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A facile and green synthetic approach toward fabrication of starch-stabilized magnetite nanoparticles
Accepted Manuscript Title: A facile and green synthetic approach toward fabrication of starch-stabilized magnetite nanoparticles Authors: Nurul Hidayah Abdullah, Kamyar Shameli, Ezzat Chan Abdullah, Luqman Chuah Abdullah PII: DOI: Reference:
S1001-8417(17)30071-2 http://dx.doi.org/doi:10.1016/j.cclet.2017.02.015 CCLET 3988
To appear in:
Chinese Chemical Letters
Received date: Revised date: Accepted date:
10-11-2016 3-1-2017 27-2-2017
Please cite this article as: Nurul Hidayah Abdullah, Kamyar Shameli, Ezzat Chan Abdullah, Luqman Chuah Abdullah, A facile and green synthetic approach toward fabrication of starch-stabilized magnetite nanoparticles, Chinese Chemical Letters http://dx.doi.org/10.1016/j.cclet.2017.02.015 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.
Original article A facile and green synthetic approach toward fabrication of starch-stabilized magnetite nanoparticles Nurul Hidayah Abdullah a, Kamyar Shameli a, , Ezzat Chan Abdullah a, Luqman Chuah Abdullah b a
Department of Environmental Engineering and Green Technology (EGT), Malaysia-Japan International Institute of Technology (MJIIT), Universiti Teknologi Malaysia (UTM), Jalan Sultan Yahya Petra, Kuala Lumpur 54100, Malaysia b Department of Chemical and Environmental Engineering, Faculty of Engineering, Universiti Putra Malaysia, Serdang Selangor 43400, Malaysia
Corresponding author. E-mail address: [email protected]
Graphical Abstract
Highly dispersed spherical starch/Fe3O4-NPs can be synthesized by ultrasonic assisted co-precipitation method. Starch was used as a stabilizer for controlled size of Fe3O4-NPs. ABSTRACT A facile and green synthetic approach for fabrication of starch-stabilized magnetite nanoparticles was implemented at moderate temperature. This synthesis involved the use of iron salts, potato starch, sodium hydroxide and deionized water as iron precursors, stabilizer, reducing agent and solvent respectively. The nanoparticles (NPs) were characterized by UV-vis, PXRD, HR-TEM, FESEM, EDX, VSM and FT-IR spectroscopy. The ultrasonic assisted co-precipitation technique provides well formation of highly distributed starch/Fe3O4-NPs. Based on UV-vis analysis, the sample showed the characteristic of surface plasmon resonance in the presence of Fe3O4-NPs. The PXRD pattern depicted the characteristic of the cubic lattice structure of Fe 3O4-NPs. HR-TEM analysis showed the good dispersion of NPs with a mean diameter and standard deviation of 10.68±4.207 nm. The d spacing measured from the lattice images were found to be around 0.30 nm and 0.52 nm attributed to the Fe3O4 and starch, respectively. FESEM analysis confirmed the formation of spherical starch/Fe3O4-NPs with the emission of elements of C, O and Fe by EDX analysis. The magnetic properties illustrated by VSM analysis indicated that the as synthesized sample has a saturation magnetization and coercivity of 5.30 emu/g and 22.898 G respectively. Additionally, the FTIR analysis confirmed the binding of starch with Fe 3O4NPs. This method was cost effective, facile and eco-friendly alternative for preparation of NPs. Keywords: Nanoparticles Fe3O4 Starch Magnetic properties Vibrating sample magnetometer
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1. Introduction. Major advances in nanotechnology field have broadened the emergence of novel nanomaterials with exceptional properties and wide range of applications. The unique properties of nanomaterials have been exploited for several prospective uses especially in medicine [1], optical and electronic devices application [2], catalysis, ceramics and magnetic data storage [3]. Several important aspects have been taken into account in improving the physical and chemical properties of the materials by controlling the chemical composition, size, shape and morphology [2]. Nanomaterials are inherently unstable, therefore they have strong intrinsic tendency to agglomerate to maintain the state of lower energy [3-5]. Green synthesis approach has drawn much attention among researchers due to the concern of safety towards human and environment. Several researches have been conducted in reducing or eliminating the use or generation of dangerous substances by green synthetic routes [6-9]. Green technology has been established to pursue strategies to mitigate toxicity by exploitation of natural resources as biological tools for NPs synthesis and simultaneously provide advantages by lowering the operating expenses, reduced environment impacts, superior biocompability and higher stability [10]. Thus, practice in green marketing which incorporates a broad range of activities such as the product modification, changes to the production process, packaging changes, as well as modifying advertising of the environment friendly commodities will contribute to environmental sustainability in the future [11]. Magnetic nanomaterials have been the subject of numerous investigations due to their great potential applications in bio-separation [12], biosensor [13], magnetic resonance imaging (MRI) contrast agents [14], targeted drug delivery [12, 14] and food analysis [15]. Particular attention has been devoted to the synthesis of magnetite (Fe 3O4) nanoparticles due to the interesting features of low toxicity and biocompatibility in addition to superparamagnetism [12, 16, 17]. Furthermore, a variety of methods have been established for the synthesis of magnetic nanoparticles such as thermal decomposition method [18], chemical co-precipitation [19], hydrothermal route [20], microwave irradiation [21], solvothermal synthesis [22], microemulsion [23] and ultrasonic chemical co-precipitation [24]. Co-precipitation technique is one of the simple, cheap and effective methods for fabrication of nanomaterials in large scale synthesis [25, 26]. This method has been employed in the synthesis of magnetite NPs by mixing of ferric and ferrous ions at certain molar ratio in highly basic solutions at room temperature or at elevated temperature. Different sizes and shapes of the NPs can be obtained by varying the salt type (such as chlorides, sulfates, nitrates, perchlorates, etc.), the