Preparation of highly efficient ion-imprinted polymers with Fe3O4 nanoparticles as carrier for removal of Cr(VI) from aqueous solution

Journal Pre-proof Preparation of highly efficient ion-imprinted polymers with Fe3O4 nanoparticles as carrier for removal of Cr(VI) from aqueous solution

Zhiyong Zhou, Xueting Liu, Minghui Zhang, Jian Jiao, Hewei Zhang, Jian Du, Bing Zhang, Zhongqi Ren PII:

S0048-9697(19)34325-6

DOI:

https://doi.org/10.1016/j.scitotenv.2019.134334

Reference:

STOTEN 134334

To appear in:

Science of the Total Environment

Received date:

23 July 2019

Revised date:

5 September 2019

Accepted date:

5 September 2019

Please cite this article as: Z. Zhou, X. Liu, M. Zhang, et al., Preparation of highly efficient ion-imprinted polymers with Fe3O4 nanoparticles as carrier for removal of Cr(VI) from aqueous solution, Science of the Total Environment (2019), https://doi.org/ 10.1016/j.scitotenv.2019.134334

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© 2019 Published by Elsevier.

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Preparation of highly efficient ion-imprinted polymers with Fe3O4 nanoparticles as carrier for removal of Cr(VI) from aqueous solution Zhiyong Zhou,a Xueting Liu,a Minghui Zhang,a Jian Jiao,a Hewei Zhang,a Jian Du,a Bing Zhang*b and Zhongqi Ren*a a

College of Chemical Engineering, Beijing University of Chemical Technology, No.

College of Mechanical and Electrical Engineering, Beijing University of Chemical

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b

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15, North Third Ring Road East, Beijing 100029, People’s Republic of China.

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Technology, No. 15, North Third Ring Road East, Beijing 100029, People’s Republic

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of China.

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Abstract

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*Email: [email protected]; [email protected]

Fe3O4 magnetic nanoparticles were prepared by hydrothermal synthesis and their

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surface was modified by the sol-gel method. Polymers imprinted with magnetic Cr (VI) were prepared by using Cr2O72− as template ion, 4-vinyl pyridine (4-VP) as monomer, isopropanol as solvent and Fe3O4 as matrix. The effects of solvent type, amount of Cr (VI) addition and volume of crosslinking agent on the adsorption properties of the imprinted polymers were investigated. The polymers were characterized by Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). The adsorption equilibrium was reached within 50 min, and the maximum adsorption capacity was 201.55 mg·g−1. The adsorption 1

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process conformed to the Langmuir model, and the results of kinetic fitting showed that the pseudo-first-order kinetic model applied. In the Cr2O72−/AlF4− and Cr2O72−/CrO42− competitive systems, the imprinted polymer showed good selectivity to the template ions, with relative selectivity factors of 6.91 and 5.99, respectively. When the imprinted polymer was reused 6 times, the adsorption capacity decreased

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by only 8.2%, demonstrating good reusability.

capacity; Adsorption selectivity; Reusability

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1. Introduction

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Keywords: Ion-imprinted polymer; Fe3O4 magnetic nanoparticles; Adsorption

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Chromium is in great demand in industry and has a wide range of uses, but

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chromium-containing wastewater and waste residue pose high risks of pollution.

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While chromium in the ecosystem consists of a mixture of +3 and +6 valence states (Dhal et al., 2013), in industrial wastewater the +6 state dominates, mostly in the form

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of CrO42− and Cr2O72− anions. Chromium is also an essential trace element in the human body, where its main form is the +3 valence state. Although the total content of Cr (III) in the body is just a few milligrams, it is an indispensable part of the skin and many other important organs (Chen et al., 2015). However, Cr (VI) can cause serious harm, being both carcinogenic and around 100 times more toxic than Cr (III), and more absorbable by the body. Cr (VI) can enter through the diet, breathing or contact with the skin, and accumulates in the liver, kidneys and other important organs. Cr (VI) inhaled during the respiratory process can deposit in the lungs, and cause rhinitis, pharyngitis and other forms of inflammation (Wu et al., 2018). Like other heavy metal 2

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elements, the bioaccumulation and continuous intake of chromium jeopardizes the growth of aquatic plants, and ultimately threatens human health through the food chain. As awareness grows of the harm caused by chromium pollution, methods to control this danger have been actively explored. Overall, the main approaches can be

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divided into three categories: chemical precipitation (Barrera-Díaz et al., 2012), bioremediation (Chai et al., 2009) and physical chemistry methods. Hlihor et al. (2016)

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inoculated a glutinous arthrobacterial biofilm onto a pristine polyethylene stent, which

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under acidic conditions reached a maximum Cr (VI) adsorption capacity of 20.37

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mg·g−1. Gherasim et al. (2011) synthesized a polyvinyl alcohol (PVA) / polymer

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inclusion membrane (PIM) with a membrane flux of 27 µmol·m2·s−1 for Cr (VI) and 0

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for all other ions, which could be reused more than 15 times. Adsorption methods, which are firmly established in the field of wastewater treatment, have the advantages

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of high removal capacity, technical simplicity, low price and recyclability. Among the many kinds of adsorbents for chromium removal, the most common is activated carbon. Recently, with the development of technology, many new adsorbents have emerged, such as composite ceramics, carbon nanofibers, ferrihydrite (Kumar et al., 2017) and crosslinked chitosan (Roosen et al., 2016). Ion imprinting technology (IIT) is an offshoot of molecular imprinting technology (MIT) (Yoshikawa et al., 2016; Cecchini et al., 2017; Berghaus et al., 2014; Kupai et al., 2015; Mosbach, 1994). Ion-imprinted materials are widely regarded as “intelligent” because their binding sites show a memory effect toward the target ions 3

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(He et al., 2018). The applications of imprinting technology include wastewater treatment (Ahmed et al., 2018; Díaz de León-Martínez et al., 2018), sensors (Wang et al., 2010; Gui et al., 2018; Zhao et al., 2011), solid phase extraction (Ji et al., 2018) and chromatographic separation (Liang et al., 2017; Wang et al., 2017) among others. At present, the main preparation methods of molecularly imprinted polymers (MIPs)

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are bulk polymerization (Behbahani et al., 2013; Huang and Wang, 2018), suspension and emulsion polymerization (Zhu et al., 2017; Branger et al., 2013), precipitation

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polymerization (Tao et al., 2017; Taghizadeh et al., 2017) and surface imprinting (Pan

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et al., 2016). Zhou et al. (2018) prepared Ni (II)-IIPs (ion-imprinted polymers) by

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bulk polymerization, which showed a maximum adsorption capacity of 86.3 mg·g−1

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for Ni (II). Cai et al. (2014) prepared Pb (II)-IIPs by suspension polymerization with

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methacrylic acid (MAA) and 4-vinyl pyridine (4-VP) as functional monomers. The IIPs showed a high adsorption capacity for Pb2+ when MAA was used as the

