Introduction

In recent years, perovskite materials have been well studied. The most prominent ABO3 ferroelectric materials have attracted considerable attention as catalysts due to their geometric and electronic stability, higher dissolution resistance in aqueous and non-aqueous solutions, and cost-efficiency. There is rare existence of crystalline multiferroic compounds in which ferromagnetism and ferroelectricity coexist at room temperature1. Due to their potential application in the developing field of information storage, spintronics, and multiple-state memory storage devices, such compounds are currently under intensive study2,3. Enormous attempts were made to improve the room temperature ferromagnetism and ferroelectricity in perovskite ceramics. Various approaches are underway to explore the possibility of synthesizing materials with superior multiferroic efficiency. Another possible method of magnetic doping is of TM (transition metal) ions (Fe3+, Co2+, Ni2+, Mn2+, etc.) through ferroelectric materials4,5.

A major class of ferroelectric material that shows a piezoelectric effect and a high dielectric permittivity for technological applications, such as transducers, surface acoustic waves (SAW), and ferroelectric random-access memories (FeRAM) devices6. In the composition of perovskite ABO3, both cations (A and B), whereas the A atoms are greater than the B atoms. The ionic radii of Fe3+ (0.645 Å) are larger than Ti4+ (0.605 Å), whereas Ba2+ has larger ionic radii (1.35 Å). BTO has a general ABO3 configuration in which Ba2+ and O2− ions create a close-packed cubic lattice with Ti4+ ions occupying the oxygen (O2−) generated octahedral holes. The BaTiO3 structure has a three-dimensional array of TiO6 corners sharing octahedral with Ba2+ ions in the 12-fold cavities between the polyhedra. The arrangement of the atoms is known as the close-packed array of the A2+ and O2− ions together7. In addition to its structure and size, the properties of BTO depend on its chemical composition. Doping with equivalent elements, perovskite material shows interesting electrical characteristics for the BaTiO3 based on the chemical states of the components and the surface chemistry of the specimens. However, the major phenomenon of these nanomaterials is the partial substitution of the cations at the A and B sites of ABO3 as well as their ability to preserve the stability in the crystal structure of uncommon mixed oxidation states8,9. An interesting aspect of Ba, Ti, Fe, and O ions in bulk materials has been discussed concerning both electronic deficiency and surface toxicity. Several recent studies have been addressed based on photoelectron spectroscopy for the chemical analysis (ESCA) of calcined BaTiO3 nanomaterial doped with Fe3+ ions9,10,11,12. ESCA or XPS is a surface morphological technique that can be used to obtain information on the chemical state or valence state and the electronic information at the core level for the constituent element9,10,11,12. Pure BaTiO3 has lower ionic conductivity and acts as an insulator at room temperature. The defect model indicates that the substitution of the Ti-site by the acceptor impurities is the reason for the formation of charge carrier and oxygen vacancies that increase both the ionic and electronic conductivity. The dominant charge carrier depends on the synthesis conditions and the amount of unintentional impurities of the acceptor and the donor. In BaTiO3 ceramics, Fe3+ ions usually replace Ti4+, where Fe3+ ions are considered to have a 3 + valence. Therefore oxygen vacancy should be created to preserve the charge neutrality of the perovskite structure (BaTi1-xFexO3-δ, δ-oxygen vacancy). Abdel Aal et al. 2014 successfully prepared BaTi1-xFexO3 by sol–gel, where the trivalent ions (Fe3+) replace the tetravalent ions Ti4+ and create oxygen vacancy to maintain the charge neutrality of the compound13.

Understanding the impact of the substitution of TM on structural, physical, and microstructural properties will be a significant step in the explanation of these properties14,15,16. Nickel ferrite, as an inverse spinel-type with molecular form (NiFe2O4), offers ferrimagnetism behavior that originates from trivalent (Fe3+) and the divalent (Ni2+) cations distribution in B and A locations. In the NiFe2O4 structure, (Ni2+) ions are in B-sites, and trivalent (Fe3+) ions are equally divided between both (A and B) sites17. NiFe2O4 nanoparticles are used in various applications because of their extraordinary properties including lower toxicity, small magnetic anisotropy, excellent electrochemical activity, elevated electrical conductivity, and lower Curie temperature. Usually, their properties are constructed on synthesis manner, size scale, and the grain shape of the NiFe2O4 material18,19,20.

Abou Hammad et al. 2020 have prepared Perovskite/spinel nanocomposites by advanced sol–gel, where they prepared the spinel ferrite CoFe2O4 powders then they coated it by ZnTiO3 through dispersing the CoFe2O4 nanopowders in ZnTiO3 solutions and drying the solution with slow rate to enable building up the shell layer (ZnTiO3)21.

