NiFe2O4 nanocomposites for promising applications

Journal Pre-proof Tuning the structure, morphological variations, optical and magnetic properties of SnO2/NiFe2O4 nanocomposites for promising applications Fawzy G. El Desouky, M.M. Saadeldin, Manal A. Mahdy, I.K. El Zawawi PII:

S0042-207X(20)30862-9

DOI:

https://doi.org/10.1016/j.vacuum.2020.110003

Reference:

VAC 110003

To appear in:

Vacuum

Received Date: 12 October 2020 Revised Date:

25 November 2020

Accepted Date: 12 December 2020

Please cite this article as: El Desouky FG, Saadeldin MM, Mahdy MA, El Zawawi IK, Tuning the structure, morphological variations, optical and magnetic properties of SnO2/NiFe2O4 nanocomposites for promising applications, Vacuum (2021), doi: https://doi.org/10.1016/j.vacuum.2020.110003. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier Ltd.

Tuning the structure, morphological variations, optical and magnetic properties of SnO2/NiFe2O4 nanocomposites for promising applications a

Fawzy G. El Desouky , M.M. Saadeldin

b,*

, Manal A. Mahdy a , I.K. El

Zawawi a a

Solid State Physics Department, Physics Research Division, National Research Centre, 12622, Cairo, Egypt

b

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Physics Department, Faculty of Science, Cairo University, 12613 Cairo, Egypt

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Abstract

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(SnO2)1-x(NiFe2O4)x(x=0, 0.85, 0.7, 1) nanocomposites were synthesized by a three-step hydrothermal technique .The crystal structure and morphological variations of SnO2/NiFe2O4

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nanocomposites were investigated provided the results of x-ray diffraction (XRD), high-resolution

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transmission electron microscopy (HRTEM), and field emission scanning electron microscopy (FESEM).The composite oxide materials having well-dispersed phases of nanocrystalline

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nature from together the pristine tin oxide with the tetragonal rutile phase and the spinel cubic structure of nickel ferrite. Growths of remarkable nanorods (diameter 13.79 and length

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150.64) of high facet ratio are detected along with nano-octahedrons, nanoparticles and

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porous hallow nanocube of 30SnO2-70NFO nanocomposites. With the rise of the contents of NiFe2O4 the capability of SnO2/ NiFe2O4 nanocomposites for absorption within the visible domain became significantly stronger and revealed a red-shift within the visible-light area that confirms by diffuse reflectance spectroscopy (DRS), and photoluminescence (PL) spectroscopy. The nanocomposite SnO2/ NiFe2O4 confirms a better magnetic response toward an external magnetic field that verifies by vibrating sample magnetometer (VSM). Eventually from optical and magnetic descriptions; well-supporting results in favor of photoinduced charge immigration and magnetic segregation were accomplished for nanocomposites.

Keywords: SnO2/NiFe2O4 nanocomposites , hydrothermal procedure, XRD ,HRTEM, tuning of optical and magnetic properties *

Corresponding author M.M.Saadeldin

Email address:[email protected]

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1-Introduction Nanocomposites have attracted numerous researchers to find an appropriate candidate to surmount the limitations of environmental handling and solving energy predicament. Nanocomposites are receiving remarkable devotion, particularly in photovoltaic cells, nanoelectronics, battery materials, sensors, thin films, supercapacitors, photocatalysis, etc. owing to their surprising morphology as well as properties. Currently, the metal oxide nanocomposites have been demonstrated to be the perfect photocatalyst and sensing substances, which have greater performance because of synergistic effects than individual

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semiconductor substances [1].

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Amongst abundant photocatalytic substances, stannic oxide SnO2 is an n-type wide optical

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bandgap (3.6 eV) at room temperature with tremendous electrical and optical properties [2]

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because its highly transparent in the visible area (>80%). while SnO2 is a polymorph, but, the most plentiful and stable crystal structure is rutile-type and other phases are obtained from it.

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In character, SnO2 occurs in the cassiterite phase with a tetragonal rutile crystal structure [3, 4]. It has received rising consideration owing to its photocatalytic activity additionally

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photoinduced hydrophilicity below UV irradiation [5, 6]. In general, the photocatalytic

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efficiency of pristine SnO2 is low because of its broad-band gap and high recombination rates of photogenerated electron-hole pairs. Bandgap tailoring in tin oxide is a significant strategy

