization of CaCO3 @SiO2 core–shell nanoparticles, Powder Technol. 141 (2004) 75–79. [33] J.F. Chen, J.X. Wang, R.J. Liu, L. Shao, L.X. Wen, Synthesis of porous silica structures with hollow interiors by templating nanosized calcium carbonate, Inorg. Chem. Commun. 7 (2004) 447–449. [34] Y. Sahoo, A. Goodarzi, M.T. Swihart, T.Y. Ohulchanskyy, N. Kaur, E.P. Furlani, P.N. Prasad, Aqueous ferrofluid of magnetite nanoparticles: fluorescence labeling and magnetophoretic control, J. Phys. Chem. B 109 (2005) 3879–3885. [35] S.Y. Yu, H.J. Zhang, J.B. Yu, C. Wang, L.N. Sun, W.D. Shi, Bifunctional magnetic–optical nanocomposites: grafting lanthanide complex onto core–shell magnetic silica nanoarchitecture, Langmuir 23 (2007) 7836–7840.
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Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa
Preparation and characterization of magnetic hollow PMMA nanospheres via in situ emulsion polymerization Chunlei Wang a , Juntao Yan a , Xuejun Cui a,∗ , Dengli Cong b , Hongyan Wang a,∗ a b
College of Chemistry, Jilin University, Qianjin Street 2699, Changchun 130012, China School of Pharmaceutical Sciences, Jilin University, Changchun 130012, China
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Article history: Received 12 January 2010 Received in revised form 31 March 2010 Accepted 12 April 2010 Available online 18 April 2010 Keywords: Magnetic hollow nanospheres PMMA In situ emulsion polymerization
a b s t r a c t Magnetic hollow polymethyl methacrylate (PMMA) nanospheres were successfully obtained by etching the template of CaCO3 in the core–shell Fe3 O4 @CaCO3 @PMMA nanospheres, which were synthesized via in situ emulsion polymerization in the presence of oleic acid-modified Fe3 O4 @CaCO3 composite nanoparticles. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements demonstrated that the core–shell Fe3 O4 @CaCO3 @PMMA nanospheres were uniform and possessed narrow size distributions. And a perfect spherical profile of magnetic hollow PMMA nanospheres could be also observed by TEM. Both the Fourier transform infrared (FTIR) spectrometry, high resolution TEM (HRTEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) provided the sufficient evidences for the presence of Fe3 O4 in the magnetic hollow PMMA nanospheres. Thermogravimetric analysis (TGA) investigated the composition of the resulting composite nanospheres. Moreover, the magnetic testing experiment could give us a direct proof of the presence of Fe3 O4 in magnetic hollow PMMA nanospheres. And the magnetic hollow PMMA nanospheres had a promising future in controlled drug delivery and targeted drug applications. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Magnetic nanoparticles have widespread applications in magnetic bioseparation, drug delivery, magnetic resonance imaging contrast enhancement and targeted drug, due to its excellent properties of superparamagnetism, high saturation magnetization, high magnetic susceptibility, biocompatibility and low toxicity [1–5]. Therefore, more and more researchers have focused on the fascinating feature of targeting [6–9]. However, owing to bare magnetic nanoparticles are liable to aggregation, and rapid biodegradation when they are exposed to a biological system, coupled with a limited carrying capacity, so that it is necessary to combine magnetic nanoparticles with other carriers to achieve targeted delivery efficiently [10–13]. Various inorganic or polymeric materials have been reported as carriers of magnetic materials [14,15]. The polymeric carriers that possessed functional groups can regulate the carrier properties for the desired applications [16,17], hence, inorganic core/organic shell hybrid composite exhibits its remarkable priority over other composites, which can perfectly combine their own unique properties of both magnetic material and polymeric materials.
