PVA Aerogels for Reversible CO2 Capture from

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Materials and Interfaces

Quaternized chitosan/PVA aerogels for reversible CO2 capture from ambient air Juzheng Song, Jie Liu, Wei Zhao, Yan Chen, Hang Xiao, Xiaoyang Shi, Yilun Liu, and Xi Chen Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b00064 • Publication Date (Web): 21 Mar 2018 Downloaded from http://pubs.acs.org on March 26, 2018

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Industrial & Engineering Chemistry Research

Quaternized chitosan/PVA aerogels for reversible CO2 capture from ambient air Juzheng Song1, Jie Liu2, Wei Zhao3, Yan Chen1, Hang Xiao3, 5, Xiaoyang Shi5, Yilun Liu4, *, Xi Chen3, 5, * 1

International Center for Applied Mechanics, State Key Laboratory for Strength and Vibration of Mechanical Structures, School of Aerospace, Xi’an Jiaotong University, Xi’an 710049, China 2

College of Chemistry and Environment engineering, China University of Mining & Technology, Beijing 100083, China 3

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School of Chemical Engineering, Northwest University, Xi’an 710069, China

State Key Laboratory for Strength and Vibration of Mechanical Structures, School of Aerospace, Xi'an Jiaotong University, Xi'an 710049, China

5

Columbia Nanomechanics Research Center, Department of Earth and Environmental Engineering, Columbia University, New York, NY 10027, USA

ACS Paragon Plus Environment

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Industrial & Engineering Chemistry Research 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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ABSTRACT

Developing inexpensive and high efficient CO2 air capture technologies is an important solution for solving the greenhouse problem. In this work, we used the low cost quaternized chitosan (QCS)/poly (vinyl alcohol) (PVA) hybrid aerogels with quaternary ammonium groups and hydroxide ions to reversibly capture CO2 from ambient air by humidity swing. The CO2 capture capacity and adsorption rate of the aerogels was investigated over the temperature range 10-30°C. The CO2 capture capacity of the aerogels was measured to be about 0.18mmol/g, which is 38% higher than the state-of-the-art commercial membrane. In addition, we proposed a modified pseudo-first-order kinetic model considering both of the CO2 adsorption and the H2O desorption, which describes the experimental results very well. For the first time, the moisture swing CO2 adsorbent is built by low-cost biomass material, which opens up a new approach for the design of the moisture swing CO2 adsorbent.


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1. Introduction

As one of the major greenhouse gases contributing to the global warming, CO2 in the atmosphere has increased from 280 parts per million (ppm) in 1800 to 406 ppm now due to the mass consumption of fossil fuels.1-3 Even worse, the atmospheric CO2 concentration will range from 535 ppm to 983 ppm by 2100, passing the level commonly invoked as a ceiling above which the risk of dangerous climate change becomes unacceptably high.3-6 CO2 capture and sequestration (CCS) is an important technology to control the CO2 emissions from point sources such as power plants and cement plants.7-11 The adsorbents for point sources CO2 capture are usually solid amine sorbents using temperature swing, such as amine-modified SiO2 aerogel7, which contain alkaline amine groups that can react with CO2. These adsorbents usually have a strong affinity with CO2 and a high efficiency of CO2 capture. However, they require high temperature to desorb CO2 resulting in high equipment cost and high energy consumption. CO2 emissions from mobile sources, such as automobiles, account for about 50% of anthropic CO2 emissions, which cannot be disposed by point source CCS.12, 13 Moisture-swing CO2 sorbent is a novel CO2 capture sorbent proposed by Lackner for direct CO2 capture from ambient air which is considered as an important complementary technology of point source CCS.14, 15 The most popular moisture swing adsorbent in literature is an ion exchange resin with quaternary ammonium groups as the positive site to carry negative carbonate ions or bicarbonate ions. To improve the adsorption performance, the resin particles are usually ground to power. For practical use, these powders are mixed with polypropylene15 or polyvinyl chloride3 to form a heterogeneous membrane. The reversible CO2 capture is realized through the transformation between the carbonate ions and the bicarbonate ions in resin by moisture swing, as shown in


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Figure 1. Based on the similar approach, materials containing quaternary ammonium groups, such as modified carbon black16 and porous polymer5, are prepared for reversible CO2 capture by moisture swing. Compared with traditional temperature swing adsorption technology, the moisture swing CO2 technology has a low energy consumption, which is believed to provide a new approach for economical and large-scale direct CO2 capture from ambient air.14 Although moisture swing CO2 capture technology is a potential technology to control the increase of CO2 concentration in the atmosphere, there are few materials available for this technology since the relevant research is still in the mechanism exploration, CO2 absorption and desorption testing. If biomass materials such as cellulose, starch and chitosan, which are abundant in nature, can be prepared for CO2 adsorbents, the cost of CO2 adsorbents would be greatly reduced and the large-scale CO2 air capture from ambient air may take a step forward. As a natural polymer enriched with amine groups, chitosan has been used for metal ions adsorption17-19, gas adsorption20-22, biological medicine23, gene delivery26, and other fields27,

