Preparation and adsorption properties of enhanced magnetic zinc ferrite-reduced graphene oxide nanocomposites via a facile one-pot solvothermal method

Preparation and adsorption properties of enhanced magnetic zinc ferrite-reduced graphene oxide nanocomposites via a facile one-pot solvothermal method

Accepted Manuscript Preparation and adsorption properties of enhanced magnetic zinc ferrite-reduced graphene oxide nanocomposites via a facile one-pot...

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Accepted Manuscript Preparation and adsorption properties of enhanced magnetic zinc ferrite-reduced graphene oxide nanocomposites via a facile one-pot solvothermal method Peng Fei, Qiang Wang, Ming Zhong, Bitao Su PII:

S0925-8388(16)31641-3

DOI:

10.1016/j.jallcom.2016.05.279

Reference:

JALCOM 37799

To appear in:

Journal of Alloys and Compounds

Received Date: 6 February 2016 Revised Date:

25 May 2016

Accepted Date: 26 May 2016

Please cite this article as: P. Fei, Q. Wang, M. Zhong, B. Su, Preparation and adsorption properties of enhanced magnetic zinc ferrite-reduced graphene oxide nanocomposites via a facile one-pot solvothermal method, Journal of Alloys and Compounds (2016), doi: 10.1016/j.jallcom.2016.05.279. 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.

ACCEPTED MANUSCRIPT

Preparation and adsorption properties of enhanced magnetic

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zinc ferrite-reduced graphene oxide nanocomposites via a facile

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one-pot solvothermal method

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Peng Fei a, b∗, Qiang Wang c, Ming Zhong d, Bitao Su b**

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a

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Datong 037009, China

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b

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Education of China, Key Laboratory of Polymer Materials of Gansu Province,

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College of Chemistry and Chemical Engineering, Northwest Normal University,

School of Chemistry and Environmental Engineering, Shanxi Datong University,

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Key Laboratory of Eco-Environment-Related Polymer Materials, Ministry of

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Lanzhou 730070, China

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c

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d

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Materials, TKL of Metal and Molecule-Based Material Chemistry, Nankai University,

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Tianjin 300350, China

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Abstract: The wide application of reduced graphene oxide (rGO) in water

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treatment is mainly suffered from high cost and difficult reusage. To addressing

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these issues, a series of zinc ferrite-reduced graphene oxide (ZF-rGO)

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nanocomposites with enhanced magnetic properties were successfully prepared

Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China

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School of Materials Science and Engineering, National Institute for Advanced

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Corresponding author Tel.: +86 13609385281;

[email protected], [email protected] (Bitao Su); ∗

Corresponding author Tel.: +86 18734270152;

[email protected], (Peng Fei). 1

ACCEPTED MANUSCRIPT using graphene oxide (GO), Fe3+, Zn2+ and ethylene glycol (EG) via a one-pot

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solvothermal method and the adsorption property was evaluated by the adsorption

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amount of methylene blue (MB) solution on the samples. The results indicate the

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as-prepared materials possess good adsorption and cycling properties for MB

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molecules. The dominated reason is mainly ascribed to the π-π stacking between

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dye molecules and rGO. Simultaneously, the adsorption kinetic behavior of MB

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molecules is also discussed and follows pseudo-second-order kinetic very well.

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Particularly, the introduction of Fe2+ enhances the magnetic property of ZF

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component in ZF-rGO composite by the reducing action of EG, which ensures the

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outstanding magnetic separability of the ZF-rGO materials as the adsorbent. Thus,

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the as-prepared nanocomposite material can be a potential excellent absorbent for

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removing dye pollutants.

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Keywords:

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solvothermal method; enhanced magnetic property; adsorption property

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1. Introduction

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ferrite-reduced

graphene

oxide

nanocomposites;

one-pot

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zinc

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Dyes are extensively used as coloring agents in industries, such as the textile,

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paper, food, printing, leather and plastics industries. Up to now, surface and ground

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water pollution by many kinds of dyes is a global environmental issue and a threat to

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human being and aquatic life [1]. Many kinds of treatments, including

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electrochemical

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photochemical degradation, reverse osmosis, flocculation-coagulation, aerobic or

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anaerobic treatment and adsorption [1-3], have been developed and applied

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techniques,

oxidation

or

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ozonation,

membrane

separation,

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getting special interest due to its high efficiency, low-energy, and simple operation

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process [2-4]. Some kinds of carbon materials have been used as the adsorbent for the

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wastewater treatment. For example, activated carbon (AC) materials possess high

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adsorption capacity due to their abundant porosity and large surface area and have

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been widely employed in dye wastewater treatment industry [1, 5]. Carbon nanotubes

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(CNTs), as another kind of carbon materials, have also been used as adsorbents to

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remove various organic and inorganic pollutants from water owing to their large

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specific surface area, small pore size, hollow and layered structure [6, 7].

