Modification of structural and magnetic properties of Co0.5 Ni0.5 Fe2O4 nanoparticles embedded Polyvinylidene Fluoride nanofiber membrane via electrospinning method

Nano-Structures & Nano-Objects 22 (2020) 100428

Contents lists available at ScienceDirect

Nano-Structures & Nano-Objects journal homepage: www.elsevier.com/locate/nanoso

Modification of structural and magnetic properties of Co0.5 Ni0.5 Fe2 O4 nanoparticles embedded Polyvinylidene Fluoride nanofiber membrane via electrospinning method ∗

Gun Anit Kaur a , Mamta Shandilya a , , Poonam Rana a , Shweta Thakur b , Poonam Uniyal c a

School of Physics and Materials Science, Shoolini University, Solan, HP 173229, India Department of Physics, Eternal University, Baru Sahib, Sirmour, HP 173101, India c Smart Materials Laboratory, Thapar Institute of Engineering & Technology, Patiala 147004, India b

article

info

Article history: Received 2 November 2019 Received in revised form 21 December 2019 Accepted 21 January 2020 Keywords: FTIR Nanocomposites Ferrites Electrospinning Nanofibers Coercivity

a b s t r a c t Ferrite nanoparticles have garnered significant attention due to their remarkable ferromagnetic properties. However, the functionality of the ferrite nanoparticles can be enhanced with the development of nanofiber membranes. This helps to control the surface, structural and magnetic properties of the composite nanofiber membrane. Herein, we report the fabrication of novel nanofiber membrane containing Co0.5 Ni0.5 Fe2 O4 -Polyvinylidene Fluoride (PVDF) via electrospinning method. The Co0.5 Ni0.5 Fe2 O4 nanoparticles were synthesized with the help of sol–gel combustion method. Investigations on the effect of Co0.5 Ni0.5 Fe2 O4 nanoparticles embedded within PVDF polymer nanofiber membrane on structural, morphological and magnetic properties are discussed. XRD line profile analysis revealed cubic spinel structure of the Co0.5 Ni0.5 Fe2 O4 nanoparticles To determine the crystallite size of the samples; Scherrer, Williamson–Hall (W–H), and Size-Strain plot (SSP) were carried out with the help of XRD spectra. The crystallite size of the nanoparticles reduced as they were embedded within PVDF polymer. FTIR studies confirmed that the presence of Co0.5 Ni0.5 Fe2 O4 pristine nanoparticles within the polymeric nanofiber membrane was accountable for the enhanced β -phase bands which makes a significant effect on the ferroelectric properties of the nanofiber membrane. In addition, the VSM technique was used to study the ferromagnetic properties. The enhanced remnant magnetization and saturation magnetization of the nanoparticles was responsible for magnetic nature of the non-magnetic polymer PVDF. © 2020 Elsevier B.V. All rights reserved.

1. Introduction In the past few decades, nanotechnology has gained enormous attention and been exploited to a wide range of applications. One of the most prominent area of current research and development is the polymer matrix-based nanofiber membrane via electrospinning technique. Various methods including vapor deposition polymerization (VDP), chemical vapor deposition (CVD), supercritical fluid techniques, have been reported in literature for the fabrication of the nanofibers [1–3]. However, the aforementioned methods are not economically viable, yields non-uniform nanofibers, and the synthesis process is much more complex than electrospinning method. Recently, spinel ferrites (MFe2 O4 , M= Co, Cu, Ni, Mn, Zn) have garnered significant attention for their role in waste water treatment, fabrication of super-capacitors, electromagnetic interference (EMI) shielding for high frequency ∗ Corresponding author. E-mail address: [email protected] (M. Shandilya). https://doi.org/10.1016/j.nanoso.2020.100428 2352-507X/© 2020 Elsevier B.V. All rights reserved.

bands [4–7]. Due to their innate remarkable properties like high surface to volume ratio, low electrical conductivity, biocompatibility, modifiability and robust ferromagnetic properties at room temperature. However, the ceramic composites of ferrites are limited by deleterious reactions at the interface regions hindering practical applicability of such materials [8]. In order to combat this problem, the development of polymer-based nanofiber membrane has become a subject of intensive research [9–12]. Moreover, the incorporation of inorganic magnetic materials within the polymer matrix can enhance its performance for aforementioned applications. Poly(vinylidene fluoride) (PVDF) is a semicrystalline polymer exhibiting excellent properties like high elasticity, transparency and mechanical flexibility [13,14]. Though the feasibility of electrospun polymer-complex ferrite nanostructure with desirable functionalities is a promising candidate for various applications, however, one issue suppressing the extensive development of ferrites is the limited availability of methods capable of accessing complex compositions [15]. The method of preparation plays a pivotal role to enhance the structural and magnetic

2

G.A. Kaur, M. Shandilya, P. Rana et al. / Nano-Structures & Nano-Objects 22 (2020) 100428

Fig. 1. Schematic representation of preparing Co0.5 Ni0.5 Fe2 O4 -PVDF nanofiber membrane.

