Polyethyleneimine Modified Membranes for CO2 Capture and in-situ

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Applications of Polymer, Composite, and Coating Materials

Polyethyleneimine Modified Membranes for CO Capture and in-situ Hydrogenation 2

Yanzi Wang, Yongzhen Chen, Caihong Wang, Jing Sun, Zhi-Ping Zhao, and Wenfang Liu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b08636 • Publication Date (Web): 30 Jul 2018 Downloaded from http://pubs.acs.org on July 31, 2018

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ACS Applied Materials & Interfaces

Polyethyleneimine Modified Membranes for CO2 Capture and in-situ Hydrogenation

Yanzi Wang, Yongzhen Chen, Caihong Wang, Jing Sun, Zhiping Zhao and Wenfang Liu1∗

School of Chemistry and Chemical Engineering, Beijing Institute of Technology,

Beijing 102488,

China

Keywords: polyethyleneimine; CO2 hydrogenation; formic acid; surface modification; membrane

∗

Corresponding author: Email: [email protected] 1

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract: Enzymatic CO2 reduction can provide value-added chemicals from greenhouse gases at ambient temperature and pressure. However, poor solubility of CO2 results in low conversion rate. In this work, polyethyleneimine (PEI) was attached onto the surface of polyacrylic acid (PAA)-grafted polyethylene membranes, and then the membranes were used in an integrated process of CO2 capture and in-situ hydrogenation. Modification conditions were optimized with surface amino group density of PEI-modified membranes as the characteristic parameter, and then SEM, FTIR and XPS analyses were conducted. The effect of PEI-modified membranes on enzyme catalyzed CO2 conversion to formic acid, regeneration conditions and reusability were studied. The results show that when the grafting ratio of PAA increased, surface amino group density of PEI-modified membranes increased up to 6.00×10-7 mol/cm2 and then kept constant. The optimum modification time, temperature and PEI concentration was 40 min, 40 °C and 0.3 wt.%. With the same concentration, PEI-1800 could bring more amino groups than PEI-600. SEM, FTIR and XPS results further confirmed PEI attachment. Introduction of membrane-supported PEI with 5.86×10-6 mol amino groups facilitated greatly enzymatic CO2 hydrogenation and the initial reaction rate increased from 0.280 to 6.90 µM/min. After regenerated in ammonia, PEI-modified membranes could be reused and the relative reaction rate was separately 88.0% and 65.7% after five and ten cycles.

2


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1 Introduction As a by-product of the combustion of fossil fuels, CO2 will cause atmospheric pollution and greenhouse effect, which is one of the main challenges the earth faces nowadays

1-2

.

However, recent researches show that fossil fuels will still be the most important energy source during a long time of future 3. Therefore, the capture and utilization of CO2 as effective and feasible measures to reduce CO2 emission 4-5 are still necessary and urgent. Currently, the available techniques for CO2 capture mainly include chemical absorption, cryogenic fractionation, adsorption and membrane separation 6. Comparatively, adsorption is preferred especially in the sequestration of low concentrations of CO2

6

and a variety of

materials such as porous carbons, zeolites, metal-organic frameworks and porous polymers have been developed 7. However, it is usually difficult to achieve high selectivity and capacity together in one material 8. Introducing amino groups with high affinity for CO2 to the surface of these materials is an effective method to solve the preceding problem 9. Compared to the discrete amino compounds, amino-containing polymer such as polyethylenimine (PEI) has a larger amount of amino groups and a lower adsorption heat for CO2 10-11, and thus higher capture efficiency can be achieved. Besides, it is non-volatile and has good chemical stability 12

that makes it a widely studied modifier. CO2 hydrogenation is a common route of CO2 utilization, in which high-value chemicals

such as formic acid, formaldehyde, methanol and methane can be produced via specific catalysts 13-14. Although heterogeneous hydrogenation has achieved considerable progress over the past years 15-17, harsh conditions like high temperature and pressure to activate the catalysts are still inevitable. As a potential alternative, enzymatic catalysis characterized by high 3



specificity and mild reaction conditions has attracted much interest 18. However, CO2 hydration is rather slow 19 and its solubility is very low under normal pressure, which severely limits the reaction rate of biosynthesis