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rGO material with excellent adsorbent property is a new booming carbon-based

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material and is widely noted as a potential adsorbent material in removal of dye

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molecules from water [8, 9]. However, the most obstacles of rGO for wide application

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are the difficulties for separation of suspended adsorbent from the treated water and

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the recyclability, which may cause the cost escalation and bring the secondary

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pollution.

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As a rapid and effective technology, magnetic separation technology has been

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used in many fields, especially in water treatment. Its main advantage exists in its

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capability of treating large amount of the wastewater within a short time and

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producing

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CoFe2O4-functionalized graphene [11] have been prepared for the removal of dyes

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from water. Herein, a key technology for its widespread application in the wastewater

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treatment field is the preparation of magnetic ferrite material and ferrite-rGO

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no

contaminants.

At

present,

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graphene/Fe3O4

[10]

and

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nanocomposite adsorbents with high saturation magnetization, which can ensure a

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super magnetic separability of the adsorbent. In this study, an easy and effective one-pot solvothermal method was developed

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by our group and successfully used to prepare a series of magnetic zinc

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ferrite-reduced graphene oxide (ZF-rGO) nanocomposite materials. The results

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indicate that the as-prepared ZF-rGO nanocomposite materials show high adsorption

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activity for the removal of MB from water. What’s more, due to the substitution of

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Fe2+ ions for a portion of Zn2+ ions in ZF, the enhanced magnetic properties of the

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nanocomposite ZF-rGO ensure the super magnetic separability of the nanocomposite ZF-rGO as the adsorbents.

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2. Experimental

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2.1 Materials

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Graphite powder was purchased from BASF Chemical Co., Ltd. (Tianjin, China).

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The ferric chloride hexahydrate (FeCl3·6H2O) and zinc chloride (ZnCl2) were

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purchased from Yantai Shuangshuang Chemical Co., Ltd. Ammonium acetate (NH4Ac)

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was obtained from Laiyang Shuangshuang Chemical Co., Ltd. Ethylene glycol (EG)

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was purchased from Kaixin chemical industry Co., Ltd. Methylene blue (MB) was

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obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Ethanol

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was obtained from Laiyang Shuangshuang Chemical Co., Ltd. All of the reagents

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were analytically pure and used without further purification. Double distilled water

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was used throughout our work.

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2.2 Preparation of zinc ferrite-reduced graphene oxide (ZF-rGO) nanocomposites

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An effective one-pot solvothermal method was developed and used to prepare a

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series of ZF-rGO nanocomposites with different rGO content (0.0, 5.0, 10.0, 15.0,

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20.0, and 25.0 wt %) from GO, ZnCl2 and FeCl3·6H2O. GO was prepared from graphite powder by the Hummers method [12, 13].

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A typical experiment for preparing ZF-rGO nanocomposite with 25.0 % rGO

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content is as follows: 0.1609 g GO, 0.2726 g ZnCl2 and 1.0812 g FeCl3·6H2O were

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added into 60 mL EG with sonication for 2 h to obtain a well-distributed suspension.

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2.3125 g NH4Ac was added to the suspension under vigorously stirring. The mixture

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was transferred into a Teflon-lined stainless autoclave and heated at 200 oC for 24 h

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under autogenous pressure and then naturally cooled to ambient temperature. The

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resulted product was washed with double-distilled water and ethanol for several times

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and dried at 60 oC in a vacuum oven for 12 h. 25.0 % ZF-rGO nanocomposite was

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obtained.

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A series of ZF-rGO nanocomposites from 0.0 to 25.0 % were prepared by

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changing the amount of added GO in the above process and labeled as ZF-rGO-0 (0.0

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wt %), ZF-rGO-1 (5.0 wt %), ZF-rGO-2 (10.0 wt %), ZF-rGO-3 (15.0 wt %),

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ZF-rGO-4 (20.0 wt %) and ZF-rGO-5 (25.0 wt %), respectively.

