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Applied Surface Science

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Rapid adsorption of bisphenol A from wastewater by β-cyclodextrin-functionalized mesoporous magnetic clustersJi Hwan Lee, Seung-Yeop Kwak⁎

Department of Materials Science and Engineering, and Research Institute of Advanced Materials, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826,Republic of Korea

A R T I C L E I N F O

Keywords:Bisphenol A β-cyclodextrinMesoporous magnetic clusterAdsorptionWater purification

A B S T R A C T

To develop a novel magnetic adsorbent for the removal of endocrine-disrupting chemicals, mesoporous magneticclusters (MMCs) functionalized with β-cyclodextrin (β-CD), henceforth denoted CD-MG, were prepared by afacile chemical strategy and were applied to bisphenol A (BPA) removal for the first time. Fourier-transforminfrared spectroscopy and thermogravimetric analysis revealed that β-CD was successfully linked to the MMCsurfaces. X-ray diffraction, field emission scanning electron microscopy, and high-resolution transmissionelectron microscopy confirmed that the morphologies and crystal structures of the MMCs were well preserved inCD-MG. A pseudo-second-order kinetic model and Langmuir isotherm model were used to describe the BPAadsorption behavior of CD-MG. The kinetic model yielded a BPA adsorption rate constant of0.0367 gmg−1min−1, while the isotherm model yielded a maximum BPA adsorption capacity of 52.7mg g−1.Furthermore, CD-MG exhibited a good recovery efficiency of 84.5% in the reusability tests, even after fourcycles. The fast adsorption kinetics, high adsorption capacity, and good recovery efficiency indicated that CD-MG could be an effective magnetic adsorbent for the removal of endocrine-disrupting chemicals.

1. Introduction

The occurrence of organic contaminants like endocrine-disruptingchemicals (EDCs) in water resources is a global issue and poses a gravethreat to human health and aquatic ecosystems [1–3]. Given the toxi-city of EDCs, considerable attention has been paid to their removal fromwastewater. Bisphenol A (BPA) is one such EDC, mainly used for thesynthesis of unsaturated polyester-styrene resins, epoxy and poly-carbonate resins, and flame retardants [4]. Unfortunately, BPA caneasily leach out of products and migrate into the aquatic environment[5], and may provoke reproductive and developmental disorders inwildlife and humans due to its endocrine-disrupting effects [6]. Greatefforts have been devoted to devising means of removing organiccontaminants from the aquatic environment, including adsorption[7–9], photocatalytic degradation [10,11], microbial degradation [12],membrane filtration [13], and electrochemical treatment [14]. Amongthese, adsorption is considered a relatively cost-effective and efficientmeans of organic contaminant removal [15,16].

β-cyclodextrin (β-CD) is composed of seven D(+)-glucopyranose

units with α-(1,4)-linkages and has a toroidal structure with a hydro-philic surface and a hydrophobic cavity [17]. Its hydrophilic surfaceand hydrophobic cavity contribute to its ability to selectively trap size-matched organic molecules via host–guest interactions (e.g. hydro-phobic interaction, van der Waals forces, steric effects, and hydrogenbonding) [18–20]. Since β-CD is highly soluble in water, it should bepresent in a water-insoluble form to enable its easy separation fromwater after the removal of the EDCs [21].

Being a type of well-established nanomaterial, magnetic nano-particles (MNPs) have many environmental applications since MNPspossess high specific surface areas and can be magnetically separatedfrom water [22–24]. β-CD-functionalized MNPs have recently been thesubject of considerable attention for the removal of various con-taminants from aqueous solutions. There are two general functionali-zation strategies: (1) physical incorporation of β-CD into MNPs and (2)chemical introduction of β-CD to MNPs. The physical incorporation ofβ-CD into MNPs is a facile functionalization method. For instance, manyresearch groups have physically incorporated β-CD into MNPs using asimple chemical co-precipitation method [25–28]. However, β-CD can

https://doi.org/10.1016/j.apsusc.2018.10.054Received 18 July 2018; Received in revised form 5 October 2018; Accepted 5 October 2018

Abbreviations: MMC, mesoporous magnetic cluster; MNP, magnetic nanoparticle; EDC, endocrine-disruption chemical; BPA, bisphenol A; β-CD, β-cyclodextrin; FT-IR, Fourier-transform infrared; TGA, thermogravimetric analysis; XRD, X-ray diffraction; HR-TEM, high-resolution transmission electron microscopy; FE-SEM, fieldemission scanning electron microscopy; EG, ethylene glycol; HMDI, hexamethylene diisocyanate; TEA, triethylamine; DMF, dimethylformamide

⁎ Corresponding author.E-mail address: sykwak@snu.ac.kr (S.-Y. Kwak).