28

24

, heterogeneous organocatalytic25,

, due to its low cost, easy degradation, environmental

friendliness. Because of the amine functional groups, chitosan can adsorb CO2 when prepared into porous aerogels.20, 21 However, similarly to other solid amine sorbents, the regeneration of the chitosan aerogel after CO2 adsorption requires high-energy consumption. Indeed, the amine groups of chitosan can be easily modified to quaternary ammonium groups, similar to the ion-exchange resin that contains quaternary ammonium groups for moisture swing CO2 capture.15, 26, 29 However, the quaternized chitosan is water soluble29 which renders it not suitable for moisture swing adsorbent. Meanwhile, the quaternized chitosan crosslinked by threedimensional networks, such as poly (vinyl alcohol) (PVA), could effectively overcome the shortcoming of water-soluble. Besides, the porous structures could improve the adsorption


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performance of adsorbent, due to higher contact area between gas and solid.21 Currently, freezedrying of hydrogel is a typical method for preparing porous materials. Water, as the pore agent, can easily generate the ordered and continuous porous structures. Many carbon materials such as carbon nanotubes, activated carbon and graphene have been prepared into excellent porous structures.30 After being freeze-dried, the hydrogels formed by QCS and PVA three-dimensional network can be converted into porous aerogels. Here, we report a new moisture swing CO2 adsorbent built with QCS/PVA hybrid aerogels. This work is the first studies of the moisture swing CO2 adsorbent using biomass materials. CO2 can be adsorbed in low humidity environment by the aerogel, while CO2 desorbs when the humidity of the surrounding environment is high. The influence of temperature on adsorption performance has been investigated. The adsorption capacity and the adsorption rate of the adsorbent are selected as the characteristics to evaluate the adsorption performance of moisture swing adsorbents. The modified Pseudo-first order model is proposed to describe the adsorption kinetics which agrees with the experimental results very well.

Figure 1. Schematic illustration of reversible CO2 capture by humidity swing


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2. MATERIALS AND METHODS

2.1. Preparation of quaternized chitosan

Figure 2. Preparation of quaternized chitosan

Quaternized chitosan was prepared from purified chitosan by a typical method24, 31 with the modification that is outlined in Figure 2. Briefly, 5g chitosan was suspended in 200ml deionized water, then 1ml AcOH was added to the suspension. The chitosan-AcOH mixture was stirred for 30min and 28g GTMAC was gradually added into the mixture. Then, the reaction further continued for 18h at 55°C. Following that, the undissolved polymer was removed by centrifugation of the mixture at 4000 rpm for 20 min at room temperature. Subsequently, the solution was filtered and pre-cooled acetone/ethyl alcohol mixture (1:1, v/v) was added. Then the quaternized chitosan was precipitated accordingly. The above purification process was repeated three times, and the purified quaternized chitosan (QCS) was obtained after dried in a vacuum oven at 35°C for 5 days. Here, chitosan (CS) (95% purity), Glycidyl trimethyl ammonium chloride(GTAC), polyvinyl alcohol(PVA) and Glutaraldehyde(GA) (50% aqueous solution)


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were purchased from Shanghai Macklin Inc. And Acetic acid(AcOH), anhydrous ethanol, sodium hydroxide (NaOH) and Hydrochloric Acidcid (HCl) were purchased from Shanghai Aladdin Chemical Reagent Co. All other reagents were of analytical grades and were used without purification.

2.2. Preparation of QCS/PVA aerogel Schematic illustration of the preparation of QCS/PVA aerogel was shown in Figure 3. First, 2.5g QCS synthesized above was dissolved in 125ml deionized water to get a 2wt. % QCS solution. And 6.25g PVA was dissolved in 125ml deionized water under stirring at 95°C to obtain a 5 wt. % PVA solution. Then, the 83ml PVA solution was added into the 125 ml QCS solution under stirring to form a clean QCS/PVA solution, and pH was adjusted to 5 with a dilute hydrochloric acid solution. Subsequently, 2ml crosslinking agent (GA) was dropwise added under constant stirring for 30min. The mixture solution was further reacted at 60°C for 6h to form a white hydrogel, as shown in the inset (a) of Figure 3. The detailed information about the reaction mechanism of QCS/PVA crosslinked by GA was reported in previous literature32. Furthermore, the QCS/PVA hydrogels were soaked in a 1mol/L NaOH solution for ion-exchange with NaOH for 24h as shown in Figure 4. During ion exchange, the free chlorine ions in hydrogels were replaced by hydroxide ions. After cleaning the excess sodium hydroxide with deionized water, the hydrogels were freeze-dried at -50°C for 48h to obtain QCS/PVA aerogels. The photograph of the aerogels was shown in inset (b) of Figure 3.


