polyethylenimine through a facile one-pot deposition route

Accepted Manuscript Preparation and characterization of iron oxide (Fe3O4) nanoparticles coated with polyvinylpyrrolidone/polyethylenimine through a facile one-pot deposition route Isa Karimzadeh, Mustafa Aghazadeh, Mohammad Reza Ganjali, Taher Doroudi, Peir Hossein Kolivand PII: DOI: Reference:

S0304-8853(16)33163-8 http://dx.doi.org/10.1016/j.jmmm.2017.02.048 MAGMA 62509

To appear in:

Journal of Magnetism and Magnetic Materials

Received Date: Revised Date: Accepted Date:

24 November 2016 20 February 2017 25 February 2017

Please cite this article as: I. Karimzadeh, M. Aghazadeh, M.R. Ganjali, T. Doroudi, P.H. Kolivand, Preparation and characterization of iron oxide (Fe3O4) nanoparticles coated with polyvinylpyrrolidone/polyethylenimine through a facile one-pot deposition route, Journal of Magnetism and Magnetic Materials (2017), doi: http://dx.doi.org/ 10.1016/j.jmmm.2017.02.048

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Preparation and characterization of iron oxide (Fe3O4) nanoparticles coated with polyvinylpyrrolidone/polyethylenimine through a facile one-pot deposition route Isa Karimzadeh a,b, Mustafa Aghazadeh c,*, Mohammad Reza Ganjali d,e, Taher Doroudi a and Peir Hossein Kolivand a a

Shefa Neuroscience Research Center, Khatam ol Anbia Specialty and Subspecialty Hospital, Tehran, Iran

b

Department of Physics, Faculty of Science, Central Tehran Branch, Islamic Azad University, Tehran, Iran

c

NFCRS, Nuclear Science and Technology Research Institute (NSTRI), P.O. Box 14395-834, Tehran, Iran

d

Center of Excellence in Electrochemistry, Faculty of Chemistry, University of Tehran, Tehran, Iran

e

Biosensor Research Center, Endocrinology and Metabolism Molecular-Cellular Sciences Institute, Tehran University of Medical Sciences, Tehran, Iran

Corresponding author Email address: [email protected] Tel/Fax: +98-21-8264289

Abstract In this article, we report the electrochemical synthesis and simultaneous in situ coating of magnetic iron oxide nanoparticles (MNPs) with polyvinylpyrrolidone (PVP) and polyethylenimine (PEI). The cathodic deposition was carried out through electro-generation of OH–on the surface of cathode. An aqueous solution of Fe(NO3)3.9H2O (3.4g/L) and FeCl2.4H2O (1.6g/L) was used as the deposition bath. The electrochemical precipitation experiments were performed in the direct current mode under a 10 mA cm–2 current density for 30 min. Polymer coating was performed in an identical deposition bath containing of 0.5g PVP and 0.5g PEI. The deposited uncoated and PVP-PEI coated MNPs were characterized through powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), dynamic light scattering (DLS), vibrating sample magnetometer (VSM), and Fieldemission scanning and transmission electron microscopies (FE-SEM and TEM). Structural XRD and IR analyses revealed both samples to be composed of pure crystalline magnetite (Fe3O4). Morphological

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observations through FE-SEM and TEM proved the product to be spherical nanoparticles in the range of 10-15nm. The presence of two coating polymers (i.e. PVP and PEI) on the surface of the electrosynthesized MNPs was proved by FTIR and DLS results. The percentage of the polymer coating (31.8%) on the MNPs surface was also determined based on DSC-TGA data. The high magnetization value, coercivity and remanence values measured by VSM indicated the superparamagnetic nature of both prepared MNPs. The obtained results confirmed that the prepared Fe3O4 nanoparticles had suitable physico-chemical and magnetic properties for biomedical applications.

Keywords: Magnetite nanoparticles, Electrosynthesis, Double coating, Magnetic properties