∗ Corresponding authors. Tel.: +86 431 85168470; fax: +86 431 85168470. E-mail addresses: cui [email protected] (X. Cui), wang [email protected] (H. Wang). 0927-7757/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2010.04.016
Hollow structure materials have gained increasing attention for their various emerging applications in the medicine, immobilizing enzyme, controlled release for drugs, dyes and perfumes, catalysis and many other fields [18–20]. Several methods for synthesizing hollow structure materials have been reported, including polymerization [21], layer-by-layer self-assembly [22], and template method [23–28], etc. Among these methods, the template method is known to be one of the most effective approaches to achieve hollow nanostructures. Successful examples on synthesizing hollow materials are the use of these templates, such as inorganic nanoparticles [23–25], emulsion droplets [26], vesicular solution [27] and organic polymeric sphere [28]. There are many reports about nano-silicon dioxide [25] and gold nanoparticles [23,24] used as templates to prepare hollow nanostructures due to their considerable stability in the process of preparation, however, the very strong corrosive hydrofluoric acid (HF) is needed for etching the templates to achieve the hollow nanostructures. As is known to all, calcium carbonate (CaCO3 ) is the cheapest commercially available inorganic particles. Moreover, CaCO3 could be easily etched by weak acid and its decomposition is nontoxic and friendly to environment. Up to date, there has been numerous reports in terms of two major aspects, one is to prevent the agglomeration of CaCO3 by encapsulating polymers [29], the other is to enhance the mechanical properties of rubber or plastics by filling the CaCO3 [30,31]. In contrast, there are only a few studies concerning the synthesis of hollow materials using CaCO3 as templates [32,33]. Zhou et al.
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Fig. 1. Schematic showing the synthesis of magnetic hollow PMMA nanospheres via in situ emulsion polymerization.
[20] have achieved porous magnetic hollow silica nanospheres with CaCO3 /Fe3 O4 composite particles template by sol–gel method. But no work has yet been performed that magnetic hollow polymer nanospheres were achieved via in situ emulsion polymerization with Fe3 O4 @CaCO3 composite nanoparticles template. Herein we develop a facile method to prepare the core–shell Fe3 O4 @CaCO3 @PMMA nanospheres via in situ emulsion polymerization in the presence of oleic acid-modified Fe3 O4 @CaCO3 composite nanoparticles, and obtain the magnetic hollow PMMA nanospheres by etching the template of CaCO3 . The resultant magnetic hollow PMMA nanospheres not only possessed magnetic property, but also hollow space in the PMMA nanospheres, both of which will make it possible for our following potential applications in the fields of controlled release, drug delivery, targeted drug
and so on. And the resultant magnetic hollow PMMA nanospheres were characterized by means of FTIR, XRD, TEM, DLS, TGA and so on. 2. Experimental 2.1. Materials Methyl methacrylate (MMA, 99%, Aldrich) was used without purification. Ammonium persulfate (APS, Beijing Chemical Reagent Company, China) was of reagent grade. Sodium dodecylbenzene sulfonate (SDBS, Shanghai Chemical Reagents Company, China) used as the surfactants without further purification are of reagent grade. Oleic acid (OA, Tianjin Guangfu Chemical Reagents Company, China) was analytical reagent. Calcium oxide (CaO), acetic acid (HAc) and ammonia (NH4 OH, Beijing Chemical Reagent Company, China) was of reagent grade. Ferric chloride hexahydrate (FeCl3 ·6H2 O) and ferrous chloride tetrahydrate (FeCl2 ·4H2 O) were purchased from Tianjin Guangfu Chemical Reagents Company, China. And the water used was distilled followed by deionization. 2.2. Synthesis The core–shell Fe3 O4 @CaCO3 @PMMA nanospheres were successfully synthesized via in situ emulsion polymerization in the presence of OA-modified Fe3 O4 @CaCO3 composite nanoparticles.
Fig. 2. IR spectrum of: (a) pure PMMA; (b) magnetic hollow PMMA nanospheres; (c) core–shell Fe3 O4 @CaCO3 @PMMA composite nanospheres; (d) OA-modified Fe3 O4 @CaCO3 composite nanoparticles; (e) the Fe3 O4 @CaCO3 @PMMA composites after calcined at 550 ◦ C for 6 h.
Fig. 3. XRD patterns of: (a) Fe3 O4 @CaCO3 @PMMA composite nanospheres; (b) magnetic hollow PMMA nanospheres.
