Synthesis and characterization of Fe2O3-Bi2O3-TiO2nanoparticles and its magnetic properties

Objectives: The current research work was investigated magnetic properties of Fe2O3-Bi2O3-TiO2 nanoparticles (NPS). Methods/Statistical analysis: The Fe2O3-Bi2O3-TiO2 has been synthesized by a simple precipitation method. The samples were characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier-Transform Infrared Spectroscopy (FTIR) and UV-vis. absorption (reflectance) spectra. The magnetic properties of the magnetite nanoparticles were calculated by vibrating sample magnetometer (VSM) at ambient temperature. Findings: The effect of calcination on the magnetic and structural properties of Fe2O3-Bi2O3-TiO2 nanoparticles was studied. The Fe2O3-Bi2O3TiO2 nanocrystal was subjected to calcination up to 200◦C, magnetite was converted tomagnetite; the second transition was in the range of 300-400◦Cwhich changed it to hard ferromagnetic hematite. Application/Improvements: This research provides promising results concerned with magnetic sensing probes for magnetic resonance imaging for in-vitro diagnostics and contrast agents.


Introduction
The use of nanomaterials for water purification has become an interesting research area in recent years. Nanomaterials are a growingly important nanotechnology products. They contain nanoparticles in at least one dimension which are smaller than 100 nm. These nanomaterials are coming into health care, electronics, cosmetics and other areas (1,2) . Due to many potential innovative applications, Nanoparticles research has received considerable attention. They have unique and novel magnetic, optical, electronic and catalytic properties (3) .
Magnetite is known as the black iron oxide and the oldest known source of magnetic oxides. Especially hematite and maghemite, have been used as pigments since ancient times to give pottery reddish coloration. Similar to hematite, magnetite is a semiconductor with a band gap of around 2 eV, although the specific value of the gap based on the electron spin (4,5) . The iron atom has a strong magnetic moment in its 3D orbitals, due to four unpaired electrons. Paramagnetic materials reveal randomly https://www.indjst.org/ distributed dipoles in the absence of the magnetic field. The magnetic response of the paramagnetic materials is relatively weak. Ferromagnetic materials are characterized by their spontaneous magnetization regardless of the absence or presence of an external magnetic field. The magnetic moments are aligned parallel in one specific direction depending on the crystal structure. The ferromagnetism originates from exchange interactions occurring in ordered magnetic solids. The difference between ferromagnetic and ferrimagnetic materials is related to the alignment of adjacent dipoles. In ferrimagnetic materials, nonmagnetic field weaker magnetic dipoles aligned antiparallel to their adjacent stronger dipoles reduces the net magnetization. The most common iron oxide (Fe 2 O 3 ) has important magnetic properties as well. From the standpoint of basic research, iron (III) oxide is a convenient compound for the general polymorphism study and nanoparticles ' magnetic and structural phase transitions. It is well established that amorphous Fe 2 O 3 and four polymorphs (alpha, beta, gamma, and epsilon) exist (6) . The most common polymorphic structure "alpha" (hematite) with hexagonal rhombohedral, prototype corundum structures, and "gamma" (maghemite) cubic spinel structure was found in nature. At a temperature of 650 • C, hematite turns into Fe 3 O 4 with a high energy loss. The Bim + 1Fem -3Ti 3 O 3 m + 3 compounds combine ferroelectric, Semiconducting and ferromagnetic properties (7)(8)(9) , making them potentially attractive to applications in electrical engineering, e.g. as magnetic recording media. The Electrical properties of compounds have been observed in the Bi 2 O 3 -TiO 2 -Fe 2 O 3 system (10)(11)(12)(13) . Nature and conduction mechanism of a dielectric relaxation model proposed by Jonscher is interrelated (14) . Literature reports are available on the synthesis of TiO 2 -based magnetic photocatalysts (15) . Several complexes such as Fe 2 O 3 , WO 3 , BiVO 4 , Bi 2 WO 6 , and Ag 3 PO 4 have been tested as visible light photocatalyst (16) . Our investigation mainly focused on the synthesis of Fe 2 O 3 -Bi 2 O 3 -TiO 2 nanoparticles and the observation of magnetic properties of nanoparticles as a function of nanoparticle morphologies.

Materials and methods
All analytical grade chemicals were used in the experiment. Double distilled water was used for all experiments. Co-doped nanoparticles were prepared by using the following protocol. Nano iron (II, III) oxide (Spherical, diameter 20nm, 99.5%) was purchased from Shanghai Chemical Co., Ltd., China. Ammonia solution and isopropyl alcohol were obtained from Merck Ltd. Bismuth Nitrate (Bi 2 NO 3 ) and tetra butyl titanate (TBOT) were purchased from Merck, China. Anhydrous ethanol was obtained from Hangzhou Changzheng Chemical Reagent Co., Ltd., China.

Preparation of Fe
The Fe 3 O 4 NPs (0.25 g) were sonicated for 1hr, allowing anhydrous ethanol (40 mL) to disperse uniformly. Concentrated ammonium hydroxide (4.5 mL) was diluted to the above solution, and 0.75 g of Bi (NO 3 ) 3 5H 2 O was quickly added under intense stirring. The solution was left up to heat for 12 hr. The commodity was obtained by centrifugation and washed with anhydrous ethanol three times.