1. Introduction Iron oxide nanoparticles (NPs), including magnetite (Fe3O4) and maghemite (γ-Fe2O3), have received great attention due to their interesting bio-medical applications in the fields of bio-sensors, magnetic resonance imaging (MRI) contrast agents, and magnetic fluid hyperthermia [1−3]. The performance of iron oxide NPs in the mentioned fields is directly related to their size, surface coating and magnetic behavior [4,5]. Hence, currently extensive efforts have been applied to the preparation and functionalization of iron oxide NPs for use in the mentioned applications. On the other hand, the physicochemical characteristics of Fe3O4 NPs are strongly affected by their preparation methods [6,7]. Preparation of magnetite nanoparticles (MNPs) with proper-biocompatible properties has long been a challenge for researchers. Two main challenges in the area are; (i) optimization of the preparation conditions in order to prepare mono-dispersed MNPs of suitable size, and (ii) the development of repeatable procedures to avoid using expensive precursors, as well as complex preparation and purification steps. In this regard, significant improvements have been reported in the common methods used for the preparation of MNPs (e.g. co-precipitation, solvothermal, hydrothermal, thermal decomposition, microwave synthesis and sol-gel) [8-19]. However, the precise control of the particle size and distribution are dominant problems that should be addressed. For example, it is difficult to control the process of the formation of the particles through chemical precipitation, which conventionally leads to the 2

production of aggregated nanoparticles with a broad size distributions, irregular morphologies, mixed phases (i.e. Fe3O4 with γ-,α-Fe2O3). Also, the decomposition processes used require high temperature (100–300 oC), toxic and expensive precursors, and offer limited controllability on the particle size and morphology. Therefore, the development of synthesis methods resulting in high-quality MNPs with proper particle size distribution, crystallinity and spherical shape is a major area of research. One of promising alternative route for the preparation of MNPs is cathodic electrodeposition offering simplicity and facility. The method can effectively control the composition, crystallinity, purity, particle size and deposit properties through manipulation or adjustment of the deposition conditions including the direct currents and/or potentials applied to the system [20-24]. The method, however, has been rarely applied to the preparation of MNPs and only few reports are available on it in the literature [25-28]. The first report on the preparation of Fe3O4 NPs through cathodic electrodeposition was published by Verelst et al. [27,28] who found that MNPs with controlled size and dispersion could be easily prepared through cathodic electrodeposition from a nitrate bath. Recently, we reported the cathodic electrodeposition of Fe3O4 NPs from an aqueous medium and its in situ surface coating with polyethylene glycol, polyvinyl chloride and poly(vinylpyrrolidone) [29-32]. In this work, we applied a cathodic electrodeposition procedure for the preparation of doubly coated MNPs with desired size and magnetic behavior from iron(II) nitrate/chloride bath. Poly(vinylpyrrolidone) (PVP) and polyethylene imine (PEI) were selected as the coating agents. During the deposition procedure, the electrochemical conditions were first optimized to obtain bare or uncoated MNPs with proper physico-chemical characters. The crystalline phase, nano-size range, morphology and superparamagnetic properties of the bare NPs were identified via XRD, FE-SEM, TEM and VSM analyses. Next, PVP/PEI coatings were formed on MNPs electrodeposited under identical conditions except for the composition of the electrodeposition bath (i.e. the bath contained PVP and PEI at 0.5 g/L). The obtained product was referred to as PEI/PVP coated MNPs. The nature of the coating on the surface of the deposited MNPs was confirmed by FT-IR, DSC-TGA and DLS analyses. Although most used chemical routes are multistepped procedures requiring long times (8-12h) and high temperatures (40-150°C) during the coating 3

process, the suggested method enjoys the advantages of the in situ approach in terms of being fast and straight forward. 2. Experimental 2.1. Materials Ferric nitrate nonahydrate (Fe(NO3)3.9H2O, 99.9%), ferrous chloride tetrahydrate (FeCl2 .4H2O), poly(vinylpyrrolidone) (PVP, Mw=6000), polyethyleneimine (PEI, Mw~25000) and ethanol (C2H5OH) were purchased from Merck. Graphite plate and stainless steel (316L) were purchased from local companies. All chemicals used were of reagent grade. 2.2. Preparation procedure of the nanoparticles 1.6g of FeCl2.4H2O and 3.4 g Fe(NO3)3.9H2O were dissolved in 1 liter of deionized water and used as the deposition bath solution. A two-electrode system containing a stainless-steel cathode centered between two graphite anodes was used as the electrodeposition set-up, as shown in Fig. 1. Un-coated NPs were deposited on the steel cathode through a cathodic electrochemical deposition procedure. This way, a galvanostatic regime was applied in the electrodeposition experiments. The applied current density and bath temperature were 10 mA cm-2 and 27 oC, respectively. A DC power source (PROVA 8000) was used as shown in Fig. 1. A current density of 10 mA cm-2 was applied for 30 min to the electrochemical cell and the black deposit was formed on the cathode surface. After the deposition step, the steel substrate was removed from the electrolyte and rinsed with distilled water several times to remove the free anions. Then, the black deposit was scraped form the electrode surface and dispersed in an ethanol solution and then centrifuge at 6000 rpm for 30 min. After this step, the deposits were washed with ethanol several times, separated by a magnet, and dried in a vacuum oven (70oC for 1h).