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Available online 08 October 20180169-4332/ © 2018 Elsevier B.V. All rights reserved.

T

migrate from β-CD-functionalized MNPs into the aquatic environmentbecause β-CD only interacts with MNPs through non-covalent bonding.To overcome these disadvantages, β-CD should be introduced chemi-cally to MNPs through covalent bonding [29–31]. However, this che-mical introduction generally involves a tedious and multi-step func-tionalization procedure, which takes time, consumes energy, and iscostly. Furthermore, MNPs are capable of only a relatively weak mag-netic response to overcome Brownian motion; therefore, their separa-tion from water would take a long time, making it necessary to apply astrong external magnetic field (enough to overcome the Brownianmotion of the MNPs) [32]. Mesoporous magnetic clusters (MMCs),however, have a sufficient specific surface area despite their largecluster size, due to their mesoporous structure. MMCs can be magne-tically separated from water more rapidly than MNPs because their

having a larger cluster size than MNPs makes them less susceptible tothe Brownian motion [33].

Herein, to overcome the as-mentioned shortcomings of β-CD-func-tionalized MNPs as adsorbents, we focused on the use of MMCs insteadof MNPs as a water-insoluble support and the simple chemical in-troduction of β-CD into MMCs to prepare MMCs functionalized with β-CD, henceforth denoted CD-MG, for the removal of EDCs from waste-water, based on the hypothesis that the mesoporous structure, sufficientspecific surface area, and large cluster size of CD-MG would provide fastBPA adsorption kinetics, high BPA adsorption capacity, and efficientmagnetic separation from wastewater. The synthesized CD-MG ad-sorbent offers the possibility of developing economical and efficientprocesses for the removal of organic contaminants in wastewater.

2. Materials and methods

2.1. Materials

Iron (III) chloride hexahydrate (FeCl3·6H2O), trisodium citrate

Fig. 1. The results of characterizations for C-MG and CD-MG (a) FT-IR spectra (b) TGA curves.

Fig. 2. X-ray diffraction patterns of CD-MG.

Fig. 3. Magnetization curves for CD-MG as a function of the applied field,measured at room temperature.

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dihydrate (Na3Cit·2H2O), ammonium acetate (NH4Ac), ethylene glycol(EG), hexamethylene diisocyanate (HMDI), triethylamine (TEA), β-CD,BPA, and dimethylformamide (DMF) were purchased from SigmaAldrich and were used without further purification. The water used inall syntheses and analyses was deionized with a resistivity exceeding18.0MΩ cm.

2.2. Synthesis of carboxyl-functionalized MMCs

Carboxyl-functionalized mesoporous magnetite clusters (C-MG)were synthesized using a slight modification of the process described inthe literature [34]. First, FeCl3·6H2O (1.35 g) was dissolved in EG(60mL), yielding a clear solution. Then, Na3Cit·2H2O (0.72 g) wasadded to the ferric solution with magnetic stirring, followed by theaddition of NH4Ac (1.54 g). After vigorous stirring, the mixture wassealed in a Teflon-lined autoclave and heated at 200 °C for 12 h. Theblack precipitate was collected and washed several times with ethanoland distilled water to eliminate any unbound reactants. Finally, theproduct was vacuum-dried overnight at 50 °C.

2.3. Synthesis of β-CD-functionalized MMCs

Typically, to incorporate β-CD into the MMCs, the surface of the C-MG was first modified with HMDI followed by reaction with β-CD. C-MG (0.5 g), dispersed in DMF using ultrasonication, was dropwiseadded to a mixture of HMDI (2.5 mL) and DMF (10mL). The dispersionwas heated at 80 °C for 3 h and washed with DMF. Then, the isocyanate-functionalized C-MG was re-dispersed in DMF (90mL), and a mixture ofβ-CD and DMF (1:8 w/v, 20mL) was added to the dispersion. The dis-persion was then allowed to react at 80 °C and held at that temperaturefor 18 h. The product, denoted CD-MG-1, was sequentially washed withDMF and ethanol and then vacuum-dried at 50 °C overnight. Thesereactions were catalyzed by small amounts of TEA. If the amount ofHMDI was changed to 5mL or 20mL while keeping the other condi-tions constant, CD-MG-2 or CD-MG-3 would be obtained, respectively.

