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Materials Research

Print version ISSN 1516-1439On-line version ISSN 1980-5373

Mat. Res. vol.20 no.6 São Carlos Nov./Dec. 2017  Epub Aug 24, 2017

http://dx.doi.org/10.1590/1980-5373-mr-2017-0213 

Articles

Synthesis and Characterization of Hybrid Ni0.5Zn0.5Fe2O4@SiO2/chitosan

Polyana Tarciana Araújo dos Santosa  * 

Patrícia Tatiana Araújo dos Santosa 

Pascally Maria Aparecida Guerra de Araújoa 

Daniel Reinaldo Cornejob 

Ana Cristina Figueiredo de Melo Costaa 

aDepartment of Materials Engineering, Federal University of Campina Grande, Campina Grande, PB, Brazil.

bDepartment of Physics of Materials and Mechanics, Institute of Physics, University of São Paulo, São Paulo, SP, Brazil.

ABSTRACT

In this work we evaluate the use of silane agent 3-aminopropyltrimethoxysilane and biopolymer chitosan to functionalize ferrites Ni0.5Zn0.5Fe2O4 using the solvent evaporation method aiming at obtaining hybrid material Ni0.5Zn0.5Fe2O4@SiO2/chitosan for use as a biosensor. The nanoparticles before and after the functionalization showed the major phase Ni0.5Zn0.5Fe2O4. The FTIR spectra showed absorption bands characteristic of CO, axial deformation of CN and SiO band from the silane agent which proved functionalization. The functionalization of ferrite Ni0.5Zn0.5Fe2O4 with chitosan caused a 36.36% reduction in saturation magnetization as compared with ferrite synthesized, however it maintained the ferrimagnetic characteristic indicating to be a promising material for the use in biotechnological applications as for example in magnetic biosensors.

Keywords: biopolymer; magnetic nanoparticles; chitosan

1. Introduction

Hybrid materials (HM) combine the advantages of organic polymers (e.g., photoluminescence, flexibility, easy processing) with those of inorganic compounds, such as thermal and chemical stability1. Many approaches have been reported recently about the preparation of hybrid compounds, such as enzyme immobilization2, drug carriers, optical imaging3, gene therapy4 and electrochemical sensors5.

Of the important applications of magnetic nanoparticles in nanotechnology can be mentioned diagnosis and treatment of cancer, immobilization and isolation of biomolecules and various enzymes, targeted drug delivery, diagnostic agents magnetically guided, biosensor, hyperthermia6-11.

Biosensors comprise a number of different components among which the most important part constitutes magnetic particles12. The implication of magnetic particles in biosensors means that it is important to have a better understanding of the properties of magnetic particles. Recently, great attention has been devoted to syntheses of various magnetic nanoparticles due to their widespread applications in many fields such as biomedicine, biotechnology, materials science and environmental areas13,14.

The Ni-Zn ferrites are one of the most versatile magnetic materials for magnetic biosensor development, since it presents saturation magnetization and high Curie temperature, chemical stability as well as low coercivity15 and in the case of systems formed by nanoparticles may exhibit superparamagnetism16, which is the most promising magnetic behavior for biomedical applications. Furthermore, for use in biological and medical fields, they must be monodisperse magnetic nanoparticles and bind to biomolecules15.

Ni-Zn ferrites have been used with different polymer matrices producing hybrid materials. For a better compatibility between the inorganic oxide and the polymer it is necessary to pre-treat the ferrite through the ion exchange or the chemical modification of the surface of the particles15.

In this process of chemical modification of the inorganic nanoparticles either by silane agents or biocompatible polymers or even by the combination of both makes possible these materials, the reduction of toxicity, biological compatibility and antimicrobial activity16,17 and also with the purpose of avoiding aggregation, sedimentation of the particles, as well as grant bridges of biological conjunction.

Polymer-coated magnetic nanoparticles have aroused great interest and application in the fields of biotechnology and medicine in recent years, since they can be separated and collected from the medium with the application of a magnetic field18.

Among the various polymers used for the immobilization of biomolecules and biosensor applications, chitosan, has unique properties of biopolymers, particularly due to the presence of primary amino groups19, reactive groups distributed in a polymer matrix, which allows biological conjugation.

Chitosan is a biopolymer interesting for this purpose due to their excellent film-forming ability, high permeability, mechanical strength, non-toxicity, biocompatibility, low cost and good availability20. Chitosan is a product with a high deacetylated molar mass of chitin, the second most abundant polysaccharide in nature, has structural characteristics similar to glycosaminoglycans and has numerous interesting biological properties21.

