- Email: [email protected]
zeolite nanocomposites for energy application in a single-step procedure
Accepted Manuscript Facile and green preparation of magnetite/zeolite nanocomposites for energy application in a single-step procedure Nurul Hidayah Abdullah, Kamyar Shameli, Mohammad Etesami, Ezzat Chan Abdullah, Luqman Chuah Abdullah PII:
S0925-8388(17)31602-X
DOI:
10.1016/j.jallcom.2017.05.028
Reference:
JALCOM 41758
To appear in:
Journal of Alloys and Compounds
Received Date: 26 January 2017 Revised Date:
27 April 2017
Accepted Date: 3 May 2017
Please cite this article as: N.H. Abdullah, K. Shameli, M. Etesami, E. Chan Abdullah, L.C. Abdullah, Facile and green preparation of magnetite/zeolite nanocomposites for energy application in a single-step procedure, Journal of Alloys and Compounds (2017), doi: 10.1016/j.jallcom.2017.05.028. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. 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.
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Facile and green preparation of magnetite/zeolite nanocomposites
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for energy application in a single-step procedure
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Nurul Hidayah Abdullah1, Kamyar Shameli1, *, Mohammad Etesami2, Ezzat Chan Abdullah1,
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Luqman Chuah Abdullah3
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International Institute of Technology (MJIIT), Universiti Teknologi Malaysia (UTM), Jalan
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Sultan Yahya Petra, 54100 Kuala Lumpur, Malaysia
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Department of Macromolecular Science and Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
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Department of Environmental Engineering and Green Technology (EGT), Malaysia-Japan
Department of Chemical and Environmental Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang Selangor, Malaysia *
Correspondence: [email protected] Tel: +6017 3443492, +603 22031228
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Highlights
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A green, facile and rapid method to prepare magnetite/zeolite nanocomposites.
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The nanocomposites show good performance towards oxygen reduction reaction in alkaline medium.
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The nanocomposites have a great potential for energy application.
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ABSTRACT
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This paper presents a green, facile and rapid method to prepare magnetite/zeolite-
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nanocomposites (NCs) in one step procedure at ambient temperature. The powder X-ray
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diffraction (PXRD) pattern of iron oxide nanoparticles (NPs) with the sole zeolite showed the
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broadening of zeolite peaks attributed to the incorporation of Fe3O4. Field-emission scanning
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electron microscopy (FESEM) analysis depicted that the Fe3O4‒NPs were formed on the
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surface of porous zeolite framework. Transmission electron microscopy (TEM) analysis
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displayed the Fe3O4 nanoparticles (NPs) were mostly in spherical shape with a mean diameter
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and standard deviation of 2.40±0.41 nm. The selected-area electron diffraction (SAED)
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pattern confirmed the presence of cubic Fe3O4 phase. The vibrating sample magnetometer
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(VSM) results indicated the as-synthesized sample has a saturation magnetization of around
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6.52 emu.g⁻1. The magnetite/zeolite-NCs can be considered as a low-cost alternative catalyst
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for oxygen reduction reaction (ORR) process. The electrochemical measurement showed that
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the performance of magnetite/zeolite-NCs towards the ORR increased as the scan rate
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increased from 20 mV.s−1 to 500 mV.s−1. The ORR is a diffusion-controlled process in the
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alkaline medium.
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Keywords: Green synthesis, Fe3O4 nanoparticles, zeolite, nanocomposites, oxygen reduction
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reaction
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ACCEPTED MANUSCRIPT 1. Introduction
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Nanotechnology has received worldwide attention and much effort has been devoted in
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establishing foundation knowledge to control and restructure the materials at the nanoscale
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dimensions. Nanotechnology allows the development of new functional materials in nanosize
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scale of approximately 1-100 nm which possessed distinct properties from the bulky
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materials. Additionally, according to trend analysis, nanotechnology is destined to become
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the main core for a general purpose technology across the globe in 2020 [1,2].
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Currently, many attempts have been made to synthesize nanocomposites (NCs) for the
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fabrication of high performance materials due to their superior properties and unique design
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possibilities. NCs can be described as a solid that consist of two phases where one of the
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phases shows dimensions in the nanometer scale [3,4]. The improvement of NCs
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performance over monolithic and microcomposite counterparts make them suitable
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candidates to prevail over the limitations of the presently existing materials and devices [4].
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Magnetic nanoparticles (MNPs) are known to be non-toxic, highly recyclable, reusable
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and can be easily separated upon applying an external magnetic field [5]. The self-assembly
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of MNPs in composite material endow the formation of magnetic materials with superior
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magnetic properties than their individual components for technological advances [6]. The
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incorporation of NPs in solid substrates can enhance the chemical stability, biocompatibility,
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less aggregation and better control of the size and shape of the NPs [7,8].
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Magnetite (Fe3O4) is known as a class of iron oxide compound with a cubic inverse
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spinel structure and has face centered cubic close packed oxygen anions and Fe cations
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occupying interstitial tetrahedral and octahedral sites [9,10]. It is among commonly
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investigated MNPs that have been used as magnetic core in enhancing the physical or
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chemical properties as well as maintaining the stability of the prepared hybrid materials
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[11,12].
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Among low cost materials, zeolites are highly recognized due to their interesting features
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such as high surface area, individual micro-pores, a variety of channels, and high resistance
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towards chemical and heat treatment [13]. Zeolites are well known hydrated alumino-silicates
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mineral that can be obtained either from naturally occurring deposits or manufactured
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synthetically [14,15].
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The fabrication of magnetic iron oxide NPs in solid supports is frequently done by co-
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precipitation technique [16]. Co-precipitation technique is most preferable owing to its
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simplicity, cost effective and high amount of product can be obtained [17,18]. The synthesis 4
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of MNPs in solid supports can be carried out in environmentally benign solvents, have good
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atom economy, generate less waste and minimize environmental pollution [5]. The magnetic
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iron oxide NCs have potential application as adsorbent for contaminants removal [8],
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magnetically guided drug delivery [19], biosensor [20], supercapacitor [21], lithium ion
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battery [22] and cathode catalysts for fuel cell applications [23]. Oxygen reduction reaction (ORR) is recognized as one of the outstanding alternatives for
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generation of clean energy as it entails the breaking and conversion of chemical energy
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accumulated in double bonds of oxygen molecules to produce electrical energy [24].
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Recently, much effort has been made in developing highly durable, stable and low-cost
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electrocatalysts with superior activity to replace the scarce platinum and simultaneously solve
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the worldwide energy predicament [23–25]. The development of new non-precious cathode
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catalysts in ORR for fuel cell and battery application are essential due to highly demands for
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renewable energy generation and storage resources [23–27].