2.3. Preparation procedure of polymer coated NPs

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Similar electrochemical set-up and conditions used for the preparation of uncoated NPs, were also used for the preparation of polymer coated nanoparticles. The bath composition, used for preparing the coated particles was only different in containing 0.5g of both dissolved PVP and PEI. The deposition experiments in the presence of PVP and PEI polymers were run under a current density of 10 mA cm-2 for 30 min. After the deposition step, the purification steps were followed. First the steel cathode was removed from the deposition cell and washed several times with deionized water, before the deposits were scraped from its surface and dispersed in an ethanol solution. The solid product was next washed repeatedly washed with ethanol to remove the free and uncoated polymer and the deposits were dispersed in ethanol and centrifuged at 6000 rpm for 30min, before the black powder was finally separated from ethanol the solution with a magnet and dried in a vacuum oven (70 oC for 1h). The prepared powder was referred to as PVP/PEI-coated-MNPs.

2.4. Characterization procedure The XRD patterns obtained for the prepared MNPs were recorded using a Philips powder diffractometer PW-1800 instrument with a Co Kα radiation (λ=1.789 Å). The crystallite sizes were estimated from the X-ray line broadening using Scherrer equation. The infrared spectra were recorded in the range 4000–400 cm−1 on a Fourier transform infrared spectrometer (FTIR, Bruker Vector 22 spectroscope). The morphological micrographs were acquired by field-emission scanning electron microscopy (FE-SEM, TE-SCAN Model MIRA3, operating voltage 30 kV) and Zeiss transmission electron microscopy (TEM, model EM 900 with an accelerating voltage of 80 kV) was used for determining the particle sizes. Thermal behavior analyses (DTA-TG) were performed in an N2 atmosphere between room temperature and 600 oC at a heating rate of 5oC min−1 using a STA-1500 thermo-analyzer. Dynamic light scattering (DLS) was performed using a Malvern 4700 Autosizer with a 7132 digital correlator for the determination

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of hydrodynamic diameter. Vibrating sample magnetometer (VSM, Model: Lake shore 7400, United States) was used to study the hysteresis loops and the magnetic properties of the magnetite nanoparticles.

3. Results and discussion The XRD patterns of both coated and uncoated samples are shown in Fig. 2, where it can be easily observed that the prepared samples are composed of a crystalline single-phase cubic inverse spinel Fe3O4 structure, with the position and relative intensity of all diffraction peaks very well matching those from the JCPDS Card No. 88-0315 for magnetite. No peak corresponding to impurities was observed. Notably, the characteristic peaks of coated nanoparticles did not have any shifts in their positions but underwent some broadening, indicating that the coated samples have smaller crystalline sizes as compared with uncoated particles. Furthermore, the peak intensity of the coated sample is lower than that of the uncoated one due to the presence of the PVP/PEI coating on the surface of Fe3O4 nanoparticles. The crystallite size was calculated by measuring the half-height width of the strongest reflection planes (i.e. 311), using the well-known Scherrer equation (i.e. D=0.9λ/β cos (θ), β being the full width at half maxima (FWHM) of the (311) peak). Based on the calculations, the crystallite sizes of the bare and coated MNPs were estimated to be 9.2 and 7.6 nm, respectively. These findings indicated that the pure magnetite Fe3O4 can be easily synthesized by the proposed direct current cathodic deposition procedure. FT-IR analysis is an invaluable technique for confirming the presence of the coating agents on the surface of the iron oxide nanoparticles. Fig. 3 exhibits the IR spectra of the electro-synthesized iron oxide nanoparticles. The FT-IR spectrum of the uncoated NPs (in Fig. 4a) contains two main absorption bands at around 1633 and 3448 cm–1, which correspond to to the stretching and deformation vibrations of hydroxyl groups connected to the surface of iron oxide nanoparticles [30,32]. In the range of 400-700 cm– 1

, the vibrations relating to the Fe—O bond show peaks at 625, 558 and 431 cm–1, which are characteristic

absorbance bands of nano-sized magnetite [33]. The IR spectrum of the coated MNPs has the two of mentioned at around 576 and 629 cm–1, which indicate a mild blue shift, which is due to the changes in

