Journal Pre-proofs Two-dimensional Covalent Organic Frameworks (COF-LZU1) Based Mixed Matrix Membranes for Pervaporation Guorong Wu, Xiaoyu Lu, Yongliang Li, Zhiqian Jia, Xingzhong Cao, Baoyi Wang, Peng Zhang PII: DOI: Reference:
S1383-5866(19)34220-0 https://doi.org/10.1016/j.seppur.2019.116406 SEPPUR 116406
To appear in:
Separation and Purification Technology
Received Date: Revised Date: Accepted Date:
16 September 2019 6 December 2019 6 December 2019
Please cite this article as: G. Wu, X. Lu, Y. Li, Z. Jia, X. Cao, B. Wang, P. Zhang, Two-dimensional Covalent Organic Frameworks (COF-LZU1) Based Mixed Matrix Membranes for Pervaporation, Separation and Purification Technology (2019), doi: https://doi.org/10.1016/j.seppur.2019.116406
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Two-dimensional Covalent Organic Frameworks (COF-LZU1) Based Mixed Matrix Membranes for Pervaporation Guorong Wua, c, Xiaoyu Lu a, Yongliang Lid, Zhiqian Jia*a , Xingzhong Cao*b, Baoyi Wang b and Peng Zhang b a
Lab for Membrane Science and Technology, College of Chemistry, Beijing Normal
University, Beijing 100875, PR China. E-mail:
[email protected]. b
Multi-discipline Research Division, Institute of High Energy Physics, Chinese
Academy of Sciences, Beijing 100049, China) c
School of Chemistry, Biology and Materials Science, East China University of
Technology, Nanchang, 330013, PR China d
Analytical and Testing Center, , Beijing Normal University, Beijing 100875, PR
China. Abstract Two-dimensional covalent organic frameworks (COF-LZU1) based PDMS mixed matrix membranes (MMMs) were fabricated and employed for pervaporation of 3.6 wt% n-butanol solution. The effects of COF-LZU1 loading on membrane properties (hydrophobicity, swelling degree and partition coefficient) and PV performance, as well as the influences of membrane thickness and feed temperature, were investigated. It was found that, after incorporating COF-LZU1, the hydrophobicity and n-butanol partition coefficient of MMMs were enhanced, and anti-trade-off effects between permeation flux and separation factor were demonstrated successfully. The PV performance could be further optimized by reducing the membranes thickness and increasing the feed temperature. The permeation flux and separation factor of MMMs attained 2694 g m-2 h-1 and 38.7 respectively, demonstrating great potential in industrial application. Keywords: COF-LZU1, Pervaporation, N-butanol, Mixed matrix membranes
1. Introduction Pervaporation (PV) is an attractive membrane technology for liquids separation[1,2]. Poly(dimethylsiloxane) (PDMS) is widely employed in organophilic pervaporation because of its good chemical stability, strong hydrophobicity, low cost and excellent film forming property[3]. In order to further improve the pervaporation performance and stability of PDMS membranes, mixed matrix membranes (MMMs), such as ZIF-71/PDMS[4], silicalite-1/PDMS[5], ZIF-8/PDMS[6], etc., were developed. However, the compatibility between the fillers and PDMS is still limited, leading to compromised pervaporation performance of MMMs. As one emerging class of porous materials, two dimensional covalent organic frameworks (2D COFs)[7,8], assembled by triazine, imine, boronate or borosilicate linkages[9], possess extremely low densities, high surface areas, permanent porosity, straight and tunable pores structure[9], and have found applications in gas storage[10– 12], separations[13], catalysis[14] and chemical sensing[15]. Nevertheless,
the
application of COFs in MMMs for pervaporation has not been paid enough attentions. Recently, COF-SNW-1/sodium alginate (SA) MMMs were employed for the pervaporation dehydration of 90 wt% ethanol aqueous solution, and the MMMs exhibited excellent pervaporation performance with flux of 2397 g/m2 h and separation factor of 1293 [16] . 2D COF-LZU1, synthesized by p-phenylenediamine and 1,3,5-triformylbenzene (Scheme 1), possesses excellent stability, hydrophobicity and straight and large pores (1.8 nm)[17]. We proposed that the strong hydrophobicity, large pores of COF-LZU1
favor the sorption and diffusion of alcohols. In this paper, COF-LZU1 were prepared and employed to fabricate COF-LZU1/PDMS MMMs for PV of dilute n-butanol solutions. The effects of COF-LZU1 loading on membrane properties (hydrophobicity, swelling degree and partition coefficient) and PV performance, as well as the influences of membrane thickness and feed temperature, were investigated, and the expected anti-trade-off effects between permeation flux and separation factor were demonstrated successfully.