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functional monomer, and the polymers doubly imprinted with MAA and 4-VP retained a good adsorption performance for Pb2+ in the presence of the competitive cations Cu2+, Cd2+, Zn2+ and Mn2+. Taghizadeh et al. (2017) prepared a new type of adsorption material by precipitation polymerization of Cr (VI) on the surface of magnetic multi-wall carbon nanotubes (MMWCNTs), using 4-VP as a complex monomer and 2-hydroxyethyl methacrylate (2-HEMA) as a copolymer. Liu et al. (2016) prepared a molecularly imprinted polymer with dual recognition ability by using GO as matrix, MAA and boric acid as functional monomers. It can identify luteolin and separate it efficiently. In recent years, with continued progress in the 4

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technology of ionic imprinting, ion-imprinted materials have been widely studied as efficient adsorbents that can specifically identify target templates. Using mesoporous silica (SBA-15) as the matrix, Liu et al. (2013) prepared a Cr (III)-IIP by a one-step sol-gel method and surface imprinting technology. The maximum adsorption capacity for Cr (III) was 38.50 mg·g−1, roughly twice that of the corresponding NIP

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(non-imprinted polymer). Bayramoglu and Arica (2011) prepared a Cr (VI)-IIP with 4-VP as a functional monomer and 2-HEMA as an auxiliary monomer by bulk

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polymerization. The maximum adsorption capacity for Cr (VI) was 3.31 mmol·g−1.

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The selectivity coefficients in the Cr (VI)/Cr (III) and Cr (VI)/Ni (II) systems were

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13.8 and 11.7.

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Surface imprinting is a technique based on the use of a solid substrate as the

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carrier. Polymerization occurs on the substrate surface, which imprints a layer of a certain thickness. Magnetic ferroferric oxide, silicon dioxide carbon nanotubes and

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graphene are the most commonly used solid substrate materials. Nanomaterials have become a research hotspot due to their special properties like small size effect. However, the particle size of nanomaterial is too small to be separated from the system by conventional separation methods, which has caused great difficulties in the research and application of nanomaterials in the fields of chemistry and medicine. To solve this problem, people thought of combining nanotechnology with magnetic materials to produce magnetic nanomaterials. Magnetic nanomaterials combine the properties of magnetic materials and nanomaterials (Jiang et al., 2018; Chen et al., 2019). With their nanoscale particle size and large specific surface area, together with 5

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magnetic responsiveness, they can be quickly separated from the solution under an external magnetic field. At present, the most widely studied magnetic nanomaterials are based on metal alloys (such as Fe, Co, Ni) and iron oxides (such as Fe3O4). Among the many ways to prepare magnetic nanoparticles, the physical methods are mainly divided into mechanical grinding, freeze-drying, ion sputtering and

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evaporation condensation methods (Hashimoto et al., 2004). These methods offer simplicity, but are offset by several disadvantages such as wide particle size

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distribution, slow preparation and high energy consumption. At present, therefore,

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chemical methods are more commonly used to prepare magnetic nanoparticles. These

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mainly include pyrolysis, co-precipitation (Wu et al., 2011), sol-gel (Selvan et al.,

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2007) and hydrothermal synthesis methods (Gan et al., 2010). Chemical methods are

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able to produce magnetic materials with uniform particle size and strong magnetic properties.

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The materials modified to produce magnetic nanoparticles can be either inorganic or organic. Inorganic materials mainly include elemental metals, metal oxides and nonmetallic oxides. Organic materials include both small-molecule compounds (such as oleic acid and silane coupling agents) and large-molecule compounds (such as PVA, chitosan, and polyethylene glycol (PEG))..mercapto and carboxyl groups, which can interact with the hydroxyl groups on the surface of magnetic nanoparticles to form covalent bonds, thus becoming surface-bound. Zhang et

al.

(2015)

modified

Fe3O4

magnetic

nanoparticles

with

3-glycidoxypropyltrimethoxysilane and polylysine to remove anionic dyes from 6

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aqueous solution. The particle size of Fe3O4 nanoparticles is often very small, and the surface energy is very high. Thus, the thermodynamic properties are extremely unstable and prone to agglomeration, oxidation or self-adsorption. The crystal conditions of the atoms on the surface and inside of the magnetic nanoparticles are not the same, and the difference in their binding ability will produce more unsaturated

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bonds. Hence, the surface of the nanoparticles will produce many active binding sites and easily bond with other atoms in the system. The magnetism of the magnetic

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nanoparticles themselves makes them easier to aggregate. Due to the presence of

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these functional groups on the surface of nanoparticles, they can be modified in a

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variety of ways. The surface modification of Fe3O4 particles can enhance the

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thermodynamic stability and dispersion, reduce the agglomeration among particles,

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change the physical and chemical properties of its surface, and change its compatibility with other components in the system.

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In this work, magnetic Cr (VI)-IIPs were prepared by surface imprinting with Fe3O4 nanoparticles as a matrix. The imprinting process was mainly localized to the magnetic nanoparticles’ surface, and template ion elution proved relatively easy. The prepared polymer had a large specific surface area and fast adsorption rate, as well as magnetic responsiveness. After the adsorption reached equilibrium, the polymer could be quickly separated from the solution under an external magnetic field, and loss of the polymer during the separation process was minimal.

2. Experimental 2.1. Materials 7

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Ferric trichloride (FeCl3), sodium acetate (anhydrous), ethylene glycol, concentrated sulfuric acid, phosphoric acid, potassium dichromate (K2Cr2O7), potassium permanganate (KMnO4) and methylbenzene were supplied by Beijing Chemical Plant (Beijing, China). 3-(Methacryloxy)propyltrimethoxysilane (MPS) was purchased from Beijing Huawei Ruike Chemical Co. Ltd. (Beijing, China). Potassium

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chromate (K2CrO4), methyl alcohol and isopropanol were supplied by Sinopharm Chemical Reagents (Beijing, China). Polyvinylpyrrolidone (PVP) was purchased from

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Shanghai Aladdin Reagent Co., Ltd. (Shanghai, China). Tetraethyl orthosilicate

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(TEOS) was purchased from Tessie Aihua Industry Co., Ltd. (Shanghai, China).

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Potassium tetrafluoroaluminate (KAlF4) was purchased from Shanghai Macklin

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Biochemical Co., Ltd (Shanghai, China). Diphenylcarbazide and acetonitrile were

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purchased from Tianjin Guangfu Technology Development Co. Ltd. (Tianjin, China). 4-VP was purchased from Alfa Aesar. Ethyleneglycol dimethacrylate (EGDMA) and

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azodiisobutyronitrile (AIBN) were supplied by Beijing J&K Scientific Co., Ltd (Beijing, China).

