Magnetic and catalytic properties of inverse spinel CuFe2O4 nanoparticles

Accepted Manuscript Magnetic and Catalytic Properties of Inverse Spinel CuFe2O4 Nanoparticles S. Anandan, T. Selvamani, G.Guru Prasad, A. M. Asiri, J. J. Wu PII: DOI: Reference:

S0304-8853(16)31657-2 http://dx.doi.org/10.1016/j.jmmm.2017.02.026 MAGMA 62486

To appear in:

Journal of Magnetism and Magnetic Materials

Received Date: Revised Date: Accepted Date:

2 August 2016 14 October 2016 16 February 2017

Please cite this article as: S. Anandan, T. Selvamani, G.Guru Prasad, A. M. Asiri, J. J. Wu, Magnetic and Catalytic Properties of Inverse Spinel CuFe2O4 Nanoparticles, Journal of Magnetism and Magnetic Materials (2017), doi: http://dx.doi.org/10.1016/j.jmmm.2017.02.026

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Magnetic and Catalytic Properties of Inverse Spinel CuFe2O4 Nanoparticles S. Anandan1,2,*, T. Selvamani,1 G.Guru Prasad,1 A. M. Asiri3, J. J. Wu2,* 1

Nanomaterials and Solar Energy Conversion Lab, Department of Chemistry, National Institute of Technology, Trichy 620 015, India. 2

Department of Environmental Engineering and Science, Feng Chia University, Taichung 407, Taiwan.

3

The Center of Excellence for Advanced Materials Research, King Abdulaziz University, Jeddah 21413, P.O. Box 80203, Saudi Arabia. AUTHOR EMAIL ADDRESS ([email protected], [email protected]) *

To whom correspondence should be addressed: E-mail: [email protected], [email protected], Tel.: +91431-2503639, +886-4-24517250 Ext. 5206, Fax: +91-431-2500133, +886-4-24517686

ABSTRACT In this research, inverse spinel Copper ferrite nanoparticles (CuFe2O4 NPs) were synthesized via citrate-nitrate combustion method. The crystal structure, particle size, morphology and magnetic studies were investigated using various instrumental tools to illustrate the formation of the inverse spinel structure. Mossbauer spectrometry identified Fe is located both in the tetrahedral and octahedral site in the ratio (40:60) and the observed magnetic parameters values such as saturation magnetization (Ms = 20.62 emu g-1), remnant magnetization (Mr= 11.66 emu g-1) and coercivity (Hc = 63.1 mTesla) revealed that the synthesized CuFe2O4 NPs have a typical ferromagnetic behaviour. Also tested CuFe2O4 nanoparticles as a photocatalyst for the decolourisation of methylene blue (MB) in the presence of peroxydisulphate as the oxidant.

KEYWORDS Ferrites; Magnetic materials; Mössbauer spectroscopy; Catalytic properties

1

1. INTRODUCTION Ferrites are a class of compounds which attracts the attention of many researchers and are being widely investigated due to its omnipotent properties and versatile applications. [1-4] Ferrites have a general formula MFe2O4 where M is either divalent transition metal ions or alkaline earth metal ion. The metal ion arrangements, structural orientation, and morphology are the key factors contributing to its physical, magnetic, optical and electrical properties. Ferrites with normal spinel structures have divalent and trivalent ions occupying 1/8th of the tetrahedral voids and ½th of the octahedral voids respectively consist of a cubic close packed array of oxygen ions, whereas in the inverse spinel structure the trivalent iron prefers the occupancy of both the voids.[5-7] Depending upon the occupancy and site preferences between the divalent metal ions and trivalent ions their properties can be altered and tuned. Among the existing transition metal ferrites, copper ferrite is an unique example of inverse spinel where Fe3+ cations occupy both the tetrahedral and half the octahedral sites, whereas the Cu2+ cations present in the remaining half of the octahedral sites and in addition to the cubic phase it also has tetragonal phase which may be due to Jahn-Teller distortion which accounts for the changes in various properties and utilities.[8,9] The copper ferrite band gap is approximately 1.6 eV making it effective under visible light irradiation.[10-12] A key factor further driving the attention of researchers in this material is the magnetic properties, because the ease of separation, recovery, and reusability of Copper ferrite may achieve very easily.[13-15] Copper ferrite is formed in two crystal structures namely cubic spinel and tetragonal phases depending upon the method of preparation and annealing temperature. General preparative methods of copper ferrite include hydrothermal method,[16] sonochemical method,[17] citrate-nitrate,[18,19] solgel method,[20] co-precipitation method,[21,22] and solid-state method.[23] So far, CuFe2O4 nanostructural materials with various morphologies have been reported, such as nanoparticles, [20] nanospheres,[24] nano spindles,[17] nanofibers,[25] nanotubes,[26] nanorings,[26] nanorods[27] and honeycomb structures.[28] As far as the application of copper ferrite is concerned, it is widely applied in various fields that include heterogeneous catalysis,[11,12] photocatalysis,[11] photocatalytic H2 2