Scheme 1. Synthesis of COF-LZU1.
2. Experimental
2.1 Materials
N-heptane (99.0%), n-butanol (99.0%), dichloromethane (99.5%), acetone (99.5%), concentrated hydrochloric acid (36-38%), acetic acid ᧤99.5%᧥᧨tetrahydrofuran᧤99%᧥ and
methanol ᧤ 99.5% ᧥ were
bought
from
Beijing
chemical
factory.
Polydimethylsiloxane (PDMS, MW50, 000), tetraethyl orthosilicate (TEOS, 98.0%) and dibutyltine dilaurate (98.0%) were used (Jinan Xingfeilong chemical factory). 1,4-diaminobenzene᧤PDA, 99.0%, Adamas᧥and 1,3,5-benzenetricarboxaldehyde ᧤TFB, 98%, Zhenzhou Ames Chemical Co., Ltd.᧥were employed. Polyvinylidene fluoride ultrafiltration membranes (PVDF, MWCO 100,000-150,000) were provided by Beijing Saipuruite Company.
2.2 Synthesis of COF-LZU1
TFB (0.3200 g) was dissolved in 1, 4-dioxane (20 ml). Then PDA (0.3200 g) was added, stirred and ultrasonicated to get a clear solution. Acetic acid (3 M, 0.4 mL) was introduced and stood for 3 days at room temperature. The as-obtained precipitate was centrifuged, washed with tetrahydrofuran, acetone and methanol for 3 times, and then dried at 120 °C for 12 h in vacuum oven.[18]
2.3 Preparation of COF-LZU1/PDMS MMMs
COF-LZU1 were added in n-heptane (10 ml) at room temperature, stirred for 30 min and ultrasonicated for 40 min. Then PDMS solution (1.9543 g of PDMS, 10 ml of n-heptane) was added and stirred for 3 h, followed by introduction of dibutyltin dilaurat and ethyl orthosilicate, and stirring for 3 min. The liquid was casted on PVDF membranes and dried [19].
2.4 Characterization
The schematic PV apparatus was given in our previous work [20]. The PV performance was evaluated by permeation flux (J), separation factor (β), pervaporation separation index (PSI), permeance (PiG/l, GPU) and selectivity (αij)[20,21].
ൌ
ொ ൈο௧
(1)
Τ ೕ
Ⱦ ൌ Ȁ
(2)
ೕ
ൌ ൈ Ⱦ
ಸ
ൌ
బ ି
ൌ
ಸ Ȁ
ߙ ൌ ಸ
(3)
(4)
ఊ ఊ ೄ ି
(5)
Ȁ
where Q, A and Δt are the permeate weight (g), effective membrane area (m2) and permeation time (h), respectively; X and Y denote the weight fraction of the components in the feed and permeate, and i and j represent butanol and water respectively, Ji is the molar flux of component i ( mol cm-2 s-1 ), Pi and Pi are the 0
l
partial pressure of component i on the feed and permeate sides of the membrane, xi ,
g i and Pi S are the molar concentration, activity coefficient, and saturated vapor pressure of component i, respectively. g was obtained from the Wilson equation with Aspen Plus 7.2 software, Pi S was calculated by the Antonine equation.
The simulated PXRD patterns of COF-LZU1 were obtained by Mercury 1.4. The contact angles of membranes with DI water were measured at 20 °C (OCA 20, Dataphysics, Germany). The free volume of the membranes was analyzed by positron annihilation lifetime spectroscopy (PALS) with a fast-slow coincidence system [22].
The radius of the free volume cavities (R, nm) was calculated as Eq. (1), and the apparent fractional free volume (f) was expressed as Eq. (2).