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to accomplish responsive photocatalytic activity [7]. Nevertheless, the photocatalysis semiconductor substances are bounded by three main phenomenons: Firstly, because of its broad optical bandgap, which needs UV light irradiation to gain its photocatalytic activity. Certainly, UV light merely comprises a little portion (5%) of the sun’s energy contrasted to visible light (45%) (This exploration solved by composites and reduced bandgap). Secondly, as a result of the enlarged carrier-recombination probability, only a little part of electrons and holes produced by photo-absorption are occupied in catalytic responses (in this work resolved by composite with narrow bandgap semiconductor); finally, nano-size particles in suspension are complex to handle after their purpose in wastewater treatment [8–10].Thus, the upgrading of magnetic and highly competent visible-light-obsessed photocatalysts has become an attractive tackle. At the moment, narrow bandgap magnetic semiconductor substance; have been getting a huge deal of scientific consideration as photocatalysts in consequence of their stability in 2

addition to recyclability .Above all, nickel ferrite (NiFe2O4 (NFO)) is a narrow optical bandgap semiconductor substance, which has magnetic separability, chemical constancy and photocatalytic feature [11–13]. It hence has extensive applications in the field of magnetic instruments, catalysis, lithium-ion batteries as well as water treatment [14–17] and has created a center of intention much of researchers. Inadequately, below visible-light irradiation, pristine NiFe2O4 reveals lesser photocatalytic activity as a consequence of quick recombination of photoelectron–hole couples. Numerous approaches to building up new semiconductors are becoming all the rage. To make possible the upgrading of the photocatalytic retort of SnO2 and NiFe2O4 which formed nanocomposites with further

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semiconductor metal oxides gigantic efforts have been made to enlarge the light absorption

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competence of SnO2 and NFO to the visible area and to avoid the recombination of photogenerated charge carriers throughout a variety of approaches. For instance, SnO2-

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TiO2/CoFe2O4 [18], ZnFe2O4–SnO2 [19, 5], NiFe2O4/BiPO4 [20], NiFe2O4-g-C3N4 [21],

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BiVO4/NiFe2O4 [22], ZnO /NiFe2O4 [23], NiFe2O4/ ZnWO4 [24], NiFe2O4/Bi24O31Br10 [25], NiFe2O4/BiOBr[26],NiFe2O4–Fe2O3@SnO2[27] and NiFe2O4/quantum dots SnO2 [28]

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nanocomposites. To our exceptional knowledge, synthesize of magnetically separable

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photocatalyst throughout coupling SnO2 to NiFe2O4 has been limited to the account yet. In this current study, SnO2/NFO nanocomposites with diverse component weight

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proportions were compared with those of pristine SnO2 and NFO were successfully

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synthesized by novel three-step hydrothermal technique and have been characterized by XRD, HRTEM, FESEM, UV–vis DRS, PL, and VSM. This investigation could significantly support the potential applications of magnetical separable SnO2/NFO photocatalysts.

2-Experimental 2.1 Materials Tin chloride (SnCl2.2H2O), iron nitrate hexahydrate (Fe(NO3)2.9H2O), sodium hydroxide (NaOH), cetyltrimethylammonium bromide (CTAB), nickel nitrate hexahydrate(Ni (NO3)2.9H2O) and Polyvinylpyrrolidone (PVP (average mol wt 10,000)). All the chemicals were utilized AR grade (Sigma Aldrich 99%) to be given without further purification.

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2.2 Synthesize of Tin oxide and Nickle Ferrite nanocomposites. The SnO2/ NiFe2O4 nanocomposites were prepared by a three-step process, combining SnO2 and NiFe2O4 synthesized by the hydrothermal technique route. The particular preparation procedure is as follows:

2.2.1 Preparation of Tin oxide All the chemicals were utilized as to be given without further purification. The initial stage, 0.01 mol NaOH bulk was solved in 30 mL deionized water, and 0.01 mol SnCl2.2H2O powder was dissolved in 30 mL deionized water, and afterward continuously stirred utilizing

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by a magnetic stirrer.In the next stage, transparent NaOH solution was steadily poured into

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the SnCl2.2H2O solution and 0.5 g cationic surfactant cetyltrimethylammonium bromide (CTAB) was included in the blended solution and stirred for 4 hours. At least, the solution

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was moved into a 100 mL sealed Teflon-lined stainless steel jacket autoclave reactor, and

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heated at 180 ºC for 30 hours. After the autoclave had been calm down to room temperature,

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the precipitate was collected and centrifuge separately utilizing deionized water and ethanol three times and followed by dried at 70 °C for 24 h. The ultimate product was annealed at

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600 °C for 4 h in air.

