Interfacially crosslinked β-cyclodextrin polymer composite porous membranes for fast removal of organic micropollutants from water by flow-through adsorption

Journal Pre-proof Interfacially crosslinked ␤-cyclodextrin polymer composite porous membranes for fast removal of organic micropollutants from water by flow-through adsorption Zhanghui Wang, Shuang Guo, Bin Zhang, Jinchao Fang, Liping Zhu

PII:

S0304-3894(19)31141-0

DOI:

https://doi.org/10.1016/j.jhazmat.2019.121187

Reference:

HAZMAT 121187

To appear in:

Journal of Hazardous Materials

Received Date:

16 August 2019

Revised Date:

6 September 2019

Accepted Date:

7 September 2019

Please cite this article as: Wang Z, Guo S, Zhang B, Fang J, Zhu L, Interfacially crosslinked ␤-cyclodextrin polymer composite porous membranes for fast removal of organic micropollutants from water by flow-through adsorption, Journal of Hazardous Materials (2019), doi: https://doi.org/10.1016/j.jhazmat.2019.121187

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Interfacially

crosslinked

β-cyclodextrin

polymer

composite

porous

membranes for fast removal of organic micropollutants from water by flow-through adsorption

Zhanghui Wang, Shuang Guo, Bin Zhang, Jinchao Fang, Liping Zhu*

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MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, China

Corresponding author: Pro. L. P. Zhu

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E-mail: [email protected]

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Highlights

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1. β-CD was crosslinked on porous membranes used for removal of organic micropollutants. 2. The typical membrane showed high adsorption capacity with 100% of removal efficiency.

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3. The membranes exhibited stable treating capacity under acidic or neutral conditions. 4. The treating capacity was greatly enhanced by adding salts into pollutant test solution.

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5. The used membranes could be fully regenerated by ethanol cleaning.

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Abstract

Persistent organic micropollutants have seriously damaged aquatic ecological equilibrium and affected human health. Conventional adsorbents are limited due to slow adsorption rate. Therefore, it’s significant to integrate adsorbent into porous membrane to develop a highly efficient continuous filtration method for water purification. Herein, βcyclodextrin polymer (β-CDP) composite porous membranes were prepared via convenient

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interfacial cross-linking. The membranes combined the adsorption ability of β-CDP and the convective mass transport process of filtration membrane to quickly remove contaminants from water by flow-through adsorption. In optimized preparation conditions, the composite

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membrane exhibited a 100% of removal efficiency towards bisphenol A and a high treating capacity up to 440 mg m-2. The treating capacity kept nearly unchanged in acidic and neutral

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pH condition, while increased greatly with the addition of salts due to the salting-out effect. Also, the membrane could completely remove pollutants with ultrahigh flux up to 2500 L·m-

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·h-1. In addition, the used membranes were fully regenerated by mild ethanol cleaning.

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Keywords: β-cyclodextrin polymers; Porous membranes; Flow-through adsorption; Organic

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micropollutants

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1. Introduction During the past decades, man-made persistent organic micropollutants have penetrated into aquatic ecosystems and seriously affected the human health[1,2]. According to the reported literature, it’s detected that there are various organic pollutants in worldwide rivers and oceans[3,4]. These organic pollutants enter into human body by drinking and cause diseases like cancers, endocrine disorders and teratogenesis[5–7]. As a result, water purification has become an urgent global issue and it is significant to develop a new method

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to rapidly remove contaminants from water. Several treatment techniques are available to remove organic pollutants in water, but all of them suffer from deficiencies. The activated sludge technique is a biochemical process for

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disposing of conventional organics but has difficulty in resolving persistent organic pollutants with poor biodegradability[8]. Advanced oxidation is a chemically intensive process

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involving the addition of extra chemicals and may introduce secondary pollutants into

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water[9]. Nanofiltration (NF) membrane separation can remove some organic molecules, but this technique often requires a high filtration pressure and thus suffers from high energy consumption[10,11]. Adsorption is the most widely used water purification method due to its

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simplicity and cost efficiency[12,13]. Adsorbent is the key material in the adsorption technique.

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β-cyclodextrin (β-CD) has become a promising candidate for adsorbing organic

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micropollutants due to its virtues of green ingredient, specific affinity[14,15], convenient design[16,17] and easy regeneration[18,19]. β-CD can form inclusion complexes with specific organic micropollutants by the host-guest interaction, which is due to the size/shape match and the binding forces between the host β-CD and guest molecules such as hydrophobic interactions, Van der Waals interactions and hydrogen bonding[20]. Currently, most studies on β-CD based adsorbent are focused on the synthesis of insoluble cross-linked β-CD polymers (β-CDP) (in the form of powder), which exhibit slow removal rate due to the 3

limited intraparticle diffusion[21–28]. Also, the recovery of used β-CDP requires extra filtration procedure, which is energy-consuming[29]. In addition, the adsorption is often conducted in batch experiments, which hamper the continuous operation[30,31]. What’s more, packed columns face the disadvantage of being compacted and then it needs larger pressure to realize larger permeability[29]. To develop a consecutive highly efficient water purification process, it’s necessary to integrate β-CD into porous membrane to construct a β-CD based porous membrane. The β-CD based porous membrane combines the adsorption ability of β-

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CD and the convection mass transport process of filtration membrane to achieve fast removal of contaminants from water. However, to the best of our knowledge, little work has been done on the β-CD based porous membrane used for permeating adsorption of pollutants. Therefore,

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it is significant to explore a convenient method to construct the β-CD based porous membrane. Herein, the β-CD based porous membranes were prepared via convenient interfacial

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cross-linking on microfiltration membrane support. Water soluble β-CDP with high molecular weight was firstly synthesized and then reacted with trimesoyl chloride (TMC) to obtain the

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β-CDP composite porous membrane. The embedded numerous β-CDPs in membrane pores offered abundant adsorption sites to achieve highly efficient removal of organic

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micropollutants from water. The relationship of membrane preparation, structure and adsorption property was investigated in detail and the preparation parameters were optimized.