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Fig. 1

As showing in Fig.1, during the above-described solvothermal procedure, Fe3+

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and Zn2+ ions were firstly adsorbed on the surface of GO sheets (named as

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Zn2+/Fe3+-GO) due to the existence of the oxygen-containing functional groups and

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then in-situ converted to ZF on the carbon matrix, meanwhile the GO was reduced to

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ACCEPTED MANUSCRIPT rGO. It was worth mentioning that GO and a portion of Fe3+ ions were simultaneously

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reduced to reduced graphene oxide (rGO) and Fe2+ ions by regent EG, respectively

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(demonstrated by the results of FT-IR and XPS spectra). The presence of Fe2+ ions

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was proved to be beneficial for improving the magnetic property of the as-prepared

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materials (seen in magnetic properties of the samples).

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2.3 Characterization

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X-ray diffraction (XRD) measurements were recorded on an X-ray

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diffractometer (Rigaku D/Max-2000 Japan) with Cu Kα radiation (λ = 0.154 nm)

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operated at 40 kV and 100 mA. The Fourier transform infrared (FT-IR) spectra were

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measured on a FTS3000FX infrared spectrometer (DIGILAB, America). The

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morphologies were observed by transmission electron microscope (TEM; JEOL,

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JEM-2010, Japan). The Magnetic measurements were carried out on vibrating sample

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magnetometer (VSM, Lakeshore 7304, USA) at room temperature. X-ray

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photoelectron spectroscopy (XPS) measurement was performed on a Thi-5702

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photoelectron spectrometer (America) with Al Kα X-ray radiation as the X-ray source

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for excitation. Nitrogen adsorption/desorption measurements were carried out on an

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ASAP 2020 (Micromeritics) and the Brunauer-Emmett-Teller (BET) method was

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utilized to calculate the specific surface areas.

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2.4 Adsorption property

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The adsorption kinetics experiments were performed in a batch. 50 mg of the

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as-prepared adsorbent was added into 50 mL MB solution (10 mg·L-1) and stirred

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under the darkness condition. At predetermined time intervals, the concentration (Ct)

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of MB solution, from which the adsorbent was removed by magnetic separation, was

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determined by measuring the absorbance at 664 nm (λmax of MB solution) using a

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Shimadzu UV-2550 UV-vis spectrophotometer. The adsorption amount qt (mg·g-1) is calculated by the following equation:

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qt = [(C0-Ct) × V] /m

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in which qt is the amount of adsorbed MB molecules on the adsorbent per gram, C0

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and Ct (mg·L-1) are the concentrations of the MB solution at the initial time t =0 and

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adsorption time t, respectively. V (L) is the initial volume of the MB solution and m (g)

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is the mass of the adsorbent.

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ZF-rGO was reused to investigate its recycling property for the removal of MB

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after the absorbent ZF-rGO was separated, washed with ethanol, and dried in a

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vacuum oven.

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3. Results and discussion

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3.1 Characterization of the samples

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Fig. 2

The crystal phases of the samples are firstly analyzed by XRD measurement. Fig.

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2A shows the XRD patterns of graphite (a), GO (b) and ZF-rGO-5 (c). In the XRD

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pattern of graphite, the sharp peak (002) of the graphite at 26.2o indicates an interlayer

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spacing of 0.34 nm. In Fig. 2A (b), the characteristic graphite peak (002) disappears

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and is replaced by a well-defined peak at 2θ = 9.80o, corresponding to the (001)

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reflection of GO with 0.90 nm of d-spacing. Compared to 0.34 nm d-spacing of the

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graphite (002), the increased d-spacing of GO is due to the presence of abundant

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atomic-scale roughness of the GO sheet [14], which indicates the successful

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preparation of GO from graphite via the Hummers method. In Fig. 2A (c), the

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diffraction peaks correspond to the (111), (220), (311), (400), (422), (511), and (440)

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crystal planes of cubic spinel structural zinc ferrite (ZF) (JCPDS No. 22-1012),

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respectively. The sharp and strong peaks confirm that ZF nanoparticles are well

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crystallized in the composites, while the disappearance of typical diffraction peak of

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rGO (002) can be ascribed to the fact that the regular stacking of rGO is destroyed

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with the further exfoliation due to the introduced ZF particles [15].

