Generation of a Molecular Imprinted Membrane by Coating Cellulose

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The generation of a molecular imprinted membrane by coating cellulose acetate onto a ZrO2-modified alumina membrane for the chiral separation of mandelic acid enantiomers Huichang Li, Qiang Huang, Dan Li, Shujie Li, Xiaoru Wu, Longfei Wen, and Chunlan Ban Org. Process Res. Dev., Just Accepted Manuscript • DOI: 10.1021/acs.oprd.7b00054 • Publication Date (Web): 31 Jan 2018 Downloaded from http://pubs.acs.org on February 1, 2018

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Organic Process Research & Development

The generation of a molecular imprinted membrane by coating cellulose acetate onto a ZrO2-modified alumina membrane for the chiral separation of mandelic acid enantiomers Huichang Li, Qiang Huang*, Dan Li, Shujie Li, Xiaoru Wu, Longfei Wen, Chunlan Ban

School of Chemical Engineering and Energy, Zhengzhou University, Zhengzhou 450001, P.R. China

∗ Corresponding author. Tel.: +86 871 67781292;. E-mail addresses: [email protected]

1

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Abstract: An alumina template modified with ZrO2 was coated with cellulose acetate (CA) containing imprinted molecules for a novel enantioselective membrane. The preparation, morphologies and properties of the different membranes were introduced and investigated. The morphologies of the membranes were examined using a scanning electron microscope. The best performance of CA amounts in casting solution was observed when it was 15 wt.% and choose as the preparation of resulting membrane. S-(+)-mandelic acid was used as imprinted molecules to prepare the molecular imprinted nanochannel membrane which enhanced the permselectivity and flux compared with the traditional membrane and the separation factor was as high as 35. And this membrane has the best separation effect on the (R, S)-mandelic acid when compared with (R, S)-malic acid and (R, S)-lactic acid. Key words: Mandelic acid; Cellulose acetate; Chiral separation; Nanochannel; Molecular imprinted membrane

1．． Introduction Mandelic acid (MA), which called alpha-hydroxybenzene acetic acid, is a chiral molecule (Fig. 1). Obvious differences can be discovered in the chiral isomers such as physiological activity, efficacy and toxicity. Available data shows that more than 50 % of worldwide-approved drugs are chiral. Thus, an economical, practical and convenient method for chiral separation of enantiomers is of importance. Currently, many classical approaches for the separation of racemic compounds are known

1, 2

but these conventional methods have many procedural and financial shortcomings, 2


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particularly when processing small amounts of optically active compounds in a single operation

3-5

. Because membrane technology has the advantages of good

operability, this technology has been proved to be a robust approach for large-scale chiral separation with a good prospect

6, 7

. Considering the drawbacks of

conventional methods and potential advantages of membrane processing, membrane technology has been an emerging technology for the chiral separation of racemic compounds 8-14. There are two types of membrane separation methods: liquid membrane separation and chiral solid membrane separation

15-18

. However, liquid membrane

processes have low stability and a short lifetime when tested under industrial separation conditions

5, 16, 19

. Therefore, in recent years, a chiral solid film, called

chiral selective polymer film, has been used. This solid membrane can be prepared via molecular imprinting technology 20-23. Molecular imprinting technique（MIT）is a technique for preparation of polymer networks with selective recognition of the spatial structure of a particular molecule. The technique of the molecular imprinting technique（MIT）has developed rapidly in recent years because of its predictability, recognizability and practicability. So it has a good application prospect in the field of chiral separation, simulated enzyme catalysis, membrane separation and so on. Cellulose acetate (CA) is polysaccharide derivative which was widely used in separating and analysing of chiral samples

12, 24, 25

. Because it exhibits high

selectivity, easy processing, strong plasticity and easy film formation, etc. In recent years, it has been reported that CA has been successfully incorporated into an 3