2.2. Analysis and characterizaiton The concentration of Cr (VI) was determined by the diphenylcarbonyl hydrazine spectrophotometric method. The synthesized Cr (VI)-IIPs were characterized by Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). 2.3. Synthesis of Cr (VI)-imprinted polymer 8

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Details of the preparation of magnetic Fe3O4 nanoparticles and the synthesis and modification of Fe3O4@SiO2 magnetic particles can be found in Supporting Information. K2Cr2O7 of a certain mass was accurately weighed and added to a 25 mL conical flask. It was dissolved in 20 mL solvent under magnetic stirring conditions, and then 0.5 mL 4-VP was added. The mixture was stirred for 2 h. Then, a certain

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volume of EGDMA and 40 mg of AIBN were added to the solution, and stirred for another 0.5 h. Modified Fe3O4@SiO2 (0.1 g) was weighed and added into a 50 mL

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two-mouth flask. Then, the above solution was transferred to the flask and nitrogen

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was injected into the flask for 15 min. Then, it was sealed with a nitrogen sphere and

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polymerized in an oil bath at 60 ℃ for 24 h. Then, the solid particles were separated

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from the solution with an external magnetic field. The obtained solid particles were

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eluted with 1 mol·L−1 NaOH solution. After the elution of the Cr (VI)-imprinted solid particles was completed, the solid particles were washed and neutralized with

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deionized water and dried at 60 ℃. The resulting particles are denoted magnetic Cr (VI)-IIP. An NIP was prepared similarly to the above procedure, except that K2Cr2O7 was not added.

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Fig. 1 Schematic of preparation of Cr (VI) ion-imprinted polymer by surface

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imprinting.

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2.4. Adsorption experiments

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The materials’ adsorption ability for Cr (VI) ions was expressed by the adsorption

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capacity (q), which was calculated as follows: (1)

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where q is the equilibrium adsorption capacity of Cr (VI)-IIP or Cr (VI)-NIP (mg·g−1). C0 is the concentration of Cr (VI) ions in the solution before adsorption. Ce is the concentration of Cr (VI) ions in the adsorbent-treated solution (mg·L−1). V is the volume of solution (L). m is the mass of adsorbent (g). The imprinting factor, IF, was used to quantify the difference between the adsorption performance of IIP and NIP. IF was calculated as follows:

IF=

(2)

where qIIP is the adsorption capacity of IIP, and qNIP is the adsorption capacity of NIP. Both adsorption capacities have units of mg·g−1.

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2.5. Selectivity experiments The details of selectivity experiments were described in Supporting Information. The adsorption selectivity of IIP and NIP for Cr (VI) ions was quantified by the partition coefficient Kd, selectivity coefficient k and relative selectivity coefficient k′. These values were calculated as follows: (3)

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Kd = k=

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k’=

(4) (5)

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where M represents Mn (VII), Cr (VI) or Al (III) ions, and kIIP and kNIP are the

3.1.1. FT-IR

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3.1. Characterizations

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3. Results and discussion

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selectivity coefficients of the imprinted and non-imprinted polymers, respectively.

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Firstly, the Fe3O4 nanoparticles, Fe3O4@SiO2 , and the Fe3O4@SiO2 modified by MPS were characterized by FT-IR spectroscopy. As shown in Fig. 2A, the peak at 601.3 cm−1 in spectrum (a) is the absorption of the Fe-O bond in Fe3O4, which moves to the vicinity of 573.6 cm−1 in (b) and (c) after coating with a silica layer. The absorption peak of –OH near 3441.1 cm−1 probably arose from the hydroxyl groups on the surface of Fe3O4 or the water in the sample. The peak at 1634.1 cm−1 is the stretching vibration of the C=O bond. In (b) and (c), the peaks at 476.1 cm −1 and 796.3 cm−1 are Si-O vibration, and that at about 1096.6 cm−1 is the bending vibration of the Si-O-Si bond. Together, these verify that Fe3O4 was successfully covered by a 11

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Fe3O4

（ c）

Fe3O4@SiO2

951.4 796.3

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（ b）

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% Transmittance

Modified Fe3O4@SiO2

（ a）

573.6 476.1 1096.6

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1634.1

4000

3500

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3441.1

3000

2500

2000

1500

1043.8

601.3

1000

500

-1

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Wavenumbers(cm )

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Fig. 2A FT-IR spectra of Fe3O4 (a), Fe3O4@SiO2 (b) and MPS-modified Fe3O4@SiO2 (c).

IIP NIP

（ d）

821.3

% Transmittance

3065.2

1454.7

567.4 478

2950.2 1600.1 1144.8

1728.8

（ e）

4000

3500

3000

2500

2000

1500

1000

500

-1

Wavenumbers(cm )

Fig. 2B FT-IR spectra of imprinted (d) and non-imprinted polymer (e). 12

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Fig. 2B shows the FT-IR spectra of Cr (VI)-IIP and Cr (VI)-NIP. The characteristic peak of the –CH bond can be seen near 2950 cm−1 in (d) and (e). The peak at 1728.8 cm−1 is the absorption of the C=O bond in the EGDMA ester group. The unsaturated C=C bond peaks around 1454.7 and 1417.7 cm−1 presumably come from 4-VP, while those at 3065.2 and 1600.1 cm−1 are the absorption of pyridine ring groups, which together indicate that the functional monomer 4-VP was successfully

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polymerized in the prepared polymer. The peak at 1144.8 cm−1 is characteristic of

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C-O, while that at 758.3–956.5 cm−1 is characteristic of unsaturated hydrocarbons in

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the carbon chain, which come from the 4-VP and EGDMA functional groups. The

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absorption peaks of Fe-O can still be seen in (d) and (e), proving that the

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polymerization reaction proceeded on the surface of Fe3O4.

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3.1.2. XPS

The XPS results of the Fe3O4 nanoparticles and of Fe3O4@SiO2 after coating of

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the silica layer are shown in Fig. 3A. The corresponding elemental analysis is shown in Table 1. Besides the C, O and Fe contents, there were small amounts of Si and Na in the non-silica-coated Fe3O4, which may have come from the raw materials. Specifically, the Na content may be a residue of the sodium acetate used during the preparation of the Fe3O4 nanoparticles. The Fe3O4@SiO2 sample contained C, O, N, Si and Fe, and the contents of O and Si increased significantly after the coating, while the content of Fe decreased, indicating that Fe3O4 was successfully coated by a layer of silica. The trace N content in the sample came from the aqueous ammonia used to adjust the pH. 13

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Fe3O4 Fe3O4@SiO2

（ b）

Na1s N1s

（ a） Fe2p O1s

C1s

1200

1000

800

600

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Si2p

400

0

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Binding Energy/eV

200

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Fig. 3A XPS spectra of Fe3O4 (a) and Fe3O4@SiO2 (b).

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The XPS spectra of Cr (VI)-IIP and NIP are shown in Fig. 3B. The

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corresponding elemental analysis is shown in Table 1. IIP and NIP contained five

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elements, C, O, N, Si and Na. Compared with Fe3O4@SiO2, both samples contained higher contents of C and N after polymerization. The C content mainly came from the

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EGDMA crosslinking process, while the increased N content was mainly a result of polymerization of 4-VP. The content of N in IIP was higher than in NIP, indicating a larger amount of functional monomers and imprinting sites in the former. For this reason, the adsorption performance of IIP was higher than that of NIP, as will be discussed.

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O1s C1s

IIP NIP

Na1s

（ c） N1s

Si2p

1000

800

600

400

200

0

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1200

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（ d）

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Binding Energy (eV)

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Fig. 3B XPS spectra of imprinted (c) and non-imprinted polymer (d).