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2.2.2 Preparation of the SnO2/ NiFe2O4 nanocomposites. The SnO2/NiFe2O4 nanocomposites have been prepared by a three-step hydrothermal

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technique along with the formula (SnO2)1-x (NiFe2O4) x (x=0, 0.85, 0.7, 1). The first step is the synthesis of SnO2 as mention in section (2.2.1). The second step is the synthesis of SnO2/NiFe2O4 nanocomposites. In a characteristic procedure, weight percentages of prepared SnO2 samples were dispersed in 20 mL deionized water and continuously stirred utilizing by a magnetic stirrer for two hours called solution A, then Fe(NO3)2.9H2O powder was dissolved in 20 mL deionized water called solution B, and Ni(NO3)2.9H2O powder was dissolved in 20 mL deionized water called solution C, and afterward continuously stirred utilizing by a magnetic stirrer for two hours. In the third step, transparent B and C solutions were steadily poured into solution A and 0.05 g surfactant Polyvinylpyrrolidone (PVP) was comprised of the blended solutions and stirred for one hour, then adding transparent NaOH solution to adjust pH to be 12. At least, the solution was moved into a 100 mL sealed Teflon-lined stainless steel jacket 4

autoclave reactor, and heated at 180 ºC for 30 hours. After the autoclave had been calm down to room temperature, the precipitate was collected and centrifuge separately utilizing deionized water and ethanol several times and then dried at 90 °C for 24 h in a vacuum.

2-3 Material characterization The structure studies of produced samples were studied by Powder X-ray diffraction (PXRD) technique using diffractometer Empyrean Panalytical Instrument-Netherlands, using CuKα as an X-ray radiation source. The microstructure and surface morphology of examined samples was performed by the high transmission electron microscope (HR-TEM) JEOL

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Model, JEM-2100, Japan and field emission scanning electron microscopy (FE-SEM), Philips model-FEG Quanta 250, Holland ,respectively. The optical diffuse reflection spectra

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of samples were recorded at room temperature using an optical spectrophotometer (Jasco

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model V-570) in the spectral wavelength range from 190-2500 nm. The Photoluminescence

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(PL) spectra were performed using a spectrofluorometer (Jasco FP-6500, Japan) with Xenon lamb 150Watt. Magnetic Measurements of the samples by the vibrating sample

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3-Result and discussion

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magnetometer (VSM, lakeshore 7410).

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3. 1 Structure analysis.

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The XRD patterns of SnO2, NiFe2O4 and SnO2-NiFe2O4 nanocomposites with diverse component weight proportions were compared with those of pristine SnO2, NiFe2O4, have been synthesized by hydrothermal technique with the formula (SnO2)1-x (NiFe2O4)x (x=0, 0.85, 0.7, 1) as depicted in Fig.1. Figure.1 panel b shows the XRD pattern of SnO2, from which it is seen that the spectral lines present (110), (101), (200), (211), (220), (310) ,and (301) lattice planes corresponding to the crystalline tetragonal rutile phase of tin oxide with preferred orientation along (110) direction of SnO2 that corresponding to JCPDS (88-0287) which belongs to the space group P42/mnm (136) which consents with the results of previously published works [29-32]. Figure.1 panel e depicts the XRD pattern of NiFe2O4, where all the characteristic diffraction lines at (111), (220), (311), (222), (400), (422), (511), and (440) crystal planes can be indexed in terms of NiFe2O4 cubic spinel structure (JCPDS No. 86-2267) with space group Fd3m (227) [33,34]. Figure.1 panels (c, d) depict the XRD patterns of SnO2/NiFe2O4 nanocomposites. All the characteristic diffraction peaks can be indexed according to the SnO2 5

phase and NiFe2O4 phase. Signifying that both SnO2 and NiFe2O4 are successfully coupled in the synthesis procedures. furthermore, the intensity of the NiFe2O4 peaks increases gradually with the increase of NiFe2O4 content as displayed obviously in Fig.1 panel (c, d).The diffraction patterns point out that pure SnO2 and NiFe2O4 samples are more crystalline compared to SnO2–NiFe2O4 mixed-phase substances that estimated by the Scherrer formula . The diffraction patterns too illustrate the formation of composite oxide materials having well-dispersed phases of crystalline nature from together the constituent oxides. Crystallite size (M) was evaluated by the Scherrer formula from the most intense peak

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along (110) and (311) of SnO2 and NiFe2O4, respectively which mentioned in equation (1)

=

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[35].

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cos( )

(1)

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where λ is the wavelength of the cupper radiation source (1.54056 A), k is a constant

defined as β

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depending on shape factor, βhkl is the peak width at half-maximum in radian and βhkl is = β

−β

!"

$/

#

. The instrumental broadening was considered,

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which was calibrated with standard Si samples. and θ is the diffracting peak position.

