Evaluation of New Properties of Calcined Magnetite Doped with Zinc and Lanthanum Nanoparticles Prepared in Oxygen and Nitrogen Atmospheres


 The aim of the present research is the preparation of magnetite nanoparticles doped with Zn and La of the general formula ZnLa(x)Fe(3-x)O4 where x =0.0, 0.1, 0.15, 0.2, 0.25 and 0.3; which were prepared via co-precipitation method, separated and calcined at 800oC under oxygen and nitrogen atmospheres. The stoichiometric ratios of the elements in the given general formula had been proved and confirmed by elemental analyses using XRF. Various techniqueshave been used to analyze the prepared nanoparticles. X-ray diffraction (XRD) confirmed the formation of one single phase of nanoparticles components with average crystalline size ranged from 6 to 9 nm at oxygen atmosphere and from 6 to 8 at nitrogen atmosphere.These size values had been calculated by Debye-Scherrer equation. The optical properties carried out by Cary Eclipse fluorescence spectrophotometer.The morphology of the prepared magnetite nanoparticles was studied using field emission scanning electron microscope (FE-SEM) and high-resolution transmission electron microscope (HRTEM). Optical properties were demonstrated by UV–visible–NIR spectrophotometer. The high absorbance values of Zn La(x)Fe(3-x)O4 were found to 80-97 and 80-99 % in the visible wavelength range of 400-800 nm for the prepared samples in presence of O2 and N2 gas at room temperature, respectively. These proved the lower values of energy band gap in both conditions. The lowering of energy band gap of 1.89 eV for nanoparticles prepared in O2 gas and 1.78 eV for prepared in N2 gas in most samples may be attributed to incorporation of Zn cation. These results are confirmed by photo luminscence spectra (PL) measurements of the prepared samples. Magnetic properties of the given samples obtained from vibrating sample magnetometer (VSM);showed that most of these samples exhibited almost superparamagnetic behavior. These magnetic values (32.87 and 24.79 emu/g) infer super saturation magnetization of the given samples prepared in O2 and N2 gas at room temperature, respectively. Examination of the magnetic properties revealed decrease in saturation magnetization with increasing La ion concentrations incorporation up to x = 0.3. The evaluated magnetic and optical properties of the novel prepared ZnLa(x)Fe(3-x)O4nano-materials revealed their possible use in different industrial fields like bio-applications, in electronic components, cosmetics, antibacterial agents, and in solar cells. The antibacterial activity study of the prepared NPs revealed them highly efficient against different kinds of bacteria that increase with increase of La % doped in their entity.


