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Novel porous magnetic nanospheres functionalized by β-cyclodextrin polymer and its application in organic pollutants from aqueous solution
Accepted Manuscript Novel porous magnetic nanospheres functionalized by β-cyclodextrin polymer and its application in organic pollutants from aqueous solution Desheng Liu, Zheng Huang, Minna Li, Ping Sun, Ting Yu, Lincheng Zhou PII:
S0269-7491(18)35468-X
DOI:
https://doi.org/10.1016/j.envpol.2019.04.079
Reference:
ENPO 12480
To appear in:
Environmental Pollution
Received Date: 4 December 2018 Revised Date:
9 March 2019
Accepted Date: 15 April 2019
Please cite this article as: Liu, D., Huang, Z., Li, M., Sun, P., Yu, T., Zhou, L., Novel porous magnetic nanospheres functionalized by β-cyclodextrin polymer and its application in organic pollutants from aqueous solution, Environmental Pollution (2019), doi: https://doi.org/10.1016/j.envpol.2019.04.079. 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
Novel porous magnetic nanospheres functionalized by β-cyclodextrin
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polymer and its application in organic pollutants from aqueous solution
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Desheng Liu 1a, Zheng Huang 1a, Minna Li a, Ping Sun a, Ting Yu a, and Lincheng Zhou *a, b
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a. State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Institute of
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Biochemical Engineering & Environmental Technology, Lanzhou University, Lanzhou 730000, P. R. China.
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b. Zhongwei High-tech Institute of Lanzhou University, 755000, P. R. China.
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1.These authors contributed equally to this work and should be considered as co-first authors.
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Desheng Liu
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Address: College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, P.R.China
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Zheng Huang
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Address: College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, P.R.China
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Minna Li
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Address: College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, P.R.China
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Ping Sun
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Address: College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, P.R.China
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Ting Yu
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Address: College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, P.R.China
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Lincheng Zhou
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Address: College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, P.R.China
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Fax: 86-0931-8912113
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Abstract Magnetic β-cyclodextrin (β-CD) porous polymer nanospheres (P-MCD) was fabricated
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by one-pot solvent thermal method using β-CD immobilized Fe3O4 magnetic nanoparticles
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with tetrafluoroterephthalonitrile as the monomer. Compared with the β-CD polymerization
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method reported in the literature, the synthetic route is effective and simple, thereby
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overcoming the harsh conditions that require nitrogen protection and always maintain
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anhydrous and oxygen-free. Moreover, the immobilization of β-CD on magnetic nanoparticles
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is combined with the cross-linking polymerization of the cross-linker, leading to a good
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synergistic effect on the removal of contaminants. Meanwhile, the dispersibility of the
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magnetic carrier enhances the dispersion of the β-CD porous polymer in the aqueous phase,
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and improves the inclusion adsorption performance and the adsorption process. P-MCD
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exhibited superior adsorption capacity and fast kinetics to MB. The maximum adsorption
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capacity of MB for P-MCD was 305.8 mg g
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magnetic nanoparticles (Fe3O4@β-CD). Moreover, the material had a short equilibrium time
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(5 min) for MB, high recovery and good recyclability (the adsorption efficiency was still
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above 86% after five repeated uses).
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, which is more than β-CD modified Fe3O4
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Keywords: Porous nanospheres, β-cyclodextrin polymer, Adsorption, Organic pollutants,
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Magnetic
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1. Introduction Nowadays, the use of a large number of dyes and pigments in the chemical industry
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seriously pollutes the world’s ecosystem. Waste water from dyes comprises numerous
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pollutants that pose a threat to agriculture, food chains and human health (Zhao et al., 2015).
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Hence, removal of dyes has become a considerable issue that has evoked increasing attention
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(Hu et al., 2011).
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β-cyclodextrin (β-CD), which possesses a stable property and a torus shape, is a kind
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type of cyclic oligosaccharide with seven glucose units that connected by α-(1,4)-glucosidic
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linkages (Chen et al., 2010). Owing to the particular annular structure of β-CD, which is
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hydrophobic inside and hydrophilic outside; thus, non-covalent host-guest inclusion
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complexes could can be generated (Ncube et al., 2014). Thence, β-CD also possesses the
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potential to remove dye molecules in wastewater due to its ability to form inclusions with
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different types of organic contaminant molecules (Wang et al., 2015; Zhang et al., 2019). In
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recent years, cyclodextrin graft polymers in which cyclodextrin host molecules are linked to
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polymers or magnetic nanoparticles by covalent bonds have received considerable attention
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(Sanchez-Trujillo et al., 2013; Tarasi et al., 2016).
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Polymer materials containing cyclodextrin have significant applications in environmental
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monitoring and wastewater treatment (Zhao et al., 2015). Therefore, it is expected that a novel
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material with higher stability will be obtained by preparing a polymer using a β-CD derivative.
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The cyclodextrin externally surface-active functional group is bonded to other porous
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polymers to act as an adsorbent. Owing to the hydrophobic structure of the β-CD inner cavity,
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it forms an inclusion complex with organic pollutants in the water to remove it. However,
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β-CD has relatively good solubility in water, and it is difficult to recycle in the aqueous phase,
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which greatly limits its application in water treatment. Therefore, the main research focus in
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recent years is to crosslink β-CD with a crosslinking agent to form water-insoluble polymers
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(Li et al., 2018a). The β-CD-derived polymer maintains the distinctive properties of the β-CD
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matrix and has the advantages of superior polymer stability and chemical adjustability.
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However, crosslinked β-CD polymers also have disadvantages such as low surface area and
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poor removal performance. In recent years, the covalent loading of β-CD has also been an important direction for its
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application expansion (Fan et al., 2012). The immobilization can not only maintain its
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inherent cavity structure and its properties well, but also conquer its shortcomings such as
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good water solubility and difficulty in recovery. By constructing β-CD on other supports, it is
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possible to synthesize a water-insoluble adsorbent material with a long service life,
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distinguished mechanical properties or superior dispersibility (Jiang et al., 2018). The carriers
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that were commonly applied to immobilize β-CD are mainly inorganic molecular and natural
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polymers. The inorganic carrier generally includes carbon nanotube (Hu et al., 2011; Wang et
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al., 2012), SiO2 nanoparticles (Ghosh et al., 2011; Zhang et al., 2015), magnetic Fe3O4
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nanoparticles (Badruddoza et al., 2013; Cai et al., 2011; Fan et al., 2012; Lv et al., 2016;
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Wang et al., 2015; Wang et al., 2014; Zhou et al., 2016), whereas the natural polymer carrier
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has chitosan and sodium alginate (Chen et al., 2014; Huang et al., 2013; Jiang et al., 2018).
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Therefore, the multi-functional magnetic β-CD porous polymer composite, obtained by
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crosslinking β-CD derivative and constructed on the magnetic nanoparticles, has a good
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application prospect in environmental field.
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In this study, we adopted a two-step synthesis strategy to synthesize highly uniform
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particle size distribution of magnetic β-CD porous polymer nanospheres. Firstly, β-CD was
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immobilized on the surface of magnetic nanoparticles by a one-pot method to obtain
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β-CD-modified magnetic nanoparticles (Fe3O4@β-CD). Then, the magnetic porous polymer
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nanospheres were obtained by cross-linking polymerization of Fe3O4@β-CD and
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tetrafluoroterephthalonitrile cross-linking agent by a solvothermal method. Compared with
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the β-CD polymerization method reported in the literature (Alsbaiee et al., 2016), the
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synthetic route is more effective and simple, thereby overcoming the harsh conditions that
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require nitrogen protection and invariably maintain anhydrous and oxygen-free. Meanwhile,
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the crosslinked β-CD porous polymer not only has superior stability and recyclability, but also
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has a large specific surface area and outstanding adsorption performances. The adsorption
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capacity of P-MCD was also investigated through adsorption equilibrium isotherms and
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dynamics. The results revealed that P-MCD has a superior removal efficiency on the organic
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molecules in aqueous solution, and the maximum adsorption capacity can reach 305.8 mg g -1.
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Therefore, the magnetic porous nanospheres has a fine application prospect in the field of
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environmental remediation.
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2.
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2.1 Materials
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Experimental section
The biochemical reagent β-CD (99.0%) and carboxymethyl-β-cyclodextrin (CM-β-CD)
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(99.9%) were purchased from Shanpu Chemical Co., Ltd. (Shanghai, China). The
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tetrafluoroterephthalonitrile (99.0%) was obtained from Sigma Aldrich. Anhydrous sodium
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acetate, anhydrous potassium carbonate and ferric chloride hexahydrate were purchased from
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Guangfu Reagent (Tianjin, China). Dimethylformamide (DMF), tetrahydrofuran (THF),
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ethylene glycol and ethanol were purchased from Li AnlangBohua Pharmaceutical Chemical
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Co., Ltd. The other chemical reagents applied in this work were analytical grade. The water
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applied in the work was ultrapure water.
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2.2 Synthesis of Fe3O4@β-CD
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Fe3O4@β-CD nanoparticles were synthesized by a one-pot solvothermal method. First,
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FeCl3·6H2O (2.7 g) and anhydrous sodium acetate (7.2 g) were added to a three-necked flask
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containing 80 mL of anhydrous ethylene glycol solution, and completely dissolved by
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ultrasonic stirring until the mixture became a yellow solution. Then, 0.4 g of β-CD was added
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to the above mixture solution, which was vigorously stirred for 1 h to disperse uniformly. The
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mixture solution was finally sealed in an autoclave and heated at 200 °C for 8 h. The product
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was carefully gathered through a magnet after the autoclave was cooled to room temperature.
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Fe3O4@β-CD was washed three times with ultrapure water and ethanol, respectively, and
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vacuum dried at room temperature.
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2.3 Synthesis of P-MCD
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P-MCD nanospheres were also fabricated using a one-pot hydrothermal method.