ଵ
߬ ൌ ͳ െ ଶ ோ
ோೕ
ೕ ାǤଵହ
݂ ൌ
ଶగோೕ ଵ ൬ ൰൨ ଶగ ோೕ ାǤଵହ
ସగ ଷ ܫ ݎ ଷ
ିଵ
(6)
(7)
where ߬᧤j = 3, 4᧥is ortho-positronium annihilation lifetime, ns; ܫ is the intensity of ortho-positronium. In the measurement of sorption degree, the dry membrane was
weighed (Wd) and then immersed in DI water, 3.6 wt% n-butanol solution and n-butanol at room temperature for 24 h, respectively. Then the swollen membrane was weighed (Ws) after removing the surficial water [25]. The sorption degree (SD) is calculated as follows, ൌ
ௐೞ ିௐ ൈ ௐ
ͳͲͲΨ (8)
The partition coefficients of n-butanol in pristine PDMS and MMMs were characterized by soaking the membranes in 3.6 wt% n-butanol aqueous solution at room temperature for 20 h [21]. Then the equilibrium composition of solution was measured. The partition coefficients of n-butanol in pristine PDMS membrane (K) and MMMs (K’) are expressed as, ൌ
ᇱ ൌ
ುವಾೄ ೞ
(9)
ಾಾಾೞ ೞ
(10)
where mPDMS, ݉ெெெ௦ and msol are the n-butanol concentration in PDMS, MMMs and solution respectively. As we know, the MMMs include the PDMS matrix and the
COF-LZU1 phase, and the n-butanol concentration in MMMs (Kg/Kg MMMs) can be
written as, ݉ெெெ௦ ൌ ݉ெௌ ܯெௌ ݉ைிିଵ ܯைிିଵ ൌ ݉ܭ௦ ܯெௌ ܭԢԢ݉௦ ܯெௌ
(11)
where mCOF-LZU1 is the n-butanol concentration in COF-LZU1, K′′ is the partition coefficient of n-butanol in COF-LZU1, MPDMS and MCOF-LZU1 are mass fraction of PDMS and COF-LZU1 in MMMs, respectively.
3. Results and discussion
3.1 Characterization of COF-LZU1
The SEM image shows that the as-prepared COF-LZU1 particles are about 276 nm in size (Fig. 1a). The PXRD patterns (Fig. 1b) show that COF-LZU1 are crystalline with layered structure[18], and the experimental PXRD data is consistent with the simulated data. Fig. 1c gives the FTIR spectra of TFB, PDA and COF-LZU1. The peak at 1697 cm-1 represents the stretching vibration of C=O in TFB. The bands at 3375 cm-1 and 3306 cm-1 are assigned to asymmetric and symmetric stretching vibration of N-H in PDA. For COF-LZU1, the above peaks disappear
while
the
C=N
bonds
(1620
cm-1)
appear[18].
The
N2
adsorption/desorption results show that the BET specific surface area is 324.8 m-2 g-1, and the BJH desorption pore diameter is 2.433 nm (Fig. 1d). The contact angle of COF-LZU1 particles tablet with water is 82.8º, indicating the hydrophobicity of COF-LZU1.
Fig. 1. (a) SEM images of COF-LZU1 (b) The experimental and calculated PXRD patterns of COF-LZU1. The insertion is the crystal structure.[23] (c) FTIR spectra of TFB, PDA and COF-LZU1. (d) N2 adsorption/desorption isotherms of COF-LZU1. The insertion is the pore size distribution of COF-LZU1.
3.2 Characterization of COF-LZU1/PDMS MMMs
Fig. 2 shows the SEM images of COF-LZU1/PDMS membranes (1.0 wt% loading). It can be seen there are no apparent defects in MMMs. The EDX mapping of Si and F atoms in the cross-section clearly displays the COF-LZU1/PDMS layer and PVDF layer in the membrane (Fig 2c and 2d). Due to the low theoretical content of N (15.39%) in COF-LZU1 and the low loading of COF-LZU1 (0.25%~2.0%) in PDMS membranes, the theoretical content of N in MMMs is estimated to be below 0.3%.