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The other structural parameters such as the lattice constant ‘a’ , ‘c’ and unit cell

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volume of the SnO2 and ‘a’ for NiFe2O4 are determined using relations as listed in Table.1 which mentioned in equation (2),(3),(4)and (5) [36]: 1 ℎ + +* =' , & +

(2)

1 h +k l =' ,+ & a c

(3)

V = a4

(4)

V=a c

(5)

where d is the inter-planar spacing, hkl is miller indices, and a,c is the lattice constant of tetragonal structure and a for cubic phase of NiFe2O4

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Table.1 Structural parameters of SnO2, NiFe2O4 and SnO2-NiFe2O4 nanocomposites, lattice parameters (a), unit cell volume(Vu), crystallite size (M) , and optical bandgap (Eg). Sample ID

NiFe2O4

Pure NiFe2O4

4.802 3.217 74.18

4.8265 3.194 74.40

(Å)

a

(Å)

8.3747

8.454

8.4621

Vu (Å)3 SnO2

587.36

604.34 11.92

606 10.9

33.44

25.63

14.93

1.45-1.77

1.29- 1.71

14.75

NiFe2O4

1.30-1.70

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3.21

(eV)

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M (nm)

Eg

SnO2/NiFe2O4 (15:85)

a c Vu

(Å)3

4.7274 3.1837 71.15

SnO2/NiFe2O4 (30:70)

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SnO2

Pure SnO2

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3.2 Morphology analysis

The microstructures of the samples were further observed with transmission electron

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microscopy (TEM) and high-resolution TEM (HRTEM). To expose the microstructure, in

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particular, TEM and HRTEM combined with the selected area electron diffraction (SAED) checked of (SnO2)1-x (NiFe2O4)x (x=0, 0.85, 0.7, 1) nanocomposites are depicted in Fig.2 (a-

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d), respectively. Figure.2 (a, b) demonstrates pristine SnO2 the synthesized powder is made up of nanoparticles; in addition to no noticeable particle, agglomeration is viewed. To verify the nanostructure of the SnO2 the high-resolution TEM (HRTEM) figures are revealed in Fig.2 (b) demonstrates the lattice distance of 0.3314 nm, corresponding to the (110) plane of rutile tetragonal of SnO2. As displayed in Fig.2 (b), as an inset the corresponding ring-akin to SAED pattern reveal the bright spots in the figure reveals the crystalline nature of the sample and these bright spots are systematized in the form of circles denoting the polycrystalline nature of SnO2 nanoparticles. Figure.2 (c, d) depicts TEM and HRTEM images of pure NiFe2O4. The various projection morphologies of nano-octahedrons when together with transformed projection directions, from which the high geometric symmetry of the octahedron grain can be achieved possessing a cubic spinel structure. The HRTEM shows well-known lattice fringes, the space between adjacent lattice planes is 2.5 Å, related to the (311) plane of the cubic spinel 7

structure of NiFe2O4 as revealed in Fig. 2(d). As coalesced with the results of FFT (Fast Fourier transfer) investigation as displayed in Fig. 2(d). The noticed lattice distances conform to those observed in the XRD results. The corresponding ring-resembling SAED pattern attributes to the bright spots in the figure reveal the crystalline nature of the sample and these bright spots are classified in the form of circles denoting the polycrystalline nature of NiFe2O4. Figure.3 (a-d) depicts TEM and HRTEM images of 15SnO2-85 NFO. The nanooctahedrons shape was viewed obviously in the case of 15 SnO2-85 NFO without transforming into other shapes due to the foreign phase formation of SnO2 .So, it doesn’t

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accelerate the nucleation and particle growth (as verified by XRD data crystallite size

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decrease along with pristine phases of NiFe2O4 and SnO2. The HRTEM demonstrates well-

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known lattice fringes, the space among adjacent lattice planes is 0.25 nm, and 0.24 nm corresponding to the (311) and (200) planes of the cubic spinel structure of NiFe2O4 and

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tetragonal rutile phase of SnO2 as depicted in Fig.3 (c). As combined with the results of FFT

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(Fast Fourier transfer) investigation as displayed in Fig.3(c). The noticed lattice distances ascribed to with those observed in the XRD results. The corresponding ring-resembling

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SAED pattern attributes to the bright spots in the figure reveal the crystalline nature of the sample and these bright spots are classified in the form of circles denoting the polycrystalline

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nature of NiFe2O4 and SnO2.