reaction temperature, the ferric and ferrous ions ratio, the pH value, ionic strength of the media, and other reaction parameters (e.g. stirring rate, dropping speed of basic solution) [12, 26, 27]. Additionally, the surface modification of iron oxide NPs can be attained by introducing organic materials or inorganic materials, such as polymers, biomolecules, silica and metals for better controlled in sizes and particle distribution. In spite of several progresses have been made in synthesis of iron oxide NPs, simultaneous control of their shape, stability, biocompatibility, surface structure, and magnetic properties is still a major challenges [12]. Ultrasonic irradiation is one of the promising methods for the preparation of various materials with nanometer dimensions. This method has been massively employed due to the relatively cheap, simple and energy saving for fabrication of smaller size particles with higher surface area [28-31]. Studies have shown that different kind of nanomaterials with various sizes and morphology can be prepared by sonication method. In general, frequency range from 20 kHz to 1 MHz is used in sonochemistry process, whereas at higher frequency of more than 1 MHz is usually applied in nondestructive testing and medicine [32]. The extreme conditions during the sonication were favourable to form the new phase, and have a shear effect for agglomeration, which is prone to prepare the highly monodispersive NPs [12]. Several studies have been conducted for the preparation of water-dispersible magnetite nanoparticles with better control of particle size, fast magnetic response, desirable surface properties and aqueous dispersibility [33]. A major effort also has been put forward to develop various types of magnetic nanocomposites that possess pre-designed architectures with improved and complementary properties [34]. A number of approached have been reported for the production of water-dispersible magnetite nanoparticles based on monomeric stabilizers, inorganic materials and polymer stabilizers [26]. For instance, modified solvothermal technique has been employed for the synthesis of biocompatible and highly water-dispersible magnetite particles in the presence of trisodium citrate (Na3Cit) as a stabilizer [35]. The synthesis of magnetic nanocomposites on various types of inorganic substrates such as silica and zeolites with well-defined core−shell structure also has been reported to possess higher saturation magnetization and good dispersibility in water [36-38]. These materials have been recognized for their outstanding features of enhanced stability, being able to shield the active species from harsh environments, improved physical, chemical and photoelectric properties, and ease of surface functionalization [34]. Several polymers such as dextran [14, 39, 40, 41], polyethylene glycol (PEG) [42, 43], polyvinyl alcohol (PVA) [44, 45], alginate [46, 47], chitosan [13, 48] and starch [49, 50] also have been used for the size controlled synthesis of magnetite nanoparticles. Starch is widely known as one of the most abundant naturally occurring polysaccharides and possesses many unique properties, such as low cost, renewability and biodegradability [51, 52]. The granular form of starch obtained from the plant has a complex semicrystalline structure with diameter between 1μm and 100 μm [53]. It has been recognized as a potential candidate of biomaterial as drug carriers and coating agents for MR purposes owing to its biocompatibility, biodegradability, and nontoxicity [49]. The polymers functionalized iron oxide NPs has gained much attention due to the advantages of polymers coating will increase the repulsive forces to
balance the magnetic and the van der Waals attractive forces acting on the NPs [12]. Besides, the incorporation of polymer surface complexing agents during the formation of magnetite can provide better control over the particle sizes [26]. In this study, magnetic starch/Fe3O4-NPs were synthesized by ultrasonic assisted co-precipitation method. The combination of these two techniques can lead to the formation of biocompatible iron oxide NPs and better control of the particle shape, small sizes distribution and less aggregation of particles. Starch and iron chloride salts were used as a stabilizer and iron precursors respectively. The simple, rapid and low cost raw materials that implemented in this study can be utilized for the preparation of various types of NPs with controlled morphology and sizes. Additionally, due to the awareness of green chemistry approach, no toxic chemical and solvents were used to avoid the generation of harmful substances as well as reducing the environmental pollution as much as possible. 2. Results and discussion 2.1.
Synthesis of starch/Fe3O4 nanoparticles
The magnetite NPs were obtained by the reaction of aqueous mixture of Fe 3+ and Fe2+ ions at a 2:1 ratio in hot starch solution and reduction by NaOH till pH 11 was achieved. The suspension changed from white cloudy solution (Fig. 1a) to dark brown colour (Fig. 1b) after addition of NaOH and followed by stirring and sonication for 1 h. The NPs were easily attracted to a permanent magnet which indicated the formation of Fe3O4-NPs (Fig. 1c). Eq. 1 illustrates the ions were compounded with starch and complex ions were generated [starch/2Fe3+:1Fe2+]. In the Eq. 2, addition of sodium hydroxide results to reduce of the ions in [starch/2Fe 3+:1Fe2+] suspension to [starch/Fe3O4]. The overall reaction for the formation of starch/Fe3O4-NPs may be written as follows. Starch + H2O(l) + 2Fe3+(aq) + Fe2+(aq) [starch /2Fe3+:1Fe2+]+8OH-(aq)
[Starch/2Fe3+:1Fe2+] [Starch/ Fe3O4] (s) + 4H2O(l)
(1) (2)
The schematic representation for the synthesis of starch/Fe 3O4-NPs shown in Fig. 2 illustrates the interaction between the external surface of Fe3O4 nanoparticles with positive charge and the oxygen atoms in hydroxyl group of starch as a negative charge. Starch acts as a polymer surface complexing agents to control the sizes of the NPs. Additionally, the chelation of these organic ions on the iron oxide surface can either prevent nucleation and then lead to larger particles sizes or inhibit the growth of the crystal nuclei, leading to small NPs [26].