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Fig. 2B presents the FT-IR spectra of GO (a) and ZF-rGO-5 (b). In Fig. 2B (a),

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the characteristic peaks at around 1727 cm-1 (C=O stretching vibrations of COOH

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groups), 1395 cm-1 (deformation vibrations of tertiary C-OH), and 1065 cm-1

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(stretching vibrations of C-O groups) [16, 17] suggest that GO was successfully

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prepared from graphite. The absorption at 1626 cm-1 may be attributed to skeletal

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vibrations of unoxidized graphitic domains [17, 18]. In the spectrum of ZF-rGO-5, the

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peaks corresponding to the oxygen-containing functional groups become very weaken,

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suggesting that GO is reduced to rGO during the process of one-pot solvothermal

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preparation [19], and the characteristic peak at around 1571 cm-1 could be assigned to

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the stretching vibrations of the conjugated carbon backbone, which also proves the

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successful reduction of GO [20]. In addition, another new peak appears at 579 cm-1 is

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attributed to the stretching vibrations of M-O in ZF, confirming the existence of ZF in

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the nanocomposite [21].

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The elemental composition and chemical status of composite (ZF-rGO-5) are

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further analyzed by X-ray photoelectron spectroscopy (XPS). XPS results indicate

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that the composite contained Zn, Fe, O and C (Fig. 3A). Fig. 3B, C, and D show the

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high-resolution XPS spectra for C 1s, Zn 2p and Fe 2p, respectively. In Fig. 3B, the

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XPS peaks of C 1s at 289.3, 287.5, 286.3, and 284.8 eV are assigned to the C=O,

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C-O-C, C-OH, and C=C, respectively [19] and the peaks of Zn-C or Fe-C are not

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found. As mentioned above, graphene can be obtained by removal of the oxygen from

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graphene oxide via the hydrothermal reaction in the presence of EG. The XPS results

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indicate a decrease of oxygen content in the composite compared with that of GO

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(The inset in Fig. 3B). The intensities of some oxygen-containing groups (C-O-C,

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especially) on carbon in the composite are obviously reduced, indicating the

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deoxygenation of graphene oxide. Meanwhile, the result also shows that a tiny

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amount of oxygen-containing groups would be residual in rGO via hydrothermal

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process [19]. Two peaks with binding energy values at 1045.4 and 1022.3 eV

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exhibited in the Zn 2p spectrum (Figure 3C) can be attributed to Zn 2p1/2 and Zn 2p3/2,

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respectively, indicating the Zn2+ oxidation state of zinc ferrite. Fig. 3D shows the XPS

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spectrum of Fe 2p of the sample [22]. The peaks at 712.8 and 725.2 eV are

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characteristics of Fe3+ while the peaks at 710.4 and 723.5 eV are characteristics of

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Fe2+[23-25]. The presence of Fe2+ and Fe3+ in the sample further confirms the partly

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reduction of Fe3+ through the hydrothermal process in the presence of EG, which is

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important for the enhanced magnetism.

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ACCEPTED MANUSCRIPT Fig. 4

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TEM images of rGO and ZF-rGO-5 are showed in Fig.4. In Fig. 4A, TEM image

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of rGO displays a wrinkled paper-like structure of the ultrathin sheets and stacking of

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sheets. From the Fig. 4B, it can be observed that ZF nanoparticles are closely

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anchored on the rGO sheets. Therefore, it can be speculated that the rGO sheets can

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suppress the aggregation of ZF nanoparticles while the ZF nanoparticles also can

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prevent the aggregation of the stack and wrinkle of rGO sheets [14].

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3.2 Magnetic properties of the samples

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Fig. 5 shows the magnetic hysteresis loops of the samples ZF-rGO-0~5 at room

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temperature. All of the samples indicate typical ferrimagnetism and their magnetic

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properties change with different content of rGO. The magnetic parameters are listed in

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Table 1.