2.4. Characterization

Fourier-transform infrared (FT-IR) spectra were recorded for KBrpellets using a Nicolet iS10 IR spectrophotometer (Thermo FisherScientific, USA). Thermogravimetric analysis (TGA) was performed on aQ500 system (TA Instruments, USA) at a scan rate of 10 °Cmin−1 in anitrogen atmosphere. X-ray diffraction (XRD) patterns were acquiredusing a New D8 Advance X-ray diffractometer (Bruker, USA) with a CuKα X-ray source (λ= 1.541 Å). Vibrating sample magnetometry (VSM)for magnetization measurements were performed on a VSM-7410magnetometer (Lake Shore, USA) at 300 K. Field-emission scanningelectron microscopy (FE-SEM) was performed using a SUPRA 55VPmicroscope (Zeiss, Germany) with an applied voltage of 2.0 kV. High-resolution transmission electron microscopy (HR-TEM) was performedusing a JEM-3010 (JEOL, Japan) microscope operated at an accel-erating voltage of 300 kV. Nitrogen adsorption/desorption measure-ments were performed using an ASAP 2000 system (Micromeritics,USA) at 77 K. The multipoint Brunauer-Emmett-Teller (BET) methodwas used to calculate the specific surface areas. The specific surfacearea and mean pore size were obtained using the Micromeritics DensityFunctional Theory Plus software package.

2.5. Batch adsorption experiments

All the adsorption experiments were performed in an incubatorshaker using 10mL of an aqueous solution of BPA at pH 6.5–7.0. CD-MG (10mg) was added to the BPA aqueous solution, and the dispersedsuspension was shaken for various durations (200 rpm, 30 °C). After theadsorption process, CD-MG could be magnetically separated within afew minutes. The residual BPA concentration in the supernatant wasdetermined using a Lambda 25 UV–vis spectrometer (Perkin Elmer,USA) at a wavelength of 276 nm.

The adsorption capacity of the adsorbent was determined using Eq.(1):

=q C C VM

( )e

e0(1)

where qe (mg g−1) is the adsorption capacity of CD-MG at equilibrium,

Fig. 4. FE-SEM (left) and HR-TEM (right) images for C-MG and CD-MG.

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and C0 and Ce (mg L−1) are the initial and equilibrium BPA con-centrations in the solution, respectively, V (mL) is the volume of thesolution, and M (mg) is the mass of CD-MG.

The adsorption kinetics were evaluated using the pseudo-first-orderand pseudo-second-order kinetic models, which can be expressed byEqs. (2) and (3), respectively [35,36]:

= ( )q q e1t ek t1 (2)

=+

qq k t

k q t1te

e

22

2 (3)

where qt (mg g−1) is the adsorption capacity of CD-MG at time t, and k1(min−1) and k2 (gmg−1min−1) are the pseudo-first-order and pseudo-second-order rate constants, respectively.

The equilibrium adsorption isotherm was explained using theFreundlich and Langmuir isotherm models, which can be expressed byEqs. (4) and (5), respectively [37,38]:

=q K Ce F en1/ (4)

=+

qq bC

bC1eL e

e (5)

where KF ((mg g−1) (Lmg−1)n) and n are the Freundlich constants re-lated to the capacity and intensity of adsorption, respectively, and KL(Lmg−1), and qL (mg g−1) are the Langmuir constants related to theadsorption energy and the maximum adsorption capacity, respectively.

2.6. Regeneration experiments

The regeneration of the adsorbents after BPA adsorption wasachieved by dispersing them in ethanol (100mL) under ultrasonicationfor 10min. The regenerated adsorbents could be magnetically sepa-rated within a few minutes and then reused for subsequent adsorptioncycles.

The recovery efficiency of the adsorbent was calculated using Eq.(6):

= ×Rqq

% 100r

i (6)

where qi and qr are the adsorption capacities of the adsorbent beforeand after regeneration, respectively.