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Fig. 4. TEM images of: (a) citrate modified Fe3 O4 nanoparticles; (b) OA-modified Fe3 O4 @CaCO3 composite nanoparticles; (c) HRTEM image of a single Fe3 O4 @CaCO3 nanoparticle; inset (d) and (e) are FFT patterns of the corresponding HRTEM image.
The in situ emulsion polymerization was conducted under nitrogen atmosphere in a 250 ml four-neck flask fitted with reflux condenser, mechanical stirrer, dropping funnels and inlet for nitrogen gas and heated in the water bath. The overall schematic procedure used to synthesize the magnetic hollow PMMA nanospheres was illustrated in Fig. 1, and the detailed procedure of preparation was described as followed. 2.2.1. Synthesis of OA-modified Fe3 O4 @CaCO3 composite nanoparticles Firstly, CaO was digested into Ca(OH)2 slurry, 125 ml of 0.2 M Ca(OH)2 slurry was then charged into the 250 ml four-necked flask fitted with a mechanical overhead stirrer, coupled with a condenser, the obtained mixture was stirred with a speed of 300 rpm in a ice-water bath. Secondly, 10 ml of citrate-stabilized water-based magnetic fluid (2 wt%), which was successfully obtained by means of the approach reported in the references [7,34], was introduced into the above mixture. After fully mixed, the mixed gas of carbon dioxide and nitrogen (the volume ratio of CO2 to N2 was 1:2) was charged into the slurry at a rate of 80 l/h with a vigorous agitate. When the pH value of the solution reached 7.0, the mixed gas was terminated and the Fe3 O4 @CaCO3 composite nanoparticles were obtained. At the same time, the resultant composite nanoparticles
were heated to 75 ◦ C in a water bath, and the 4 wt% oleic acid that relative to the composite nanoparticles was added dropwise into the flask under continuous stirring for 1 h, after which the superfluous oleic acid was washed with alcohol aqueous solution for several times, then the OA-modified Fe3 O4 @CaCO3 composite nanoparticles with a strong hydrophobic feature were achieved, which significantly ameliorated the compatibility between inorganic particles and monomer. And the aqueous suspension of OA-modified Fe3 O4 @CaCO3 composite nanoparticles was adjusted to 8 wt% for further use. 2.2.2. Synthesis of magnetic hollow PMMA nanospheres First, 65 ml deionized water and 0.1 g SDBS were added into the flask. After complete dissolution of SDBS in deionized water, 15 ml OA-modified Fe3 O4 @CaCO3 composite nanoparticles aqueous suspension were introduced into the flask at room temperature with a vigorous stirring to achieve a fully dispersion phase. 1/5 of monomer (the total amount of MMA was 5 ml) was charged into the above mixture, and the flask was heated to 80 ◦ C gradually in a water bath with a stirring rate of 300 rpm. Then, 1/4 ammonium persulfate (APS) aqueous solution (0.1 g APS dissolved in 20 ml deionized water) was added into the flask, simultaneously, the stirrer speed was turned down to 250 rpm so as to
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Fig. 5. TEM images of: (a) and (b) Fe3 O4 @CaCO3 @PMMA composite nanospheres; (c) magnetic hollow PMMA nanospheres; (d) the EDS spectrum of magnetic hollow PMMA nanospheres.
achieve expected core–shell structure. When examining reflux of the flask wall was decreased, the remaining MMA and APS aqueous solution were added dropwise lasting for 0.5 h by the respective dropping funnels, the polymerization was maintained for 3 h. And the resultant product was purified by centrifugationredispersion cycles for three times in order to remove the above liquid containing homopolymer of MMA, and the obtained precipitation was dried at 60 ◦ C in vacuum for 10 h to achieve core–shell Fe3 O4 @CaCO3 @PMMA nanospheres. Then the resultant core–shell nanospheres were immersed into acetic acid (HAc) aqueous (the volume ratio of HAc to H2 O was 1:15) for 20 h to etch the template of CaCO3 , and the latex was washed three times by deionized water, centrifuged to achieve the magnetic hollow PMMA nanospheres. 2.3. Measurements X-ray diffraction (XRD) data were collected on a Rigaku D/MAX 2550 diffractometer with Cu K␣ radiation. Fourier transform infrared (FTIR) spectra of KBr powder-pressed pellets were recorded on a Nicolet Instruments Research Series 5PC Fourier Transform Infrared spectrometer. The particle sizes and their distribution of composite nanospheres were measured by dynamic light scattering (DLS) with a Malven zetasizer 3000 HSA particle sizer. Transmission electron microscopy (TEM) micrographs were performed on a JEM-2010 transmission microscope at an accelerating voltage of 200 kV, and sample preparation for TEM observation was performed by dropping a dilute suspension of the nanoparticles on the amorphous carbon-coated copper grids and drying at room temperature, then coating a layer of amorphous carbon film on the sample to protect it. Thermogravimetric analysis (TGA) was performed with a Pyris 1TGA (PerkinElmer) under the nitrogen atmosphere at a heating rate of 10 ◦ C/min from 25 to 650 ◦ C.
