The preparation of novel adsorbent materials with efficient adsorption performance for both chromium and methylene blue

The preparation of novel adsorbent materials with efficient adsorption performance for both chromium and methylene blue

Accepted Manuscript Title: The preparation of novel adsorbent materials with efficient adsorption performance for both chromium and methylene blue Aut...

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Accepted Manuscript Title: The preparation of novel adsorbent materials with efficient adsorption performance for both chromium and methylene blue Author: Leilei Li Feng Liu Huimin Duan Xiaojiao Wang Jianbo Li Yanhui Wang Chuannan Luo PII: DOI: Reference:

S0927-7765(15)00396-3 http://dx.doi.org/doi:10.1016/j.colsurfb.2015.06.023 COLSUB 7153

To appear in:

Colloids and Surfaces B: Biointerfaces

Received date: Revised date: Accepted date:

19-1-2015 27-5-2015 10-6-2015

Please cite this article as: L. Li, F. Liu, H. Duan, X. Wang, J. Li, Y. Wang, C. Luo, The preparation of novel adsorbent materials with efficient adsorption performance for both chromium and methylene blue, Colloids and Surfaces B: Biointerfaces (2015), http://dx.doi.org/10.1016/j.colsurfb.2015.06.023 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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Regeneration

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MG-ILs-OH

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The adsorption and regeneration of MB and Cr(VI) on MG-ILs-OH

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Highlights

1. ILs-OH modified magnetic chitosan /graphene oxide to form composite adsorbent (MG-ILs-OH) through simple methods.

efficiently adsorption of chromium in batch systems.

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2. MG-ILs-OH could effective adsorption of not only methylene blue but also

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3. MG-ILs-OH has high adsorption because of its large number of adsorption

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sites(hydroxy and amino groups)

4. The MG-ILs-OH could be repeatedly used by simple treatment without obvious

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structure and performance degradation.

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The preparation of novel adsorbent materials with efficient adsorption performance for both chromium and methylene blue Leilei Lia, Feng Liub, Huimin Duana, Xiaojiao Wanga, Jianbo Lia, Yanhui Wanga, Chuannan

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Luoa,* a

Key Laboratory of Chemical Sensing & Analysis in Universities of Shandong (University of

JINAN URBAN CONSTRUCTION GROUP, Jinan 250031, China

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b

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Jinan), School of Chemistry and Chemical Engineering, University of Jinan, Jinan 250022, China

Corresponding Author

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*Phone: (86) 531-89736065; e-mail: [email protected] (C. N. Luo).

ABSTRACT

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The hydroxy-functionalized ionic liquids (ILs) modified with magnetic chitosan/grapheneoxide(MG-ILs-OH) were synthesized. The surface morphology of

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MG-ILs-OH was characterized by transmission electron microscopy, X-ray diffraction,

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thermo gravimetric analysis and Fourier transform infrared spectroscopy techniques. It was found that the adsorption kinetics is well fitted by apseudo-second-order model

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and the adsorption isotherms agree well with the Langmuir model, and the MG-ILs-OH could be repeatedly used by simple treatment.

The results showed that

the addition of ILs-OH can largely increase the adsorption sites (hydroxy and amino groups) and adsorption properties. The MG-ILs-OH were used as adsorbent for the removal of methylene blue (MB) and Cr(VI) from simulated wastewater with a fast solid−liquid separation in the presence of external magnetic field. The maximum

obtained adsorption capacities of MB and Cr(VI) were 243.31 mg/g and 107.99 mg/g, respectively. The application of MG-ILs-OH could effectively solve the problem that the adsorbent only adsorb similar adsorbate. Keywords Ionic liquids, Hydroxy functional, Adsorption, Methylene blue, Chromium, Regeneration 3

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1. Introduction Ionic liquids (ILs) are normally organic salts in which the ions are poorly bonded, and possess low melting points. Therefore, ILs show potential applications in gas

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separation, biomass conversion, electrolytes in battery and solar cells, materials preparation, catalysis and so on [1-3]. Currently, functionalized ILs with special properties which are related to their surface functional groups have been applied to

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solve problems in the environment protection [4–6], and results show that these ILs

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have great value in use and infinite prospect of development potential. Although the ionic liquid has many advantages, there is a disadvantage limits its application as well as efficiency, which is the liquidity. Consequently, one of the major themes in

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research is the immobilization of ILs on solid supports, which may improve their applicability in industrial fields.