20

. To address the aforementioned problem, carbonic anhydrase

has been applied to facilitate the uptake of CO2 20-22. Although the reaction rate can be improved, the cost and life time of biocatalyst are not satisfactory. Due to large specific surface area, good mechanical properties and chemical stability, and low production cost

23-24

, polymer hollow fiber membranes (HFMs) have important

applications in CO2 membrane contactors

25-26

. In the present work, polyacrylic acid

(PAA)-grafted polyethylene (PE) HFMs were amino-functionalized with PEI and then an integrated process of CO2 capture and in-situ hydrogenation was developed by incorporating membrane-supported PEI into an enzymatic system for the first time. The effects of modification conditions including the grafting ratio of PAA, modification time and temperature, PEI concentration and molecular weight on surface amino group density of PEI-modified membranes were investigated, and then SEM, FTIR and XPS techniques were used to analyze the membranes before and after modification. Subsequently, the synergetic effect of membrane-supported PEI on enzyme catalyzed CO2 conversion to formic acid, regeneration conditions and reusability were studied. 2 Experimental 2.1 Materials PE HFMs (see Figure S1 in SI file) prepared by stretching method were presented as a gift by Institute of Chemistry, Chinese Academy of Sciences. PEI (Mw=600 and Mw=1800, 99%) was purchased from Aladdin Biochemical Technology Co., Ltd. Acrylic acid (AA) and 4


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formic acid (purity≥98%) were produced by Tianjin Fuchen Chemical Reagent Co., Ltd. Benzophenone (BP) of chemical grade was from Tianjin Bodi Chemical Industry Co., Ltd. Acid orange 7 was produced by Sinopharm Group Chemical Reagent Co., Ltd. Analytical grade

anhydrous

ethanol,

acetone,

hydrochloric

acid,

sodium

hydroxide,

N,

N-dimethylformamide (DMF) and ammonia were purchased from Beijing Chemical Works. CO2 (purity≥99.99%) was supplied by Beijing Huayuan Gases Chemical Co. Ltd. Formate dehydrogenase (FDH) from Candida boidinii (EC 1.2.1.2, lyophilized powder, 0.76 U/mg solid), reduced nicotinamide adenine dinucleotide (NADH, lyophilized powder, purity≥98%) and pentafluorobenzene bromide (PFBBr, purity≥98%) were imported from Sigma-Aldrich. Chromatographic methanol and acetonitrile were from Fisher Scientific. 2.2 Preparation of PEI-modified membranes 2.2.1 Carboxylation of PE membranes PE membranes were cut into small pieces with the length of 1 cm and then carboxyl-functionalized by ultraviolet radiation grafting (see Scheme S1) according to the procedures reported

27

. PAA-modified PE membranes were labeled as PAA-PE. The grafting

ratio of PAA was calculated as the increased mass of the membranes after grafting divided by that before grafting. 2.2.2 Attachment of PEI on PAA-PE membranes PAA-PE membranes were soaked in 10 mL of 0.5 wt.% aqueous solution of PEI-600. After stirring for 40 min at 40 °C, the membranes were taken out and washed three times with the deionized water, subsequently dried at 60 °C for 5 h. The resultant membranes were expressed as PEI-PAA-PE. The preparation route of PEI-modified membranes is illustrated in 5



Scheme 1.