On the other hand, the development of reliable and sensitive sensors for hydrogen peroxide detection by an easy method using a low-cost way is important. Many analytical techniques have been carried out for H2O2 detection, such as chemiluminescence22, fluorescence23, spectrophotometry, chromatography, and electrochemistry24,25,26,27. Electrochemical detection is distinctive due to simplicity, selectivity, sensitivity, and low cost28,29,30,31,32,33,34. The electrochemical biosensor is an ideal detection tool for the fast, sensitive, and accurate detection of drugs35, biological samples, and the diagnosis of diseases36. All of these interesting properties of the electrochemical sensors depend on the type of electrode materials. Hence, it is necessary to provide new nanomaterials that have electro-catalytic properties to evaluate an effective electrochemical sensor platform(s). When controlled the energy band of BTO-nanostructures, the optoelectronic and catalytic activity will be developed to meet the advanced applications.

Therefore, in this work, the piezoelectric BTO shielded with ferrites will acquire a partial semiconducting property hybridized with efficient electric, catalysts, and electrochemical performance can lead to significantly enhanced catalysis operation according to the piezo-nanomagnetic catalysis effect.

Hence, the study of spinel ferrites as a shield layer for the perovskite is considered of scientific and industrial enormous importance because of their new properties, significant magnetic and electrical properties, excellent chemical stability, and wider applications. The present study investigates the impact of doping of NFO NPs with various concentrations on BTF nanoperovskite. Also, the ability of nano-oval BaTi0.7Fe0.3O3@NiFe2O4 nanocomposites as an effective platform for the determination of H2O2 is investigated. The structural, thermal, optical, dielectric, and electrochemical properties of the nanomaterials have been studied. Due to the high electrocatalytic activity properties of doping of NiFe2O4 ions with various concentrations on the BTF materials, there are modifications on the screen-printed electrodes surface, and the direct electrochemical oxidation of peroxide was studied using cyclic voltammetry and chronoamperometric techniques. The prepared nanostructures showed high sensitivity toward peroxide detection, which can be effective in the enzymatic biosensor fields.

Materials and methods

Materials

For the synthesis of Ba Fe0.3Ti0.7O3and NiFe2O4phases, high grade titanium (IV) isopropoxide Ti[OCH(CH3)2, barium acetate (Ba(CH3COO)2,99.9%), iron nitrate Fe(NO3)3. 9H2O (99.9%),Ni(NO3)2.6H2O (98%), acetyl acetone (AcAc, C5H8O2, and nitric acid(HNO3) were used as a raw materials. Potassium ferrocyanide, potassium ferricyanide, potassium chloride, potassium dihydrogen phosphate, potassium monohydrogen phosphate, hydrochloric acid (HCl), sodium hydroxide (NaOH), and hydrogen peroxide were purchased from Sigma-Aldrich.

Synthesis of multiferroic BaTi0.7Fe0.3O3 shielded with NiFe2O4 nanocomposites

First, in the NiFe2O4 coating layer, the stoichiometric amounts of Fe(NO3)3·9H2O/H2O and Ni(NO3)2·6H2O/H2O are mixed in (1:2) ratio with a dissolved citrate acid (CA) under stirring. After hard stirring for 1 h, the NFO sols aged at room temperature (RT) for 5 h before coating BTF nanocrystallites.

Iron barium titanate (BTF) shielded with nickel ferrite (NiFe2O4, NF) was synthesized by the adapted sol–gel process. The sol–gel process allows the formation of multiferroic magnetoelectric and the controlled coexisting of magnetic and electric phases in one structure.

Barium titanate iron nanocrystallites were prepared by sol–gel process using the evaluated amounts of barium acetate, titanium (IV) isopropoxide, and iron nitrate as a source of Ba, Ti, and Fe, respectively. Acetic acid (HAc) and acetylacetone (AcAc, C5H8O2) were used as suitable solvents. Titanium (IV) isopropoxide was dissolved in acetylacetone, while both barium acetate and iron nitrate were dissolved in acetic acid/water. The solutions were mixed, stirred for 1.30 min, and dried at 200 °C. Further, thermal treatment was done at 450 °C for 2 h, after which barium titanate iron powder was shaped (Fig. 1).

Figure 1
figure 1

Synthesis steps of multiferroic BaTi0.7Fe0.3O3 shielded with NiFe2O4 nanocomposites.

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For BTF/(x) NF (x = 0, 1, 3, and 5), the resulting BTF nanopowder, after calcination at 450 °C, was added to the solution of NiFe2O4 according to the desired weight percent. The obtained solution was stirred for 1 h at 80 °C. The solution dried at 200 °C and turned into a viscous brawn gel, and started yielding xerogel form after evaporating the aqueous media. Finally, the obtained xerogels were calcinated at 600 °C. The constructed nanocomposite samples were labeled with symbols 0B, 1B, 2B, and 3B.