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Table 1 Element contents of Fe3O4, Fe3O4@SiO2, IIP and NIP

Element content (%)

30.62

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Materials

45.09

——

3.07

17.9

3.32

20.99

49.57

0.92

25.55

2.97

——

74.69

19.86

4.19

0.82

——

0.45

74.15

22.27

2.38

0.79

——

0.4

Fe3O4 Fe3O4@SiO2 IIP NIP

O

N

Si

Fe

Na

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C

3.1.3. TEM The Fe3O4 nanoparticles and the prepared polymer were characterized by TEM. As can be seen from Fig. 4, the average particle size of Fe3O4 was about 200 nm, but the particle size dispersion was undesirably wide, and serious agglomeration occurred. The large specific surface area and high surface energy of Fe3O4 particles result in 15

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poor stability. The particle size of Fe3O4@SiO2, which was prepared by coating Fe3O4 with a layer of silica gel by the sol-gel method, was slightly larger than that of Fe3O4. From the TEM images, it can be seen that the coating is uniform, and the Fe3O4@SiO2 shows clearly reduced agglomeration between particles and enhanced dispersion in water. The morphological features of the IIP, which was produced by

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surface imprinting on the silica gel-coated substrate, were similar to those of the non-imprinted NIP with the Fe3O4 core at the center and a reticular adhesion structure

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on the outside of the imprinted layer. However, the reticular structure of the IIP was

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more complex. In the IIP, the Fe3O4 core took up a smaller proportion of the particle

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size, and the effective surface area was larger, which was expected to allow more

(b)

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(a)

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contact with Cr (VI) ions.

(d)

(c)

Fig. 4 TEM images of Fe3O4 (a), Fe3O4@SiO2 (b), Cr (VI)-IIP (c) and NIP (d). 16

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3.1.4. TGA In any surface-imprinted polymer prepared with Fe3O4 as the matrix, the content of Fe3O4 will greatly affect the magnetic properties. Therefore, herein, the content of magnetic components in the materials was characterized by TGA under a nitrogen atmosphere at a heating rate of 10 ℃·min−1. As can be seen from Fig. 5, Fe3O4 had

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good thermal stability in the range of 40–500 ℃ without obvious weight loss, and the final mass fraction was about 99.5%, which can be considered as the mass of pure

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Fe3O4 nanoparticles. The TGA curve of Fe3O4@SiO2 is similar to that of Fe3O4, with

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a roughly linear weight loss from 40 to 500 ℃. However, the slope of the curve is

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steeper than that of Fe3O4, indicating greater weight loss, and the final mass fraction is

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about 94.7%. Meanwhile, the IIP and the NIP show similar TGA curves. For both

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materials, the curve begins to steepen around 200 ℃, and the majority of the weight loss occurs in the range 300–350 ℃. The final mass fraction of the IIP was 14.3% and

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the final mass fraction of the NIP was 28.8%. Assuming complete organic matter decomposition, the residual masses should be those of the polymerized Fe3O4. The proportion of non-matrix content in the mass of IIP is higher than in NIP, which contributes to its greater adsorption performance, as will be discussed.

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100 90

Fe3O4 Fe3O4@SiO2 IIP NIP

80

Weight(%)

70 60 50 40 30 20

0 0

50

100

150

200

250

300

350

400

450

500

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Temperature(℃ )

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10

-p

Fig. 5 TGA curves of Fe3O4, Fe3O4@SiO2, IIP and NIP.

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3.2. Optimization of preparation conditions for magnetic Cr (VI)-imprinted

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3.2.1. Influence of solvent type

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polymers

Solvents often have a measurable impact on the adsorption performance of

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imprinted polymers. The common solvents can be divided into polar and non-polar. The polar solvents most commonly used include methanol, ethanol, acetonitrile, isopropanol and dimethyl formamide, while the non-polar solvents include chloroform, toluene and acetone. In this study, five typical solvents, methanol, acetonitrile, toluene, isopropanol and acetone, were selected and their effects on the adsorption properties of the prepared polymers were investigated. The order of polarity of these five solvents is acetonitrile > methanol > isopropanol > acetone > toluene. The results showed that the polymerization reaction could not take place when 18

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we used acetone or toluene as solvent. Acetone is volatile, with a boiling point of 56.5 ℃, while polymerization reactions generally need temperatures in excess of 60 ℃. Meanwhile, toluene has too small a polarity, which is not conducive to the polymerization reaction. The adsorption performance of the other three solvents decreased with the increase of polarity, indicating that the strongly polar solvents also

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had an adverse effect on the adsorption performance of the polymer. Therefore,

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isopropanol was selected for subsequent experiments.

-p

120

108.14

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96.51

60

40

20

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0

lP

80

na

q(mg·g-1)

100

111.63

acetonitrile

methanol

isopropanol

Types of solvent

Fig. 6 Effect of solvent type on adsorption performance of imprinted adsorbent for Cr (VI) ions. 3.2.2. Influence of Cr (VI) addition amount In the experiments, 0.01 mmol and 0.02 mmol Cr (VI) were completely dissolved in 20 mL isopropanol. However, when the amount of Cr (VI) addition was increased, insoluble particles appeared in the system. This indicates that at the end of the polymerization reaction, some Cr (VI) remained in the solution without being 19

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involved in the reaction. These unreacted Cr (VI) ions may have hindered the occurrence of polymerization to some extent and thus the adsorption performance of the IIPs (Ren et al., 2014).

140

of

120

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q(mg·g-1)

130

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100 0.00

-p

110

0.02

0.04

0.06

0.08

0.10

lP

Molar mass of Cr(VI)

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Fig. 7 Effect of additive amount of Cr (VI) on adsorption performance of imprinted

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adsorbent for Cr (VI) ions.

3.2.3. Influence of dosage of crosslinking agent The amount of EGDMA affected the degree of polymerization and the final form of the prepared IIPs. When the volume of added EGDMA was lower than 0.4 mL, the surface of the Fe3O4@SiO2 matrix did not change significantly after the polymerization reaction, indicating that the polymerization did not occur or the degree of polymerization was very low. The adsorption capacity of Cr (VI)-IIP was very low when the volume of EGDMA was 0.4 mL. When the volume of EGDMA was increased to 0.5 mL, after 4 hours of polymerization, gray and white particles

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appeared in the system, and the polymer adsorption capacity significantly increased. When the volume of EGDMA was increased stepwise from 0.5 mL to 1.0 mL, the adsorption capacity of the obtained IIP showed an upward trend. This can be attributed to the increased polymerization degree of IIP with larger doses of the crosslinking agent, which enhances the number of surface imprinting sites. However,

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when the volume of EGDMA was further increased to 1.5 mL, large solids appeared in the reaction system, and the adsorption capacity decreased. When an excessive

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amount of crosslinking agent is used, the polymer becomes highly rigid, and the

-p

spatial structure also becomes more complex, which reduces the pore size of the

re

imprinting sites and thus impairs the adsorption of Cr (VI). Therefore, the volume of

lP

EGDMA was selected as 1.0 mL for the subsequent experiments.

na

140

Jo ur

120

-1

q(mg.g )

100

80

60

40

20

0 0.4

0.6

0.8

1.0

1.2

1.4

1.6

Volume of EGDMA(mL)

Fig. 8 Effect of amount of crosslinker on adsorption performance of imprinted adsorbent for Cr (VI) ions.