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Additionally, the influences of solution chemistry (pH, ionic strength) on adsorption ability of

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the membrane were studied to enhance the effectiveness of decontamination in practical application. The regeneration ability of the membranes was evaluated by mild ethanol filtration. It’s expected that this composite membrane could efficiently remove organic micropollutants from water by flow-through adsorption.

2. Experimental section 2.1 Materials 4

Commercially available nylon microfiltration (MF) membranes (average pore size = 0.45 μm) with spongy porous structure were supplied by Shanghai Xingya Purification Material Company (Shanghai, China). β-CD, hydrochloric acid (HCl, ~ 36%) and sodium hydroxide (NaOH, > 99%) were purchased from Sinopharm Group Chemical Reagent Co. Ltd. Epichlorohydrin (EPI) was provided by Aladdin Reagent Co., Ltd. TMC was purchased from Shanghai Kaisai Chemical Co., Ltd. China. Bisphenol A (BPA, > 99%) was obtained from Energy Chemical Co. Ltd. All reagents were commercially analytical and used without further

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purification.

2.2 Synthesis of the water soluble β-CDP

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The synthesis of the water soluble high molecular weight β-CDP followed Sebille’s work [32]. A typical synthesis procedure for a molar ratio EPI/β-CD = 10 and NaOH = 33% w/w

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was described as follows: 5 g of β-CD (0.44 mmol) was homogenously dissolved in 8 mL of

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NaOH solution, then, the mixture was heated to 30 ℃ and 4 g of EPI was added rapidly. After 2 h, the reaction was stopped by the addition of HCl to adjust the solution pH to 7.0. The transparent viscous β-CDP solution was dialyzed with dialysis bag (molecular weight cut-off

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further use.

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= 3500 Da) to remove unreacted small molecules and then the solution was stored at 4 ℃ for

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2.3 Fabrication of the β-CDP composite porous membrane The β-CDP composite porous membrane was fabricated via interfacial cross-linking on

nylon MF membrane as schemed in Figure 1. Firstly, the nylon MF membrane was immersed into aqueous alkaline solution (0.4 – 8.0 mol L-1) containing β-CDP (0 – 14 %) under shake for 10 min. The membrane was air-dried at room temperature for 30 min until there was no remaining liquid. Then, it was put into hexane solution containing TMC (0 – 2 %) for a certain time (5 - 30 min). Afterwards, the membrane was treated at 60 °C for 10 min for 5

further cross-linking. Finally, the obtained membrane was alternatively washed with deionized water and ethanol to remove residual chemicals and stored in deionized water for

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further use.

Figure 1. Schematic representation of the preparation and fitration adsorption process of the β-CDP

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composite porous membrane.

1. M2−M1

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Weight gain =

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The weight gain (WG) of composite membrane was calculated by the following equation

Am

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Where M1 (g) and M2 (g) represented the weight of dry original membrane and β-CDP

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composite membrane respectively; Am (m2) meant the area of membrane.

2.4 Filtration adsorption experiments of the β-CDP composite porous membranes The filtration adsorption performance of the β-CDP composite porous membrane was

measured via a dead-end stirred cell (XFUF047, Millpore Co., USA.) at ambient temperature. The composite membrane (d = 4.7 cm) was placed in the stirred cell and deionized water was forced to pass through it at 1 bar. The volume of the water in the outflow side was collected in

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a certain time and the water flux (F) of the membrane was calculated by the following equation 2. F=A

∆V

2

m ×∆t

Where ∆V (L) was the volume of water in the outflow side; Am (m2) was the membrane area; ∆t (h) was the testing time. Then, the pollutant solution was poured into the cell and the outflow was analysed by ultraviolet–visible (UV-vis) spectroscopy to calculate the treating capacity of the membrane.

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Wavelength of the maximum absorbance for BPA was 276 nm. The averages of three paralleled experiments were used to calculate the treating capacity of the membrane (mg m-2) based on the 100% of removal efficiency as shown in the following equation 3. Cp ×V100%

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Treating capacity =

Am

3

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Where cP (mg L-1), V100% (L) and Am (m2) represented the concentration of initial pollutant solution in feed side, the volume of outflow during 100 % of removal efficiency and

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the membrane area individually.