3. Results and discussion

3.1. Characterization of β-CD-functionalized MMCs

Fig. 1(a) shows that the FT-IR spectra of C-MG and CD-MG contain astrong band at ca. 600 cm−1, attributed to the Fe–O stretching vibra-tions [39]. The FT-IR spectrum of C-MG exhibits bands at 2928, 2855,1638, and 1407 cm−1, attributed to the asymmetric and symmetric–CH2– stretching vibrations and asymmetric and symmetric COO−

stretching vibrations, respectively. These IR bands indicate that citratemolecules were bound to the magnetite particles [40]. The MMCsmodified with β-CD exhibited strong IR bands corresponding to thecarbonyl group and the urethane linkage between the HMDI and β-CD

Fig. 5. Adsorption kinetics of CD-MG for BPA (a), Adsorption isotherms of CD-MG for BPA (b), recovery efficiencies of CD-MG over four adsorption–desorp-tion cycles (c).

Table 1Adsorption kinetic parameters for adsorption of BPA by CD-MG.

Sample Pseudo-first-order kinetic Pseudo-second-order kinetic

qe (mg g−1) k1 (min−1) R2 qe (mg g−1) k2 (gmg−1min−1) h (mg g−1min−1) R2

C-MG 7.1 0.2175 0.9982 7.3 0.0976 5.2 0.9988CD-MG-1 34.0 0.2809 0.9949 34.6 0.0307 36.8 0.9985CD-MG-2 47.9 0.3210 0.9985 48.4 0.0367 86.0 0.9995CD-MG-3 32.2 0.0553 0.9618 35.2 0.0023 2.8 0.9925

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near 1720 and 1560 cm−1, respectively. Furthermore, CD-MG exhibitedcharacteristic IR bands at around 1050 and 1150 cm−1, ascribed to itsantisymmetric glycosidic νa (C–O–C) vibrations and coupled ν (C–C/C–O) stretching vibration, respectively [41].

TGA results provided quantitative information on the compositionof CD-MG. Fig. 1(b) shows that the weight losses below 100 °C were dueto the elimination of the physically adsorbed water from CD-MG. Themajor weight losses occurred between 100 and 500 °C. At 500 °C, C-MG,CD-MG-1, CD-MG-2, and CD-MG-3 lost 17.9%, 20.3%, 22.6%, and34.8% of their weights, respectively. The immobilized β-CD weightratios were calculated to be approximately 2.4%, 4.7%, and 16.9% forCD-MG-1, CD-MG-2, and CD-MG-3, respectively. In short, the FT-IR andTGA measurements revealed that the C-MG had been well functiona-lized by β-CD, with the amount of β-CD increasing in the order of CD-MG-1, CD-MG-2, and CD-MG-3.

The crystalline structures of CD-MG were analyzed by XRD analysis.Fig. 2 shows that CD-MG exhibits well-crystallized magnetite phasesand no characteristic peaks of impure phases, consistent with JCPDScard no. 19-0629, even after the incorporation of β-CD into the MMCsurfaces. The broadened and weakened CD-MG peaks indicated that theamount of incorporated β-CD increased in the order of CD-MG-1, CD-

MG-2, and CD-MG-3 [42].The magnetization of CD-MG was measured using VSM. Fig. 3

shows that there was no hysteresis loop, implying that each CD-MG hadsuperparamagnetic properties [43]. The magnetization values at795.8 kAm−1 for CD-MG-1, CD-MG-2, and CD-MG-3 were 37.0, 26.4,and 11.9 Am2 kg−1, respectively, sufficient to enable efficient magneticseparation of the MMCs from aqueous solutions [15], as shown in theinset of Fig. 3. The saturation magnetizations of CD-MG decreased inthe order of CD-MG-1, CD-MG-2, and CD-MG-3, possibly due to thereduced weight ratios of the MMCs in CD-MG caused by the increasedamount of non-magnetic organic substances on the MMC surfaces [44].

The effects of the β-CD modification on the MMC morphologieswere investigated using FE-SEM and HR-TEM, as shown in Fig. 4. TheFE-SEM images revealed that the C-MG and CD-MG had rough surfacesconsisting of small magnetite nanoparticles with diameters of ca.200 nm. The HR-TEM images demonstrated that organic layers, as-sumed to be β-CD layers, covered CD-MG surfaces. Particularly, thespherical morphologies and agglomerated structures of the MMCspersisted even after β-CD was introduced.