properties of the Co0.5 Ni0.5 Fe2 O4 nanoparticles [16]. We anticipate that the synergistic effect of polymer- ferrite nanostructure materials-based nanofiber membrane can help to ameliorating the quality of water without compromising on human health as well as can prove to be suitable candidates for high-frequency electronic device applications. In this study, we report the structural and magnetic properties of novel Co0.5 Ni0.5 Fe2 O4 -PVDF composite nanofiber membrane by using electrospinning technique. The Co0.5 Ni0.5 Fe2 O4 nanoparticles were prepared with the help of sol–gel combustion method, which yields homogeneous and ultrafine powder. The ease of fabrication and functionalization of nanofiber membrane via electrospinning technique with outstanding properties like high porosity, robust mechanical strength, high surface area, controllable pore sizes, and small fiber-to-fiber distance were realized. The nanofiber membrane can be used as a surface modification layer, which adds more functionality to the Co0.5 Ni0.5 Fe2 O4 nanostructure. The structural and magnetic properties of the fabricated Co0.5 Ni0.5 Fe2 O4 -PVDF nanofiber membrane were studied with the help of XRD, FTIR, FE-SEM and VSM. 2. Materials and method 2.1. Synthesis of Co0.5 Ni0.5 Fe2 O4 nanoparticles The schematic representation to synthesize nanofiber membrane is shown in Fig. 1. The starting chemicals were weighed according to the desired composition Co0.5 Ni0.5 Fe2 O4 . All chemicals with a high purity of 99.99% were purchased from Sigma-Aldrich. Cobalt Nitrate [Co(NO3 )2 ·6H2 O], Ferric nitrate [Fe(NO3 )3 ·9H2 O], and Nickel nitrate [Ni(NO3 )2 .6H2 O] were used as starting raw materials to form the precursor solution. All the raw materials were dissolved in deionized water using magnetic stirrer and citric acid was added to this mixture to initiate the combustion process. The pH of the solution was maintained by adding a small amount of ammonia to the aforementioned continuously stirring solution. The solution was heated under stirring at 80 ◦ C causing the excess solvent to evaporate to form a gel. The residual was then transferred into a bowl and heated up to 200 ◦ C to form a dry gel. The whole gel started burning due to the auto-combustion effect and transformed into powder form. Finally, the powder was calcined at 900 ◦ C for 5 h to obtain the final product.

Fig. 2. Comparison between XRD plot of Co0.5 Ni0.5 Fe2 O4 nanoparticles and Co0.5 Ni0.5 Fe2 O4 -PVDF nanofiber membrane.

2.2. Preparation of Co0.5 Ni0.5 Fe2 O4 -PVDF nanofiber membrane 3:2 N, N-Dimethylformamide (DMF; Loba Chemie) /Acetone (Sigma Aldrich) was used to disperse PVDF (Polyvinylidene Fluoride; (Mw=2,75,000 g/mole, Mn=1,07,000 g/mole, Sigma Aldrich) pellets (10 wt% solution) at 50 ◦ C. 2 wt% of Co0.5 Ni0.5 Fe2 O4 nanoparticles (w.r.t polymer) were separately mixed with the same solvent mixture and stirred for 1h with the help of magnetic stirrer. Finally, both the prepared solutions were mixed together and constantly stirred at 50 ◦ C for 24 h until the desired viscosity was achieved. The as prepared solution was filled into the plastic syringe of 5ml and the spinneret was clipped with the positive terminal of the high voltage power supply, while the other wire was clipped to the aluminum foil placed on the collector plate. The solution was fed at the rate of 0.5 mL/h. The distance between the collector and the tip of the spinneret was 15 cm, and the applied voltage was set at 16 kV. After the completion of electrospinning process, the electrospun nanofiber membrane was peeled off from the aluminum foil. 2.3. Instruments used for characterization The electrospun cobalt nickel ferrite nanofiber membrane was characterized by XRD, FE-SEM, FTIR, and VSM techniques. The structural properties were studied by XRD pattern using PW3040 Philips X-ray diffractometer with CuKα radiation (λ = 0.15406 nm) and FT-spectra by using Cary630, Agilent Technologies FTIR spectrophotometer in the range of 4000–650 cm-1 . The lattice morphology and structure of these samples were characterized by FE-SEM (Hitachi SU8010 series). The magnetic properties of the as-spun nanofibers were studied at room temperature with the help of vibrating sample magnetometer (VSM; Cryogenic). 3. Results and discussion 3.1. Structural properties 3.1.1. X-ray Diffraction (XRD) Analysis The study of structural properties was carried out with the help of XRD technique as shown in Fig. 2. The nanofiber membrane composite showed all the characteristic peaks of the Co0.5 Ni0.5 Fe2 O4 nanoparticles i.e. 30.2◦ , 35.7◦ , 37.2◦ , 43.4◦ , 54.1◦ , 57.3◦ and 62.9◦ with well pronounced spinel cubic structure

G.A. Kaur, M. Shandilya, P. Rana et al. / Nano-Structures & Nano-Objects 22 (2020) 100428

3

Fig. 3. Comparison between FWHM of diffracted peaks as observed from XRD analysis.