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Fig. 5

Tab. 1

As we know, Fe3+ and Fe2+ ions are magnetic but Zn2+ ion is nonmagnetic. In our

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work, Ms of pure ZF (ZF-rGO-0) are 70.33 emu·g-1 and much higher than that of the

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reports (16.3 emu·g-1 [26] and 31.9 emu·g-1 [27]), in which ZF was prepared using the

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traditional method. The partial reduction of Fe3+ to Fe2+, by the reducing action of EG

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solvent, is herein considered as one of the main reasons. The existence of Fe2+ in the

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ZF nanocrystals has been proved by the XPS of Fe 2p in Fig. 3. The produced Fe2+

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ions can enter into the A site of spinel structure and substitute for a portion of Zn2+,

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which can lead to a further change of the structure from normal to mixed spinel type

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[28] and the superexchange interaction between A site and B site could be further

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enhanced. According to the equation Ms = ϕ ms, where ϕ is the volume fraction of the

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magnetic ferrite particles and ms is the saturation moment of a single particle, it is

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clear that Ms of the composite is dependent on the volume fraction of the magnetic

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ferrite particles (ϕ), and hence, Ms of the nanocomposite materials ZF-rGO-1~5

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should be lower than ZF-rGO-0 (pure ZF) and decrease with the reducing ϕ of the

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magnetic ZF [29] due to the contribution of the non-magnetic rGO to the total

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magnetization. Hc of the ZF-rGO nanocomposites is higher than that of ZF. It is

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because that combining ZF with rGO can increase the surface anisotropy of ZF

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nanocrystal [27, 30].

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From the inset in Fig. 5, it can be seen that the black ZF-rGO-5 is attracted

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toward the magnet rapidly, showing the extraordinary magnetic separability rooted in

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the enhanced magnetism, which makes the nanocomposite material as a potential

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absorbent of reusability and non-secondary pollution as possible.

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3.3 Adsorption properties of the samples

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Fig. 6

From Fig. 6A, it can be seen that pure ZF (ZF-rGO-0) basically shows no

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adsorption performance whereas ZF-rGO-1~5 possess increased adsorption activities

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with the increase of rGO content. For example, the adsorption amounts of MB on

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ZF-rGO-4 and ZF-rGO-5 can achieve 9.40 mg·g-1 and 9.73 mg·g-1 respectively in a

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MB solution within 30 min, showing the best adsorption activities in the five samples,

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while the adsorption amounts of MB on ZF-rGO-1~3 are less than 8.51 mg·g-1 within

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150 min. It is noteworthy that the adsorption properties of MB molecule on the

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composites are quite rapid in the first 30 min and then increase gradually as the

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adsorption

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nanocomposites originates from the rGO of the nanocomposites ZF-rGO. The

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high-performance of the absorbents is mainly related to the π-π stacking between dye

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molecules and π-conjugation regions of the rGO. In addition, the electrostatic

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interaction between cationic MB molecule and negatively charged residual

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oxygen-containing functional groups on the surface of rGO is another reason for the

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good adsorption activity. In fact, the introduction of ZF nanoparticles is also

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beneficial to increasing the adsorption activity of the nanocomposite samples because

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compositing rGO with ZF can bring about unfolding and further exfoliating of rGO

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wrinkled sheets and prevent the aggregation of rGO sheets [14], resulting in the

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increase of the surface area.

prolongation.

The

high

adsorption

performance

of

the

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The pseudo-second-order kinetic model is used to investigate the kinetics

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behavior of MB adsorption on the nanocomposites, which is defined as follows [14,

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31]:

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t / qt=t / qe+1/k2qe2

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where qe (mg·g-1) is the adsorption amount at equilibrium, the parameter k2

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(g·mg-1·min -1) represents the pseudo-second-order rate constant of the kinetic model.

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Obviously, the qe and k2 can be calculated from the slope and intercept of the linear

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plot of t/qt vs. t. The plots of t/qt versus t for ZF-rGO-5, the sample with best

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adsorption property, is given in Fig. 6B and the parameters of qe, k2, and R2 (the

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correlation coefficient) for all the samples are shown in Tab. 2. Tab. 2

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Fig. 6B and Tab. 2 show that the calculated qe values (qecal) from the

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pseudo-second-order model match well with the experimental data (qeexp), showing a

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good linearity with the correlation coefficients (R2) above 0.99. Therefore, the

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adsorption kinetic follows the pseudo-second-order model.

