Synthesis and properties of bisphenol A molecular imprinted particle for selective recognition of BPA from water

Journal of Colloid and Interface Science 367 (2012) 355–361

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Synthesis and properties of bisphenol A molecular imprinted particle for selective recognition of BPA from water Yueming Ren a,b, Weiqing Ma a, Jun Ma b,⇑, Qing Wen a, Jun Wang a, Fangbo Zhao a a

Key Laboratory of Superlight Materials & Surface Technology, Ministry of Education, College of Material Science and Chemical Engineering, Harbin Engineering University, Harbin 150001, PR China b State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, PR China

a r t i c l e

i n f o

Article history: Received 27 June 2011 Accepted 2 October 2011 Available online 12 October 2011 Keywords: Surface molecular imprinting BPA Sol–gel Equilibrium binding Selectivity recognition

a b s t r a c t Molecularly imprinted particle for bisphenol A (BPA-MIP) was prepared using the surface molecular imprinting technique with a sol–gel process on the surface of silica nanoparticles. The dosages of diethylenetriaminepentaacetic acid (DTPA) as a functional monomer and teraethyl orthosilicate (TEOS) as a cross-linker were optimized, respectively. The prepared BPA-MIP was characterized by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), Fourier transform infrared spectrometer (FTIR), thermogravimetric analysis (TGA), and a standard Brunauer–Emett–Teller (BET) analysis. Moreover, the proper binding and selective recognition ability were also investigated by a single batch binding experiment. The equilibrium data fitted well to the pseudo-second-order kinetic and the Langmuir model for BPA binding onto BPA-MIP, respectively. The saturate binding capacity of BPA-MIP was found to be 30.26 lmol g1, which was three times higher than that of BPA non-molecular imprinted particle (BPA-NIP). The satisfactory results demonstrated that the obtained BPA-MIP showed an appreciable binding specificity toward BPA than similar structural compounds in water phase. The BPA-MIP could serve as an efficient selective material for determining or removing BPA from water environment. Ó 2011 Elsevier Inc. All rights reserved.

1. Introduction Bisphenol A (BPA, 2,20 -bis (4-hydroxyphenyl) propane) is one of the volume endocrine disruptors with over six billion pounds produced worldwide each year [1,2]. It is widely used as a primary monomer in plastics or resins, as an antioxidant in plasticizers and as a polymerization inhibitor in polyvinyl chloride (PVC) [3]. BPA is frequently detected in environmental water and also can be detected in baby bottles, other consumer plastics, food chains and therefore the human diet [4]. The concern about BPA has risen in that it can interfere with natural hormone systems and cause a wide array of health problems even at low doses [5,6]. Since its ubiquitous nature and estrogenic activity potential, BPA has been included in the environmental water monitoring study by several techniques [7,8]. Thus far, a large number of analytical methods have been available for quantification of BPA, such as liquid chromatography, fluorescence spectrometry, liquid chromatography– mass spectrometry, gas chromatography–mass spectrometry, and enzyme-linked immunosorbent assay (ELISA) [9–11]. However, the extraction and concentration of BPA from water sample require time-consuming and large volumes of organic solvent. Moreover, the common materials for sample pretreatment are lack of selec⇑ Corresponding author. Fax: +86 451 82368074. E-mail address: [email protected] (J. Ma). 0021-9797/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2011.10.009