2.2.
UV-visible analysis
From Fig. 3, the absorption spectrum depicted by UV-vis spectroscopy showed that no absorption peak (red) associated with the starch compound was observed. On the other hand, the absorption band underwent transformation with the observation of plasmon resonance after formation of magnetite NPs. Nonetheless, the decrease in the absorption intensity was observed with the increase of the wavelength in the region of 300-800 nm with no distinct strong peak was identified in this region (blue). Rahman et al. have reported about the similar finding in the UV-vis spectrum at absorption band of 330-450 nm corresponding to the absorption and scattering of UV radiation by magnetite NPs [54].
2.3.
Powder X-ray diffraction
The PXRD measurement was employed to identify the crystalline structure and purity of the prepared sample. The PXRD patterns of potato starch and starch/Fe3O4-NPs are shown in Fig. 4a-b. From Fig. 4(a), the observed peaks at 2θ = 11.71°, 14.47°, 17.46°, 19.94°, 22.56°, 24.47°, 26.66° and 34.91° were matched well with the JCPDS file no. 039-1912 of potato starch. From Fig. 4(b), the appearance of peaks at 2θ = 30.47°, 35.75°, 43.51°, 53.85°, 57.50°, 63.11° and 74.54° were correlated to the JCPDS File no. 01-0750033 of cubic phase Fe3O4. The decreased in the intensities of the starch peaks at 2θ = 11.72°, 14.58°, 17.37°, 19.70°, 22.49°, 24.53° and 26.68° were observed attributed from the incorporation of Fe 3O4 within the starch molecule. The average crystallite size of the nanoparticles can be estimated by applying the Scherrer formula D = kλ/βcosθ where D is the crystallite dimension, k is Scherrer constant (0.89), λ wavelength of the Cu-Kα (0.154) irradiation, βhkl is the full width at half maximum (FWHM) (hkl) of diffraction peak in radian unit, and θhkl is the diffraction angle [55, 56]. Based on the equation, the average crystallite sizes for starch/Fe 3O4-NPs calculated from Debye Scherrer equation was around 9.30 nm. No impurities phase was detected indicated the high purity crystalline sample.
2.4.
High resolution-transmission electron microscopy analysis
HR-TEM images in Fig. 5a revealed that the sample composed of highly distributed NPs with a spherical shape. A histogram illustrated in Fig. 5b showed that the synthesized NPs have a mean diameter and standard deviation of 10.68±4.207 nm. The counted
NPs were around 71. The mean particle sizes obtained were in accordance with the estimated average crystallite sizes calculated from the Scherrer’s equation. The NPs were uniformly distributed with almost no agglomeration. Fig. 5c displays the HR-TEM image of an individual Fe3O4-NPs with a lattice spacing of ~0.30 nm corresponds to d spacing of the [220] cubic plane of Fe 3O4 (JCPDS file No. 01-075-0033). In addition, Fig. 5d depicts the lattice spacing of ~0.52 nm for individual starch meeting at an angle 17.37° which is consistent with the XRD peak shown in Fig. 4b (JCPDS file No. 039-1912).
2.5. Field emission scanning electron microscopy analysis The surface morphology characterized by FESEM analysis revealed that the highly dispersed spherical magnetite NPs were formed (Fig. 6a). The starch hinders the Fe3O4-NPs from agglomeration and serves as stabilizer. Furthermore, the existence of polymeric starch on the surface of magnetite nanoparticles may prevents further oxidation [49]. The appearance of emission of C, O and Fe elements attributes from the formation of starch/iron oxide NPs was verified by EDX analysis (Fig. 6b).
2.6. Vibrating sample magnetometer analysis The magnetic properties of this material were studied by VSM and the result was presented in Fig. 7. The sample exhibit magnetic properties at room temperature with coercivity (H c) and remanance (Mr) of 22.898 G and 0.123 emu/g respectively. The saturation magnetization (Ms) obtained was around 5.30 G. The low saturation magnetization of 4.62 emu/g also has been reported based on superparamagnetic graphene oxide/magnetite-NPs [57]. They reported that the low Ms value was attributed to the rather smaller size of the Fe3O4 nanoparticles and the relatively low loaded amount of Fe3O4 on the graphene oxide. Although the value of the magnetization obtained by starch/Fe3O4-NPs was quite low, the particles were easily attracted to the external magnet in aqueous solution and in the powder form as shown in Fig. 1 and Fig. 4 respectively. 2.7. Fourier transform infrared analysis The observed FT-IR spectra for potato starch and starch/Fe3O4-NPs are shown in Fig. 8a-b. The appearance of peaks in the spectrum of potato starch at 3407, 2926, 1163 and 983 cm -1 were due to the -OH stretching, -CH stretching and O-C stretching of anhydroglucose ring group [58]. The appearance of doublet peaks at 2926 cm-1 indicated the C-H stretching and antisymmetric stretching of starch [59]. Furthermore, the appearance of intense overlapped bands in the region of 800-1300 cm–1 were attributed from CO, CC stretching and COH bending modes. Meanwhile, several bands below 800 cm –1 correspond to ring and skeletal modes [60, 61]. The presence of bound water of –OH bending vibration in starch was appeared at 1654 cm-1 [59, 62]. The peaks attributes to the stretching vibration of Fe-O bond were overlapped with the starch peaks at wavelength 573 cm -1 [63]. From Fig. 8b, the present system exhibits similar functional groups as starch but increased in the intensities were observed indicated the interaction between starch and iron oxide NPs. 3. Conclusion The present work provides information about the ultrasonic assisted co-precipitation method to produce highly dispersed starch/Fe3O4-NPs. The synthesized material showed surface plasmon resonance attributed to the absorption and scattering of UV radiation by magnetic NPs. High purity crystalline starch/Fe3O4–NPs were obtained with estimated average crystallite sizes of 9.30 nm. The HR-TEM analysis showed that the starch/Fe3O4-NPS exhibit spherical shape with a mean diameter and standard deviation of 10.68 ± 4.207 nm. The d-spacing of ~0.30 nm and ~0.52 nm corresponds to the Fe 3O4 and starch was observed, respectively. The detailed morphological characterization by FESEM revealed well distribution of spherical starch/Fe 3O4-NPS. The specific saturation of Fe3O4‒NPs was around 5.30 G. The FTIR spectrum before and after the formation of Fe 3O4-NPs in starch remained unchanged but increased in the peak intensities was well noticed. The prepared Fe 3O4-NPs can be easily separated by magnet in the aqueous solution. The green synthesis method proposed in this study does not use any toxic chemicals and the production scale-up can be easily done at low cost. This synthesis strategy can be developed into a generic protocol for preparation of other metal oxide with controlled sizes and shapes. 4. Experimental 4.1.