Considering the detection limit and background interference of EDX, the mapping of N atoms is not employed. Fig. 3 shows the FTIR spectra of membranes. The adsorption bands at 2962 and 2851, 1258 and 1015, and 1082 and 799 cm-1, represent the asymmetric and symmetric stretching vibration of –CH3, Si-O-Si and C-C, respectively. The peak at 865 cm−1 is assigned to the stretching vibration of Si-C. For MMMs, the stretching vibration of C–H (2923 cm-1) and C-N (1309 cm-1) and the skeletal vibration of benzene ring (1560, 1459 and 1413 cm-1) of COF-LZU1 appear.
Fig. 2. SEM of COF-LZU1/PDMS MMMs with 2.0 wt% loading. (a) Surface. (b) Cross-section. (c) EDX mapping of Si atoms in the cross-section of membrane. (d) EDX mapping of F atoms in the cross-section of membrane.
Fig. 3. FTIR spectra of membranes. 3.3 Properties of membranes The wettability is useful for estimation of the affinity of membranes to liquids[24]. As shown in Fig. 4a, the contact angle of pristine PDMS membrane with water is 109.1°. With increasing loading of COF-LZU1 (0.25, 0.50, 1.0, 1.5 and 2.0 wt%), the contact angle of MMMs with DI water gradually rises (109.2°, 109.7°, 112.1°, 113.1° and 114.7°) owing to the hydrophobic nature of COF-LZU1. [4,21] Fig. 4b depicts the effects of COF-LZU1 loading on sorption degrees of membranes in DI water, 3.6 wt% n-butanol and n-butanol. The sorption degrees of all the membranes in DI water and 3.6 wt% n-butanol are less than 0.2% due to the hydrophobicity of membranes. In n-butanol, the sorption degrees firstly decrease and then increase, and display minimum value of 12.4% at about 1.0 wt% loading. The incorporation of COF-LZU1 enhances the rigidity of PDMS chains, leading to the declined sorption degree in solutions. Nevertheless, too much loading causes the aggregation of particles and thus risen sorption degree [25, 26]. In addition, the sorption degree of membranes in
n-butanol was much larger than that in 3.6 wt% n-butanol and DI water owing to the strong affinity of n-butanol to membranes. Fig. 4c shows the effects of loading on n-butanol partition coefficient in 3.6 wt% n-butanol solution. The partition coefficient of n-butanol in pristine PDMS was 0.34. With the increased COF-LZU1 loading, the partition coefficients of n-butanol in MMMs increase gradually, and the n-butanol partition coefficients in COF-LZU1 rise firstly and then drop down, and display the maximum (93.2) at 1.0 wt% loading, about 274 times that of pristine PDMS. These results confirm the strong affinity of n-butanol to MMMs and COF-LZU1[21]. The free volume size and fraction of the membranes are shown in Table 1, in which r3 corresponds to the small free volume and r4 to the large one. With the increased loading of COF-LZU1, r3 and f3 firstly decline due to the rigidity of PDMS upon the introduction of COF-LZU1 and displays minimum at about 0.5% loading; r4 does not show apparent change, and f4 rises owning to the incorporation of COF-LZU1 and displays maximum at about 1% loading.
Fig. 4. Effects of COF-LZU1 loading on the membranes. (a) Contact angle, (b) Sorption degree, (c) Partition coefficient.
Table 1 Free volume of membranes.