In this context, the aim of this study was to obtain the hybrid Ni0.5Zn0.5Fe2O4@SiO2/chitosan, from the functionalization of Ni-Zn ferrite with silane agent 3-aminopropyltrimethoxysilane and biopolymer chitosan aiming its use in biomedicine as magnetic biosensor. To this end, an investigation of the structure, morphology, thermal and magnetic properties was conducted.

2. Material and Methods

For the synthesis of NPMs all the precursors used for this synthesis were high purity chemicals obtained from VETEC, the following reagents were used: Urea - CO (NH2)2; iron nitrate nonohydrate - Fe(NO3)3.9H2O; zinc nitrate hexahydrate - Zn(NO3)2.6H2O; nickel nitrate hexahydrate - Ni (NO3)2.6H2O; Cobalt nitrate II trihydrate - Co(NO3)2.3H2O.

The solutions containing the oxidizing reagents and source of metal cations and the urea (reducing agent) were obtained from the total valence of the oxidizing and reducing reagents using the theory of propellants and explosives proposed by Jain et al.(1981)22, in order to favor the stoichiometric oxidant/fuel ratio, Φe = 1.

The redox mixture of the oxidizing and reducing reagents prepared according to the preset stoichiometry was obtained in a vessel with a capacity of 20g batch and submitted to direct heating in a conical reactor with electrical resistance (temperature approximately 600 ºC)23 Until it reaches the auto-ignition (combustion). Then the reaction product (porous flakes) was de-agglomerated in 325 (mesh ABNT 45 µm) and submitted to the characterizations. The sample of ferrite Ni-Zn (Ni0.5Zn0.5Fe2O4) as synthesized was designated of NZ and were submitted for characterizations.

For the signaling process all the precursors used for this synthesis were high purity chemicals obtained from SIGMA ALDRICH, The following reagents were used: 3-aminopropyltrimethoxysilane - APTS - [H2N(CH2)3Si(OCH3)3]; Toluene - C7H8; Ethyl alcohol - C2H6O.

For the modification of the surface of the NPMs under study were placed 5g of the NPMs previously oven dried at 100°C with 5mL of APTS reagent mixed in 50mL of anhydrous toluene in a three-necked round bottom flask of 500mL. The mixture was refluxed at 100°C under stirring for 72 hours.

After the silanization reaction the solution was transferred to test tubes and centrifuged in a baby model FANEM centrifuge at 500 rpm speed for 30 minutes in order to promote the sedimentation of the NPMs. Afterwards, the washing process was started using ethyl alcohol, the process repeated for 8 repetitions and then placed for FANEM Model 315 drying at 150°C for 12 hours. The signaling of the resulting sample was designated NZ@SiO2 and were submitted for characterizations.

For the functionalization process with chitosan the following reagents were used: chitosan - Qs - (C12H24N2O9) - 98% - ALDRICH; Glacial acetic acid (CH3COOH) - SYNTH and sodium hydroxide (NaOH) - SYNTH.

To functionalize of NPMs, 5 g of the silanized NPMs were added in 50 ml of a solution of acetic acid (1% v/v) and 1 g of chitosan under mechanical stirring over a period of 2 hours. The mixture was poured into Petri dishes and dried in the oven at a temperature of about 60 °C for a period of 24 hours for complete evaporation of the solvent, resulting in a dry product. The product was allowed to immerse in basic solution for 2 hours.

After the neutralization reaction, the product was washed with distilled water (switching the water 8 times) and then dried at room temperature for 24 hours. Samples resulting from chitosan functionalization were designated as NZ@SiO2/chitosan and subsequently subjected to characterizations.

The determination of the phases present, crystallinity and crystallite size were determined from the diffraction data using an X-ray diffractometer SHIMADZU (model XRD 6000, radiation CuK). The crystallinity was determined from the ratio of the integrated area of the peak of crystalline phase and the amorphous area referring to the fraction. The average crystallite size was calculated from the line broadening of X-rays (d311) by deconvolution of secondary diffraction line polycrystalline cerium (used as standard) using the equation of Scherrer.