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Presently, various materials show great and broad application prospect in the field of material surface modification. As an abundant natural biopolymer, chitosan is

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recognised as an excellent natural adsorbent for the removal of metal ions due to the

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presence of the amino (–NH2) and hydroxyl (–OH) groups, which serve as the coordination and binding sites [7]. Magnetic nanoparticles have received much

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attention in many areas, such as industrial chemistry and biomedical engineering, for separation, transportation, and imaging in external magnetic fields [8-11]. Graphene oxide (GO) has many carbonyl, carboxylic, alcoholic groups on its monolayer surface which can be used as functional groups [12]. Previous studies have shown that GO could be used as efficient removal for various organic substances and metal ions from water [13-16]. Based on the favorable inherent properties of these three chemical materials, researchers synthesized chitosan–GO composite as bio-adsorbents[17], and the magnetic-chitosan layer on graphene nanosheets can solve the aggregation problem of individual graphene nanosheets and nanomaterials [19], increasing the adsorption sites. Methylene blue (MB) is widely used to color products in textile industries. One of the major problems concerning textile wastewaters is the treatment of colored 4

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effluent. The wastewater contains a variety of organic compounds and toxic substances, which are harmful to water animals and plants [19]. In addition, the emission of Cr(VI) from extensive industries such as mining, cement ceramics, glass industries fossil fuel, battery manufacturing industries and production of plastics is

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another main contribution to water pollution [20]. The wastewater is highly toxic and can cause cancer, skin allergies and genetic defects [21]. Thus, the effective removal

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of dyes and metal ions from water systems is an important task for environmental engineering with challenging.

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In this paper, the preparation of effective adsorbent for removing dyes and metal ions from aqueous solution is expected to meet the demand of environmental

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protection. In the present work, we grafted hydroxyl-functionalized ILs onto magnetic chitosan /graphene oxide(MG) to formed hydroxyl-functionalized ILs modified

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magnetic chitosan /graphene oxide(MG-ILs-OH). The chitosan reaction with Fe3O4 through crosslinking formed magnetic chitosan, and then the magnetic chitosan

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reaction with graphene oxide through the dehydration condensation reaction, and the hydroxyl-functionalized ILs reaction with MG through the hydrogen bonding

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interaction finally. The addition of ILs-OH can largely increase the adsorption sites

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(hydroxyl and amino groups). The physicochemical properties of the adsorbent were investigated using FTIR, SEM, TEM and XRD. The adsorption capacity and desorption behaviors was investigated in MB and Cr(VI) aqueous solution, respectively. The effect of solution pH, contact time and concentration were investigated. Kinetic, thermodynamic and adsorption isotherm analysis were performed to understand the mechanism of adsorption process. Furthermore, the role of functional groups was discussed. Moreover, these composites exhibit superior magnetic properties, efficient adsorption and reusability. To the best of our knowledge, the adsorption of MB and Cr(VI)on Fe3O4 magnetic nanoparticles modied by hydroxyl-functionalized ILs has not been previously reported.

2. Experimental 2.1. Materials 5

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Chitosan with 80 mesh, 96% degree of deacetylation and average-molecular weight of 6.36×105 was purchased from Qingdao Baicheng Biochemical Corp. (China). FeCl2·4H2O (99.7%) and FeCl3·6H2O (99 %) were purchased from Damao Chemical

Agent

Company

(Tianjin,

China).

The

reagents

of

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1-ethyl-3-(3-dimethylaminoprophy) carbondiimide hydrochloride (EDC) (95%), N-hydroxyl succinimide (NHS) (98%), sodium hydroxide (96%), glutaradehyde(25%)

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and acetic acid (99.5%) were Aldrich products, N-(3-Aminopropyl)-imidazole (95%) was purchased from Sun Chemical Technology (Shang hai)Co., Ltdand and

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2-Bromoethanol (96%) was purchased from Aladdin. Sulfuric acid (95%-98%) was procured from Merck India. All other reagents used in this study were analytical grade,

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and distilled or double distilled water was used in the preparation of all solution. 2.2. Preparation of ILs-OH

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N-(3-Aminopropyl)-imidazole (0.1mol) and 2-Bromoethanol (0.12mol) were added into three-necked flask(250 mL). The mixture was stirred and refluxed under

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a nitrogen atmosphere at 80 ◦C for 24h. The solid was washed several times with

obtained.

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anhydrous ethylether. After evaporating, the hydroxyl-functional ionic liquids were

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2.3. Preparation of MG-ILs-OH Graphene oxide was prepared from purified natural graphite by the modified

Hummers method [22]. Magnetic chitosan and graphene oxide was prepared following the method of Fan L. et al [23]. A solution of 0.05 M EDC and 0.05 M NHS was added to the graphene oxide dispersion with continuous stirring for 2 h in order to activate the carboxyl groups of graphene oxide [24]. To adjust the pH of the solution and make it remained 7.0. 0.1 g of magnetic chitosan and the activated graphene oxide solution were added in a flask and dispersed in distilled water by ultrasonic dispersion for 10 min. After ultrasonic dispersion, the mixed solution were stirred at 60 ◦C for 2 h. The precipitate was washed with 2% (w/v) NaOH and distilled water in turn until pH was about 7. Then, the obtained product was collected by the aid of an adscititious magnet and dried in a vacuum oven at 50 ◦C. The obtained product was 6

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magnetic chitosan /graphene oxide. 1.0 g of ILs-OH was dissolved in 15 mL methanol. 1.0 g of magnetic chitosan /graphene oxide was taken in a round bottom flask and the dissolved ionic liquids were added dropwise and sonicated (Ultrasonic bath, Biotechnics, India) for 2 h with a 15 min intermittent time interval. The resulting

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solution was centrifuged, washed with methanol and the resulting MG-ILs-OH was

dried at room temperature and used for further adsorption studies. The preparation of

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MG-ILs-OH is shown in Fig. 1.