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2.5 Determination of β-CD content in the β-CDP. The β-CD content in β-CDP was determined by quantifying the reducing sugar content

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of the polymer on the basis of concentrated H2SO4 acidolysis and phenol colorimetric analysis [33]. Firstly, a calibration curve about absorbance versus glucose concentration was carried

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out. Briefly, 1 mL of various concentrations of glucose solution (0-100 mg L-1) was mixed with 1 ml of phenol standard solution (4 %), then, 7 ml of concentrated H2SO4 was added rapidly and the mixture was shaken well. After 30 min, absorbance of the mixture was measured at 490 nm using a UV-vis spectroscopy. The absorbance was plotted versus the glucose concentration to obtain the calibration curve (Figure S1). Subsequently, 3 mg of βCDP was dissolved in 30 ml of H2SO4 (0.5mol L-1) and the solution was stirred at 100 ℃ for 7

10 h to ensure a complete acidolysis. The final solution was diluted to test the glucose content in the polymer based on the calibration curve. The β-CD content in β-CDP was calculated as shown in the following equation 4. C×V×M

β − CD content = 180×7×3 × 100%

4

Where C (mg L-1), V (L) and M (g mol-1) was the glucose concentration, the volume of mixed solution and the molar mass of β-CD, respectively.

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2.6 Regeneration experiment of the β-CDP composite porous membranes

In the regeneration experiment of the β-CDP composite porous membrane, 65 mL of ethanol solution was passed through the membrane to desorb the adsorbed pollutant

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molecules. Subsequently, 20 mL of deionized water was permeated through the membrane to wash the residual ethanol. And then, the second filtration adsorption-desorption experiment

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2.6 Characterizations

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the reusability of the membrane.

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was duplicated. The above adsorption-desorption cycle was conducted for five times to assess

The chemical structure of the synthesized β-CDP was analysed by Fourier transform

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infrared spectroscopy (FTIR, Vector-22, Switzerland) in the range of 400–4000 cm-1. The molecular weight of β-CDP was determined by gel permeation chromatography (GPC, Water-

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515, USA). The column setting was calibrated with PS standards of known molecular weights. The membrane morphology was observed by Field Emission-Scanning Electron Microscopy (FE-SEM, HitachiS-4800, Japan) after the samples were sputtered with a platinum layer. The surface chemical composition was obtained via infrared spectrophotometer equipped with an attenuated total reflection accessory (ATR-FTIR, Nicolet 6700, USA) and X-ray photoelectron spectroscopy (XPS, PHI 5000C ESCA System, USA) with Mg Kα radiation (hv

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= 1253.6 eV) and a take-off angle of 90 °. The concentration of pollutant solution was measured via UV-vis spectroscopy using a spectrophotometer (UV-1601, Shimadzu, Japan).

3. Results and discussion 3.1 Synthesis and characterizations of the soluble β-CDP Water soluble β-CDP was synthesized via a polycondensation reaction of β-CD and bifunctional EPI in alkaline medium and a brief reaction of β-CD and EPI was schemed in

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Figure 2a. There existed not only the reaction of β-CD with EPI but also the selfpolymerization of EPI. Chemical composition of the obtained β-CDP was characterized by FTIR (Figure 2b) and H1 NMR (Figure S2). Compared with FTIR spectra of β-CD, the

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wavenumber of O-H in β-CDP increased for the introduction of EPI destroyed the

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intermolecular hydrogen bonding between β-CD. Meanwhile, there appeared a new peak at 2870 (-CH2-) in the spectra of β-CDP, suggesting the presence of EPI in product. Also, the H1

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NMR spectra confirmed the successful synthesis of β-CDP for the narrow peaks for small molecules (β-CD/EPI) changed to broad peaks for the polymer. Furthermore, the weight-

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average molecular weight of β-CDP was around 19600 Da (Figure 2c), and this high molecular weight β-CDP was beneficial to the large loading amount in the membrane

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pores[34], and thus, guaranteed the high adsorption capacity of the composite membrane. Additionally, the content of β-CD in β-CDP was determined by quantifying the reducing

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sugar content on the basis of concentrated H2SO4 acidolysis and phenol colorimetric analysis[33]. It was found that the content of β-CD in β-CDP was around 68 %, indicating there were about 7 hydroxypropyl ether segments per β-CD in the polymer.

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Figure 2. a, Reaction scheme of β-CD and bifunctional EPI in alkaline medium. b, FTIR spectra of β-

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CD and β-CDP. c, GPC spectra of β-CDP.

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3.2 Preparation and characterizations of the β-CDP composite porous membrane The β-CDP composite membrane was fabricated via a convenient interfacial cross-

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linking between aqueous solution containing β-CDP and hexane solution containing TMC on a nylon MF membrane as illustrated in Figure 1. Surface compositions of the composite

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membrane were analysed by ATR-FTIR spectrometer and obtained results were shown in Figure 3a. In the spectrum of the composite membrane, the characteristic peaks of β-CDP

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(3500 cm−1/-OH and 1240 cm−1 /C-O-C) and TMC (1600, 1450 cm−1/benzene) were observed. An evident new peak at 1730 cm−1, assigned to the formed ester groups[35,36], appeared in the spectrum of the composite membrane, suggesting the successful cross-linking between βCDP and TMC. Furthermore, XPS was conducted to analyse the quantitative surface composition of the composite membrane as shown in Figure 3b. It was found that the content of N element dropped from 11.3% (nylon membrane) to 0.9% (composite membrane), 10

indicating the successful incorporation of β-CDP in nylon membrane surface. The number of β-CD-hydroxypropyl ether repetitive units in β-CDP per TMC was estimated from the peaksplit results of O1s (Figure 3c, 3d), which ranged from 1.8 to 3.7 under two extreme scenarios (all of the hydroxyl groups reacted and none of them did). Furthermore, the molar number of β-CD units in the membrane was calculated, which ranged from 4.8 mM m-2 to 5.0 mM m-2. The high percentage of β-CD in composite membrane was beneficial to the highly

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efficient removal of micropollutants from water.