tivity for these high-sensitivity detection methods [12]. Hence, it needs to prepare a highly selective recognition material for BPA detecting. Molecular imprinted technology (MIT) is an emerging molecular recognition technique, which shapes the specific recognition sites in synthetic polymers by using templates or imprinted molecules [13]. Lately, molecularly imprinted polymers (MIPs) are used in environmental monitoring, food and beverage analysis, and industrial process surveillance [14,15]. In the related literatures, most MIPs are prepared by bulky organic co-polymerization or precipitation polymerization reaction of functional monomers and cross-linkers in the presence of a template molecule. Whereas the conventional MIPs exhibit high selectivity but low binding efficiency, difficult fabrication, embedded imprinted sites in bulk polymer matrices, and hard recognition in water phase [16–21]. Surface molecular imprinting allows binding sites on the surface of support with large surface area, high affinity and selectivity, more accessible sites, and fast binding kinetics. Generally, the surface imprinting technique can be based on the precipitation polymerization or the surface modification of silica gel particles by sol–gel process. Surface imprinted sol–gel materials are fabricated by a conventional sol–gel process and incorporate the template into rigid inorganic or inorganic–organic networks. The most widely used functional monomers have been methacrylic acid (MAA) and 4-vinylpyridine (4-VP) all the time. And so far, the

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common cross-linker is selected as ethylene glycol dimethacrylate (EGDMA) [16]. Today, more techniques about the surface imprinting based on silica gel are reported and paid close attention extensively [22,23]. Very recently, a surface sol–gel imprinting method is reported, for incorporating template and amino-functionalized silica gel into inorganic network through teraethyl orthosilicate (TEOS) hydrolyzation process [24–26]. In addition, the imprinted binding sites are situated on the surface and the particles have good selective recognition and capacity in water phase. However, there are no reports about using the carboxyl group to modify the silica gel particles for BPA imprinting by TEOS hydrolyzation of a sol–gel surface imprinting technique. Herein, we presented a highly selective molecularly imprinted particle for BPA (BPA-MIP) recognition in water phase, with binding sites situated at the surface of silica gel. DTPA and TEOS were selected as a functional monomer and a cross-linker agent, respectively. The optimum molar ratio of BPA to DTPA and BPA to TEOS was studied. The prepared samples were characterized by SEM, EDS, FTIR, TGA, and BET method. The virtue of BPA-MIP and BPANIP was estimated by binding kinetics and isotherms. The selective recognition of BPA from mixture solution was evaluated by static binding tests. BPA-MIP developed in this work can serve as an efficient selective material for enriching and determining BPA from water environment. 2. Experimental 2.1. Materials and chemicals Bisphenol A (BPA), 3,30 ,5,50 -tetrabromobisphenol A (TBBPA), phenol, phenol red (PSP), TEOS, DTPA, acetic acid (AcOH), and all other chemicals were purchased from Sinopharm Chemical Reagent Co., Ltd. (Taijin, China). All the chemicals used were of analytical grade and obtained commercially. Distilled water used throughout the experiments was obtained from laboratory purification system. 2.2. Instrumentations The surface micrograph and element distribution of the prepared samples were assessed by a S4800HSD scanning electron microscope (Japan). FTIR spectra were recorded using an AVATAR 360 FTIR spectrometer with a spectral range of 4000–400 cm1 (USA). The surface area and the pore parameters of the samples were measured by an ASAP 2020 multipoint Brunauer–Emett– Teller apparatus (USA). Thermogravimetric analysis was performed by a NETZSCH STA 409 PC/PG (China). UV-spectrophotometer Tu-1810D (China) was used for detecting the concentration of BPA.