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Fe3O4@β-CD (100 mg), CM-β-CD (200 mg), tetrafluoroterephthalonitrile (100 mg), and
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K2CO3 (300 mg) were dissolved in mixture solutions with 8 mL of DMF and 22 mL of THF.
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The mixed solution was then transferred into an autoclave and heated at 120 °C for 72 h.
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Subsequently, P-MCD was obtained when it cooled to room temperature through the magnetic 5
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separation, washed with deionized water and alcohol, respectively, and dried under vacuum at
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room temperature.
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2.4 Characterization FT-IR spectra were obtained from FT-IR spectrometer (Model 170-SX, American Nicolet
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Corp.) at room temperature using powder-pressed KBr pellets. The morphology of the
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P-MCD was characterized by SEM (JSM-6701F) and TEM (Tecnai G2 F30). Magnetic
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hysteresis
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LAKESHORE-7304, USA) at room temperature. The X-ray photoelectron spectroscopy (XPS)
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was carried out through an ESCALab220i-XL electron spectrometer (VG Scientific) with
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300W Al-Kα radiation and X-ray diffraction (XRD) spectra were obtained from Rigaku
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D/MAX-2400 with Ni-filtered Cu-Kα radiation. Ultraviolet–visible spectroscopy (UV-Vis,
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TU-1810PC) was applied to investigate the adsorption effect of MB. The specific surface area
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of the nanospheres was measured at liquid N2 temperature (76 K) using a Micromeritics
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ASAP 2010M apparatus.
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2.5 Adsorption
were
obtained
using
vibrating
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magnetometry
(VSM,
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P-MCD (5.0 mg) was dissolved in the aqueous solution with the different initial MB
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concentration. The same set of mixtures was placed in a constant-temperature shaker and
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shaken at 298 K with a shaking speed of 250rpm for 6 h, and the equilibrium concentration of
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MB was analyzed by UV-Vis. The equilibrium adsorption capacity Qe (mg g-1) was obtained
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by the following equation:
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(C0 Ce ) V m
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Where C0 (mg L-1) and Ce (mg L-1) means the initial concentration and equilibrium
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concentration of MB, respectively. V (mL) represents the volume of MB solutions, and m (g)
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means the mass of absorbent.
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2.6 Desorption and recycling study
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In the desorption experiment, the MB-adsorbed P-MCD nanospheres was washed
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thoroughly with ultrapure water. The nanospheres was then extracted several times in an
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ethanol solution containing 5% (V/V) acetic acid. After each extraction was completed, the 6
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residual MB concentration in the solution was analyzed with an UV-Vis. In order to
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investigate the reusability of the adsorbent, the washed P-MCD was reused in the adsorption
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experiment. Meanwhile, the same process was repeated seven times.
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3.
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3.1 Preparation of magnetic porous polymer nanospheres
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Results and discussion
Scheme 1 shows the procedure of P-MCD fabrication and MB adsorption and desorption. First, Fe3O4@β-CD nanoparticles were synthesized via solvent thermal method, which grafted
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β-CD on the Fe3O4 surface to retain magnetic responsive property of the material and
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contribute to the separation. Similarly, P-MCD was fabricated via solvent thermal method
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using Fe3O4@β-CD nanoparticles, CM-β-CD, and tetrafluoroterephthalonitrile monomer. The
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polymerization reaction is a nucleophilic reaction, nucleophilic aromatic substitution of
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hydroxyl groups of β-CD by tetrafluoroterephthalonitrile. High temperature and high-pressure
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are more conducive to the substitution of fluorine on the benzene ring and hydroxyl groups of
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the β-CD, making the nucleophilic reaction easier. Meanwhile, the whole reaction system is in
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an oxygen-free state during the reaction. Therefore, under the same experimental conditions,
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the polymerization reaction can still be conducted. Subsequently, P-MCD nanospheres were
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dispersed in MB solution and shaken for a short time. After the magnetic separation, the MB
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solution became clear.
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3.2 Characterization of magnetic nanospheres
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3.2.1 Morphology and structure characterization
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The SEM image of Fe3O4@β-CD (Fig.S1a and Fig.S2) reveals its smooth morphology
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because of the relatively small β-CD grafted to the Fe3O4. However, the P-MCD has a porous
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structure was observed in the surface morphology (Fig. S1b). Compared with the
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Fe3O4@β-CD, P-MCD became rougher and larger, which indicates that the polymer layer was
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successfully assembled on the surface of the Fe3O4 magnetic nanoparticles.
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As shown in Fig.1, Fe3O4@β-CD nanoparticles are spherical shape and have an average
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diameter of 185 nm (Fig.1a), whereas P-MCD nanospheres exhibit a larger size with a
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diameter of approximately 200 nm. As shown in Fig.1b, it can be seen that about 20 nm of
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polymer layer was coated on the surface of Fe3O4@β-CD, which indicates that the polymer 7
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layer was triumphantly grafted onto the surface of the matrix through radical polymerization.
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Fig.1b and d, proves the successful prepared of P-MCD nanospheres that are uniformly
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spherical shape and narrow size distribution. The particle size distribution of P-MCD is
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shown in Fig.S3. The surface morphology and chemical element distribution of P-MCD were analyzed by
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HAADF-STEM, and the results are shown in Fig.2. The image distinctly demonstrates that
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P-MCD is primarily comprises of Fe, C, N, O and F elements. Furthermore, the presence of N
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and F elements on the surface of the nanospheres also verifies that the porous β-CD polymer
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layer has been faultlessly coats on the surface of Fe3O4@β-CD magnetic nanoparticles.
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3.2.2 FT-IR characterization
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The strong absorption bands at 584 cm
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Fe-O in Fe3O4 nanoparticles, which corresponds to the literature (Li et al., 2011). In
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comparison with the three IR spectra, the characteristic peaks of Fe3O4@β-CD and P-MCD at
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3340 cm
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respectively. Furthermore, there is a strong C-O stretching vibration at 1033 cm -1, which
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indicates that the spectral features of intact β-CD, as stated in the literature (Cai et al., 2011).
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In addition, the P-MCD exhibit absorbance at 1648 cm -1 and 1443 cm -1 are corresponding to
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C–C aromatic stretches, which corresponds to the nitrile stretch. Moreover, the absorption at
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1267 cm
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vibration of C-F. These results indicate that the β-CD porous polymer layer successfully
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polymerized on the Fe3O4@β-CD surface.
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3.2.3 Thermogravimetric analysis of the nanospheres
and 2932 cm
-1
could be attributed to the stretching vibration of
are assigned to O-H and aliphatic C-H stretching vibration,
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TGA of Fe3O4@β-CD and P-MCD are shown in Fig.3b. The amount of polymer layers
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coated on the Fe3O4 surface was estimated via TGA of Fe3O4@β-CD without polymerization.
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As shown in Fig.S4a, the thermogravimetric loss is approximately 1% when the temperature
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is about 200 ℃, which is belonging to the volatilization of water and solvents. In addition,
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the major weight loss from 250 °C to 800 °C stemmed from the decomposition of grafted
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β-CD, and the weight loss to 8.6% of initial weight with a slower rate could be attributed to 8
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the grafting of β-CD. As shown in Fig.S4b, the thermogravimetric loss is near 28.5% when
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the temperature is about between 250 ℃ and 800 ℃, which can be assigned to the loss of
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β-CD porous polymer layer.
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3.2.4 Magnetic properties of the nanospheres The magnetic of Fe3O4@β-CD and P-MCD nanospheres were measured by VSM in the
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field range of -20 to +20 kOe at room temperature. Fe3O4@β-CD and P-MCD porous
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nanospheres can explicitly observe the magnetic hysteresis loops, which is characteristic of
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superparamagnetism behavior, are presented in Fig.3c. The saturation magnetizations (Ms) of
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the above samples are 70.2 emu g
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these nanospheres can be readily segregated from the solution under an external magnetic
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field. The insert of Fig.3c illustrates that the separation of P-MCD from solution using a
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magnet only takes several minutes, confirming the fast magnetic responsiveness of the
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material. The result declared that the Ms of P-MCD is weaker than that of Fe3O4@β-CD, this
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is principally due to the presence of a polymer layer on the surface of Fe3O4@β-CD
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nanoparticles.
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3.2.5 XRD characterization
and 44.8 emu g -1, respectively, which indicating that
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The XRD patterns of Fe3O4@β-CD and P-MCD are shown in Fig.3d. The diffraction
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peaks at 2θ of 30.0°, 35.5°, 43.2°, 53.8°, 57.2° and 62.6° are attributed to (220), (311), (400),
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(422), (511) and (440) crystal planes, respectively. This is consistent with the characteristic
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peaks of the pure Fe3O4 nanoparticles with spinel structure (Shao et al., 2016). This indicates
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that the structure of Fe3O4 nanoparticle can remain stable when it was modified with the β-CD
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polymer layer. The crystal sizes of P-MCD ascertain from the XRD pattern with Scherrer’s
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equation [Dh kl = 0.9λ/(βcosθ), where Dh kl means the crystalline average diameter, λ indicates
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X-ray wavelength, β signifies the half width of XRD diffraction lines and θ represents Bragg’s
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angle(°)] are found to be 204 nm, which are slightly larger than that observed from the TEM
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image. In this study, the (311) peak of highest intensity was chosen to calculate the particle
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size of P-MCD nanospheres.
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3.2.6 XPS characterization
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The XPS spectra of Fe3O4@β-CD and P-MCD nanospheres are shown in Fig.4. The 9
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which are assigned to C 1s, O 1s and Fe 2p, respectively (He et al., 2014). The results show
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that the composition contains Fe, O and C elements exist. However, in the spectral of P-MCD,
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new peaks appearing at 400.3 eV and 689.88 eV can be assigned to N 1s and F 1s,
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respectively, which reveals that the presence of the N and F elements causes the porous
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polymer layer to be successfully polymerized onto the Fe3O4@β-CD surface. The Fe 2p
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spectrum can be divided into two peaks centered at 727.9 and 714.2 eV, which are associated
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with the peaks of Fe 2p1/2 and Fe 2p3/2, respectively (Uyar et al., 2008), confirming that the
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existence of Fe3O4 nanoparticles with spinel structure. Moreover, Fig.4b shows the high
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resolution spectrum of C 1s, and the binding energy at 288.9, 287.3 eV is assigned to the
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C=O-O- (carboxyl) species and the C=O form of the carbon atom (carbonyl), respectively (Qu
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et al., 2014). In addition, the presence of COO− peak at 288.9 eV declares that the carboxyl
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groups on CM-β-CD polymer reacted with surface hydroxyl groups to form metal carboxylate.