Figure 3. a, ATR-FTIR spectra of the nylon membrane and the composite membrane. b, wide-scan XPS spectra of nylon membrane and the composite membrane. c, d, Peak-split of O1s of nylon membrane and the composite membrane, respectively.

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Membrane surface and cross-section morphologies were observed by SEM as shown in Figure 4. It was clear that the composite membrane surfaces (top and bottom surface) were coated with cross-linked β-CDP layer. Also, the membrane pores through the cross-section were embedded with cross-linked β-CDP coating, which was the result of the successful penetration of the β-CDP into the interior membrane pores owing to the macropores of support membrane (average pore size = 0.45 μm). The surface and pore-inside loading of βCDP provided abundant adsorption sites to ensure the highly efficient removal of organic

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micropollutants from water. In addition, the stress–strain curves of the β-CDP composite

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membrane showed that the membrane possessed passable mechanical property (Figure S3).

Figure 4. Surface and cross-sectional SEM images of the cotrol nylon membrane and the typical βCDP composite porous membrane.

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3.3 Effect of preparation conditions on the β-CDP loading and membrane filtration adsorption performance Under the synergy of adsorption ability of β-CDP and energy-efficient and time-saving characteristics of porous filtration membrane, the β-CDP composite porous membrane was expected to achieve ultrafast removal of organic micropollutants with low energy consumption. BPA, an important raw material of polycarbonate and epoxy resins, was

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chosen as the representative of organic micropollutants in aqueous ecosystem since it has severely disrupted human endocrine system[37,38]. The operation conditions were as follows: BPA concentration in feed solution was 10 mg L-1 and permeantion flux during

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adsorption process was 80 L m-2 h-1.

The water decontamination performance of the β-CDP composite porous membrane was

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evaluated via a flow-through process in which the pollutant solution was forced to pass

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through the membrane at a certain flux meanwhile the pollutants were adsorbed into β-CDP as schemed in Figure 5a. The adsorption breakthrough curve about removal efficiency versus permeation volume was recorded, as Figure 5b showed. To evaluate the adsorption

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ability of the β-CDP membrane, its treating capacity was calculated as mg of pollutants

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adsorbed by per m2 of membrane based on 100 % of removal efficiency

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Figure 5. a, Schematic representation of the fitration adsorption process of the β-CDP composite membrane towards BPA. b, Adsorption breakthrough curve of the β-CDP composite membrane towards BPA.

A key parameter in the interfacial cross-linking of hydroxyl monomer and acyl chloride was pH of the aqueous solution[39]. At high pH, hydroxyls of β-CDP ionized to form more reactive alkoxide ions, which enhanced the reaction rate and increased the loading amount of

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adsorption sites[39]. Therefore, the aqueous solution was added with NaOH to control the pH, and the effect of NaOH concentration on the loading amount and filtration adsorption performance of the membrane was firstly investigated. As shown in Figure 6a, the β-CDP

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loading first increased and then levelled off with the increasing NaOH concentration. Meanwhile, the water flux of the membrane first decreased and then tended to a steady level.

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Additionally, the variation trend of treating capacity of the membrane was in accordance with that of β-CDP loading as shown in Figure 6b. The transition point occurs at about 4 %

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of NaOH concentration, indicating that 4 % of NaOH concentration is enough to promote the reaction rate of β-CDP and TMC. In addition, the corresponding interfacial cross-linking

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without support membrane was also carried out to visually observe the effect of NaOH concentration on reaction process. There appeared discrete thin film at the interface during

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10 min of reaction time when the added NaOH concentration was 2 %. And a continuous thin film was observed at the interface during 5 min of reaction time when the NaOH

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concentration was increased to 4 %. This phenomenon further proved that the 4 % of NaOH concentration was needed to obtain a consecutive thin film, which was in accordance with the result of composite membrane. In short, the composite membrane exhibited excellent adsorption performance when the NaOH concentration was not less than 4%.

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Figure 6. a, Effect of NaOH concentration on β-CDP loading amount and water flux of the membrane. b, Effect of NaOH concentration on treating capacity of the membrane. Preparation condition: cβ-CDP = 7.0 %, cTMC = 1.5 %, reaction time = 10 min.

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The β-CDP concentration and TMC concentration also greatly affected the loading

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amount and membrane filtration adsorption performance. Firstly, the effect of β-CDP concentration on the loading amount and treating capacity of the composite membrane was

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explored to seek the optimal membrane for water decontamination as shown in Figure 7a and 7b. It can be seen that the loading amount increased and membrane flux decreased with

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the increasing β-CDP concentration, which was attributed to the increasement of adsorbed βCDP molecules in membrane pores. And the treating capacity of the composite membrane

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increased and then levelled off with the increasing β-CDP concentration, manifesting that the effective adsorption layer was limited to the surface layer of cross-linked β-CDP coating

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with a certain thickness. Considering the membrane flux and treating capacity, the optimized β-CDP concentration was 7 %. Additionally, the influence of TMC concentration on the loading amount and treating capacity of the composite membrane was further studied as shown in Figure 7c and 7d. The loading amount first increased and then levelled off while the membrane flux decreased and then remain unchanged as the TMC concentration increased. The treating capacity also showed same variation trend with the loading amount.