Material characterizations

The prepared perovskite-NiFe2O4 nanocomposites were characterized using the powder X-ray Diffraction (XRD-XPERT) through (Cu Kα) radiation. The profiles of XRD for the nano-oval BaTi0.7Fe0.3O3@NiFe2O4 nanocomposites were then refined using fixing the instrumental and shape parameters by Full-prof software (the Pseudo-Voigt fitting-model) and geometrical assembly was drawn by the VESTA: win64 software37,38. Transmission electron microscopy (High-resolution-TEM, (FEI; Tecnai- T20)) was used.

Thermogravimetric analysis measurements (TGA) in flowing imitation air (flow rate 20 ml/min, heating rate 50 K/min) of the pre-dried 200 °C solutions was achieved using Netzsch (STA 449 system), with a heating rate of (10 °C/min).

The optical bandgap of the nano-oval composites was evaluated using UV–Vis-diffuse reflectance spectroscopy (JASCO: V550) and also the optical bandgap can be evaluated through Tauc Plot manner.

Dielectric capacities were achieved using (LCR METER-IM3536) by a frequency range of 4 Hz–8 MHz. The samples were pressed in a distinct die (diameter = 10 mm) to procedure tablets with a thickness of ~ 1.2 mm.

Electrochemical analyses

Screen printed electrodes (SPEs) were used as the sensing platform for testing the electrochemical properties of the newly synthesized nanocomposites. Electrochemical techniques (cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS)) were conducted using CHI-potentiostat. For electrode surface modification with the nanomaterials, 5.0 mg of the synthetic nanocomposite was added to 1.0 ml double distilled water and then ultra-sonicated for up to 30 min to produce a homogenous suspension. Then 30 μl of the suspended solution was dropped on the SPE surface and left to dry. For SPE characterization, CV and EIS measurements were carried out in a solution containing 5 mM of the ferricyanide [Fe (CN)6]3‑/4‑ and 0.1 M KCl. For H2O2 detection chronoamperometric measurements were carried out in a PBS buffer. The following figure (Fig. 2) shows the simple modification method of SPEs with the 0B, 1B, 2B, and 3B nanocomposites for testing their electrochemical performance34.

Figure 2
figure 2

Steps of SPEs modification with 0B, 1B, 2B and 3B nanostructures before testing their electrochemical performance.

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Results and discussion

phase identification (XRD)

The formation of nano-oval BaTi0.7Fe0.3O3 shielded (1, 3, 5 mol.%) NiFe2O4 nanocomposites are confirmed by the XRD profile/ FullProf as revealed in Fig. 3a–d. Obviously, the growth of hexagonal BaTi2Fe4O11 and cubic NiFe2O4 phases indicated that the lower calcination core BTF nanoparticles had been reacted with the shield NiFe2O4 for new arrangement within the BaTi0.7Fe0.3O3@ NiFe2O4 complex. Figure 3a, d show a presence of a secondary phase ( monoclinic phase of Ba3Fe10.168Ti0.832O20). The monoclinic phase can disappear with increasing the calcination temperature higher than 800 °C. The calcination of nao-oval composites at 600 °C exhibited a well crystalline degree, with sharp and high intensity peaks. Additionally, the average crystallite size (ca. 21–23 nm) of the BaTi0.7Fe0.3O3 shielded NiFe2O4 nanocomposites, which was calculated from the Scherrer formula20,21,42. It is declared that the BTF is well shielded with the NiFe2O4 and has adequate stabilization.

Figure 3
figure 3

XRD patterns of (a) BaTi0.7Fe0.3O3 shielded by NiFe2O4 NPs with concentrations (b) 1, (c) 3, and (d) 5 mol., calcined at 600 °C.

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The Rietveld analysis and the lattice parameters of the phases were given in Table 1. The XRD results indicated the good shielding of BTF nanoparticles in NFO NPs matrix, produced from the modification of BTF nanoparticles using NFO and calcination at 600 °C.

Table 1 the lattice parameters for the formed phases.
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The X-ray density can be obtained from applying the following equation.43,44,45:

$${\varvec{\rho}}_{{\varvec{x}}} = \frac{{8{\varvec{M}}}}{{{\varvec{N}}_{{\varvec{A}}} {\varvec{V}}}}$$

M is the molecular mass, V is the volume, and NA is the Avogadro number.

