In contributing to the improvement of Ferrite Magnetic nanoparticles, the effects of Poly (Vinyl Pyrrolidone) (PVP) and annealing on the structural and magnetic properties of Zinc ferrite nanoparticles (ZFNPs) synthesis were investigated in this work. The effects were evaluated using the X-ray diffraction (XRD) spectroscopy, Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and Vi-brating sample magnetometer (VSM). The XRD analysis confirms a good formation of the inverse spinel crystal structure with an average particle size of 1.3 nm to 15.2 nm and from 1.6 nm to 21.1 nm for the ZFNPs as-prepared and PVP mediated ZFNPs for the un-annealed and annealed samples, respectively. The SEM image reveals an increase in the particle size for both the as-prepared and PVP mediated samples after annealing at 500 °C. The FTIR also reveals the inverse spinel structure for the as-prepared and annealed samples, which witnesses a vibrational red shift towards a higher wave number for the annealed samples. The VSM analysis indicates the superparamagnetic behavior of PVP mediated and annealed sample with zero remanence magnetization (Mr) and Coercivity (Hc). The saturation magnetization (Ms) increases from 1.31 emu/g, for the as-prepared samples, to 4.31 emu/g after the annealing and from 1.18 emu/g, for the PVP mediated, to 6.38 emu/g after annealing. These effects have been attributed to the cationic re-arrangement on the lattice site after the annealing. This presents a superior material for various applications in nanotechnology.
The advancement of Nanoparticles (NP) in recent times has been superior, especially due to the enhancement of their properties in relation to their bulk materials [
However, the most commonly studied FMNP is the spinel ferrite (SF) nanocrystals. These are very important inorganic nanomaterials when compared to their bulk counterpart as well as their optical, electronic, electrical and magnetic properties, respectively [
There are challenges in controlling the shapes and dispersibility of the ZFNPs due to their large surface to volume ratio, which induces the large surface energy that is thermodynamically unstable and then produces an aggregation [
In one of such studies, [
In this work, we report on the surface effect of PVP mediated and the annealing on the structural and magnetic properties of ZFNPs using the co-precipitation method. The objectives include evaluating the effect of the PVP and the annealing on the particle size, determining the degree of crystallinity and the phase composition, and establishing the presence of the metal oxide bands. The results should present a superior material for the various applications.
The analytical grade, without further purification, of iron (III) nitrate nonahydrates (Fe (NO3)3∙9H2O) 99%, zinc nitrate hexahydrate (Zn (NO3)2∙6H2O) 99%, poly (vinyl pyrrolidone) (C6H9NO)n 99.9% (MW = 29,000) were used as precursors in the experiment. These were purchased from Sigma Aldrich and used without further purification. Distilled water (DW) was used all through the synthesis procedures.
An aqueous solution of 0.2 mm of iron nitrate in 100 ml of DW and 0.1 mm of Zinc nitrate in 50 ml of DW were prepared. The mixed reaction was obtained in the stoichiometric ratio (Fe:Zn = 2:1) and stirred with a magnetic stirrer for 2 hours to obtain a homogeneous solution. The obtained solution was added, in a dropwise, into a reaction container of 100 ml of DW at 90˚C of 0.1 g PVP. The mixture was poured into an evaporating dish and heat at 80˚C in an evaporating heater to evaporate the water and later transferred to the oven for 24 hrs to complete the drying. The dried orange colored solid ZFNPs, and the PVP mediated ZFNPs that remained, were pulverized to form a powder. The ZFNPs powder and the polymer mediated ZFNPs were washed several times and later annealed at 500˚C for 3 hrs to enhance the crystallinity of the nanocrystals and the decomposition of organic compounds in an air atmosphere.
Zn 2+ + Fe 2 + + H + → ZnFe 2 O 4 + H 2 O (1)
The PVP mediated ZFNPS samples were characterized by powder X-ray diffraction (XRD). The powder crystallite samples were used at room temperature, employing a Shimadzu diffractometer model XRD 6000 with the CuKα (0.154 nm) radiation source in a 2θ range of 10˚ - 80˚. The surface morphology and the elemental composition of the samples were determined by the Scanning Electron Microscope (SEM) obtained using JEOL_SEM1010 SEM instrument. The elemental compositions of the samples were obtained by the energy-dispersive X-ray spectroscopy (EDX) attached to SEM microscope. The Fourier Transform Infrared (FTIR) (PerkinElmer FT-IR spectra 1650, version 10.03.02) model spectrometer with 256 scans and 6 cm−1 resolution in the range of 4000 cm−1 to 500 cm−1 gave the functional groups. The magnetization via hysteresis loop at room temperature was conducted using a vibrating sample magnetometer (VSM) (lake shore 4700) with a magnetic field range from −5 KOe to +5 KOe. Noteworthy is that the microstructure and morphology of the nanoparticles is not within the scope of this study hence the samples were not exposed to the transmission electron miscroscopy.