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This indicated that TMC concentration at turning point (1.5 %) was enough to completely cross-link β-CDP molecules. In addition, reaction time is a vital factor in loading amount and treating capacity of the membrane as shown in Figure 7e and 7f. The loading amount increased and then tended to be steady while the membrane flux decreased and then remained flat with the increasing reaction time. Meanwhile, the treating capacity increased and then levelled off with the increasing reaction time. So, 10 min of reaction time was enough to achieve the cross-linking reaction of

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β-CDP and TMC. In summary, the optimized preparation conditions for β-CDP composite porous membranes are as follows: 4.0 % of NaOH concentration, 0.7 % of β-CDP concentration, 1.5 % of TMC concentration, 10 min of reaction time for interfacial cross-

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linking. In the optimized conditions, the loading amount, permeation flux and treating capacity of the composite membrane was up to 6.2 g m-2, 1300 L m-2 h-1 at 1 bar, and 440 mg

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m-2, individually. This membrane with high loading amount was obtained by convenient

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interfacial cross-linking, which exhibited superior decontamination performance along with high flux. This optimal membrane was used to explore its filtration adsorption performance

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under harsh operation conditions in later researches.

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Figure 7. a, b, Effect of β-CDP concentration on the loading amount and treating capacity of the

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composite membrane, respectively. cNaOH = 4.0 %, cTMC = 1.5 %, reaction time = 10 min. c, d, Effect of TMC concentration on the loading amount and treating capacity of the composite membrane,

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respectively. Preparation condition: cNaOH = 4.0 %, cβ-CDP = 7.0 %, reaction time = 10 min. e, f, Effect of reaction time on the loading amount and treating capacity of the composite membrane, respectively. Preparation condition: cNaOH = 4.0 %, cβ-CDP = 7.0 %, cTMC = 1.5 %.

3.4 Effect of operation conditions on the membrane filtration adsorption performance

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The effect of solution chemistry (pH of BPA solution and ionic strength) on the treating capacity of the membrane was investigated to enhance the effectiveness of decontamination in practical application. As shown in Figure 8a, the membrane exhibited stable treating capacity towards BPA (440 mg m-2) when the pH of BPA solution was in the range of 2.0 to 9.0. The treating capacity of the membrane started to decrease from 440 to 0 mg m-2 when the pH increased from 9.0 to 12.0. This was mainly because the presence of strong base promoted the ionization of BPA (pKa ≈ 10)[40,41] and thus inhibited the formation of hydrogen bonding

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between BPA and β-CD. Thus, the adsorption was stable in the pH range from acid to neutral but there was bare adsorption of BPA under strong alkaline conditions.

Further research on the treating capacity under different ionic strength was conducted as

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shown in Figure 8b. The treating capacity increased from 440 to 955 mg m-2 in the presence of NaC1 from 0 to 1.5 mol L-1. It should be note-worthy that the treating capacity was

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increased by 2.1 times when the NaC1 concentration was 1.5 mol L-1. This was attributed to

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the salting-out effect of BPA under high salt concentration, which decreased the interaction force between BPA and water and thus facilitated the adsorption of BPA on β-CD

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molecule[42]. Therefore, the treating capacity of membrane was enhanced when NaCl was

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added in feed solution.

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Figure 8. a, Effect of the pH of BPA solution on the treating capacity of the membrane. Operation conditions: cBPA = 10 mg L-1, flux = 80 L m-2 h-1. b, Effect of the ionic strength on the treating capacity of the membrane. Operation conditions: cBPA = 10 mg L-1, flux = 80 L m-2 h-1, pH = 7.0.

Also, permeation flux played a crucial role in the filtration adsorption process and the influence of the permeation flux on treating capacity was investigated as shown in Figure 9a and 9b. The removal efficiency maintained 100 % even at 2500 L m-2 h-1 of permeation flux

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due to numerous adsorption sites in the membrane. And the treating capacity of the membrane slowly decreased and then quickly decreased with the increasing permeation flux, which was attributed to the shorter residence time for BPA molecules to interact with the adsorption sites

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at higher permeation flux. It should be noted that the treating capacity of the membrane only fell by 32 % (from 445 to 300 mg m-2) when the permeation flux increased two orders of

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magnitude (from 20 to 2500 L m-2 h-1). The high treating capacity of the membrane at up to 2500 L m-2 h-1 of permeation flux, approximately two orders of magnitude higher than that of

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commercial nanofiltration membranes with similar removal performance, suggested its promising potential in water purification process.

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To achieve higher treating volume, the membrane can be stacked to be used in practical application owing to its high flux. As shown in the Figure S4, 1 dm2 of the membrane can

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only filter 0.44 L of water for 10 mg L-1 BPA solution based on 100% of removal efficiency. But a stack of two membranes and three membranes can filter 0.90 L and 1.35 L of water for

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10 mg L-1 of BPA solution at permeation flux of 80 L m-2 h-1, respectively. The treating capacity of individual membrane was not impaired by stacking, which provided an economical highly efficient method for water decontamination.

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Figure 9. a, Adsorption break-through curves of the β-CDP composite membrane at various permeation fluxes. b, Effect of permeation flux on the treating capacity of the membrane. Operation conditions: cBPA = 10 mg L-1, flux = 80 L m-2 h-1, pH = 7.0.