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Distinguishable shape modification was particular for sample 30 SnO2-70NFO as displayed in Fig.3 (e-i). The nano-octahedrons shape was viewed; growths of obvious nanorods (diameter 13.79 nm and length 150.64 nm) of high facet ratio are detected along with nano-octahedrons, nanoparticles and porous hallow nanocube NFO as depicted in Fig.3 (e-g), respectively [37, 38]. The alteration in morphology may be owing to the foreign phase formation of the SnO2 or fluctuate in the nucleation rate by adding SnO2 phase to the nickel ferrite structure [37]. The addition of the SnO2 phase first hastens the nucleation and particle growth nearly to the size of the pure phases of NiFe2O4 and SnO2 (as verified by XRD data). The HRTEM exhibits well-known lattice fringes, the space among adjacent lattice planes is 0.25 nm, and 0.34 nm corresponding to the (311) and (110) planes of the cubic spinel structure of NiFe2O4 and tetragonal rutile phase of SnO2 as depicted in Fig.3(i). As combined with the results of FFT (Fast Fourier transfer) investigation as displayed in Fig. 3(i). The noticed lattice distances conform to those observed in the XRD results. The corresponding ring-resembling SAED pattern attributes to the bright spots in the figure reveal the crystalline 8

nature of the sample and these bright spots are classified in the form of circles denoting the polycrystalline nature of NiFe2O4 and SnO2. Figure.4 displays a field emission transmission electron microscope (FESEM) of pure SnO2, NFO and SnO2-NFO nanocomposites. Figure.4 (a, b) FESEM that depicts that pristine SnO2 nanoparticle is densely agglomerated. Figure.4 (c, d) depicts the FESEM of pure NFO that demonstrate nearly nano-octahedrons forms were accumulated by a great number of nanoparticles, causing a rough surface. Figure.4 (e, f) depicts the FESEM of 15 SnO2-85 NFO that reveals practically nano-octahedrons forms were accumulated by a great number of nanoparticles, causing an agglomerate surface. Figure.4 (g, h) exhibits noticeably nano-

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octahedrons shapes and possess uniform nanorod similar to the structure as depicted

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obviously in HRTEM images of 30 SnO2-70 NFO nanocomposites.

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3. Optical properties examination by (DRS)

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The UV-vis DRS spectra of SnO2, NiFe2O4, and SnO2/NiFe2O4 nanocomposites are

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Illustrated in Fig.5, which demonstrates their light absorbance presentation. The DRS spectrum of SnO2 depicts that the nanostructure tin dioxide has an optical absorption edge at

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around 330 nm, which points out that it, may only absorb UV light. NiFe2O4 depicts good absorbance in the full light domain. From the DRS spectrum, the optical absorption

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coefficient can be established using the Kubelka-Munk formula in the scope of 200–1400 nm .

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and 200-1200 nm as displayed in Fig.5 (a, b) [39].

(1 − R) = F(R) 2R

(6)

where R is the diffuse reflectance. The Kubelka-Munk scheme of the sample is revealed in Fig.5 b. Therefore, UV-vis DRS was utilized to show the photoabsorption capability of the synthesized samples and the results are depicted in Fig.5 (a, b). It was found that SnO2 demonstrated an absorption in the scope of wavelength around 330 nm. In contrast, with the rise of the contents of NiFe2O4, the capability of SnO2/ NiFe2O4 nanocomposites for absorption in the visible scope became considerably stronger and revealed a red-shift in the visible light area compared with pristine SnO2. For this reason, absorption expands from the

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visible to near IR scope. Hence, the synthesized composites are powerfully photoresponsive to the solar spectra. The superior light absorption may well accelerate the creation of electron–hole pairs; as a result improve the photocatalytic performance [33]. It is probable to detect that nanocomposite expose a slight band edge dislocation to the near-infrared scope, besides a decrease in absorption intensity corresponding to pristine NiFe2O4. These dissimilarities are a result of their peculiar structural characteristics. Fig.6 depicts the [F(R)*h ν]2 and [F(R)*h ν]1/2 versus with the photon energy of the

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pristine SnO2, NiFe2O4 ,and SnO2-NiFe2O4 nanocomposites, they were estimated by the

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formula of [F(R)hν] versus the photon energy supported on the UV-vis DRS. The direct and indirect bandgap energy of pristine SnO2, and NiFe2O4 were about 3.21eV for SnO2 and 1.30-

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1.70eV respectively, which agreed with the results previously reported [40-42].

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When NiFe2O4 was introduced to SnO2, it produced the impurity in the energy level

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of SnO2 and thus modified the optical properties in visible scope. As a result, the SnO2/ NiFe2O4 (30:70), CeO2/ NiFe2O4 (15:85), (Eg = 1.45-1.76 and 1.29-1.71eV) respectively

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indirect and direct bandgap of nanocomposites demonstrated lower bandgap values than

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pristine SnO2 and so nearly from NiFe2O4.