Materials and apparatus
FeCl3⋅6H2O (97% Sigma Aldrich), FeCl2⋅ 4H2O (> 99% Sigma Aldrich), NaOH (99% R&M Chemicals) and starch with chemical formula (C6H10O5)n (R&M Chemicals) were used as received without further purification. Deionized water was obtained from ELGA Lab Water Purification System, UK for medium preparation. The pH of the solution was controlled by channel Benchtop pH meter. The ultrasonic liquid processor (Hielscher Ultrasound Technology UP 200S, Germany) was used during sonication process. The synthesized material was dried in an Esco Isotherm Forced Convection Laboratory Oven. 4.2.
Preparation of starch/Fe3O4 nanoparticles
The material was prepared by addition of Fe3+ and Fe2+ salts solutions with 1:2 molar ratio into hot starch solution at temperature of 60 °C. Then, NaOH (0.5 mol/L) was added dropwise until the pH was adjusted to 11. After that, the NPs suspension was stirred continuously for 30 min at the temperature around 40 °C. The suspension was further exposed to high-intensity sonochemical irradiation for 30 min at amplitude of 70% and 0.5 of cycle by ultrasonic liquid processor with the immersion of probe into the solution. The precipitates were centrifuged at 10 000 rpm for 10 minutes, washed several times with deionized water, and finally dried in an oven at 50 °C for 24 h. 4.3.
Characterization of starch/Fe3O4 nanoparticles
The characterization of the starch/Fe3O4-NPs was performed using ultra-violet visible spectroscopy (UV-vis), powder X-ray diffraction (PXRD), high resolution transmission electron microscopy (HR-TEM), field emission electron microscopy (FESEM) equipped with Energy Dispersive X-Ray (EDX), vibrating sample magnetometer (VSM) and Fourier transform infrared spectroscopy (FT-IR). UV-Vis spectrophotometer (UV-1800, Shimadzu) was employed to determine the absorption peaks of NPs in the region of 300-800 nm by simply adding a colloidal dispersion (in deionized water) into a cuvette, and gently shaken before the reading was taken. Powder X-Ray diffraction patterns were used to determine the crystal structure and phase purity of the samples in the range of 5° to 80° (scanning rate=2°/min) on an XRD PAN analytical X’pert PRO at an applied current of 20 mA and accelerating voltage of 45 kV with Cu Kα radiation (λ = 1.54Å). The mean particle size, size distribution and morphology of the samples were obtained by HR-TEM model JEM-2100F. The sample was observed under the microscope after dripping the dispersed nanoparticles onto the 300-mesh copper grids and air dried. The surface morphology of the NPs was observed by fixing a thin layer of powder sample on the carbon tape and analyzed by FEI-HELIOS NANOLAB G3 equipped with EDX from Oxford Instrument spectrometer. The magnetic nanoparticles properties were investigated by vibrating sample magnetometer (VSM, Lakeshore model 7404) at room temperature. The determination of the functional group associated with the compounds were recorded over the range of 400–4000 cm−1 using the Thermo Scientific Nicolet 6700 spectrometer by viewing the pellet sample formed after grounding the dried samples with potassium bromide (KBr).
Acknowledgment This research was supported by the Malaysian Ministry of High Education and Universiti Teknologi Malaysia (UTM) under Tier 1 grant (No. Q.K130000.2543.12H95). We also thank to the Research Management Centre (RMC) and Malaysia-Japan International Institute of Technology (MJIIT) of UTM for providing an excellent research environment to complete this work.
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Fig. 1. Starch suspension (a), starch/Fe3O4-NPs (b), separation of starch/Fe3O4-NPs from reaction mixture using an external magnet (c)
Fig. 2. Schematic illustration of the synthesis starch/Fe3O4 nanoparticles
Fig. 3. UV-vis spectra of starch (a), starch/Fe3O4-NPs (b).
Fig. 4. PXRD patterns of potato starch (a), starch/Fe3O4-NPs (b)
Fig. 5. HR-TEM images of starch/Fe3O4-NPs (a), Particle size distribution histogram of the synthesized starch/Fe3O4-NPs (b), the lattice spacing of Fe3O4 (c) and starch (d) respectively
Fig. 6. FESEM images of starch/Fe3O4-NPs (a), EDX analysis (b)
Fig. 7. Magnetization versus applied magnetic field for starch/Fe3O4-NPs at 300 K
Fig. 8. The near FT-IR spectra of potato starch (a), starch/Fe3O4–NPs (b).