Introduction
Nanotechnology is exactly meant any technology that carried out in the nanoscale and has many applications in the real world, where the size of the atoms for the matter is about 1 to 100 nm as mentioned by I. Amato, et.al (1999) [1]. The peerless physical and chemical properties of nanomaterials have a profound effect by B. Bhushan (2015) [2] on commercial applications and for novel performance that bene ts societyNanomaterials have distinct physicochemical and biological properties. Particularly, their small size and diffusion abilities, shape, chemical composition, surface structure and charge, aggregation and agglomeration, and solubility can affect their interactions with biomolecules, cells, and organs. So, it can get into the human body in various ways, such as skin penetration, inhalation, or injection by Rahmandoust, M. et.al (2019) [3].Magnetic nanoparticles present many applications in synthetic methods such as co-precipitation are given by Rao, et. al (2018) [9], while thermal decomposition are given by Ibrahim, et. al (2018) [10], and hydrothermal and solvo thermal syntheses, sol-gel synthesis are given by de Mello, et. al (2019) [11].The variety of magnetic materials can be formed from iron atom which has four unpaired electrons in its 3d orbital. The magnetic behavior of the materials can be classi ed into six types, depending on the particular response of the materials in the presence of a magnetic eld. The materials are categorized bySpaldin, et. al (2010) [12]; into diamagnetic, paramagnetic, ferromagnetic, antiferromagnetic and superparamagnetic, on the basis of net magnetic moment of their atoms.Due to the advanced propertiesof nanomaterials, it was widely used by Ma, et. al (2010) [13] and Nel, et. al (2006) [14] in electronic components, cosmetics, antibacterial agents, and solar cells. During the last few decades there has been an increasing interest in utilizing nanoparticles and nanotechnology in cancer diagnosis and treatment by Barkalina, et. al (2014) [15] and Hofmann, et. al substitution on structural and dielectric properties of Fe 3 O 4 were studied by L. Hu, et.al (2012) [21] investigated the effect of cobalt substitution on the size evolution, crystal structure, and magnetic properties of Fe 3 O 4 nanoparticles. Mono-disperse Co x Fe 3−x O 4 nanoparticles were prepared, using a onestep method, by the direct heating process of iron (III) and cobalt (II) acetylacetonates in a high-boilingpoint inert organic solvent.The magnetic moments of magnetite nanoparticles were dramatically enhanced by J. Byrne, et.al (2014) [22]through the addition of zinc in a microbiologically driven synthesis procedure.Super-paramagnetic iron oxide nanoparticles (SPIONs) had been approved by R. Hergt, et.al (2006) [23] for clinical use due to their salient super-paramagnetic properties and low toxicity. Zn 2+ doped SPIONs possess signi cantly higher magnetic susceptibility than that of conventional SPIONs. Here we evaluated the potential toxicity of Zn 2+ doped Fe 3 O 4 nanoparticles (Zn 0 .4Fe 2 .6O 4 NPs) in the liver and kidney of mice after repeated intragastric administration for 30 days.E. Fantechi et al. (2015) [24] found that magnetite nanoparticles (NPs) are widely carried out for biomedical applications, particularly as contrast agents for Magnetic Resonance Imaging and as heat mediators in Magnetic Fluid Hyperthermia.Y. Zhang, et.al (2002) [25]stated that, Superparamagnetic magnetite nanoparticles were surface-modi ed with poly (ethylene glycol) (PEG) and folic acid, respectively, to improve their intracellular uptake and ability to target speci c cells.A progress report by Q. Pankhurst, et.al (2009) [26] shows that, a selection of scienti c, technological and commercialadvances in the biomedical applications of magnetic nanoparticles since 2003.G. R. J. Allard.et al. (2015) [27] had been prepared the nanoparticles via the co-precipitation route and masked with 3-phosphonopropionic acid   [33] presented study to evaluated the bacterial toxicity of lanthanum oxide micron and nano-sized particles using shake ask method against gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacteria.It was speculated that lanthanum oxide produced this effect by interacting with the grampositive bacterial cell wall. Furthermore, lanthanum oxide bulk particles were found to enhance the pyrocyanin pigment production in Pseudomonas aeruginosa.
In the present study, an composite has been made to synthesis La3+ doped ZnFe2O4 nanoparticles by the two-step sol gel method. Here, we report the synthesis and characterization of ZnFe 2 −xLaxO 4  was purchased from International company for SUP and MED industries. The distilled water used in all preparations usually collected from all glass equipment.

Analyses
The spectrophotometric measurements of Fe 2+ and Fe 3+ in nano-materials solutions using selective indicators were carried out using recording Spectrophotometer, UV-Vis range from 150-1100 nm model Unicam UV 300 and quartz cell of 1 cm optical length was used. Then total iron and zinc determination had been performed using atomic absorption spectrophotometer model AA.6300 SHIMADZU with an airacetylene ame. X-ray diffraction analyses were carried out using (analytical-x' Pertpro with Cukα1 target, λ=1.5404 Å, 45 kV, 40 mA, the Netherland) to identify the formation of the samples in pure single phase.Vibrating sample magnetometer (VSM) of (Model DMS 4HF) was used to measure the magnetic behavior of magnetic materials.The morphology of the various materials was disclosed using eld emission scanning electron microscopy (FE-SEM-QUANTA FEG 250) attached with EDX unit (Energy dispersive X-ray Analyses.HRTEM instrument of Zeiss Sigma 500 VP Analytical FE-SEM Accelerating voltage range 0.2 to 30 kV Variable pressure range: 2-133 Pa was used to characterize the particle size, shape, and grain size and to con rm the lattice parameter variation across the interfaces using selected area electron diffraction (SAED) pattern.
In the present work, the properties of the synthesized magnetic nanoparticles were investigated. The characteristics of the nanocomposites depend upon their crystal sizes, shapes and structures; which were characterized by advanced and sophisticated methods of analyses using different spectroscopic techniques. So, samples were completely analyzed by UV-Vis spectrophotometry and their solid state structures were investigated by XRD, EDX, HTEM and FESEM. The magnetic properties of the prepared materials were determined by means of the magnetic susceptibility and VSM. Thermal gravimetric analysis (TGA) was performed using a SDT Q 600 V20.9 build 20 (TA Instruments) thermo analyzer with a heating rate of 10 •C/min, using a O 2 at a ow rate of 50 mL/min. The photoluminescence spectra of the prepared nano compounds were performed using Cary Eclipse Absolute PL Quantum Fluorescence QM-40 Spectrometer and a Ge photodetector coupled to a data acquisition system composed of a microcomputer-controlled SR530 lock-in ampli er. The 350.7 nm excitation wavelength of a krypton ion laser (Coherent Innova) was used, with the laser output kept at 200 mW.The biological activities nanocomposites had been studied.