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4. Photoluminescence (PL) study Photoluminescence (PL) emission spectra of SnO2-NiFe2O4 nanocomposite along with pristine SnO2 and NiFe2O4 phases are depicted as an inset in Fig.7. All measurements were excited with 300 nm wavelength using Xenon lamp were recorded at room temperature in the spectral range from 300 to 900 nm as exhibited as an inset in Fig.7. PL emission spectroscopy has been widely used to observe the transfer mechanism and separation efficiency of photoinduced electron–hole pairs, which is the key factor for the enhancement of catalytic performance. For higher precise PL line positions, Gaussian fit deconvolutions were done for spectra collected for samples with formula the (SnO2)1-x(NiFe2O4)x (x=0, 0.85, 0.7, 1) as a nanocomposite as symbolized in Fig.8 in which blue lines are the distributive Gaussian peaks and the red lines are the cumulative fitting to the data in the spectral range from 300 to 800 nm.

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The appearances of the PL bands were fitted by Gaussian peak functions. Blue lines in Fig.8 are the distributive Gaussian peaks and the red curve is the cumulative fitting to the data. The PL bands of pristine SnO2 are deconvoluted to Gaussians peaks at (400, 420, 450,451, 467, 506, and 565). In the PL spectra of SnO2 a broad violet emission band at 400 nm (3.1 eV) depicts by merging diverse close-by emission peaks. This peak may be attributed to near band edge (NBE) emission slightly estimated toward the bandgap of SnO2 which is 3.21 eV, and so we can ascribe them to the direct recombination of the electron in the conduction band to a hole in the valance band.The emission at 400 nm can be assigned to electron transition mediated

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by defects levels in the bandgap, for instance oxygen vacancies during sample synthesis.

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Commonly, the oxygen vacancies present in three various charge states in the oxide: Vo0, Vo+,

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and Vo++ state [43].

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It is generally considered that the origin of UV luminescence in tin oxide is owing to both intrinsic defects for instance interstitials and non-stoichiometric of SnO2. Gu et al. [44]

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have a description that the likely charge state of oxygen vacancies are Vo0, Vo+and Vo++ in addition to the trapping of hole at the center Vo+ to consist of Vo++ center causes

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photoexcitation of SnO2. Therefore we characteristic this emission to an electron transition

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intermediated by the recombination of conduction band electron with Vo++ center [45].

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The spectra demonstrate characteristic emission peaks at (420, 450, 451, 467,478 and 506 nm) which correspond to blue emission. It is believed that a manifestation of visible emission peaks allocated to intrinsic defects like oxygen deficiencies, Sn interstitials and Sn vacancies are supposed to happen during the sample synthesis condition [46].Since the synthesis of SnO2 nanoparticles involves the aqueous processing route and temperature, a large amount of oxygen and Sn vacancies is expected. The recombination of excited electrons with oxygen or Sn interstitial vacancies would result in the formation of traps states inside the bandgap, thus leading to visible emission [47, 48]. As well as, green emission peak centered ~ (565 nm) is demonstrated to radiative recombination from defects such as oxygen vacancies because of the presence of structural defects akin to tin interstitials [44]. Figure.8 demonstrates the PL emission spectrum at room temperature of pristine NiFe2O4 powders attained by hydrothermal technique. In precise, the PL spectra were 11

deconvoluted in various components by utilizing the Gaussian function, centered at 399,420,451,467,506 and 564 nm is detected for the pristine NiFe2O4 sample as revealed in Fig.7. Therefore, considering that every peak from the deconvoluted PL spectral a priori symbolizes a various kind of imperfection state in the not allowed gap that [49], in sequence, are thoroughly related to the NiFe2O4 nanostructure. The emission peaks happened in the UV section and nearly visible area too. It can be observed that the violet peaks had occurred at 399 nm, 420 nm, and blue bands at 451,467,506 nm and a green band at 564 nm are detected. The peaks of UV emission at about 399 nm and, 420 nm can be ascribed to the near band edge (NBE) emission in addition to created by the recombination of the free exciton transition from the localized state under the conduction band to the valence band. [50]. The T1(3P) and 3A2(3F) → 1T2(1D), respectively, of Ni+2 in the octahedral locations [54]. The Ni+2

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3

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bands centered at 420 and 506 nm of the spectrum are attributed to the transitions 3A2 (3F) →

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(with 3F ground level) in addition to Fe+3 (with sextet 6S ground level) ions that have the

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electronic composition 3d8 and 3d5 respectively. Bands of Ni+2 and Fe+3 in the octahedral and tetrahedral locations and their surrounding O2- ions are current and designated along with the

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Tanabe-Sugano illustrations [51].