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asymmetric chiral polymer membrane, and the membrane has a selective permeation ability to trans-1,2-two phenyl ethylene oxide enantiomers, however, while increasing the percentage of enantiomers excess (% e.e.), the flux decreased suggesting a trade-off relationship. Therefore, the focus of the study is how to increase the flux and the percentage of enantiomers excess (% e.e.) at the same time. In this article, the cellulose with imprinted molecules coated on the aluminum oxide template was studied, with the goal of increasing both enantiomers excess and flux. H OH

H

OH O

O

OH

OH R-(_)-MA

S-(+)-MA

Figure 1. Chemical structure of MA enantiomers

2. Experimental details 2.1. Materials Cellulose acetate (CA), with an acetyl content of 54.5-56.0%, was purchased from Sinopharm Chemical Reagent Co., Ltd, and used without purification. (R,S)-mandelic acid and S-(+)-mandelic acid were purchased from Heze Chenxu Chemicals Co., Ltd. S-(+)-mandelic acid was used as print molecules without further purification. (R,S)-malic acid was purchased from Zhengzhou Tianshun Food Additive Co., Ltd. (R,S)-lactic acid was purchased from Shanghai BaYuan Chemicals Co., Ltd. N,N-Dimethylformamide (DMF) was purchased from The Recovery of Tianjin 4


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Science And Technology Development Co., Ltd. Acetone was purchased from Luoyang Chemical Reagent Plant. Alumina template was purchased from Hefei Primeton Nano Technology Co., Ltd with pores of 40-70 nm，80-100 nm，and 100-150 nm. All reagents were analytical grade and used without any further purification. The water was purified using an ultrapure water system (Simpli Lab, Millipore S.A. Molsheim, France) and subsequently used as solvent in feed solutions. A scanning electron microscope (JEOLJSM-6700F) was used to examine the morphology of the membranes. The optical rotation of the receiving liquid measured using a digital optical instrument under 20℃±2℃ was purchased from Shanghai Precision Science Co., Ltd（WZZ-1S）.

2.2 Membrane preparation 2.2.1 The preparation of cast film liquid and the molecular imprinted membrane CA was dissolved in a mixture of acetone and DMF (16/6, v/v). Different thicknesses can be formed with different concentration of CA, followed by stirring for 24 hours with S-(+)-mandelic acid used as imprinted molecules, ultrasound for 30 min and deforming. The ratio of imprinted molecules to CA was 1:10. Under conditions of 40% humidity and 10 °C, the resulting uniform casting film liquid was coated onto a smooth flat glass plate using a casting knife, followed by static evaporation for 5 min for the phase separation of the cast film liquid and subsequent immersion in pure water at 10 °C. The membrane was detached from the glass plate

5



and washed in an aqueous ethanol solution for 24 hours. After washing five times, until the concentration of acetone, DMF, and the imprinted molecules were changed to 0 with the analysis of UV at the wavelength of 210 nm. The membrane was washed with pure water and stored in pure water until further use. The membrane formation of the non-imprinted molecular membrane was found using the same procedures as the imprinted molecular membrane. 2.2.2 Preparation of the alumina nanochannel membrane modified with zirconia According to the literature, the instability of alumina film, the most promising film for the application of nanofiltration is zirconia film 26, 27. Compared with Al2O3 film materials, ZrO2 film has a higher mechanical strength and better thermal and chemical stability 28, 29. The alumina nanochannel film was modified with ZrO2 through the deposition of ZrO2 onto the inner wall and all the surface of the alumina film nanopore using the sol-gel template synthesis method. A sol precursor solution was prepared after mixing anhydrous ethanol and distilled water at the mass ratio of 1:1 and subsequently added the solution to the ZrOCl2·8H2O formulated Zr+ transparent solution at a concentration of 1 mol/L. Next, H2O2 was added to the solution mixture and stirred for 30 min. Ammonia was slowly added to the solution, while rapidly stirring, resulting in the gradual formation of a transparent sol (pH=4). The sol was stored at room temperature for 48-72 hours prior to the formation of wet sol. The alumina film was immersed in the wet sol solution, followed by ultrasound 6