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The graphene material possesses high specific surface area with the theoretical

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value of 2630 m2·g-1 and it leads to an excellent adsorption activity. However, in fact,

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the specific surface area of rGO and its composites are much lower than the

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theoretical value. Fig. 7 depicts changes of adsorption capacity as a function of BET

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specific surface area for the samples with different rGO content. It can be seen that qe

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and specific surface area are improved with the increase of rGO content, which is the

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same as the result of the work by Li and the co-workers [11], meanwhile, the results

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also indicate that the adsorption active component in the composite is the rGO.

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Fig. 8

In the recycling process of the absorbents, the adsorption properties decrease

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because of the strong π-π stacking interaction between MB molecules and rGO.

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Therefore, it is difficult to release MB molecule from the adsorbent in the washing

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process, which prevents further adsorption of MB molecule. For evaluating the

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reusability of the nanocomposites, the ZF-rGO-5 was separated by a magnet, washed,

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ACCEPTED MANUSCRIPT dried, and then reused for the removal of MB (without considering the loss of the

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adsorbents). The recycled adsorbed effects are shown in Fig. 8. It can be seen that qe

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was over 5.79 mg·g-1 after being reused in five cycles, indicating that the

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nanocomposites show good reusable adsorption performance for removal of MB.

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4. Conclusions

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A series of the ZF-rGO nanocomposites in the rGO content range of 0.0 to

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25.0 % were successfully prepared via a facile one-pot solvothermal method,

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developed by our group. ZF nanoparticles are anchored on the surface of rGO sheets

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and bring about unfolding and further exfoliating of rGO wrinkled sheets. The

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enhanced magnetic property of as-prepared ZF and ZF-rGO is ascribed to the

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substitution of Fe2+ ions, originated from the reduction of Fe3+ by the EG solvent, for

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a portion of nonmagnetic Zn2+ ions in ZF nanocrystal, resulting in the enhanced

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superexchange interaction between A and B sites in the spinel structure, which makes

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the nanocomposites as potential separable absorbents to remove dye pollutants from

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water as possible. The nanocomposites exhibit extraordinary adsorption performance

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for MB in water and the adsorption activities increase with the increasing rGO content

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in nanocomposites. In summary, the nanocomposites can be a potential absorbent to

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remove dye pollutants with excellent magnetic separability.

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Acknowledgments

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This work was financially supported by Doctoral Scientific Research Foundation

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of Shanxi Datong University (2014-B-11), National Natural Science Foundation of

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China (No. 21503252), National Natural Science Foundation of China (Project

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ACCEPTED MANUSCRIPT 21174114), Program for Changjiang Scholars and Innovative Research Team in

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University of Ministry of Education of China (Project No. IRT1177), Scientific and

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Technical plan project of Gansu province (No. 1204GKCA006), and Natural Science

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Foundation of Gansu Province (Project No.1010RJZA024).

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34-40.

[8] T.H. Liu, Y.H. Li, Q.J. Du, J.K. Sun, Y.Q. Jiao, G.M. Yang, Z.H. Wang, Y.Z. Xia,

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W. Zhang K.L. Wang, H.W. Zhu, D.H. Wu, Colloids Surf. B 90 (2012) 197-203.

[9] G.K. Ramesha, A.V. Kumara, H.B. Muralidhara, S. Sampath, J. Colloid Interface Sci. 361 (2011) 270-277.

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[10] T.T. Qi, C.C. Huang, S. Yan, X.J. Li, S.Y. Pan, Talanta 144(2015) 1116-1124.

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[11] N.W. Li, M.B. Zheng, X.F. Chang, G.B. Ji, H.L. Lu, L.P. Xue, L.J. Pan, J.M. Cao,

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J. Solid State Chem. 184 (2011) 953-958.

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[13] L.J. Cote, F. Kim, J.X. Huang, J. Am. Chem. Soc. 131 (2009) 1043-1049.

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[15] Y,S. Fu, H.Q. Chen, X.Q. Sun, X. Wang, Appl. Catal. B 111-112 (2012) 280-287.

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[19] Y.S. Fu, X. Wang, Ind. Eng. Chem. Res. 50 (2011) 7210-7218.

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[20] C.Y. Hou, Q.H. Zhang, M.F. Zhu, Y.G. Li, H.Z. Wang, Carbon 49 (2011) 47-53.

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[21] Z. Shahnavaz, P.M. Woi, Y. Alias, Ceram. Int. 41(2015) 12710-12716.