Preparation of Fe
Their sultan's product was redisposed in anhydrous ethanol (40mL). Subsequently, a proper amount of TBOT (5.0mL) dissolved in isopropyl alcohol (40.0mL) was introduced to the system drop wise, followed by heating the solution at about70 • C. The entire process underwent vigorous stirring. The reddish-brown precipitate was washed with distilled water and ethanol five times after 12h and dried in a vacuum oven at 80 • C for 24 hr. They eventually calcinated the items at 500 • C for 2hr.

Characterization of magnetic nanoparticles
A Shimadzu UV-1700 spectrophotometer was used to test the UV -Vis absorption spectra. A Shimadzu X-ray diffractometer equipped with Cu Kα radiation source using Ni as a filter configuration of 45 kV/40 mA was used to analyze the crystalline existence of NPs. A total of 2 scans ranging from 10 to 90. KBr pellet method was used to obtain the Fourier transform infrared spectra (FT-IR) in the range 4,000 to 400 cm −1 . They collected the FE-SEM micrographs using a JEOL 6335F FE-SEM. The particle size and morphology of the sample were analyzed by transmission electron microscopy (TEM), and UV-vis absorption spectrum diffuse reflectance (UV-Vis DRS) was measured using a UV-vis spectrometer (U-4100, Hitachi).

Vibrating sample Magnetometer (VSM)
Using the Vibrating Sample Magnetometer (VSM) test, to determine the macroscopic magnetic properties of the nanoparticles Fe 2 O 3 -Bi 2 O 3 -TiO 2 . The VSM was completed at room temperature. The vibrating sample magnetometer (VSM) is one of https://www.indjst.org/ the most successful implementations of a magnetometer. In comparison with alternating gradient magnetometer, the VSM is indifferent to the mass and size of the sample up to a considerable range. The sample is inserted in a constant uniform external magnetic field that induces a sample magnetization. It causes disturbances in the external magnetic field when the magnetized sample is then vibrated. A set of coils or some magnetic field sensors can be arranged around the sample to measure these perturbations. For example in the case of coils, magnetic flux piercing the coils will change resulting in the generation of an EMF (electromotive force) in coils. The VSM can measure the magnetic susceptibility, at room temperature, of magnetic nanostructured samples. For this scheme, the first crucial step in the construction of a vibrating mechanism that can vibrate the sample with measurable and controllable amplitude. Then we need an electromagnet to provide the magnetic field required to magnetize the sample. Finally, detection coils are required to detect the magnetic field perturbations produced by vibrating the magnetized sample in the applied magnetic field.

XRD patterns
The inset from Figure 1  Where, D is the average crystallite size, λ the X-ray wavelength, β the angular line width at half maximum intensity, θ Bragg's angle. https://www.indjst.org/ Figure 2 shows the UV-Vis DRS absorption spectra of un-doped TiO 2 , Fe 2 O 3 -Bi 2 O 3 , and Fe 2 O 3 -Bi 2 O 3 -TiO 2 samples. Undoped TiO 2 and Fe 2 O 3 -Bi 2 O 3 -TiO 2 are strongly absorbed in the UV region due to the band-to-band transition. Compared to pure TiO 2 , 1.00 percent of Fe-Bi 2 O 3 /TiO 2 presents a small hump at around 480 nm in the visible-light region.

SEM analysis of Fe 2 O 3 -Bi 2 O 3 -TiO 2 NPs
The surface morphology of the acquired Fe 2 O 3 -Bi 2 O 3 -TiO 2 NPs was investigated using SEM and the obtained image is shown in Fi Figure 4 at 500 magnification level. FESEM image indicated that the Fe 2 O 3 -Bi 2 O 3 -TiO 2 NPs have smooth surfaces. In the SEM images, the agglomeration of NPs is also visible. NPs are uniform and cylindrical. A particle-size-distribution histogram determined from a TEM image showed a large variation in the particle sizes. The particles with an average diameter of 60 nm ( Figure 6).

Magnetic properties
The magnetic properties of the synthesized nanocrystals were examined by using VSM at room temperature. The nanoparticles after heating at temperatures 200 to 500 • C are shown in Figure 7. The as-synthesized nanoparticles Ms value ( Table 1) increases and then decreases on increasing calcination temperature from 200 to 500 • C. The increase of Ms may be an aspect of the https://www.indjst.org/ increase of particle size due to the coalescence of the particles by solid-state diffusion. By increasing calcination temperature from 400 to 500 • C, Ms decreases respectively from 56 to 0.58 emu/g and the Hc increases respectively from 44.94 to 1190.3 Oe. This is due to the phase transition of ferromagnetic Fe 2 O 3 to weak ferromagnetic α-Fe2O 3 at 500 • C. Otherwise, the coercivity value is low and in the single-domain ferromagnetic region, it sharply increases with increasing particle size. https://www.indjst.org/