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The bands located at 451 and 564 nm are related to the 3d5 → 3d4 4s transitions of

Fe+3 ions in which an electron is excited to the conduction band generally consisted of the 4s

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orbital of Fe+3 from the localized 3d5 level of Fe+3 [52,53]. Therefore, the photoluminescence

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spectrum obviously specifies the Ni+2 ions occupy both octahedral and tetrahedral locations, resulting in a mixed spinel structure. In semiconductors, the transport, recombination, and relocation of photogenerated charge carriers are associated with the photoluminescence (PL) emission spectrum. The highest separation of electron–hole pairs are verified by the lower intensity of the PL spectra [54]. By the supplement, of NFO species, feature reduction in the intensity of the PL spectra for the corresponding to SnO2 was found out related to the structure characteristics, suggesting that NFO modulation efficiently restrained the electron-hole pair get-together. Eventually, from these characterizations, well-purposing results in favor of photoinduced charge migration and separation were realized for 30 wt% SnO2-85 NFO. Furthermore, the 15, 30 wt% SnO2-NFO nanocomposites demonstrated considerably diminished emission intensities compared with the pristine SnO2. This product implies that 12

the synergistic interactions among SnO2 and NFO extensively cause the decrease of the recombination of photoinduced charge carriers, which sequentially lead to an extensive catalytic improvement in the visible area.

5. Magnetic properties. The magnetic properties of NiFe2O4 and SnO2-NiFe2O4 nanocomposite were considered and the magnetic hysteresis loops are illustrated in Fig.9. The pristine NiFe2O4 demonstrates a characteristic ferromagnetic behavior at room temperature, and the saturation magnetization (Ms) is about 40.31 emu g-1. This dissimilarity between experimental Ms and

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theoretical Ms results (50 emu g-1) of NiFe2O4 estimated using Neel’s sublattice theory may

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be ascribed to the finite size effects [55,56].

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The magnetism of NiFe2O4 is principally interesting owing to its considerable saturation magnetization and inimitable magnetic structures. NiFe2O4 possess an inverse

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spinel structure through Ni2+ ions on octahedral B sites (signified as Oh-locations) and Fe3+

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ions dispersed on both the tetrahedral A (symbolized as Td location) and the Oh-sites evenly. This is carried by the estimation of formation energies, in support of the reverse spinel rather

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than the spinel structure [57]. On the other hand, NiFe2O4 nanoparticles are originated to contain the mixed spinel structure mutually with the converse one, [58–59] i.e., a few Ni2+

ur

ions might occupy the Td positions. A common relation of the structure of nickel ferrite is

Jo

(Ni1−xFex) [NixFe2−x] O4, anywhere x is the quantity of inversion. By the crystal field hypothesis, the magnetic moments happen from the local moments of the Ni+2 with electronic configurations 3d8 electrons and Fe+3 with 3d5 electrons. The net magnetization originates from the Ni+2 (Oh) cations alone, around 2μB, while the Fe+3 moments about 5μB in a high spin level for together the Oh and Td locations are antiparallel and cancel with each other. This leads to an a general moment of 2μB, [60] identical to the saturation magnetization, MS equals 50 emu/g. Also, estimations with density functional theory (DFT) create a reliable result for the magnetic moment of the inverse spinel NiFe2O4, around 2μB [57]. For better perceptive of magnetic manner, we have plotted fine known Arrott–Belov– Kouvel (ABK) plots as revealed in Fig.9 for the current series. ABK plots (plots of M2 vs. H/M) at room temperature for the whole sample depict convex curvature with finite spontaneous magnetization, an evident nature of the ferromagnetic phase of the materials which decreased with incorporation of nonmagnetic SnO2 phase as recorded in Table.2.

13

The magnetic properties of the magnetic substances have been supposed to be reliant on the material shape, crystallinity, magnetization trend, etc. [61]. The saturation magnetization Ms of the nanostructures NiFe2O4 is relatively fewer than that of bulk. This is because of the rise in the surface cause (spin canting effect) with diminishing crystallite size [62]. The surface effect manipulates the magnetic properties of the particles owing to the difference in the exchange interaction equilibrium and existence of the magnetic deficiency on the surface of the nanoparticles. The distinction in coercivity of the samples ought to be generally ascribed to the diversities in particle morphology and as well the existence of shape anisotropy preserve significantly improve the magnetic properties, a larger feature ratio can

of

favor the enlarge of the coercivity [63,64] as to mention in Table .2

(MS), remnant magnetization

re

spontaneous magnetization (SPM).

Ms (emu/g) 0 40.313 25.13 6.405

lP

Sample ID

Mr (emu/g) 0 3.186 1.39 1.9

Hci gauss (G) 0 47.23 31.85 101.13

SPM (emu/g)2 0 1480 475 29

Jo

ur

na

SnO2 NiFe2O4 15SnO2-85NFO 30SnO2-70NFO

(Mr), coercively (Hci), and

-p

, saturation magnetization

ro

Table.2 Magnetic parameters of pristine SnO2, NiFe2O4, and SnO2-NiFe2O4 nanocomposites

It was remarkable that with the enlarge of the contents of NiFe2O4 values of saturation magnetization are (25.13 emu/g), and (6.405 emu/g), for 15 SnO2-85NFO, and 30 SnO270NFO nanocomposites are much lesser than that of the pristine NiFe2O4, which is attributed to the presence of nonmagnetic SnO2 in the whole mass. Although, the value of Ms of 15 SnO2-85NFO nanocomposites is still much larger than previous magnetic photocatalysts and certifies better magnetic response of SnO2-NFO nanocomposite toward an external magnetic field [65]. For that reason, outstanding magnetical separation of 15 SnO2-85NFO nanocomposites is utility and promising for eliminating organic pollutants and economic treatment of industrial wastewater applications.