3. Results and discussion 3.1. FTIR spectra In order to confirm the components of OA-modified composite nanoparticles, the core–shell Fe3 O4 @CaCO3 Fe3 O4 @CaCO3 @PMMA composite nanospheres and magnetic hollow PMMA nanospheres, FTIR spectrum was employed and the results were presented in Fig. 2. The curve (Fig. 2(a)) displayed the characteristic adsorption peaks of PMMA at 1731, 1386–1452, and 1140–1267 cm−1 , which were attributed to vibration adsorption of carbonyl, bending vibrations of CH3 , stretching vibrations of C–O–C, respectively. The curve (Fig. 2(d)) of OA-modified Fe3 O4 @CaCO3 composite nanoparticles not only exhibited the characteristic adsorption peaks of CaCO3 (1453 and 876 cm−1 ) and oleic acid (2860 and 2930 cm−1 ), but also the characteristic adsorption peak of Fe3 O4 (578 cm−1 ) [35], and the results suggested that Fe3 O4 existed in the OA-modified Fe3 O4 @CaCO3 composites. Based on the curve (Fig. 2(c)) of core–shell Fe3 O4 @CaCO3 @PMMA composite nanospheres, it was noted that there were the intensive specific adsorption peaks of CaCO3 at 1453 and 876 cm−1 , adsorption peak of Fe3 O4 at 578 cm−1 , and the characteristic adsorption peaks of PMMA as well, it suggested that both CaCO3 and Fe3 O4 nanoparticles existed in PMMA composites. Moreover, Fig. 2(e) was the curve of the core–shell Fe3 O4 @CaCO3 @PMMA composites after calcined at 550 ◦ C for 6 h, which was well coincident with that of Fig. 2(d), it indicated that OA-modified Fe3 O4 @CaCO3 composite nanoparticles were fully encapsulated by PMMA. In addition, comparison was made between the core–shell Fe3 O4 @CaCO3 @PMMA composite nanospheres and magnetic hollow PMMA nanospheres by the FITR spectrum, it was found that specific adsorption peak of CaCO3 at 1453 and 876 cm−1 were not
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Fig. 6. The particle size distribution of: (a) citrate modified Fe3 O4 nanoparticles; (b) OA-modified Fe3 O4 @CaCO3 composite nanoparticles; (c) core–shell Fe3 O4 @CaCO3 @PMMA composite nanospheres; (d) magnetic hollow PMMA nanospheres.
existed in Fig. 2(b), which demonstrated that CaCO3 template was thoroughly eliminated from the core–shell Fe3 O4 @CaCO3 @PMMA composite nanospheres. On the basis of the above analysis, we could find that there was the characteristic adsorption peak of Fe3 O4 at 578 cm−1 in the curves of Fig. 2(b–e), it was confirmed that Fe3 O4 was existed in the composite particles. 3.2. XRD patterns Based in Fig. 3(a), characteristic diffraction peak of [1 0 4], [1 1 0], [1 1 3], [2 0 2], [0 1 8], and [1 1 6] were observed, it could be indexed to the typical calcite structure of CaCO3 nanoparticles, however, the characteristic diffraction peak of Fe3 O4 nanoparticles were not found, and this phenomenon can be interpreted that the strong characteristic diffraction peak of CaCO3 covered up the weak diffraction peak of Fe3 O4 . In contrast, Fig. 3(b) indicated that magnetic hollow PMMA nanospheres possessed standard spinel structure of Fe3 O4 nanoparticles with characteristic diffraction peaks of [2 2 0], [3 1 1], [4 0 0], [4 2 2], [5 1 1], and [4 4 0], but the diffraction peaks of CaCO3 were not detected, which implied that the templates of CaCO3 were fully etched by acetic acid and Fe3 O4 nanoparticles were remained. Therefore, it was concluded that spinel structure of Fe3 O4 nanoparticles were not damaged during
the process of acid etching, which further provided evidence for the exist of Fe3 O4 in the hollow PMMA nanospheres as well as TEM results.