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for 30 min. The saturated wet sol was subsequently placed in the air for 10 min. After sonicating in pure water for 3 min to remove the impurities adsorbed onto the channel, the ZrO2-modified alumina film was placed into a vacuum drying box. 2.2.3 Preparation of a molecular imprinted nanochannel membrane The ZrO2-modified channel membrane was immersed in acetone, followed by ultrasonication for 5 min. After rinsing with water and drying, the membrane was immersed in cast film liquid with S-(+)-mandelic acid used as imprinted molecules, followed by ultrasonication for 30 min. Next, the membrane was subjected to static evaporation for 5 min for the liquid phase separation of the cast film and subsequently immersed in pure water at 10 °C, followed by washing in an ethanol aqueous solution for 24 hours to remove the acetone and DMF, and the imprinted molecules were barely detectable using UV analysis (Fig. 2). The final prepared film was stored in water until further use.

Alumina nanochannel film

ultrasonication static evaporation

Modified

Alumina nanochannel membrane

immersed in solution containted

with ZrO2

modified with zirconia

with CA and imprinted molecule

Modified film was coated with CA and imprinted molecule

immersed in pure water

Form

washing in an ethanol aqueous

nanochannel membrane

the

imprinted

Figure 2. Flow chart of the process for the preparation of the molecularly imprinted nanochannel membrane.

7



2.3 Permeation experiment The prepared membrane (effective area of 7.0 cm2) was fixed in the membrane test apparatus (Fig. 3) with a 100-mL capacity. A total of 50 mL of (R,S)-mandelic acid at a concentration of 10 mmol/L was used as the feed solution. The received filtrate was sealed and stored to measure rotation using an optical instrument. In this experiment, the driving force was the pressure obtained after adjusting the rotation of the measuring device using nitrogen. The permeation experiments were performed under 2 kgf/cm2 pressure18 at room temperature, and all membranes were only used once.

Figure 3. Schematic diagram of the membrane cell used: (1) N2; (2) pressure release valve; (3) nut; (4) inlet of feed solution; (5) feed solution; (6) stirring bar; (7) porous plate; (8) lampstand; (9) compacting bar; (10) membrane; (11) permeate.

2.4 Membrane performance definitions The flux of the aqueous mandelic acid solution was measured according to the following equation 4: 8


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Flux(mg/cm ∗ min) =

(1)

where Q is the mass of the solute permeated for a given time, t is the permeation time and A is the effective membrane area. The selective permeation of the membrane is represented as the percentage enantiomers excess [e.e.(%)], using the following equation:

e. e(%) = where

!"

× 100

(2)

is the S-enantiomer concentration and

!#

is the R-enantiomer

concentration in the permeation. The separation factor α is determined based on the upstream and downstream concentration, using the equation α = (

!" ⁄ !# )⁄( &" ⁄ &# ) ,

where

!#

and

!"

represent the concentrations of the R- and S-isomers in the permeation, respectively, and

&#

and

&"

represent the concentrations of R- and S-isomers in the feed

solution, respectively. Because

&"

and

&#

are equal, the formula can be

simplified as

α=

'()

(3)

'(*

The separation of series (N) was calculated according to the equation as follows: 0

O. P. % = 1 − [1]3

(4)

Where O. P. % is the optical purity to be achieved, α is the separation factor, and N is the separation of series.

3. Results and discussion 3.1 The morphology of the ZrO2-modified Al2O3 membrane 9



Cross section

Top surface

a

b

c

d

Figure 4. SEM images of Al2O3 film (a and b, the pore is 80-100 nm) and Al2O3 film modified with ZrO2(c and d)

A scanning electron microscope (SEM) was used to characterize the top surface and the cross-section of Al2O3 film before and after ZrO2 modification. To investigate the cross-section, the area of the alumina template film where ZrO2 was deposited was placed onto the vertical surface, demonstrating that the thickness of ZrO2 on the Al2O3 surface was 6.00 µm (Fig. 4 (c)). The membrane of the loaded ZrO2, whether from a cross section or top surface perspective, was not the same as 10


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the crude channel film (Fig. 4 (a) and (b)). The top surface was inhomogeneous and some holes on the top surface had been covered with zirconium oxide compared with the crude channel film.