Finally, to remove BPA template, the resulting particles were washed for 14 h with a mixture of methanol and acetic acid (9:1, v/v) by Soxhlet extraction and then dried under vacuum at 80 °C for 12 h. As a reference, BPA-NIP was prepared by the same protocol without the template. 2.4. Batch binding and regeneration experiments Single batch binding experiments were conducted to test the binding kinetics, isotherms, and selectivity of BPA onto the BPAMIP. All binding experiments were carried out in 100 mL flasks, each containing 30 mL adsorbate solution. 0.1 g BPA or its analogs (TBBPA, phenol or PSP) was dissolved in 1 L distilled water to form BPA stock solution. The adsorbate solution was diluted by their each stock solution. After the addition of 0.015 g of the prepared particles each, the flasks were shaken at 200 rpm and 25 ± 2 °C for 4.0 h (having achieved the binding equilibrium). The pH of the mixture was remained at about 7.0. For the binding kinetics experiment, the specimens were sampled at defined time intervals from 10 to 360 min with 8.77 lmol L1 BPA initial concentration. The binding isotherms were investigated over various initial concentrations ranging from 2.19 to 87.72 lmol L1 of BPA solution. The selectivity adsorption experiments were conducted by preparing single solution of BPA, TBBPA, phenol, or PSP with each initial concentration of 2 mg L1. TBBPA, phenol, and PSP were used as compared agents since their chemical molecular structures are similar to BPA to a certain extent. In order to test the reproducibility, the experiments were carried in duplicate and the reproducibility was found to be within ± 2%. After binding equilibrium, the saturated sample was separated by centrifugation, and the residual concentrations of BPA, TBBPA, phenol, and PSP were determined by a UV-spectrophotometer at 276, 290.5, 270, and 314 nm, respectively. The binding capacity (q) and efficiency (E) were calculated by the following equations [28]:

ðC 0  C e ÞV W C0  Ce E¼  100% C0

q¼

ð1Þ ð2Þ

where q (lmol g1) is the adsorbate binding capacity, C0 and Ce (lmol L1) are the initial and equilibrium adsorbate concentrations

Imprinted sites

2.3. Preparation of samples The uniform silica nanoparticles were synthesized by TEOS hydrolysis with ammonium hydroxide according to the report by Stöber [27]. The nanoparticles were finally washed with anhydrous ethanol and dried. BPA-MIP was prepared by the surface molecular imprinting technique with a sol–gel method. First, 0.4 g silica was dispersed homogeneously in 20 mL methanol by ultrasonic dispersion for 20 min to form suspension A. 0.4 g BPA was dissolved in 2 mmol DTPA aqueous solution to form an uniform solution B. Then, the solution B, different dosages of TEOS and AcOH were sequentially added into the suspension A under stirring. The polymerization reaction was carried out at 30 °C under stirring for 18 h to obtain particles with a high cross-linking structure. Subsequently, the obtained products were washed several times with ethanol to neutral and dried at 80 °C for 12 h in a vacuum oven.

prone to hydrolysis

Fig. 1. Schematic procedure of BPA-MIP preparation.

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100 90 80

E (%)

70 60 50 40 30 20 10 0

1:0.4

1:0.6

1:1

1:1.2

1:1.6

molar ratio (BPA to DTPA)

1:5

1:10

1:15

group of BPA [20]. And the other carboxyl groups in DTPA might react with alkoxysilane to form Si–O–C. It was quite prone to hydrolysis in the presence of water, but the hydrolysis products would not destroy the imprinting sites proved by the reuse test. A large number of BPA tailor-made vacancies were formed on the surface of silica nanoparticles after the binding BPA was removed. These imprinted cavities had complementation into the form, size, and chemical property of the BPA molecule. Moreover, the delicate imprinted cavities were stabilized due to the target molecule was imprinted as a stable complex with a functional monomer formed via hydrogen bonding with a similar bond distance. That is, carboxylic acid groups were left in the cavities, which could give hydrogen bonds to the templates or bind with the templates through electrostatic attraction.

molar ratio (BPA to TEOS) 3.2. Selection of DTPA and TEOS dosages

Fig. 2. Effect on BPA-MIP preparation (indicated by E%) of different DTPA and TEOS dosages (indicated by molar ratio with BPA). Sorbent: 0.5 g L1, C0: 8.77 lmol L1, pH: 7, T: 25 °C, t: 4.0 h.

in the solution, respectively, V (L) is the volume of the solution, m (g) is the amount of the samples added to the solution. BPA-MIP was desorbed using Soxhlet extraction with a mixture of methanol and acetic acid (9:1, v/v) at 90 °C for 12 h. Then, the samples were used in the next binding cycle after washing and drying.