Scheme 1 Preparation route of PEI-modified membranes. 2.3 Surface characterization of membranes 2.3.1 Surface amino group density Surface amino group density of PEI-PAA-PE membranes was determined using an acid orange 7 staining method 28. 2.3.2 SEM A JSM-7500F (JEOL Company) scanning electron microscope (SEM) was applied to observe the changes in surface morphology of the membranes before and after modification. The sample needs to be predried and sprayed with gold in vacuum. 2.3.3 ATR-FTIR Fourier transform infrared spectroscopy (FTIR) was conducted via a Nicolet 380 FTIR spectrometer (Thermo Analytic, Madisnn Company) equipped with an attenuated total reflectance (ATR) accessory. 2.3.4 XPS The composition and distribution of the chemical elements on the membrane surface were analyzed using X-ray multifunctional photoelectron spectroscopy (XPS) techniques at an ESCALAB 250Xi (Thermo Scientific Company) equipped with a monochromatic Al Kα X radiation. The operating power was 200 W and the basis vacuum for analysis was 3×10-9 6


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Mbar. 2.4 Enzymatic reaction Enzyme catalyzed reaction (as shown in Equation 1) was conducted at 37 °C and 170 rpm in 0.05 M phosphate buffer (pH 6.0), and in a sealed stainless-steel reactor 29. Typically, PEI-PAA-PE membranes were added into the reaction solution containing 10 mM NADH and 2 mg FDH. After purged with CO2, the reactor was sealed and kept at 0.5 MPa. After a certain period of time, the sample solution was taken out and analyzed using high performance liquid chromatography (HPLC) after derivation 29. (1) 2.5 Regeneration and reuse of PEI-modified membranes In most cases, the used PEI-PAA-PE membranes were regenerated by immersing them in ammonia and then stirring for 1 h at ambient temperature. The ammonia solution with different pH value was obtained by diluting ammonia with the deionized water. When regenerated by heating, the used membranes were washed three times with the deionized water and then dried for 5 h at 85 °C. After regenerated in ammonia (pH 11.6), the reusability of PEI-modified membranes was examined in the enzymatic reaction under the same conditions. The relative reaction rate was calculated with the initial reaction rate in the first use as 100%. 3 Results and Discussion 3.1 Optimization of PEI modification process Usually, the formation of the amide linkages between the carboxyl and amino groups need the assist of condensing agents such as carbodiimide derivative and N-hydroxy succinimide

30-31

, without which PEI molecules were anchored to carboxyl groups mainly 7



through electrostatic interactions

31

. Here, for the introduction of amino groups to the inert

surface of PE, the membranes were carboxyl-functionalized beforehand and then covered by a PEI coating via the impregnation method. The effect of the grafting ratio of PAA on surface amino group density was investigated and shown in Figure 1. As can be seen, surface amino group density of PEI-PAA-PE membranes increased with the grafting ratio of PAA, and it did not further increase when the grafting ratio of PAA was above 15.8%. The maximum value of surface amino group density was about 6.0×10-7 mol/cm2. This result suggests that for a certain concentration of PEI (0.5 wt.%), a grafting ratio of PAA of 15.8% is enough, at which the surface of PAA-PE membranes has been entirely occupied by PEI molecules. 7

6 (10-7 mol/cm2)

Surface amino group density

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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5 4 3

2 11

12

13

14

15

16

17

18

Grafting ratio of PAA (%)

Figure 1 Effect of the grafting ratio of PAA on surface amino group density of PEI-PAA-PE. For PAA-PE membranes with three different grafting ratios of PAA, the change tendency of surface amino group density of PEI-PAA-PE with prolonged modification time is shown in Figure 2. For all investigated membranes, surface amino group density rapidly increased with modification time and then reached saturation at around 40 min. In a range from 30 to 80 °C, the effect of modification temperature on surface amino group density of PEI-PAA-PE was examined. From Figure 3, it can be seen that surface amino group density increased from 8


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4.31×10-7 to 5.81×10-7 mol/cm2, with the temperature increased from 30 to 40 °C. This may be resulted from a higher viscosity and a lower mobility of PEI at a lower temperature

32

.

Nevertheless, when the temperature further rose, surface amino group density fundamentally fell in a range from 5.70×10-7 to 5.85×10-7 mol/cm2, indicating that the adsorption amount of PEI on PAA-PE membranes reached saturation at 40 °C, and a higher temperature was unavailing as a compromise of adsorption kinetics and thermodynamics 33.