0
6.23
߬ଷ (ns)
0.25
7.10
1.15
0.50
6.50
1.0 1.5
Loading (wt%)
I3 (%)
1.254
ݎଷ (nm)
݂ଷ
0.203
߬ସ (ns)
ସ (nm)
0.405
݂ସ
3.684
0.406
0.831
30.35
3.650
0.404
0.836
0.193
30.35
3.661
0.404
0.840
0.252
29.70
3.676
0.405
0.827
I4 (%)
0.219
29.03
0.189
0.200
29.74
1.08
0.179
0.155
7.00
1.14
0.187
4.78
1.49
0.233
3.670
0.807
3.4 Pervaporation performance
Fig. 5a shows the influences of COF-LZU1 loading on the PV performance of 3.6 wt% butanol at 34 ć. The permeation flux and separation factor of pristine PDMS membrane 803 g m-2 h-1 and 24.2 respectively. With increasing loading of COF-LZU1ˈ the permeation flux and separation factor of MMMs rise firstly and then decline, and display maximum values of 881 g m-2 h-1 and 36.6 ( increased by 9.7% and 51.2% in comparison with that of pristine PDMS) at 1.0 wt% loading, demonstrating obvious anti-trade-off effects. The reason is that COF-LZU1 is hydrophobic (Fig. 4a), which is beneficial for the sorption and partition selectivity of n-butanol[6,21] (Fig. 4b, c). Meanwhile, 2D COF-LZU1 is porous with pores size of 1.8 nm, providing lots of permanent and straight diffusion channels for the components. Fig. 5b and 5c show the effects of COF-LZU1/PDMS layer thickness on PV performance. With increasing thickness (7, 14, 21, 28, 35 and 70 μm), the permeation flux gradually declines linearly and the separation factor rises, which are consistent with the literature. [19,
20–22]. When the thickness is 21 μmˈthe PSI of MMMs displays maximum value of 33240 g m-2 h-1, and the corresponding permeation flux and separation factor is 947 g
m-2 h-1 and 35.1 respectively. Fig. 5. (a) Effects of COF-LZU1 loading on permeation flux and separation factor.˄b˅
Effects of MMMs thickness on permeation flux and separation factor.˄c˅Effects of MMMs thickness on PSI. Fig 6a shows the effects of feeding temperature (34 °C, 39 °C, 45 °C, 58 °C, 64 °C, 68 °C, 76 °C) on PV performance of MMMs (thickness of 21 μm, loading of 1.0 wt%). It can be seen that, the permeation fluxes rise with the increase in temperature, and the separation factor displays maximum value of 38.7 at 64 °C. The increased permeation flux is ascribed to the fast thermal motion of the polymer chain and thus increased free volume in MMMs. Furthermore, the vapor pressure difference of the components between the feed side and the permeate size also rises with temperature (Fig. 6c)[3,30,31], resulting in increased mass-transport driving force. These trends are consistent with the literature reports[6,32,33][34]. The temperature dependence of partial fluxes(J) of butanol and water follow the Arrhenius formula˖ ா
ൌ ܬ ሺെ ோ் ሻ
(12)
where EJ is the apparent activation energy; R is the gas constant and T is the feed temperature. EJ is influenced by the molecule size of the components, the affinity of components to membrane, and the interactions between the permeating molecules[34]. From the plot of logarithmic permeation flux versus the reciprocal of feed temperature (Fig. 6b), the average activity energy of water and n-butanol are found to be 33.2 kJ mol-1 and 35.2 kJ mol-1 respectively. It indicates that the n-butanol flux is more sensitive to temperature than water, and thus the separation factor rises with the temperature. Nevertheless, when the temperature is too high ( >64 ć), the vapor pressure difference of water increase more significantly than that of butanol (Fig. 6c),
and meanwhile the membrane structure tends to loose, resulting in the decrease in separation factor. Table 2 gives the comparison of PDMS MMMs for removal of n-butanol from water. It can be seen that, COF-LZU1/PDMS MMMs exhibit more outstanding separation performance than that of ZIF-71, zeolite, CNT, POSS, silicalite and PAF-11 PDMS MMMs. The reasons are ascribed to the strong hydrophobicity, good compatibility with PDMS, and large pore size of COF-LZU-1 (e.g. for pore size: ZIF-71, 0.48 nm; zeolite NaA, 0.41 nm; silicalite-1, ~0.5 nm; PAF-11, 0.5-1.2 nm).