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The O1s spectrum can be divided into three peak components, and the binding energy peaks
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at 536.8 and 535.5 eV can be ascribed to O=C-O and C-OH/C-O-C species, respectively.
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However, the peak of O1s at 533.5 eV corresponds to the characteristic peak of Fe-O-C in the
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composite (S.Srivastava and S.Badrinararyanan, 1985).
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3.2.7 BET characterization
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The specific surface area and the pore-size-distribution curve of the as-prepared
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Fe3O4@β-CD and P-MCD nanospheres were confirmed by N2 adsorption–desorption
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isotherms, as shown in Fig.5. The BET surface areas of Fe3O4@β-CD and P-MCD were
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measured to be 44.44 m ² g -1 and 70.63 m ² g -1, respectively. The P-MCD had the larger BET
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surface area, thus, it also had the larger adsorption capacity. The pore size of the obtained
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P-MCD nanospheres is 5.59 nm, which is 0.8 nm larger than the diameter of MB (Ma et al.,
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2014). The diameter of the P-MCD nanospheres channel is consistent with the molecular size
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of the MB molecule, demonstrating the strong adsorption capacity of P-MCD for MB.
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3.3 Adsorption properties of P-MCD
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3.3.1Effect of pH and MB concentration
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The effect of solution pH on MB adsorption on P-MCD nanospheres is shown in Fig.S4. 10
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3.0 to 11.0. As shown in Fig.S4, the removal efficiency and capacity are worst in the acidic
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conditions, resulting to only 80% removal efficiency. A high adsorption capacity was
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achieved with the aggrandize in pH of the solution, which could be assigned to that the
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dimethylamine group in MB molecule and the hydroxyl groups in β-CD that were positively
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charged at low pH value. Moreover, protonated MB was not beneficial to come into being the
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host–guest inclusion complex with protonated β-CD by reason of a repelling interaction
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(Chen et al., 2014; Zhang et al., 2013). As the pH increased, the activated deprotonation
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hydroxyl groups could come into being electrostatic interaction with MB molecules. In
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addition, when the pH of the solution is greater than 7.0, the adsorption capacity became
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almost a stable value. As a result, all of the following studies were carried out at the initial
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solution pH value of 7.0. As indicated in Fig.6a, the initial adsorption rate decreased
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significantly with the increase of MB concentration. But a larger MB concentration would
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result in the block of cavities β-CD, thereby slowing down the subsequent adsorption rate.
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With the progress of time, removal efficiency could be more than 98% when it reached
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adsorption equilibrium.
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3.3.2 Adsorption kinetics
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The effect of contact time on the adsorption of MB onto P-MCD with various initial
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MB concentrations is shown in Fig.6a. The initial MB concentration supplies the essential
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driving force to alleviate the mass transfer resistance of MB between the aqueous phase and
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solid phases (Karago¨z et al., 2008). Equilibrium was reached in approximately 2 min and 5
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min by P-MCD. Moreover, the amount of MB at the equilibrium aggrandized with the initial
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MB concentration increasing. Within almost 5 min, MB removal efficiency can reach
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97.3%-100% at equilibrium was achieved, which indicates that P-MCD could adsorb MB
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from the aqueous solution rapidly and effectively.
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The Lagergren pseudo-first-order and pseudo-second-order kinetic models were
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employed to investigate the adsorption kinetics of MB onto P-MCD nanospheres (Shao et al.,
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2017; Wu et al., 2018). Adsorption kinetic curve and pseudo-second-order fitting curves are
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indicated in Fig.6b. The two dynamic equations are as follows: 11
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log( Qe Qt ) log Qe
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k1 t 2.303
(2)
t 1 t Qt k2Qe 2 Qe
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(3)
Where Qe and Qt represent the amounts of MB adsorbed when the adsorption attained
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equilibrium and t, respectively. k1 indicates the pseudo-first-order rate constant (min -1) and k2
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means the pseudo-second-order rate constant (g mg -1 min -1).
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The adsorption on high heterogeneous adsorbents can be expressed by the Elovich
325
equality (Li et al., 2017), which is idealized by assuming αβ≫t and using the critical
326
conditions Qt = 0 at t=0 and Qt = Qt at t = t, shown as follows:
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Where α (mg g
-1
1
ln( )
1
ln t
(4)
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Qt
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min -1) indicates the initial adsorption rate, and β (g mg -1) represents
the desorption constant. The results are shown in Fig.6c, and Table S1 lists the values of the
330
R2 of P-MCD. In Comparison with the pseudo-second-order model, the depiction of Elovich
331
model is not accurate.
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The mechanism of adsorption is invariably associated with the Weber and Morris
333
equality (Hosseini et al., 2011). In general, the adsorption process contains three steps, namely,
334
bulk diffusion, film diffusion, intra-particle diffusion or pore diffusion. The model can be
335
expressed as follows:
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qe KWM t C
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Where KWM and C indicate the diffusion rate constant (mg g
(5) -1
min 1/2) and the intercept,
respectively.
339
As shown in Fig.6d, the intra particle diffusion is not the only step that can be dominated
340
by rate. The adsorption kinetic curve can be divided into three sections, namely, surface
341
diffusion, intra-particle diffusion, and singularly low MB concentration in aqueous solution,
342
which depicts the steps of adsorption. Scheme 2 shows the MB adsorption mechanism of
343
P-MCD. In sum, the adsorption performance of P-MCD could be concluded with three
344
processes, namely, host–guest complex interaction, π-π stacking interaction and multiple 12
ACCEPTED MANUSCRIPT hydrogen bonding. With regard to host–guest interaction, β-CD-based polymer existing in
346
P-MCD could catch MB molecules. MB has benzene rings that could form a π-π stacking
347
intermolecular force between MB and P-MCD. Besides, during the preparation of P-MCD,
348
some residual oxygen/nitrogen-containing groups such as hydroxyl and cyano groups
349
remaining in the P-MCD. Therefore, another interaction is the hydrogen bond originated by
350
the oxygen/nitrogen-containing groups of both MB and P-MCD.
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The correlation parameters of the three kinetic models are indicated in Table S1. The
352
data demonstrate that the pseudo-second-order rate model depicted the MB adsorption
353
(R2>0.999) more accurately, which the calculated Qe is close to the Qe from the experimental
354
data, whereas much worse or no relevance was found in the pseudo-first-order model. These
355
results indicate that the adsorption process of MB molecules by P-MCD nanospheres is
356
dominated by chemical adsorption.
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Besides, the function of the layer polymerized by tetrafluoroterephthalonitrile was
358
investigated through the adsorption behavior of Fe3O4@β-CD, provided in Fig. S5a and S5b.
359
The adsorption kinetic model parameters at different concentrations are shown in Table S1.
360
Same dosages of Fe3O4@β-CD and P-MCD were added into MB solution and the result
361
indicated that the latter exhibit higher adsorption capacity under the same condition, which
362
indicates that the cross-linking of β-CD and rigid aromatic groups provides a high surface
363
area and a large number of adsorption sites for the contaminants.
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3.3.3 Adsorption isotherms
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Adsorption isotherms are usually applied to describe the distribution of adsorbed
366
substances between the liquid phase and the solid phase. The adsorption isotherms of P-MCD
367
were measured with the different MB concentration at different temperatures. As shown in
368
Fig.7a, the adsorption capacity aggrandizes with the temperature increasing.
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Two distinguished Langmuir and Freundlich isotherm models were utilized to describe
370
the equilibrium isotherms for the adsorption regarding interaction and capacity at different
371
temperatures, respectively (Fang et al., 2014). The Langmuir isotherm is indicated as Eq. (6),
372
which assumed that monolayer adsorption is obtained by uniform adsorption, there is no
373
interaction between the adsorbed substances, and the energy of each adsorption site is 13
ACCEPTED MANUSCRIPT 374 375 376
uniform.
Ce 1 C e Qe Qm K L Qm
(6)
Where Qm indicates the maximum adsorption capacity (mg g -1), Qe and Ce represent the
377
adsorption capacity (mg g
378
respectively; and KL means the adsorption equilibrium constant (L mg -1).
381
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) and concentration (mg L -1) at the adsorption equilibrium,
The Freundlich isotherm in Eq. (7) is geared to the empirical models, which is primarily applied for multilayers adsorption (Aghagoli and Shemirani, 2017).
ln Qe ln K F
1 ln C e n
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-1
(7)
Where KF and n represent empirical constants of the relative adsorption capacity and
383
adsorption intensity, respectively. The linearly fitted Freundlich isotherm adsorption is shown
384
in the Fig.7c. As shown in Table S2, adsorption is favorable when 0.1 < 1/n< 1 (Li et al.,
385
2018b). Hence, the adsorption to MB on P-MCD is favorable under the experimental
386
conditions owing to the values of 1/n is 0.128.
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The energy relationship described by Temkin equation is that the adsorption heat
388
decreases linearly with the amount of adsorption (Wu et al., 2018). The Temkin isotherm is
389
typically used as given by:
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Qe Bt ln Kt Bt ln Ce
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In the equation, Kt (L mg
-1
(8)
) indicates the equilibrium binding constant, which
corresponds to the maximum binding energy. And compared with the Langmuir parameters,
393
the latter is better to describe the adsorption process. The linearly fitted Temkin isotherm
394
adsorption is shown in Fig.7d, and adsorption isotherm model parameters at different
395
temperatures are illustrated in Table S2.