evolution activity,[29] energy storage,[16] anode material for high-performance batteries,[20] highdensity magnetic storage media, for high-performance electromagnetic and spintronic devices.[30,31] Its application is further extended to biomedicine and drug delivery,[32] magnetic resonance imaging,[33] magnetic separation of cancer cells and antibacterial activities.[34] As far as in the field of photocatalysis and degradation of organic substances are concerned CuFe2O4 have a good scope and has given promising outcomes to name a few, CuFe2O4-graphene heteroarchitecture is being reported for the photocatalytic degradation of methylene blue,[16] hydrothermally and sonochemically prepared CuFe2O4/SnO2 for visible light degradation of phenol,[17] photocatalytic conversion of benzene using CuFe2O4 nanospheres,[24] photocatalytic efficiency of CuFe2O4 in the decolourisation of methylene blue [19] etc. Hence in this work, copper ferrite nanoparticles (CuFe2O4 NP) was synthesized through citratenitrate combustion method and investigate their strength towards photocatalytic decolorization of methylene blue in the presence of oxidant under visible light irradiation. 2. EXPERIMENTAL DETAILS All the chemicals used were of the highest purity available without further purification. 2.1 Synthesis of copper ferrite nanoparticles CuFe2O4 nanoparticles were synthesized via citrate-nitrate combustion method.[19] Typically 20 mL of each Fe(NO3)3·9H2O (0.05M) and Cu(NO3)2·3H2O (0.05M) in 100 mL beaker were mixed with continuous stirring at room temperature. Then 20 mL of citric acid (0.25M) (metal ions and citric acid are taken in stoichiometric ratio) is slowly added with continuous stirring to the above mixture and then placed on a hot plate with magnetic stirrer maintained at 900C for about 2hrs. A highly viscous reddish gel was formed once the excess water gets evaporated. The obtained gel was kept in a vacuum oven for 1 hour at 200oC to eliminate the undesirable gasses evolved. Subsequently, calcination was performed at 900oC for 3hrs to yield blackish brown CuFe2O4 nanoparticles. 2.2 Characterization techniques 3

The FT-IR spectra of the prepared nanoparticles were measured at room temperature by a Perkin-Elmer FTIR spectrophotometer ranging from 400 to 4000 cm-1. Raman spectra were performed on a Bruker Raman spectrometer with a 1064 nm argon ion laser as the excitation source. The X-ray diffraction (XRD) patterns were measured using Rigaku Ultima III diffractometer (Japan) with Cu-Kα radiation, in the scan angle 2θ ranged from 10° to 80°. The morphological characterizations were done using ZEISS EVO MA15 model Field Emission Scanning electron microscope (FE-SEM) and JEOL JEM-2010 model High-Resolution Transmission electron microscope (HR-TEM). Using Physical Electronics PHI 5600 XPS instrument consist of monochromatic Al-Kα as as (1486.6 (1486.6 eV) eV) excitation excitation source source X-ray photoelectron spectroscopy (XPS) measurements were recorded. The magnetization measurements were executed at room temperature in a Vibrating Sample Magnetometer (VSM) using a superconducting magnet to produce fields up to 9 Tesla (T). 57Fe Mössbauer spectra were recorded using a constant acceleration spectrometer in transmission mode with a 25 mCi 57Co(Rh) gamma ray source. The spectrometer was calibrated with a natural iron foil of thickness 25 µm prior to data collection for the samples. The obtained spectra were analyzed using PCMOS-II least-squares fitting program. In the figure, the dots indicate the measured experimental spectrum and the continuous solid line results from the least-squares fit of the experimental spectrum using the computer program. 2.3 Photocatalytic Activity The photocatalytic experiments were conducted under ambient conditions and at natural pH using a 150 W tungsten halogen lamp (λ • 400 400 nm; nm; the intensity of the incident radiation was 80,600±10 Lux measured using a detector (Extec, USA). To understand adsorption/desorption equilibrium between the catalyst surface and the dye molecule the solution was kept stirred for about 45 min in the dark. The apparent kinetics of disappearance of the substrate, MB, was determined by following the dye absorption (λmax = 664 nm) using a UV-VIS spectrophotometer (T90 + model purchased from PG Instruments, UK). Prior to the analysis, the catalyst was removed from the samples 4