21

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3.3. Effect of operating conditions on adsorption performance 3.3.1. Effect of adsorbent quantity To obtain the maximum adsorption performance at minimal cost, the effect of the quantity of imprinted adsorbents on the adsorption performance was investigated. The details of the experiments were described in Supporting Information. It can be seen

of

from Fig. 9 that the removal efficiency of Cr (VI) increased gradually when the quantity of IIP was increased. When using 50 mg of IIP, the removal efficiency

ro

reached 95.42%. With greater mass of the adsorbent, more active groups are involved

-p

in the adsorption reaction, and a greater number of Cr (VI) can be adsorbed. When

re

using either 5 or 10 mg of adsorbent, the adsorption capacities were similar, both

lP

exceeding 130 mg·g−1. However, as the mass of the adsorbent continued to increase,

na

the adsorption capacity decreased, eventually falling to 41.71 mg·g−1 at 50 mg. This is attributed to the reduced amount of space between adsorbent particles in the solution

Jo ur

as the mass of adsorbent increases, which reduces the probability of collision between adsorbent particles and Cr (VI) ions, thus lowering the utilization rate of the functional groups in IIP. Thus, to maximize the adsorption capacity for Cr (VI), the mass of adsorbent was set as 10 mg for further study.

22

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100

q Removal effiency

140

90 80 70

q(mg·g-1)

100

60 80

50

60

40 30

40

Removal efficiency(%)

120

20

of

20 0 10

20

30

40

0

50

ro

0

10

-p

Adsorbent dose(mg)

re

Fig. 9 Effect of adsorbent dose on adsorption performance of imprinted adsorbent for

3.3.2 Effect of pH

lP

Cr (VI) ions.

na

The pH of the solution had a significant effect on the adsorption performance of

Jo ur

Cr (VI)-IIP and Cr (VI)-NIP. The details of the experiments were described in Supporting Information. As shown in Fig. 10, when the pH of K2Cr2O7 solution increased from 1.5 to 2.0, the adsorption capacity of IIP and NIP increased. However, when the pH was raised further from 2.0 to 4.0, the adsorption capacity of the two decreased significantly. This is related to the pH dependence of the different forms in which Cr (VI) exists in solution. As shown in Fig. S1, the main forms of Cr (VI) in solution are Cr2O72−, CrO42−, HCrO4− and H2CrO4 (Rakhunde et al., 2012). When the pH of the solution is less than 1, the main form of Cr (VI) is H2CrO4. Therefore, the concentration of Cr (VI) in ionic form is low, and the binding force between Cr (VI)

23

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and the pyridine ring in 4-VP is weak. At pH between 1.0 and 6.0, Cr (VI) mainly exists as Cr2O72− and HCrO4−. The degree of protonation of N atoms in the pyridine ring is highest at pH 2.0, which is also the pH at which the adsorption of Cr (VI) on the polymer is maximized. However, as the pH continues to increase, the degree of protonation of N atoms is reduced, and the binding of Cr (VI) with Cr2O72− and

of

HCrO4− is weakened, so the amount of adsorption is gradually decreased.

ro

140

re

80 60

lP

q(mg·g-1)

100

40

na

20 0

IIP NIP

-p

120

2.0

2.5

3.0

3.5

4.0

pH

Jo ur

1.5

Fig. 10 Effect of pH on adsorption performance of ion-imprinted and non-imprinted adsorbent for Cr (VI).

3.3.3. Adsorption isotherms The isothermal adsorption curves of Cr(VI)-IIP and Cr(VI)-NIP provide important information on the process of Cr(VI) adsorption by those materials. The details of the adsorption isotherm investigation were described in Supporting Information. As shown in Fig. 11, when the Cr (VI) concentration of the solution increased from 10 mg·L−1 to 200 mg·L−1, the adsorption capacity of both IIP and NIP 24

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increased rapidly. However, when the concentration of Cr (VI) was further increased, the gain in adsorption capacity of both started to slow down. At concentrations exceeding 1600 mg·L−1, the adsorption capacity of IIP and NIP remained essentially constant, showing that adsorption equilibrium had been reached.

IIP NIP

of

200

ro

100

-p

q(mg·g-1)

150

0 0

200

400

lP

re

50

600

800

1000

1200

1400

1600

1800

2000

na

Initial concentration

Jo ur

Fig. 11 Effect of Cr (VI) concentration on the adsorption performance of adsorbents. Then, the Langmuir and Freundlich models were solved in order to determine which was a better fit for the data of the adsorption of Cr (VI) on IIP and NIP. (6) (7) where Ce (mg·L−1) represents the concentration of Cr (VI) in the solution at adsorption equilibrium, qe (mg·g−1) and qmax (mg·g−1) are the equilibrium adsorption capacity and theoretical maximum adsorption capacity, respectively, KL is the Langmuir isothermal constant, and KF (with units of mg1−(1/n)·L1/n·g−1) and n are the

25

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Freundlich constants. As shown in Fig. S2 and Table 2, the multiple correlation coefficients squared (R2) of the IIP and NIP for the Langmuir model (0.9750, 0.9877) are better than those for the Freundlich model (0.8239, 0.8197) in describing the adsorption process. This shows that the adsorption of Cr (VI) was a uniform and single-layer process.

of

References

Langmuir model Adsorbents

IIP

263.85

0.006886

NIP

169.20

0.01002

KF

R2

0.9750

2.63

14.249

0.8239

0.9877

2.90

13.1484

0.8197

lP

na

3.3.4. Kinetics of adsorption

Freundlich model

n

re

KL

-p

R2

qmax

ro

Table 2 Parameters of Langmuir and Freundlich isotherm models.

The details of the adsorption kinetics investigation were described in Supporting

Jo ur

Information. As shown in Fig. 12, the quantity of Cr (VI) adsorbed by IIP grew rapidly in the first 20 min, then the adsorption slowed down between 20 and 50 min. The adsorption capacity remained essentially unchanged after 50 min and tended to be equilibrium. In the initial stage of adsorption, a large number of imprinting sites were available on the surface of the adsorbent, so the adsorption was relatively fast. With the passage of time, the number of imprinting sites on the polymer surface that remained unoccupied by Cr (VI) gradually decreased. Over time, both the concentration of Cr (VI) in the solution and the adsorption force also decreased, the latter sharply. Therefore, the increase of the amount of adsorbed Cr (VI) continually 26

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slowed, and finally the adsorption essentially reached saturation.