3. Results and discussion 3.1. Preparation of BPA-MIP Fig. 1 shows the possible reaction mechanism of BPA-MIP preparation. In this procedure, DTPA was used as a functional monomer and combined with BPA mainly by abundant carboxyl groups [29]. TEOS acting as a cross-linker reagent was easy to hydrolyze under the existence of AcOH catalyst. On the one hand, the hydrolytic products designed to graft the carboxyl groups on the surface of silica nanoparticles by polymerization. On the other hand, these hydrolytic products rebound the template in the imprinting network on the surface of silica nanoparticles. Concretely, the BPA-imprinted sites were obtained by the hydrogen bond coactions between the generated carboxyl group of DTPA and hydroxyl

The suitable dosages of functional monomer and cross-linker were crucial factors effecting on the number of imprinted sites formation. The binding efficiency of BPA onto BPA-MIP was studied at different dosages of DTPA and TEOS (indicated by molar ratio with BPA). As seen in Fig. 2, the binding efficiency increased with the increasing DTPA dosage and reached the maximum value of 91.2% at the molar ratio of BPA to DTPA for 1:1. Then, the values decreased with further increasing DTPA dosage. In the same way, BPA-binding efficiency increased gradually with the increasing TEOS dosage and achieved the maximum value of 90.1% at the molar ratio of BPA to TEOS for 1:10. Hence, the optimum dosage was 1:1:10 M ratio of BPA to DTPA and TEOS in BPA-MIP synthesis process. 3.3. Characterization of prepared samples 3.3.1. Physical properties The morphology and the element distribution of SiO2, BPA-NIP, and BPA-MIP are shown in Fig. 3. The difference between the SiO2 nanoparticle and BPA-MIP was obviously. The SiO2 microparticles displayed uniform spherical shape with smooth surface and the average particle size of approximately 300 nm. However, the surface of BPA-MIP had a mass of floccules-like film as shown in Fig. 3e. Moreover, the average particle size expanded to about 450 nm, because the formation of molecularly imprinted polymer

(a)

(c)

(e)

(b)

(d)

(f)

Fig. 3. The SEM micrographs of (a) SiO2, (c) BPA-NIP, and (e) BPA-MIP, element distribution of (b) SiO2, (d) BPA-NIP, and (f) BPA-MIP.

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BPA-MIP

4000

3500

3000

2500

2000

1500

1000

-1

qt (µmol g )

1078 919

474

1064 978 810

14

Legends: Experimental Lines : Theoretical Pseudo-first-order Pseudo-Second-order

12 10 8 6 4

474

1128 986 810

1637 1407

1407

1637

3414 3414

SiO2

3414

DTPA

BPA-MIP BPA-NIP

16

2 0

0

50

wavenumber (cm-1)

film on the surface of silica. The transfer of the elemental distribution on SiO2 nanoparticles and BPA-MIP showed a qualitative evaluation of surface modification. Only Si and O element signals occurred in SiO2 nanoparticles with its own elements (Fig. 3b). Contrastively, the C element signal appeared in BPA-MIP (Fig. 3f). Therefore, the appearance of carbon demonstrated the BPA-MIP had been successfully prepared. While the surface topography and element distributions of BPA-MIP were not greatly different from BPA-NIP (Fig. 3c and d). The specific surface area of BPA-MIP and BPA-NIP were found to be 173.8 m2 g1 and 102.4 m2 g1, respectively. Furthermore, the total pore volume and average pore diameter of BPA-MIP were 0.8335 cm3 g1 and 26.04 nm, which were 15.3 and 3.1 times more than that of BPA-NIP, respectively (data not shown). After imprinting, the BPA-MIP was featured of greater specific surface area, pore volume, and pore size. 3.3.2. FTIR and TGA analysis FTIR employed to characterize SiO2, DTPA, and BPA-MIP samples are shown in Fig. 4. The IR spectrum of SiO2 showed that the binding bands around 1128 cm g1 and 986 cm1 indicated Si–O–Si vibration. And the peaks around 810 cm1 and 474 cm1 were attributed to Si–OH and Si–O stretching vibrations in the form of silica nanoparticles, respectively [15,30,31]. Seen from IR spectrum of DTPA, the bands near 1637 cm1 and 1407 cm1 represented C@O and CAOH bandings of carboxylate in DTPA, respectively [30–32]. Moreover, the bands at 1078 cm1 and 919 cm1 were connected to CAOAC and CAH stretching

100

98

96 BPA-NIP

94

BPA-MIP

90 100

200

300

400

500

600

700

o

Temperature ( C) Fig. 5. TGA curves of BPA-NIP and BPA-MIP.