FTIR spectra were obtained using a spectrometer FT-IR/FT-NIR brand model 400 Perkin Elmer, between 4000 and 400 cm-1 at 4 resolution and 20 scans. The micrographs were obtained using a scanning electron microscope, Hitachi, model TM 1000. The thermogravimetric curves were obtained on a thermobalance, Shimadzu TGA-60, in nitrogen atmosphere with an alumina crucible, a flow of 50 mL/min and heating rate 10°C/min, a temperature range varying ambient to 1000°C.

The coercivity, remanent magnetization and saturation magnetization were obtained from the graph of hysteresis, observing the behavior of the curves near the origin of the cartesian plane. The hysteresis loss were determined by the area of MxH. The cycles of magnetic hysteresis curve of the samples were obtained using an alternating gradient magnetometer (AGM).

3. Results

The Figure 1 illustrates the x-ray diffractogram for the ferrite Ni0.5Zn0.5Fe2O4 obtained by combustion reaction (NZ) silanised with 3-aminopropyltrimethoxysilane silane agent (NZ@SiO2) and functionalized with chitosan (NZ@SiO2/Chitosan).

Figure 1 X-ray diffraction patterns for: (a) pattern JCPDS, (b) NZ, (c) NZ@SiO2 and (d) NZ@SiO2/Chitosan. 

For all samples it was observed the presence only of the main peaks characteristic of the inverse spinel structure as crystallographic forms JCPDF 52-0278. Comparing the X-ray spectra of the sample NZ samples NZ@SiO2 and NZ@SiO2/Chitosan it is observed that they were similar, indicating that therefore, the addition of the silane agent followed by functionalization with the biopolymer chitosan did not cause structural change neither phase transition in the synthesized material, therefore, the structure of inverse spinel was preserved. There are also peaks with a considerable basal width in all reflections and they are well defined, indicating that they are crystalline materials with nanostructural characteristics.

Covaliu and his collaborators, 201324 obtained nanostructured hybrid materials of CoFe2O4 coated with biopolymers polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG) for biomedical applications and using the DRX technique concluded that nanostructured hybrid materials of CoFe2O4 after coating with PVP and PEG kept preserved the crystalline structure of ferrite. These results are in agreement with the results obtained by this work, ie, the biopolymer chitosan after added to the NiZn ferrite did not alter the structure of the ferrite.

Figure 2 presents the vibrational spectrum in the infrared region in the range of 4000 - 450 cm-1, samples of ferrite Ni0.5Zn0.5Fe2O4 obtained by combustion reaction (NZ), after signaling the agent silane 3- aminopropyltriethoxysilane (NZ@SiO2) and functionalized chitosan (NZ@SiO2/Chitosan).

Figure 2 FTIR (a) NZ e (b) NZ@SiO2 and (c) NZ@SiO2/Chitosan. 

According to the spectra of Figure 2, there are two absorption bands below 1000 cm-1, the bands v1 and v2, which are characteristic of the crystal lattice of AB2O4 spinel. It was observed that the absorption band v1 was localized approximately in the range of 815 cm-1 being attributed to the vibrations of the tetrahedral sites and v2 band was located approximately in the range of 490 cm-1 corresponding to the vibrations of the octahedral sites.

In Figure 2a, bands in the range of about 3660 cm-1 and 1500 cm-1 were observed, characteristics of O-H-O bonds, possibly of the presence of water in the sample, which can be obtained by atmospheric adsorption of atmospheric air that refers to Water adsorbed free and/or physically and also because of the KBr used for its preparation, which is hygroscopic and absorbs moisture easily.

Figure 2b shows stretching bands in the 2914 cm-1 region attributed to the aliphatic type v(CH) sp3. In 1635 cm-1 we observe an extensible band referring to the CO, it can be attributed to the CO2 of the atmosphere. The multiple bands around 1124 cm-1 and 1033 cm-1 correspond to the asymmetric stretching vass Si-O, confirming the effectiveness of the silanization process. Also, bands below 1000 cm-1 are observed, which is characteristic of Ni0.5Zn0.5Fe2O4 spinel.

In Figure 2c, from 3450 to 3200 cm-1 weak absorptions attributed to NH bonds of primary amines are observed. The stretching bands in the region of 2919 cm-1 and 2773 cm-1 are caused by asymmetric and symmetrical stretching vibrations of CH, respectively, of methyl radicals belonging to chitosan groups. The bands at 1740 cm-1 and 1554 cm-1 are related to the vibrations of CO and NH, respectively.