Morphological analysis using TEM

The particle nature of nano-oval BaTi0.7Fe0.3O3 shielded with NiFe2O4 nanocomposites was investigated using transmission electron microscopy (TEM). Figures 4 showed the TEM images of the nano-oval BaTi0.7Fe0.3O3 shielded with 5 NiFe2O4 nanocomposites. The results confirmed that the samples have nano-spherical and nano-ovals morphology (with the average size of 12 − 25 nm in diameter).The microstructures of the shielded ovals nanocomposite indicated that the BTFO phase is obviously described by regular grains, which are homogeneously distributed and connected with the NFO matrix. The samples showed a significant clustering to affect the XRD intensity. The occurrence of certain accumulated dark spots in the TEM images is due to the shielding of BTF with NFO and the interaction among magnetic NFO nanoparticles with the higher surface energies of the BTF. The crystal lattice displayed no clearly lattice deficiencies with clear boundaries. The internal distance between the two neighboring lattice planes is evaluated to be 0.292 nm associated with the main XRD peak of BTF and 0.235 nm associated with the main XRD peak of BTF@NFO, which confirmed the successful shielding with the NFO nanoparticles. The TEM results indicated that the NiFe2O4 is highly shielded and well adhesion with the BTF nanoparticles. Moreover, the TEM data is supporting the XRD results. TEM images are evidence that the magnetic particle aggregation lies in the nanometric region.

Figure 4
figure 4

TEM images of nano-oval BaTi0.7Fe0.3O3 and shielded with 5 NiFe2O4 nanocomposites, calcined at 600 °C.

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Thermal study

The thermogravimetric test TGA is a technique that records the weight variations when a solid is warmed up at a uniform speed to evaluate its thermostability and volatile ingredient fraction. Since the object is processed under different conditions, the TGA technique falls under the category of thermal analysis40. The approach allows simultaneous measurement of the temperature, time, and mass of a sample in a managed flexible setting. These assessments are based on the fluctuation in weight of the material as a response to warming a condition46,47. Therefore, a certain weight amount will be destroyed and evaluated as volatiles or decomposed, and this loss is detected with precision balance. The material is loaded in a cylinder pan built specifically for this testing. Temperature variations are determined by a tailored temperature program, which may include isothermal and ramp stages with varying warming levels39. The temperature of the cuvette is monitored using thermocouples in connection with it. For weight monitoring, the cuvette is normally put on a test stand which is attached to a mass-sensitive instrument. The sample holding cuvettes of a TGA device can be of various forms and compositions. They must be able to properly keep the sample, inert to it, and the heating conditions. Alumina, platinum, and aluminum are the most common materials used to make testing cuvettes40. An exhaust gas flowing into the oven creates an atmosphere that can be neutral, such as nitrogen or argon, oxidative, such as air or oxygen, or reductive, such as a mixture of hydrogen and nitrogen. The amount of moisture inside the oven could range from dry to saturated40.

In this work, thermogravimetric analysis was carried out by TA instruments Lab Q5 in a nitrogen gas environment at temperatures ranging from 25 to 900 °C at a 10 °C/min heating rate. The TA Instruments Q50 TGA monitors the change in sample weight as a function of temperature. It employs delicate microbalance as well as precise heating management. The specimen mass limit is 1 g with an accuracy of 0.1 g.

The TGA curves of nanocomposites in the N2 climate with a heating rate of 10 °C/min are shown in Fig. 5. The behavior shows two main decomposition reactions; the first one is mostly due to the dehydration and evaporation of organic components44,45between (125–205 °C), (117–189 °C), (110–177 °C) and (97–167 °C) for the samples, respectively. The mass loss of 0, 0.1, 0.3, and 0.5 NiFe2O4 is approximately 9, 11, 13, and 14% of the initial weight, respectively. Because the range of events that occur in the first reaction decreases, the NiFe2O4 nanoparticle shells are not favorable to the thermal stability of the nanocomposites45,48.

Figure 5
figure 5

TGA curves of the prepared nanocomposites in the range of ambient to 900° C in an N2 atmosphere with a heating rate of 10 °C/min.

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The second stage situated in the range of (457–481 °C), (434–460 °C), (412–434 °C), and (282–401 °C) for, 0.1, 0.3, and 0.5 NiFe2O4, respectively. This stage reflects the decomposition of the nanomaterial43,48. The samples (0.1, 0.3, and 0.5 NiFe2O4) loss was about 25, 30, 34, and 36% of their initial weight, respectively. The addition of NiFe2O4 nanoparticle shells led to a decrease in the range of occurrence of the process.