140 120

q(mg·g-1)

100 80 60

of

40

0

10

20

30

40

ro

20

50

60

70

-p

Time(min)

re

Fig. 12 Effect of time on the adsorption performance of imprinted adsorbent for Cr

lP

(VI) ions.

na

To further explore the mechanism controlling the adsorption process, chemical reaction rate and other factors, the experimental kinetic results were fitted by

Jo ur

pseudo-first-order and pseudo-second-order kinetic equations: (8) (9)

where qt and qe (mg·g−1) are the amount of chromium ions adsorbed at adsorption time t and when adsorption reaches equilibrium, respectively. k1 (min−1) and k2 (g·min−1·mg−1) are the adsorption rate constants of first-order and second-order kinetics, respectively. The results are shown in Figs. S3A, S3B and Table 3. The R2 values using the pseudo-first-order and pseudo-second-order models were very close, but the 27

Journal Pre-proof pseudo-first-order model predicted an equilibrium adsorption of 129.36 mg·g−1, which is very close to the experimental result of 131.40 mg·g−1. Therefore, the adsorption process conforms to the pseudo-first-order kinetic model. Table 3 Results of pseudo-first- and second-order models. pseudo- first- order model

131.40

qe,c

k1

R2

129.36

0.00585

0.9769

qe,c 163.93

k2

R2

0.00041

0.9705

ro

100

qe,exp

of

C0

pseudo -second-order model

-p

The comparison of adsorption performances of prepared Cr (VI)-IIP in this work with other adsorbents reported previously in the literature is listed in Table 4.

re

Table 4 Comparison of adsorption performances of various adsorbents for Cr(VI). Equilibrium time

lP

Adsorbents

Qmax (mg.g-1)

References

360

21.34

Wang et al., 2010

IIP 4-VP/HEMA

40

172.12

Bayramoglu et al., 2011

Kapok-polyaniline

~90

65.66

Zheng et al., 2012

Commercial activated carbon

~100

15.45

Kouakou et al., 2013

NH2-polyacrylonitrile

90

156.0

Avila et al., 2014

Alginate-polyaniline

60

75.82

Karthik et al., 2015

Arthrobacter viscosus

-

20.37

Hlihor et al., 2016

MMWCNTs-IIPs

30

56.1

Taghizadeh et al., 2017

Fe3O4-IIPs

50

201.55

This work

Jo ur

Carbon black

na

(min)

3.3.5 Selectivity of adsorption 28

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Compared with other adsorption materials, IIPs have the advantage that the template ions are matched with the imprinted holes, so that they can specifically identify the template ions. Experiments were performed using AlF4− and CrO42− as the competitive ions of Cr2O72− to investigate the adsorption selectivity of IIP and NIP. Because the Cr ions in both CrO42− and Cr2O72− are in the +6 valence state, their respective concentrations cannot be determined in a mixed solution. Therefore, the

of

adsorption selectivity of Cr2O72− relative to CrO42− was studied in a single-solute

ro

solution with a Cr (VI) concentration of 100 mg·L−1, while the adsorption selectivity

-p

of Cr2O72− relative to AlF4- was studied in a mixed solution with the same

re

concentration of Cr2O72−.

lP

As can be seen from Table 5, for both the Cr2O72−/AlF4− and Cr2O72−/CrO42−

na

systems, the selectivity coefficients were greater than 1, indicating that the adsorbents had high adsorption selectivity for Cr (VI) ions in the form of Cr2O72−. However, the

Jo ur

Kd value of IIP was much higher than that of NIP, and the relative selectivity coefficient k′ was also very high, indicating that both the adsorption performance and selectivity of IIP for Cr (VI) ions in Cr2O72− were better than that of NIP. Table 5 Selective adsorption of Cr (VI) from binary metal ion solutions. Kd (mL·g-1) Metals

Adsorbents

k Kd(Cr)

Kd(X)

Imprinted

2508.73

54.13

46.35

Non-imprinted

692.48

103.27

6.71

Cr2O72-/AlF4-

k’

6.91

29

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Imprinted 2-

3084.23

174.52

17.67

2-

Cr2O7 /CrO4

5.99 Non-imprinted

1901.45

644.56

2.95

3.4. Reusability To test the reusability of the imprinted polymer, it was desorbed with NaOH solution and then reused to adsorb Cr (VI), the process being repeated six times. As

of

can be seen from Fig. 13, the adsorption capacity of IIP was 132.56 mg·g−1 at the

ro

initial adsorption cycle. After six cycles of regeneration, the adsorption of the imprinted material was only 8.2% lower than that of the first cycle, with very small

-p

decreases between successive reuses. These results show that the imprinted polymer is

140

132.56

127.52

2

3

130.62

125.97

124.42

121.71

4

5

6

Jo ur

120

na

lP

decrease in adsorption performance.

re

stable in structure and properties, and can be reused multiple times without significant

q(mg·g-1)

100

80 60 40 20

0 1

Times of regeneration

Fig. 13 Regeneration of imprinted adsorbent for Cr (VI) ion removal.

4. Summary and Conclusions 30

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Fe3O4 nanoparticles were prepared by hydrothermal synthesis, and subjected to surface modification. Cr (VI)-IIPs were prepared by the surface imprinting method. The solvent conditions, amount of template ion addition and amount of crosslinking agent were optimized. The optimized preparation conditions are as follows: 20 mL isopropanol as solvent, 0.01 mmol Cr (VI), and 1.0 mL EGDMA as crosslinking agent.

of

The Cr (VI)-imprinted polymer was characterized by TEM, FT-IR, TGA and XPS. The effects of IIP mass and solution pH on the adsorption performance were

ro

investigated. 10 mg was selected as the suitable addition of Cr (VI)-IIP adsorbent for

-p

further study. With the increase of pH value, the adsorption capacity of IIP showed a

re

trend of first increasing and then decreasing. The optimal pH value was 2.0.

lP

Adsorption isotherm experiments showed that the equilibrium adsorption capacity

na

was 201.55 mg·g−1. Through kinetic fitting, it was found that the process was more consistent with the Langmuir model, indicating monomolecular adsorption. Kinetic

Jo ur

experiments showed that the adsorption equilibrium could be reached within 50 min. The theoretical maximum adsorption capacity calculated by the pseudo-first-order kinetic model is 129.36 mg·g−1, which is close to the experimental result of 131.40 mg·g−1. The adsorption selectivity of IIP to Cr (VI) in the form of Cr2O72− in the presence of competitive ions (AlF4− and CrO42−) was investigated, and the imprinted polymers showed good selectivity in the Cr2O72−/AlF4− and Cr2O72−/CrO42− systems, with relative selectivity coefficients of 6.91 and 5.99. The results of the reusability experiment showed that the adsorption capacity of the imprinted polymer decreased by only 8.2% after six reuses, indicating that the prepared adsorbent had a stable 31

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adsorption performance and could be reused multiple times.

Acknowledgments We thank Leo Holroyd, PhD, from Liwen Bianji, Edanz Group China (www.liwenbianji.cn/ac), for editing the English text of a draft of this manuscript. This work was supported by the National Natural Science Foundation of China

of

(21576010, 21606009, U1607107 and U1862113), Beijing Natural Science Foundation (2172043) and Big Science Project from BUCT (XK180301). The authors

-p

References

ro

gratefully acknowledge these grants.

re

Ahmed, M.A., Abdelbar, N.M., Mohamed, A.A., 2018. Molecular imprinted

lP

chitosan-TiO2 nanocomposite for the selective removal of Rose Bengal from

na

wastewater. Int. J. Biol. Macromol. 107, 1046-1053. Barrera-Díaz, C.E., Lugo-Lugo, V., Bilyeu, B., 2012. A review of chemical,

Jo ur

electrochemical and biological methods for aqueous Cr (VI) reduction. J. Hazard. Mater. 223-224, 1-12.