2.3a. Biological anti-bacterial studies
The antimicrobial activities of the test samples were determined by means of a modi ed Kirby-Bauer disc diffusion method by BrabuBalusamyet al [35] under standard conditions using Mueller-Hinton agar medium (tested for composition and pH), as described by

HR-TEM Comparison
Lanthanum oxides have low magnetic characters similar to magnesium oxides in nature that coming after magnetite. Lanthanum has at or cylindrical pipes crystal shape but it is diffused when mixed with magnetite less than 0.2 %[38]. Therefore, these shapes increased in size or its diameter when La% increased from 0.1 to 0.3 % and the La at shapes become more common than the cylindrical common shape of magnetite and the most common shape of nano-material becomes more at shape as shwen in Fig.1. For zinc in nano-material goes around magnetite and it takes nano-cylindrical or hexagonal together with uctuation of their crystal shapes. It is also noticed that, the variation of oxygen into nitrogen atmosphere change crystalline structures the doped Zn-magnetite with different ratios of La especially when ignited at 800°C. At which in nitrogen atmosphere it takes collective cylindrical Nano pipes groups under the effect of its homogeneity with magnetite [39]. In case of oxygen atmosphere (Fig.2) La appear with magnetite as big layers within which magnetite appears as spots; this means that La oxides crystals are homogenized with some magnetite oxides via oxygen -oxygen boding. Generally heating of nano-materials to 800°C leads to homogeneity of their crystalline structures and consequently increasing in their magnetic properties gradually with increasing ratio of La.  Figure 1 depicts FE-SEM micrographs and reveals that nanostructures show spherical geometry, with diameters near 20 nm, which form irregular agglomerates with diameters from 50 to 70 nm. This agglomerate formation indicates that the surface energy of the nanoparticles is relatively strong. Similar results are obtained by [40]. Fig.3 clearly showed the uniform distribution of Fe, O and La elements in the structure of Zn La(x)Fe (3-x) O 4 NPs. The iron and oxygen presence is related with iron oxide core. La was also veri ed in the scanning and its presence is consistent with the La nanolayer (shell). The FE-SEM results are similar that obtained by [41]. Fig.1, 2 demonstrated a micrograph performed by FE-SEM and the chemical distribution obtained to Zn La(x)Fe (3-x) O 4 NPs in N 2 atmosphere. Fig.4 con rms the agglomerate formation with dimensions near 100 nm to 300 nm that depict the presence of iron, oxygen and La elements, respectively.Compared to the ZnFe 3 O 4 core, the outside surfaces became coarse after the growth of La layers on the surface process, as shown in Fig.1 in 0.1, 0.2 and 0.3 % La. We can say from the TEM images (Fig.1,2) indicates that the La are successfully loaded onto the surfaces of ZnFe 3 O 4 spheres clearly demonstrating the formation of core-shell nanostructures.The average size of ZnFe 3 O 4 and Zn La(x)Fe (3-x) O 4 NPs even at O 2 or N 2 atmosphere (Fig.3,4)are 30 and 50 nm, respectively. Fig. 2 indicates that core-shell heterostructure is the predominant morphology of the products [42], which agrees well with the SEM observation (Fig 4). Obviously, the thickness of the outer shell with light contrast is about 10 nm, while the diameter of the inner core with dark contrast is about 30-25 nm. The magni ed TEM image further con rms that the shell is porous and composed of nanoparticles (Fig. 2).

Particle Size distribution
The hydrodynamic diameter provides information about inorganic core along with functionalized/coated material and the solvent layer attached to the particle as it moves under the in uence of Brownian motion.Usually, the magnetic properties of nanomaterials can be varied by increase of surface to volume ratio of particles and variation of their size.Decreasing of particles size in nanometer scales led to creation of magnetic death layer on the particles surface due to deviation of magnetic moments orientation, formation of disordering con guration of moments that are caused to develop superparamagnetic behavior (below speci c critical size) [43], making a difference in normal cationic distribution in crystalline structure, and nally variation of some surface properties like ability of water absorption on surface. Furthermore, decreasing of particle size and increasing of their surfaces are very useful for biological and medical applications. In contrast, when particles size is decreased less than 10 nanometers (for many of materials), the crystallinity of particles is also decreased, so the amount of saturation magnetization is dropped off [44].
Particle size was determined by atomic force microscopy. The average size derived from the height scan was below 40 nm. The distribution pro le of sizes from the TEM height scan is shown in Fig.5a. A section of the AFM scan is included in the inset. The results from the TEM correspond to the distribution acquired from DLS (Fig.5b). The hydrodynamic diameter distribution of the Zn La(x)Fe (3-x) O 4 NPs was of 36 nm and volume ratio of 16.9%. The hydrodynamic diameter by DLS is slightly larger than that determined by AFM, as expected. A similar study has been performed elsewhere and it was observed that DLS was limited for accurate particle sizing and mostly DLS provides higher values. Fig.5 indicates that the optimized co-precipitation method effectively produces a well-dispersed and narrower distribution of particle diameters [45]. The high stability of Zn La(x)Fe (3-x) O 4 NPs is given by their very low electrostatic potential.