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Redlich–Peterson model is applied to describe the adsorption isotherm, which belongs to
397
the three parameter equations (van Hullebusch et al., 2004). The Redlich–Peterson isotherm is
398
typically used as given by:
Qe 399
ACe
1 BCe
(9) 14
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In the equation, A, B and β mean the Redlich–Peterson model isotherm constant (L g -1),
401
the model constant (L mg -1) and exponent, respectively. Adsorption characteristic curves of
402
Redlich–Peterson isotherm equation are illustrated in Fig.S6, and its model parameters at
403
different temperatures are demonstrated in Table S2. The Langmuir model (R2=0.9999) is more accurate than the Freundlich model
405
(R2=0.9254) in describing the MB adsorption owing to its superior coefficients. MB
406
adsorption could be regarded as monolayer adsorption, which is in accordance with a few past
407
researcher that has focused on the MB adsorption on imprinted polymers (Li et al., 2014).
408
Table S2 summarizes the values of Qm, KL, KF, n and R2, which indicates that the Langmuir
409
model is more consistent with isotherm data. Moreover, the Qmax of MB adsorbed on P-MCD
410
at different temperatures was shown in Table S2.
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In addition, in order to confirm the function of the polymer layer generated by
412
tetrafluoroterephthalonitrile, we also investigated the adsorption isotherm of Fe3O4@β-CD on
413
MB, and the adsorption isotherm results are shown in Fig. S5c and S5d. Moreover, the
414
adsorption isotherm model parameters of MB adsorption on Fe3O4@β-CD at different
415
temperatures are shown in Table S2. The maximum adsorption capacity of MB adsorbed by
416
Fe3O4@β-CD and P-MCD are 74.79 mg g -1 and 305.8 mg g -1, respectively. The results show
417
that the latter has a higher adsorption capacity than Fe3O4@β-CD, indicating that the high
418
surface area and porous structure of P-MCD increased the adsorption sites, which were
419
conducive to MB adsorption. Meanwhile, the maximum MB adsorption capacity in this work
420
was compared with several other recently reported adsorbents. The comparison results were
421
shown in Table S3 that P-MCD has higher adsorption capacity than other reported adsorbents.
422
This is mainly because the P-MCD contains a porous polymer and a large specific surface
423
area.
424
3.3.4 Adsorption thermodynamics
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To further investigate the spontaneity of the adsorption process, the thermodynamic
426
parameters containing Gibb’s free energy change (∆Gθ), enthalpy change (∆Hθ) and entropy
427
change (∆Sθ) can be obtained as follows:
428
G RT ln K
(10) 15
ACCEPTED MANUSCRIPT 429
ln K
S H R RT
(11)
Where K (L mg -1) indicates the constant of the Langmuir equilibrium, T (K) denotes the
431
temperature, and R represents the molar gas constant, the value of which is 8.314 J mol-1 K-1.
432
The values of ΔHθ and ΔSθ could be enumerated from the slopes and intercepts of the lnKd and
433
1/T Van't Hoff curves, respectively.
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The calculated thermodynamic parameters are shown in Table S4. The negative values of
435
∆Gθ at different temperatures demonstrate that the spontaneity of the adsorption process. The
436
positive values of ∆Hθ at different temperatures indicates that the reaction of P-MCD to
437
adsorb MB is an endothermic reaction, demonstrating that the adsorption was more favorable
438
in higher temperature. The chemical reaction heat between 20.9 KJ mol-1 and 418.4 kJ mol-1
439
is generally considered to be a chemical adsorption process (Zhao et al., 2015). In this work,
440
the value of ∆Hθ was higher than 20.90 kJ mol−1, indicating that the adsorption of MB onto
441
P-MCD was a chemical adsorption process.
442
3.3.5 Applicability of P-MCD
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The adsorption performance of P-MCD on MB was not only discussed, but the
444
expansion of the research on the adsorption of other water pollutants was also performed. The
445
removal efficiency and the maximum adsorption capacity are shown in Table S5. Fig.S7
446
presents a histogram of P-MCD removal efficiency for various water pollutants, which shows
447
that the material possessed a broad range of organic pollutants. The performance showed by
448
developed nanocomposites for adsorbing various organic materials could be ascribed to three
449
interaction, namely, host–guest interaction, π-π stacking interaction and multiple hydrogen
450
bonding. Meanwhile, the high surface area and porous structure of P-MCD increased the
451
number of adsorption sites, which were beneficial to MB adsorption.
452
3.3.6 Desorption and recycling study
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Desorption and regeneration experiments were carried out to investigate the
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recyclability of the P-MCD. MB desorption was conducted using ethanol solution containing
455
5% (V/V) acetic acid. Ethanol solution containing 5% acetic acid was selected in examining
456
recycling study due to acid condition could disrupt both the electrostatic interaction and the 16
ACCEPTED MANUSCRIPT 457
host-guest interaction. As shown in Fig.S8, the removal efficiency remained at 86.35% even
458
after seven cycles. These results indicated that P-MCD not only exhibit higher adsorption
459
capacity for pollutants in wastewater, but also has recyclability in practical applications.
460
3.3.7 Analysis of actual water samples Fig.S9 shows the results of UV-Vis that P-MCD adsorbed in the simulation of the
462
Yellow River water in 10 min. A certain amount of MB, Rh B and malachite green are used to
463
contaminate the actual sample of the Yellow River water. Figure (a), (b), and (c) represent
464
ultraviolet maximum absorption wavelengths of Rh B (554 nm), Malachite green (619 nm),
465
and MB (664 nm), respectively. The absorbance of Malachite green was almost 0 after
466
absorption. The same situation occurred in the absorbance of MB. It is clearly shown in the
467
inset of Fig.S9 that the absorbance of Rh B is only minimal. The removal efficiency of the
468
three dyes after adsorption is presented in Fig.S10. These results imply that the P-MCD has a
469
good prospect in practical applications of organic pollutant adsorption.
470
4. Conclusions
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In summary, a kind of well-defined magnetic β-CD porous polymer nanospheres were
472
successfully prepared for MB extraction via one-pot solvent thermal method. The P-MCD
473
combined the properties of the core (Fe3O4 nanoparticles), which had a rapid magnetic
474
response to material separation, with the surface porous β-CD polymer layer that having the
475
fast kinetics and satisfactory broad adsorption range of organic micro-pollutants. The rapid
476
kinetics of the material could be ascribed to the large specific surface area and numerous of
477
β-CD cavities. Meanwhile, the dispersibility of magnetic nanoparticles enhances the
478
dispersion of the β-CD porous polymer in the aqueous phase, which was beneficial to
479
improve the inclusion adsorption performance and the adsorption process. The results show
480
that P-MCD not only have good recyclability but also have high removal efficiency for
481
pollutants in wastewater. Thus, it is expected that the P-MCD could be a promising adsorption
482
material in environmental remediation.
483
Conflicts of interest
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There are no conflicts to declare. Acknowledgements 17
ACCEPTED MANUSCRIPT The authors would like to express their appreciation for research funding provided by the
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National Natural Science Foundation of China (No.21374045, No.21074049) and the
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National Science Foundation for Fostering Talents in Basic Research of the National Natural
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Science Foundation of China (Grant No. J1103307). In addition, sincere appreciation is also
490
expressed to the Electron Microscopy Centre of Lanzhou University for the microscopy and
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microanalysis of our specimens.
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Graphical Abstract
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In this work, we adopted a two-step synthesis strategy to synthesize uniform particle size distribution of β-CD polymer functionalized magnetic nanospheres. Firstly, β-CD was modified on the surface of magnetic nanoparticles to obtain β-CD modified magnetic nanoparticles
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(Fe3O4@β-CD), followed by solvent thermal method for Fe3O4@β-CD, β-CD and tetrafluoroterephthalonitrile monomer was polymerized to
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obtain magnetic β-CD porous polymer nano-spheres. The maximum adsorption capacity of MB for P-MCD was 305.8 mg g −1, which is more
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than Fe3O4@β-CD (71.89 mg g -1). Moreover, the material had a high recovery and good recyclability.
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Figures
Scheme 1 Schematic procedures of fabricating magnetic porous β-CD polymer nano-spheres and procedures of
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MB adsorption and desorption.
Fig.1 TEM image of Fe3O4@β-CD (a, c) and P-MCD (b, d).
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Fig.2 The STEM image of the P-MCD (a), element distribution of Fe-K (b), C-K (c), N-K (d), O-K (e), and F-K
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(f).
Fig.3 Characterization of Fe3O4@β-CD and P-MCD: (a) FT-IR spectra, TGA curves (b), Magnetization curves (c), and XRD spectra (d). The inset of Fig.3c shows the solution of P-MCD in the presence of a magnet.
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P-MCD.
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Fig.4 XPS survey spectra of Fe3O4@β-CD and P-MCD (a), and fine spectra of C 1s (b), O 1s (c) and Fe 2p (d) of
Fig.5 (a) N2 adsorption-desorption isotherms of Fe3O4@β-CD and P-MCD and (b) the size distribution curve.
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Fig.6 Effects of contact time on adsorption of MB onto P-MCD (a), pseudo-second-order kinetic plots (b),
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Elovich kinetic plots (c) and Webber and Morris kinetic models (d).
Scheme 2 Adsorption Mechanism of MB on P-MCD
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Fig.7 Equilibrium adsorption isotherms of P-MCD to MB with the different temperature (a), Langmuir
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adsorption model (b), Freundlich adsorption model (c) and Temkin model (d).
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Highlights
1. Magnetic β-cyclodextrin (β-CD) porous polymer nano-spheres (P-MCD) was
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fabricated by one-pot solvent thermal method. 2. The obtained materials exhibit high adsorption capacity for MB.
3. The adsorption mechanism of the obtained nanospheres on MB is mainly based on
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host-guest interaction, π-π stacking interaction and hydrogen bonding.