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2.4. Adsorption experiments

All batch adsorption experiments of MB and Cr(VI) were performed on a model KYC-1102 C thermostat shaker (Ningbo, China) with a shaking speed of 180

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rpm, respectively. Simulated wastewater with different adsorbate concentration was prepared with DI water. MG-ILs-OH (0.10 g) was added to 100 mL of the above

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adsorbate solution under mechanical agitation. For all adsorption tests, the initial pH values of the MB and Cr(VI) solution were adjusted with 0.1 M HCl solution or 0.1

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mol·L−1 NaOH solution. After the adsorption processes, MG-ILs-OH was

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conveniently separated by magnetic separation and the supernatant was immediately analyzed by atomic absorption spectrometry (WFX-1F2, China) and UV–Vis

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spectrophotometry. To study the influence of initial pH on the removal of adsorbate, the initial pH values of the solution were adjusted to a series of pH from acid to alkali. The concentration of MG-ILs-OH was 1.0 g·L−1. The initial MB concentration was 40,

60, 80, 100, 120 and 140 mg·L−1, the initial Cr(VI) concentration was 20, 40, 60, 80, 100 and 120 mg·L−1, the concentration of MB and Cr(VI) after adsorbed was

calculated by standard curve. The adsorption capacity and adsorption rate were calculated based on the difference in the adsorbate concentration in the aqueous solution before and after adsorption, according to the following equation: Q=(C0-Ce)V/W

(1)

Where, C0 and Ce are the initial and equilibrium concentrations of adsorbate in mg·L-1, respectively, V is the volume of adsorbate solution, in L, and W is the weight of the MG-ILs-OH used, in g. 7

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2.5. Replication of batch experiment Each batch adsorption experiment was conducted twice and the data shown are the average values. The individual values were generally within 5%.

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2.6. Characterization methods A HH-15 vibrating sample magnetometer (Nanjing, China) was used to measure magnetization curve of samples. XRD patterns were recorded by a D8 ADVANCE

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X-ray diffraction spectrometer (Bruker, German) with a Cu Kα target at a scan rate of

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0.02° 2θ s-1 from 5° to 70°. Morphological structures of samples were investigated by SEM with a Hitachi SX-650 machine (Tokyo, Japan). FT-IR spectra were recorded by

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Perkin-Elmer 580B IR spectrophotometer using the KBr pellet.

3. Results and discussion

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3.1. Characterization of MG-ILs-OH

The morphology and structure of the GO, MG and MGoo-ILs-OH were

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observed by SEM. As shown in Fig. 2a, the GO presents the sheet-like structure with smooth surface and wrinkled edge. Combination magnetic chitosan with GO, the MG

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composite was formed (Fig. 2b), The BET surface area of MG estimated from

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Barret–Joyner–Halenda (BJH) analysis of the isotherms were determined to be 342.2 m2/g, the MG showed much rougher surface and large thickness, revealing that the

small magnetic chitosan had been assembled on the surface of GO layers. It can be seen that a specific morphology and structure appeared with the impregnation of MG with ILs-OH (Fig. 2c), revealing that the ILs-OH was well dispersed on the surfaces of MG, indicating a homogeneous combination of the constituents. The interaction mechanism for the formation of MG-ILs-OH composite is mainly the cross-linking of MG mediated by ILs-OH, which is resulted from MG interacting with the ILs-OH with the π-π or/and π-cationic, hydrophobic and electrostatic attraction [25]. The BET surface area of MG-ILs-OH estimated from Barret–Joyner–Halenda (BJH) analysis of the isotherms were determined to be 412.2 m2/g. The difference of SEM images

indicated the interaction between GO with magnetic chitosan and ILs-OH in the 8

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composite materials. To obtain further information on the structure and topology of material, we also examined GO, MG and MG-ILs-OH by FT-IR, which is shown in Fig. 2d. The FTIR pattern of GO, reveals the presence of the oxygen-containing functional groups. The peaks at 1068, 1396, 1624 cm−1 correspond to C-O-C

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stretching vibrations, C-OH stretching, C-C stretching mode of the sp2 carbon skeletal network, respectively. While peaks located at 1732, and 3144 cm−1 correspond to C-O

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stretching vibrations of the -COOH groups, and O-H stretching vibration, respectively. As shown in MG, except for the characteristic peaks of GO, 1634cm-1 correspond to

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the C-O stretching vibration of -NHCO- and 1140 cm-1 correspond to N-H bending vibration of -NH2, 580 cm-1 is the characteristic peak of Fe3O4. The major

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characteristic peaks for MG-ILs-OH can be assigned as follows: 1038、1228 cm-1 correspond to C-N bending vibration, N-H bending vibration. After impregnated ionic

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liquid, N-H bending vibration transfer from 1140 cm-1 to 1228 cm-1, C-N bending vibration transfer from 1068 cm-1 to 1038 cm-1. These changes may be due to the

d

formation of intermolecular hydrogen bonding between ILs-OH and MG. 3440cm-1 correspond to O-H stretching vibration.