X-RD and XRF analysis
The crystalline structures of the Zn Fe 3 O 4 before and after doping with La were investigated by XRD (Fig.   6a).
The framework peaks were weakened or vanished after La was added onto Zn Fe 3 O 4 -. Obvious peaks of As the La ratio was increased from 1 and 0.3%, no obvious differences were observed, and the Zn Fe 3 O 4 were delaminated at high La ratio. Fig. 2 shows the XRD patterns of the Zn La(x)Fe (3- 1 1), (0 0 4) Brags re ection . The average particle size of the synthesized nanoparticles was 60 nm, which was obtained using the Debeys-Scherrer equation [49].  Table .1. The % of oxygen is relatively high due to the contribution of oxygen from LaO used in coating the surface of ZnFe 3 O 4 nanoparticles. Further functionalization with La element is shown in Table .1. The % of oxygen is dramatically increased due to contribution of oxygen from LaO [50].

Zeta optional of nanoparticles
Zeta-potential measurements were further used to con rm the presence of La on the surface of ZnFe 3 O 4 NPs. As shown in Fig. 8a&b, the zeta potential of (N 2 ) ZnFe 3 O 4 NPs is increased with increasing La percentagedue to presence of La metal not La oxide on the surface, while the zeta potential of(O 2 ) ZnFe 3 O 4 NPs is decreases derived from the -ve charge of surface LaO as shown in Fig.8a. The (O 2 ) La 0.3 ZnFe 3 O 4 NPs shows a higher zeta potential of -13.2 mV derived from the -ve charge of LaO.
Calcinations of Zn La(x)Fe (3-x) O 4 NPs in N 2 atmosphere (Fig.8b) , lead to a increases of zeta potential, which is due to the fact that the La have +ve not LaO (-ve) charge crystal [50,51]. So the biomedical activity of ZnFe 3 O 4 NPs calcinated in N 2 atmosphere is more effective in killing bacteria with respect to O 2 calcinated samples.

Photoluminescence spectroscopy analysis
The separation of between electron and hole is one of the important parameters in uencing photocatalytic performance. In this context, photoluminescence spectroscopy was employed in order to evaluate the recombination rate for the photo generated electron-hole pairs for the ZnLa (x) Fe (3-x) O 4 at N 2 and O 2 calcinations conditions (see Fig. 9).
The   (Fig 9b). For both composites enhancement in intensity was observed with increasing La concentration ( Fig. 9) and this enhancement was larger for C1 con rming more effective interaction with Fe (3-x) O 4 . In fact, low intensity in PL spectrum of ZnLa (x) Fe (3-x) O 4 calcinated in O 2 atmosphere indicates that separation between the charge carriers is enhanced, leading to contribution of more electrons and holes in the oxidation and reduction reactions. The PL spectra appeared in the region between 700 and 800 nm, being identical for all the samples. In this way, the peaks around 733 nm arise from defect state luminescence. Besides, the bands at around 423 nm can also be related to recombination of free excitations. Therefore, the electron-hole separation e ciency can be improved, resulting in the increase in photo catalytic activity. The spectrum of ZnLa (x) Fe (3-  G 5, G 4, G 1, G 12, G 8, G 7, G 6& G 3, G 9, G 11 and G 13 mg/mL. Fig. 11 showed that Laincreasing inhibitory effects and decreasing bacterial growth numbers of different kinds of positive and negative bacteriaas the concentrations increasedLainZnLa(x)Fe (3-x) O 4 NPsmay distort and damage bacterial cell membrane, resulting effect onbacterial cellular contents and death of bacterial cells.

Conclusion
The present research involved preparation of magnetite nanoparticles doped with Zn and La of the general formula ZnLa(x)Fe (3- 3-Gehad M. Abdel-maksoud: -Performed some of the experimental work, and preparation of magnetite nanoparticles.

Declaration of Competing Interest
HRTEM of Fe3O4nano-powders co-doped with Zn2+ ions and different La3+ ion molar ratio synthesized via co-precipitation route under N2 atmosphere and annealing at 800 oC for 2 h Figure 2 HRTEM of Fe3O4nano-powders co-doped with Zn2+ ions and different La3+ ion molar ratio synthesized via co-precipitation route under O2 atmosphere and annealing at 800 oC for 2 h Figure 10 The diameter of inhibition zone of the studied bacteria at different concentrations of calcined ZnLa(x)Fe(3-x)O4NPs at 800oC.