3.3. Morphology and particle size analysis Both TEM and HRTEM measurements could provide further insights into the structure of composite nanoparticles, therefore TEM and HRTEM measurements were employed in this paper. TEM images of citrate modified Fe3 O4 nanoparticles (Fig. 4(a)) and OAmodified Fe3 O4 @CaCO3 composite nanoparticles (Fig. 4(b)) were shown in Fig. 4. Seen from Fig. 4(a), Fe3 O4 nanoparticles were of spherical shape with a particle size in the range of 10–18 nm. Fig. 4(b) displayed the TEM images of OA-modified Fe3 O4 @CaCO3 composite nanoparticles, it is noted that the resultant composite nanoparticles were cubic, and possessed a particle size in the range of 55–90 nm. Moreover, vivid microstructure of resultant composite nanoparticles demonstrated that Fe3 O4 nanoparticles were successfully embedded in the CaCO3 particles, which facilitated the achievement of magnetic hollow PMMA nanospheres. In addition, based on the HRTEM image (Fig. 4(c)) of a single Fe3 O4 @CaCO3 nanoparticle and FFT patterns (Fig. 4(d and e)) of the corresponding HRTEM image, it was found that the edge area of the
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Fig. 7. TGA curves of: (a) pure PMMA; (b) magnetic hollow PMMA nanospheres; (c) Fe3 O4 @CaCO3 @PMMA composite nanospheres.
HRTEM image (Fig. 4(c)) was one dimensional lattice fringes with an interplanar spacing about 0.2811 nm, which corresponded to the (0 0 6) lattice plane of the calcite CaCO3 (0.2843 nm). And the center area of the HRTEM image was two-dimensional lattice fringes with an interplanar spacing about 0.2823 and 0.2553 nm, which corresponded to the (0 0 6) lattice plane of the calcite CaCO3 (0.2843 nm) and the (3 1 1) lattice plane of the cubic Fe3 O4 (0.2529 nm), respectively. To investigate the morphology of the core–shell Fe3 O4 @CaCO3 @PMMA nanospheres and magnetic hollow PMMA nanospheres, TEM measurement was performed, the TEM images of resultant nanospheres were showed in Fig. 5, and the EDS spectrum of magnetic hollow PMMA nanospheres as well. It was proved that the clear core–shell structure of Fe3 O4 @CaCO3 @PMMA composite nanospheres (Fig. 5(a)) was observed with a shell thickness of 10 nm, and the core–shell composite nanospheres (Fig. 5(b)) were uniform with an average diameter of 100 nm. As could be vividly seen from Fig. 5(c), the magnetic hollow PMMA nanospheres possessed a perfect spherical profile. Moreover, it was noted that Fe3 O4 nanoparticles with a diameter of 15 nm could be examined in the hollow space, which endowed hollow PMMA nanospheres with magnetic properties. Thus, the magnetic hollow PMMA nanospheres brought about potential applications in the various fields of controlled release, drug delivery, targeted drug and so on. Furthermore, EDS spectrum of magnetic hollow PMMA nanospheres (Fig. 5(d)) indicated that besides C and Cu peaks from the TEM grid, only Fe and O were observed, however, Ca peak was not detected, which further proved that CaCO3 was completely etched. In addition, the results of DLS measurement in Fig. 6 also indicated that both citrate modified Fe3 O4 nanoparticles (Fig. 6(a)), OA-modified Fe3 O4 @CaCO3 composite nanoparticles (Fig. 6(b)), the core–shell Fe3 O4 @CaCO3 @PMMA composite nanospheres (Fig. 6(c)), and magnetic hollow PMMA nanospheres (Fig. 6(d)) possessed narrow size distributions, with an average diameter of 16, 80, 110 and 115 nm, respectively, which were consistent with the results of TEM. 3.4. TGA and magnetic testing Thermogravimetric analysis was also employed to investigate the composition of the resulting composite nanospheres, and the detailed results were depicted in Fig. 7. Pure PMMA (Fig. 7(a)) showed no residual weigh due to the complete decomposition of PMMA. When incorporating the Fe3 O4 @CaCO3 nanoparticles into
Fig. 8. The photographs of magnetic testing: (a) the magnetic hollow PMMA nanospheres in aqueous solution, and (b) the directed movement under an external magnetic field.