S1001-8417(17)30071-2 http://dx.doi.org/doi:10.1016/j.cclet.2017.02.015 CCLET 3988
To appear in:
Chinese Chemical Letters
Received date: Revised date: Accepted date:
10-11-2016 3-1-2017 27-2-2017
Please cite this article as: Nurul Hidayah Abdullah, Kamyar Shameli, Ezzat Chan Abdullah, Luqman Chuah Abdullah, A facile and green synthetic approach toward fabrication of starch-stabilized magnetite nanoparticles, Chinese Chemical Letters http://dx.doi.org/10.1016/j.cclet.2017.02.015 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.
Original article A facile and green synthetic approach toward fabrication of starch-stabilized magnetite nanoparticles Nurul Hidayah Abdullah a, Kamyar Shameli a, , Ezzat Chan Abdullah a, Luqman Chuah Abdullah b a
Department of Environmental Engineering and Green Technology (EGT), Malaysia-Japan International Institute of Technology (MJIIT), Universiti Teknologi Malaysia (UTM), Jalan Sultan Yahya Petra, Kuala Lumpur 54100, Malaysia b Department of Chemical and Environmental Engineering, Faculty of Engineering, Universiti Putra Malaysia, Serdang Selangor 43400, Malaysia
Corresponding author. E-mail address: [email protected]
Graphical Abstract
Highly dispersed spherical starch/Fe3O4-NPs can be synthesized by ultrasonic assisted co-precipitation method. Starch was used as a stabilizer for controlled size of Fe3O4-NPs. ABSTRACT A facile and green synthetic approach for fabrication of starch-stabilized magnetite nanoparticles was implemented at moderate temperature. This synthesis involved the use of iron salts, potato starch, sodium hydroxide and deionized water as iron precursors, stabilizer, reducing agent and solvent respectively. The nanoparticles (NPs) were characterized by UV-vis, PXRD, HR-TEM, FESEM, EDX, VSM and FT-IR spectroscopy. The ultrasonic assisted co-precipitation technique provides well formation of highly distributed starch/Fe3O4-NPs. Based on UV-vis analysis, the sample showed the characteristic of surface plasmon resonance in the presence of Fe3O4-NPs. The PXRD pattern depicted the characteristic of the cubic lattice structure of Fe 3O4-NPs. HR-TEM analysis showed the good dispersion of NPs with a mean diameter and standard deviation of 10.68±4.207 nm. The d spacing measured from the lattice images were found to be around 0.30 nm and 0.52 nm attributed to the Fe3O4 and starch, respectively. FESEM analysis confirmed the formation of spherical starch/Fe3O4-NPs with the emission of elements of C, O and Fe by EDX analysis. The magnetic properties illustrated by VSM analysis indicated that the as synthesized sample has a saturation magnetization and coercivity of 5.30 emu/g and 22.898 G respectively. Additionally, the FTIR analysis confirmed the binding of starch with Fe 3O4NPs. This method was cost effective, facile and eco-friendly alternative for preparation of NPs. Keywords: Nanoparticles Fe3O4 Starch Magnetic properties Vibrating sample magnetometer
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1. Introduction. Major advances in nanotechnology field have broadened the emergence of novel nanomaterials with exceptional properties and wide range of applications. The unique properties of nanomaterials have been exploited for several prospective uses especially in medicine [1], optical and electronic devices application [2], catalysis, ceramics and magnetic data storage [3]. Several important aspects have been taken into account in improving the physical and chemical properties of the materials by controlling the chemical composition, size, shape and morphology [2]. Nanomaterials are inherently unstable, therefore they have strong intrinsic tendency to agglomerate to maintain the state of lower energy [3-5]. Green synthesis approach has drawn much attention among researchers due to the concern of safety towards human and environment. Several researches have been conducted in reducing or eliminating the use or generation of dangerous substances by green synthetic routes [6-9]. Green technology has been established to pursue strategies to mitigate toxicity by exploitation of natural resources as biological tools for NPs synthesis and simultaneously provide advantages by lowering the operating expenses, reduced environment impacts, superior biocompability and higher stability [10]. Thus, practice in green marketing which incorporates a broad range of activities such as the product modification, changes to the production process, packaging changes, as well as modifying advertising of the environment friendly commodities will contribute to environmental sustainability in the future [11]. Magnetic nanomaterials have been the subject of numerous investigations due to their great potential applications in bio-separation [12], biosensor [13], magnetic resonance imaging (MRI) contrast agents [14], targeted drug delivery [12, 14] and food analysis [15]. Particular attention has been devoted to the synthesis of magnetite (Fe 3O4) nanoparticles due to the interesting features of low toxicity and biocompatibility in addition to superparamagnetism [12, 16, 17]. Furthermore, a variety of methods have been established for the synthesis of magnetic nanoparticles such as thermal decomposition method [18], chemical co-precipitation [19], hydrothermal route [20], microwave irradiation [21], solvothermal synthesis [22], microemulsion [23] and ultrasonic chemical co-precipitation [24]. Co-precipitation technique is one of the simple, cheap and effective methods for fabrication of nanomaterials in large scale synthesis [25, 26]. This method has been employed in the synthesis of magnetite NPs by mixing of ferric and ferrous ions at certain molar ratio in highly basic solutions at room temperature or at elevated temperature. Different sizes and shapes of the NPs can be obtained by varying the salt type (such as chlorides, sulfates, nitrates, perchlorates, etc.), the reaction temperature, the ferric and ferrous ions ratio, the pH value, ionic strength of the media, and other reaction parameters (e.g. stirring rate, dropping speed of basic solution) [12, 