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Previous study has reported about the increased in the efficiency of electron transfer via
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an ideal ORR process using noble Pt/C electrocatalyst [28]. However, this material has some
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disadvantages mainly due to the crossover effects, CO poisoning, unsatisfactory stability and
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prohibitive cost which limit their possibility to be commercialize in large scale industry [28].
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Furthermore, the gradual degradation of Pt catalysts in alkaline medium also has been
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reported to cause particle dissolution and aggregation due to the surface oxide formation
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[29]. Thus, it is significant to discover and investigate electrocatalyst based on low cost and
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non-noble materials as an alternative to resolve some problems related to the currently
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existing materials.
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Metal oxide NPs have been rapidly investigated as promising alternative catalyst for
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ORR. The development of electrocatalyst based on iron oxide NPs have been introduced as
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non-noble catalyst with excellent catalytic ability, low cost, high abundance and better
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durability [23,24]. However, iron oxide is often suffering from dissolution, sintering, and
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agglomeration, resulting in poor electrocatalytic activity [30]. In this context, the problems
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can be overcome by deposition of iron oxide on solid support such as graphene [28,31],
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carbon nanotube [23,30] and perovskite [24]. The incorporation of iron oxide on solid
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substrates can improved the electrocatalytic activity and stability due to enhanced in their
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interfacial contact and suppress the dissolution/agglomeration of nanoparticles [23,24,30,31].
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Furthermore, the development of iron oxide NCs also demonstrated the improvement in the
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activity towards oxygen reduction reaction as compared to bare iron oxide as well as to avoid
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the defects on weak conductivity and agglomeration of iron oxide particles during
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electrochemical process [23,24]. In this study, co-precipitation method was implemented in the production of
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magnetite/zeolite-NCs at room temperature and air atmosphere. So far, no study reported
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about the use of magnetite/zeolite-NCs for application as electrode catalyst in ORR process.
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Besides, the green synthetic route was implemented by utilizing non-hazardous solvent and
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eco-friendly chemicals. The technique was facile and rapid which can be applied for
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production of large amount of product. Zeolite 3Å was used as a substrate for the preparation
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of magnetite/zeolite-NCs. The prepared magnetite/zeolite-NCs was further used as a low cost electrocatalyst to study the electrochemical performance towards the ORR process.
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2. Experimental details
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2.1. Materials and instrumentation
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All chemicals used in this work were of analytical grade and used as received without further
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purification. Ferric chloride hexahydrate (FeCl3⋅6H2O, 97%), ferrous chloride tetrahydrate
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(FeCl2⋅ 4H2O ≥96%) and zeolite 3Å powder (0.6 K2O: 4.0 Na2O: 1 Al2O3: 2.0 ± 0.1 SiO2: x
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H2O) were supplied by Sigma Aldrich. Sodium hydroxide (NaOH) was obtained from R&M
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Chemicals. All the aqueous solutions were prepared by deionized water from ELGA Lab
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Water Purification System, UK. The benchtop pH Meter model sensION + MM374 GLP 2
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was employed to control the pH of the solution. The prepared sample was dried in an Esco
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Isotherm Forced Convection Laboratory Oven.
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2.2. Synthesis of zeolite/Fe3O4 nanocomposites
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Synthesis of magnetite/zeolite-NCs was conducted by suspension of 2.0 g of zeolite in 50 mL
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of deionized water and mixed with NaOH (0.5 M). The suspension was stirred for 20 minutes
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and 50 ml of solution containing Fe3+(0.228 M) and Fe2+(0.114 M) ions (pH ~1.40) with 2:1
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M ratio was added into the zeolite suspension (pH~12.80). A subsequent amount of NaOH
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(0.5 M) was added for complete formation of Fe3O4-NPs. The composite suspension was
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stirred continuously for another 30 minutes. The precipitates were centrifuged, washed
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several times with deionized water, and finally dried in an oven at 50 °C. All the experiments
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were conducted under air atmosphere at room temperature.
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The prepared magnetite/zeolite-NCs was characterized by ultra-violet visible spectroscopy
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(UV-vis), powder x-ray diffraction (PXRD), transmission electron microscopy (TEM), field
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emission electron microscopy (FESEM) equipped with energy dispersive X-ray (EDX),
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vibrating sample magnetometer (VSM), fourier transform infrared spectroscopy (FT-IR) and
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atomic absorption spectrophotometer (AAS). The UV-vis spectra were recorded by UV-vis
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spectrophotometer (UV-1800, Shimadzu) over the range of 300-800 cm−1. The PXRD
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patterns were recorded by PAN analytical X’pert PRO at a scan speed of 2°/minute with
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Cukα1 irradiation (λ=1.5406 Å) in the 2θ range of 5°- 80° to determine the phase purity and
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crystallinity of the samples. The surface morphology and elemental composition of the
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magnetite/zeolite-NCs were determined by FESEM-JEOL, JSM-7600F equipped with an
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EDX, Oxford Instrument spectrometer operating at accelerating voltage from 5-15 kV with
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magnification from 5 KX to 100 KX. The TEM images were taken using FEI Tecnai™ G2
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F20 to measure the particle sizes and determine the morphology of the sample. The
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accelerating voltage of the microscope was from 20-200 kV and the standard magnification
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was from 22 X to 930 KX. The preparation of the sample was carried out by dripping one
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drop of sonicated suspended solid on 300-mesh copper grid and air dried before viewing
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under TEM microscope. The VSM analysis was conducted at room temperature to determine
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the saturation magnetization of the sample associated with the magnetic properties of the
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compound. The instrument employed for the VSM analysis was Lakeshore Model 7404. The
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FT-IR spectra were recorded over the range of 400–4000 cm−1 using the Nicolet 6700 FT-IR
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spectrophotometer to identify the functional group based on the bonds present in a molecule.
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2.4. Electrochemical test
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The electrochemical tests were conducted by a Versa STAT3 equipped with Versa Studio
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software in a conventional three-electrode cell. A Pt wire and an Ag/AgCl (in the saturated
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KCl) were used as the auxiliary and reference electrodes, respectively. A dispersed solution
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of 1 mg/mL of the NCs was prepared by sonicating the dispersion for 30 min. 30 µL of the
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dispersion was dropped at the surface of clean glassy carbon electrode (GCE) and the
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modified electrode was left in an oven (55 °C) for 6h. The NCs/GCE was used as the
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working electrode. The linear sweep voltammetry (LSV) technique was employed to study
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the electrochemical performance of the NCs towards oxygen reduction reaction (ORR). The
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the electrochemical tests.