250

300

350

vibrations of the DTPA unit, respectively [22,30,31]. In IR spectrum of BPA-MIP, the binding bands at 1064 cm1 and 978 cm1 which represented SiAOAC stretching vibrations appeared in the FTIR spectra of BPA-MIP. Besides, the characteristic peaks of C@O (1637 cm1) and CAOH (1407 cm1) bandings in DTPA also presented in the FTIR spectra of BPA-MIP. These results suggested that DTPA had successfully grafted on the surface of silica nanoparticles and the BPA-imprinted groups were formed. After BPA imprinting, the thermal stability of BPA-MIP enhanced. As shown in Fig. 5, the weight loss processes of BPA-MIP experienced three periods: the loss of absorbed water at temperature from 25 to 100 °C, the break of the functional groups (little hydroxy and abundant carboxylic groups) on the surface of silica at temperature from 100 to 392 °C, and the rapid decomposition of entire floccules-like film on the surface of silica beyond 392 °C. Moreover, the weight loss trend of BPA-NIP was similar to that of BPA-MIP. According to the weight loss obtained from TGA analysis, the amount of entire coating was estimated as 7.7% of the total mass for BPA-MIP and 6.0% of the total mass for BPA-NIP, respectively. Such distinction was due to the existence of floccules-like imprinting coating on the surface of silica during the imprinting process. 3.4. Binding kinetics In our study, two most common kinetic models are employed to simulate the binding procedure: Lagergren pseudo-first-order (Eq. (3)) and pseudo-second-order model (Eq. (4)) [28]:

logðqe  qt Þ ¼ log qe 

0

200

t (min)

t 1 1 ¼ þ t qt k2 q2e qe

92

150

Fig. 6. Adsorption kinetics of BPA binding onto BPA-MIP and BPA-NIP. Sorbent: 0.5 g L1, C0: 8.77 lmol L1, pH: 7, T: 25 °C.

Fig. 4. FTIR spectra of SiO2, DTPA, and BPA-MIP.

weight (%)

100

500

800

ð3Þ k1 t 2:303

ð4Þ

where qe (lmol g1) and qt (lmol g1) are the amount of BPA binding on the samples at equilibrium and t (min), respectively, k1 (min1) and k2 (g lmol1 min1) are the first-order and the second-order rate constant, respectively, k2 q2e (lmol g1 min1) is the second-order initial binding rate as t ? 0. It was readily apparent from Fig. 6 that significant BPA-binding equilibrium on BPA-MIP and BPA-NIP occurred in 180 min and 90 min, respectively, and no appreciable changes in terms of binding were noticed after that. Compared with BPA-NIP, it was a much higher binding capacity for BPA binding onto BPA-MIP. These indicated that molecular imprinting process had resulted in the formation of specific recognition sites on the surface of BPA-MIP. However, the imprinting floccules-like films postponed the binding

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Y. Ren et al. / Journal of Colloid and Interface Science 367 (2012) 355–361 Table 1 The kinetics parameters of BPA binding onto BPA-MIP and BPA-NIP. qe, exp (lmol g1)

Samples

Pseudo-first-order model 2

1

k1 (min BPA-MIP BPA-NIP

15.44 8.86

35

0.0078 0.0079

R

qe, cal (lmol g

0.760 0.306

4.65 1.06

BPA-MIP Experimental BPA-NIP Experimental

30 25

Langmuir model

-1

qe (µmol g )