3.2. BPA removal of β-CD-functionalized MMCs

It is suggested that the ability of β-CD to remove BPA from waste-water decreases under basic conditions because BPA becomes depro-tonated at pH > ca. 8.0 [45], thus leading to a decrease in the amountof neutral BPA that can be captured within the hydrophobic cavity of β-CD. This implicates that the adsorption ability of CD-MG is affected bythe pH. Cao and co-workers reported that the prepared adsorbent ex-hibits the maximum BPA adsorption capacity in a pH range of 3.0–9.0[46]. Therefore, we conducted BPA adsorption experiments at pH6.5–7.0, which was attained by adding CD-MG to the BPA aqueoussolution, to achieve the maximum BPA adsorption efficiency.

The BPA adsorption kinetics of CD-MG, with an initial BPA con-centration of 130mg L−1 from 0 to 960min, are shown in Fig. 5(a).BPA adsorption occurred rapidly for the first 10min and achievedequilibrium at around 40min for CD-MG-1 and CD-MG-2. However, forCD-MG-3, adsorption gradually increased until near-equilibrium wasachieved at 130min. It was also confirmed that the C-MG adsorbs asmall amount of BPA, with an equilibrium adsorption capacity of7.1 mg g−1. The kinetics of the adsorption of BPA onto CD-MG wereinvestigated using pseudo-first-order and pseudo-second-order kineticmodels. All the corresponding kinetic parameters were calculated andare presented in Table 1. The results indicate that the BPA adsorption

Table 2Adsorption isotherm parameters for adsorption of BPA by CD-MG.

Freudlich Langmuir

KF (mg1−(1/n) L1/n g−1)) n R2 qL (mg g−1) KL (Lmg−1) RL R2

10.2730 2.8 0.9291 52.7 0.1129 0.0632–0.5838 0.9945

Fig. 6. Schematic of host-guest interaction and hydrogen bonding between BPAand CD-MG.

Table 3Comparison of the adsorption parameters of different magnetic adsorbents for BPA.

Adsorbent Adsorption rate constant Maximum adsorption capacity Reference

CD-poly(glycidyl methacrylate)-MNPs Not evaluated 0.15mg g−1 [28]CD-poly(glycidyl methacrylate)-SiO2-MNPs Not evaluated 22.8mg g−1 [29]POSS-PCL-β-CD/Fe3O4 micelles Not evaluated 28.4mg g−1 [15]Chitosan/fly-ash-cenospheres/γ-Fe2O3

a0.0282 gmg−1min−1 31.9mg g−1 [7]CDP-MNPs a0.0004 gmg−1min−1 74.6mg g−1 [27]β-Cyclodextrin capped graphene-magnetite nanocomposite b2.1 mg g−1min−1 66.0mg g−1 [30]CD-MG a0.0367 gmg−1min−1 52.7mg g−1 This study

b86.0 mg g−1min−1

a Pseudo-second-order adsorption rate constant, K2.b Initial adsorption rate, h.

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by CD-MG can be approximately described using a pseudo-second-orderkinetic model due to the higher correlation coefficient(0.9925–0.9995). Furthermore, CD-MG-2 was selected as the optimumsample for further investigations because it showed the highest equili-brium adsorption capacity (qe), rate constant k2, and initial adsorptionrate (h) for BPA ( = ×h k qe2

2) among the samples.The BPA adsorption isotherms of CD-MG were obtained at various

aqueous BPA concentrations (4–130mg L−1); Fig. 5(b) shows that theisotherm is nonlinear over a wide range of aqueous equilibrium con-centrations. The BPA adsorption behavior of CD-MG was analyzed usingthe Freundlich and Langmuir isotherm models. The calculated isothermmodel parameters are listed in Table 2, which shows that the correla-tion coefficients for the Freundlich and Langmuir isotherm models are0.9291 and 0.9945, respectively, implying that the BPA adsorption ofCD-MG fitted better with the Langmuir model. The maximum BPAadsorption capacity of CD-MG (qL) was 52.7 mg g−1, which was in goodagreement with the experimental maximum value of 49.1 mg g−1.Furthermore, the adsorption characteristics can be classified using theequilibrium parameter or the separation factor RL, defined using Eq.(7):

=+

RK C1

1LL 0 (7)

where KL (Lmg−1) is the Langmuir constant and C0 (mg L−1) is theinitial BPA concentration.