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the chemical environment of the MNPs after coating with PVP/PEI, in which new chemical bonds are formed between Fe3O4 and -NH2 groups of PEI and also C=O groups of PVP. After coating of MNPs with PVP/PEI, some new IR bands have been appeared, which can be seen in Fig. 3b. The bands at 3435 and 1628 cm−1 correspond to the vibrations modes of -NH2 groups in PEI [34]. Further the bands at 2882 cm−1 and 1471 cm−1 arise from the bending and scissoring vibrations of CH2 and the ones at around 1357 cm−1 and 1295 cm−1 originate from the wagging and twisting of CH2 [35]. Notably, all the peaks represent the various vibration modes of methyl groups in both PVP and PEI backbones. The peak around 954 cm−1 can be attributed to the out-of-plane bending vibrations of CH [30,31] and the broad peak at 1005-1015 cm−1 originates from the stretching of C-N in both PVP and PEI polymers. he bonds at 1174 cm−1 and 1338 cm−1 are due to the vibrations of C-C bands (i.e. stretch and bending vibration, respectively) [30,36], the sharp peak at 1628 cm−1 is due to the vibration of the C=O groups of PVP [35,37], and the peaks located at 1124 cm−1 and 2812 cm−1 arise from the stretches of C-N and N-C-H, respectively [38]. From these data, it is clearly specified that the IR spectrum of the coated MNPs have all the vibrations peaks of PVP and PEI including C-N, C-C, C-H, C=O, N-H, and also CH2, NH2 and CH3 groups. It has been reported that the vibrations of C=O group in pure PVP and the -NH2 group in pure PEI are observable at about 1649 cm−1 and 1705 cm−1, respectively [29,42]. In the IR spectrum of the coated MNPs (Fig. 3b), the location of the peaks representing these vibrations shows a little shift, implicating the chemical interactions among C=O and –NH2 groups and the Fe3O4 nanoparticles. These results completely confirm the presence of the PVP/PEI coating on the surface of the electrodeposited MNPs. FE-SEM results obtained for the deposited nanoparticles are represented in Fig. 4. The uncoated nanoparticles have partially spherical shapes and are rather agglomerated as seen in Fig. 4a. It seems that each spherical particle observed in Fig. 4a, is composed of several iron oxide particles. For the coated MNPs, the same morphology and configuration is seen in the FE-SEM observations (Fig. 4b), yet they have better dispersion and less agglomeration as compared with uncoated NPs.

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TEM images of both MNPs are shown in Fig. 5. The TEM observations in Fig. 5a reveal that the uncoated particles have spherical shapes 8-10 nm in size. However, the uncoated particles are rather agglomerated as clearly observable in the TEM image in Fig. 5a. The TEM studies on the polymer coated iron oxide (Fig. 5b) reveal that this sample has better spherical-shaped particles with sizes in the range of 10-12 nm. Furthermore, it is clearly seen that the PEI/PVP coated particles have better dispersion and are less agglomerated as seen in FE-SEM image (Fig. 4b). The thermal behavior, as reflected by the DSC and TGA curves of the coated and uncoated MNPs are given in Fig. 6. The DSC curve of the naked MNPs (Fig. 6a) includes no special endo-/exothermic peaks between the scanned temperatures of 25 to 600 oC. This indicates that the deposited Fe3O4 nanoparticles are thermally stable up to 600 oC. Notably, only one endothermic peak is observed below 150 oC, which can be assigned to the removal of OH– groups and water molecules from the surface of the Fe3O4 nanoparticles. Subsequently, the TG curve of the uncoated particles indicates a mere 2.01% weight loss during heating up to 600 oC as clearly seen in Fig. 6b. The DCS curve shows that the polymer coated MNPs have a completely different thermal behavior as compared with bare MNPs. This different behavior may be caused by the presence of the PVP/PEI coat on the surface of MNPs. For the coated NPs, the DSC curve in Fig. 6a contains two exothermic peaks in the temperature range of 25-600 °C. The first simple endothermic peak (between 25-100 oC) is related to the removal of OH- groups from the surface of MNPs. Respectively, the TG curve reveals a weight loss of 9.5% in this range. After this stage, the DSC curve has a multi-step and complex endothermic peak at in the temperatures range of 120-350 oC, with two maxims at 210 oC and 255 oC. The TG curve also shows a sharp weight loss of about 22.3% at this temperature range (Fig. 6b). It has been observed that the PEI coating on the surface of MNPs decomposes in the temperature range of 200-400 oC, as indicated by the relatively sharp peak at 250 oC [39-42]. It has been also reported that pure PVP starts to decompose at about 350°C, while PVP coatings on Pt NPs reportedly undergo thermal decomposition at 350°C, which is 30° lower than that for pure PVP [43]. Hence, the weight loss observed at the temperature range of 100-