)

Pseudo-second-order model

20

Freundlich model 15 10

Langmuir model

5

Freundlich model 0 0

10

20

30

40

50

60

70

-1

Ce (µmol L ) Fig. 7. Adsorption isotherms of BPA binding onto BPA-MIP and BPA-NIP. Sorbent: 0.5 g L1, pH: 7, T: 25 °C, t: 4.0 h.

equilibrium time for BPA-MIP. As shown in Table 1, the pseudosecond-order model was perfectly suitable to describe (R2 > 0.99) BPA binding onto BPA-MIP and BPA-NIP. The theoretical qe values perfectly agreed with the experimental qe values, while very poor or no correlation was found for the pseudo-first-order model. The BPA initial binding rates (k2 q2e ) were 1.50 and 1.85 lmol g1 min1 for BPA-MIP and BPA-NIP, respectively. The slow uptake rate might be attributed to availability of the actual binding sites in BPA-MIP [33]. Thus, the pseudo-second-order mechanism was predominant and the chemisorption might be the rate-limiting step controlling the BPA-binding process [34].

3.5. Binding isotherm Langmuir and Freundlich isotherm models are used for describing the results of BPA binding onto BPA-MIP and BPA-NIP. They are expressed as [28]:

Ce Ce 1 ¼ þ K L qm qe qm log qe ¼ log K F þ

ð5Þ 1 log C e n

ð6Þ

where qe (lmol g1) and Ce (lmol L1) are the same as in Eqs. (3) and (1), qm (lmol g1) is the maximum binding capacity, KL (L lmol1) is Langmuir binding coefficient, KF ((lmol g1) (L lmol)1/n) is Freundlich binding coefficient, and n is Freundlich binding constant.

1

)

k2 (g lmol1 min1)

R2

qe, cal (lmol g1)

0.0058 0.0229

0.999 0.999

16.04 8.98

As shown in Fig. 7 and Table 2, the results indicated that Langmuir model of BPA binding onto BPA-MIP and BPA-NIP ideally matched with the experimental data (R2 > 0.99). Apparently, the binding occurred on a homogeneous surface by monomolecular layer sorption without any interaction between the bound molecules in the transverse action [33]. Moreover, the maximum binding capacity (qm) from the Langmuir isotherm of BPA-MIP (qmBPA-MIP = 30.26 lmol g1) was approximately three times higher than that of BPA-NIP (qmBPA-NIP = 10.09 lmol g1). Obviously, the imprinting process had greatly improved the high binding capacity for BPA. Ikegami et al. [20] prepared a kind of BPA-imprinted polymer with the binding capacity of 10.7 lmol g1. Takeda et al. [18] reported a MIP powder, and the binding capacity for the imprinted BPA was 20 lmol g1. Generally, the reported BPA molecularly imprinted polymers were synthesized by conventional organic polymerization reaction with methacrylic acid or methacrylic derivatives as functional monomers and usually applied in HPLC and SPE field to identify in organic phase such as methanol and ethanol [9,19]. After comparing our results with the literatures, BPA-MIP prepared in our work possessed higher binding ability and selectivity, which could distinguish BPA from pure water phase. Above all, the synthetic materials of BPA-MIP were cheaper and environmentally friendly.