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4. P-MCD has excellent removal efficiency for a variety of environmental pollutants.
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5. P-MCD exhibited perfect reusability after a simple ethanol cleaning.
S0269-7491(18)35468-X
DOI:
https://doi.org/10.1016/j.envpol.2019.04.079
Reference:
ENPO 12480
To appear in:
Environmental Pollution
Received Date: 4 December 2018 Revised Date:
9 March 2019
Accepted Date: 15 April 2019
Please cite this article as: Liu, D., Huang, Z., Li, M., Sun, P., Yu, T., Zhou, L., Novel porous magnetic nanospheres functionalized by β-cyclodextrin polymer and its application in organic pollutants from aqueous solution, Environmental Pollution (2019), doi: https://doi.org/10.1016/j.envpol.2019.04.079. 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
Novel porous magnetic nanospheres functionalized by β-cyclodextrin
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polymer and its application in organic pollutants from aqueous solution
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Desheng Liu 1a, Zheng Huang 1a, Minna Li a, Ping Sun a, Ting Yu a, and Lincheng Zhou *a, b
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a. State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Institute of
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Biochemical Engineering & Environmental Technology, Lanzhou University, Lanzhou 730000, P. R. China.
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b. Zhongwei High-tech Institute of Lanzhou University, 755000, P. R. China.
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1.These authors contributed equally to this work and should be considered as co-first authors.
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Desheng Liu
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Address: College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, P.R.China
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Zheng Huang
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Address: College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, P.R.China
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Minna Li
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Address: College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, P.R.China
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Ping Sun
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Address: College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, P.R.China
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Ting Yu
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Address: College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, P.R.China
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Lincheng Zhou
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Address: College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, P.R.China
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Fax: 86-0931-8912113
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E-mail: [email protected]
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E-mail:[email protected]: 86-0931-8912113
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Abstract Magnetic β-cyclodextrin (β-CD) porous polymer nanospheres (P-MCD) was fabricated
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by one-pot solvent thermal method using β-CD immobilized Fe3O4 magnetic nanoparticles
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with tetrafluoroterephthalonitrile as the monomer. Compared with the β-CD polymerization
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method reported in the literature, the synthetic route is effective and simple, thereby
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overcoming the harsh conditions that require nitrogen protection and always maintain
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anhydrous and oxygen-free. Moreover, the immobilization of β-CD on magnetic nanoparticles
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is combined with the cross-linking polymerization of the cross-linker, leading to a good
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synergistic effect on the removal of contaminants. Meanwhile, the dispersibility of the
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magnetic carrier enhances the dispersion of the β-CD porous polymer in the aqueous phase,
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and improves the inclusion adsorption performance and the adsorption process. P-MCD
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exhibited superior adsorption capacity and fast kinetics to MB. The maximum adsorption
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capacity of MB for P-MCD was 305.8 mg g
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magnetic nanoparticles (Fe3O4@β-CD). Moreover, the material had a short equilibrium time
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(5 min) for MB, high recovery and good recyclability (the adsorption efficiency was still
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above 86% after five repeated uses).
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, which is more than β-CD modified Fe3O4
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Keywords: Porous nanospheres, β-cyclodextrin polymer, Adsorption, Organic pollutants,
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Magnetic
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1. Introduction Nowadays, the use of a large number of dyes and pigments in the chemical industry
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seriously pollutes the world’s ecosystem. Waste water from dyes comprises numerous
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pollutants that pose a threat to agriculture, food chains and human health (Zhao et al., 2015).
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Hence, removal of dyes has become a considerable issue that has evoked increasing attention
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(Hu et al., 2011).
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β-cyclodextrin (β-CD), which possesses a stable property and a torus shape, is a kind
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type of cyclic oligosaccharide with seven glucose units that connected by α-(1,4)-glucosidic
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linkages (Chen et al., 2010). Owing to the particular annular structure of β-CD, which is
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hydrophobic inside and hydrophilic outside; thus, non-covalent host-guest inclusion
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complexes could can be generated (Ncube et al., 2014). Thence, β-CD also possesses the
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potential to remove dye molecules in wastewater due to its ability to form inclusions with
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different types of organic contaminant molecules (Wang et al., 2015; Zhang et al., 2019). In
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recent years, cyclodextrin graft polymers in which cyclodextrin host molecules are linked to
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polymers or magnetic nanoparticles by covalent bonds have received considerable attention
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(Sanchez-Trujillo et al., 2013; Tarasi et al., 2016).
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Polymer materials containing cyclodextrin have significant applications in environmental
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monitoring and wastewater treatment (Zhao et al., 2015). Therefore, it is expected that a novel
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material with higher stability will be obtained by preparing a polymer using a β-CD derivative.
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The cyclodextrin externally surface-active functional group is bonded to other porous
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polymers to act as an adsorbent. Owing to the hydrophobic structure of the β-CD inner cavity,
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it forms an inclusion complex with organic pollutants in the water to remove it. However,
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β-CD has relatively good solubility in water, and it is difficult to recycle in the aqueous phase,
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which greatly limits its application in water treatment. Therefore, the main research focus in
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recent years is to crosslink β-CD with a crosslinking agent to form water-insoluble polymers
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(Li et al., 2018a). The β-CD-derived polymer maintains the distinctive properties of the β-CD
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matrix and has the advantages of superior polymer stability and chemical adjustability.
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However, crosslinked β-CD polymers also have disadvantages such as low surface area and
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poor removal performance. In recent years, the covalent loading of β-CD has also been an important direction for its
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application expansion (Fan et al., 2012). The immobilization can not only maintain its
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inherent cavity structure and its properties well, but also conquer its shortcomings such as
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good water solubility and difficulty in recovery. By constructing β-CD on other supports, it is
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possible to synthesize a water-insoluble adsorbent material with a long service life,
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distinguished mechanical properties or superior dispersibility (Jiang et al., 2018). The carriers
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that were commonly applied to immobilize β-CD are mainly inorganic molecular and natural
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polymers. The inorganic carrier generally includes carbon nanotube (Hu et al., 2011; Wang et
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al., 2012), SiO2 nanoparticles (Ghosh et al., 2011; Zhang et al., 2015), magnetic Fe3O4
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nanoparticles (Badruddoza et al., 2013; Cai et al., 2011; Fan et al., 2012; Lv et al., 2016;
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Wang et al., 2015; Wang et al., 2014; Zhou et al., 2016), whereas the natural polymer carrier
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has chitosan and sodium alginate (Chen et al., 2014; Huang et al., 2013; Jiang et al., 2018).
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Therefore, the multi-functional magnetic β-CD porous polymer composite, obtained by
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crosslinking β-CD derivative and constructed on the magnetic nanoparticles, has a good
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application prospect in environmental field.
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In this study, we adopted a two-step synthesis strategy to synthesize highly uniform
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particle size distribution of magnetic β-CD porous polymer nanospheres. Firstly, β-CD was
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immobilized on the surface of magnetic nanoparticles by a one-pot method to obtain
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β-CD-modified magnetic nanoparticles (Fe3O4@β-CD). Then, the magnetic porous polymer
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nanospheres were obtained by cross-linking polymerization of Fe3O4@β-CD and
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tetrafluoroterephthalonitrile cross-linking agent by a solvothermal method. Compared with
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the β-CD polymerization method reported in the literature (Alsbaiee et al., 2016), the
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synthetic route is more effective and simple, thereby overcoming the harsh conditions that
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require nitrogen protection and invariably maintain anhydrous and oxygen-free. Meanwhile,
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the crosslinked β-CD porous polymer not only has superior stability and recyclability, but also
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has a large specific surface area and outstanding adsorption performances. The adsorption
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capacity of P-MCD was also investigated through adsorption equilibrium isotherms and
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dynamics. The results revealed that P-MCD has a superior removal efficiency on the organic
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molecules in aqueous solution, and the maximum adsorption capacity can reach 305.8 mg g -1.
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Therefore, the magnetic porous nanospheres has a fine application prospect in the field of
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environmental remediation.
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2.
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2.1 Materials
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Experimental section
The biochemical reagent β-CD (99.0%) and carboxymethyl-β-cyclodextrin (CM-β-CD)
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(99.9%) were purchased from Shanpu Chemical Co., Ltd. (Shanghai, China). The
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tetrafluoroterephthalonitrile (99.0%) was obtained from Sigma Aldrich. Anhydrous sodium
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acetate, anhydrous potassium carbonate and ferric chloride hexahydrate were purchased from
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Guangfu Reagent (Tianjin, China). Dimethylformamide (DMF), tetrahydrofuran (THF),
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ethylene glycol and ethanol were purchased from Li AnlangBohua Pharmaceutical Chemical
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Co., Ltd. The other chemical reagents applied in this work were analytical grade. The water
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applied in the work was ultrapure water.
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2.2 Synthesis of Fe3O4@β-CD
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Fe3O4@β-CD nanoparticles were synthesized by a one-pot solvothermal method. First,
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FeCl3·6H2O (2.7 g) and anhydrous sodium acetate (7.2 g) were added to a three-necked flask
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containing 80 mL of anhydrous ethylene glycol solution, and completely dissolved by
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ultrasonic stirring until the mixture became a yellow solution. Then, 0.4 g of β-CD was added
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to the above mixture solution, which was vigorously stirred for 1 h to disperse uniformly. The
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mixture solution was finally sealed in an autoclave and heated at 200 °C for 8 h. The product
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was carefully gathered through a magnet after the autoclave was cooled to room temperature.
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Fe3O4@β-CD was washed three times with ultrapure water and ethanol, respectively, and
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vacuum dried at room temperature.
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2.3 Synthesis of P-MCD
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P-MCD nanospheres were also fabricated using a one-pot hydrothermal method.
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Fe3O4@β-CD (100 mg), CM-β-CD (200 mg), tetrafluoroterephthalonitrile (100 mg), and
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K2CO3 (300 mg) were dissolved in mixture solutions with 8 mL of DMF and 22 mL of THF.