The adsorption process can be classified according to the RL value:irreversible (RL=0), favorable (0 < RL < 1), linear (RL=1), andunfavorable (RL > 1). The RL values evaluated here were0.0632–0.5838, meaning that the adsorption of BPA onto CD-MG wasfavorable. The Langmuir model suggested that CD-MG had a homo-geneously distributed adsorption site and adsorbed BPA as a monolayer[38]. For CD-MG, three adsorption mechanisms were proposed whichinvolve (1) host–guest interactions in the CD cavities, (2) hydrogenbonds between the hydroxyl groups in the BPA and β-CD and (3) hy-drogen bonds between the hydroxyl groups in the BPA and carboxylgroups in C-MG (Fig. 6).

The adsorption parameters (e.g. adsorption rate constant and max-imum adsorption capacity) of CD-MG must be compared with those ofpreviously reported magnetic adsorbents, because doing so would allowus to determine the potential of CD-MG as an adsorbent for the removalof EDCs. The maximum BPA adsorption capacity of CD-MG is com-parable with those reported in the literature, as shown in Table 3.Notably, only two magnetic adsorbents have adsorption capacitiesgreater than that of CD-MG; however, CD-MG exhibited an adsorptionrate constant several tens or hundreds of times greater than those ofother magnetic adsorbents. These may be ascribed to the mesoporousstructure of CD-MG, with a mean pore size of 8.7 nm and a specificsurface area of 35.7m2 g−1 (Fig. S1). Commercial magnetite nano-particles with diameters of 50–100 nm exhibit a specific surface area ofca. 60m2 g−1. In general, nonporous particles with diameters of ca.200 nm should have a specific surface area which is four to sixteentimes smaller than the nanoparticles with diameters of 50–100 nm. Wetherefore concluded that CD-MG has a sufficient specific surface areadespite the diameters being ca. 200 nm due to the mesoporous struc-ture. The mesoporous structure and sufficient specific surface area ofthe adsorbent can enable the rapid and efficient removal of organiccontaminants from water due to the rapid diffusion of the organiccontaminants towards the large number of adsorption sites on the ad-sorbent surfaces [1,47].

Supplementary data associated with this article can be found, in theonline version, at https://doi.org/10.1016/j.apsusc.2018.10.054.

3.3. Regeneration of β-CD-functionalized MMCs

In each round of the reusability tests, after adsorbing BPA fromwastewater, CD-MG was magnetically extracted from the purified

water, and finally the BPA was desorbed from the extracted CD-MG bywashing with ethanol. The regenerated CD-MG was then used in thenext round of reusability tests.

Fig. 5(c) shows that the recovery efficiency of CD-MG was 84.5%after four ad/desorption cycles. This can be attributed to the reversiblenature of BPA adsorption by β-CD, with adsorption in water and des-orption in ethanol because BPA has higher solubility in ethanol than inwater. Conventional adsorbents like activated carbon require the ap-plication of cost-ineffective regeneration procedures which constituteca. 75% of their total maintenance and operating costs [48]. However,CD-MG can be regenerated simply by washing in ethanol for 10min.This could possibly be ascribed to the rapid diffusion of ethanol mole-cules toward β-CD on the CD-MG surfaces due to the mesoporousstructure of the adsorbent. Thus, we concluded that CD-MG is a pro-mising BPA adsorbent, and can be used in water purification processesbecause of its fast adsorption kinetics, high adsorption capacity, andefficient separation.

4. Conclusions

In summary, MMCs functionalized with β-CD (CD-MG) were pre-pared and used to remove BPA from wastewater for the first time. TheFT-IR and TGA results confirmed that β-CD was successfully introducedonto the MMC surfaces by a simple chemical crosslinking. The XRD, FE-SEM, and HR-TEM analyses revealed that the crystal structures andmorphologies of MMCs did not change significantly upon the chemicalintroduction of β-CD to MMC surfaces. Adsorption of BPA onto CD-MGfollowed the pseudo-second-order kinetic model and Langmuir iso-therm model with a superior BPA adsorption rate and capacity to thoseobtained using MNP-based adsorbents. CD-MG can also be regeneratedwith ethanol and reused for the adsorption of BPA without much loss inits adsorption capacity for up to four cycles. The fast adsorption ki-netics, high adsorption capacity, and good recovery efficiency makeCD-MG an attractive candidate material for the efficient and econom-ical purification of industrial wastewater.

Acknowledgments

This research was supported by Basic Science Research Programthrough the National Research Foundation of Korea (NRF) funded bythe Ministry of Science, ICT & Future Planning (No. NRF-2015R1A2A2A01005651).

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