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3.5 Regeneration performance of the β-CDP composite porous membrane

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Reuse ability of the adsorbent was a critical parameter for its potential practical application values. It is well-known that ethanol, a good solvent for organic micropollutants,

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can break down the binding interaction between β-CD and aromatics to desorb the adsorbed organic micropollutants[43]. So, ethanol was used to investigate the regeneration ability of the

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β-CDP composite porous membranes. As shown in Figure 9a, the ethanol was filtrated through the membrane to extract the adsorbed BPA molecules when the BPA concentration in

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outflows was larger than zero. In a continuous adsorption–desorption cycle, the β-CDP composite membrane not only fully removed the BPA molecules but also achieved almost

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complete BPA recovery by simple ethanol filtration. During five adsorption-desorption cycles (Figure 9b), the membrane still showed almost same treating capacity towards BPA, indicating the exceptional reuse ability of this membranes by simple and mild ethanol cleaning.

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Figure 9. a, Adsorption-desorption cycles of the β-CDP composite porous membrane. b, Treating capacity of the β-CDP composite porous membrane during five adsorption–desorption cycles.

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Operation conditions: cBPA = 10 mg L-1, flux = 80 L m-2 h-1, pH = 7.0.

4. Conclusions

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β-CD was successfully integrated into porous membrane via convenient interfacial crosslinking between β-CDP and TMC to develop a highly efficient water purification method. The

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β-CDP composite porous membranes combined the adsorption ability of β-CDP and the convection mass transport process of membranes filtration to quickly remove contaminants

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from water. The optimized preparation condition is as follows: 4.0 % of NaOH concentration, 0.7 % of β-CDP concentration, 1.5 % of TMC concentration, 10 min of reaction time for

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interfacial cross-linking. In the optimized conditions, loading amount, permeation flux and

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treating capacity of the composite membrane was up to 6.2 g m-2, 1300 L m-2 h-1 at 1 bar, and 440 mg m-2 (100% of removal efficiency), individually. And the membrane showed stable treating capacity in the pH range from acid to neutral and the treating capacity was greatly enhanced after the addition of salts owing to the salting-out effect. Also, the membrane could completely remove pollutants with ultrahigh flux up to 2500 L·m-2·h-1. The host-guest interaction between β-CD and organic pollutants was responsible for the adsorption mechanism. In addition, the used membranes were fully regenerated by simple and mild 21

ethanol filtration. Given the convenient fabrication method, excellent adsorption and regeneration performance, the β-CDP composite membranes have enormous commercial potential applications in fast potable water purification.

Acknowledgements We are grateful for the financial supports from the National Natural Science Foundation of China (Grant No. 51573159, 51773175 and 51828301) and the Fundamental Research Funds

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for the Central Universities (Grant No. 2019QNA4062). The authors also thank Ms. Li Xu in State Key Laboratory of Chemical Engineering, Zhejiang University, China for the polymer

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characterizations.

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References

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[1] K. Bakker, Water Security: Research Challenges and Opportunities, Science. 337 (2012) 914–915. doi:10.1126/science.1226337. [2] N. Ratola, A. Cincinelli, A. Alves, A. Katsoyiannis, Occurrence of organic microcontaminants in the wastewater treatment process. A mini review, Journal of Hazardous Materials. 239–240 (2012) 1–18. doi:10.1016/j.jhazmat.2012.05.040. [3] C.J. Voeroesmarty, P.B. McIntyre, M.O. Gessner, D. Dudgeon, A. Prusevich, P. Green, S. Glidden, S.E. Bunn, C.A. Sullivan, C.R. Liermann, P.M. Davies, Global threats to human water security and river biodiversity, Nature. 467 (2010) 555–561. doi:10.1038/nature09440. [4] C. Huang, L.-H. Wu, G.-Q. Liu, L. Shi, Y. Guo, Occurrence and Ecological Risk Assessment of Eight Endocrine-Disrupting Chemicals in Urban River Water and Sediments of South China, Arch Environ Contam Toxicol. (2018) 1–12. doi:10.1007/s00244-018-0527-9. [5] Å. Bergman, J.J. Heindel, T. Kasten, K.A. Kidd, S. Jobling, M. Neira, R.T. Zoeller, G. Becher, P. Bjerregaard, R. Bornman, I. Brandt, A. Kortenkamp, D. Muir, M.-N.B. Drisse, R. Ochieng, N.E. Skakkebaek, A.S. Byléhn, T. Iguchi, J. Toppari, T.J. Woodruff, The Impact of Endocrine Disruption: A Consensus Statement on the State of the Science, Environ Health Perspect. 121 (2013) a104–a106. doi:10.1289/ehp.1205448. [6] A.M. Soto, C. Sonnenschein, Environmental causes of cancer: endocrine disruptors as carcinogens, Nature Reviews Endocrinology. 6 (2010) 363–370. doi:10.1038/nrendo.2010.87. [7] C. Liu, L. Cheng, Y. Zhao, L. Zhu, Interfacially crosslinked composite porous membranes for ultrafast removal of anionic dyes from water through permeating adsorption, Journal of Hazardous Materials. 337 (2017) 217–225. doi:10.1016/j.jhazmat.2017.04.032. 22