Diffuse reflectance

Diffused reflectance is the phenomenon resulting from reflection, refraction, diffraction, and absorption orientated in all directions. The discrete light absorption as well as the size-dependent are developed due to the confinement of quantum size19. In the case of nanocrystalline semiconductors, linear (one exciton per particle) and nonlinear (multiple excitons per particle) properties arise as a result of the transition from an electron and an electron hole to discrete (quantized) electronic shells. Optical absorption of the nanosized oxides is influenced by nonstoichiometric defects which are size-dependent. In nanostructured oxides, the point defects concern the presence of dopant and/or the vacancies of cation or oxygen. In proportion to the number of defects, gap states are introduced by vacancy defects.

Diffuse reflectance was used to study the optical properties of the prepared BaTi0.7Fe0.3O3/(0, 1, 3, 5) NiFe2O4 (BTFO/NFO ) nanocomposites in the wavelength range of 200 to 2500 nm, as shown in Fig. 6. The diffuse reflectance of all samples increases with wavelength increase until about 1870 nm, where the interference takes place.

Figure 6
figure 6

(a) Diffuse reflectance and (b) absorptance spectra of BaTi0.7Fe0.3O3/(0, 0.1, 0.3, 0.5) NiFe2O4 nanocomposites in the wavelength range of 200 to 2500 nm.

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Furthermore, in Fig. 6a, the increase in NiFe2O4 leads to a decrease in diffuse reflectance values. Previously49, it was observed that the absorption spectrum of the BTO exhibits a sharp absorption edge above 3 eV and peaks at 3.51 eV roughly taken as the value of the band gap, that is, 3.51 eV. This edge corresponds to the band-to-band absorption scenario in the 'extrinsic band insulator of the tetragonal BaTiO3−δ49. In that case, the oxygen deficiency content δ, which is quite small, can be qualitatively reflected from a long tail below the rising edge in the range of photon energies between 2 and 3 eV49. In the current work, the absorption spectrum of the BTFO becomes broadening (Fig. 6b), which spans a wide range of photon energies from the ultraviolet region to the near-infrared one. This spectrum can be spectroscopically de-convoluted into two Lorentzian components as shown in Fig. 6b, whose peaks are at about 340 nm and 520 nm, respectively. The first component may be attributed to a combination of multiple absorption processes to donor levels in the forbidden band49.

However, the second component is due to band-to-band absorption for hexagonal BTFO, i.e., Fe-doped hexagonal BTO, with a band gap Eg 2.7 eV smaller than that of the undoped tetragonal BTO (Eg ≈ 3.51 eV)49. In addition, the red shift observed for UV–VIS absorption spectra is a direct consequence of the change of the band structure from the tetragonal BTO crystal to the hexagonal BTFO one, which is caused by substituting the Fe ion for Ti4+ to create Fe ions with an oxidation state of about 3.92 and positively charged oxygen vacancies as the electron trapping centers.

The method of Kubelka and Munk (K–M) was employed to determine the optical band gap (Eg) of the BTF/NiFO materials, which is based on the conversion of the diffused reflectance measurements. The Kubelka–Munk equation is given below for a specific wavelength:

$$F\left( {R_{d} } \right) = \left( \frac{k}{s} \right)\left( {1 - R_{d} } \right)^{2} /2R_{d}$$
(1)

where F(Rd) is the K–M function or the absolute reflectance of the material. In reflectance measurements, barium sulphate (BaSO4) is used as a standard sample. ‘k’ is the coefficient of molar absorption and ‘s’ is the scattering coefficient. The relation between the optical band gap and the absorption coefficient of semiconductor oxide materials was determined by Wood and Tauc in the case of a parabolic band structure. According to them, the following equation is based on the optical band gap in absorption and photon energy50:

$$F\left( {R_{d} } \right)h\nu = C\left( {h\nu - E_{g} } \right)^{n}$$
(2)

where ‘α’ is the absorption coefficient of the samples and ‘hυ’ is the photon energy. C is the constant factor, Eg is the optical band gap, and ‘n’ is a constant correlated with various types of electronic transition (n = 1/2 for a direct allowed transition, n = 2 for an indirect allowed, n = 3/2 for a direct forbidden, and n = 3 for an indirect forbidden transition) as previously reported in the literature19,51.

