Core–shell and multilayered magnetite nanoparticles—Structural and Mössbauer studies

Accepted Manuscript Title: Core-shell and multilayered magnetite nanoparticles–structural and M¨ossbauer studies Author: B. Kalska-Szostko U. Wykowska D. Satuła PII: DOI: Reference:

S0169-4332(14)00867-8 http://dx.doi.org/doi:10.1016/j.apsusc.2014.04.102 APSUSC 27702

To appear in:

APSUSC

Received date: Revised date: Accepted date:

20-11-2013 15-4-2014 16-4-2014

Please cite this article as: B. Kalska-Szostko, U. Wykowska, D. Satula, Core-shell and multilayered magnetite nanoparticlesndashstructural and M¨ossbauer studies, Applied Surface Science (2014), http://dx.doi.org/10.1016/j.apsusc.2014.04.102 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Core-shell and multilayered magnetite nanoparticles – structural and Mössbauer studies B. Kalska-Szostko, U. Wykowska, D. Satuła*

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Institute of Chemistry, Hurtowa 1, 15-399 Białystok, Poland *Faculty of Physics, Lipowa 41, 15-424 Białystok, Poland

Abstract

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In the paper, we present the effective method of the preparation of nanosized core-shell or multilayered nanoparticles with various layer compositions. Metals like Cu, Ag and Au have been used as a surface or spacer material in magnetite based particles. In further steps, functionalization of obtained nanoparticles was done. The resulting nanoparticles were structurally examined by X-ray diffraction, infra-red spectroscopy, transmission electron microscopy and differential scanning calorimetry. Magnetic properties of the nanoparticles were tested by Mössbauer spectroscopy. Keywords: core-shell nanoparticles, Mossbauer spectroscopy, magnetic nanoparticles

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Introduction

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Magnetic nanoparticles with different core-shell structures have become very popular among many researches in last decades. A varied composition of a shell layer can add novel properties to magnetic nanoparticles. A metallic spacer layer influences magnetic properties of the system. When other magnetic material is used, such as a shell layer (like α-Fe2O3, γFe2O3, Co, Ni), it influences very strongly all magnetic properties of the nanoparticle. On the other hand, using nonmagnetic, metallic elements (such as copper, silver, or gold), much less pronounced modification of magnetic properties can be obtained but, in addition, such modification causes lower toxicity, higher antibacterial properties, or effective antifungal resistivity, etc. [1,2]. A surface layer of noble metals causes an increase on the palette of compounds possible to connect to magnetic nanoparticles. This effects in the protection of the core and surface of nanoparticles from external factors and, at the same time, isolates them from each other. Moreover, the shell composed of noble metals does not allow agglomeration processes of the cores and provides better biocompability and resistance to physiological conditions: for example, specific pH, enzymes interaction, etc. The shell of noble metals also guarantees high stability of nanoparticles in various solvents while keeping their core properties stable. All these arguments indicate a wide range of usage of core-shell nanoparticles in medicine, for example, in MRI contrast, in cancer treatment as hyperthermia agents [3], in chemistry in NMR spectroscopy. In case of a nonmetallic (e.g. silica, polymers) layer present in the core-shell, nanoparticles provide for its possible extensive applications as nucleators, reagents, carriers, chromatography fillers, etc. Therefore the shell layer becomes a key factor affecting the uniform dispersion of the particles, their further overall properties [4] and widespread application. The preparation of nanoparticles can be done in many various ways, which can be, in general, divided to chemical and physical one. As a first example, a chemical synthesis consisting of thermal decomposition of acetylacetonate salts of iron and other metals in organic solutions can be presented [5,6]. Core-shell nanoparticles can be also obtained in aqueous solutions by co-precipitation based on iron (II), iron (III) chlorides and ammonia solution [7,8]. In this case, more intermixing of the elements in the structure can be expected 1