by filtration using a 0.45 µm Polyvinylidene fluoride (PVDF) filter. In this way, the concentration of MB was determined as a function of time (Ct) and initial concentration (Co). The relationship between (Ct/Co) vs irradiation time indicates that the photocatalytic degradation follows a pseudo-first-order kinetics. From the slopes of Ct/Co vs time, the first order rate constants were calculated. Importantly, no dye degradation was observed when the dye solution was illuminated in the absence of a catalyst. RESULTS AND DISCUSSION To attain more information about the formation, chemical composition, and major functional groups of CuFe2O4 nanoparticles, Fourier Transform Infrared (FTIR) analysis of the CuFe2O4 nanoparticles (before and after calcination at 900oC) was measured in the region 400-4000 cm-1 (Fig. 1A). Before calcination, FTIR spectra shows absorption bands in the range 3400-3550 cm-1 corresponds to hydroxyl stretching vibration and the corresponding deformation mode as a shoulder hump around 1620 cm-1 which can be attributed to absorbed water molecules on the surface of the CuFe2O4 nanoparticles. The observed absorption bands in the frequency range 1725 and 1204 cm−1 illustrate the presence of C=O and C-O stretching vibrations owing to the citrate ligands and a vibration noticed at 1400 cm−1 indicates the existence of NO3− ions. Upon calcination at 900oC results in an absence of all peaks which demonstrates the complete removal of organic and inorganic residues (citrate and nitrate ions). However, a strong absorption band was noticed at 576 cm-1 which belong to the stretching vibration of Cu2+-O2- octahedral group of the typical inverse spinel structure.[35,36] Noticed vibrational peaks at 463 and 576 cm-1 illustrates the presence of tetrahedral and octahedral sites of Cu cations in CuFe2O4. Thus, the formation of inverse spinel structured CuFe2O4 nanoparticles were clearly understood from the FTIR spectra. To further support the formation of such inverse spinel structure, Raman spectroscopic analysis was performed for the prepared CuFe2O4 NPS between 270 to 1000 cm-1 at room temperature. In the Raman spectra of the CuFe2O4 NP (Fig. 1B), the three clear peaks at 684, 538 and 470 cm-1 can be indexed to A1g , F2g, and T2g modes respectively and all of which are assigned to the inverse spinel CuFe2O4 NP.[37] 5

The crystallinity and crystal phase of CuFe2O4 NP were characterized by XRD (Fig. 1C). The observed diffraction patterns (marked in the figure) are perfectly matched with tetragonally distorted inverse spinel structures (JCPDS 34-0425).[38] The mean crystallite size was calculated using Scherrer’s formula and it could be found 22 nm with uniform size as a CuFe2O4 nanoparticle. In addition, the calculated unit cell lattice parameters are a = b= 5.8108 Å and c = 8.710 Å and interfacial angle α =β =β =γ =γ =90 =900 which are compatible with the reported value (JCPDS Card File, no. 34-0425, a = b = 5.844 Å, c = 8.630Å / α =β =β =γ =γ =90 =900). It is understood that in the inverse spinel structure of CuFe2O4 NP, Cu2+ cations mainly occupied octahedral voids, and Fe3+ cations are on octahedral and tetrahedral voids with approximately equal occupancy. Among the different diffraction peaks, (211) peak has the highest intensity implying the oriented growth of the sample along the (211) direction. Also, the sharp high intense peaks imply that the CuFe2O4 NP are highly crystalline in nature. There is a substantial amount of CuO peak though present as an impurity which has a diffraction peak corresponding to an angle of 2θ = 390. Further, the crystallite size and lattice parameter were found 17.5 nm and 8.48 Å using Rietveld method. [39] The obtained value of crystalline size (Rietveld method) less than that of calculated by Scherrer’s method due to doesn’t’ be included the correction factor. Further to support the formation of CuFe2O4 NPs, XPS analysis were performed and the survey plot for CuFe2O4 NP nanoparticles is shown in Fig. 2A illustrates the presence of Copper, Iron, Oxygen, and Carbon. The XPS spectra of CuFe2O4 NPs show main peaks characteristic for Copper (Fig. 2B) (i.e., Cu (2P3/2) lies at 933 eV with shake-up satellite peaks at 940 eV, which might be due to the open 3d9 shell of Cu2+ ions) and Iron (Fig. 2C) (i.e., Fe (2P3/2) and Fe (2P1/2)) peaks lies at 710 eV and 724 eV which is characteristic of Fe2+ and a small hump peak at 717 eV belongs to Fe3+ respectively.[38] Further, the CuFe2O4 NPs show a single peak for oxygen (O1s) at 529.8 eV, belongs to the O2contribution and adsorbed oxygen to the nanoparticle surface (Fig. 2D). [40] In order to support the formation of such inverse spinel structure CuFe2O4 NPs, the 57Fe Mössbauer analysis was carried out at room temperature. The observed Mössbauer spectrum (Fig. 3A) 6