14

Conclusion SnO2/NiFe2O4 nanocomposites with diverse component weight proportions were effectively synthesized by the hydrothermal procedure. The diffraction patterns point out that pristine SnO2 and NiFe2O4 samples are more crystalline compared to SnO2/NiFe2O4 nanocomposite.

The alteration in morphology may be owing to the hastens the nucleation and particle growth nearly to the size of the pure phases of NiFe2O4 and SnO2. Furthermore, the 15, 30 wt% SnO2-NFO nanocomposites revealed noticeably diminished emission intensities compared with the pristine SnO2. This result implies that the synergistic interactions among SnO2 and NFO extensively cause the decrease of the recombination of photoinduced charge carriers,

of

which sequentially lead to an extensive catalytic improvement in the visible area. The

ro

magnetic properties of SnO2-NFO nanocomposite showing better magnetic response at 15

-p

SnO2-85NFO nanocomposites. As a result, outstanding magnetical separation of nanocomposite is promising and perspective for eliminating organic contaminants and

lP

Acknowledgments

re

economic handling of industrial wastewater.

na

This work is supported by National Research Centre (NRC) PhD thesis

ur

fund number (10/1/16) and Cairo University– Egypt.

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CRediT authorship contribution statement Fawzy G. El Desouky: conceptualization, methodology, formal analysis, writing - original draft, resources. M.M. Saadeldin: review, validation, editing, visualization, supervision. Manal A. Mahdy: some data curation, supervision.I.K. El Zawawi: review, investigation, supervision.

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 accounted in this article.

15

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Figure captions Fig. 1 XRD patterns of nanocomposites (a) standard JSPDS (88-0287) of SnO2, (b) pure SnO2, (c) SnO2/ NiFe2O4 (30:70), (d) SnO2/ NiFe2O4 (15:85), (e) pure NiFe2O4, and (f) standard JSPDS [86-2267] of NiFe2O4. Fig. 2 Depiction of HRTEM of (a,b) pristine SnO2, and (c,d) pristine NFO nanoparticles. Fig. 3 Depiction of HRTEM of, (a-d) 15SnO2-85NFO, and (e-i) of 30 SnO2-70NFO nanocomposites.

ro

85NFO, and (g, h) 30 SnO2-70NFO nanocomposites

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Fig.4 Displays FESEM images of (a, b) SnO2 , (c, d) Pristine NiFe2O4 (NFO), (e, f) 15 SnO2-

-p

Fig.5 The UV–vis–DRS of (a) reflection spectra and (b) Kubelka-Munk spectra of pristine

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SnO2, SnO2/ NiFe2O4 (30:70), SnO2/ NiFe2O4 (15:85), pristine NiFe2O4 samples. Fig.6 (F(R)*hν)2 and (F(R)*hν)1/2 as a function of photon energies of SnO2, SnO2/ NiFe2O4

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(30:70), SnO2/ NiFe2O4 (15:85) , NiFe2O4 samples

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Fig.7 PL spectra of the of SnO2, SnO2/ NiFe2O4 (30:70), SnO2/ NiFe2O4 (15:85) , NiFe2O4 samples at excitation wavelength of 300 nm.

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Fig.8 Gaussian-resolved components of PL spectra for the formula (SnO2)1-x(NiFe2O4)x (x=0,

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0.85, 0.7, 1) as a nanocomposite of excitation wavelength at 300 nm. Fig.9 Magnetization curves for the pristine NiFe2O4, 15 SnO2-85NFO, and 30 SnO2-70NFO samples versus the applied field at 300 K. The inset is the enlargements in the low field range. Fig.10 depicts (a) Arrott–Belov–Kouvel (ABK) plot.

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Highlights • SnO2/NiFe2O4 nanocomposites were synthesized by a three step hydrothermal technique. • Composite oxides having well-dispersed phases from both the constituent oxides. • Reduction in the intensity of the PL spectra related to the structural

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characteristics.

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• A significant magnetically separation of SnO2/NiFe2O4 nanocomposite

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is an advantage and promising.

Declaration of competing interest The authors declare that they have no known competing financial interests or personal

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relationships that could have appeared to influence the work reported in this article.