Fig. 6. (a) Effects of feed temperature on permeation flux and separation factor of MMMs (COF-LZU1 loading of 1 wt%, separation layer thickness of 21 μm). (b) Arrhenius plots of partial fluxes. (c) Effect of temperature on the partial pressure
difference of n-butanol and water. Table 2. Comparison of PV performance of PDMS MMMs in the recovery of n-butanol. Filler
Thickness
Feed1
T
J
(ć)
m-2
(g
β
Reference
h-1)
PTMS2
᧤µm᧥ 10
1/99
30
34
249
[35]
ZIF-71
12
5/95
50
1700
30.2
[36]
Zeolite CNT3
100 200
1.5/98.5 1.4/98.6
80 80
377.2 244.3
33 32.9
[37] [25]
POSS
9
1/99
40
79
28.9
[38]
19-50
1/99
70
607
93
[39]
200
2/98
37
41
52
[40]
Silicalite Polyethyle ne PAF-11
15
5/95
28
2256
14
[21]
COF-LZU
21
3.6/96.4
64
2694
38.7
This work
1.n-butanol/water (wt%/wt%) 2. Phenyltrimethoxysilane 3. Carbon Nanotube
4. Conclusions 2D COF-LZU1/PDMS MMMs were prepared and employed in pervaporation of 3.6 wt% n-butanol. With the increasing loading of COF-LZU1, the hydrophobicity and n-butanol partition coefficient of MMMs gradually enhanced, and the permeation flux and separation factor increased firstly and then decreased, displaying apparent anti-trade-off effects. The PV performance can be further optimized by reducing the selective layer thickness and increasing the feed temperature. The permeation flux and separation factor of MMMs (thickness of 21 μm and 64 °C) attained 2694 g m-2 h-1 and 38.7 respectively, demonstrating great potential in industrial application. Acknowledgements The authors gratefully acknowledge the support from the National Natural Science Foundation of China and Qinghai Qaidam Saline Lake Chemical Science Research Joint Fund (No. U1607109). The authors thank Zhenzhen Xu for simulating the PXRD pattern of COF-LZU1.
References [1] G. Wu, X. Chen, Y. Li, Z. Jia, Preparation of submicron PAF-56 particles and application in pervaporation, Microporous Mesoporous Mater. 279 (2019) 19– 25. [2] G. Wu, Z. Jia, Metal-organic frameworks based mixed matrix membranes for pervaporation, Microporous Mesoporous Mater. 235 (2016) 151–159. [3] X. Liu, Y. Li, Y. Liu, G. Zhu, J. Liu, W. Yang, Capillary supported ultrathin homogeneous silicalite-poly(dimethylsiloxane) nanocomposite membrane for bio-butanol recovery, J. Membr. Sci. 369 (2011) 228–232. [4] H. Yin, C.Y. Lau, M. Rozowski, C. Howard, Y. Xu, T. Lai, M.E. Dose, R.P. Lively, M.L. Lind, Free-standing ZIF-71/PDMS nanocomposite membranes for the recovery of ethanol and 1-butanol from water through pervaporation, J. Membr. Sci. 529 (2017) 286–292. [5] X. Zhuang, X. Chen, Y. Su, J. Luo, S. Feng, H. Zhou, Y. Wan, Surface modification of silicalite-1 with alkoxysilanes to improve the performance of PDMS/silicalite-1 pervaporation membranes: Preparation, characterization and modeling, J. Membr. Sci. 499 (2016) 386–395. [6] H. Fan, N. Wang, S. Ji, H. Yan, G. Zhang, Nanodisperse ZIF-8/PDMS hybrid membranes for biobutanol permselective pervaporation, J Mater Chem A. 2 (2014) 20947–20957. [7] H. Yang, H. Wu, Z. Yao, B. Shi, Z. Xu, X. Cheng, F. Pan, G. Liu, Z. Jiang, X.