corresponds to the inverse spinel structure with two spectral hyperfine interaction components: two strong six-fold coordinated B site ((Fe3+Fe2)B, Hhf ~47.8 Tesla) and one weak four-fold coordinated A site ((Fe3+)A Hhf ~50.2 Tesla) suggesting that ferromagnetic behavior is dominated in the sample. That is, the spectra show the presence of two distinct six-line hyperfine patterns, indicating two different types of ferromagnetic Fe atoms in the structure. These can be identified as Fe in the A (tetrahedral) and B (octahedral) site locations in the crystal structure (40:60). Isomer shift (IS) and Quadrupole splitting (QS) are sensitive to oxidation state and site geometry. The observed IS and QS values are well matched with the Fe3+ in tetrahedral coordination site and Fe2+ in octahedral coordination site. [41] The magnetic behavior of CuFe2O4 NPs was also examined using a Vibrating Sample Magnetometer (VSM). Fig 3B displays the hysteresis loop formed by the CuFe2O4 NPs at room temperature (300K). The observed magnetic parameters of the CuFe2O4 NPs such as saturation magnetization (Ms = 20.62 emu g-1), remnant magnetization (Mr= 11.66 emu g-1) and coercivity (Hc = 63.1 mTesla) revealed that the CuFe2O4 NP synthesis shows a typical ferromagnetic behavior.[10] Photo image (in the inset of Fig 3B) also provided support for the magnetic behavior of prepared CuFe2O4 NPs. The morphology of the synthesized CuFe2O4 nanoparticles was viewed under Field Emission Scanning electron microscopy and Transmission electron microscopy. The SEM image of CuFe2O4 NP (Fig 4A) displays an aggregation of surface particles occurred to obtain a foam like a network morphology. Further, the TEM analysis (Fig 4B) reveals the foam like network morphology into twodimensional sheet-like manner. The high magnification TEM image displays fine lattice fringes (Fig 4C), indicating a high crystalline structure in nature. Here, the observed regular d-spaces between lattice fringes are measured to be 4.83Å corresponds to (101) plane of inverse spinel CuFe2O4 NP. The selected area electron diffraction (SAED) pattern shows diffraction rings, suggesting the polycrystalline nature of inverse spinel CuFe2O4 NP and the diffraction ring pattern are comparable with the XRD patterns (Fig 4D). Energy dispersive X-ray analysis (EDX) has determined the elemental concentration distribution of the sample (Fig 4E). Herein, the EDX data have pointed out the presence of Fe, Cu, and the distribution 7

of elements in the product was calculated as an atomic percentage, with Fe = 62.41% and Cu = 37.59%. The calculated BET surface area and the pore diameter of the CuFe2O4 nanoparticles are about 13.9 m²/g and 34.7 nm, respectively. The photocatalytic activity of the as-synthesized inverse spinel CuFe2O4 nanoparticles (50 mg) for MB (3x10-5 M) degradation under visible light irradiation in the presence of oxidant

λ

(peroxydisulphate; PDS; 0.2 mM) was evaluated by UV-Vis spectrometry (Fig 5A). The absorption at max

= 664 nm is found to decreases upon visible light irradiation. Here, CuFe2O4 nanoparticles show a