(10-7 mol/cm2)


8

6

4

11.8% 13.2% 17.2%

2

0

0

30

60

90

120

Modification time (min)

Figure 2 Effect of modification time for PAA-PE membranes with different grafting ratio of PAA on surface amino group density of PEI-PAA-PE. PEI concentration was 0.5 wt.%.

6

2

mol/cm )

8

4

(10

-7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


2

0

30

60 35 50 70 40 o Modification temperature ( C)

80

Figure 3 Effect of modification temperature on surface amino group density of PEI-PAA-PE. The grafting ratio of PAA was 17.2% and PEI concentration was 1.0 wt.%. Figure 4 illustrates the influence of PEI concentration on surface amino group density of 9



PEI-PAA-PE. Surface amino group density increased approximately linearly from 3.51×10-7 to 5.95×10-7 mol/cm2 with PEI concentration increased from 0.05 wt.% to 0.3 wt.%, and then basically remained unchanged when PEI concentration was further upgraded to 0.8 wt.%, demonstrating that PEI concentration reached saturation at 0.3 wt.% and all available carboxyl groups on PAA-PE membranes had been occupied. To examine the influence of PEI molecular weight on the modification, PEI-1800 was also attempted and compared to PEI-600. As shown in Figure 5, with the same modification time and PEI concentration, PEI-1800 modified membranes exhibited a higher surface amino group density than that of PEI-600. This may be ascribed to a longer branch and more amino groups in the former than the latter.

6 (10-7 mol/cm2)


8

4

2

0 0.0

0.2

0.4

0.6

0.8

1.0

PEI concentration (wt.%)

Figure 4 Effect of PEI concentration on surface amino group density of PEI-PAA-PE. The grafting rate of PAA was 15.8%. 8 PEI-600 PEI-1800

6 (10-7 mol/cm2)


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4

2

0

0

20

40

60

80

Modification time (min)

10


100

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Figure 5 Effect of PEI molecular weight on surface amino group density of PEI-PAA-PE. The grafting rate of PAA was 14.0% and PEI concentration was 0.5 wt.%. 3.2 Surface characterization of PEI-modified membranes 3.2.1 SEM SEM images of PE membranes before and after modification are given in Figure 6, from which we can see that the surface of the original PE membrane was rough and there were some large apertures (Figure 6a) caused by stretching during the membrane production. After the carboxylation, the apertures were sharply reduced and the membrane surface became smooth (Figure 6b), implying that PAA was successfully grafted onto the membrane surface and distributed uniformly. After PEI modification, the membrane pores were further reduced and some slight bulges were observed (Figure 6c), proving the introduction of PEI coating and a multi-layer cladding.

10µm

10µm

10µm

Figure 6 SEM photos (×1000) of (a) PE, (b) PAA-PE and (c) PEI-PAA-PE. 3.2.2 ATR-FTIR ATR-FTIR spectra of PE, PAA-PE and PEI-PAA-PE are shown in Figure 7. For the original PE membrane, the peaks at 3000-2750 cm-1 and 1460 cm-1 were attributed to the stretching vibration of methylene and the bending vibration of C-H, respectively. Compared to PE membrane (Figure 7a), a strong absorbance peak at 1710 cm-1 appeared for PAA-PE (Figure 7b), corresponding to the characteristic peak of C=O in PAA. After PEI modification, 11



the weak peak appearing around 1638 cm−1 could be assigned to the stretching vibration of C=O in amide, and the peaks at 1556 and 1400 cm−1 could be ascribed to the bending vibration of N-H and the stretching vibration of C-N. It is thus concluded that there were a small amount of the valence bonds formed between amino and carboxyl groups in the process of PEI modification. Whereas, the peak of the N-H stretching vibration at 3500-3300 cm-1 was not obvious, this may be because the amino groups on the membrane surface dominantly existed in the form of tertiary and secondary amines. a

b C=O 1710

c C=O 1638 1556

1400 C-N

N-H

4000

3500

3000

2500

2000

1500

1000

Weavenumbers (cm-1)