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3. Results and Discussion
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3.1. Preparation of nanocomposites
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White cloudy solution of zeolite suspension was stirred for 20 minutes in 0.5 M of sodium
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hydroxide solution to create mesoporosity and enhance the diffusional properties by
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removing the intracrystalline and intercrystalline amorphous Si/Al species in the gap among
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zeolite [32]. The addition of iron chloride salts to the suspension results in substantial
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changed of the solution to dark brown colour and reduced the pH of the solution. The
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subsequent amount of aqueous NaOH (0.5M) was added to assure the pH was maintained at
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around 11 for complete transformation of iron chloride salts to Fe3O4 precipitates. Fig. 1
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showed that the magnetite/zeolite-NCs was attracted to the magnet. The overall reaction may
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be written as follows:
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Zeolite(s) + 2Fe3+(aq) + Fe2+(aq) + 8OH-(aq) ሱۛۛۛۛሮ[Zeolite/ Fe3O4](s) + 4H2O(l)
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(Eq. 1)
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Fig. 1. Zeolite suspension (a), magnetite/zeolite-NCs (b), separation of synthesized Fe3O4-
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NPs from reaction mixture using an external magnet (c).
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3.2 UV-Visible Spectral Analysis
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vis spectrum showed no evidence of absorption for the zeolite substrate (red). However,
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when the zeolite was loaded with magnetite, the decrement in the absorption intensity was
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observed with the increased of the wavelength in the range of 300-800 nm but no obvious
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peak was observed in this region (blue). Similar observation also has been reported about no
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distinct peak associated with the Fe3O4-NPs was formed in the region of 320-600 nm [12].
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Fig. 2. UV-visible spectra of (a) zeolite, (b) magnetite/zeolite -NCs.
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3.3. Powder X-ray diffraction
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The comparison between the PXRD patterns of the zeolite, zeolite treated NaOH and
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magnetite/zeolite-NCs are shown in Fig. 3(a‒d). All samples exhibit strong and sharp peaks
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with high intensities attributed to the well crystallinity of the zeolite phase. From Fig. 3(b-c),
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after treatment with NaOH and incorporation of Fe3O4 species, the characteristic peaks of
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zeolite were slightly shifted to high angle and decreased in the intensities were observed. In
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this study, treatment with alkaline solution was essential to initiate the mesoporosity and
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enhanced the diffusional properties within the zeolite porous structure.
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amorphous Si/Al species in the gap among zeolite crystallines can be removed for easy
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formation of Fe3O4-NPs in the zeolite frameworks structure.
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Besides, the
However, severe alkaline
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treatment not only results in removal of amorphous species, but may also results to further
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destruction of zeolite framework and decreased of the crystallinity and Si/Al ratio [32,33]. Fig. 3(c) showed that the most intense peaks of magnetite/zeolite-NCs sample were
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observed at 2θ of 7.49°, 10.49°, 12.76° 21.96°, 24.28°, 27.41°, 30.23°, and 34.47°. The
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diffraction pattern was consistent with the reference pattern of zeolite A with cubic phase
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structure (JCPDS file number 038-0241). From the pattern, no impurities were observed
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indicated a high purity of the sample. Bosinceanu et al. [34] have reported about a partial loss
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of host crystallinity of zeolite samples after formation of some iron (III) oxide nanoparticles
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on the zeolite external surface. From the findings, they emphasized that the process of
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clusters formation involves the aggregation within the large cages of the parent zeolite and
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the local destruction of the network pores. Moreover, the XRD pattern of magnetite/zeolite-
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NCs indicated that the peaks attributed to the Fe3O4 phases were not found due to the low
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amount of Fe3O4‒NPs embedded in zeolite frameworks [35]. The overlapping peaks of
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Fe3O4‒NPs can be observed at 2θ=30.23°, 36.03°, 43.13°, 53.56°, 56.72° and 62.98° (Fig. 3
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(d)). The formation of Fe3O4‒NPs only results to the peak broadening at 2θ=36.03° and
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62.98° which are corresponding to the most intense of magnetite peaks at lattice planes of
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(311) and (440) (JCPDS file number 019-0629). Other study also revealed no evidence of
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FeO(OH), (FexOy), Fe3O4, γ-Fe2O3, α-Fe2O3 in the XRD patterns of zeolite samples with the
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small contents of iron oxides and only decreased in the zeolite peaks and some small shifts
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of XRD peak position were observed with the increased in iron oxide loading [34].
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Fig. 3. PXRD patterns of zeolite (a), zeolite treated with NaOH (b) and magnetite/zeolite-
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NCs (c, d). 11
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From FESEM analysis, the cubic structure of zeolite (Fig. 4(a)) showed smooth surface
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before embedded with Fe3O4-NPs. However, after formation of Fe3O4-NPs, the zeolite surface
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become rough and more opening of the zeolite pores can be observed (Fig. 4(c)). This was
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attributed from the significant induce of mesoporosity after desilication with NaOH [33].
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High distribution of NPs was formed on the surface of cubic zeolite substrate and some
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agglomeration also appeared. Based on the EDX analysis, zeolite composition showed the
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appearance of elements (Al, Si, Na and O) ((Fig. 4(b)). Similar elements were observed in the
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zeolite/Fe3O4-NCs as well as the appearances of new peaks correspond to Fe element in the
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regions at approximately 0.7, 6.4 and 7.1 KeV (Fig. 4(d)). According to EDX analysis, the
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Si/Al ratio was reduced from 1.02 to 0.87 indicated the desilication of synthetic zeolite after
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NaOH treatment and formation of Fe3O4-NPs.
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Fig. 4. FESEM and EDX images of zeolite (a, b), magnetite/zeolite-NCs (c, d).
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The TEM image of the spherical Fe3O4-NPs formed in the zeolite substrate was shown in Fig.
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5(a). A histogram depicted that the synthesized NPs have diameter and standard deviation of
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2.4 ± 0.41 nm (Fig. 5(b)). Fig. 5(c) displayed the formation of agglomerated Fe3O4 on the
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zeolite frameworks. Agglomeration of NPs was observed due to the formation of small
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particle sizes and magnetic behaviour possessed by Fe3O4 [36]. Fig. 5(d) showed the
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selected-area electron diffraction (SAED) pattern where rings can be seen attributed to the
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polycrystalline nature of the sample. The pattern corresponds to the cubic Fe3O4 planes of
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[220], [311], [400], [511] and [440] are in agreement with the XRD pattern with JCPDS file number of 019-0629.
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Fig. 5. TEM images of magnetite/zeolite-NCs (a, c), Particle size distribution histogram (b)
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SAED pattern of iron oxide (d).