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XRD patterns of pure Fe3O4, GO and MG-ILs-OH are shown in Fig. 2e, indicating

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the existence of iron oxide particles (Fe3O4), which has magnetic properties and can be used for the magnetic separation (Fig. 2f). Six characteristic peaks for Fe3O4 (2θ= 30.1°, 35.5°, 43.3°, 53.4°, 57.2° and 62.5°), marked by their indices ((220), (311), (400), (422), (511), and (440)), were observed for MG-ILs-OH. The broad and relatively weak diffraction peak at 2θ=10.03° (d =0.87 nm), which corresponds to the typical diffraction peak of graphene oxide nanosheets. The characteristic peaks of chitosan are observed at 2θ= 20.16° [26].

3.2 Effect of pH value The effect of the initial pH value of the sample solution on the adsorption of MB and Cr(VI) onto the surface of MG-ILs-OH was investigated at different pH values ranging from 2.0 to 12.0 for MB and from 2.0 to 10.0 for Cr(VI), respectively. The initial concentrations of MB and Cr (VI) were all set at 100 mg/L. In addition, the 9

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adsorption of MB onto MG were also been made a comparative study. The results are depicted in Fig. 3. It shows that the pH of the sample solution could significantly affect the extent of adsorption of the MB and Cr(VI). Adsorption of MB was enhanced at higher pH of the solution, and the adsorption capacity of MB increased

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sharply with the increase of pH from 8.0 to 12.0. However, the Cr(VI) was decreased as the pH was increasing. In addition, it can be seen that the adsorption capacity of

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MB and Cr(VI) onto MG-ILs-OH is much higher than MG under all the pH values, this shows that the addition of ILs-OH improved the adsorption properties of

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adsorbent significantly due to the increase of the adsorption sites(- NH2 and –OH). As the pH of the MB solution increases, the electrostatic attraction between the

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negatively charged surface of the MG-ILs-OH and MG and cationic MB molecule increases, resulting in an increase in the adsorption capacity of MB. For adsorption of —

is the major form of Cr(VI),

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chromium, When the pH value range from1to 6, HCrO4

and the MG-ILs-OH and MG would be protonated, The positively charged surface

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electrostatic attraction.

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improves greatly the adsorption capacity of Cr(VI) on adsorbent because of the

3.3. Adsorption isotherm modeling.

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Profiles for MB and Cr(VI) uptake by MG-ILs-OH and MG at various initial concentrations are shown in Fig. S1. It can be seen that increase in initial concentration of MB and Cr(VI) was observed to increase the adsorption uptake. The

adsorption process is commonly described by using adsorption isotherm models. The equilibrium adsorption data for MB and Cr(VI) onto MG-ILs-OH were analyzed using Langmuir and Freundlich models. Models fitted to equilibrium adsorption results of the two adsorbates were assessed based on the values of the correlation coefficients (R2) of their linear regression plots. The linear form of the Langmuir model could be expressed as follows [27]: ce / qe=1/ (KL qm) + ce / qm

(2)

The linear form of the Freundlich model could be expressed as follows [28]: Ln qe= ln KF + (1/n) lnce

(3)

10

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ce is the equilibrium concentration of adsorbate in aqueous solution (mg/ L), qe is the adsorption amount (mg/g) at equilibrium and qm is the maximum adsorption capacity to form monolayer, KL represents enthalpy of sorption and should vary with temperature, and KF and n are the Freundlich constants related to the sorption capacity

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and sorption intensity, respectively.

Table 1 shows Langmuir and Freundlich parameters, and the isotherm constants

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and correlation coefficients. The result indicated that the adsorptions of MB and

Cr(VI) on MG-ILs-OH are better described by the Langmuir model with high R2 and

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the Freundlich model(Fig S2) was no fitted. The reason may be due to the homogeneous distribution of active sites on the surface of MG-ILs-OH. The Qmax

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value for MB and Cr(VI) sorption on MG-ILs-OH are 243.31 mg/g and 107.99 mg/g, respectively.

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Comparing to Qmax values of Cr(VI) adsorption on other chitosan-based adsorbent such as ethylenediamine-modified cross-linked magnetic chitosan resin (48.78 mg.g-1)[29], chitosan beads (76.92 mg.g-1)[30], cross-linked magnetic chitosan

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(69.4 mg.g-1)[31]. Comparing to Qmax values of MB adsorption on other

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chitosan-based adsorbent such as Chitosan hydrogel beads (100 mg.g-1)[32] and

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chitosan composite (142 mg.g-1) [33], it could be see that MG-ILs-OH present the highest adsorption capacity of other chitosan-based adsorbent. This shows that the MG-ILs-OH is an efficient adsorbent for both MB and

Cr(VI), it overcomes the disadvantage of the material as adsorbent which can only adsorb metal or dye. The large adsorption capacity could belong to the strong adsorption affinity of MG-ILs-OH towards MB and Cr(VI), and the main force is surface electrostatic and hydrophobic interactions between the adsorbate and MG-ILs-OH. The resulting plots for the Langmuir model are shown in Fig. 4(a).