3.6. Selectivity binding and reuse characters The selective binding character of BPA-MIP was evaluated toward BPA, TBBPA, phenol, and PSP, which were selected as latent interferon due to their similar chemical molecular structures. As shown in Fig. 8, the binding efficiency of BPA, TBBPA, phenol, and PSP could be up to 91.2%, 34.7%, 20.2%, and 14.6% after treated by BPA-MIP, respectively. However, BPA-NIP had a low binding efficiency for these four adsorbates. The binding difference between BPA-MIP and BPA-NIP for TBBPA was only 13.2% but for BPA could reach 55.9%. It showed that BPA-MIP was sensitive to the presence of BPA and had a good selectivity and efficiency for recognition of the imprinted BPA molecular. Otherwise, BPA-NIP had no selectivity. It was difficult to explain such selective binding mechanism. As pointed out by ‘‘gate effect’’ model [35], the reason of BPA-MIP recognizing its template molecule was due to the existence of memory cavities. After BPA imprinted, the template could be analogous to the ‘‘key’’, and the sites in BPA-MIP for exclusive rebinding with BPA could correspond to the ‘‘lock’’ in the ‘‘gate’’ analogy. As confirmation by binding results [36] might be helpful in such an explanation. There were two possible explanations for the selectivity of the imprinted molecule over the analogs. The first key factor was the molecular volume. The second was that the strength of the interaction between the target molecule and

Table 2 The Langmuir and Freundlich isotherm model parameters of BPA binding onto BPA-MIP and BPA-NIP. Samples

BPA-MIP BPA-NIP

Langmuir model

Freundlich model

qm (lmol g1)

KL (L lmol1)

R2

KF ((lmol g1) (L lmol)1/n)

1/n

R2

30.26 10.09

0.296 0.183

0.999 0.994

9.671 2.798

0.298 0.324

0.789 0.838

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 BPA-MIP displayed a mass of floccules-like film on the surface, average particle size of 450 nm and the specific surface area of 173.8 m2 g1. The total pore volume and average diameter were 15.3 and 3.1 times than that of BPA-NIP, respectively. DTPA was successfully grafted and the imprinted sites formed on the surface of silica nanoparticles.  The BPA binding onto BPA-MIP process reached the equilibrium at 180 min, the initial adsorption rate was 1.50 lmol g1 min1. The binding kinetics closely followed the pseudo-second-order kinetic model.  Langmuir isotherm was fitted for the experimental data of BPA binding onto BPA-MIP. The maximum binding capacity was 30.26 lmol g1, which was three times higher than that of BPA-NIP.  BPA-MIP had highly selective binding character toward similar chemical molecular structures in aqueous solution; it could be reused more than five times without weakening the binding capacity significantly.

100

E (%)

80 60 40 20 0 BP

A -M

IP

BP

A-

P NI

PS P

H

C

O

S

l

PSP

Phenol

TBBPA

BPA

Ph en o

BP A TB BP A

Acknowledgment

Br

Fig. 8. Binding efficiency and stereo-models of different competitive molecules. Sorbent: 0.5 g L1, Cadsorbate: 2 mg L1, pH: 7, T: 25 °C, t: 4.0 h.

100

80

We appreciate the financial support of National Natural Science Foundation of China (Nos. 51108111, 51178134), Open Project of State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology (No. ES201006), Fundamental Research Funds for the Central Universities (HEUCFZ 1107), and China–Japan–Korea Joint Research Collaboration Program (2010D FA92460).

E (%)

References 60

40

20

0 1

2

3

4

5

Times Fig. 9. BPA-binding efficiencies onto BPA-MIP after five reuse cycles.

binding sites. We considered that the different molecular volume and dimensional structure between the binding sites in the floccules-like film on the silica surface and the targets would determine the selectivity of BPA molecular recognition. The reuse cycles of BPA binding were repeated five times for the same BPA-MIP by Soxhlet extraction. Interestingly, as seen in Fig. 9, the binding efficiency still remained as 85% after five cycles, and BPA-MIP could be effectively regenerated for further use with only about 6% loss of initial binding capacity. 4. Conclusions BPA-MIP was prepared by the surface molecular imprinting technique with a sol–gel process on the surface of silica nanoparticles; it presented a good selectivity binding for BPA in water phase. The results clearly confirmed that BPA-MIP had a potential use in BPA monitoring or a rapid selective enrichment application in water environmental. The main results were as follows:  DTPA and TEOS were used as a functional monomer and a crosslinker, respectively. The optimum molar ratio of BPA to DTPA and TEOS is 1:1:10 M for BPA-MIP preparation.

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