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3.6. Vibrating sample magnetometer analysis
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The magnetic behaviour of the synthesized magnetite/zeolite-NCs showed the saturation
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magnetization (Ms) of 6.52 emu.g-1 (Fig. 6). The coercivity of the sample was 56.78 G. The
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Ms obtained was much lower as compared to the pure magnetite due to the low percentage of
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Fe3O4 incorporated in zeolite structure. Besides, the low Ms of magnetite/zeolite-NCs also
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attributed to the size dependent magnetization of the magnetic nanoparticles. As when the
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size of magnetic NPs decreases, the NPs moves toward superparamagnetism but may have a
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reduced in Ms [37]. Nah et al. [38] reported that the zeolite has zero magnetization and
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coercivity. They demonstrated that both bulk magnetization and coercivity were increased
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with the presence of magnetite nanoparticles in pure zeolites.
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Fig. 6. (a) Magnetization versus applied magnetic field for magnetite/zeolite-NCs at 300 K
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(b) coercivity of magnetite/zeolite-NCs
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3.7. Fourier transform infrared analysis
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Fig. 7(a-c) shows the comparison of FT-IR spectra for the silicate host structure of zeolite,
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treated zeolite, and magnetite/zeolite-NCs. The relatively wide and strong bands were
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observed for O-H stretching in the spectral regions of 3100 to 3500 cm-1 due to the H2O
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interporous structure [39]. The position of the vibration bands in the region of 1653-1655 cm-
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1001-1003 cm⁻1 was resulted from the stretching and bending modes of Si-O or Al-O within
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zeolite framework associated with the asymmetric and symmetric stretching modes of
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external linkages [40]. The presence of bands at region of 665 and 666 cm-1 were due to the
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Al-O vibration and the bands observed at 553-464 cm-1 were attributed to the Si-O-Si
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bending vibration [39].
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were attributed from the H-O-H bending vibration. Besides, the appearance of bands at
Fig. 7(c) showed there was non-bond chemical interaction were observed between the
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zeolite structure and Fe3O4‒NPs. This might be due to the overlapping of Fe-O band with the
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strong vibrations of Si-O bending at 464 cm-1. However, the presence of Fe3O4 in the zeolite
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frameworks, results in slightly shifting of O-H stretching band towards lower wavelength and
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decreased in the peaks intensities were observed. Sagir et al. also demonstrated no Fe-O
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vibration peak present in the spectrum of magnetite/zeolite due to the overlapping with Si-O
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band attributed from the zeolite molecular structure [41]. Non-bond chemical interaction and
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rigidity of the silicate layers also has been reported between the Fe3O4-NPs and talc-Fe3O4
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[18]. In this study, the patterns remained unchanged for all samples which indicated rigidity
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and well preserved of zeolite structure after treatment with NaOH and incorporation with
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Fe3O4-NPs. However, if the desilication was carried out using high concentration of base, it
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may result in significant destruction of zeolite and led to the formation of protonic sites (not
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Si–OH–Al groups) of weak acid strength [42]. Hence, low concentration of NaOH should be
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used to induce the mesoporosity in zeolite frameworks.
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Fig. 7. The near FT-IR spectra of zeolite (a), zeolite treated NaOH (b), and magnetite/zeolite-
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NCs (c).
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3.8. Electrochemical study
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The oxygen reduction reaction (ORR) was studied on the NCs as electrocatalyst. The ORR is
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a key reaction in most of the electrochemical energy devices such as fuel cells and metal-air
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batteries. ORR can occur through a two-electron or four-electron transfer mechanisms [23].
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During the two-electron transfer mechanism, hydrogen peroxide molecules (as the
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intermediates) are generated on the surface of catalyst while no hydrogen peroxide can be
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detected during the direct four-electron transfer mechanism. Regardless the pathway of ORR
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process, the overall reduction reaction in alkaline aqueous medium is as follows:
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O2 + H2O + 4e → 4 OH− (Eq. 2)
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The ORR process was studied in the N2- and O2-saturated 0.1 M KOH by linear scan
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voltammetry (LSV). Fig. 8 shows the polarization curves attributed to the prepared NCs at a
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scan rate of 50 mV.s−1 in the oxygen-free and O2-saturated alkaline solution. The
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electrochemical performance of the NCs in N2-saturated KOH solution is negligible while the
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solution.
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As it is seen in the Fig. 8, the oxygen reduction occurs with the onset potential of 0 V and two
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consecutive reduction peaks at −0.45 V and −1 V which follows by the hydrogen evolution
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reaction at the potentials more negative than −1.35 V.
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Fig. 8. LSV of magnetite/zeolite-NCs in N2- (dotted line) and O2-saturated (solid line) 0.1 M
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KOH at a scan rate of 50 mV.s−1.
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Different scan sweep potential rates were also applied to the working electrode for ORR
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process. It was observed that the performance of Fe3O4-NCs towards the ORR increases by
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increasing the scan rate from 20 mV.s−1 to 500 mV.s−1 (Fig. 9). The magnitude of square root
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of the scan rate decreases linearly versus the peak current in ORR process (Fig. 10) which
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Fig. 9. LSV of magnetite/zeolite-NCs in O2-saturated 0.1 M KOH at scan rates of 20, 50,
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100, 125, 150, 200, 300, 400 and 500 mV.s−1.
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Fig. 10. Plot showing square root of the scan rate versus current
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4. Conclusions
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Magnetite/zeolite-NCs was successfully synthesized by a green synthesis technique. The
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employed technique for synthesizing magnetite/zeolite-NCs is cost effective, facile, and
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environmentally friendly that can be applied for production of large amount of NCs without
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utilizing high pressure, energy and temperature. The synthesized magnetite/zeolite-NCs
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showed saturation magnetization of 6.52 emu.g⁻1 which demonstrated sufficient
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magnetization for the separation by external permanent magnet. High distribution of NPs
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having diameter around 2.40±0.41 nm was formed in the cubic zeolite substrate. The
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magnetite/zeolite-NCs show good performance towards oxygen reduction reaction in alkaline
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medium. The as synthesized magnetite/zeolite-NCs may have potential as one of the effective
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non-precious electrocatalyst for fuel cells and batteries applications.
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Acknowledgement
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This research was supported by the Malaysian Ministry of Higher Education and Universiti
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Teknologi Malaysia (UTM) under Tier 1 grant (PY/2015/05182). We also would like to
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thank to the Research Management Centre (RMC) and Malaysia-Japan International Institute
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of Technology (MJIIT) of UTM for providing an excellent research environment to complete
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this work.
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Highlights •
A green, facile and rapid method to prepare magnetite/zeolite nanocomposites.
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The nanocomposites show good performance towards oxygen reduction reaction in alkaline medium.
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The nanocomposites have a great potential for energy application.