3.4 Adsorption kinetic modeling. The effects of stirring (contact) time on the performance of MG-ILs-OH and MG for adsorbing the MB and Cr(VI), and the adsorption capacity of the adsorbent for the MB and Cr(VI) as a function of stirring time was shown in Fig. S3. It can be seen that 11

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the adsorption capacity is no longer increases after 60min. To describe the adsorption behavior and rate, the data obtained from adsorption kinetic experiments were evaluated using pseudo-frst-order and pseudo-second-order reaction rate models. The linear expressions of the models are expressed thus:

log( qe − qt) = log( qe) −(k1/2.303)t

(4)

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The pseudo-first order equation of Lagergren is expressed as follows [34]:

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qe and qt are the adsorption amount (mg/g) at equilibrium and at time t(min), respectively, and k1 is the rate constant of pseudo-first order adsorption (1/min).

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The pseudo-second order equation is expressed as follows [35]: t/qt=1/ k2 qe2 + (1/qe ) t

(5)

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k2 is the rate constant of pseudo-second order adsorption(g.mg−1.min−1). Table 2 gives a summary of the corresponding constants along with the correlation

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coefficients for the linear regression plots of MB and Cr(VI). Higher values of R2 were obtained for pseudo-second order than for pseudo-first order adsorption rate

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models indicating that the pseudo-second-order model (Fig.4(b)) best fitted the adsorption data than pseudo-first-order model(Fig S4), which indicates that the

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rate-limiting step may be chemical sorption or chemisorption involving valency forces

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through sharing or exchange of electrons between adsorbent and adsorbate [36-37].

3.5 Thermodynamics of adsorption. The temperature effect on the adsorption of MB and Cr(VI) was studied in order

to obtain the relevant thermodynamic parameters. Temperature variations of 303, 313 and 323 K were used for the study. It was shown in Fig.S5. The thermodynamic parameters such as change in Gibbs free energy(ΔG0), enthalpy (ΔH0) and

entropy(ΔS0) are calculated using the following equations: ΔG0= –RTln K0

(6)

ln K0=ΔS0/R – ΔH0/(RT)

(7)

Where R is the universal gas constant (8.314 J.mol-1.K-1), T is the temperature in Kelvin. The sorption equilibrium constant, K0, can be calculated by plotting lnKd versus ce and extrapolating ce to zero. ΔH0 and ΔS0 were obtained from the slope and 12

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intercept of Van’t Hoff plots of ln(K0) versus 1/T (Fig.4(c) and Fig.4(d)). The thermodynamic adsorption parameters determined are summarized in Table 3. Table 3 presents the values of ΔH0, ΔS0, and ΔG0.

As for the adsorption of

MB, the positive value of ΔH0 confirms the endothermic nature of the MB adsorption

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process, i.e. higher adsorption can be obtained at higher temperatures. And the positive value of ΔS0 obtained showed that there was an affinity between the MB

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molecules and MG-ILs-OH surface, and the degree of dispersion of the process

increased with increase temperature rise. For the adsorption of Cr(VI), the values of

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ΔH0 and ΔS0 are negative, and the values are low, so it can be seen from Fig.S5 that the adsorption change of Cr(VI) is small with the increase of temperature. The

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negative value of ΔG0 is decreased with an increase in temperature, indicating that the adsorption behavior of MB and Cr(VI) is a spontaneous process and the adsorption

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process is more spontaneous at higher temperature [38].

3.6. Regeneration of Saturated Adsorbents

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For potential applications, the regeneration and reusability of an adsorbent are

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important factors to be reported. To evaluate the possibility of regeneration and reusability of MG-ILs-OH as an adsorbent, we performed the desorption experiments.

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Desorption of MB and Cr(VI) from MG-ILs-OH is demonstrated using 0.5 mol/L NaOH. The regeneration study results are presented in Fig. 5(a). The study revealed that the adsorption capacity of MB and Cr(VI) on the adsorbents decreased slowly with increasing cycle number. It still remains high adsorption capacity in the first four cycles for MB, and then the uptake capacity decreased rapidly. After six recycles, the adsorption capacity changed small. For the regeneration study of Cr(VI), the adsorption capacity remains high in the first three cycles, after that it decreased quickly. The adsorption capacity over 50 mg/g is relatively good [31], so the optimal repeated time is six for MB and four for Cr(VI). The reusability of the adsorbents in several successive separation processes was tested and the results showed that the MG-ILs-OH has the very good repetition of usability. The adsorption and regeneration of MB and Cr(VI) was shown in Fig.5(b): 13

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4. Conclusions The hydroxy-functionalized ILs modified magnetic chitosan /graphene oxide(MG-ILs-OH) was synthesized and used for the adsorption of MB and Cr(VI).