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Experimental

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in respect to the previous method. Both ways are quite well known and become a source of various modifications described in many research papers [9,10,11]. Those magnetite syntheses, however, are significantly different in preparation conditions, which causes other physical-chemical properties like magnetization, agglomeration, hydrophilicity, etc., of resultant particles. Among scientists there are also widespread many physical methods of nanoparticles fabrication. A first example of the top-down approach is the reduction of size by long lasting grinding or ball milling. This method has two main disadvantages: firstly, it needs preparation of bulk material, which is time and energy consuming, secondly, the size and size distribution of prepared nanoparticles is poorly controlled [12]. Other popular methods are based on very sophisticated high vacuum systems where nanomaterials fabrication is obtained on the basis of the following phenomena: co-sputtering, laser vaporization, co-deposition of gas-phase, cluster beam deposition, etc. [13,14,15,16,17,18]. This represents bottom-up approaches of nanomaterials production where physical methods are involved. High vacuum methods are ideal to study individual cluster/particle magnetism, collective dynamics or random anisotropy [19,20]. On the contrary, chemical methods are important due to lower cost and much easier production procedures. In this paper, the magnetite core of nanoparticles was obtained from thermal decomposition of Fe(acac)3 in organic solution. The shell layer of the nanoparticles was prepared from Cu, Ag and Au metal complexes. Furthermore, the obtained nanoparticles were functionalized with –SH groups, and next immobilization of glucose oxidase was tested. The obtained core-shell nanoparticles and their respective biocomposites were measured by infrared spectroscopy (IR), X-ray diffraction (XRD), transmission electron microscopy (TEM) imaging and differential scanning calorimetry (DSC). Magnetic properties were characterized by Mössbauer spectroscopy (MS).

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Material and apparatus To obtain core-shell nanoparticles with a various shell, the following chemicals were purchased from Aldrich: Fe(acac)3, Cu(acac)2, Gold(III) chloride 1,2-hexadecanediol, phenyl ether. AgNO3 and oleic acid were bought from POCH. In addition, 1-octadecanol and oleyl amine were obtained from Fluka. Cleaning and separation of nanoparticles were performed with the use of acetone, sonication bath and permanent magnet. IR spectra were collected in range 400-4000 cm-1 by Nicolet 6700 infrared spectrometer working in reflection mode. For the experiment a small amount of powder was pressed against a diamond window. Morphology of nanopowders was checked by transmission electron microscope Tecnai G2 X-TWIN (FEI). Properly diluted particles solution was deposited on Cu grid covered with amorphous carbon. Differential scanning calorimeter STAR system was used to analyze temperature stability of nanomaterials. For that measurement roughly 2mg of particles were placed in Al crucible closed with a lid. Verification of the crystal structure was done by X-ray diffractometer by Agilent Technologies SuperNova with a Mo microfocused source. Particles powder was placed with help of oil onto a nylon loop fixed to a pin. Mössbauer spectra were obtained using the spectrometer working in constant acceleration mode with a 57Co(Cr) radioactive source. Iron foil was used as reference material. Preparation of the magnetic core – seeds particles

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The magnetite nanoparticles were prepared by the modified procedure developed by S. Sun [5, 21]. The seeds of magnetic particles were fabricated by mixing of Fe(acac)3, oleic acid, oleyl amine, diphenyl ether and 1,2-hexadecanediol. The whole substrate solution was deoxygenated under argon flow and vigorously mixed by magnetic stirrer in temperature of 240°C. At this temperature the solution was kept for 30 minutes. After that time, the product was cooled down to room temperature. In effect, small seeds particles were obtained and used for further modification. Preparation of magnetic and nonmagnetic second layer