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S0925-8388(17)31602-X
DOI:
10.1016/j.jallcom.2017.05.028
Reference:
JALCOM 41758
To appear in:
Journal of Alloys and Compounds
Received Date: 26 January 2017 Revised Date:
27 April 2017
Accepted Date: 3 May 2017
Please cite this article as: N.H. Abdullah, K. Shameli, M. Etesami, E. Chan Abdullah, L.C. Abdullah, Facile and green preparation of magnetite/zeolite nanocomposites for energy application in a single-step procedure, Journal of Alloys and Compounds (2017), doi: 10.1016/j.jallcom.2017.05.028. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. 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.
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Facile and green preparation of magnetite/zeolite nanocomposites
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for energy application in a single-step procedure
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Nurul Hidayah Abdullah1, Kamyar Shameli1, *, Mohammad Etesami2, Ezzat Chan Abdullah1,
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Luqman Chuah Abdullah3
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International Institute of Technology (MJIIT), Universiti Teknologi Malaysia (UTM), Jalan
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Sultan Yahya Petra, 54100 Kuala Lumpur, Malaysia
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Department of Macromolecular Science and Engineering, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
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Department of Environmental Engineering and Green Technology (EGT), Malaysia-Japan
Department of Chemical and Environmental Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 Serdang Selangor, Malaysia *
Correspondence: [email protected] Tel: +6017 3443492, +603 22031228
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Highlights
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A green, facile and rapid method to prepare magnetite/zeolite nanocomposites.
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The nanocomposites show good performance towards oxygen reduction reaction in alkaline medium.
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The nanocomposites have a great potential for energy application.
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ABSTRACT
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This paper presents a green, facile and rapid method to prepare magnetite/zeolite-
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nanocomposites (NCs) in one step procedure at ambient temperature. The powder X-ray
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diffraction (PXRD) pattern of iron oxide nanoparticles (NPs) with the sole zeolite showed the
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broadening of zeolite peaks attributed to the incorporation of Fe3O4. Field-emission scanning
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electron microscopy (FESEM) analysis depicted that the Fe3O4‒NPs were formed on the
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surface of porous zeolite framework. Transmission electron microscopy (TEM) analysis
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displayed the Fe3O4 nanoparticles (NPs) were mostly in spherical shape with a mean diameter
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and standard deviation of 2.40±0.41 nm. The selected-area electron diffraction (SAED)
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pattern confirmed the presence of cubic Fe3O4 phase. The vibrating sample magnetometer
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(VSM) results indicated the as-synthesized sample has a saturation magnetization of around
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6.52 emu.g⁻1. The magnetite/zeolite-NCs can be considered as a low-cost alternative catalyst
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for oxygen reduction reaction (ORR) process. The electrochemical measurement showed that
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the performance of magnetite/zeolite-NCs towards the ORR increased as the scan rate
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increased from 20 mV.s−1 to 500 mV.s−1. The ORR is a diffusion-controlled process in the
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alkaline medium.
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Keywords: Green synthesis, Fe3O4 nanoparticles, zeolite, nanocomposites, oxygen reduction
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ACCEPTED MANUSCRIPT 1. Introduction
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Nanotechnology has received worldwide attention and much effort has been devoted in
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establishing foundation knowledge to control and restructure the materials at the nanoscale
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dimensions. Nanotechnology allows the development of new functional materials in nanosize
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scale of approximately 1-100 nm which possessed distinct properties from the bulky
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materials. Additionally, according to trend analysis, nanotechnology is destined to become
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the main core for a general purpose technology across the globe in 2020 [1,2].
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Currently, many attempts have been made to synthesize nanocomposites (NCs) for the
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fabrication of high performance materials due to their superior properties and unique design
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possibilities. NCs can be described as a solid that consist of two phases where one of the
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phases shows dimensions in the nanometer scale [3,4]. The improvement of NCs
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performance over monolithic and microcomposite counterparts make them suitable
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candidates to prevail over the limitations of the presently existing materials and devices [4].
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Magnetic nanoparticles (MNPs) are known to be non-toxic, highly recyclable, reusable
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and can be easily separated upon applying an external magnetic field [5]. The self-assembly
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of MNPs in composite material endow the formation of magnetic materials with superior
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magnetic properties than their individual components for technological advances [6]. The
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incorporation of NPs in solid substrates can enhance the chemical stability, biocompatibility,
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less aggregation and better control of the size and shape of the NPs [7,8].
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Magnetite (Fe3O4) is known as a class of iron oxide compound with a cubic inverse
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spinel structure and has face centered cubic close packed oxygen anions and Fe cations
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occupying interstitial tetrahedral and octahedral sites [9,10]. It is among commonly
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investigated MNPs that have been used as magnetic core in enhancing the physical or
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chemical properties as well as maintaining the stability of the prepared hybrid materials
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[11,12].
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Among low cost materials, zeolites are highly recognized due to their interesting features
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such as high surface area, individual micro-pores, a variety of channels, and high resistance
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towards chemical and heat treatment [13]. Zeolites are well known hydrated alumino-silicates
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mineral that can be obtained either from naturally occurring deposits or manufactured
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synthetically [14,15].
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The fabrication of magnetic iron oxide NPs in solid supports is frequently done by co-
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precipitation technique [16]. Co-precipitation technique is most preferable owing to its
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simplicity, cost effective and high amount of product can be obtained [17,18]. The synthesis 4
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of MNPs in solid supports can be carried out in environmentally benign solvents, have good
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atom economy, generate less waste and minimize environmental pollution [5]. The magnetic
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iron oxide NCs have potential application as adsorbent for contaminants removal [8],
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magnetically guided drug delivery [19], biosensor [20], supercapacitor [21], lithium ion
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battery [22] and cathode catalysts for fuel cell applications [23]. Oxygen reduction reaction (ORR) is recognized as one of the outstanding alternatives for
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generation of clean energy as it entails the breaking and conversion of chemical energy
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accumulated in double bonds of oxygen molecules to produce electrical energy [24].
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Recently, much effort has been made in developing highly durable, stable and low-cost
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electrocatalysts with superior activity to replace the scarce platinum and simultaneously solve
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the worldwide energy predicament [23–25]. The development of new non-precious cathode
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catalysts in ORR for fuel cell and battery application are essential due to highly demands for
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renewable energy generation and storage resources [23–27].
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Previous study has reported about the increased in the efficiency of electron transfer via
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an ideal ORR process using noble Pt/C electrocatalyst [28]. However, this material has some
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disadvantages mainly due to the crossover effects, CO poisoning, unsatisfactory stability and
17
prohibitive cost which limit their possibility to be commercialize in large scale industry [28].
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Furthermore, the gradual degradation of Pt catalysts in alkaline medium also has been
19
reported to cause particle dissolution and aggregation due to the surface oxide formation
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[29]. Thus, it is significant to discover and investigate electrocatalyst based on low cost and
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non-noble materials as an alternative to resolve some problems related to the currently
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existing materials.