The BTFO/NiFO nanocomposites show an optical absorption spectrum caused by the direct and indirect electronic transition with a higher probability of the direct one. In the direct mechanism, electrons in the higher energy state in a VB move to the lowest energy states in the CB under the same point in the Brillouin zone after the electronic absorption process52,53. Therefore, by plotting and extrapolating a graph between [F(R) hυ]n and hυ for n = 2 and 1/2, Eg values corresponding to the different concentrations of Ni-ion in BTFO samples are calculated by the linear portion of the curve (Fig. 7a and b). Figure 7c, the Eg values measured to be 1.021, 0.289, 0.289, and 0.289 eV for BTFO/xNiFO (x = 0.0 to 0.5) nanocomposites in the direct case, and 2.674, 1.482, 1.482, and 1.482 eV in the indirect case. This gap is due to the presence of intermediate energy levels for both the valence band (VB) and conduction band (CB). In the case of Ni-doped BTFO materials, the Eg values decrease with doping. The incorporation of Ni ion BTFO introduces ‘B-site’ vacancies, which contribute to structural deformation and distortion49,53. These vacancies of the ‘B site’ introduce shallow defects in the optical band gap and therefore the Eg value decreases. The B-site vacancies increase with the doping and resulting in the creation of the free carriers that have a many-body effect, which reduces electron energy as compared to a noninteracting carrier network. Such interaction can take the form of interaction between electron–electron, electron-donor, electron–hole, hole-hole, and hole-acceptor49,53.

Figure 7
figure 7

Plot of [F(R) hυ]n and hυ for (a) n = 2 and (b) n = 1/2, and (c) the behavior of energy band gap with the Ni content in both direct and indirect cases.

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The material refractive index is known to minimize with energy gap. Consequently, both these common quantities are thought to have a particular relationship. There were different efforts to locate an acceptable correlation (empirical and semiempirical) between the refractive index and the energy gap of semiconductors. Some of these attempts are the Moss relation and Vandamme relation54,55. The claimed relationships have already been presented with justifications for obtaining a satisfactory agreement to experimental results54,55 and so it will be used here to calculate the refractive index of the prepared samples from the obtained energy gaps.

Figure 8a shows the change of the refractive index with Ni content calculated by different attempts described before for direct and indirect transition cases. It is obvious that there are small differences between the n values calculated by different methods and this may be due to the difference in the mathematical approximation methods used in every attempt. Also, the refractive index increases by NFO addition, and then the behavior is kept constant with NFO content increasing. This means that the prepared nanocomposites are desirable in applications that need a constant refractive index such as military applications, space, and optical devices.

Figure 8
figure 8

(a) Refractive index, (b) Optical dielectric constant, and (c) Electronegativity of BaTi0.7Fe0.3O3/(0, 1, 3, 5) NiFe2O4 nanocomposites in the wavelength range 200–2500 nm.

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The material dielectric constant is linked to the refractive index54 by (\(\varepsilon_{\infty } = n^{2}\)). The dielectric constants of the prepared samples are given in Fig. 8b for direct and indirect gap cases respectively. It was noted that the dielectric constant change behavior with Ni change is similar to the behavior of the refractive index.

Duffy56 has demonstrated the earlier view and presented it as optical electronegativity (Δχ*) and get the formula that links it by energy gap (\(\Delta \chi^{*} = 0.2688 E_{g}\)). The Duffy relation is used in calculating the optical electronegativity of the prepared samples for the direct and indirect transition gaps, and the resulting values were presented in Fig. 8c. The presented data shows that the BTFO/NiFO optical electronegativity lies between (0.7–0.07) for both direct and indirect cases, respectively. Following Pauling's57 indication, the current samples are covalent as predicted by XRD.

Magnetic properties

Figure 9 shows the magnetic hysteresis loop of iron barium titanate shielded with nickel ferrite (nano-oval BaTi0.7Fe0.3O3 shielded (0.1, 0.2, 0.5) NiFe2O4) nanocomposites. The M–H curve of the composites exhibits a saturated magnetic hysteresis loop that the composites samples have a ferromagnetic nature. This hysteresis loop for all samples is small, which is a specific feature for a soft ferrite NiFe2O4.The composites gained their magnetic property from the presence of the ferromagnetic phase (NiFe2O4). The magnetic nature of NiFe2O4 nanopowder results from the antiparallel distribution of the magnetic centers (Ni2+ and Fe3+) between the octahedron and the tetrahedron sites. Therefore, increasing the concentration of the ferromagnetic phase (NF) in the composite increases the magnetic centers in the composite samples, and hence the total magnetic moment of the samples increases too. Therefore the saturation magnetization of the composites increases with increasing the NF concentration. The diamagnetic phase BTF decreases the interaction between the magnetic centers NF and hinders the rotation of the magnetic centers with the applied magnetic field, therefore the saturation magnetization decreases with increasing the diamagnetic phase concentration58,59. The magnetic parameters (saturation magnetization Ms, Remanent magnetization Mr, and coercive field Hc) of the composites are listed in the inset of Fig. 9 to highlight that increasing the ferrite content in the composite improves the magnetic properties of the composites. This can be explained on the basis of the presence of Ni2+ and Fe3+ ions present in the NiFe2O4 system as a coated layer. Since the increase of their contents may be causing the increase of their unit cell, thereby increasing the lattice parameter and exchange interactions within A and B sites. Also, the presence of Fe3 + in the based BaTi0.7Fe0.3O3 and in the NFO layer enhances the magnetization of the B-site.