the polymerization system, the resultant Fe3 O4 @CaCO3 @PMMA composite nanospheres (Fig. 7(c)) exhibited a residual weight of about 22%, which was attributed to the presence of Fe3 O4 @CaCO3 nanoparticles. Compared with Fig. 7(c), the magnetic hollow PMMA nanospheres (Fig. 7(b)) possessed a residual weight of about 2%, which further suggested that CaCO3 nanoparticles were effectively etched from the Fe3 O4 @CaCO3 @PMMA composite nanospheres by using diluted acetic acid and Fe3 O4 nanoparticles were remained. Moreover, based on the above results, it could be concluded that magnetic content of the magnetic hollow PMMA nanospheres was about 2%. In order to further explore the magnetic properties of magnetic hollow PMMA nanospheres, the separation and redispersion process of the magnetic hollow PMMA nanospheres were conducted. As shown in Fig. 8, the magnetic hollow PMMA nanospheres in aqueous solution were brown emulsion (Fig. 8(a)), and they could do oriented movement in an external magnetic field (Fig. 8(b)), once the external magnetic field was removed, they would be redispersed into the emulsion with agitation. On the basis of the above separation and redispersion process, the magnetic nanoparticles were vividly proved to be existed in the PMMA hollow space. 4. Conclusion In summary, magnetic hollow PMMA nanospheres were successfully obtained by etching the template of CaCO3 in the core–shell Fe3 O4 @CaCO3 @PMMA nanospheres, which were synthesized via in situ emulsion polymerization in the presence of OA-modified Fe3 O4 @CaCO3 composite nanoparticles. And the resultant magnetic hollow PMMA nanospheres were characterized by means of FTIR, XRD, TEM, DLS, EDS and so on. TEM images and DLS measurements demonstrated that the obtained core–shell Fe3 O4 @CaCO3 @PMMA nanospheres were uniform and possessed narrow size distributions. Furthermore, TEM images showed that the magnetic hollow PMMA nanospheres with a shell thickness of 10 nm possessed a perfect spherical profile. Based on the results of IR, XRD, EDS and magnetic testing experiment, Fe3 O4 was proved to be existed in the magnetic hollow PMMA nanospheres, which endowed the hollow PMMA nanospheres with magnetic properties. Owing to their particular hollow structures and magnetic properties, the resultant magnetic hollow PMMA nanospheres could
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bring about potential applications in the various fields of controlled release, drug delivery, targeted drug and so on. Acknowledgements This work was supported by the Personnel Exchange Program (PPP) (No. [2008]3070) approved by China Scholarship Council (CSC) and German Academic Exchange Service (DAAD), the Specialized Research Fund for the Doctoral Program of Higher Education of