3.2 Elemental analysis 3.2.1 Elemental analysis of the ZrO2-modified Al2O3 film surface

Figure 5. Results and data of the elemental analysis of Al2O3 film modified with ZrO2 (High voltage: 20.5 kV, Pulse: 1.87 kcps)

Table 1. Data of the elemental analysis of the top surface El

AN

Series

Unn.[wt.%]

Norm.[wt.%]

Atom.[at.%]

Error (1Sigma) [wt.%]

O

8

K-series

37.00

44.20

53.76

5.29

Al

13

K-series

33.51

40.02

28.86

1.56

C

6

K-series

7.98

9.54

15.45

2.24

Zr

40

L-series

3.73

4.45

0.95

0.20

Cl

17

K-series

1.49

1.79

0.98

0.10

11



Total:

83.72

100.00

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100.00

3.2.2 Elemental analysis of the Al2O3 film channel

Figure 6. Results and data of the elemental analysis of Al2O3 film channel modified with ZrO2 (High voltage: 20.5kV, Pulse: 1.87 kcps)

Table 2. Data of the elemental analysis of the cross section El

AN

Series

Unn.[wt.%]

Norm.[wt.%]

Atom.[at.%]

Error (1Sigma) [wt.%]

O

8

K-series

39.47

45.27

55.71

5.2

Al

13

K-series

31.87

36.55

26.67

1.6

C

6

K-series

8.00

9.18

15.04

1.9

Zr

40

L-series

6.22

7.14

1.54

0.3

Cl

17

K-series

1.62

1.86

1.03

0.1

87.17

100.00

100.00

Total:

The chemical component was determined through elemental analysis using a large membrane (inset in Fig. 5 and 6), and the results are elaborated in Fig. 5, 6 and Tables 1, 2. Table 1 shows that the surface of the ZrO2-modified Al2O3 film contains 12


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oxygen, aluminium, carbon, zirconium, and chlorine, with 53.76 at.% 28.86 at.% 15.45 at.%, 0.95 at.% and 0.98 at.%, respectively. The carbon content on the film was high, likely reflecting the conductive adhesive under the film, which contains carbon element. Table 2 shows that the channel of the Al2O3 film contains oxygen, aluminium, carbon, zirconium, and chlorine, with 55.71 at.%, 26.67 at.%, 15.04 at.%, 1.54 at.%, and 1.03 at.%, respectively.

These results demonstrate that ZrO2 is not only loaded onto the surface but also coated in the channels of the film.

3.3 Effect of CA concentration on the morphologies and properties of the CA membrane Cross section

Top surfac

a

b

13



c

d

e

f

Figure 7. SEM images of the CA membrane prepared with 10 wt.% (a and b), 15 wt.% (c and d), and 20 wt.% CA (e and f).

To demonstrate the morphology of the membranes, the surface and cross section of the membranes were characterized through SEM. Representatives images are shown in Fig. 7. Prior to the scanning analysis, the wet membrane was prepared and treated with propanol and heptane to retain the original structures. The surface and cross section structure of the film was observed on the SEM after coating with gold using an ion sputtering apparatus. As we can see in Fig. 7 (b ,d ,f) clearly, the surface has obvious holes and a homogeneous structure. As the amount of CA increased, on the one hand, the number of holes decreased, which could be described in the flux of Fig. 8. On the other hand, the film thickness which is shown on the cross-section of 14


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membrane increased in Fig. 7 (a ,c ,e), and the film thickness is 1.69µm, 17.1µm and 28.1µm, respectively.

Figure 8. Flux and e.e.(%) in the enantioseparation of (R,S)-mandelic acid through CA membranes fabricated with 10, 15, and 20 wt.% CA. The operating pressure and feed concentration were 2 kgf/cm2 and 10 mmol/L, respectively.