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In the next step, previously obtained seeds of magnetic nanoparticles were used to prepare different core-shell nanoparticles with magnetite core, Cu, Ag, Au or Fe oxide as a shell. To obtain Fe3O4 shell, Fe(acac)3, oleic acid, oleyl amine and 1-octadecanol were used. The solution was vigorously stirred, deoxygenated and heated in temperature of 200°C for 30 minutes [5]. To obtain Cu shell, we have modified the method described by Subramanian [22]. In this case, Cu(acac)2, diphenyl ether, 1,2-hexadecanediol were mixed and deoxygenated to 100°C, and then oleic acid and oleyl amine were added and the whole mixture was kept in 200°C for 20 minutes. Ag shell was prepared from AgNO3, diphenyl ether, 1,2-hexadecanediol and oleyl amine. The mixture was stirred and deoxygenated for 15 minutes in room temperature, next for 2h in 30°C and finally for 30 minutes in 140°C. This procedure of the preparation of Ag shell layer on magnetite nanoparticles was adopted from Lu [2]. In the last kind of particles, Au shell was prepared by the modified Robinson method [23]. To obtain Au shell, 20 ml of diphenyl ether was added to magnetite nanoparticles, stirred and heated under argon flow to 85°C. Then, HAuCl4, oleyl amine and 5 ml of diphenyl ether were added and kept in this temperature for 1h. The schematic presentation of core-shell nanoparticles fabricated as described above is presented in Fig.1. All resultant products were cooled down to room temperature. The obtained fluids were washed few times with deoxygenated acetone and dried to powder form in vacuum evaporator. Fig. 1 Schematic presentation of obtained core-shell nanoparticles. Functionalization of core-shell nanoparticles with thiol The obtained multilayered nanoparticles were modified by thiol in the same way as described before in our previous publications [8]. The solution of 1 ml of hexadecanethiol and magnetic nanoparticles (NPs) was stirred in a sonification bath for a while and then kept in an oven in temperature of 50 °C for 18 hours. After that time, modified nanoparticles were separated from the reaction medium, washed with ethanol a few times and then dried at room temperature. Immobilization of glucose oxidase on modified core-shell nanoparticles The core-shell nanoparticles functionalized by thiol were dispersed in a solution of glucose oxidase (3 mg of enzyme dissolved in 0.5 ml of Tris-HCl buffer at pH=7,4) [8]. All reagents were stirred in a sonication bath from time to time for 2 hours at room temperature. After this time, the nanoparticles were separated from the solution and washed with a Tris-HCl (1 ml). The obtained composites were dried at room temperature.

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Results and discussion 1. Transmission Electron Microscopy studies

Fig. 2. TEM images of respective double and triple layered nanoparticles.

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The samples selected from the series were characterized by transmission electron microscopy, which allows a reader to follow changes in the particles size and structure. TEM images of the prepared nanoparticles are depicted in Fig. 2. They are organized in the series according to the layered structure and type of Me (Ag, Au, Cu or Fe3O4).

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It can be seen that the images of the fabricated particles show a good correlation between the postulated structure and particle size. The imaged particles show a tendency of average particles size increase as a function of growing number of layers (seeds have 5±1nm, doublelayered particles have 11±1nm, triple-layered 14±1nm). The layered structure was possible to observe especially in case of Fe oxide/Au (Ag and Cu) particles. Particles with Ag have the most regular round shape in comparison to other presented series. More studies on this subject will be published elsewhere. The layered structure cannot be imaged for triple-layered particles due to the limitation of TEM method. Overlapping, roughness and presence of different chemical compositions of subsequent layers causes difficulties in the interpretation of the images. 2. X-ray studies of core-shell magnetic nanoparticles

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The obtained nanoparticles with different shells composition were examined by XRD method. The results of the diffraction analysis are presented in Fig. 3A. Pure magnetite nanoparticles show typical diffraction patterns of magnetite crystalline compound and the following reflexes can be indexed (111) (220) (311) (222) (400) (331) (422) (511), which is in good agreement with the published data [24,25].

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Fig. 3 X-ray diffraction of core-shell nanoparticles with respective (A) Fe3O4 and Ag, (B) Fe3O4 and Au layers, (C) Fe3O4 and Cu, When the magnetite core is combined with Ag layer, typical magnetite patterns are present as well. In addition, intensive peaks which correspond well to described in literature crystalline Ag structure are detected. New signals appearing in Fig. 3A can be ascribed as (111) (200) (220) of the Ag crystallites [26]. Those patterns we also observed before in other kinds of particles modified by Ag [27]. The incorporation of Au layer to the particles structure (Fig. 3B), besides magnetite signals, also causes the presence of the patterns typical for Au crystals (111) (200) (220) (311) as was reported in the reference [23]. These signals are much weaker in comparison to Ag but the obtained Au layer is expected to be much thinner. The effectiveness of core layer fabrication in case of Au is also proved by the concentration of Au precursor variation during the synthesis process and their results as increasing reflexes intensity in diffactrograms. The thickness of Au layer and therefore intensity of patterns typical for Au crystalline structure is proportional to the amount of used Au compound, which will be discussed in details in another paper.