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The mixed solution was then transferred into an autoclave and heated at 120 °C for 72 h.
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Subsequently, P-MCD was obtained when it cooled to room temperature through the magnetic 5
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separation, washed with deionized water and alcohol, respectively, and dried under vacuum at
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room temperature.
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2.4 Characterization FT-IR spectra were obtained from FT-IR spectrometer (Model 170-SX, American Nicolet
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Corp.) at room temperature using powder-pressed KBr pellets. The morphology of the
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P-MCD was characterized by SEM (JSM-6701F) and TEM (Tecnai G2 F30). Magnetic
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hysteresis
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LAKESHORE-7304, USA) at room temperature. The X-ray photoelectron spectroscopy (XPS)
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was carried out through an ESCALab220i-XL electron spectrometer (VG Scientific) with
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300W Al-Kα radiation and X-ray diffraction (XRD) spectra were obtained from Rigaku
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D/MAX-2400 with Ni-filtered Cu-Kα radiation. Ultraviolet–visible spectroscopy (UV-Vis,
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TU-1810PC) was applied to investigate the adsorption effect of MB. The specific surface area
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of the nanospheres was measured at liquid N2 temperature (76 K) using a Micromeritics
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ASAP 2010M apparatus.
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2.5 Adsorption
were
obtained
using
vibrating
sample
magnetometry
(VSM,
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P-MCD (5.0 mg) was dissolved in the aqueous solution with the different initial MB
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concentration. The same set of mixtures was placed in a constant-temperature shaker and
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shaken at 298 K with a shaking speed of 250rpm for 6 h, and the equilibrium concentration of
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MB was analyzed by UV-Vis. The equilibrium adsorption capacity Qe (mg g-1) was obtained
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by the following equation:
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(C0 Ce ) V m
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Where C0 (mg L-1) and Ce (mg L-1) means the initial concentration and equilibrium
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concentration of MB, respectively. V (mL) represents the volume of MB solutions, and m (g)
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means the mass of absorbent.
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2.6 Desorption and recycling study
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In the desorption experiment, the MB-adsorbed P-MCD nanospheres was washed
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thoroughly with ultrapure water. The nanospheres was then extracted several times in an
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ethanol solution containing 5% (V/V) acetic acid. After each extraction was completed, the 6
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residual MB concentration in the solution was analyzed with an UV-Vis. In order to
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investigate the reusability of the adsorbent, the washed P-MCD was reused in the adsorption
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experiment. Meanwhile, the same process was repeated seven times.
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3.
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3.1 Preparation of magnetic porous polymer nanospheres
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Results and discussion
Scheme 1 shows the procedure of P-MCD fabrication and MB adsorption and desorption. First, Fe3O4@β-CD nanoparticles were synthesized via solvent thermal method, which grafted
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β-CD on the Fe3O4 surface to retain magnetic responsive property of the material and
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contribute to the separation. Similarly, P-MCD was fabricated via solvent thermal method
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using Fe3O4@β-CD nanoparticles, CM-β-CD, and tetrafluoroterephthalonitrile monomer. The
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polymerization reaction is a nucleophilic reaction, nucleophilic aromatic substitution of
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hydroxyl groups of β-CD by tetrafluoroterephthalonitrile. High temperature and high-pressure
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are more conducive to the substitution of fluorine on the benzene ring and hydroxyl groups of
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the β-CD, making the nucleophilic reaction easier. Meanwhile, the whole reaction system is in
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an oxygen-free state during the reaction. Therefore, under the same experimental conditions,
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the polymerization reaction can still be conducted. Subsequently, P-MCD nanospheres were
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dispersed in MB solution and shaken for a short time. After the magnetic separation, the MB
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solution became clear.
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3.2 Characterization of magnetic nanospheres
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3.2.1 Morphology and structure characterization
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The SEM image of Fe3O4@β-CD (Fig.S1a and Fig.S2) reveals its smooth morphology
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because of the relatively small β-CD grafted to the Fe3O4. However, the P-MCD has a porous
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structure was observed in the surface morphology (Fig. S1b). Compared with the
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Fe3O4@β-CD, P-MCD became rougher and larger, which indicates that the polymer layer was
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successfully assembled on the surface of the Fe3O4 magnetic nanoparticles.
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As shown in Fig.1, Fe3O4@β-CD nanoparticles are spherical shape and have an average
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diameter of 185 nm (Fig.1a), whereas P-MCD nanospheres exhibit a larger size with a
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diameter of approximately 200 nm. As shown in Fig.1b, it can be seen that about 20 nm of
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polymer layer was coated on the surface of Fe3O4@β-CD, which indicates that the polymer 7
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layer was triumphantly grafted onto the surface of the matrix through radical polymerization.
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Fig.1b and d, proves the successful prepared of P-MCD nanospheres that are uniformly
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spherical shape and narrow size distribution. The particle size distribution of P-MCD is
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shown in Fig.S3. The surface morphology and chemical element distribution of P-MCD were analyzed by
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HAADF-STEM, and the results are shown in Fig.2. The image distinctly demonstrates that
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P-MCD is primarily comprises of Fe, C, N, O and F elements. Furthermore, the presence of N
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and F elements on the surface of the nanospheres also verifies that the porous β-CD polymer
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layer has been faultlessly coats on the surface of Fe3O4@β-CD magnetic nanoparticles.
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3.2.2 FT-IR characterization
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The strong absorption bands at 584 cm
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Fe-O in Fe3O4 nanoparticles, which corresponds to the literature (Li et al., 2011). In
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comparison with the three IR spectra, the characteristic peaks of Fe3O4@β-CD and P-MCD at
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3340 cm
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respectively. Furthermore, there is a strong C-O stretching vibration at 1033 cm -1, which
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indicates that the spectral features of intact β-CD, as stated in the literature (Cai et al., 2011).
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In addition, the P-MCD exhibit absorbance at 1648 cm -1 and 1443 cm -1 are corresponding to
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C–C aromatic stretches, which corresponds to the nitrile stretch. Moreover, the absorption at
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1267 cm
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vibration of C-F. These results indicate that the β-CD porous polymer layer successfully
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polymerized on the Fe3O4@β-CD surface.
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3.2.3 Thermogravimetric analysis of the nanospheres
and 2932 cm
-1
could be attributed to the stretching vibration of
are assigned to O-H and aliphatic C-H stretching vibration,
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TGA of Fe3O4@β-CD and P-MCD are shown in Fig.3b. The amount of polymer layers
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coated on the Fe3O4 surface was estimated via TGA of Fe3O4@β-CD without polymerization.
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As shown in Fig.S4a, the thermogravimetric loss is approximately 1% when the temperature
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is about 200 ℃, which is belonging to the volatilization of water and solvents. In addition,
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the major weight loss from 250 °C to 800 °C stemmed from the decomposition of grafted
231
β-CD, and the weight loss to 8.6% of initial weight with a slower rate could be attributed to 8
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the grafting of β-CD. As shown in Fig.S4b, the thermogravimetric loss is near 28.5% when
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the temperature is about between 250 ℃ and 800 ℃, which can be assigned to the loss of
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β-CD porous polymer layer.
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3.2.4 Magnetic properties of the nanospheres The magnetic of Fe3O4@β-CD and P-MCD nanospheres were measured by VSM in the
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field range of -20 to +20 kOe at room temperature. Fe3O4@β-CD and P-MCD porous
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nanospheres can explicitly observe the magnetic hysteresis loops, which is characteristic of
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superparamagnetism behavior, are presented in Fig.3c. The saturation magnetizations (Ms) of
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the above samples are 70.2 emu g
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these nanospheres can be readily segregated from the solution under an external magnetic
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field. The insert of Fig.3c illustrates that the separation of P-MCD from solution using a
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magnet only takes several minutes, confirming the fast magnetic responsiveness of the
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material. The result declared that the Ms of P-MCD is weaker than that of Fe3O4@β-CD, this
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is principally due to the presence of a polymer layer on the surface of Fe3O4@β-CD
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nanoparticles.
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3.2.5 XRD characterization
and 44.8 emu g -1, respectively, which indicating that
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The XRD patterns of Fe3O4@β-CD and P-MCD are shown in Fig.3d. The diffraction
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peaks at 2θ of 30.0°, 35.5°, 43.2°, 53.8°, 57.2° and 62.6° are attributed to (220), (311), (400),
250
(422), (511) and (440) crystal planes, respectively. This is consistent with the characteristic
251
peaks of the pure Fe3O4 nanoparticles with spinel structure (Shao et al., 2016). This indicates
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that the structure of Fe3O4 nanoparticle can remain stable when it was modified with the β-CD
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polymer layer. The crystal sizes of P-MCD ascertain from the XRD pattern with Scherrer’s
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equation [Dh kl = 0.9λ/(βcosθ), where Dh kl means the crystalline average diameter, λ indicates
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X-ray wavelength, β signifies the half width of XRD diffraction lines and θ represents Bragg’s
256
angle(°)] are found to be 204 nm, which are slightly larger than that observed from the TEM
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image. In this study, the (311) peak of highest intensity was chosen to calculate the particle
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size of P-MCD nanospheres.
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3.2.6 XPS characterization
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The XPS spectra of Fe3O4@β-CD and P-MCD nanospheres are shown in Fig.4. The 9
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which are assigned to C 1s, O 1s and Fe 2p, respectively (He et al., 2014). The results show
263
that the composition contains Fe, O and C elements exist. However, in the spectral of P-MCD,
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new peaks appearing at 400.3 eV and 689.88 eV can be assigned to N 1s and F 1s,
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respectively, which reveals that the presence of the N and F elements causes the porous
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polymer layer to be successfully polymerized onto the Fe3O4@β-CD surface. The Fe 2p
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spectrum can be divided into two peaks centered at 727.9 and 714.2 eV, which are associated
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with the peaks of Fe 2p1/2 and Fe 2p3/2, respectively (Uyar et al., 2008), confirming that the
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existence of Fe3O4 nanoparticles with spinel structure. Moreover, Fig.4b shows the high
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resolution spectrum of C 1s, and the binding energy at 288.9, 287.3 eV is assigned to the
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C=O-O- (carboxyl) species and the C=O form of the carbon atom (carbonyl), respectively (Qu
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et al., 2014). In addition, the presence of COO− peak at 288.9 eV declares that the carboxyl
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groups on CM-β-CD polymer reacted with surface hydroxyl groups to form metal carboxylate.