To detect the effect of the CA concentration on transmission selection, membranes with three different CA concentrations in the casting solution were prepared at cellulose acetate concentrations of 10 wt.%, 15 wt.% and 20 wt.%, respectively. Fig. 8 shows that the flux of the membrane decreased with increasing cellulose acetate concentration and test duration. This finding likely reflects the fact that the number of membrane pore decreased, indicating that the structure of the membrane became increasingly more compact with increasing CA concentration in the casting solution and the flux of the membrane decreased.

15



Figure 9. The separation factors in the enantioseparation of (R,S)-mandelic acid through CA membranes prepared with 10, 15, and 20 wt.% CA. The operating pressure and feed concentration were 2 kgf/cm2 and 10 mmol/L, respectively.

Fig. 9 shows that when the CA concentration was 15 wt.%, the membrane exhibited the best selectivity, and when the CA concentration was 10 wt.%, the membrane exhibited the worst selectivity. In Fig. 10, the small gray diamond represents the chiral recognition site and the denser the number of diamond, the more chiral recognition sites on the membrane. When cellulose content in the casting solution was 10 wt.%, after formation of the membrane, the chiral recognition sites were limited. That is, the feed solution from one chiral site was too far to reach another site (Fig. 10 (a)), thereby decreasing the e.e.(%). When the cellulose content in the casting solution was 15 wt.%, the distance between the two chiral sites was appropriate, and the feed liquid could be sequentially identified according to each chiral recognition site (Fig. 10 (b)), thereby increasing the e.e.(%). However, when the cellulose content in the casting solution was 20 wt.%, many chiral recognition sites were observed in the membrane and the feed solution flowed to the next chiral 16


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recognition site, having more selections, which might promote partial feed solution flow in the vertical direction or even in the opposite direction (Fig. 10(c)). However, because of the relatively high recognition sites, these results were better than the findings at 10 wt.%.

Figure 10. Chiral recognition sites schematics of the membrane. a, b, and c represent CA membranes prepared with 10, 15, and 20 wt.% CA, respectively.

3.4 Effect of molecular imprinting on the morphologies and properties of molecular imprinted CA membrane Cross section

Top surface

17



Figure 11. SEM images of a CA membrane prepared with 15 wt.% CA using molecular imprinting.

Fig. 11 shows the SEM images of the top surface and cross section (22.5µm) of the imprinted membrane (non-imprinted membranes in Fig. 7). These images suggest that both the imprinted membrane and the non-imprinted membrane have the same structure, indicating that both the imprinted and non-imprinted membranes have normal infiltration membrane structures.

Figure 12. Flux and e.e.(%) in the enantioseparation of (R,S)-mandelic acid through a CA membrane fabricated with 15 wt.% CA using molecular imprinting. The operating pressure and feed concentration were 2 kgf/cm2 and 10 mmol/L, respectively.

18


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Fig. 12 shows that both the flux and e.e.(%) of cellulose membranes containing molecular imprinted molecules are better than those without molecular imprinting. Several holes were formed when the imprinted molecules were gradually washed off, resulting in a higher flux than that of the ordinary CA membrane, and because the molecular imprinting increased the number of chiral recognition sites and e.e.(%) also increased.

3.5 Effect of the pore size on the morphologies and properties

of

the

molecular

imprinted

nanochannel

membrane Fig. 13 shows the SEM images of channel membranes modified with zirconia and loaded at 15 wt.% CA. It can be seen from the cross section, CA with imprinted molecules covers the pores of the upper surface of the alumina and the thickness of CA and alumina template is 75.5µm and 80.6µm respectively, so it can be proved that most of the CA is only loaded on the upper surface. The top surface of the membrane is not much different from other membranes.

Cross section

Top surface

19



Figure 13. SEM images of a channel membrane modified with zirconia and loaded with 15 wt.% CA.