P R China (No. 20090061120078/3M2102261412) and the Special Fund for Basic Scientific Research of Central Colleges, Jilin University (No. 421031481412). References [1] H.H. Yang, S.Q. Zhang, X.L. Chen, Z.X. Zhuang, Magnetite-containing spherical silica nanoparticles for biocatalysis and bioseparations, Anal. Chem. 76 (2004) 1316–1321. [2] K. Woo, J. Hong, S. Choi, H.W. Lee, J.P. Ahn, C.S. Kim, Easy synthesis and magnetic properties of iron oxide nanoparticles, Chem. Mater. 16 (2004) 2814– 2818. [3] L. Levy, Y. Sahoo, K.S. Kim, E.J. Bergey, P.N. Prasad, Nanochemistry: synthesis and characterization of multifunctional nanoclinics for biological applications, Chem. Mater. 14 (2002) 3715–3721. [4] T. Fried, G. Shemer, G. Markovich, Ordered two-dimensional arrays of ferrite nanoparticles, Adv. Mater. 13 (2001) 1158–1161. [5] D.K. Kim, Y. Zhang, W. Voit, K.V. Rao, M. Muhammed, Synthesis and characterization of surfactant-coated superparamagnetic monodispersed iron oxide nanoparticles, J. Magn. Magn. Mater. 225 (2001) 30–36. [6] J. Kim, J.E. Lee, J. Lee, Y. Jang, S.W. Kim, K. An, J.H. Yu, T. Hyeon, Generalized fabrication of multifunctional nanoparticle assemblies on silica spheres, Angew. Chem. Int. Ed. 45 (2006) 4789–4793. [7] Y.S. Han, D. Radziuk, D. Shchukin, H. Moehwald, Sonochemical synthesis of magnetic protein container for targeted delivery, Macromol. Rapid Commun. 29 (2008) 1203–1207. [8] B. Zebli, A.S. Susha, G.B. Sukhorukov, A.L. Rogach, W.J. Parak, Magnetic targeting and cellular uptake of polymer microcapsules simultaneously functionalized with magnetic and luminescent nanocrystals, Langmuir 21 (2005) 4262– 4265. [9] N. Nasongkla, E. Bey, J. Ren, H. Ai, C. Khemtong, J.S. Guthi, S.F. Chin, A.D. Sherry, D.A. Boothman, J. Gao, Multifunctional polymeric micelles as cancer-targeted, MRI-ultrasensitive drug delivery systems, Nano Lett. 6 (2006) 2427–2430. [10] I.J. Brucea, J. Taylorb, M. Toddb, M.J. Daviesb, E. Borionib, C. Sangregorioa, T. Sen, Synthesis, characterisation and application of silica-magnetite nanocomposites, J. Magn. Magn. Mater. 284 (2004) 145–160. [11] X.Q. Liu, Z.Y. Ma, J.M. Xing, H.Z. Liu, Preparation and characterization of aminosilane modified superparamagnetic silica nanospheres, J. Magn. Magn. Mater. 270 (2004) 1–6. [12] P.A. Dresco, V.S. Zaitsev, R.J. Gambino, B. Chu, Preparation and properties of magnetite and polymer magnetite nanoparticles, Langmuir 15 (1999) 1945–1951. [13] S.H. Sun, H. Zeng, Size-controlled synthesis of magnetite nanoparticles, J. Am. Chem. Soc. 124 (2002) 8204–8205. [14] J.L. Arias, V. Gallardo, S.A. Gómez-Lopera, R.C. Plaza, A.V. Delgadoa, Synthesis and characterization of poly(ethyl-2-cyanoacrylate) nanoparticles with a magnetic core, J. Control. Release 77 (2001) 309–321.