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Metal oxide NPs have been rapidly investigated as promising alternative catalyst for
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ORR. The development of electrocatalyst based on iron oxide NPs have been introduced as
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non-noble catalyst with excellent catalytic ability, low cost, high abundance and better
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durability [23,24]. However, iron oxide is often suffering from dissolution, sintering, and
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agglomeration, resulting in poor electrocatalytic activity [30]. In this context, the problems
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can be overcome by deposition of iron oxide on solid support such as graphene [28,31],
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carbon nanotube [23,30] and perovskite [24]. The incorporation of iron oxide on solid
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substrates can improved the electrocatalytic activity and stability due to enhanced in their
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interfacial contact and suppress the dissolution/agglomeration of nanoparticles [23,24,30,31].
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Furthermore, the development of iron oxide NCs also demonstrated the improvement in the
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activity towards oxygen reduction reaction as compared to bare iron oxide as well as to avoid
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the defects on weak conductivity and agglomeration of iron oxide particles during
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electrochemical process [23,24]. In this study, co-precipitation method was implemented in the production of
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magnetite/zeolite-NCs at room temperature and air atmosphere. So far, no study reported
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about the use of magnetite/zeolite-NCs for application as electrode catalyst in ORR process.
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Besides, the green synthetic route was implemented by utilizing non-hazardous solvent and
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eco-friendly chemicals. The technique was facile and rapid which can be applied for
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production of large amount of product. Zeolite 3Å was used as a substrate for the preparation
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of magnetite/zeolite-NCs. The prepared magnetite/zeolite-NCs was further used as a low cost electrocatalyst to study the electrochemical performance towards the ORR process.
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2. Experimental details
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2.1. Materials and instrumentation
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All chemicals used in this work were of analytical grade and used as received without further
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purification. Ferric chloride hexahydrate (FeCl3⋅6H2O, 97%), ferrous chloride tetrahydrate
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(FeCl2⋅ 4H2O ≥96%) and zeolite 3Å powder (0.6 K2O: 4.0 Na2O: 1 Al2O3: 2.0 ± 0.1 SiO2: x
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H2O) were supplied by Sigma Aldrich. Sodium hydroxide (NaOH) was obtained from R&M
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Chemicals. All the aqueous solutions were prepared by deionized water from ELGA Lab
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Water Purification System, UK. The benchtop pH Meter model sensION + MM374 GLP 2
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was employed to control the pH of the solution. The prepared sample was dried in an Esco
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Isotherm Forced Convection Laboratory Oven.
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2.2. Synthesis of zeolite/Fe3O4 nanocomposites
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Synthesis of magnetite/zeolite-NCs was conducted by suspension of 2.0 g of zeolite in 50 mL
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of deionized water and mixed with NaOH (0.5 M). The suspension was stirred for 20 minutes
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and 50 ml of solution containing Fe3+(0.228 M) and Fe2+(0.114 M) ions (pH ~1.40) with 2:1
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M ratio was added into the zeolite suspension (pH~12.80). A subsequent amount of NaOH
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(0.5 M) was added for complete formation of Fe3O4-NPs. The composite suspension was
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stirred continuously for another 30 minutes. The precipitates were centrifuged, washed
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several times with deionized water, and finally dried in an oven at 50 °C. All the experiments
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were conducted under air atmosphere at room temperature.
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The prepared magnetite/zeolite-NCs was characterized by ultra-violet visible spectroscopy
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(UV-vis), powder x-ray diffraction (PXRD), transmission electron microscopy (TEM), field
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emission electron microscopy (FESEM) equipped with energy dispersive X-ray (EDX),
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vibrating sample magnetometer (VSM), fourier transform infrared spectroscopy (FT-IR) and
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atomic absorption spectrophotometer (AAS). The UV-vis spectra were recorded by UV-vis
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spectrophotometer (UV-1800, Shimadzu) over the range of 300-800 cm−1. The PXRD
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patterns were recorded by PAN analytical X’pert PRO at a scan speed of 2°/minute with
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Cukα1 irradiation (λ=1.5406 Å) in the 2θ range of 5°- 80° to determine the phase purity and
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crystallinity of the samples. The surface morphology and elemental composition of the
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magnetite/zeolite-NCs were determined by FESEM-JEOL, JSM-7600F equipped with an
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EDX, Oxford Instrument spectrometer operating at accelerating voltage from 5-15 kV with
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magnification from 5 KX to 100 KX. The TEM images were taken using FEI Tecnai™ G2
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F20 to measure the particle sizes and determine the morphology of the sample. The
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accelerating voltage of the microscope was from 20-200 kV and the standard magnification
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was from 22 X to 930 KX. The preparation of the sample was carried out by dripping one
17
drop of sonicated suspended solid on 300-mesh copper grid and air dried before viewing
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under TEM microscope. The VSM analysis was conducted at room temperature to determine
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the saturation magnetization of the sample associated with the magnetic properties of the
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compound. The instrument employed for the VSM analysis was Lakeshore Model 7404. The
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FT-IR spectra were recorded over the range of 400–4000 cm−1 using the Nicolet 6700 FT-IR
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spectrophotometer to identify the functional group based on the bonds present in a molecule.
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2.4. Electrochemical test
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The electrochemical tests were conducted by a Versa STAT3 equipped with Versa Studio
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software in a conventional three-electrode cell. A Pt wire and an Ag/AgCl (in the saturated
27
KCl) were used as the auxiliary and reference electrodes, respectively. A dispersed solution
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of 1 mg/mL of the NCs was prepared by sonicating the dispersion for 30 min. 30 µL of the
29
dispersion was dropped at the surface of clean glassy carbon electrode (GCE) and the
30
modified electrode was left in an oven (55 °C) for 6h. The NCs/GCE was used as the
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working electrode. The linear sweep voltammetry (LSV) technique was employed to study
32
the electrochemical performance of the NCs towards oxygen reduction reaction (ORR). The
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3. Results and Discussion
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3.1. Preparation of nanocomposites
5
White cloudy solution of zeolite suspension was stirred for 20 minutes in 0.5 M of sodium
6
hydroxide solution to create mesoporosity and enhance the diffusional properties by
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removing the intracrystalline and intercrystalline amorphous Si/Al species in the gap among
8
zeolite [32]. The addition of iron chloride salts to the suspension results in substantial
9
changed of the solution to dark brown colour and reduced the pH of the solution. The
10
subsequent amount of aqueous NaOH (0.5M) was added to assure the pH was maintained at
11
around 11 for complete transformation of iron chloride salts to Fe3O4 precipitates. Fig. 1
12
showed that the magnetite/zeolite-NCs was attracted to the magnet. The overall reaction may
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be written as follows:
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Zeolite(s) + 2Fe3+(aq) + Fe2+(aq) + 8OH-(aq) ሱۛۛۛۛሮ[Zeolite/ Fe3O4](s) + 4H2O(l)
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(Eq. 1)
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Fig. 1. Zeolite suspension (a), magnetite/zeolite-NCs (b), separation of synthesized Fe3O4-
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NPs from reaction mixture using an external magnet (c).