26, 27]. Additionally, the surface modification of iron oxide NPs can be attained by introducing organic materials or inorganic materials, such as polymers, biomolecules, silica and metals for better controlled in sizes and particle distribution. In spite of several progresses have been made in synthesis of iron oxide NPs, simultaneous control of their shape, stability, biocompatibility, surface structure, and magnetic properties is still a major challenges [12]. Ultrasonic irradiation is one of the promising methods for the preparation of various materials with nanometer dimensions. This method has been massively employed due to the relatively cheap, simple and energy saving for fabrication of smaller size particles with higher surface area [28-31]. Studies have shown that different kind of nanomaterials with various sizes and morphology can be prepared by sonication method. In general, frequency range from 20 kHz to 1 MHz is used in sonochemistry process, whereas at higher frequency of more than 1 MHz is usually applied in nondestructive testing and medicine [32]. The extreme conditions during the sonication were favourable to form the new phase, and have a shear effect for agglomeration, which is prone to prepare the highly monodispersive NPs [12]. Several studies have been conducted for the preparation of water-dispersible magnetite nanoparticles with better control of particle size, fast magnetic response, desirable surface properties and aqueous dispersibility [33]. A major effort also has been put forward to develop various types of magnetic nanocomposites that possess pre-designed architectures with improved and complementary properties [34]. A number of approached have been reported for the production of water-dispersible magnetite nanoparticles based on monomeric stabilizers, inorganic materials and polymer stabilizers [26]. For instance, modified solvothermal technique has been employed for the synthesis of biocompatible and highly water-dispersible magnetite particles in the presence of trisodium citrate (Na3Cit) as a stabilizer [35]. The synthesis of magnetic nanocomposites on various types of inorganic substrates such as silica and zeolites with well-defined core−shell structure also has been reported to possess higher saturation magnetization and good dispersibility in water [36-38]. These materials have been recognized for their outstanding features of enhanced stability, being able to shield the active species from harsh environments, improved physical, chemical and photoelectric properties, and ease of surface functionalization [34]. Several polymers such as dextran [14, 39, 40, 41], polyethylene glycol (PEG) [42, 43], polyvinyl alcohol (PVA) [44, 45], alginate [46, 47], chitosan [13, 48] and starch [49, 50] also have been used for the size controlled synthesis of magnetite nanoparticles. Starch is widely known as one of the most abundant naturally occurring polysaccharides and possesses many unique properties, such as low cost, renewability and biodegradability [51, 52]. The granular form of starch obtained from the plant has a complex semicrystalline structure with diameter between 1μm and 100 μm [53]. It has been recognized as a potential candidate of biomaterial as drug carriers and coating agents for MR purposes owing to its biocompatibility, biodegradability, and nontoxicity [49]. The polymers functionalized iron oxide NPs has gained much attention due to the advantages of polymers coating will increase the repulsive forces to
balance the magnetic and the van der Waals attractive forces acting on the NPs [12]. Besides, the incorporation of polymer surface complexing agents during the formation of magnetite can provide better control over the particle sizes [26]. In this study, magnetic starch/Fe3O4-NPs were synthesized by ultrasonic assisted co-precipitation method. The combination of these two techniques can lead to the formation of biocompatible iron oxide NPs and better control of the particle shape, small sizes distribution and less aggregation of particles. Starch and iron chloride salts were used as a stabilizer and iron precursors respectively. The simple, rapid and low cost raw materials that implemented in this study can be utilized for the preparation of various types of NPs with controlled morphology and sizes. Additionally, due to the awareness of green chemistry approach, no toxic chemical and solvents were used to avoid the generation of harmful substances as well as reducing the environmental pollution as much as possible. 2. Results and discussion 2.1.
Synthesis of starch/Fe3O4 nanoparticles
The magnetite NPs were obtained by the reaction of aqueous mixture of Fe 3+ and Fe2+ ions at a 2:1 ratio in hot starch solution and reduction by NaOH till pH 11 was achieved. The suspension changed from white cloudy solution (Fig. 1a) to dark brown colour (Fig. 1b) after addition of NaOH and followed by stirring and sonication for 1 h. The NPs were easily attracted to a permanent magnet which indicated the formation of Fe3O4-NPs (Fig. 1c). Eq. 1 illustrates the ions were compounded with starch and complex ions were generated [starch/2Fe3+:1Fe2+]. In the Eq. 2, addition of sodium hydroxide results to reduce of the ions in [starch/2Fe 3+:1Fe2+] suspension to [starch/Fe3O4]. The overall reaction for the formation of starch/Fe3O4-NPs may be written as follows. Starch + H2O(l) + 2Fe3+(aq) + Fe2+(aq) [starch /2Fe3+:1Fe2+]+8OH-(aq)
[Starch/2Fe3+:1Fe2+] [Starch/ Fe3O4] (s) + 4H2O(l)
(1) (2)
The schematic representation for the synthesis of starch/Fe 3O4-NPs shown in Fig. 2 illustrates the interaction between the external surface of Fe3O4 nanoparticles with positive charge and the oxygen atoms in hydroxyl group of starch as a negative charge. Starch acts as a polymer surface complexing agents to control the sizes of the NPs. Additionally, the chelation of these organic ions on the iron oxide surface can either prevent nucleation and then lead to larger particles sizes or inhibit the growth of the crystal nuclei, leading to small NPs [26].
2.2.