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The O1s spectrum can be divided into three peak components, and the binding energy peaks
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at 536.8 and 535.5 eV can be ascribed to O=C-O and C-OH/C-O-C species, respectively.
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However, the peak of O1s at 533.5 eV corresponds to the characteristic peak of Fe-O-C in the
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composite (S.Srivastava and S.Badrinararyanan, 1985).
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3.2.7 BET characterization
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The specific surface area and the pore-size-distribution curve of the as-prepared
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Fe3O4@β-CD and P-MCD nanospheres were confirmed by N2 adsorption–desorption
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isotherms, as shown in Fig.5. The BET surface areas of Fe3O4@β-CD and P-MCD were
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measured to be 44.44 m ² g -1 and 70.63 m ² g -1, respectively. The P-MCD had the larger BET
283
surface area, thus, it also had the larger adsorption capacity. The pore size of the obtained
284
P-MCD nanospheres is 5.59 nm, which is 0.8 nm larger than the diameter of MB (Ma et al.,
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2014). The diameter of the P-MCD nanospheres channel is consistent with the molecular size
286
of the MB molecule, demonstrating the strong adsorption capacity of P-MCD for MB.
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3.3 Adsorption properties of P-MCD
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3.3.1Effect of pH and MB concentration
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The effect of solution pH on MB adsorption on P-MCD nanospheres is shown in Fig.S4. 10
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3.0 to 11.0. As shown in Fig.S4, the removal efficiency and capacity are worst in the acidic
292
conditions, resulting to only 80% removal efficiency. A high adsorption capacity was
293
achieved with the aggrandize in pH of the solution, which could be assigned to that the
294
dimethylamine group in MB molecule and the hydroxyl groups in β-CD that were positively
295
charged at low pH value. Moreover, protonated MB was not beneficial to come into being the
296
host–guest inclusion complex with protonated β-CD by reason of a repelling interaction
297
(Chen et al., 2014; Zhang et al., 2013). As the pH increased, the activated deprotonation
298
hydroxyl groups could come into being electrostatic interaction with MB molecules. In
299
addition, when the pH of the solution is greater than 7.0, the adsorption capacity became
300
almost a stable value. As a result, all of the following studies were carried out at the initial
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solution pH value of 7.0. As indicated in Fig.6a, the initial adsorption rate decreased
302
significantly with the increase of MB concentration. But a larger MB concentration would
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result in the block of cavities β-CD, thereby slowing down the subsequent adsorption rate.
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With the progress of time, removal efficiency could be more than 98% when it reached
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adsorption equilibrium.
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3.3.2 Adsorption kinetics
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The effect of contact time on the adsorption of MB onto P-MCD with various initial
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MB concentrations is shown in Fig.6a. The initial MB concentration supplies the essential
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driving force to alleviate the mass transfer resistance of MB between the aqueous phase and
310
solid phases (Karago¨z et al., 2008). Equilibrium was reached in approximately 2 min and 5
311
min by P-MCD. Moreover, the amount of MB at the equilibrium aggrandized with the initial
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MB concentration increasing. Within almost 5 min, MB removal efficiency can reach
313
97.3%-100% at equilibrium was achieved, which indicates that P-MCD could adsorb MB
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from the aqueous solution rapidly and effectively.
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The Lagergren pseudo-first-order and pseudo-second-order kinetic models were
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employed to investigate the adsorption kinetics of MB onto P-MCD nanospheres (Shao et al.,
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2017; Wu et al., 2018). Adsorption kinetic curve and pseudo-second-order fitting curves are
318
indicated in Fig.6b. The two dynamic equations are as follows: 11
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log( Qe Qt ) log Qe
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k1 t 2.303
(2)
t 1 t Qt k2Qe 2 Qe
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(3)
Where Qe and Qt represent the amounts of MB adsorbed when the adsorption attained
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equilibrium and t, respectively. k1 indicates the pseudo-first-order rate constant (min -1) and k2
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means the pseudo-second-order rate constant (g mg -1 min -1).
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The adsorption on high heterogeneous adsorbents can be expressed by the Elovich
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equality (Li et al., 2017), which is idealized by assuming αβ≫t and using the critical
326
conditions Qt = 0 at t=0 and Qt = Qt at t = t, shown as follows:
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Where α (mg g
-1
1
ln( )
1
ln t
(4)
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Qt
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min -1) indicates the initial adsorption rate, and β (g mg -1) represents
the desorption constant. The results are shown in Fig.6c, and Table S1 lists the values of the
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R2 of P-MCD. In Comparison with the pseudo-second-order model, the depiction of Elovich
331
model is not accurate.
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The mechanism of adsorption is invariably associated with the Weber and Morris
333
equality (Hosseini et al., 2011). In general, the adsorption process contains three steps, namely,
334
bulk diffusion, film diffusion, intra-particle diffusion or pore diffusion. The model can be
335
expressed as follows:
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qe KWM t C
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Where KWM and C indicate the diffusion rate constant (mg g
(5) -1
min 1/2) and the intercept,
respectively.
339
As shown in Fig.6d, the intra particle diffusion is not the only step that can be dominated
340
by rate. The adsorption kinetic curve can be divided into three sections, namely, surface
341
diffusion, intra-particle diffusion, and singularly low MB concentration in aqueous solution,
342
which depicts the steps of adsorption. Scheme 2 shows the MB adsorption mechanism of
343
P-MCD. In sum, the adsorption performance of P-MCD could be concluded with three
344
processes, namely, host–guest complex interaction, π-π stacking interaction and multiple 12
ACCEPTED MANUSCRIPT hydrogen bonding. With regard to host–guest interaction, β-CD-based polymer existing in
346
P-MCD could catch MB molecules. MB has benzene rings that could form a π-π stacking
347
intermolecular force between MB and P-MCD. Besides, during the preparation of P-MCD,
348
some residual oxygen/nitrogen-containing groups such as hydroxyl and cyano groups
349
remaining in the P-MCD. Therefore, another interaction is the hydrogen bond originated by
350
the oxygen/nitrogen-containing groups of both MB and P-MCD.
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The correlation parameters of the three kinetic models are indicated in Table S1. The
352
data demonstrate that the pseudo-second-order rate model depicted the MB adsorption
353
(R2>0.999) more accurately, which the calculated Qe is close to the Qe from the experimental
354
data, whereas much worse or no relevance was found in the pseudo-first-order model. These
355
results indicate that the adsorption process of MB molecules by P-MCD nanospheres is
356
dominated by chemical adsorption.
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Besides, the function of the layer polymerized by tetrafluoroterephthalonitrile was
358
investigated through the adsorption behavior of Fe3O4@β-CD, provided in Fig. S5a and S5b.
359
The adsorption kinetic model parameters at different concentrations are shown in Table S1.
360
Same dosages of Fe3O4@β-CD and P-MCD were added into MB solution and the result
361
indicated that the latter exhibit higher adsorption capacity under the same condition, which
362
indicates that the cross-linking of β-CD and rigid aromatic groups provides a high surface
363
area and a large number of adsorption sites for the contaminants.
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3.3.3 Adsorption isotherms
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Adsorption isotherms are usually applied to describe the distribution of adsorbed
366
substances between the liquid phase and the solid phase. The adsorption isotherms of P-MCD
367
were measured with the different MB concentration at different temperatures. As shown in
368
Fig.7a, the adsorption capacity aggrandizes with the temperature increasing.
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Two distinguished Langmuir and Freundlich isotherm models were utilized to describe
370
the equilibrium isotherms for the adsorption regarding interaction and capacity at different
371
temperatures, respectively (Fang et al., 2014). The Langmuir isotherm is indicated as Eq. (6),
372
which assumed that monolayer adsorption is obtained by uniform adsorption, there is no
373
interaction between the adsorbed substances, and the energy of each adsorption site is 13
ACCEPTED MANUSCRIPT 374 375 376
uniform.
Ce 1 C e Qe Qm K L Qm
(6)
Where Qm indicates the maximum adsorption capacity (mg g -1), Qe and Ce represent the
377
adsorption capacity (mg g
378
respectively; and KL means the adsorption equilibrium constant (L mg -1).
381
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) and concentration (mg L -1) at the adsorption equilibrium,
The Freundlich isotherm in Eq. (7) is geared to the empirical models, which is primarily applied for multilayers adsorption (Aghagoli and Shemirani, 2017).
ln Qe ln K F
1 ln C e n
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-1
(7)
Where KF and n represent empirical constants of the relative adsorption capacity and
383
adsorption intensity, respectively. The linearly fitted Freundlich isotherm adsorption is shown
384
in the Fig.7c. As shown in Table S2, adsorption is favorable when 0.1 < 1/n< 1 (Li et al.,
385
2018b). Hence, the adsorption to MB on P-MCD is favorable under the experimental
386
conditions owing to the values of 1/n is 0.128.
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The energy relationship described by Temkin equation is that the adsorption heat
388
decreases linearly with the amount of adsorption (Wu et al., 2018). The Temkin isotherm is
389
typically used as given by:
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Qe Bt ln Kt Bt ln Ce
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In the equation, Kt (L mg
-1
(8)
) indicates the equilibrium binding constant, which
corresponds to the maximum binding energy. And compared with the Langmuir parameters,
393
the latter is better to describe the adsorption process. The linearly fitted Temkin isotherm
394
adsorption is shown in Fig.7d, and adsorption isotherm model parameters at different
395
temperatures are illustrated in Table S2.