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3.2 UV-Visible Spectral Analysis
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vis spectrum showed no evidence of absorption for the zeolite substrate (red). However,
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when the zeolite was loaded with magnetite, the decrement in the absorption intensity was
4
observed with the increased of the wavelength in the range of 300-800 nm but no obvious
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peak was observed in this region (blue). Similar observation also has been reported about no
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distinct peak associated with the Fe3O4-NPs was formed in the region of 320-600 nm [12].
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Fig. 2. UV-visible spectra of (a) zeolite, (b) magnetite/zeolite -NCs.
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3.3. Powder X-ray diffraction
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The comparison between the PXRD patterns of the zeolite, zeolite treated NaOH and
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magnetite/zeolite-NCs are shown in Fig. 3(a‒d). All samples exhibit strong and sharp peaks
14
with high intensities attributed to the well crystallinity of the zeolite phase. From Fig. 3(b-c),
15
after treatment with NaOH and incorporation of Fe3O4 species, the characteristic peaks of
16
zeolite were slightly shifted to high angle and decreased in the intensities were observed. In
17
this study, treatment with alkaline solution was essential to initiate the mesoporosity and
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enhanced the diffusional properties within the zeolite porous structure.
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amorphous Si/Al species in the gap among zeolite crystallines can be removed for easy
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formation of Fe3O4-NPs in the zeolite frameworks structure.
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Besides, the
However, severe alkaline
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treatment not only results in removal of amorphous species, but may also results to further
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destruction of zeolite framework and decreased of the crystallinity and Si/Al ratio [32,33]. Fig. 3(c) showed that the most intense peaks of magnetite/zeolite-NCs sample were
4
observed at 2θ of 7.49°, 10.49°, 12.76° 21.96°, 24.28°, 27.41°, 30.23°, and 34.47°. The
5
diffraction pattern was consistent with the reference pattern of zeolite A with cubic phase
6
structure (JCPDS file number 038-0241). From the pattern, no impurities were observed
7
indicated a high purity of the sample. Bosinceanu et al. [34] have reported about a partial loss
8
of host crystallinity of zeolite samples after formation of some iron (III) oxide nanoparticles
9
on the zeolite external surface. From the findings, they emphasized that the process of
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clusters formation involves the aggregation within the large cages of the parent zeolite and
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the local destruction of the network pores. Moreover, the XRD pattern of magnetite/zeolite-
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NCs indicated that the peaks attributed to the Fe3O4 phases were not found due to the low
13
amount of Fe3O4‒NPs embedded in zeolite frameworks [35]. The overlapping peaks of
14
Fe3O4‒NPs can be observed at 2θ=30.23°, 36.03°, 43.13°, 53.56°, 56.72° and 62.98° (Fig. 3
15
(d)). The formation of Fe3O4‒NPs only results to the peak broadening at 2θ=36.03° and
16
62.98° which are corresponding to the most intense of magnetite peaks at lattice planes of
17
(311) and (440) (JCPDS file number 019-0629). Other study also revealed no evidence of
18
FeO(OH), (FexOy), Fe3O4, γ-Fe2O3, α-Fe2O3 in the XRD patterns of zeolite samples with the
19
small contents of iron oxides and only decreased in the zeolite peaks and some small shifts
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of XRD peak position were observed with the increased in iron oxide loading [34].
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Fig. 3. PXRD patterns of zeolite (a), zeolite treated with NaOH (b) and magnetite/zeolite-
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From FESEM analysis, the cubic structure of zeolite (Fig. 4(a)) showed smooth surface
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before embedded with Fe3O4-NPs. However, after formation of Fe3O4-NPs, the zeolite surface
4
become rough and more opening of the zeolite pores can be observed (Fig. 4(c)). This was
5
attributed from the significant induce of mesoporosity after desilication with NaOH [33].
6
High distribution of NPs was formed on the surface of cubic zeolite substrate and some
7
agglomeration also appeared. Based on the EDX analysis, zeolite composition showed the
8
appearance of elements (Al, Si, Na and O) ((Fig. 4(b)). Similar elements were observed in the
9
zeolite/Fe3O4-NCs as well as the appearances of new peaks correspond to Fe element in the
10
regions at approximately 0.7, 6.4 and 7.1 KeV (Fig. 4(d)). According to EDX analysis, the
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Si/Al ratio was reduced from 1.02 to 0.87 indicated the desilication of synthetic zeolite after
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NaOH treatment and formation of Fe3O4-NPs.
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Fig. 4. FESEM and EDX images of zeolite (a, b), magnetite/zeolite-NCs (c, d).
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The TEM image of the spherical Fe3O4-NPs formed in the zeolite substrate was shown in Fig.
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5(a). A histogram depicted that the synthesized NPs have diameter and standard deviation of
4
2.4 ± 0.41 nm (Fig. 5(b)). Fig. 5(c) displayed the formation of agglomerated Fe3O4 on the
5
zeolite frameworks. Agglomeration of NPs was observed due to the formation of small
6
particle sizes and magnetic behaviour possessed by Fe3O4 [36]. Fig. 5(d) showed the
7
selected-area electron diffraction (SAED) pattern where rings can be seen attributed to the
8
polycrystalline nature of the sample. The pattern corresponds to the cubic Fe3O4 planes of
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[220], [311], [400], [511] and [440] are in agreement with the XRD pattern with JCPDS file number of 019-0629.
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Fig. 5. TEM images of magnetite/zeolite-NCs (a, c), Particle size distribution histogram (b)
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SAED pattern of iron oxide (d).
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3.6. Vibrating sample magnetometer analysis
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The magnetic behaviour of the synthesized magnetite/zeolite-NCs showed the saturation
4
magnetization (Ms) of 6.52 emu.g-1 (Fig. 6). The coercivity of the sample was 56.78 G. The
5
Ms obtained was much lower as compared to the pure magnetite due to the low percentage of
6
Fe3O4 incorporated in zeolite structure. Besides, the low Ms of magnetite/zeolite-NCs also
7
attributed to the size dependent magnetization of the magnetic nanoparticles. As when the
8
size of magnetic NPs decreases, the NPs moves toward superparamagnetism but may have a
9
reduced in Ms [37]. Nah et al. [38] reported that the zeolite has zero magnetization and
10
coercivity. They demonstrated that both bulk magnetization and coercivity were increased
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with the presence of magnetite nanoparticles in pure zeolites.