Fig. 4. (a) Scherrer plot, (b) Williamson–Hall (W–H) plot, (c) Size-Strain plot for Co0.5 Ni0.5 Fe2 O4 -PVDF nanofiber membrane and pristine Co0.5 Ni0.5 Fe2 O4 nanoparticles.

4

G.A. Kaur, M. Shandilya, P. Rana et al. / Nano-Structures & Nano-Objects 22 (2020) 100428

Fig. 5. FT-IR of (a) PVDF nanofiber membrane and (b) Co0.5 Ni0.5 Fe2 O4 -PVDF nanofiber membrane.

indexed as the plane of (220), (311), (222), (400), (422), (511), and (440) respectively [17,18]. A plausible reason for the peaks observed at 2θ = 24.1◦ , 33.2◦ , 40.9◦ , 49.5◦ , 62.5◦ , and 64.0◦ was due to the presence of hematite phase of iron oxide which can be indexed according to the standard JCPDS card no. #871166. The presence of polymer PVDF reduces the peak intensity of the Co0.5 Ni0.5 Fe2 O4 -PVDF nanofiber membrane [19]. Additionally, the peaks of nanofiber membrane were slightly shifted towards smaller angle with two additional characteristic peaks observed at 2θ = 18.5◦ and 20.1◦ which indicated the presence of α and β phase of PVDF respectively. The parameters of structural properties are mentioned in Table 1. It was observed that the value of lattice parameters and volume of the cell decreases when nanoparticles were embedded within the polymer PVDF. The average crystallite size of Co0.5 Ni0.5 Fe2 O4 nanoparticles was calculated from the Full-Width Half Maxima (FWHM) of diffracted planes by using Debye–Scherrer’s relation [20]. given

by Eq. (1): d=

k·λ

β · cos θ

(1)

where d is the average crystallite size, k is Scherrer’s constant, λ is the wavelength of radiation for Cu Ka, θ is diffracted angle and β is FWHM of diffracted peaks. The physical parameters such as lattice strain and crystallite size are evaluated with the help of X-ray peak broadening analysis. It can be clearly seen from Eq. (1) that the crystallite size (d) of nanoparticles is inversely proportional to the peak broadening (β ) of the diffracted peaks. Fig. 3 shows the comparison between the values of FWHM of pristine Co0.5 Ni0.5 Fe2 O4 nanoparticles and PVDF embedded Co0.5 Ni0.5 Fe2 O4 nanoparticles. Thus, it can be concluded that as the Co0.5 Ni0.5 Fe2 O4 nanoparticles were embedded within the polymer, the crystallite size was reduced drastically. Since the peak intensity depends on the content of the simple cell, it was also be observed that the peak intensity of the Co0.5 Ni0.5 Fe2 O4

G.A. Kaur, M. Shandilya, P. Rana et al. / Nano-Structures & Nano-Objects 22 (2020) 100428

5

Table 1 Structural parameters of Co0.5 Ni0.5 Fe2 O4 nanoparticles and Co0.5 Ni0.5 Fe2 O4 -PVDF nanofiber membrane. Co0.5 Ni0.5 Fe2 O4

Co0.5 Ni0.5 Fe2 O4 -PVDF

Lattice parameters (A◦ )

a = b = c = 8.3625

Volume (A◦ )

584.80

dobs

dcal

hkl

2.9568 2.5129 2.4149 2.0832 1.6937 1.6065 1.4763

2.9566 2.5214 2.4140 2.0906 1.7070 1.6094 1.4783

220 311 222 400 422 511 440

Lattice parameters (A◦ )

a = b = c = 8.3357

Volume

579.20

dobs

dcal

hkl

2.9471 2.5167 2.4175 2.0921 1.7014 1.6069 1.4786

2.9471 2.5133 2.4063 2.0839 1.7015 1.6042 1.4736

220 311 222 400 422 511 440

Table 2 Crystallite size from Scherrer, Williamson–Hall (W–H) and Size-Strain plot (SSP) method. Sample

D (nm) (Scherrer Method)

D (nm) (W–H method)

D (nm) (SSP method)

Co0.5 Ni0.5 Fe2 O4 Co0.5 Ni0.5 Fe2 O4 -PVDF

66.39 55.47

42.38 34.41

60.52 52.18

nanoparticles is decreased in the nanofiber membrane. The Scherrer plot of Co0.5 Ni0.5 Fe2 O4 - PVDF nanofiber membrane and pristine Co0.5 Ni0.5 Fe2 O4 nanoparticles is shown in Fig. 4(a) with a linear relationship between y- co-ordinate as cos θ and x-coordinate as 1/β . The βsize is the peak broadening due to the fine grain size, βstrain is the peak broadening due to the lattice strain and βinst . is the peak broadening due to the instrumental effects. Estimation of the instrumental broadening (βinst .) is desirable to correct the width of different peaks and was determined by fitting the XRD patterns to a Gaussian function. The crystallite size and lattice strain can evaluated by analyzing the XRD peak broadening, using the Williamson–Hall (W–H) method [21,22] as shown in Fig. 4(b). The size and strain-induced broadening are deconvoluted by considering the peak width as a function of 2θ . 2 2 2 2 βobs = βsize + βstrain + βinst .