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The introduction of Cu layer into nanoparticles (Fig. 3C) results in new peaks appearing, which can be described as typical signals of well-known Cu structure and indexed as (111) (200) (220) (311) (222) observed also previously [28,29]. In Table 1 XRD data are summarized. The presence of these peaks and the results of TEM measurements suggest successful fabrication of Cu crystalline layer inside nanoparticles regardless of the positioning of the layer as it was suggested previously [25]. The presence of separate two kinds of the particles, for example magnetite and Au, is prohibited due to magnetic field assisted separation method used in the fabrication procedure. Table 1. Table with summarized XRD peak positions and respective Miller indexes. Ag Au Cu Fe3O4 ± 0,2[°]

(111)/17,5 (200)/20,1 (220)/28,6 (311)/34,0 -

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± 0,2[°]

(111)/19,6 (200)/22,7 (220)/32,4 (311)/38,2 (222)/40,1 -

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± 0,2[°]

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(hkl)/2

(111)/13,9 (220)/16,2 (311)/19,7 (222)/24,0 (400)/25,5 (331)/27,9 (422)/32,5 (511)/38,1

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(111)/17,4 (200)/28,7 (220)/33,6 -

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(hkl)/2

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The results obtained from X-ray diffraction performed on layered nanoparticles (where Ag, Au and Cu serve, e.g., shell or interlayer) confirm successful modifications in the layered manner of the described particles. In all cases, besides the magnetite structure, additional crystalline patterns were observed typical for used elements, respectively. Such modification opens new possibilities for nanoparticles fabrication and their application where, besides magnetic properties, additional features of the particles can be utilized. The obtained diffractograms served as a base for determination of the average grain size of core-shell nanoparticles. For quantitative analysis, Debye-Scherrer’s equation (1) was used [30]:

0,9 ⋅ λ (1) B1 / 2 ⋅ cos θ where: D – grain size [Å], λ – wavelength (for Mo source is 0,70931 Å), B1/2 – full width at half maximum intensity of the peak [rad], and – diffraction angle [rad]. Calculated results for these particles were compiled in Table 2. It should be mentioned that this formula describes the average size of the coherently diffracting zone which in some cases is not exactly the same as the average particle size. It can cause ambiguity especially in case of the layered nanoparticles, however, it is a good estimation of the particle’s diameter. D=

Table 2. Grain size of tested nanoparticles determined by X-ray diffractions. Nanoparticles

Fe3O4/ Fe3O4 Fe3O4/Cu Fe3O4/ Fe3O4/Cu Fe3O4/Cu/ Fe3O4

Grain size ±0,8 [nm] 12,3 11,4 18,6 18,5

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10,6 12,3 12,4 10,8 13,5 12,4

Fe3O4/Ag Fe3O4/ Fe3O4/Ag Fe3O4/Ag/ Fe3O4 Fe3O4/Au Fe3O4/ Fe3O4/Au Fe3O4/Au/ Fe3O4

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The results collected in Table 2 show that the addition of subsequent shells causes increase of the average particles grain size in the series. Moreover, the increase of the amount of Au precursor used in the synthesis causes modification of the average grain size of modulated nanoparticles, which is in good agreement with the prediction where subsequent layers are obtained (data not shown here, Ref. 31). The discrepancy between TEM and XRD results can be expected due to not the same amount of probed particles. XRD averages over a large number of particles when in TEM much less particles can be counted. In addition to widening of XRD peaks, other effects have influence, such as: defects, structural dislocations, local chemical modulations, etc.

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3. DSC studies

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The thermal analysis of magnetic core-shell nanoparticles runs with Mettler Toledo Differential Scanning Calorimeter. A quick heating and cooling cycle in temperature range 2450 °C with scan rate of 10°C/min was conducted. As a reference, in the same convention an empty pan was used. For DSC measurement, a quantity of roughly 2 mg of total weight was separated. The obtained curves were depicted in Fig. 4.

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Fig. 4. DSC curves of various core-shell (A) Fe3O4 -Ag, (B) Fe3O4-Au, (C) Fe3O4-Cu nanoparticles.