UV-visible analysis
From Fig. 3, the absorption spectrum depicted by UV-vis spectroscopy showed that no absorption peak (red) associated with the starch compound was observed. On the other hand, the absorption band underwent transformation with the observation of plasmon resonance after formation of magnetite NPs. Nonetheless, the decrease in the absorption intensity was observed with the increase of the wavelength in the region of 300-800 nm with no distinct strong peak was identified in this region (blue). Rahman et al. have reported about the similar finding in the UV-vis spectrum at absorption band of 330-450 nm corresponding to the absorption and scattering of UV radiation by magnetite NPs [54].
2.3.
Powder X-ray diffraction
The PXRD measurement was employed to identify the crystalline structure and purity of the prepared sample. The PXRD patterns of potato starch and starch/Fe3O4-NPs are shown in Fig. 4a-b. From Fig. 4(a), the observed peaks at 2θ = 11.71°, 14.47°, 17.46°, 19.94°, 22.56°, 24.47°, 26.66° and 34.91° were matched well with the JCPDS file no. 039-1912 of potato starch. From Fig. 4(b), the appearance of peaks at 2θ = 30.47°, 35.75°, 43.51°, 53.85°, 57.50°, 63.11° and 74.54° were correlated to the JCPDS File no. 01-0750033 of cubic phase Fe3O4. The decreased in the intensities of the starch peaks at 2θ = 11.72°, 14.58°, 17.37°, 19.70°, 22.49°, 24.53° and 26.68° were observed attributed from the incorporation of Fe 3O4 within the starch molecule. The average crystallite size of the nanoparticles can be estimated by applying the Scherrer formula D = kλ/βcosθ where D is the crystallite dimension, k is Scherrer constant (0.89), λ wavelength of the Cu-Kα (0.154) irradiation, βhkl is the full width at half maximum (FWHM) (hkl) of diffraction peak in radian unit, and θhkl is the diffraction angle [55, 56]. Based on the equation, the average crystallite sizes for starch/Fe 3O4-NPs calculated from Debye Scherrer equation was around 9.30 nm. No impurities phase was detected indicated the high purity crystalline sample.
2.4.
High resolution-transmission electron microscopy analysis
HR-TEM images in Fig. 5a revealed that the sample composed of highly distributed NPs with a spherical shape. A histogram illustrated in Fig. 5b showed that the synthesized NPs have a mean diameter and standard deviation of 10.68±4.207 nm. The counted
NPs were around 71. The mean particle sizes obtained were in accordance with the estimated average crystallite sizes calculated from the Scherrer’s equation. The NPs were uniformly distributed with almost no agglomeration. Fig. 5c displays the HR-TEM image of an individual Fe3O4-NPs with a lattice spacing of ~0.30 nm corresponds to d spacing of the [220] cubic plane of Fe 3O4 (JCPDS file No. 01-075-0033). In addition, Fig. 5d depicts the lattice spacing of ~0.52 nm for individual starch meeting at an angle 17.37° which is consistent with the XRD peak shown in Fig. 4b (JCPDS file No. 039-1912).
2.5. Field emission scanning electron microscopy analysis The surface morphology characterized by FESEM analysis revealed that the highly dispersed spherical magnetite NPs were formed (Fig. 6a). The starch hinders the Fe3O4-NPs from agglomeration and serves as stabilizer. Furthermore, the existence of polymeric starch on the surface of magnetite nanoparticles may prevents further oxidation [49]. The appearance of emission of C, O and Fe elements attributes from the formation of starch/iron oxide NPs was verified by EDX analysis (Fig. 6b).
2.6. Vibrating sample magnetometer analysis The magnetic properties of this material were studied by VSM and the result was presented in Fig. 7. The sample exhibit magnetic properties at room temperature with coercivity (H c) and remanance (Mr) of 22.898 G and 0.123 emu/g respectively. The saturation magnetization (Ms) obtained was around 5.30 G. The low saturation magnetization of 4.62 emu/g also has been reported based on superparamagnetic graphene oxide/magnetite-NPs [57]. They reported that the low Ms value was attributed to the rather smaller size of the Fe3O4 nanoparticles and the relatively low loaded amount of Fe3O4 on the graphene oxide. Although the value of the magnetization obtained by starch/Fe3O4-NPs was quite low, the particles were easily attracted to the external magnet in aqueous solution and in the powder form as shown in Fig. 1 and Fig. 4 respectively. 2.7. Fourier transform infrared analysis The observed FT-IR spectra for potato starch and starch/Fe3O4-NPs are shown in Fig. 8a-b. The appearance of peaks in the spectrum of potato starch at 3407, 2926, 1163 and 983 cm -1 were due to the -OH stretching, -CH stretching and O-C stretching of anhydroglucose ring group [58]. The appearance of doublet peaks at 2926 cm-1 indicated the C-H stretching and antisymmetric stretching of starch [59]. Furthermore, the appearance of intense overlapped bands in the region of 800-1300 cm–1 were attributed from CO, CC stretching and COH bending modes. Meanwhile, several bands below 800 cm –1 correspond to ring and skeletal modes [60, 61]. The presence of bound water of –OH bending vibration in starch was appeared at 1654 cm-1 [59, 62]. The peaks attributes to the stretching vibration of Fe-O bond were overlapped with the starch peaks at wavelength 573 cm -1 [63]. From Fig. 8b, the present system exhibits similar functional groups as starch but increased in the intensities were observed indicated the interaction between starch and iron oxide NPs. 3. Conclusion The present work provides information about the ultrasonic assisted co-precipitation method to produce highly dispersed starch/Fe3O4-NPs. The synthesized material showed surface plasmon resonance attributed to the absorption and scattering of UV radiation by magnetic NPs. High purity crystalline starch/Fe3O4–NPs were obtained with estimated average crystallite sizes of 9.30 nm. The HR-TEM analysis showed that the starch/Fe3O4-NPS exhibit spherical shape with a mean diameter and standard deviation of 10.68 ± 4.207 nm. The d-spacing of ~0.30 nm and ~0.52 nm corresponds to the Fe 3O4 and starch was observed, respectively. The detailed morphological characterization by FESEM revealed well distribution of spherical starch/Fe 3O4-NPS. The specific saturation of Fe3O4‒NPs was around 5.30 G. The FTIR spectrum before and after the formation of Fe 3O4-NPs in starch remained unchanged but increased in the peak intensities was well noticed. The prepared Fe 3O4-NPs can be easily separated by magnet in the aqueous solution. The green synthesis method proposed in this study does not use any toxic chemicals and the production scale-up can be easily done at low cost. This synthesis strategy can be developed into a generic protocol for preparation of other metal oxide with controlled sizes and shapes. 4. Experimental 4.1.