Bayramoglu, G., Arica, M.Y., 2011. Synthesis of Cr (VI)-imprinted poly (4-vinyl pyridine-co-hydroxyethyl methacrylate) particles: its adsorption propensity to Cr (VI). J. Hazard. Mater. 187, 213-221. Behbahani, M., Bagheri, A., Taghizadeh, M., Salarian, M., Sadeghi, O., Adlnasab, L., Jalali, K., 2013. Synthesis and characterisation of nano structure lead (II) ion-imprinted polymer as a new sorbent for selective extraction and preconcentration of ultra trace amounts of lead ions from vegetables, rice, and fish samples. Food 32

Journal Pre-proof

Chem. 138, 2050-2056. Berghaus, M., Mohammadi, R., Sellergren, B., 2014. Productive encounter: molecularlyimprinted nanoparticles prepared using magnetic templates. Chem. Commun. 50, 8993–8996. Branger, C., Meouche, W., Margaillan, A., 2013. Recent advances on ion-imprinted polymers. React. Funct. Polym. 73, 859-875.

of

Cai, X.Q., Li, J.H., Zhang, Z., Yang, F.F., Dong, R.C., Chen, L.X., 2014. Novel Pb2+

ro

ion imprinted polymers based on ionic interaction via synergy of dual functional

-p

monomers for selective solid-phase extraction of Pb2+ in water samples. ACS Appl.

re

Mater. Inter. 6, 305-313.

lP

Cecchini, A., Raffa, V., Canfarotta, F., Signore, G., Piletsky, S., Macdonald, M.P.,

na

Cuschieri, A., 2017. In Vivo recognition of human vascular endothelial growth factor by molecularly imprinted polymers. Nano Lett. 17, 2307-2312.

Jo ur

Chai, L.Y., Huang, S.H., Yang, Z.H., Peng, B., Huang, Y., Chen, Y.H., 2009. Cr (VI) remediation by indigenous bacteria in soils contaminated by chromium-containing slag. J. Hazard. Mater. 167, 516-522. Chen, X.J., Huang, G., An, C.J., Feng, R.F., Yao, Y., Zhao, S., Huang, C., Wu, Y.H., 2019. Plasma-induced poly (acrylic acid)-TiO2 coated polyvinylidene fluoride membrane for produced water treatment: Synchrotron X-Ray, optimization, and insight studies. J. Clean. Prod. 227, 772-783. Chen, Y.M., Dong, Y.Q., Wu, H., Chen, C.Q., Chi, Y.W., Chen, G.N., 2015. Electrochemiluminescence sensor for hexavalent chromium based on the graphene 33

Journal Pre-proof

quantum dots/peroxodisulfate system. Electrochim. Acta 151, 552-557. Dhal, B., Thatoi, H.N., Das, N.N., Pandey, B.D., 2013. Chemical and microbial remediation

of

hexavalent

chromium

from

contaminated

soil

and

mining/metallurgical solid waste: A review. J. Hazard. Mater. 250–251, 272-291. Díaz

de

León-Martínez,

L.,

Rodríguez-Aguilar,

M.,

Ocampo-Pérez,

R.,

of

Gutiérrez-Hernández, J.M., Díaz-Barrigal, F., Batres-Esquivel, L., Flores-Ramírez, R., 2018. Synthesis and evaluation of a molecularly imprinted polymer for the

ro

determination of metronidazole in water samples. B. Environ. Contam. Tox. 100, 1-7.

-p

Gan, N., Yang, X., Xie, D.H., Wu, Y.Z., Wen, W.G., 2010. A disposable

re

organophosphorus pesticides enzyme biosensor based on magnetic composite

lP

nano-particles modified screen printed carbon electrode. Sensors-Basel 10, 625–638.

na

Gherasim, C.V., Bourceanu, G., Olariu, R.I., Arsene, C., 2011. A novel polymer inclusion membrane applied in chromium (VI) separation from aqueous solutions. J.

Jo ur

Hazard. Mater. 197, 244-253.

Gui, R.J., Jin, H., Guo, H.J., Wang, Z.H., 2018. Recent advances and future prospects in molecularly imprinted polymers-based electrochemical biosensors. Biosens. Bioelectron. 100, 56-70. Hashimoto, N., Hashimoto, T., Nasu, H., Kamiya, K., 2004. Preparation of silver thin films consisting of nano-sized particles by the evaporation-condensation method and its Linear and nonlinear optical properties. J. Ceram. Soc. Jap. 112, 204-209. He, J.N., Shang, H.Z., Zhang, X., Sun, X.R., 2018. Synthesis and application of ion imprinting polymer coated magnetic multi-walled carbon nanotubes for selective 34

Journal Pre-proof

adsorption of nickel ion. Appl. Surf. Sci. 428, 110-117. Hlihor, R.M., Figueiredo, H., Tavares, T., Gavrilescu, M., 2016. Biosorption potential of dead and living Arthrobacter viscosus biomass in the removal of Cr (VI): Batch and column studies. Process Saf. Environ. 108, 44-56. Huang, Y., Wang, R., 2018. Review on fundamentals, preparations and applications of

of

imprinted polymers. Curr. Org. Chem. 22, 1600-1618. Ji, W.H., Sun, R.H., Geng, Y.L., Liu, W., Wang, X., 2018. Rapid, low temperature

ro

synthesis of molecularly imprinted covalent organic frameworks for the highly

-p

selective extraction of cyano pyrethroids from plant samples. Anal. Chim. Acta 1001,

re

179-188.

lP

Jiang, D.N., Huang, D.L., Lai, C., Xu, P., Zeng, G.M., Wan, J., Tang, L., Dong, H.R.,

na

Huang, B.B., Hu, T.J., 2018. Difunctional chitosan-stabilized Fe/Cu bimetallic nanoparticles for removal of hexavalent chromium wastewater. Sci. Total Environ.

Jo ur

644, 1181-1189.