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The experimental results indicated that the adsorption capacity varied greatly with the increasing of pH. In addition, the adsorption kinetics and isotherms were investigated

in detail. The adsorption results indicated that the adsorption kinetics followed a

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pseudo-second-order kinetics model, and the adsorption isotherms fitted well with

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Langmuir model, which indicated that it is monolayer adsorption of MB and Cr(VI) on the surface of the MG-ILs-OH. By studying the influence of temperature on the adsorption performance can be obtained that the adsorption was a spontaneous

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process. The addition of hydroxy-functionalized ILs can not only improve the dispersivity of the adsorbent, but also increase the adsorption sites (hydroxy and

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amino). Moreover, the MG-ILs-OH could be regenerated and reused efficiently for a few cycles. From the results of this study, it indicated that the MG-ILs-OH could be

d

effectively adsorbed MB and Cr(VI), solved the defect of the adsorbent that could

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only adsorb the same kind of contaminant. The MG-ILs-OH may be suitable materials in heavy metal ion and dyes pollution cleanup if they are synthesized in large scale

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and at low price in near future.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (NSFC, Nos. 21345005 and 21205048), the Shandong Provincial Natural Science Foundation of China (No. ZR2012BM020) and the Scientific and technological development Plan Item of Jinan City in China (No. 201202088).

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cr

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and by modeling techniques, Environ. Sci. Technol., 46 (2012) 6020–6027 [15] Z. Yang, H. Yan, H. Yang, H. Li, A. Li, R. Cheng, Flocculation performance and mechanism of graphene oxide for removal of various contaminants from water, Water Res., 47 (2013), pp. 3037–3046

Guo,

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nanocomposites

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[16] J. Zhu, S. Wei, H. Gu, S.B. Rapole, Q. Wang, Z. Luo, N. Haldolaarachchige, D.P. Young, Z. decorated

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[email protected] nanoparticles for fast chromium removal, Environ. Sci. Technol., 46 (2012) 977–985.

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[17] Depan, D., Girase, B., Shah, J.S., Misra, R.D.K., Structure–process–property relationship of the polar graphene oxide-mediated cellular response and stimulated growth of osteoblasts on

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hybrid chitosan network structure nanocomposite scaffolds. Acta Biomater. 7 (2011) 3432–3445.

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[18] G.Williams, B.Seger and P.V.Kamat, TiO2-Graphene Nanocomposites. UV-Assisted Photocatalytic Reduction of Graphene Oxide, ACS Nano, 2 (2008) 1487-1491.

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[19] K.R. Ramakrishna, T. Viraraghavan, Dye removal using low cost adsorbents, Water Sci. Technol., 36 (2–3) (1997) 189–196

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[20] V. K. Gupta, S. Agarwal and T.A. Saleh, Control of start-up and operation of anaerobic

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biofilm reactors: An overview of 15 years of research, Water Res., 45 (2011) 1-10. [21] P. Miretzky, A.F. Cirelli, Cr(VI) and Cr(III) removal from aqueous solution by raw and modified lignocellulosic materials: a review, J. Hazard. Mater., 180 (2010) 1–19

[22] C.J. Cheng, T.H. Lin, C.P. Chen, K.W. Juang, D.Y. Lee, The effectiveness of ferrous iron and sodium dithionite for decreasing resin-extractable Cr(VI) in Cr(VI)-spiked alkaline soils, J. Hazard. Mater., 164 (2009) 510–516

[23] E. Salazar, M.I. Ortiz, A.M. Urtiaga, J.A. Irabien, Equilibrium, kinetics of Cr(V1) extraction with aliquat 336, Ind. Eng. Chem. Res., 31 (1992) 1516–1522 [24] M.A. Zolfigol, T. Madrakian, E. Ghaemi, S.A.A. Afkhami, S. Afshar, Synthesis of morpholinated and 8-hydroxyquinolinated silica gel and their application to water softening, Green Chem., 4 (2002) 611–614 [25] M.T. Ahmeda, S. Taha, T. Chaabane, D. Akretche, R. Maachi, G. Dorange, Removal of copper from industrial effluent using a spiral wound module — film theory and 16

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hydrodynamic approach, Desalination, 200 (2006) 419–420 [26] Y. Cao, Y. Chen, X. Sun, Z. Zhang, T. Mu, Water sorption in ionic liquids: kinet-ics, mechanisms and hydrophilicity, Physical Chemistry Chemical Physics 14 (2012) 12252–12262.

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thermodynamics, Journal of Hazardous Materials, 185 15 (2011) 306–314.

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[30] W. S. Wan Ngah · A. Kamari · S. Fatinathan ·P. W. Ng, Adsorption of chromium from aqueous solution using chitosan beads, Adsorption, 12 (2006) 249–257.

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[33] M. Auta, B.H. Hameed, Chitosan–clay composite as highly effective and low-cost adsorbent for batch and fixed-bed adsorption of methylene blue, Chemical Engineering Journal, 237( 2014) 352–361. [34] D. Depan, B. Girase, J.S. Shah, R.D.K. Misra, Structure–process–property relationship of the polar graphene oxide-mediated cellular response and stimulated growth of osteoblasts on hybrid chitosan network structure nanocomposite scaffolds, Acta Biomater. 7 (2011) 17

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3432–3445. [35] T. Fukushima, A. Kosaka, Y. Ishimura, T. Yamamoto, T. Takigawa, N. Ishii, T. Aidal, Molecular Ordering of Organic Molten Salts Triggered by Single-Walled Carbon Nanotubes, Science 300 (2003) 2072-2074.

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Am. Chem. Soc. 38 (1916) 2221-2295.