16 % MB dye degradation in 75 minutes while in the absence of CuFe2O4 nanoparticles the degradation rate is negligible (Fig 5B). However, the effect of the oxidant peroxydisulphate (PDS; 0.2 mM) in CuFe2O4 nanoparticles shows enhanced photocatalytic degradation (95% MB degradation attained in 75 minutes) whereas degradation of MB is negligible under pure PDS (12%). (Fig 5B). The pseudo firstorder rate equation (ln(C0/Ct) = kobst) was used to the calculate an apparent degradation rate constant which was obtained a straight line from the plot of ln(C/Ct) against with respective irradiation time (Fig 5C). Specifically, the solution containing CuFe2O4 nanoparticles in the presence of PDS exhibits the highest degradation rate constant (66.7 x 10-5 s-1) which is significantly higher than the one measured for bare CuFe2O4 nanoparticles (3.3 x 10-5 s-1) and bare PDS (1.6 x 10-5 s-1) under similar experimental conditions. Thus, the synthesized CuFe2O4 nanoparticles exhibit better photocatalytic activity for the degradation of MB in the presence of oxidant PDS and its mechanism is similar to degradation of MB in the presence of peroxomonosulfate and CuFe2O4 nanoparticles due to the generation of more SO4•radical. [19] The present work may serve as a preliminary step towards photocatalytic studies further studies on the visible-light-driven hydrogen production by photosplitting of water molecules is under scrutiny in our laboratory.

ACKNOWLEDGMENT 8

The research described herein was financially supported by the Department of Science and Technology, India and National Science Council (NSC), Taiwan, under the India-Taiwan collaborative research grant. Authors thank Dr. Manivel Raja (DMRL,Hyderabad) for Mossbauer studies.

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FIGURE CAPTIONS

Figure 1 (A) FTIR, (B) Raman and (C) XRD spectrum of CuFe2O4 nanoparticles.

Figure 2 XPS spectra for CuFe2O4 nanoparticles. (A) survey plot (B) corresponds to Cu2p, (C) corresponds to Fe2p, and (D) corresponds to O1S.

Figure 3 (A) Mossbauer (B) Magnetization spectrum of CuFe2O4 nanoparticles. The inset shows photo image of CuFe2O4 nanoparticles with and without the magnet.

Figure 4 FE-SEM (A), HRTEM (B-D), SAED (E) and EDX (F) image of CuFe2O4 nanoparticles.

Figure 5 (A) UV-Vis absorption spectrum of MB degradation over CuFe2O4 nanoparticles under visible light irradiation in the presence of PDS and (B) Kinetic plot [([Ct]/[C0]) vs time] for CuFe2O4 nanoparticles alone (•) , PDS alone (•) and CuFe2O4 nanoparticles in the presence of PDS (•).

13

Figure 1

A

C

(312) (105) (303) (321) (224) (400)

(202) (004) (220)

(103) (101)

1000

(112) (200)

F2g

1200

Intensity (a.u.)

Intensity (a.u)

B

A1g

T2g

(211)

1400

JCPDS - 34-0425

800 300

600

900

Raman shift (cm-1)

1200

10

20

30

40

50

60

70

2Theta (deg)

14

Figure 2

Cu 2p3/2

Cu 2P3/2 2+

Intensity (CPS)

Cu Intensity (CPS)

B

4800

A

30000

Fe 2P1/2

20000

Fe 2P3/2 O 1S 10000

4000

Cu2+

3200

C 1S 0 1000

800

600

400

200

950

0

945

Binding Energy (eV)

940

935

930

925

Binding Energy (eV)

2500 2400

C

D

Fe 2p3/2

Fe 2p1/2 2000

Intensity (CPS)

Intensity (CPS)

O1s

1500

1000

1600

800

0 740

735

730

725

720

715

Binding Energy (eV)

710

705

545

540

535

530

525

520

Binding Energy (eV)

15

Figure 3

101 20

99

Magnetisation (emu/g)

Relative transmission (%)

B

A

100

98

97

96 H(kOe) Q.S. (mm/s) I.S(mm/s)

95

94 -10

-8

-6

-4

A

502

-0.353

0.245

B

478

-0.009

0.133

-2

0

2

Velocity (mm/s)

4

raw data overall fit Sextet-1 Sextet-2

6

8

10

10

0

-10

-20

-10000

-5000

0

5000

10000

Applied Field (Oe)

16

Figure 4

A

D

B

C

E

F

17

Figure 5

18

Graphical Abstract

Magnetisation (emu/g)

20

10

0

-10

-20

-10000

-5000

0

5000

10000

Applied Field (Oe)

19

Highlights
Copper ferrite (CuFe2O4) nanoparticles were synthesized via citrate-nitrate combustion method
Spectroscopic information’s have found that CuFe2O4 nanoparticles as an inverse spinel structure
Magnetic study exhibits CuFe2O4 nanoparticles have ferromagnetic behavior
CuFe2O4 nanoparticles employed for photocatalytic decolourisation of methylene blue under visible light irradiation

20