(2)

Also, 2 2 2 βtot = βobs . − βinst .

(3)

OR 2 2 2 βtot = βstrain + βsize [from (1)]

(4)

Where

βsize. =

Kλ

(5)

Dcosθ

βstrain = 4ε tan θ

(6)

Substituting the values of Eqs. (5) and (6) in Eq. (4) and multiplying by cosθ , we get Eq. (7) which is a representation of UDM (Uniform Deformation Model) method [23].

β cos θ =

K ·Λ D

+ 4e sin θ

(7)

where D = crystallite size K = shape factor or Scherrer constant, 0.9 to 1.0 depending upon grain shape ε = effective lattice strain in material The size-strain plot (SSP) method was also used to determine the crystallite size and lattice strain of the crystal system as shown in Eq. (8). (dβ cos θ )2 =

K D

(d2 β cos θ ) +

( ϵ )2 2

(8)

Similar to Scherrer and W–H plots, in case of SSP (dβ cosθ )2 is plotted with respect to d2 β cosθ as shown in Fig. 4(c). Among all methods, SSP method is highly preferable to define the crystal perfection [24,25]. The FWHM peaks of the instrumental broadening and observed from the samples were used to determine the crystallite size and lattice strain. It was observed that the crystallite size decreases with the addition of polymer PVDF. The Williamson–Hall (W–H) plot of Co0.5 Ni0.5 Fe2 O4 -PVDF nanofiber membrane and pristine Co0.5 Ni0.5 Fe2 O4 nanoparticles is shown in Fig. 4(b) with a linear relationship between y- co-ordinate as FWHMtot cosθ and x-co-ordinate as 4sin θ . The value of lattice strain and crystallite size were extracted from the intercept and the slope of the linear fit made to the plot. The aforementioned parameters were strongly affected by the peak broadening (widening) of the XRD spectra. It was also observed that the Co0.5 Ni0.5 Fe2 O4 nanoparticles exhibit a positive lattice strain which indicated that the crystal system is under tensile strain [26,27]. whereas a negative lattice strain was observed for Co0.5 Ni0.5 Fe2 O4 -PVDF nanofiber membrane which indicated that it is under compressive strain. This compressive strain is due to the presence of polymer PVDF in the nanofiber membrane. The value of crystallite size for Co0.5 Ni0.5 Fe2 O4 -PVDF nanofiber membrane and pristine Co0.5 Ni0.5 Fe2 O4 nanoparticles by Scherrer, Williamson– Hall (W–H) and Size-Strain Plot (SSP) method are tabulated in Table 2. 3.1.2. Fourier transform infrared radiation (FTIR) spectroscopy The different configuration modes of functional groups present in the sample were carefully speculated by using Fourier Transform Infrared Radiation (FTIR) technique in the wave number range 4000–650 cm−1 as shown in Fig. 5[(a), (b)]. The peaks observed at 683, 728, and 1173 cm−1 corresponds to the characteristic absorption of the α -phase whereas 844, 1069, 1278 and 1401 cm−1 indicated the presence of PVDF with β -phase bands [28–30]. The amorphous phase of the polymer PVDF was also observed at 879 cm−1 [31]. It was observed that the peak intensity β -phase bands in nanofiber membrane [as shown in Fig. 5(b)] enhanced on the incorporation of Co0.5 Ni0.5 Fe2 O4 nanoparticles. This influence of Co0.5 Ni0.5 Fe2 O4 nanoparticles on the β -phase bands of PVDF-matrix implied that the ferroelectric property of the sample increased [32]. The relative β -phase fraction F(β ) for the pristine PVDF nanofiber membrane was determined by using Eq. (9) assuming that the infrared absorption follows the Lambert–Beer law [33,34] and found to be 49.5% and increased to 58.5% with the addition of Co0.5 Ni0.5 Fe2 O4 nanoparticles. F (β ) =

Aβ 1.23Aα + Aβ

(9)

6

G.A. Kaur, M. Shandilya, P. Rana et al. / Nano-Structures & Nano-Objects 22 (2020) 100428

Fig. 6. FE-SEM images of (a) Co0.5 Ni0.5 Fe2 O4 nanoparticles, [(b), (c)] Co0.5 Ni0.5 Fe2 O4 -PVDF nanofiber membrane, and (d) TEM image of Co0.5 Ni0.5 Fe2 O4 nanoparticles inset (d) shows the TEM image of Co0.5 Ni0.5 Fe2 O4 -PVDF nanofiber membrane.