In the range of 1456 cm-1 and 1364 cm-1 is an absorption which is attributable to symmetrical deformation of CH. In 1254 cm-1 observes a band referring to stretching Si-CH3 and in 1177 cm-1 a band assigned to the asymmetric stretching Si-O-Si. In 600 and 508 cm-1 bands were observed relating to the vibrations in the tetrahedral and octahedral sites in the spinel structure.

The Figure 3 illustrates the morphological characterization of ferrite Ni0.5Zn0.5Fe2O4 obtained by combustion reaction before (NZ), after signaling with silane agent 3-aminopropyltriethoxysilane (NZ@SiO2) and functionalized chitosan (NZ@SiO2/Chitosan).

Figure 3 MEV (a) NZ, (b) NZ@SiO2 and (c) NZ@SiO2/Chitosan. 

According to the micrograph presented in Figure 3a, were observed the formation of agglomerates larger than 5 µm, nonuniform and irregularly shaped were observed formation of agglomerates in the form of spongy blocks, frail, and presence of large pores which are released from the flue gas during synthesis.

According to the micrographs shown in Figure 3b for the NZ@SiO2 ferrites, agglomerates with a stiffer aspect and low porosity are observed, possibly due to the covalent attachment of the silane to the surface of the NPMs, thus the presence of the silane agent promoted an effect sealant on the surface of the particle agglomerates. This same behavior was reported by Nadeem et al., 201425 when they synthesized and studied SiO2 coated NiFe2O4 nanoparticles.

According to the micrographs shown in Figure 3c for ferrites after functionalization with chitosan it can be seen that agglomerated particles are not uniform in size and morphology, consisting of a film impregnated particles. It is observed so that the ferrites are presented as involved or encapsulated by chitosan. This same phenomenon was also observed by Sanjai et al. (2014)26 when they studied superparamagnetic iron oxide nanoparticles (SPIONPs) encapsulated with chitosan for use as a contrast agent for MRI, observed that for the morphology after addition of the chitosan a dispersibility of the SPIONPs, desirable for use in biomedical applications.

The Figure 4 illustrates the DTA and TGA curves for the ferrite Ni0.5Zn0.5Fe2O4 obtained by combustion reaction before (NZ), after signaling with silane agent 3-aminopropyltriethoxysilane (NZ@SiO2) and functionalized chitosan (NZ@SiO2/chitosan).

Figure 4 Thermogravimetric curves (a) NZ, (b) NZ@SiO2 and (c) NZ@SiO2/Chitosan. 

With Figure 4a, it is noted that the NZ ferrites showed mass loss in three stages, in the range of 25-125°C, of 0.581 mg equivalent to a percentage of mass loss 2.23%, associated with adsorbed water and gases on the DTA curve represented by a maximum exothermic peak in 58.48ºC. The second mass loss occurred between 125-453°C, it was 0.504 mg, which corresponds to a percentage loss 1.94%. In 453-1000°C it is observed that the nanoparticles Ni0.5Zn0.5Fe2O4 they showed a mass loss 0.424 mg equivalent to a percentage of mass loss 1.632%, shown in DTA curve of a maximum endothermic peak in 548.35ºC.

With Figure 4b, it is noted that the NZ@SiO2 ferrite showed mass loss in three stages. The first weight loss occurred at a range of 25-227°C, of 0.371 mg equivalent to a percentage of mass loss 0.932%, associated with adsorbed water and gases on the DTA curve represented by a maximum exothermic peak in 60.27ºC. The second mass loss corresponds to 0.915 mg equivalent to a percentage of mass loss 2.298%, in the temperature range of 227 up until 532°C, shown in DTA curve of a maximum endothermic peak in 319.8ºC. The third loss occurring in the range of 532-757°C of 0.154 mg equivalent to a percentage of mass loss 0.387%, shown in DTA curve of a maximum endothermic peak in 472ºC. Above 757°C reaches a step of thermal stability.

In Figure 4c, it is observed that the ferrites NZ@SiO2/Chitosan showed weight loss in two stages. The first mass loss was 0.095 mg equivalent to a percentage of mass loss 3.630%, in the temperature range of 25-159°C. The second weight loss occurred between 159-611°C it was 0.460 mg corresponding to 17.577%. Above 611°C it is observed that the nanoparticles Ni0.5Zn0.5Fe2O4 functionalized chitosan showed a level of stability. It is observed to a total mass loss of 21.2%.