Materials and apparatus
FeCl3⋅6H2O (97% Sigma Aldrich), FeCl2⋅ 4H2O (> 99% Sigma Aldrich), NaOH (99% R&M Chemicals) and starch with chemical formula (C6H10O5)n (R&M Chemicals) were used as received without further purification. Deionized water was obtained from ELGA Lab Water Purification System, UK for medium preparation. The pH of the solution was controlled by channel Benchtop pH meter. The ultrasonic liquid processor (Hielscher Ultrasound Technology UP 200S, Germany) was used during sonication process. The synthesized material was dried in an Esco Isotherm Forced Convection Laboratory Oven. 4.2.
Preparation of starch/Fe3O4 nanoparticles
The material was prepared by addition of Fe3+ and Fe2+ salts solutions with 1:2 molar ratio into hot starch solution at temperature of 60 °C. Then, NaOH (0.5 mol/L) was added dropwise until the pH was adjusted to 11. After that, the NPs suspension was stirred continuously for 30 min at the temperature around 40 °C. The suspension was further exposed to high-intensity sonochemical irradiation for 30 min at amplitude of 70% and 0.5 of cycle by ultrasonic liquid processor with the immersion of probe into the solution. The precipitates were centrifuged at 10 000 rpm for 10 minutes, washed several times with deionized water, and finally dried in an oven at 50 °C for 24 h. 4.3.
Characterization of starch/Fe3O4 nanoparticles
The characterization of the starch/Fe3O4-NPs was performed using ultra-violet visible spectroscopy (UV-vis), powder X-ray diffraction (PXRD), high resolution transmission electron microscopy (HR-TEM), field emission electron microscopy (FESEM) equipped with Energy Dispersive X-Ray (EDX), vibrating sample magnetometer (VSM) and Fourier transform infrared spectroscopy (FT-IR). UV-Vis spectrophotometer (UV-1800, Shimadzu) was employed to determine the absorption peaks of NPs in the region of 300-800 nm by simply adding a colloidal dispersion (in deionized water) into a cuvette, and gently shaken before the reading was taken. Powder X-Ray diffraction patterns were used to determine the crystal structure and phase purity of the samples in the range of 5° to 80° (scanning rate=2°/min) on an XRD PAN analytical X’pert PRO at an applied current of 20 mA and accelerating voltage of 45 kV with Cu Kα radiation (λ = 1.54Å). The mean particle size, size distribution and morphology of the samples were obtained by HR-TEM model JEM-2100F. The sample was observed under the microscope after dripping the dispersed nanoparticles onto the 300-mesh copper grids and air dried. The surface morphology of the NPs was observed by fixing a thin layer of powder sample on the carbon tape and analyzed by FEI-HELIOS NANOLAB G3 equipped with EDX from Oxford Instrument spectrometer. The magnetic nanoparticles properties were investigated by vibrating sample magnetometer (VSM, Lakeshore model 7404) at room temperature. The determination of the functional group associated with the compounds were recorded over the range of 400–4000 cm−1 using the Thermo Scientific Nicolet 6700 spectrometer by viewing the pellet sample formed after grounding the dried samples with potassium bromide (KBr).
Acknowledgment This research was supported by the Malaysian Ministry of High Education and Universiti Teknologi Malaysia (UTM) under Tier 1 grant (No. Q.K130000.2543.12H95). We also thank to the Research Management Centre (RMC) and Malaysia-Japan International Institute of Technology (MJIIT) of UTM for providing an excellent research environment to complete this work.
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Fig. 1. Starch suspension (a), starch/Fe3O4-NPs (b), separation of starch/Fe3O4-NPs from reaction mixture using an external magnet (c)
Fig. 2. Schematic illustration of the synthesis starch/Fe3O4 nanoparticles
Fig. 3. UV-vis spectra of starch (a), starch/Fe3O4-NPs (b).
Fig. 4. PXRD patterns of potato starch (a), starch/Fe3O4-NPs (b)
Fig. 5. HR-TEM images of starch/Fe3O4-NPs (a), Particle size distribution histogram of the synthesized starch/Fe3O4-NPs (b), the lattice spacing of Fe3O4 (c) and starch (d) respectively
Fig. 6. FESEM images of starch/Fe3O4-NPs (a), EDX analysis (b)
Fig. 7. Magnetization versus applied magnetic field for starch/Fe3O4-NPs at 300 K
Fig. 8. The near FT-IR spectra of potato starch (a), starch/Fe3O4–NPs (b).