Figure 7 ATR-FTIR spectra of (a) PE, (b) PAA-PE and (c) PEI-PAA-PE. 3.2.3 XPS Figure 8 gives XPS spectra of PE membranes before and after modification. The C1s peak treatment spectra of XPS are illustrated in Figure S2. The corresponding analysis results of the element content are listed in Table 1. Compared to PE membrane, a higher content of oxygen (11.2%) was observed for the surface of PAA-PE, and the corresponding O/C atomic ratio increased from 0.076 to 0.132, indicating the carboxylation of the membrane surface. For PEI-PAA-PE, the N1s peak appearing at ~401 eV and the percentage of N element increased from 0.83% to 3.89%, proving the introducing of amino groups on the surface of PAA-PE membranes. It is also noted that there were 6.89% of O element and trace amount of N 12


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element on the surface of the original membrane, which might be derived from the residual additive during the membrane preparation 34.

C1s

O1s a

b

N1s c

1200

1000

800

600

400

200

0

Binding energy (eV)

Figure 8 XPS spectra of (a) PE, (b) PAA-PE (the graft ratio of PAA was 11.9%) and (c) PEI-PAA-PE (surface amino group density was 2.97×10-7 mol/cm2). Table 1 XPS analysis results of the element content for PE membranes before and after modification Membrane

C (%)

N (%)

O (%)

PE

91.2

0.59

6.89

PAA-PE

85.4

0.83

11.2

PEI-PAA-PE

83.6

3.89

10.8

3.3 Effect of PEI-modified membranes on CO2 hydrogenation In the presence of PEI-PAA-PE membranes bearing different amount of amino groups, the enzymatic reactions were conducted and the product concentration was monitored within one hour (Figure 9a). It can be found that in most cases the concentration of formic acid increased with the reaction time. For the system without and with PEI-PAA-PE membranes, the production of formic acid was 27 and 263 µM after 60 min. Considering the initial reaction rate (within 20 min), the addition of PEI-PAA-PE membranes with 4.52×10-6 and 5.86×10-6 mol amino groups enabled the enzymatic reaction accelerate from 0.280 to 5.50 and 13



6.90 µM/min (Figure 9b), corresponding to a upgrade of 18.6 and 23.6 times. These data were much higher than that of carbonic anhydrase, with which the formate production was expedited 4.2 times under the same conditions 20. a 300

Blank 3.02×10-6 mol

Formic acid (µ M)

250

4.52×10-6 mol 5.86×10-6 mol 6.69×10-6 mol

200

7.53×10-6 mol

150 100 50 0

0

10

20

30

40

50

60

Time (min) b 8

Initial reaction rate (µM/min)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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6

4

2

0

0

2

4

6

8

Amount of amino groups (10-6 mol)

Figure 9 (a) Enzymatic reaction kinetic curves and (b) the initial reaction rate in the presence of PEI-PAA-PE membranes with different amount of amino groups. According to the previous discussion on ATR-FTIR spectra, the amino groups on the surface of PEI-PAA-PE membranes likely exist in the form of tertiary and secondary amines. The secondary amines can react with CO2 to form carbamates under humid conditions, which can be hydrolyzed to form bicarbonates and amines, as shown in Equation 2&3. Differently, the tertiary amines react firstly with water to form ammonium salts and hydroxyl ions, and 14


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then CO2 reacts with hydroxyl ions to generate bicarbonates (Equation 4&5) 35. The formed bicarbonates can act as a substrate for FDH together with CO2 in the subsequent production of formic acid (see Equation 6) 20. Synergistic effect of PEI-modified membranes on enzymatic CO2 hydrogenation is illustrated in Scheme 2.