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The examined core-shell nanoparticles exhibit in proposed temperature range few exo- and endothermic processes. Temperature scans of the nanoparticles are depicted in Fig. 4A where Ag layer is present. Here we observe similar thermal processes for Fe3O4/ Fe3O4/Ag and Fe3O4/Ag/ Fe3O4. Exothermal effects are present in 123-151 °C and 98-194 °C ranges with 18,5 mJ and -35,8 mJ of energy, respectively for Fe3O4/ Fe3O4/Ag and Fe3O4/Ag / Fe3O4. Endothermic process for Fe3O4/ Fe3O4/Ag nanoparticles is observed around 182-211 °C with 19,37 mJ of energy. Fe3O4/Ag nanoparticles show a wide endothermic process in low temperatures (116-193 °C) with around -95 mJ of energy. Subsequent DSC curves depicted in Fig. 4B show thermal behavior of core-shell nanoparticles with Au. Here small endothermic processes occur in higher temperatures (around 390 °C) with -66 mJ for Fe3O4/ Fe3O4/Au and -99 mJ of energy for Fe3O4/Au. Similar to Fe3O4/Ag/ Fe3O4 nanoparticles, the Fe3O4/Au/ Fe3O4 one does not exhibit significant thermal changes. The last set of the curves collected in Fig. 4C presents nanoparticles were Cu is the last shell. Here temperature scans show small processes of crystallization around 220 °C with about -16 mJ for Fe3O4/Cu NPs and -29 mJ for Fe3O4/ Fe3O4/Cu of energy. Nanoparticles where Cu is as an interlayer in the particles do not exhibit any such specific thermal changes. Generally, the analysis of DSC results shows that layered nanoparticles where Fe3O4 is used as a last layer have better thermal stability in comparison to those where Ag, Au or Cu served as outermost surface layer. Detailed studies of the influence of temperature treatment on particle crystal structure in respect of time and surface modification will be a subject of other papers [31,32]. 4. IR studies 6

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The obtained core-shell structures were characterized also by IR spectroscopy in reflection mode in spectral range from 4000 cm-1 to 400 cm-1 to describe surface modification taking place in various particles. All spectra depicted in Figs. 5 show signals characteristic for Fe-O bonds in magnetite which are always present below 600 cm-1 [33], which is in good agreement with our previous observations and experience [34]. In addition, C-H bonds from acetylacetonates appear at 1400 cm-1 and also C=C stretching vibrations at 1530 cm-1 and C-H in (CH2)n -NH2 at 2900 cm-1 [25], which are also typically present in case of particles obtained by this method [35]. Other present signals are variable and rather specific for a particular modification and fabrication process.

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Fig. 5 IR spectra of: (A) core-shell Fe3O4/ Fe3O4 nanoparticles with respective shell modification Ag, Au, Cu; (B) core-shell Fe3O4/Cu nanoparticles after modification with hexadecanethiol and glucose oxidase.

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The modification of the magnetite nanoparticles by metallic surfaces (Fig. 5) causes the appearance of some signals typical only for particular kinds of modification. The first new band which is observable in every modified spectrum lies around 719 cm-1 and can be described as –CH2 skeleton vibration from oleic acid chain meaning the formation of stabilizing layer on the surface of particles. Small peaks at 950-1000 cm-1 can be described as =C-H bending vibrations also in oleic acid [36]. Peaks around 1100-1200 cm-1 are typical for Ar-O-Ar and are observable in the spectra of core-shell nanoparticles where diphenyl ether was used in the synthesis procedure. Signals present in every spectrum at around 1700-1730 cm-1 can be described as C=O stretching vibrations from acetylacetonate salts. In Fe oxide /Ag core-shell particles case, it can be well observed that this modification causes the presence of new signals at 655cm-1 typical for C-H vibrations in R-CH=CH2 groups. Also wide bands around 800 cm-1 might come from N-O stretching vibrations in R-O-N=O group [36]. All recognized bonds correspond well with the modification undertaken for the particles and with synthesis procedure. 4.2 Thiol modification