Jo

ur

na

lP

re

-p

ro of

[8] Z. Aksu, Application of biosorption for the removal of organic pollutants: a review, Process Biochemistry. 40 (2005) 997–1026. doi:10.1016/j.procbio.2004.04.008. [9] I. Oller, S. Malato, J.A. Sánchez-Pérez, Combination of Advanced Oxidation Processes and biological treatments for wastewater decontamination—A review, Science of The Total Environment. 409 (2011) 4141–4166. doi:10.1016/j.scitotenv.2010.08.061. [10] A.I. Schäfer, L.D. Nghiem, T.D. Waite, Removal of the Natural Hormone Estrone from Aqueous Solutions Using Nanofiltration and Reverse Osmosis, Environ. Sci. Technol. 37 (2003) 182–188. doi:10.1021/es0102336. [11] Y.-S. Guo, Y.-F. Mi, F.-Y. Zhao, Y.-L. Ji, Q.-F. An, C.-J. Gao, Zwitterions functionalized multi-walled carbon nanotubes/polyamide hybrid nanofiltration membranes for monovalent/divalent salts separation, Separation and Purification Technology. 206 (2018) 59–68. doi:10.1016/j.seppur.2018.05.048. [12] M. Hua, S. Zhang, B. Pan, W. Zhang, L. Lv, Q. Zhang, Heavy metal removal from water/wastewater by nanosized metal oxides: A review, Journal of Hazardous Materials. 211–212 (2012) 317–331. doi:10.1016/j.jhazmat.2011.10.016. [13] I. Ali, V.K. Gupta, Advances in water treatment by adsorption technology, Nat. Protoc. 1 (2006) 2661–2667. doi:10.1038/nprot.2006.370. [14] L. Jiang, Y. Liu, S. Liu, X. Hu, G. Zeng, X. Hu, S. Liu, S. Liu, B. Huang, M. Li, Fabrication of β-cyclodextrin/poly (l-glutamic acid) supported magnetic graphene oxide and its adsorption behavior for 17β-estradiol, Chemical Engineering Journal. 308 (2017) 597–605. doi:10.1016/j.cej.2016.09.067. [15] K. Oishi, A. Moriuchi, Removal of dissolved estrogen in sewage effluents by βcyclodextrin polymer, Science of The Total Environment. 409 (2010) 112–115. doi:10.1016/j.scitotenv.2010.09.031. [16] B. Bhattarai, M. Muruganandham, R.P.S. Suri, Development of high efficiency silica coated β-cyclodextrin polymeric adsorbent for the removal of emerging contaminants of concern from water, Journal of Hazardous Materials. 273 (2014) 146–154. doi:10.1016/j.jhazmat.2014.03.044. [17] G. Chen, M. Jiang, Cyclodextrin -based inclusion complexation bridging supramolecular chemistry and macromolecular self-assembly, Chemical Society Reviews. 40 (2011) 2254–2266. doi:10.1039/C0CS00153H. [18] D.-H. Qu, Q.-C. Wang, Q.-W. Zhang, X. Ma, H. Tian, Photoresponsive Host–Guest Functional Systems, Chem. Rev. 115 (2015) 7543–7588. doi:10.1021/cr5006342. [19] G. Crini, Review: A History of Cyclodextrins, Chemical Reviews. 114 (2014) 10940– 10975. doi:10.1021/cr500081p. [20] G. Crini, M. Morcellet, Synthesis and applications of adsorbents containing cyclodextrins, J. Sep. Science. 25 (2002) 789–813. doi:10.1002/16159314(20020901)25:13<789::AID-JSSC789>3.0.CO;2-J. [21] Z. Wang, P. Zhang, F. Hu, Y. Zhao, L. Zhu, A crosslinked β-cyclodextrin polymer used for rapid removal of a broad-spectrum of organic micropollutants from water, Carbohydrate Polymers. 177 (2017) 224–231. doi:10.1016/j.carbpol.2017.08.059. [22] N. Morin-Crini, G. Crini, Environmental applications of water-insoluble β-cyclodextrin– epichlorohydrin polymers, Progress in Polymer Science. 38 (2013) 344–368. doi:10.1016/j.progpolymsci.2012.06.005. [23] H. Kono, T. Nakamura, H. Hashimoto, Y. Shimizu, Characterization, molecular dynamics, and encapsulation ability of β-cyclodextrin polymers crosslinked by polyethylene glycol, Carbohydrate Polymers. 128 (2015) 11–23. doi:10.1016/j.carbpol.2015.04.009. [24] A. Alsbaiee, B.J. Smith, L. Xiao, Y. Ling, D.E. Helbling, W.R. Dichtel, Rapid removal of organic micropollutants from water by a porous β-cyclodextrin polymer, Nature. 529 (2016) 190–194. doi:10.1038/nature16185. 23