Cao, Functionally graded membranes from nanoporous covalent organic frameworks for highly selective water permeation, J. Mater. Chem. A. 6 (2018) 583–591. [8] Y. Yin, Z. Li, X. Yang, L. Cao, C. Wang, B. Zhang, H. Wu, Z. Jiang, Enhanced proton conductivity of Nafion composite membrane by incorporating phosphoric acid-loaded covalent organic framework, J. Power Sources. 332 (2016) 265–273. [9] F.J. Uribe-Romo, C.J. Doonan, H. Furukawa, K. Oisaki, O.M. Yaghi, Crystalline Covalent Organic Frameworks with Hydrazone Linkages, J. Am. Chem. Soc. 133 (2011) 11478–11481. [10] Z. Li, X. Feng, Y. Zou, Y. Zhang, H. Xia, X. Liu, Y. Mu, A 2D azine-linked covalent organic framework for gas storage applications, Chem Commun. 50 (2014) 13825–13828. [11] M.G. Rabbani, A.K. Sekizkardes, Z. Kahveci, T.E. Reich, R. Ding, H.M. El-Kaderi, A 2D Mesoporous Imine-Linked Covalent Organic Framework for High Pressure Gas Storage Applications, Chem. - Eur. J. 19 (2013) 3324–3328. [12] T. Reich, Designed Synthesis of Halogenated Borazine-Linked Polymers and Their Applications in Gas Storage and Separation, (2011). [13] X. Feng, L. Chen, Y. Dong, D. Jiang, Porphyrin-based two-dimensional covalent organic frameworks: synchronized synthetic control of macroscopic structures [14] H. Hu, Q. Yan, R. Ge, Y. Gao, Covalent organic frameworks as heterogeneous catalysts, Chin. J. Catal. 39 (2018) 1167–1179. [15] R. Kulkarni, Y. Noda, D. Kumar Barange, Y.S. Kochergin, P. Lyu, B. Balcarova,
P. Nachtigall, M.J. Bojdys, Real-time optical and electronic sensing with a β-amino enone linked, triazine-containing 2D covalent organic framework, Nat. Commun. 10 (2019) 3228. [16] H. Yang, H. Wu, F. Pan, Z. Li, H. Ding, G. Liu, Z. Jiang, P. Zhang, X. Cao, B. Wang, Highly water-permeable and stable hybrid membrane with asymmetric covalent organic framework distribution, J. Membr. Sci. 520 (2016) 583–595. [17] G. Wu, Y. Li, Y. Geng, Z. Jia, In situ preparation of COF-LZU1 in poly(ether-block-amide)
membranes
for
efficient
pervaporation
of
n-butanol/water mixture, J. Membr. Sci. 581 (2019) 1–8. [18] Y. Peng, W.K. Wong, Z. Hu, Y. Cheng, D. Yuan, S.A. Khan, D. Zhao, Room Temperature Batch and Continuous Flow Synthesis of Water-Stable Covalent Organic Frameworks (COFs), Chem. Mater. 28 (2016) 5095–5101. [19] G. Wu, X. Chen, Y. Li, Z. Jia, Preparation of submicron PAF-56 particles and application in pervaporation, Microporous Mesoporous Mater. 279 (2019) 19– 25. [20] G. Wu, M. Jiang, T. Zhang, Z. Jia, Tunable Pervaporation Performance of Modified MIL-53(Al)-NH 2 /Poly(vinyl Alcohol) Mixed Matrix Membranes, J. Membr. Sci. 507 (2016) 72–80. [21] Z. Jia, S. Hao, M. Jiang, PAF-11/poly (dimethylsiloxane) mixed matrix pervaporation
membranes
for
dealcoholization
of
aqueous
solutions:
PAF-11/poly (dimethylsiloxane) mixed matrix pervaporation membranes, J. Chem. Technol. Biotechnol. (2018).
[22] H. Yang, X. Cheng, X. Cheng, F. Pan, H. Wu, G. Liu, Y. Song, X. Cao, Z. Jiang, Highly water-selective membranes based on hollow covalent organic frameworks with fast transport pathways, J. Membr. Sci. 565 (2018) 331–341. [23] H. Fan, A. Mundstock, A. Feldhoff, A. Knebel, J. Gu, H. Meng, J. Caro, Covalent
Organic
Framework–Covalent
Organic
Framework
Bilayer
Membranes for Highly Selective Gas Separation, J. Am. Chem. Soc. 140 (2018) 10094–10098. [24] M.N. Hyder, R.Y.M. Huang, P. Chen, Effect of selective layer thickness on pervaporation of composite poly(vinyl alcohol)–poly(sulfone) membranes, J. Membr. Sci. 318 (2008) 387–396. [25] C. Xue, G.-Q. Du, L.-J. Chen, J.-G. Ren, J.-X. Sun, F.-W. Bai, S.-T. Yang, A carbon nanotube filled polydimethylsiloxane hybrid membrane for enhanced butanol recovery, Sci. Rep. 4 (2015). [26] C. Xue, G.-Q. Du, L.-J. Chen, J.-G. Ren, J.-X. Sun, F.-W. Bai, S.-T. Yang, A carbon nanotube filled polydimethylsiloxane hybrid membrane for enhanced butanol recovery, Sci. Rep. 4 (2015). [27] L. Li, Z. Xiao, S. Tan, L. Pu, Z. Zhang, Composite PDMS membrane with high flux for the separation of organics from water by pervaporation, J. Membr. Sci. 243 (2004) 177–187. [28] F. Liu, L. Liu, X. Feng, Separation of acetone–butanol–ethanol (ABE) from dilute aqueous solutions by pervaporation, Sep. Purif. Technol. 42 (2005) 273– 282.