Figure 9
figure 9

Magnetic hysteresis loops of iron barium titanate (BTF) shielded with nickel ferrite (BTF/xNFO).

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Dielectric (relative dielectric permittivity)

The relative dielectric permittivity (ε'(ν)) of the composite samples (BTF/xNFO) against temperature at different frequencies is shown in Fig. 10. As a result, an increasing behavior in the dielectric permittivity with increasing temperature was obtained until a critical temperature. Then, a decrease in the dielectric permittivity was observed with higher temperatures. This critical temperature is the Curie temperature and represents the transition from the ferroelectric to the para-electric state. According to Fig. 10, the BTF sample has two transition temperatures; the first transition is assigned to the presence of an unstable monoclinic phase, while the second one represents the ferroelectric transition temperature.

Figure 10
figure 10

Relative dielectric permittivity (ε'(ν)) versus temperature at different frequency of iron barium titanate (BTF) and iron barium titanate shielded with nickel ferrite (BTF/xNFO).

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Electrochemical properties

Electrochemical behaviors of the prepared nanocomposite are identified, in a stranded redox mediator of ferro/ferricyanide, by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). As a result, a fast oxidation–reduction and highest faradic current of the standard redox probe were obtained for all nanocomposite-based electrodes (0, 1, 2 and 3B), as presented in Fig. 11a and b. The ascending order in the voltammetric signals is as follows: 3B > 2B > 1B > 0B, as depicted in Fig. 11a and Table 2.Therefore, the highest conductivity alongside electrochemical activity is dedicated to the modification of electrode surface with the nanocomposite (3B).

Figure 11
figure 11

(a) CV measurements of (Bar, 0, 1,2 and 3 B) were conducted in a solution of standard redox probe of ferricyanide with the 5 mM in KCl as the supporting electrolyte. Scan rate of 50 mV s − 1 was applied for all experiments. (b) Show EIS Nyquist spectra characterization of modified electrodes with the nanomaterials. The inset represent the modeled Circuit thatis used for curve fitting.

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Table 2 The electrochemical parameters (CV & EIS) obtained for the modified electrodes with the prepared nanomaterials.
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In parallel to the voltammetric studies, EIS analysis was conducted for all modified electrodes, as displayed in Fig. 11b, and Table 2. Nyquist plots, at high frequency, showed a semicircle portion reflecting the changes in the electron transfer resistances, whereas the charge transfer resistance (Rct) at the electrode interface was presented by the diameter of the semicircle. Matching with the voltammetric results, the lowest resistances were obtained from 3B-based electrode (Rct = 88.4Ω) followed by 2B (Rct = 148.7Ω), 1B (Rct = 231.2 Ω), and 0B (Rct = 407.8Ω). Worth mentioning here that the all composite-based electrodes provided lower charge transfer resistances than that obtained by the unmodified electrodes (Rct = 1400.8 Ω). The inset in Fig. 11b represents the equivalent circuit used for fitting the impedance Nyquist plots. From the CV and EIS results, we could conclude that the 3B composite has a promising property and can be exploited in electrochemical applications.

The redox peaks which appeared in the CV curves for prepared nanocomposites showed a pseudocapacitive electrode material significant feature. In the charge/discharge process, very fast reversible faradaic redox occurred along with the faradaic charge transfer and intercalation of protons at the surface of the electrodes. The effect of scan rate on the electrochemical behavior of each prepared nanomaterial (0, 1, 2, and 3B) was studied by the cyclic voltammetry method (Fig. 12A, B, C and D). In the scan rate range from 0.01 to 1.0 V/s, the redox peak currents (ipa and ipc) increased as the scan rate increased for 0, 1, 2, or 3B modified electrodes. In Fig. 13, the lower electrical conductivity of 0B is due to lower peak current values. On the other hand, the values of peak current increased in 1B and 2B.The highest peak current values were observed in 3B, which refers to its capacitive properties. However, the cyclic voltammogram exhibited a well-known hysteresis-type loop, which is significant for a supercapacitor. Furthermore, all prepared nanomaterials were stable electrochemically over various applied scan rates, and no damage was produced in the electrode-modified composition.

Figure 12
figure 12

CV of prepared nanocomposites (A) 0B, (B)1B, (C)2B, and (D) 3B at different scan rates. Screen printed electrodes were modified with a thin film of the nanomaterials and voltammetric experiments were performed in the ferricyanide (5 mM).