Representative IR spectra of core-shell nanoparticles Fe3O4/Cu after modification by hexadecanethiol are depicted in Fig. 5B. Every IR spectrum in the series shows almost some set of significant signals. Therefore one representative spectrum was chosen. The first very weak signal below 600 cm-1 belongs to FeO bonds in magnetite. Next, we observe signals around 717 cm-1 which are described as C-H observed previously in Fig. 5A. Bands at 1224 cm-1 and 1470 cm-1 can be observed due to SCH2 bonds, which proves successful modification with thiol magnetite nanoparticles [8,36]. Due to the fact that the obtained thiol layer is extremely thick, thiol as related signals dominates IR spectra regardless of the particles surface characteristic, which can suggest different types of adsorption on the surfaces where Au, Ag, Cu or Fe oxide are present. 4.3 Glucose oxidase immobilization After functionalization of the presented nanoparticles with hexadecanethiol, the experiment with immobilization of glucose oxidase on each kind of particles was performed. IR result of

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Table.3. Table summarizing all present signals in IR spectra. Wavenumber [cm-1] Bond Ref. 553-566 Fe-O (magnetite) [34][39] 716-720 C-H [25] 780 N-O (R-O-N=O) [36] 965-1037 =C-H [36] 1104-1235 Ar-O-Ar [32] 1334 N-CH2 [8] 1404-1454 C-H [25] (acetylacetonate) 1516-1558 C=C [25] 1705-1735 C=O [8] 2847-2956 (CH2)n-NH2 [25] 1224, 1470 S-CH2 [8],[36] 667 Fe-O (maghemite) [37] 909, 3104-3186 N-H [39] 1296 C-N (amines) [39] 1552 Amide I [38] 1630 Amide II [38]

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those modifications on one example (Fe3O4/Cu) is depicted in Fig. 5B. Immobilization of glucose oxidase enzyme causes the presence of additional bands in IR spectra of core-shell nanoparticles. Weak bands at 662 cm-1 are observable due to the oxidation of magnetite nanoparticles to maghemite [37]. Peaks around 1040 cm-1 were observed in our previous papers after enzymes immobilization, which proves successful modification [8]. Two sharp peaks at 1550 cm-1 and 1630 cm-1 are described as amid I and amid II bands [38]. Bands at 3200 cm-1 show –N-H bonds present in tested enzyme. Presented results show successful preparation of bionanocomposite with core-shell nanoparticles.

5. Mössbauer spectroscopy

Room temperature Mössbauer spectra for all studied samples in the series are depicted in Fig 6. Fig. 6 RT Mössbauer spectra of tested core-shell nanoparticles. For bulk magnetite characteristic room temperature Mössbauer spectra consist of two sextets whose relative intensity ratio is almost 2:1. One of them comes from the [A] site Fe3+ ions, and second from [B] mixed valence site Fe2.5+ [40]. In case of nanoparticles, quite often more components are needed due to the coexistence of few Fe oxide phases (too small amount to be detected by XRD) or surface and size effects. In most cases, the broad component with the lowest value of h.m.f. (hyperfine magnetic field) is present due to the relaxation effect characteristic for nano-systems. Therefore Mössbauer spectra of nanoparticles are much more complex in comparison to bulk spectra [9,41]. As one can see (Fig.6), most presented spectra show a broad single line shape characteristic for superparamagnetic state of iron magnetic moments. The diameters of the nanoparticles (see Table 1) are small enough to show such behavior [42]. However, in the case of triple layered samples with Ag and Au, the broad sextet is visible in the background of 8

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superparamagnetic signal. It is most clearly seen in the case of Fe3O4/ Fe3O4/Au nanoparticles. On the other hand, intensity of the sextet for Fe3O4/Au/ Fe3O4 is very small. The opposite situation is observed for nanoparticle with Ag. Here the sextet is clearly seen when Ag is used as a spacer and its intensity is much smaller when Ag is on the surface. The appearance of the sextet in the studied systems can be explained by the fact that magnetic moment of iron is frizzed due to increasing of the superparamagnetic blocking temperature in comparison to double-layered particles. Another explanation can be that at Fe3O4/Au and Fe3O4/Ag interfaces Fe magnetic moment increases significantly as it was calculated for multilayers [43]. The increase of magnetic interaction on Fe3O4/Au and Fe3O4/Ag interfaces can lead to partial suppression of superparamagnetism in studied nanoparticles. Lack of the sextet in the case of the double layer system is probably connected with smaller diameters of nanoparticles in those systems. Damping of superparamagnetic behavior is not clearly observed in the case of systems with Cu where changes are too small.