2 R 2 NH+ C O2 → R 2 N COO − + R 2 NH 2 +

(2)

R 2 NCOO− + H 2O → R 2 NH+ HCO 3-

(3)

R 3 N+ H 2O → R 3 NH + + OH -

(4)

CO 2 + OH - → HCO3-

(5) (6)

Scheme 2 Synergistic effect of PEI-modified membranes on enzymatic CO2 hydrogenation. However, the initial reaction rate of CO2 hydrogenation respectively decreased to 5.40 and 4.02 µM/min when the amount of amino groups was further increased to 6.69×10-6 and 7.53×10-6 mol, inferring that excessive amino groups may cause a rise in the local pH value around the membranes that is adverse to the enzymatic reaction from thermodynamic aspect 29, 36

. With the same amount of amino groups, the membranes modified by PEI-1800 and

PEI-600 was compared, and the kinetics curves of the enzymatic reaction nearly overlapped (see Figure 10), illustrating the loading amount of amino groups was a determining factor for 15



CO2 capture and the synergism of the enzymatic reaction rather than the molecular weight of PEI. 300 PEI-600 PEI-1800

250

Formic acid (µ M)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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200 150 100 50 0

0

10

20

30

40

50

60

Time (min)

Figure 10 Effect of PEI molecular weight on the enzymatic reaction. 3.4 Regeneration and reusability of PEI-modified membranes The stable performance of adsorption material during cyclical operation is vital for its practical application. Purging with an inert gas at elevated temperature is a common regeneration method 1. Here, two kinds of regeneration methods were compared and regeneration conditions were studied. As shown in Figure 11a, if no any treatment or regenerated by heating at 80 °C, PEI-PAA-PE membranes in the second use only achieved a relative reaction rate lower than 50%, however, it was 97.3% when the membranes were regenerated in ammonia (pH 11.6). Furthermore, if using the diluted ammonia solution instead of ammonia, the regeneration effect will be weakened. For example, when the pH value of the ammonia solution was decreased to 11.4 and 11.2, the relative reaction rate dropped to 85.3% and 54.0%, respectively. Therefore, it can be concluded that at least a half of amino groups were occupied after PEI-PAA-PE membranes were used once, causing the fall in the amount of the available amino groups in the second use. These occupied amino groups can be regenerated under a strong alkaline condition (pH>11.2), which is consistent 16


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with Equation 2.

Relative reaction rate (%)

a 100 80 60 40 20 0

b Relative reaction rate(%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


pH 11.2

No any Heating pH 10.9 treatment

pH 11.6

pH 11.4

100 80 60 40 20 0

0

1

2

3

4

5

6

7

8

9

10

Run number

Figure 11 (a) Effect of regeneration condition of PEI-PAA-PE membranes on the relative reaction rate in the second use, and (b) reusability of PEI-PAA-PE membranes when regenerated in ammonia (pH 11.6). Using ammonia with the pH value of 11.6 for regeneration, the reusability of PEI-modified membranes was investigated. As can be seen from Figure 11b, the relative reaction rate exhibited a slow decrease when the membranes were repeatedly used, which was 88.0% and 65.7% after 5 and 10 cycles. The decrease is presumed to be due to the detaching of PEI from the surface of membranes in the process of regeneration. 4 Conclusions PEI as a preferred amino-modifier is common in the field of CO2 capture while its 17



application in the in-situ hydrogenation of sequestrated CO2 has rarely been reported. In this work, PEI was attached on the surface of PAA-grafted PE membranes and then successfully applied in promoting the enzymatic conversion of CO2 to formic acid for the first time. Surface amino group density of PEI-modified membranes increases with the grafting ratio of PAA, modification time and temperature, PEI concentration and molecular weight, and then usually reaches saturation under certain conditions. Considering the synergetic effect of membrane-supported PEI on CO2 hydrogenation, the amount of amino groups introduced is critical and there exists an optimal value, at which the enzymatic reaction can be accelerated 23.6 times. PEI-modified membranes can be conveniently reused by a simple regeneration in ammonia and they also can be applied in a form of membrane contactor in the future. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was financially supported by the Beijing Municipal Natural Science Foundation (grant number 2172050).

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Polyethyleneimine Modified Membranes for CO2 Capture and in-situ

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