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Figure 13
figure 13

Influence of scan rate changes on the oxidation currents of the 0B, 1B, 2B and 3B nanostructure-based electrodes at different scan rate.

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The use of 0B, 1B, 2B and 3B nanostructures for H2O2 detection

The electrochemical properties of nanocomposite materials modified electrode is one of the key benefits to supply high electrocatalytic activity which produces fast electron transfer and direct oxidation in the field of non-enzymatic biosensors. Therefore, the study of direct electron transfer produced from the oxidation of hydrogen peroxide evaluated overall prepared nanomaterials. The direct oxidation was measured by CV and chronoamperometric methods by adding different peroxides concentrations into the electrochemical cell. The cyclic voltammetry graph and a calibration curve are represented in Fig. 14a and chronoamperometric calibration curves of bare, 0B, 1B, 2B, and 3B modified electrodes are shown in Fig. 14b. The highest signals were obtained by the 3B modified electrode. Therefore, the high electrocatalytic activity of 3B allowed the direct electrochemical oxidation of peroxide. In addition, as the concentration of H2O2 increased, an increase in oxidation peak currents were produced which revealed the high sensitivity and reliability of the 3B modified SPE.

Figure 14
figure 14

(a) Cyclic voltammety of 3B-based electrodes towards the direct voltammetric oxidations of different concentrations of H2O2 in (PBS pH = 7.0). The calibration curve is presented in the inset figure. (b) Chronoamperometric calibration curves of bare, 0B, 1B, 2B, and 3B toward different concentrations of H2O2 in (PBS pH = 7.0). (c) pH effect on the sensor performance towards the sensitivity of direct peroxides detection.

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Consequently, the amperometric signal of peroxide oxidation at different pHs was studied. As represented in Fig. 14c), the amperometric response of the 3B-based electrodes towards the peroxide’s oxidation was measured at different pHs, and the electrochemical signal increased as the pH increased from 4 up to 7 then decreased above pH = 7.0. So that, PBS buffer with pH 7.0 was selected for all subsequent experiments.

Amperometric detection of peroxide

From cyclic voltammetry (CV) detection, the peroxide oxidation peak was produced at 0.7 V. Therefore, the amperometric study was evaluated at 0.7 V by adding a standard concentration of H2O2 at a fixed time (100 s). Figure15 showed the relation between the different concentrations of peroxides and current response with a fast and high response, which approved the fast electron transfer due to the electro-catalytic behavior of the 3B-based electrodes. The calibration curve (as it is clear in Fig. 15) showed a linear range from 0.1 up to 650 µM with a detection limit of 0.01 µM, which approved the high sensitivity of the proposed electrode to be effectively applied in the non-enzymatic-based biosensors field. Additionally, a comparison of electrochemical response between electrochemical performance of the newly developed electrode for peroxide determination and the other reported materials is tabulated in Table 3.

Figure 15
figure 15

The corresponding calibration curve toward H2O2 response.

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Table 3 Comparison of the analytical performance of various Hydrogen Peroxide Sensors (with various literatures).
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Conclusion

From this work, activated NiFe2O4 nano-oval was successfully shielded with BaTi0.7Fe0.3O3 nanoperovskite synthesized via the sol–gel chemical manner and calcined at 600 °C. The XRD powder asserted the formation of bi-phases for pero-NiFe2O4 nanocomposites. The measured band gap energy was 1.021, 0.289, 0.289, and 0.289 eV in the direct case, and 2.674, 1.482, 1.482, and 1.482 eV in the indirect case, respectively for BTFO/xNiFO (x = 0 to 5) nanocomposites. The incorporation of Ni ion into BTFO introduces ‘B-site’ vacancies, which contribute to structural deformation and distortion. . With the addition of Ni ion, the electronegativity exhibits a behavior similar to that of the band gap, but the refractive index and optical dielectric constant exhibit opposite behavior. The addition of NiFe2O4 plays an appreciable role in enhancing temperature stability and increasing the permittivity of the pero-magnetic BaTi0.7Fe0.3O3@ NiFe2O4 nanocomposites. The pero-magnetic BaTi0.7Fe0.3O3@NiFe2O4 nanocomposite electrode has been used as a sensing material for H2O2 detection. The results of electrochemical data approved that the new BaTi0.7Fe0.3O3@NiFe2O4 nanocomposites can be used effectively to direct H2O2-detection in biological analysis such as enzymatic-based sensors. Eventually, the obtained results are of excessive value to progress the structural, morphological, thermal, electrical, and electrochemical properties of pero-nanomagnetic composites at different calcination and ferrites contents, which enable be projected to apply in various applications as catalytic, biosensors, electromagnetic interference shielding systems, …. etc.