Fig. 7. Energy Dispersive X-ray (EDX) spectrograph of Co0.5 Ni0.5 Fe2 O4 -PVDF nanofiber membrane.

where Aβ and Aα are the absorbance at 844 cm−1 and 683 cm−1 respectively. 3.1.3. Field-emission scanning electron microscopy (FE-SEM) The morphology of the pristine Co0.5 Ni0.5 Fe2 O4 nanoparticles and composite Co0.5 Ni0.5 Fe2 O4 -PVDF nanofiber membrane

was examined using FE-SEM images with different magnifications. Fig. 6(a) show the grain distribution of the synthesized Co0.5 Ni0.5 Fe2 O4 nanoparticles and revealed the dense, compact and uniform distribution of the nanoparticles with the existence of soft agglomeration between them. The mean particle size of Co0.5 Ni0.5 Fe2 O4 nanoparticles was found to be ∼370 ± 50 nm. Fig. 6(b) demonstrates the randomnly oriented Co0.5 Ni0.5 Fe2 O4 PVDF nanofiber membrane. Closer examination of the micrograph revealed that the Co0.5 Ni0.5 Fe2 O4 nanoparticles were embedded within the polymeric nanofiber membrane with fiber diameter lying within the range of ∼200 ± 50 nm i.e. the agglomeration of the nanoparticles was controlled by the polymer PVDF to a great extent which further reduced the crystallite size of the nanoparticles as shown in Fig. 6(c). It was observed that the randomly oriented nanofibers were free of voids or beads due to homogenous interactions between the organic polymer and inorganic phase of the Co0.5 Ni0.5 Fe2 O4 nanoparticles. This embedment of Co0.5 Ni0.5 Fe2 O4 nanoparticles was responsible for creating functional surface with hierarchical structure. As a typical electrospun fibrous structure, the porosity of the magnetic membrane can easily separate or adsorb the contaminants from waste water [35]. Fig. 6(d) show the TEM image of the Co0.5 Ni0.5 Fe2 O4 nanoparticles with an average particle size of ∼70.5 nm. The inset of Fig. 6(d) show the TEM image of nanofiber membrane which clearly reveals the presence of nanoparticles embedded within the polymer matrix PVDF. Furthermore, the Energy Dispersive X-ray (EDX) spectrograph confirm the stoichiometric presence of the expected elements in the Co0.5 Ni0.5 Fe2 O4 -PVDF nanofiber membrane as shown in Fig. 7.

G.A. Kaur, M. Shandilya, P. Rana et al. / Nano-Structures & Nano-Objects 22 (2020) 100428

7

Fig. 8. VSM plots of (a) Co0.5 Ni0.5 Fe2 O4 pristine nanoparticles and (b) Co0.5 Ni0.5 Fe2 O4 -PVDF nanofiber membrane.

Table 3 Magnetic properties and parameters of Co0.5 Ni0.5 Fe2 O4 and Co0.5 Ni0.5 Fe2 O4 -PVDF. Co0.5 Ni0.5 Fe2 O4

Co0.5 Ni0.5 Fe2 O4 -PVDF

Ms (emu/g)

Mr (emu/g)

Hc (Tesla)

Ms (emu/g)

Mr (emu/g)

Hc (Tesla)

90.316

39.734

0.140

2.443

0.2086

0.7819

3.2. Magnetic properties 3.2.1. Vibrating sample magnetometer (VSM) analysis Vibrating Sample Magnetometer was used to comprehend the magnetic properties for both the nanofiber membrane and nanostructure material at room temperature. The parameters of magnetic properties for aforementioned samples are mentioned in Table 3. The representative magnetic hysteresis (M-H) curve of the pristine Co0.5 Ni0.5 Fe2 O4 nanostructure and Co0.5 Ni0.5 Fe2 O4 PVDF nanofiber membrane are shown in Fig. 8[(a), (b)]. The nanofiber membrane demonstrated a non-linear and reversible behavior with a clear narrow hysteretic loop with high coercivity (Hc), low remanence (Mr), high energy loss and low-saturation magnetization (Ms) as compared to the nanostructure material [as shown in Fig. 8(a)]. The magnetic moment of each and individual magnetic ferrite particle is responsible for the magnetic properties induced within the magnetically dead polymer PVDF [36]. The high coercivity of the nanofiber membrane is due to the non-magnetic phase of polymer PVDF which becomes a barrier for domain interactions and domain misalignment [37]. The high value of Hc observed for the nanofiber membrane might be attributed to the compressive strain of the crystal system in the presence of polymer PVDF [38]. In fact, coercivity of a sample is dependent on the particle size of the magnetic nanoparticles [39]. Thus, the reduction of particle size of Co0.5 Ni0.5 Fe2 O4 is also accountable for the high coercivity in the case of nanofiber membrane [40]. Generally, CoFe2 O4 is known to exhibit high coercivity but addition of Nickel (Ni) decreases its value and helps to suppress any energy loss [41]. The loop confirms the softferromagnetic nature of the Co0.5 Ni0.5 Fe2 O4 nanoparticles at room temperature. Since the polymer PVDF is non-magnetic in nature, the addition of Co0.5 Ni0.5 Fe2 O4 nanoparticles induces a clear magnetic hysteresis with high Hc for the nanofiber membrane as shown Fig. 8(b). The crystallinity and particle size of the nanostructure material might be responsible for the robust magnetic