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450 oC mainly relates to the decomposition of PVP and PEI coatings. The PEI/PVP coated nanoparticles exhibited a total weight loss of 31.8% as opposed to bare NPs (2.1%). This clearly implicates the presence of a PVP-PEI coating on the surface of deposited iron oxide NPs. After 450 °C, no weight loss is observed in the temperature range up to 600 °C (Fig. 5), indicating the complete decomposition of the coated polymers. These observations completely confirmed the in situ coating of the Fe3O4 nanoparticles during their electrodeposition from iron nitrate/chloride bath containing PVP/PEI polymers. DLS analyses were performed for specifying of the hydrodynamic diameters of the electrodeposited iron oxide nanoparticles. Fig. 7 shows the measured particle size for the uncoated and PVP/PEI coated MNPs. For bare NPs (Fig. 7a), the mean hydrodynamic diameter was measured to be ~20 nm. For coated MNPs, on the other hand, this is ~72. The increase in the hydrodynamic size clearly confirmed the presence of coat layer on the surface of deposited MNPs. The magnetic behaviors of the deposited nanoparticles in the presence of a magnetic field were measured using a vibrating sample magnetometer (VSM). Fig. 8 presents the hysteresis loops of the bare and PVP/PEI coated MNPs at room temperature. The prepared MNPs showed superparamagnetic behaviors, and their magnetization reduced from a plateau value to zero upon removal of the magnetic field. Bare MNPs exhibited a saturation magnetization (Ms) of 71.5 emu/g, a small remanent magnetization (Mr≈0.71 emu/g) and coercivity (Ce~2.15 Oe) indicating their proper magnetic characteristics. The polymer coated nanoparticles exhibited Ms, Mr, and Ce values of around 32.2 emu/g, 0.57 emu/g and 0.95Oe, respectively. These confirmed that the prepared MNPs enjoy a suitable magnetic performance and can be used in various biomedical applications. 4. Conclusion Naked and polymer-coated Fe3O4 nano-particles were participated on a steel cathode from a mixed iron nitrate/chloride bath containing PVP and PEI polymers through a cathodic electrochemical deposition method. The nano-meter size, spherical shape, surface coating and super-paramagnetic performance of the prepared samples (i.e. bare and PVP/PEI coated nanoparticles) were confirmed by FT-IR, DLS, TGA, 9

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Figure Captions: Fig. 1. Electrochemical set-up used for electrodeposition of nanoparticles. The inset shows the black deposit after electrodeposition. Fig. 2. XRD patterns of the prepared (a) bare and (b) PVP/PEI coated MNPs. Fig. 3. FT-IR spectra of the prepared (a) bare and (b) PVP/PEI coated MNPs. Fig. 4. FE-SEM images of the prepared (a) bare and (b) PVP/PEI coated MNPs. Fig. 5.TEM images of the prepared (a) bare and (b) PVP/PEI coated MNPs. Fig. 6. DSC-TG curves for the prepared (a) bare and (b) PVP/PEI coated MNPs. Fig. 7. Particle size distributions of (a) bare and (b) PVP/PEI coated MNPs. Fig. 8. VSM curves for the prepared (a) bare and (b) PVP/PEI coated MNPs.

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Fig. 1. Electrochemical set-up used for electrodeposition of nanoparticles. The inset shows the black deposit after electrodeposition.

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Fig. 2. XRD patterns of the prepared (a) bare and (b) PVP/PEI coated MNPs.

Fig. 3. FT-IR spectra of the prepared (a) bare and (b) PVP/PEI coated MNPs.

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Fig. 4. FE-SEMimages of the prepared (a) bare and (b) PVP/PEI coated MNPs.

Fig. 5.TEM images of the prepared (a) bare and (b) PVP/PEI coated MNPs.

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Fig. 6. DSC-TG curves for the prepared (a) bare and (b) PVP/PEI coated MNPs.

Fig. 7. Particle size distributions of (a) bare and (b) PVP/PEI coated MNPs.

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Fig. 8.VSM curves for the prepared (a) bare and (b) PVP/PEI coated MNPs.

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Research Highlight: -

MNPs were prepared by cathodic electrodeposition In situ double polymer coating was achieved during electrodeposition The prepared MNPs have proper size and properties for biomedical applications.

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