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Figure 3. Schematic illustration of the preparation of QCS/PVA aerogel. Photograph of QCS/PVA hydrogel was shown in inset (a) and photograph of QCS/PVA aerogel was shown in inset (b)

Figure 4. Ion-exchange of QCS/PVA hydrogel with NaOH.

2.3. Adsorption-desorption experimental system The CO2 adsorption-desorption experimental system is shown in Figure 5. The aims of the experimental setup are to provide a closed system with precise temperature and humidity control to study the adsorption and desorption performance of the CO2 adsorbents by moisture swing.


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The total amount of CO2 in the closed system is constant, and the CO2 and N2 gas tanks are used to adjust the initial concentration of CO2 in the closed system. The initial CO2 concentration is adjusted to 400 ppm, the same concentration of CO2 in the atmosphere. The volume of the closed system is 1.45L, and the gas leakage rate of the closed system is 3.3 × 10 mmol/h to maintain the concentration difference of 500 ppm between the closed system and atmosphere. The total leakage of CO2 is only about 0.18% of the CO2 adsorption by the QCS/PVA aerogel. As a result, the leakage is neglected in the following analysis. The sample chamber is placed in a water bath to control the temperature and the temperature ranges from 10°C to 30°C ， similar to the atmosphere temperature for CO2 captures from ambient air by adsorbents. A homemade humidity controller is consisted of a semiconductor refrigeration module with 2ml deionized water in it. During working of the semiconductor refrigeration module the temperature in the module is smaller than that of the sample chamber. And the water vapor in the system will coagulate in the semiconductor refrigeration module which decreases the humidity in the closed system. While, if the semiconductor module stops working, the water in it will evaporate and the humidity in the system is increased. The pump provides the power for the gas circulation in the closed system and the gas flux is 6L/min. An infrared gas analyzer (IRGA) is used to record the CO2 concentration during adsorption and desorption process of the sorbent in the sample chamber. The CO2 adsorbent, i.e. QCS/PVA aerogel, was first dried in oven at 30°C for 48h to get saturation of CO2 absorption before putting into the sample chamber to trigger CO2 reversible capture under humid and dry condition. Here, a one-time CO2 adsorption reaction occurred, with


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hydroxide ions converted into bicarbonate ions2, and then the adsorbent came into the adsorption-desorption cycle as shown in Figure 1.

Figure 5. CO2 adsorption-desorption experimental system.

2.4. Adsorption kinetics Lagergren pseudo-first-order (PFO) model has been widely employed to explore the adsorption mechanisms.33-36 The PFO model assumes that the driving force of the adsorption process comes from the difference between the adsorbed quantity and equilibrium adsorption capacity of the absorbent, that is3, 33

(1)

1

(2)

1


(3)

10

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where is the adsorbed quantity at time t, k is a constant determined by absorbent and environment, is the equilibrium adsorption capacity of the absorbent, is the adsorption saturation at time t. However, the experimental results in Figure 6 show that the adsorption saturation obtained from the PFO model is always larger than the experimental results of QCS/PVA aerogel. Besides, in experiments the absorption rate isn’t the largest at the beginning (the point with the largest values of ).

Figure 6. CO2 adsorption saturation at 20°C. The solid lines are theoretical predictions of PFO model and solid lines are experimental results.

The reason is that the adsorption process is triggered by the drying of the adsorbent, so the H2O content in the absorbent is another dominant parameter to determine the absorption rate. The drying process of the adsorbent is actually the desorption process of water molecules. The dryness of adsorbent at time t is described by D(t), defined as t

/ !


(4)

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where " is the desorption water from the adsorbent at time t, " is the equilibrium desorption water of the absorbent from the wet to dry state; ! and are the final weight of adsorbent in the dry and wet state, is the weight of adsorbent at time t during the drying process. According to the experimental results in Figure 7, the relations between $% " " and t are linear at different temperatures, which satisfy PFO model and can be described as " " 1 &

(5)

1 &

(6)

Figure 7. The relations between $% " " and t at 10°C, 20°C and 30°C. The solid lines are theoretical predictions of PFO model and symbols are experimental results.