properties in case of nanofiber membrane which clearly indicates an easier and higher separation ability of water contaminants in the presence of magnetic field. 4. Conclusion In summary, the Co0.5 Ni0.5 Fe2 O4 -PVDF nanofiber membrane was successfully prepared via electrospinning technique. XRD and FTIR results show the well crystallized phase of the nanoparticles and nanofiber membrane. FE-SEM images revealed the dense and compact Co0.5 Ni0.5 Fe2 O4 nanoparticles with mean particle size 370 ± 50 nm whereas the average diameter of Co0.5 Ni0.5 Fe2 O4 PVDF nanofiber membrane was found to be ∼200 ± 50 nm. Moreover, the TEM image also confirmed the Co0.5 Ni0.5 Fe2 O4 nanoparticles embedment within the nanofiber membrane. Addition of Ni proves to mitigate any energy loss and exhibits a clear hysteretic loop elucidated by VSM analysis and incorporation of Co0.5 Ni0.5 Fe2 O4 nanostructure material enhances the magnetic properties of nanofiber membrane. These systematic studies reveal that ferritebased nanofiber membrane have a great potential to compete with the existing water purification technologies, spintronics devices and magnetic sensors. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. CRediT authorship contribution statement Gun Anit Kaur: Data curation, Writing - original draft. Mamta Shandilya: Conceptualization, Methodology, Software, Writing - review & editing. Poonam Rana: Visualization, Investigation. Shweta Thakur: Software, Validation. Poonam Uniyal: Supervision, Data curation.

8

G.A. Kaur, M. Shandilya, P. Rana et al. / Nano-Structures & Nano-Objects 22 (2020) 100428

Acknowledgment The authors are grateful to the Defence Research and Development Organization (DRDO), Govt. of India, for financial support under the research project ERIP/ER/1303129/M/01/1564. References [1] J.H. Kim, H.S. Ganapathy, S.S. Hong, Y.S. Gal, K.T. Lim, Preparation of polyacrylonitrile nanofibers as a precursor of carbon nanofibers by supercritical fluid process, J. Supercrit. Fluids 47 (1) (2008) 103–107, http: //dx.doi.org/10.1016/j.supflu.2008.05.011. [2] L. Zhao, Y. Li, Y. Zhao, Y. Feng, W. Feng, X. Yuan, Carbon nanotubes grown on electrospun polyacrylonitrile-based carbon nanofibers via chemical vapor deposition, Appl. Phys. A 106 (2012) 863–869, http://dx.doi.org/10. 1007/s00339-012-6770-4. [3] G. Zhong, T. Iwasaki, H. Kawarada, I. Ohdomari, Synthesis of highly oriented and dense conical carbon nanofibers by a DC bias-enhanced microwave plasma CVD method, Thin Solid Films 464 (2004) 315–318, http://dx.doi. org/10.1016/j.tsf.2004.06.051. [4] S.F. Soares, T. Fernandis, T. Trindade, Ana L. Daniel-da Silva, Recent advances on magnetic biosorbents and their applications for water treatment, Env. Chem. Lett. (2019) 1–14, http://dx.doi.org/10.1007/s10311-01900931-8. [5] L. Madhura, S. Singh, S. Kanchi, M. Sabela, K. Bisetty, Inamuddins, nanotechnology-based water quality management for wastewater treatment, Env. Chem. Lett 17 (2019) 65–121, http://dx.doi.org/10.1007/s10311018-0778-8. [6] M. Saini, R. Shukla, A. Kumar, Cd2+ substituted nickel ferrite doped polyaniline nanocomposites as effective shield against electromagnetic radiation in X-band frequency, J. Magn. Magn. Mater. 