The separation efficiency of mandelic acid enantiomers through functionalized membrane channels obtained at different pores of 40-70 nm，80-100 nm, and 100-150 nm was investigated. The results （Fig. 14）showed that not only flux but also the separation efficiency of mandelic acid enantiomers increased with the increasing pore size.

Figure 14. Flux and e.e.(%) in the enantioseparation of (R,S)-mandelic acid through membranes fabricated with pores of 40-70 nm，，80-100 nm, and 100-150 nm. The operating pressure and feed concentration were 2 kgf/cm2 and 10 mmol/L, respectively. 20


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Figure 15. The separation factors in the enantioseparation of (R,S)-mandelic acid through a nanochannel membrane prepared with pores of 40-70 nm，，80-100 nm，，and 2 100-150 nm. The operating pressure and feed concentration were 2 kgf/cm and 10 mmol/L, respectively.

Fig. 15 shows the separation factors of nanochannel membranes with different pores at an optical resolution of (R, S)-mandelic acid. The separation factors of membranes with a pore of 100-150 nm were higher than others, suggesting that the structure of membranes with large pores might promote increased CA loading, thereby increasing the chiral recognition sites and separation factors of the membrane. Whereas, smaller pores decrease flux and influence the diffusion selectivity.

3.6 Comparison of molecular imprinted nanochannel membrane and non-molecular imprinted nanochannel membrane 21



Figure 16. Flux and e.e.(%) in the enantioseparation of (R,S)-mandelic acid through nanochannel membrane fabricated with 110-150nm using molecular imprinting. The operating pressure and feed concentration were 2 kgf/cm2 and 10 mmol/L, respectively.

From Fig. 16 we can see that the flux of molecular imprinted nanochannel membrane and non-molecular imprinted nanochannel membrane be roughly the same. However, the value of the enantiomers excess was higher than that of the non-molecular imprinted nanochannel film. It is possible that the molecular imprinted nanochannel membrane has stereo spaces which are matched with the mandelic acid enantiomers, which leads to a high value of the enantiomers excess.

3.7 Recognition performance of the molecular imprinted nanochannel membrane on target molecule

22


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Figure 17. Flux and e.e.(%) in target molecule through membranes fabricated with 20 wt.%. The operating pressure and feed concentration were 2 kgf/cm2 and 10 mmol/L, respectively.

OH

a

O

b O

OH OH

OH The structure of mandelic acid

c

OH

O

The structure of malic acid

d

O

OH

R

RO RO

RO RO OO

O O R

O

O

R

O R=H or C

O R

CH3 n

OH The structure of lactic acid

The structure of CA

Figure 18. Chemical structures of the materials used in the present study

The separation efficiency of different target molecules through functionalized aluminium oxide nanochannels obtained with a 100-150 nm pore was investigated. Fig. 17 shows that different target molecules exhibited different flux and e.e.(%) under the same conditions. The e.e.(%) of lactic acid were roughly similar to those of mandelic acid, suggesting that the chiral recognition of a single carboxylic acid was 23



better than that of others, as both lactic acid (Fig. 18 (c)) and mandelic acid (Fig. 18 (a)) have only one carboxylic acid group, while malic acid (Fig. 18 (b)) has two

carboxylic acid groups, reflecting the distinction of the e.e.(%) for lactic acid and mandelic acid from those of malic acid. Mandelic acid had a higher flux through the membrane than lactic acid, likely reflecting the similar ring structures between mandelic acid and CA (Fig. 18 (d)), which was not available in the structure of lactic acid. Thus, the flux of mandelic acid was relatively higher than that of lactic acid. The highest flux was observed with malic acid, likely reflecting its structure. Although lactic acid and mandelic acid had similar e.e.(%), the flux of mandelic acid was relatively larger, suggesting that the membrane works better on mandelic acid.