[38] Y. Li, Z. Di, J. Ding, D. Wu, Z. Luan, Y. Zhu, Adsorption thermodynamic, kinetic and

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an

desorption studies of Pb2+ on carbon nanotubes, Water Res. 39 (2005) 605–609.

18

Page 18 of 32

Fig.1. The preparation of MG-ILs-OH Fig.2 (a) SEM images of the GO, (b) SEM images of MG, (c) SEM images of MG-ILs-OH; (d)

MG-ILs-OH; (f) The MG-ILs-OH in external magnetic field.

ip t

FTIR spectra of the GO, MG and MG-ILs-OH; (e) XRD patterns of the Fe3O4, GO and

cr

Fig.3 (a) Effect of pH on the adsorption of MB on the MG-ILs-OH and MG, (b) Effect of pH on

the adsorption of Cr(VI) on the MG-ILs-OH and MG. The concentration of MG-ILs-OH and

time was 60 min. The temperature was 303K.

us

MG was 1.0 g. L-1. The initial MB and Cr(VI) concentrations was 100 mg.L-1. The contact

an

Fig.4 (a) The Langmuir isotherm model. The concentration of MG-ILs-OH was 1.0 g. L-1. The pH of MB is 12.0, the pH of Cr(VI) is 2.0. The contact time was 60 min. The temperature was

M

303K. (b) The pseudo-second-order model. The initial MB and Cr(VI) concentrations was 100 mg.L-1. The concentration of MG-ILs-OH was 1.0 g. L-1. The pH of MB is 12.0, the pH of Cr(VI) is 2.0 The temperature was 303K. (c)Van’t Hoff plots for the uptake of MB on

d

the MG-ILs-OH, The initial MB concentrations was 100 mg.L-1. The concentration of

te

MG-ILs-OH was 1.0 g. L-1. The pH of MB is 12.0, the pH of Cr(VI) is 2.0. The contact time

Ac ce p

was 60 min. (d) Van’t Hoff plots for the uptake of Cr(VI) on the MG-ILs-OH. The initial Cr(VI) concentrations was 100 mg.L-1. The concentration of MG-ILs-OH was 1.0 g. L-1.

The pH of MB is 12.0, the pH of Cr(VI) is 2.0. The contact time was 60 min.

Fig.5 (a) Adsorption amount of MB and Cr(VI) for different cycles. The concentration of

MG-ILs-OH was 1.0 g. L-1. The initial MB and Cr(VI) concentrations was 100 mg.L-1. The contact time was 60 min. The pH of MB is 12.0, the pH of Cr(VI) is 2.0. The temperature was 303K. (b) The adsorption and regeneration of MB and Cr(VI) on MG-ILs-OH

19

Page 19 of 32

ip t cr us an M d te Ac ce p

Fig. 1. The preparation of MG-ILs-OH

20

Page 20 of 32

ip t cr us an M d te Ac ce p

Fig. 2 (a) SEM images of the GO, (b) SEM images of MG, (c) SEM images of MG-ILs-OH; (d) FTIR spectra of the GO, MG and MG-ILs-OH; (e) XRD patterns of the Fe3O4, GO and MG-ILs-OH; (f) The MG-ILs-OH in external magnetic field.

21

Page 21 of 32

ip t cr us an

(a)

150

(b)

MG-ILs-OH MG

135

MG-ILs-OH MG

M

Qe/mg.g-1

120

4

6

8

10

12

te

2

d

105

pH

90 75 60 2

4

6

8

10

pH

Ac ce p

Qe/mg.g-1

180 160 140 120 100 80 60 40 20 0

Fig. 3 (a) Effect of pH on the adsorption of MB on the MG-ILs-OH and MG, (b) Effect of pH on

the adsorption of Cr(VI) on the MG-ILs-OH and MG. The concentration of MG-ILs-OH and MG

was 1.0 g. L-1. The initial MB and Cr(VI) concentrations was 100 mg.L-1. The contact time was 60 min. The temperature was 303K.

22

Page 22 of 32

ip t cr us an M d te Ac ce p

Fig. 4 (a) The Langmuir isotherm model. The concentration of MG-ILs-OH was 1.0 g. L-1. The pH of MB is 12.0, the pH of Cr(VI) is 2.0. The contact time was 60 min. The temperature was

303K. (b) The pseudo-second-order model. The initial MB and Cr(VI) concentrations was 100 mg.L-1. The concentration of MG-ILs-OH was 1.0 g. L-1. The pH of MB is 12.0, the pH of Cr(VI) is 2.0 The temperature was 303K. (c)Van’t Hoff plots for the uptake of MB on the MG-ILs-OH, The initial MB concentrations was 100 mg.L-1. The concentration of MG-ILs-OH was 1.0 g. L-1. The pH of MB is 12.0, the pH of Cr(VI) is 2.0. The contact time was 60 min. (d) Van’t Hoff plots for the uptake of Cr(VI) on the MG-ILs-OH. The initial Cr(VI) concentrations was 100 mg.L-1. 23

Page 23 of 32

The concentration of MG-ILs-OH was 1.0 g. L-1. The pH of MB is 12.0, the pH of Cr(VI) is 2.0.