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Fig. 6. (a) Magnetization versus applied magnetic field for magnetite/zeolite-NCs at 300 K
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(b) coercivity of magnetite/zeolite-NCs
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3.7. Fourier transform infrared analysis
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Fig. 7(a-c) shows the comparison of FT-IR spectra for the silicate host structure of zeolite,
4
treated zeolite, and magnetite/zeolite-NCs. The relatively wide and strong bands were
5
observed for O-H stretching in the spectral regions of 3100 to 3500 cm-1 due to the H2O
6
interporous structure [39]. The position of the vibration bands in the region of 1653-1655 cm-
7
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1001-1003 cm⁻1 was resulted from the stretching and bending modes of Si-O or Al-O within
9
zeolite framework associated with the asymmetric and symmetric stretching modes of
10
external linkages [40]. The presence of bands at region of 665 and 666 cm-1 were due to the
11
Al-O vibration and the bands observed at 553-464 cm-1 were attributed to the Si-O-Si
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bending vibration [39].
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were attributed from the H-O-H bending vibration. Besides, the appearance of bands at
Fig. 7(c) showed there was non-bond chemical interaction were observed between the
14
zeolite structure and Fe3O4‒NPs. This might be due to the overlapping of Fe-O band with the
15
strong vibrations of Si-O bending at 464 cm-1. However, the presence of Fe3O4 in the zeolite
16
frameworks, results in slightly shifting of O-H stretching band towards lower wavelength and
17
decreased in the peaks intensities were observed. Sagir et al. also demonstrated no Fe-O
18
vibration peak present in the spectrum of magnetite/zeolite due to the overlapping with Si-O
19
band attributed from the zeolite molecular structure [41]. Non-bond chemical interaction and
20
rigidity of the silicate layers also has been reported between the Fe3O4-NPs and talc-Fe3O4
21
[18]. In this study, the patterns remained unchanged for all samples which indicated rigidity
22
and well preserved of zeolite structure after treatment with NaOH and incorporation with
23
Fe3O4-NPs. However, if the desilication was carried out using high concentration of base, it
24
may result in significant destruction of zeolite and led to the formation of protonic sites (not
25
Si–OH–Al groups) of weak acid strength [42]. Hence, low concentration of NaOH should be
26
used to induce the mesoporosity in zeolite frameworks.
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Fig. 7. The near FT-IR spectra of zeolite (a), zeolite treated NaOH (b), and magnetite/zeolite-
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NCs (c).
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The oxygen reduction reaction (ORR) was studied on the NCs as electrocatalyst. The ORR is
7
a key reaction in most of the electrochemical energy devices such as fuel cells and metal-air
8
batteries. ORR can occur through a two-electron or four-electron transfer mechanisms [23].
9
During the two-electron transfer mechanism, hydrogen peroxide molecules (as the
10
intermediates) are generated on the surface of catalyst while no hydrogen peroxide can be
11
detected during the direct four-electron transfer mechanism. Regardless the pathway of ORR
12
process, the overall reduction reaction in alkaline aqueous medium is as follows:
13
O2 + H2O + 4e → 4 OH− (Eq. 2)
14
The ORR process was studied in the N2- and O2-saturated 0.1 M KOH by linear scan
15
voltammetry (LSV). Fig. 8 shows the polarization curves attributed to the prepared NCs at a
16
scan rate of 50 mV.s−1 in the oxygen-free and O2-saturated alkaline solution. The
17
electrochemical performance of the NCs in N2-saturated KOH solution is negligible while the
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solution.
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As it is seen in the Fig. 8, the oxygen reduction occurs with the onset potential of 0 V and two
4
consecutive reduction peaks at −0.45 V and −1 V which follows by the hydrogen evolution
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reaction at the potentials more negative than −1.35 V.
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Fig. 8. LSV of magnetite/zeolite-NCs in N2- (dotted line) and O2-saturated (solid line) 0.1 M
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KOH at a scan rate of 50 mV.s−1.
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Different scan sweep potential rates were also applied to the working electrode for ORR
11
process. It was observed that the performance of Fe3O4-NCs towards the ORR increases by
12
increasing the scan rate from 20 mV.s−1 to 500 mV.s−1 (Fig. 9). The magnitude of square root
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of the scan rate decreases linearly versus the peak current in ORR process (Fig. 10) which
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indicates that ORR is a diffusion-controlled process in the alkaline medium.
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Fig. 9. LSV of magnetite/zeolite-NCs in O2-saturated 0.1 M KOH at scan rates of 20, 50,
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100, 125, 150, 200, 300, 400 and 500 mV.s−1.
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Fig. 10. Plot showing square root of the scan rate versus current
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4. Conclusions
2
Magnetite/zeolite-NCs was successfully synthesized by a green synthesis technique. The
3
employed technique for synthesizing magnetite/zeolite-NCs is cost effective, facile, and
4
environmentally friendly that can be applied for production of large amount of NCs without
5
utilizing high pressure, energy and temperature. The synthesized magnetite/zeolite-NCs
6
showed saturation magnetization of 6.52 emu.g⁻1 which demonstrated sufficient
7
magnetization for the separation by external permanent magnet. High distribution of NPs
8
having diameter around 2.40±0.41 nm was formed in the cubic zeolite substrate. The
9
magnetite/zeolite-NCs show good performance towards oxygen reduction reaction in alkaline
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medium. The as synthesized magnetite/zeolite-NCs may have potential as one of the effective
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non-precious electrocatalyst for fuel cells and batteries applications.
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Acknowledgement
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This research was supported by the Malaysian Ministry of Higher Education and Universiti
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Teknologi Malaysia (UTM) under Tier 1 grant (PY/2015/05182). We also would like to
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thank to the Research Management Centre (RMC) and Malaysia-Japan International Institute
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of Technology (MJIIT) of UTM for providing an excellent research environment to complete
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this work.
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[42] K. Sadowska, K. Góra-Marek, M. Drozdek, P. Kuśtrowski, J. Datka, J. Martinez 22
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Triguero, F. Rey, Desilication of highly siliceous zeolite ZSM-5 with NaOH and
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NaOH/tetrabutylamine hydroxide, Microporous Mesoporous Mater. 168 (2013) 195–
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205.
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ACCEPTED MANUSCRIPT
Highlights •
A green, facile and rapid method to prepare magnetite/zeolite nanocomposites.
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The nanocomposites show good performance towards oxygen reduction reaction in alkaline medium.
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The nanocomposites have a great potential for energy application.
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