3.8 Design for practical applications Due to an unmatched preponderance over traditional methods, such as low energy consumption, high operability, time saving, large processing capacity and the possibility to be used in continuous mode, membrane separation is widely believed to be a potential approach for large scale chiral separation, with a good application prospect. Comparing with other chiral membranes, the most prominent feature of the membrane used by us in practice is large flux. Owing that one-time separation is not up to the optical purity what we need, we can carry out a series of membranes to make the enantiomers flowed through each membrane in turn until it reached the ideal optical purity. The separation factor α obtained by the experiments was 35, and after computing with formula 4 we can get the ideal optical purity of 99% with a double-stage operation. 24


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4. Comparison Compared with previous studies on enantioselective membranes (Table 3), the molecular imprinted nanochannel membrane developed in the present study is more suitable for the separation of mandelic acid enantiomers, because the chiral polymer coating on the channel film of Al2O3 modified with ZrO2 increased the membrane flux while the enantiomers excess (e.e%) values have little effect when compared with previous studies in this area.

5. Conclusions A molecular imprinted nanochannel membrane was successfully incorporated using the sol-gel template synthesis method, and the membrane was characterized using SEM and other analyses. The effects of different substrates on the flux and permselectivity of the membrane was examined using aqueous solutions of (R, S)-mandelic acid, (R, S)-malic acid and (R, S)-lactic acid as feed solutions. And the results showed that the membrane separation performance was optimum with mandelic acid enantiomer since structures of (R, S)-mandelic acid, (R, S)-malic acid and(R, S)-lactic acid are different. The e.e.(%) values for lactic acid and mandelic acid were distinct from that of malic acid. Notably, with a cellulose content of 15 wt.%, the membrane separation performance peaked. In addition, switching from a non-molecular imprinted cellulose acetate membrane to a molecular imprinted membrane increased both the flux and e.e.(%). Furthermore, imprinted cellulose membrane on metal oxide films with 110-150 nm wide pores exhibited a higher flux, while the e.e.% was not affected. Thus, this method simultaneously enhanced the 25



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permselectivity and flux of the membrane, suggesting a trade-off relationship. The experiment indicates that the molecular imprinted nanochannel membrane can separate (R, S)-mandelic acid very well.

Table 3. e.e.(%), flux and separation factors (α) of the membranes generated in this and previous

studies.

NO.

Membrane

Q（mg/cm2*min）

Isolated substance

Concentration

e.e.(%)

α

References

trans-stilbene oxide

5.2 mmol/L

96

4.563*10-5

(R,S)-2-phenyl-1-propanol

15 mmol/L

97

5.952*10-5

mandelic acid

0.5 mg/ml

93

1.587*10-4

trans-stilbene oxide

0.5 mg/mL

97

1.7*10-4

63

32

mandelic acid

10 mmol/L

92

0.01545

25

(This study)

mandelic acid

10 mmol/L

94.5

0.1597

35

(This study)

Cellulose acetate 1

30

butyrate membrane

Cellulose acetate butyrate 2

38

18

membranes

Cellulose membranes

3

31

Cellulose acetate

propionate/cellulose

4

acetate

Molecular imprinted 5 cellulose membrane

Molecularly imprinted

6

nano Channel

membrane

26


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Nomenclature Q the mass of the solute permeated (mg) t the permeation time (min) Flux (mg/cm ∗ 456)

CS S-enantiomer concentration (g/l) CR R-enantiomer concentration (g/l) AS S-enantiomer peak area (%) AR R-enantiomer peak area (%) α the separation factor &#

Feed concentrations of R- isomer (g/l)

&"

Feed concentrations of S-isomer (g/l)

Phrase explanation Flux: liquid volume of a nanoscale membrane which was flowed through within a unit area per unit time that reflect the transport strength of the membrane. Separation efficiency: the ratio of s-mandelic acid to racemate during a membrane separation which reflect the output rate of s-mandelic acid. Enantiomers excess [e.e.(%)]： e. e(%) =

'(* '() '(* '()

× 100

Alumina nanochannel film: longitudinal make of which channels with different diameters on the aluminum oxide membrane, and the membrane is a merchandise. Separation factor α∶ α = (C9: ⁄C9; )⁄(C

Generation of a Molecular Imprinted Membrane by Coating Cellulose

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