[29] E.A. Fouad, X. Feng, Use of pervaporation to separate butanol from dilute aqueous solutions: Effects of operating conditions and concentration polarization, J. Membr. Sci. 323 (2008) 428–435. [30] Z. Dong, G. Liu, S. Liu, Z. Liu, W. Jin, High performance ceramic hollow fiber supported PDMS composite pervaporation membrane for bio-butanol recovery, J. Membr. Sci. 450 (2014) 38–47. [31] M.K. Mandal, P.K. Bhattacharya, Poly(ether-block-amide) membrane for pervaporative separation of pyridine present in low concentration in aqueous solution, J. Membr. Sci. 286 (2006) 115–124. [32] J. Gu, X. Shi, Y. Bai, H. Zhang, L. Zhang, H. Huang, Silicalite-Filled PEBA Membranes for Recovering Ethanol from Aqueous Solution by Pervaporation, Chem. Eng. Technol. 32 (2009) 155–160. [33] N.L. Le, Y. Wang, T.-S. Chung, Pebax/POSS mixed matrix membranes for ethanol recovery from aqueous solutions via pervaporation, J. Membr. Sci. 379 (2011) 174–183. [34] N.L. Le, Y. Wang, T.-S. Chung, Pebax/POSS mixed matrix membranes for ethanol recovery from aqueous solutions via pervaporation, J. Membr. Sci. 379 (2011) 174–183. [35] K.Y. Jee, Y.T. Lee, Preparation and characterization of siloxane composite membranes for n-butanol concentration from ABE solution by pervaporation, J. Membr. Sci. 456 (2014) 1–10. [36] Y. Li, L.H. Wee, J.A. Martens, I.F.J. Vankelecom, ZIF-71 as a potential filler to
prepare pervaporation membranes for bio-alcohol recovery, J Mater Chem A. 2 (2014) 10034–10040. (2014) 10034–10040. [37] C. Xue, D. Yang, G. Du, L. Chen, J. Ren, F. Bai, Evaluation of hydrophobic micro-zeolite-mixed matrix membrane and integrated with acetone–butanol– ethanol fermentation for enhanced butanol production, Biotechnol. Biofuels. 8 (2015). [38] G. Liu, W.-S. Hung, J. Shen, Q. Li, Y.-H. Huang, W. Jin, K.-R. Lee, J.-Y. Lai, Mixed matrix membranes with molecular-interaction-driven tunable free volumes for efficient bio-fuel recovery, J. Mater. Chem. A. 3 (2015) 4510–4521. [39] J. Huang, M.M. Meagher, Pervaporative recovery of n-butanol from aqueous solutions and ABE fermentation broth using thin-film silicalite-filled silicone composite membranes. J. Membr. Sci.192 (2001) 231–242. [40] S.-Y. Li, R. Srivastava, R.S. Parnas, Separation of 1-butanol by pervaporation using a novel tri-layer PDMS composite membrane, J. Membr. Sci. 363 (2010) 287–294.
Author Statement
Guorong Wu: Investigation process, Writing- Original draft preparation. Xiaoyu Lu and Yongliang Li: Methodology. Zhiqian Jia: Conceptualization, Supervision, Writing- Reviewing and Editing. Xingzhong Cao, Baoyi Wang and Peng Zhang: Investigation.
Highlights ► 2D COF-LZU1 based PDMS MMMs were prepared and employed for pervaporation. ► Anti-trade-off effects between permeation flux and separation factor were demonstrated. ► The permeation flux and separation factor of MMMs attained 2694 g m-2 h-1 and 38.7.
Declaration of interests The authors declare no conflict of interest.