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The comparison of the measured spectra in respect of layers sequence suggests that interlayer interaction occurs only for selected elements, which was already observed in other systems [31]. However, a kind of spacer and surface material is of crucial importance in changing the magnetic state of nanoparticles. A detailed analysis of the influence of spacer and surface layers on the magnetic properties of nanomaterials requires further study and it will be the subject of other papers.

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Conclusions

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In our opinion, the presented series of the particles have well documented layered structure. It is approved by the characterization of the structures by TEM, XRD, IR, DSC and Mössbauer spectroscopy. Subsequent reduction of all used metals complexes suggests modification of the particles core in the layered manner. The proposed way of the modification by step-by-step growth of magnetic cores of the particles allows for the fabrication of every complex structure which helps in further application of these types of particles. It is especially interesting approach when oxide or noble metal surface modification is needed due to their antitoxic, antibacterial or antifungal applications. The described series show that physical-chemical characteristic of metallic core can be well controlled even when the structure of nanoparticle is rather complex. At the same time, the presented results also support the thesis that incorporation of Au or Ag layer in the neighborhood of Fe causes their magnetic moment enhancement for thin enough layers, which was observed in multilayered system. Such scenario is not valid for Cu case. Acknowledgement

Mössbauer spectroscopy was done in close collaboration with the Department of Physics at the University of Bialystok. The work was partially financed by the EU funds via the project with contract number POPW.01.03.00-20-034/09-00 and via national grant (contract number UMO-2011/03/B/ST5/02691) References [1] L. Vekas, D. Bica, O. Marinica, Magnetic nanofluids stabilized with various chain length surfactants, Romanian Reports in Physics 58 (2006) 257-267 [2] L. Lu, W. Zhang, D. Wang, X. Xu, J. Miao, Y. Jiang, Fe@Ag core-shell nanoparticles with both sensitive plasmonic properties and tunable magnetism, Materials Letters 64 (2010) 1732-1734