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[22] X. Zhou, X. W. Li, H.B. Sun, P. Sun, X.S. Liang, F.M. Liu, X.L. Hu, G.Y. Lu,

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ACS Appl. Mater. Interfaces 7(2015) 15414-15421. [23] Z.H. Wang, M. Chen, J.X. Shu, Y. Li, J. Alloys Compd. 682 (2016) 432-440.

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[26] M. Maletin, E.G. Moshopoulou, V.V. Srdi, Phys. stat. sol. (a) 205 (2008) 1831-1834. [27] Y.B. Li, R. Yi, A.G. Yan, L.W. Deng, K.C. Zhou, X.H. Liu, Solid State Sci. 11 (2009) 1319-1324.

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(2008) 8558-8563. [29] N. Gandhi, K. Singh, A. Ohlan, D.P. Singh, S.K. Dhawan, Compos. Sci. Technol. 71 (2011) 1754-1760. [30] M.V. Limaye, S.B. Singh, S.K. Date, D. Kothari, V.R. Reddy, A. Gupta, V. Sathe, R.J. Choudhary, S.K. Kulkarni, J. Phys. Chem. B 113 (2009) 9070-9076. [31] Y.S. Ho, G. Mckay, Chem. Eng. J. 70 (1998) 115-124.

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[28] A.G. Yan, X.H. Liu, R. Yi, R.R. Shi, N. Zhang, G.Z. Qiu, J. Phys. Chem. C 112

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ACCEPTED MANUSCRIPT List of figures and tables

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Fig. 1

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Fig. 2

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Fig. 1 The formation mechanism of ZF-rGO from Zn2+, Fe3+ and GO during the

2

above solvothermal process

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Fig. 2 A: XRD patterns of graphite (a), GO (b) and ZF-rGO-5 (c) B: FT-IR spectra of GO (a) and ZF-rGO-5 (b)

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Fig. 3 The XPS of ZF-rGO-5: (A) survey, (B) C 1s, (C) Zn 2p and (D) Fe 2p. (The

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inset in B is C 1s XPS spectra of GO.)

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Fig. 4 TEM images of rGO (A) and ZF-rGO-5 (B)

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Fig. 5 Magnetic hysteresis loops of the samples ZF-rGO-0~5

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(Inset: good magnetic separable effect of the ZF-rGO-5 under an external magnetic field)

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Fig. 6 A: The time-dependent adsorption curves of MB solution on the samples

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ZF-rGO-0~5

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B: Plots of pseudo-second-order kinetics for the adsorption process of MB solution on the samples ZF-rGO-5

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Fig. 7 The variation of qe and BET surface area with increasing rGO content.

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Fig. 8 Recycling property of ZF-rGO-5 in the removal of MB

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ACCEPTED MANUSCRIPT Tab. 1 Magnetic parameters of the samples ZF-rGO-0~5

a

Ms (emu·g-1) a

Hc (Oe) b

ZF-rGO-0

70.33

30.41

ZF-rGO-1

63.98

45.61

ZF-rGO-2

57.25

ZF-rGO-3

50.85

ZF-rGO-4

46.48

ZF-rGO-5

45.94

Saturation magnetization. b Coercivity.

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Tab. 2 The pseudo-second-order kinetic parameters for the adsorption of MB solution

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on the nanocomposites ZF-rGO-1~5 qecal (mg·g-1)

qeexp (mg·g-1)

k2 (g·mg-1·min-1)

R2

ZF-rGO-1

3.42

3.34

0.0599

0.9993

ZF-rGO-2

6.89

6.62

0.0157

0.9952

ZF-rGO-3

8.66

8.51

0.0234

0.9987

ZF-rGO-4

9.78

9.40

0.0695

0.9993

ZF-rGO-5

10.23

9.73

0.0632

0.9997

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ACCEPTED MANUSCRIPT Tab. 1 Magnetic parameters of the samples ZF-rGO-0~5

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Tab. 2 The pseudo-second-order kinetic parameters for the adsorption of MB solution

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on the nanocomposites ZF-rGO-1~5

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ACCEPTED MANUSCRIPT Highlights  ZF-rGO nanocomposites were successfully prepared by one-pot solvothermal method.  Magnetic properties of ZF-rGO were enhanced by substituting Fe2+ for a part of

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Zn2+.  The composites ZF-rGO show good adsorption properties for MB removal.

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 Effective, rapid and easy magnetic separation property.