491 (2019) 165–549, http://dx.doi.org/10.1016/j.jmmm.2019.165549. [7] M. Saini, R. Shukla, S. Singh, Nickel doped cobalt ferrite/poly (Ani-coPy) multiphase nanocomposite for EMI shielding application, J. Inorg. Organomet. Polym. Mater. (2019) 1–10, http://dx.doi.org/10.1007/s10904019-01163-7. [8] L. Mitoseriu, V. Buscaglia, M. Viviani, M.T. Buscaglia, I. Pallecchi, C. Harnagea, A. Testino, V. Trefiletti, P. Nanni, A.S. Siri, BaTiO3–(Ni0. 5Zn0. 5) Fe2O4 ceramic composites with ferroelectric and magnetic properties, J. Eur. Ceram. Soc. 27 (2007) 4379–4382, http://dx.doi.org/10.1016/ j.jeurceramsoc.2007.02.167. [9] K. Sun, J. Dong, Z. Wang, G. Fan, Q. Hou, L. An, M. Dong, R. Fan, Z. Guo, Tunable negative permittivity in flexible graphene/PDMS metacomposites, J. Phys. Chem. C 123 (2019) 23635–23642, http://dx.doi.org/10.1021/acs. jpcc.9b06753. [10] K. Sun, J. Xin, Y. Li, Z. Wang, Q. Hou, X. Li, X. Wu, R. Fan, K.L. Choy, Negative permittivity derived from inductive characteristic in the percolating Cu/EP metacomposites, J. Mater. Sci. Technol. 35 (2019) 2463–2469, http://dx.doi. org/10.1016/j.jmst.2019.07.015. [11] J.-P. Méricq, J. Mendret, S. Brosillon, C.J.C.E.S. Faur, High performance PVDFTiO2 membranes for water treatment, Chem. Eng. Sci. 123 (2015) 283–291, http://dx.doi.org/10.1016/j.ces.2014.10.047. [12] J. Wongi, J. Yun, K. Jeon, H. Byun, PVdF/graphene oxide hybrid membranes via electrospinning for water treatment applications, Rsc Adv. 5 (2015) 46711–46717, http://dx.doi.org/10.1039/C5RA04439A. [13] D.R. Jennifer, S. Peldszus, P.M. Huck, X. Feng, Modification of poly (vinylidene fluoride) ultrafiltration membranes with poly (vinyl alcohol) for fouling control in drinking water treatment, Water Res. 43 (2009) 4559–4568, http://dx.doi.org/10.1016/j.watres.2009.08.008. [14] X. Zhiwei, T. Wu, J. Shi, K. Teng, W. Wang, M. Ma, J. Li, X. Qian, C. Li, J. Fan, Photocatalytic antifouling PVDF ultrafiltration membranes based on synergy of graphene oxide and TiO2 for water treatment, J. Membr. Sci. 520 (2016) 281–293, http://dx.doi.org/10.1016/j.memsci.2016.07.060. [15] Ayman E. Elkholy, F.E.T. Heakal, N.K. Allam, Nanostructured spinel manganese cobalt ferrite for high-performance supercapacitors, RSC Adv. 7 (2017) 51888–51895, http://dx.doi.org/10.1039/C7RA11020K. [16] M. Vadivel, R.R. Babu, K. Ramamurthi, M. Arivanandhan, Effect of PVP concentrations on the structural, morphological, dielectric and magnetic properties of CoFe2O4 magnetic nanoparticles, Nano-Struct. Nano-Objects 11 (2017) 112–123, http://dx.doi.org/10.1016/j.nanoso.2017.08.005. [17] S.S. Abbas, I.H. Gul, S. Ameer, M. Anees, Ce-substituted Co 0.5 Ni 0.5 Fe 2 O 4: Structural, morphological, electrical, and dielectric properties, Electron. Mater. Lett. 11 (2015) 100–108, http://dx.doi.org/10.1007/s13391-0143340-2. [18] M. Almessiere, Y. Slimani, M. Sertkol, M. Nawaz, A. Sadaqat, A. Baykal, I. Ercan, B. Ozçelik, Effect of Nb3+ substitution on the structural, magnetic, and optical properties of Co0. 5Ni0. 5Fe2O4 nanoparticles, Nanomaterials 9 (2019) 430, http://dx.doi.org/10.3390/nano9030430.