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[3] M.A. Verges, R. Costo, A.G. Roca, J.F. Marco, G.F. Goya, C.J. Serna, M.P. Morales, Uniform and water stable magnetite nanoparticles with diameters around the monodomainmultidomain limit, J. Phys. D: Appl. Phys. 41 (2008) 134003 [4] Y. Wang, Y. Ke, J. Li, S. Du, Y. Xia, Dispersion behavior of core-shell silica-polymer nanoparticles, China Particuology 5 (2007) 300-304 [5] S. Sun, H. Zeng, Size-controlled synthesis of magnetite nanoparticles, Journal of the American Chemical Society 124 (28) 2002, 8204-5. [6] B. Kalska-Szostko, M. Cydzik, D. Satuła, M. Giersig, Mössbauer studiem of core-shell nanoparticles, Acta Physica Polonica A, 119 (2011) 15-17. [7] R.Massart, V.Cabuil.Journal of Chimical Physics 84 (1987) 967 [8] B. Kalska-Szostko, M. Rogowska, A. Dubis, K. Szymański, Enzymes immobilization on Fe3O4-gold nanoparticles, Applied Surface Science 258 (2012) 2783-2787 [9] B. Kalska, J.J. Paggel, P. Fumagalli, J. Rybczynski, D. Satuła, M. Hilgendorff, M. Giersig, Magnetite nanoparticles studied by Mossbauer and magnetooptical Kerr effect, Journal of Applied Physics 95 (3) (2004) 1343-1350 [10] Y. Zhu, Q. Wu, Synthesis of magnetic nanoparticles by precipitation with forced mixing, Journal of nanoparticle research 1 (1999) 393-396 [11] P. Xu, G. Zeng, D. Huang, et. al. Synthesis of iron oxide nanoparticles and their application in Phanerochaete chrysosporium immobilization for Pb (II) removal, Colloids and Sufraces A: Physicochemical and Engineering Aspects 419 (2013) 147-155 [12] Jiang, Gao, Yang, Guo, Shen, Nanocrystalline NiZn ferrite synthesized by high energy ball milling, Journal of Material Science Letters 18 (21) (1999) 1781-1783 [13] C. Binns, K.N. Trohidou, J. Bansmann, S. H. Baker, J. A. Blackman, J.-P. Bucher, D. Kechrakos, A. Kleibert, S. Louch, K.-H. Meiwes-Broer, G.M. Pastor, A. Perez, Y. Xie; The behaviour of nanostructured magnetic materialsproduced by depositing gas-phase nanoparticles; J. Phys. D 38 (2005) R357 [14] P. Allia, M. Coisson, F. Spizzo, P. Tiberto, F. Vinai; Magnetic correlation states in cosputtered granular Ag100−xFex films; Phys. Rev. B 73 (2006) 054409 [15] J. M. Meldrim, Y. Qiang. Y. Liu, H. Haberland, D. J. Sellmyer, Magnetic properties of cluster-beam-synthesized cobalt: Noble-metal films, J. Appl. Phy. 87 (2000) 7013 [16] S. D’Addato, L. Gragnaniello, S. Valeri, A. Rota, A. di Bona, F. Spizzo, T. Panozaqi, and S. F. Schifano, Morphology and magnetic properties of size-selected Ni nanoparticle films; J. Appl. Phys. 107 (2010) 104318 [17] , A. Kleibert, J. Passig, K.-H. Meiwes-Broer, M. Getzlaff, and J. Bansman, Structure and magnetic moments of mass-filtered deposited nanoparticles; J. Appl. Phys. 101 (2007) 114318 [18] C. Johansson, T.Åklint, M. Hanson, M. Andersson, N. Tarras-Wahlberg, E. Olsson, B. Kalska, R. Wäppling and A. Rosén; Deposited nano-metre sized iron clusters,Nanostructured Materials vol. 12, no.1-4, 1999, p-187-90. (287) [19] Y. D. Zhang, J. I. Budnick, W. A. Hines, C. L. Chien, J. Q. Xiao Effect of magnetic field on the superparamagnetic relaxation in granular Co-Ag samples; Appl. Phys. Lett., 72 (1998) 2053 [20] C. Djurberg, P. Svedlindh, P. Nordblad, M. F. Hansen, F. Bødker, S. Mørup; Dynamics of an Interacting Particle System: Evidence of Critical Slowing Down; Phys. Rev. Lett. 79, 5154 [21] B. Kalska-Szostko, U. Wykowska, D. Satuła, E. Zambrzycka, Stability of core-shell magnetite nanoparticles, Colloids and Surfaces B: Biointerfaces 113 (2014) 295-301 [22] N.D. Subramanian, J. Moreno, J.J. Spivey, C.S.S.R. Kumar, Copper core-porous manganese oxide Shell nanoparticles, The journal of physical chemistry 115 (2011) 1450014506 10

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[43] B. Kalska-Szostko, M. Cydzik, D. Satuła. M. Giersig, Mossbauer studies of core-shell nanoparticles, Acta Physcica Polonica A 110 (2011) 15-17.

Figure caption:

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Fig. 1 Schematic presentation of obtained core-shell nanoparticles.

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Fig. 2. TEM images of respective double and triple layered nanoparticles.

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Fig. 3 X-ray diffraction of core-shell nanoparticles with respective (A) Fe3O4 and Ag, (B) Fe3O4 and Au layers, (C) Fe3O4 and Cu,

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Fig. 4. DSC curves of various core-shell (A) Fe3O4 -Ag, (B) Fe3O4-Au, (C) Fe3O4-Cu nanoparticles. Fig. 5 IR spectra of: (A) core-shell Fe3O4/ Fe3O4 nanoparticles with respective shell modification Ag, Au, Cu; (B) core-shell Fe3O4/Cu nanoparticles after modification with hexadecanethiol and glucose oxidase. Fig. 6 RT Mössbauer spectra of tested core-shell nanoparticles.

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Fig. 1 Kalska et al.

Fig. 2 Kalska et al. 13

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Fig. 3 Kalska et al.

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Fig. 4 Kalska et al.

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Fig. 5 Kalska et al.

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Au

Ag

Cu

Fe3O4/Fe3O4

Fe3O4/Fe3O4

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Fe3O4/Au

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core-shell nanoparticles with various shell leyers were fabricated > the influence on magnetic properties from layer composition were observed > the influence on quality of layer from their composition was tested

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