It is observed that the functionalized ferrite with chitosan (NZ@SiO2/Chitosan) presented higher mass loss when compared to the synthesized (NZ) and silanized with APTS (NZ@SiO2). Behavior similar to that which was also reported by Dodi et al., (2012)27 when studied nanocomposites magnetic particles with chitosan. This can be explained by the fact that chitosan is a polymer macromolecule that when subjected to high temperatures tend to suffer decomposition of its chain releasing subunits.

Figure 5 presents the dependence of the magnetization M as a function of applied magnetic field H for ferrite Ni0.5Zn0.5Fe2O4 obtained by combustion reaction before (NZ), after signaling with silane agent 3-aminopropyltriethoxysilane (NZ@SiO2) and functionalized chitosan (NZ@SiO2/Chitosan). It is observed that all samples have MxM narrow cycle is therefore characteristic of a soft magnetic material (which it is easy magnetization and demagnetization).

Figure 5 Hysteresis curves for (a) NZ, NZ@SiO2 and NZ@SiO2/Chitosan and (b) expansion NZ, NZ@SiO2 and NZ@SiO2/Chitosan. 

Upon the hysteresis curves in Figure 5, it can be seen that after silanization the saturation magnetization and the coercivity, remained almost constant, indicating that the silane content used did not affect the magnetic behavior in the ferrite. After functionalization with chitosan it was observed that the saturation magnetization was decreased by 37.5% and coercivity remains constant.

Wang et al., (2011)28, prepared nanoparticles of CoFe2O4 monodisperse in SiO2 and then functionalized with amino for the purpose of immobilizing enzymes and observed that the saturation magnetization has decreased after the NPMs be functionalized and attributed this to the effect of the coating layer of amorphous silica on the NPMs in agreement with the results obtained in this work.

Tang et al., (2012)29, when they studied the composite Co0.8Ni0.2Fe2O4/PVP using the silane coupling agent methacrylate, 3- (trimethoxysilyl) observed behavior similar to that reported for this work, because the saturation magnetization observed with the composite Co0.8Ni0.2Fe2O4/PVP it was lower as compared with the NPMs of Co0.8Ni0.2Fe2O4. This reduction in saturation magnetization is attributed to the presence of PVP which is non-magnetic, which influences the uniformity and magnitude of magnetization of the magnetic moment quench surface.

Table 1 presents the magnetic parameters lies (saturation magnetization, remnant magnetization, coercive field and hysteresis losses) obtained by means of hysteresis curves of these materials for ferrites NZ, NZ@SiO2 e NZ@SiO2/Chitosan.

Table 1 Hysteresis Parameters to NZ, NZ@SiO2 and NZ@SiO2/Chitosan. 

Sample Ms (meu/g) Mr (meu/g) Hc (kOe) Mr/Ms
NZ 56 5.0 74 0.089
NZ@SiO2 55 6.0 86 0.109
NZ@SiO2/Chitosan 35 4.0 80 0.114

With the data in Table 1, it was found ferrite NZ@SiO2 after signaling resulted in a saturation magnetization 1.81% lower when compared to the ferrite sintered NZ. It is observed that functionalization with chitosan ferrite causes a reduction in saturation magnetization 37.5%, when compared to the as sintered ferrite.

From these results, it is noted that the materials indicate that after the silanization and functionalization with chitosan biopolymer, the magnetic characteristics remain in the material, ie, the sample continued to be attracted by the magnetic field. For the results of remnant magnetization (Mr) and coercive field (Hc), it was observed that after the withdrawal of the external magnetic field the ferrites in the study presented values that oscillate of remnant magnetization and coercive field, thus proving that they are not superparamagnetic. For the nanoparticles to be superparamagnetic, it is necessary that they do not retain any magnetism after removal of the external magnetic field, present strong values of saturation magnetization, zero coercive field and absence of hysteresis30,31.

4. Conclusions

According to the objective of the present work, it was possible to obtain the hybrid Ni0.5Zn0.5Fe2O4@SiO2/Chitosan successfully tested for the presence of silanol and chitosan groups in the ferrite structure. The introduction of silane and biopolymer chitosan did not interfere with the ferrite structure. The presence of silane and chitosan reduced the magnetization, but maintained the ferrimagnetic characteristic presented by the ferrite. The hybrid Ni0.5Zn0.5Fe2O4@SiO2/Chitosan has been successfully obtained by being promising for use in biotechnology applications such as a magnetic biosensor.

5. Acknowledgments

The authors acknowledge the financial support of CNPq, CAPES, Inct-INAMI.

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Received: March 23, 2017; Revised: May 31, 2017; Accepted: July 26, 2017

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