[19] P.P. Dorneanu, C. Cojocaru, N. Olaru, P. Samoila, A. Airinei, L. Sacarescu, Electrospun PVDF fibers and a novel PVDF/CoFe2O4 fibrous composite as nanostructured sorbent materials for oil spill cleanup, Appl. Surf. Sci. 424 (2017) 389–396, http://dx.doi.org/10.1016/j.apsusc.2017.01.177. [20] A.L. Patterson, The scherrer formula for X-ray particle size determination, Physical review 56 (1939) 978, http://dx.doi.org/10.1103/PhysRev.56.978. [21] M. Shandilya, G.A. Kaur, Low temperature crystal growth of lead-free complex perovskite nano-structure by using sol–gel hydrothermal process, J. Solid State Chem. 280 (2019) 120988, http://dx.doi.org/10.1016/j.jssc. 2019.120988. [22] K. Venkateswarlu, A.C. Bose, N. Rameshbabu, X-ray peak broadening studies of nanocrystalline hydroxyapatite by Williamson–Hall analysis, Physica B 405 (2010) 4256–4261, http://dx.doi.org/10.1016/j.physb.2010.07.020. [23] S. Ilyas, B. Abdullah, D. Tahir, X-ray diffraction analysis of nanocomposite Fe3O4/activated carbon by Williamson–Hall and size-strain plot methods, Nano-Struct. Nano-Objects 20 (2019) 100396, http://dx.doi.org/10.1016/j. nanoso.2019.100396. [24] B.R. Kumar, B. Hymavathi, X-ray peak profile analysis of solid-state sintered alumina doped zinc oxide ceramics by Williamson–Hall and size-strain plot methods, J. Asian Ceram. Soc. 5 (2017) 94–103, http://dx.doi.org/10.1016/ j.jascer.2017.02.001. [25] A.K. Zak, W.A. Majid, M.E. Abrishami, R. Yousefi, X-ray analysis of ZnO nanoparticles by Williamson–Hall and size–strain plot methods, Solid State Sci. 13 (2011) 251–256, http://dx.doi.org/10.1016/j.solidstatesciences.2010. 11.024. [26] Y.T. Prabhu, K.V. Rao, V.S.S. Kumar, B.S. Kumari, X-ray analysis by Williamson-Hall and size-strain plot methods of ZnO nanoparticles with fuel variation, World J. Nano Sci. Eng. 4 (2014) 21, http://dx.doi.org/10. 4236/wjnse.2014.41004. [27] D. Chicot, J. Mendoza, A Zaoui, G. Louis, V. Lepingle, F. Roudet, J. Lesage, Mechanical properties of magnetite (Fe3O4), hematite (α -Fe2O3) and goethite (α -FeO· OH) by instrumented indentation and molecular dynamics analysis, Mater. Chem. Phys. 129 (2011) 862–870, http://dx.doi.org/10. 1016/j.matchemphys.2011.05.056. [28] K. Cai, X. Han, Y. Zhao, R. Zong, F. Zeng, D. Guo, A green route to a low cost anisotropic MoS2/Poly (vinylidene fluoride) nanocomposite with ultrahigh electroactive phase and improved electrical and mechanical properties, ACS Sustain. Chem. Eng. 6 (2018) 5043–5052, http://dx.doi.org/10.1021/ acssuschemeng.7b04697. [29] D. Guo, K. Cai, Y. Wang, A distinct mutual phase transition in a new PVDF based lead-free composite film with enhanced dielectric and energy storage performance and low loss, J. Mater. Chem. C 5 (2017) 2531–2541, http://dx.doi.org/10.1039/C6TC04648G. [30] L. Ourry, S. Marchesini, M. Bibani, S. Mercone, S. Ammar, F. Mammeri, Influence of nanoparticle size and concentration on the electroactive phase content of PVDF in PVDF–CoFe2O4-based hybrid films, Phys. Status Solidi A 212 (2015) 252–258, http://dx.doi.org/10.1002/pssa.201431563. [31] T. Prabhakaran, J. Hemalatha, Ferroelectric and magnetic studies on unpoled poly (vinylidine fluoride)/Fe3O4 magnetoelectric nanocomposite structures, Mater. Chem. Phys. 137 (2013) 781–787, http://dx.doi.org/10. 1016/j.matchemphys.2012.09.064. [32] P.D. Prasad, J. Hemalatha, Enhanced dielectric and ferroelectric properties of cobalt ferrite (CoFe2O4) fiber embedded polyvinylidene fluoride (PVDF) multiferroic composite films, Mater. Res. Exp. 6 (2019) 094007, http: //dx.doi.org/10.1088/2053-1591/ab30af. [33] V. Sencadas, R. Gregorio Filho, S. Lanceros-Mendez, Processing and characterization of a novel nonporous poly (vinilidene fluoride) films in the β phase, J. Non-Crystal. Solids 352 (2006) 2226–2229, http://dx.doi.org/10. 1016/j.jnoncrysol.2006.02.052. [34] L.M.S. Medina, R.M. Negri, Dielectric behavior and electro-magnetic coupling at room temperature in BiFeO3/PVDF and CoFe2O4/PVDF composites, J. Phys. Chem. C 121 (2017) 27683–27692, http://dx.doi.org/10.1021/acs. jpcc.7b07800. [35] A. Azimi, A. Azari, M. Rezakazemi, M. Ansarpour, Removal of heavy metals from industrial wastewaters: A review, Chem. Bio. Eng. Rev. 4 (2017) 37–59, http://dx.doi.org/10.1002/cben.201600010. [36] J. Rani, K. Yadav, S. Prakash, Structural and magnetodielectric properties of poly (vinylidene-fluoride)-[0.8 (Bi0. 5Na0. 5) TiO3-0.2 CoFe2O4] polymer composite films, Composites B 79 (2015) 138–143, http://dx.doi.org/10. 1016/j.compositesb.2015.04.041. [37] C. Behera, R. Choudhary, Electrical and multiferroic characteristics of PVDFMnFe2O4 nanocomposites, J. Alloys Compd. 727 (2017) 851–862, http: //dx.doi.org/10.1016/j.jallcom.2017.08.196. [38] Y. Liu, Q. Zhan, B. Wang, H. Li, Y. Wu, B. Chen, D. Sun, S. Mao, R.W. Li, Modulation of magnetic anisotropy in flexible multiferroic FeGa/PVDF heterostructures under various strains, IEEE Trans. Magn. 51 (2015) 1–4, http://dx.doi.org/10.1109/TMAG.2015.2436413. [39] M. Houshiar, F. Zebhi, Z.J. Razi, A. Alidoust, Z. Askari, Synthesis of cobalt ferrite (CoFe2O4) nanoparticles using combustion, coprecipitation, and precipitation methods: A comparison study of size, structural, and magnetic properties, J. Magn. Magn. Mater. 371 (2014) 43–48, http://dx.doi.org/10. 1016/j.jmmm.2014.06.059.

G.A. Kaur, M. Shandilya, P. Rana et al. / Nano-Structures & Nano-Objects 22 (2020) 100428 [40] J. Xiang, Y. Chu, X. Shen, G. Zhou, Y. Guo, Electrospinning preparation, characterization and magnetic properties of cobalt–nickel ferrite (Co1xNixFe2O4) nanofibers, J. Colloid Interface Sci. 376 (2012) 57–61, http: //dx.doi.org/10.1016/j.jcis.2012.02.068.

9

[41] M.M. Naik, H.B. Naik, G. Nagaraju, M. Vinuth, K. Vinu, R. Viswanath, Green synthesis of zinc doped cobalt ferrite nanoparticles: Structural, optical, photocatalytic and antibacterial studies, Nano-Struct. Nano-Objects 19 (2019) 100322, http://dx.doi.org/10.1016/j.jssc.2019.120988.