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Redlich–Peterson model is applied to describe the adsorption isotherm, which belongs to
397
the three parameter equations (van Hullebusch et al., 2004). The Redlich–Peterson isotherm is
398
typically used as given by:
Qe 399
ACe
1 BCe
(9) 14
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In the equation, A, B and β mean the Redlich–Peterson model isotherm constant (L g -1),
401
the model constant (L mg -1) and exponent, respectively. Adsorption characteristic curves of
402
Redlich–Peterson isotherm equation are illustrated in Fig.S6, and its model parameters at
403
different temperatures are demonstrated in Table S2. The Langmuir model (R2=0.9999) is more accurate than the Freundlich model
405
(R2=0.9254) in describing the MB adsorption owing to its superior coefficients. MB
406
adsorption could be regarded as monolayer adsorption, which is in accordance with a few past
407
researcher that has focused on the MB adsorption on imprinted polymers (Li et al., 2014).
408
Table S2 summarizes the values of Qm, KL, KF, n and R2, which indicates that the Langmuir
409
model is more consistent with isotherm data. Moreover, the Qmax of MB adsorbed on P-MCD
410
at different temperatures was shown in Table S2.
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In addition, in order to confirm the function of the polymer layer generated by
412
tetrafluoroterephthalonitrile, we also investigated the adsorption isotherm of Fe3O4@β-CD on
413
MB, and the adsorption isotherm results are shown in Fig. S5c and S5d. Moreover, the
414
adsorption isotherm model parameters of MB adsorption on Fe3O4@β-CD at different
415
temperatures are shown in Table S2. The maximum adsorption capacity of MB adsorbed by
416
Fe3O4@β-CD and P-MCD are 74.79 mg g -1 and 305.8 mg g -1, respectively. The results show
417
that the latter has a higher adsorption capacity than Fe3O4@β-CD, indicating that the high
418
surface area and porous structure of P-MCD increased the adsorption sites, which were
419
conducive to MB adsorption. Meanwhile, the maximum MB adsorption capacity in this work
420
was compared with several other recently reported adsorbents. The comparison results were
421
shown in Table S3 that P-MCD has higher adsorption capacity than other reported adsorbents.
422
This is mainly because the P-MCD contains a porous polymer and a large specific surface
423
area.
424
3.3.4 Adsorption thermodynamics
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To further investigate the spontaneity of the adsorption process, the thermodynamic
426
parameters containing Gibb’s free energy change (∆Gθ), enthalpy change (∆Hθ) and entropy
427
change (∆Sθ) can be obtained as follows:
428
G RT ln K
(10) 15
ACCEPTED MANUSCRIPT 429
ln K
S H R RT
(11)
Where K (L mg -1) indicates the constant of the Langmuir equilibrium, T (K) denotes the
431
temperature, and R represents the molar gas constant, the value of which is 8.314 J mol-1 K-1.
432
The values of ΔHθ and ΔSθ could be enumerated from the slopes and intercepts of the lnKd and
433
1/T Van't Hoff curves, respectively.
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The calculated thermodynamic parameters are shown in Table S4. The negative values of
435
∆Gθ at different temperatures demonstrate that the spontaneity of the adsorption process. The
436
positive values of ∆Hθ at different temperatures indicates that the reaction of P-MCD to
437
adsorb MB is an endothermic reaction, demonstrating that the adsorption was more favorable
438
in higher temperature. The chemical reaction heat between 20.9 KJ mol-1 and 418.4 kJ mol-1
439
is generally considered to be a chemical adsorption process (Zhao et al., 2015). In this work,
440
the value of ∆Hθ was higher than 20.90 kJ mol−1, indicating that the adsorption of MB onto
441
P-MCD was a chemical adsorption process.
442
3.3.5 Applicability of P-MCD
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The adsorption performance of P-MCD on MB was not only discussed, but the
444
expansion of the research on the adsorption of other water pollutants was also performed. The
445
removal efficiency and the maximum adsorption capacity are shown in Table S5. Fig.S7
446
presents a histogram of P-MCD removal efficiency for various water pollutants, which shows
447
that the material possessed a broad range of organic pollutants. The performance showed by
448
developed nanocomposites for adsorbing various organic materials could be ascribed to three
449
interaction, namely, host–guest interaction, π-π stacking interaction and multiple hydrogen
450
bonding. Meanwhile, the high surface area and porous structure of P-MCD increased the
451
number of adsorption sites, which were beneficial to MB adsorption.
452
3.3.6 Desorption and recycling study
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Desorption and regeneration experiments were carried out to investigate the
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recyclability of the P-MCD. MB desorption was conducted using ethanol solution containing
455
5% (V/V) acetic acid. Ethanol solution containing 5% acetic acid was selected in examining
456
recycling study due to acid condition could disrupt both the electrostatic interaction and the 16
ACCEPTED MANUSCRIPT 457
host-guest interaction. As shown in Fig.S8, the removal efficiency remained at 86.35% even
458
after seven cycles. These results indicated that P-MCD not only exhibit higher adsorption
459
capacity for pollutants in wastewater, but also has recyclability in practical applications.
460
3.3.7 Analysis of actual water samples Fig.S9 shows the results of UV-Vis that P-MCD adsorbed in the simulation of the
462
Yellow River water in 10 min. A certain amount of MB, Rh B and malachite green are used to
463
contaminate the actual sample of the Yellow River water. Figure (a), (b), and (c) represent
464
ultraviolet maximum absorption wavelengths of Rh B (554 nm), Malachite green (619 nm),
465
and MB (664 nm), respectively. The absorbance of Malachite green was almost 0 after
466
absorption. The same situation occurred in the absorbance of MB. It is clearly shown in the
467
inset of Fig.S9 that the absorbance of Rh B is only minimal. The removal efficiency of the
468
three dyes after adsorption is presented in Fig.S10. These results imply that the P-MCD has a
469
good prospect in practical applications of organic pollutant adsorption.
470
4. Conclusions
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In summary, a kind of well-defined magnetic β-CD porous polymer nanospheres were
472
successfully prepared for MB extraction via one-pot solvent thermal method. The P-MCD
473
combined the properties of the core (Fe3O4 nanoparticles), which had a rapid magnetic
474
response to material separation, with the surface porous β-CD polymer layer that having the
475
fast kinetics and satisfactory broad adsorption range of organic micro-pollutants. The rapid
476
kinetics of the material could be ascribed to the large specific surface area and numerous of
477
β-CD cavities. Meanwhile, the dispersibility of magnetic nanoparticles enhances the
478
dispersion of the β-CD porous polymer in the aqueous phase, which was beneficial to
479
improve the inclusion adsorption performance and the adsorption process. The results show
480
that P-MCD not only have good recyclability but also have high removal efficiency for
481
pollutants in wastewater. Thus, it is expected that the P-MCD could be a promising adsorption
482
material in environmental remediation.
483
Conflicts of interest
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There are no conflicts to declare. Acknowledgements 17
ACCEPTED MANUSCRIPT The authors would like to express their appreciation for research funding provided by the
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National Natural Science Foundation of China (No.21374045, No.21074049) and the
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National Science Foundation for Fostering Talents in Basic Research of the National Natural
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Science Foundation of China (Grant No. J1103307). In addition, sincere appreciation is also
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expressed to the Electron Microscopy Centre of Lanzhou University for the microscopy and
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microanalysis of our specimens.
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Graphical Abstract
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In this work, we adopted a two-step synthesis strategy to synthesize uniform particle size distribution of β-CD polymer functionalized magnetic nanospheres. Firstly, β-CD was modified on the surface of magnetic nanoparticles to obtain β-CD modified magnetic nanoparticles
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(Fe3O4@β-CD), followed by solvent thermal method for Fe3O4@β-CD, β-CD and tetrafluoroterephthalonitrile monomer was polymerized to
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obtain magnetic β-CD porous polymer nano-spheres. The maximum adsorption capacity of MB for P-MCD was 305.8 mg g −1, which is more
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than Fe3O4@β-CD (71.89 mg g -1). Moreover, the material had a high recovery and good recyclability.
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Figures
Scheme 1 Schematic procedures of fabricating magnetic porous β-CD polymer nano-spheres and procedures of
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MB adsorption and desorption.
Fig.1 TEM image of Fe3O4@β-CD (a, c) and P-MCD (b, d).
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Fig.2 The STEM image of the P-MCD (a), element distribution of Fe-K (b), C-K (c), N-K (d), O-K (e), and F-K
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(f).
Fig.3 Characterization of Fe3O4@β-CD and P-MCD: (a) FT-IR spectra, TGA curves (b), Magnetization curves (c), and XRD spectra (d). The inset of Fig.3c shows the solution of P-MCD in the presence of a magnet.
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P-MCD.
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Fig.4 XPS survey spectra of Fe3O4@β-CD and P-MCD (a), and fine spectra of C 1s (b), O 1s (c) and Fe 2p (d) of
Fig.5 (a) N2 adsorption-desorption isotherms of Fe3O4@β-CD and P-MCD and (b) the size distribution curve.
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Fig.6 Effects of contact time on adsorption of MB onto P-MCD (a), pseudo-second-order kinetic plots (b),
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Elovich kinetic plots (c) and Webber and Morris kinetic models (d).
Scheme 2 Adsorption Mechanism of MB on P-MCD
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Fig.7 Equilibrium adsorption isotherms of P-MCD to MB with the different temperature (a), Langmuir
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adsorption model (b), Freundlich adsorption model (c) and Temkin model (d).
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Highlights
1. Magnetic β-cyclodextrin (β-CD) porous polymer nano-spheres (P-MCD) was
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fabricated by one-pot solvent thermal method. 2. The obtained materials exhibit high adsorption capacity for MB.
3. The adsorption mechanism of the obtained nanospheres on MB is mainly based on
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host-guest interaction, π-π stacking interaction and hydrogen bonding.
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4. P-MCD has excellent removal efficiency for a variety of environmental pollutants.
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5. P-MCD exhibited perfect reusability after a simple ethanol cleaning.