Kumar, A.A., Som, A., Longo, P., Sudhakar, C., Bhuin, R.G., Gupta, S.S., Sankar, M.U., Chaudhary, A., Kumar, R., Pradeep, T., 2017. Confined metastable 2-line ferrihydrite for affordable point-of-use arsenic-free drinking water. Adv. Mater. 29, 1604260. Kupai, J., Rojik, E., Huszthy, P., Szekely, G., 2015. Role of chirality and macroring in imprinted polymers with enantiodiscriminative power. ACS Appl. Mater. Inter. 7, 9516–9525. Liang, G.H., Zhai, H.Y., Huang, L., Tan, X.C., Zhou, Q., Yu, X., Lin, H.D., 2017. 35

Journal Pre-proof

Synthesis of carbon quantum dots-doped dummy molecularly imprinted polymer monolithic column for selective enrichment and analysis of aflatoxin B1 in peanut. J. Pharmaceut. Biomed. 149, 258-264. Liu, S.C., Pan, J.M., Zhu, H.J., Pan, G.Q., Qiu, F.X., Meng, M.J., Yao, J.T., Yuan, D., 2016. Graphene oxide based molecularly imprinted polymers with double recognition

of

abilities: the combination of covalent boronic acid and traditional non-covalent monomers. Chem. Eng. J. 290, 220-231.

ro

Liu, Y., Meng, X.G., Han, J., Liu, Z.C., Meng, M.J., Wang, Y., Chen, R., Tian, S.J.,

-p

2013. Speciation, adsorption and determination of chromium (III) and chromium (VI)

re

on a mesoporous surface imprinted polymer adsorbent by combining inductively

na

36, 3949-3957.

lP

coupled plasma atomic emission spectrometry and UV spectrophotometry. J. Sep. Sci.

Mosbach, K., 1994. Molecular imprinting. Trends Biochem. Sci. 19, 9-14.

Jo ur

Pan, J.M., Yin, Y.J., Ma, Y., Qiu, F.X., Yan, Y.S., Niu, X.H., Zhang, T., Bai, X., 2016. Hierarchical porous molecule/ion imprinted polymers with double specific binding sites: Combination of pickering HIPEs template and pore-filled strategy. Chem. Eng. J. 301, 210−221. Karthik, R., Meenakshi, S., 2015. Removal of Cr (VI) ions by adsorption onto sodium alginate-polyaniline nanofibers. Int. J. Biol. Macromol. 72, 711–717. Rakhunde, R., Deshpande, L., Juneja, H.D., 2012. Chemical speciation of chromium in water: a review. Criti. Rev. Env. Sci. Tec. 42, 776-810. Ren, Z.Q., Kong, D.L., Wang, K.Y., Zhang, W.D., 2014. Preparation and adsorption 36

Journal Pre-proof

characteristics of an imprinted polymer for selective removal of Cr(VI) ions from aqueous solutions. J. Mater. Chem. A 2, 17952-17961. Roosen, J., Van Roosendael, S., Borra, C.R., Van Gerven, T., Mullens, S., Binnemans, K., 2016. Recovery of scandium from leachates of Greek bauxite residue by adsorption on functionalized chitosan-silica hybrid materials. Green Chem. 18,

of

2005–2013. Selvan, S.T., Patra, P.K., Ang, C.Y., Ying, J.Y., 2007. Synthesis of silica-coated

-p

Angew. Chem. Int. Ed. 46, 2448–2452.

ro

semiconductor and magnetic quantum dots and their use in the imaging of live cells.

re

Taghizadeh, M., Hassanpour, S., 2017. Selective adsorption of Cr (VI) ions from

lP

aqueous solutions using a Cr(VI)-imprinted polymer supported by magnetic multiwall

na

carbon nanotubes. Polymer 132, 1–11.

Tao, H.C., Gu, Y.H., Liu, W., Huang, S.B., Cheng, L., Zhang, L.J., Zhu, L.L., Wang,

Jo ur

Y., 2017. Preparation of palladium (II) ion-imprinted polymeric nanospheres and its removal of palladium (II) from aqueous solution. Nanoscale Res. Lett. 12, 583. Kouakou, U., Ello, A.S., Yapo, J.A., Trokourey, A., 2013. Adsorption of iron and zinc on commercial activated carbon, J. Environ. Chem. Ecotox. 5, 168–171. Wang, X.H., Dong, Q., Ying, L.L., Chi, S.S., Lan, Y.H., Huang, Y.P., Liu, Z.S., 2017. Enhancement of selective separation on molecularly imprinted monolith by molecular crowding agent. Anal. Bioanal. Chem. 409, 1-11. Wang, Y.T., Zhang, Z.Q., Jain, V., Yi, J.J., Mueller, S., Sokolov, J., Liu, Z.X., Levon, K., Rigas, B., Rafailovich, M.H., 2010. Potentiometric sensors based on surface 37

Journal Pre-proof

molecular imprinting:Detection of cancer biomarkers and viruses. Sensor. Actuat. B-Chem. 146, 381-387. Wu, S., Sun, A.Z., Zhai, F.Q., Wang, J., Xu, W.H., Zhang, Q., Volinsky, A.A., 2011. Fe3O4, magnetic nanoparticles synthesis from tailings by ultrasonic chemical co-precipitation. Mater. Lett. 65, 1882-1884.

of

Wu, S.P., Dai, X.Z., Cheng, T.T., Li, S.J., 2018. Highly sensitive and selective ion-imprinted polymers based on one-step electrodeposition of chitosan-graphene

ro

nanocomposites for the determination of Cr(VI). Carbohyd. Polym. 195, 199-206.

-p

Wang, X.S., Chen, L.F., Li, F.Y., Chen, K.L., Wan, W.Y., Tang, Y.J., 2010. Removal of

re

Cr (VI) with wheat-residue derived black carbon: reaction mechanism and adsorption

lP

performance. J. Hazard. Mater. 175, 816–822.

na

Zheng, Y., Wang, W.B., Huang, D.J., Wang, A.Q., 2012. Kapok fiber

154-161.

Jo ur

oriented-polyaniline nanofibers for efficient Cr(VI) removal. Chem. Eng. J. 191,

Yoshikawa, M., Tharpa, K., Dima, S.O., 2016. Molecularly imprinted membranes: past, present, and future. Chem. Rev. 116, 11500–11528. Zhang, Y.R., Su, P., Huang, J., Wang, Q.R., Zhao, B.X., 2015. A magnetic nanomaterial modified with poly-lysine for efficient removal of anionic dyes from water. Chem. Eng. J. 262, 313–318. Zhao, P.N., Yan, M., Zhang, C.C., Peng, R.X., Ma, D.S., Yu, J.H., 2011. Determination of glyphosate in foodstuff by one novel chemiluminescence-molecular imprinting sensor. Spectrochim. Acta A 78, 1482-1486. 38

Journal Pre-proof

Zhou, Z.Y., Kong, D.L., Zhu, H.Y., Wang, N., Wang, Z., Wang, Q., Liu, W., Li, Q.S., Zhang, W.D., Ren, Z.Q., 2018. Preparation and adsorption characteristics of an ion-imprinted polymer for fast removal of Ni (II) ions from aqueous solution. J. Hazard. Mater. 341, 355-364. Zhu, F., Li, L.W., Xing, J.D., 2017. Selective adsorption behavior of Cd (II) ion polymers

synthesized

by

microwave-assisted

of

imprinted

inverse

emulsion

polymerization: Adsorption performance and mechanism. J. Hazard. Mater. 321,

Jo ur

na

lP

re

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ro

103-110.

39

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Graphical abstract

40

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Highlights

• A magnetic ion-imprinted polymer was prepared for selective adsorption of Cr(VI). • Polymers have relatively fast adsorption kinetics and high adsorption capacity.

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• Polymers show highly selectivity for Cr(VI) in presence of other

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competitive ions.

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• Magnetic Cr(VI) ion-imprinted polymers show very high stability and

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reusability.

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