Ac ce p

te

d

M

an

us

cr

ip t

The contact time was 60 min.

Fig. 5 (a) Adsorption amount of MB and Cr(VI) for different cycles. The concentration of

MG-ILs-OH was 1.0 g. L-1. The initial MB and Cr(VI) concentrations was 100 mg.L-1. The

contact time was 60 min. The pH of MB is 12.0, the pH of Cr(VI) is 2.0. The temperature was 303K. (b) The adsorption and regeneration of MB and Cr(VI) on MG-ILs-OH

24

Page 24 of 32

ip t cr us an

adsorbate

Langmuir KL(L/mg)

MB

243.31

Cr(VI)

107.99

Freundlich

R2

KF(mg1-n.Ln/g)

n

0.0423

0.9857

34.6351

2.57

0.9133

0.1266

0.9954

35.4003

4.20

0.9345

R2

Ac ce p

te

d

qm(mg.g-1)

M

Table 1. Parameters for Langmuir and Freundlich isotherm model

25

Page 25 of 32

ip t cr us an

pseudo-first order

M

Table 2. Parameters for pseudo-first and pseudo-second order

R2

qe (mg/g)

MB

0.0305

58.1099

0.9617

Cr(VI)

0.0092

32.1633

0.0721

qe(mg/g)

R2

0.0012

183.8235

0.9987

-0.0088

90.4159

0.9907

K2(g.mg.min-1)

Ac ce p

te

d

adsorbate K1(min-1)

pseudo-second order

26

Page 26 of 32

ip t cr us an

0

0

ΔG (KJ.mol-1)

ΔS (J.mol .K-1)

303K

313K

323k

MB

24.5136

87.8763

-2.1129

-2.9917

-3.8705

Cr(VI)

-0.9757

-2.9927

0.0689

-0.8678

-1.8344

Ac ce p

adsorbate

te

ΔH (KJ.mol-1 )

d

0

M

Tabke 3. Thermodynamic parameters for adsorption of MB and Cr(VI) on MG-ILs-OH.

27

Page 27 of 32

ip t cr us an M Ac ce p

te

d

Fig.1. The preparation of MG-ILs-OH

28

Page 28 of 32

ip t cr us an M d te Ac ce p

Fig. 2 (a) SEM images of the GO, (b) SEM images of MG, (c) SEM images of MG-ILs-OH; (d) FTIR

spectra of the GO, MG and MG-ILs-OH; (e) XRD patterns of the Fe3O4, GO and MG-ILs-OH; (f) The MG-ILs-OH in external magnetic field.

29

Page 29 of 32

ip t cr 150 135

MG-ILs-OH MG

(b)

MG-ILs-OH MG

Qe/mg.g-1

an

120

us

(a)

2

4

6

pH

8

10

12

M

105 90 75 60

d

Qe/mg.g-1

180 160 140 120 100 80 60 40 20 0

2

4

6

8

10

pH

te

Fig.3 (a) Effect of pH on the adsorption of MB on the MG-ILs-OH and MG, (b) Effect of pH on the

Ac ce p

adsorption of Cr(VI) on the MG-ILs-OH and MG. The concentration of MG-ILs-OH and MG was 1.0 g. L-1. The initial MB and Cr(VI) concentrations was 100 mg.L-1. The contact time was 60 min. The temperature was 303K.

30

Page 30 of 32

ip t cr us an M d te

Fig.4 (a) The Langmuir isotherm model. The concentration of MG-ILs-OH was 1.0 g. L-1. The pH of

Ac ce p

MB is 12.0, the pH of Cr(VI) is 2.0. The contact time was 60 min. The temperature was 303K. (b) The pseudo-second-order model. The initial MB and Cr(VI) concentrations was 100 mg.L-1. The concentration of MG-ILs-OH was 1.0 g. L-1. The pH of MB is 12.0, the pH of Cr(VI) is 2.0 The

temperature was 303K. (c)Van’t Hoff plots for the uptake of MB on the MG-ILs-OH, The initial MB concentrations was 100 mg.L-1. The concentration of MG-ILs-OH was 1.0 g. L-1. The pH of MB

is 12.0, the pH of Cr(VI) is 2.0. The contact time was 60 min. (d) Van’t Hoff plots for the uptake of Cr(VI) on the MG-ILs-OH. The initial Cr(VI) concentrations was 100 mg.L-1. The concentration of MG-ILs-OH was 1.0 g. L-1. The pH of MB is 12.0, the pH of Cr(VI) is 2.0. The contact time was 60 min.

31

Page 31 of 32

ip t cr us an M d

te

Fig. 5 (a) Adsorption amount of MB and Cr(VI) for different cycles. The concentration of

MG-ILs-OH was 1.0 g. L-1. The initial MB and Cr(VI) concentrations was 100 mg.L-1. The contact

Ac ce p

time was 60 min. The pH of MB is 12.0, the pH of Cr(VI) is 2.0. The temperature was 303K. (b) The adsorption and regeneration of MB and Cr(VI) on MG-ILs-OH

32

Page 32 of 32