77
[15] J.D. Qiu, H.P. Peng, R.P. Liang, Ferrocene-modified Fe3 O4 @SiO2 magnetic nanoparticles as building blocks for construction of reagentless enzyme-based biosensors, Electrochem. Commun. 9 (2007) 2734–2738. [16] Y. Wu, J. Guo, W.L. Yang, C.C. Wang, S.K. Fu, Preparation and characterization of chitosan-poly(acrylic acid) polymer magnetic microspheres, Polymer 47 (2006) 5287–5294. [17] Z.Q. Shi, Y.F. Zhou, D.Y. Yan, Preparation of poly(b-hydroxybutyrate) and poly(lactide) hollow spheres with controlled wall thickness, Polymer 47 (2006) 8073–8079. [18] Z.Z. Li, L.X. Wen, L. Shao, J.F. Chen, Fabrication of porous hollow silica nanoparticles and their applications in drug release control, J. Control. Release 98 (2004) 245–254. [19] Y. Satoa, Y. Kawashimab, H. Takeuchib, H. Yamamoto, In vitro evaluation of floating and drug releasing behaviors of hollow microspheres (microballoons) prepared by the emulsion solvent diffusion method, Eur. J. Pharm. Biopharm. 57 (2004) 235–243. [20] J. Zhou, W. Wu, D. Caruntu, M.H. Yu, A. Martin, J.F. Chen, C.J. O’Connor, W.L. Zhou, Synthesis of porous magnetic hollow silica nanospheres for nanomedicine application, J. Phys. Chem. C 111 (2007) 17473–17477. [21] J. Jang, H. Ha, Fabrication of hollow polystyrene nanospheres in microemulsion polymerization using triblock copolymers, Langmuir 18 (2002) 5613–5618. [22] E. Donath, G.B. Sukhorukov, F. Caruso, S.A. Davis, H. Möhwald, Novel hollow polymer shells by colloid-templated assembly of polyelectrolytes, Angew. Chem. Int. Ed. 37 (1998) 2201–2205. [23] S.M. Marinakos, J.P. Novak, L.C. Brousseau III, A.B. House, E.M. Edeki, J.C. Feldhaus, D.L. Feldheim, Gold particles as templates for the synthesis of hollow polymer capsules. control of capsule dimensions and guest encapsulation, J. Am. Chem. Soc. 121 (1999) 8518–8522. [24] S.M. Marinakos, D.A. Shultz, D.L. Feldheim, Gold nanoparticles as templates for the synthesis of hollow nanometer-sized conductive polymer capsules, Adv. Mater. 11 (1999) 34–37. [25] H.T. Pu, F.J. Jiang, Z.L. Yang, Preparation and properties of soft magnetic particles based on Fe3 O4 and hollow polystyrene microsphere composite, Mater. Chem. Phys. 100 (2006) 10–14. [26] S. Schacht, Q. Huo, G. Voigt-Martin, G.D. Stucky, F. Schuth, Oil–water interface templating of mesoporous macroscale structures, Science 273 (1996) 768–771. [27] C.A. McKelvey, E.W. Kaler, J.A. Zasadzinski, B. Coldren, H.T. Jung, Templating hollow polymeric spheres from catanionic equilibrium vesicles: synthesis and characterization, Langmuir 16 (2000) 8285–8290. [28] K.J.C. van Bommel, A. Friggeri, S. Shinkai, Organic templates for the generation of inorganic materials, Angew. Chem. Int. Ed. 42 (2003) 980–999. [29] Y. Sheng, J.Z. Zhao, B. Zhou, X.F. Ding, Y.H. Deng, Z.C. Wang, In situ preparation of CaCO3 /polystyrene composite nanoparticles, Mater. Lett. 60 (2006) 3248–3250. [30] J. Yu, J. Yu, Z.X. Guo, Y.F. Gao, Preparation of CaCO3 /polystyrene inorganic/organic composite nanoparticles, Macromol. Rapid Commun. 22 (2001) 1261–1264. [31] X.K. Ma, B. Zhou, Y.H. Deng, Y. Sheng, C.Y. Wang, Y. Pan, Z.Z. Wang, Study on CaCO3 /PMMA nanocomposite microspheres by soapless emulsion polymerization, Colloid Surf. A 312 (2008) 190–194. [32] S.C. Zhang, X.G. Li, Synthesis and characterization of CaCO3 @SiO2 core–shell nanoparticles, Powder Technol. 141 (2004) 75–79. [33] J.F. Chen, J.X. Wang, R.J. Liu, L. Shao, L.X. Wen, Synthesis of porous silica structures with hollow interiors by templating nanosized calcium carbonate, Inorg. Chem. Commun. 7 (2004) 447–449. [34] Y. Sahoo, A. Goodarzi, M.T. Swihart, T.Y. Ohulchanskyy, N. Kaur, E.P. Furlani, P.N. Prasad, Aqueous ferrofluid of magnetite nanoparticles: fluorescence labeling and magnetophoretic control, J. Phys. Chem. B 109 (2005) 3879–3885. [35] S.Y. Yu, H.J. Zhang, J.B. Yu, C. Wang, L.N. Sun, W.D. Shi, Bifunctional magnetic–optical nanocomposites: grafting lanthanide complex onto core–shell magnetic silica nanoarchitecture, Langmuir 23 (2007) 7836–7840.