Jo

ur

na

lP

re

-p

ro of

[25] Z. Wang, F. Cui, Y. Pan, L. Hou, B. Zhang, Y. Li, L. Zhu, Hierarchically micromesoporous β-cyclodextrin polymers used for ultrafast removal of micropollutants from water, Carbohydrate Polymers. 213 (2019) 352–360. doi:10.1016/j.carbpol.2019.03.021. [26] N. Morin-Crini, P. Winterton, S. Fourmentin, L.D. Wilson, É. Fenyvesi, G. Crini, Waterinsoluble β-cyclodextrin–epichlorohydrin polymers for removal of pollutants from aqueous solutions by sorption processes using batch studies: A review of inclusion mechanisms, Progress in Polymer Science. (2017). doi:10.1016/j.progpolymsci.2017.07.004. [27] F. Zha, S. Li, Y. Chang, Preparation and adsorption property of chitosan beads bearing β-cyclodextrin cross-linked by 1,6-hexamethylene diisocyanate, Carbohydrate Polymers. 72 (2008) 456–461. doi:10.1016/j.carbpol.2007.09.013. [28] M. Kitaoka, K. Hayashi, Adsorption of Bisphenol A by Cross-Linked β-Cyclodextrin Polymer, Journal of Inclusion Phenomena. 44 (2002) 429–431. doi:10.1023/A:1023024004103. [29] R.-Y. Lin, B.-S. Chen, G.-L. Chen, J.-Y. Wu, H.-C. Chiu, S.-Y. Suen, Preparation of porous PMMA/Na+–montmorillonite cation-exchange membranes for cationic dye adsorption, Journal of Membrane Science. 326 (2009) 117–129. doi:10.1016/j.memsci.2008.09.038. [30] D. Shetty, I. Jahovic, J. Raya, Z. Asfari, J.-C. Olsen, A. Trabolsi, Porous Polycalix[4]arenes for Fast and Efficient Removal of Organic Micropollutants from Water, ACS Applied Materials & Interfaces. 10 (2018) 2976–2981. doi:10.1021/acsami.7b16546. [31] S. He, H. Fang, X. Xu, Filtering absorption and visual detection of methylene blue by nitrated cellulose acetate membrane, Korean Journal of Chemical Engineering. 33 (2016) 1472–1479. doi:10.1007/s11814-015-0231-7. [32] E. Renard, A. Deratani, G. Volet, B. Sebille, PREPARATION AND CHARACTERIZATION OF WATER SOLUBLE HIGH MOLECULAR WEIGHT PCYCLODEXTRIN-EPICHLOROHYDRIN POLYMERS, (1997) 9. [33] H. Liu, X. Cai, Y. Wang, J. Chen, Adsorption mechanism-based screening of cyclodextrin polymers for adsorption and separation of pesticides from water, Water Research. 45 (2011) 3499–3511. doi:10.1016/j.watres.2011.04.004. [34] F. Hu, C. Fang, Z. Wang, C. Liu, B. Zhu, L. Zhu, Poly (N-vinyl imidazole) gel composite porous membranes for rapid separation of dyes through permeating adsorption, Separation and Purification Technology. 188 (2017) 1–10. doi:10.1016/j.seppur.2017.06.024. [35] Y.-S. Guo, Y.-F. Mi, Y.-L. Ji, Q.-F. An, C.-J. Gao, One-Step Surface Grafting Method for Preparing Zwitterionic Nanofiltation Membrane via In Situ Introduction of Initiator in Interfacial Polymerization, ACS Appl. Polym. Mater. 1 (2019) 1022–1033. doi:10.1021/acsapm.9b00059. [36] Y.-S. Guo, X.-D. Weng, B. Wu, Y.-F. Mi, B.-K. Zhu, Y.-L. Ji, Q.-F. An, C.-J. Gao, Construction of nonfouling nanofiltration membrane via introducing uniformly tunable zwitterionic layer, Journal of Membrane Science. 583 (2019) 152–162. doi:10.1016/j.memsci.2019.04.055. [37] D. Shetty, I. Jahovic, J. Raya, Z. Asfari, J.-C. Olsen, A. Trabolsi, Porous Polycalix[4]arenes for Fast and Efficient Removal of Organic Micropollutants from Water, ACS Appl. Mater. Interfaces. 10 (2018) 2976–2981. doi:10.1021/acsami.7b16546. [38] N. Morin-Crini, G. Crini, Environmental applications of water-insoluble β-cyclodextrin– epichlorohydrin polymers, Progress in Polymer Science. 38 (2013) 344–368. doi:10.1016/j.progpolymsci.2012.06.005.

24

ro of

[39] L.F. Villalobos, T. Huang, K.-V. Peinemann, Cyclodextrin Films with Fast Solvent Transport and Shape-Selective Permeability, Advanced Materials. 29 (n.d.) 1606641. doi:10.1002/adma.201606641. [40] W. Guo, W. Hu, J. Pan, H. Zhou, W. Guan, X. Wang, J. Dai, L. Xu, Selective adsorption and separation of BPA from aqueous solution using novel molecularly imprinted polymers based on kaolinite/Fe3O4 composites, Chemical Engineering Journal. 171 (2011) 603–611. doi:10.1016/j.cej.2011.04.036. [41] C. Liu, P. Wu, Y. Zhu, L. Tran, Simultaneous adsorption of Cd2+ and BPA on amphoteric surfactant activated montmorillonite, Chemosphere. 144 (2016) 1026–1032. doi:10.1016/j.chemosphere.2015.09.063. [42] J. Xu, L. Wang, Y. Zhu, Decontamination of Bisphenol A from Aqueous Solution by Graphene Adsorption, Langmuir. 28 (2012) 8418–8425. doi:10.1021/la301476p. [43] Z. Wang, B. Zhang, C. Fang, Z. Liu, J. Fang, L. Zhu, Macroporous membranes doped with micro-mesoporous β-cyclodextrin polymers for ultrafast removal of organic micropollutants from water, Carbohydrate Polymers. 222 (2019) 114970. doi:10.1016/j.carbpol.2019.114970.

Jo

ur

na

lP

re

-p

.

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