The SEM images in Figures 1(a)-(d) shows the size distribution of the ZFNPs as-prepared, the PVP mediated samples and the annealed samples at 500˚C. The ZFNPs as-prepared is highly agglomerated with an average particle size of 52 nm, which decreases to 41 nm after the annealing. The effect of the PVP on the ZFNP is in reducing the agglomeration to an average particle size of 51 nm, whereas, after the annealing the particle reduces to 30 nm. It is obvious that the samples obtained at 500˚C were uniform in their morphology and decreased in particle size. The decrease in size is as a result of the melting of their surfaces, which were also observed in nickel ferrite and cobalt ferrite [
In the XRD result is shown the formation of cubic spinel structures without the noticeable traces of impurity phases for the PVP mediated samples coupled with annealing (
D = 0.9 λ β cos cos θ (2)
where D is the crystalline size (nm), λ is the X-ray wavelength (λ = 1.5406 Å), β is the full width at half maximum (FWHM) intensity measured in radians and θ is the Bragg diffraction angle [
The FTIR analysis results of the ZFNPs as-prepared, the PVP mediated samples and the annealed samples are presented in
Samples | Dopant | Tc (˚C) | 2θ | FWHM | Average particles size (nm) | |
---|---|---|---|---|---|---|
r* | r** | |||||
ZFNPs | - | - | 32.8399 | 6.43522 | 1.300 | - |
ZFNPs | - | 500 | 35.2463 | 0.56863 | - | 15.200 |
ZFNPs | PVP | - | 36.2015 | 5.32252 | 1.600 | - |
ZFNPs | PVP | 500 | 35.2806 | 0.41042 | - | 21.100 |
r* before annealing; r** after annealing.
The peaks at 1055 cm−1 in the ZFNPs as-prepared and 1066 cm−1 in the PVP mediated ZFNPs are attributed to the C-C stretching that changes to 1030 cm−1 after the annealing, respectively. The Carbonyl group (C=O) absorbs energy at 1634 cm−1 in the ZFNPs as-prepared and at 1622 cm−1 in the PVP mediated samples, which increased to 1634 cm−1 and 17131 cm−1 after the annealing. The peaks at 1429 cm−1 in the ZFNPs as-prepared and at 1330 cm−1 in the PVP mediated ZFNPs are attributed to CH2 bending, which increases to 1490 cm-1 and 1525 cm−1 after the annealing. The broadest peaks observed at 3204 cm−1 in the ZFNPs as-prepared and at 3216 cm−1 in the PVP mediated ZFNPs are due to an O-H group, which gives no peak for ZFNPs as-prepared and is 2975 cm−1 in the PVP mediated ZFNPs. The presence of the functional groups; C=O, C-N, C-C, C-H and O-H, confirms the presence of the PVP compound in ZFNPs.
showed zero coercivity and zero remanent magnetization (no hysteresis) at the 500˚C annealed temperature when compared with the un-annealed sample. This suggests that the superparamagnetic (SPM) behavior is in consonance with the state-of-the-art results of [
The ZFNPs as-prepared, the PVP mediated and the annealed were synthesized via the co-precipitation method. The effects of the PVP and the annealing at 500˚C on the structural and magnetic properties, respectively, have been analyzed. The XRD analysis reveals the increase in the crystallite size after the PVP mediation and the annealing of the samples, respectively. The XRD analysis of the annealed samples indicates the intense and sharp peaks when compared to the un-annealed samples. The SEM images reveal increment in the particle size of the PVP mediated and the annealed samples, respectively. The EDX analysis has revealed the strong signals of the component elements in the samples. The FTIR analysis has confirmed the presence of the PVP on the surface of ZFNPs with a red shift of the annealed sample as a result of the cationic distribution on the lattice sites. The magnetic properties of the samples changed from a ferromagnetic to an SPM as an effect of the PVP mediated and the annealing. This SPM behavior of the ZFNPs as-prepared and the PVP mediated, respectively, has been achieved by annealing the samples at 500˚C for 3 hrs. The PVP mediated and annealing effects on the structural and magnetic properties of ZFNPs present a superior material for sundry applications. However, further studies on the morphology and the microstructure of ZFNPs are imperative in enhancing the applicability.
The authors declare no conflicts of interest regarding the publication of this paper.
Okoroh, D.O., Ozuomba, J.O., Aisida, S.O. and Asogwa, P.U. (2019) Properties of Zinc Ferrite Nanoparticles Due to PVP Mediation and Annealing at 500˚C. Advances in Nanoparticles, 8, 36-45. https://doi.org/10.4236/anp.2019.82003