By considering both of the CO2 adsorption and H2O desorption, a modified pseudo-first-order (MPFO) model is proposed. Note that the actually equilibrium CO2 adsorption capacity at time t is not equal to the final equilibrium CO2 adsorption capacity, since the water content at the absorbent is not equal to value at the dry state. Therefore, we replace the equilibrium CO2 adsorption capacity at time t as , and the MPFO model is


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'

( )

) 1

* +,& & +,* * &

(7)

(8)

Therefore, the adsorption rate - ) in MPFO model is - )

'

& * . +,* +,& / & *

(9)

Adsorption half-time (the time to get half equilibrium adsorption capacity) is an important factor to evaluate the adsorption rate of CO2 adsorbent.3,

37

Based on the MPFO model, the

adsorption half-time of the QCS/PVA aerogels can be derived.

3. RESULTS AND DISCUSSION 3.1. Structural and chemical characteristics of QCS/PVA aerogel The SEM observations of the micro-structures of QCS/PVA aerogel are shown in Figure 8. The pores are formed by the ice crystals growing during freeze-drying, the diameters of which are about 50um. And the cell-walls are connected with each other through a “Y” cross which is widely observed in graphene aerogel.38 The magnified images of the cell-walls in Figure 8(b), (c) and (d) show that there are hierarchical porous structures in the cell-walls, in contrast to the chitosan aerogel.20 The reason for the formation of hierarchical porous structures may be the cross-linking between QCS and PVA. These hierarchical porous structures not only increase the surface area of QCS/PVA aerogel, but also provide ordered nano-pores for high efficient diffusion of CO2 and H2O. Here, the scanning electron microscope (SEM) observation was carried out at a Quanta FEG 250 microscope. Infrared (IR) spectra were taken on a Nicolet iS50-


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FTIR spectrometer, and the sample was mixed with KBr and ground into powder before testing. A STA449F3 thermal analyzer was used to conduct the thermogravimetric analysis (TGA).

Figure 8. Micro-structures of QCS/PVA aerogel from different scales. The scale bars in (a), (b), (c) and (d) are 100um, 5um, 2um, 1um, respectively.

Figure 9. FTIR spectra of CS, QCS and QCS/PVA aerogel.


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The FT-IR spectra of CS, QCS and QCS/PVA aerogels are shown in Figure 9. The characteristic peak at 1597 cm-1 in the spectra of CS attributes to the primary amine group (NH2) and the peak is shifted to 1562 cm-1 for QCS, and 1567 cm-1 for QCS/PVA aerogels31. Besides, the peak amplitudes corresponding to -NH2 group decreases in the spectra of QCS and QCS/PVA aerogel, due to the chemical reaction on –NH2. An obvious characteristic peak corresponding to the methyl group (-CH3) of quaternary ammonium (-N(CH3)3) is observed at 1479 cm-1 in the spectra of QCS and the peak is shifted to 1456 cm-1 in QCS/PVA aerogel, but it was not observed in unmodified chitosan.31,

39

The results of FT-IR spectra confirms the

successful conjugation of quaternary ammonium group to the primary amine group of chitosan. Thermogravimetric analysis of CS, QCS and QCS/PVA aerogel was conducted in a thermogravimetric analyzer using heating rate of 10°C/min from 30°C to 800°C and the results were shown in Figure 10. Before thermogravimetric analysis, samples were dried in a drying oven at 25°C for 24h. The curves observed in Figure 10(a) indicate that the mass loss of CS, QCS and aerogel is over the temperature range 200-500°C. One obvious feature is that both CS and QCS had only one mass loss step, which is around 280°C40, while QCS/PVA aerogel had two steps, which are around 280°C and 450°C. The first derivative of the TGA (DTG) curve is shown in Figure 10(b). The DTG curve of CS confirms that CS break down at 310 °C. Because of the grafting of quaternary ammonium groups, the thermal decomposition of QCS occurred at 285 °C, which is decreased by 25°C compared with CS, indicating that the introduction of the quaternary ammonium groups reduces the thermal stability of CS. And the thermal decomposition temperature is further reduced to 280°C owing to the cross-linking reaction between QCS and PVA, as shown in Figure 10 (b). The peak about 450°C in DTG curve of QCS/PVA aerogel is attributed to the thermal decomposition of PVA.


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Figure 10. (a) TGA of CS, QCS and QCS/PVA aerogel and (b) DTG of CS, QCS and QCS/PVA aerogel.

3.2. CO2 adsorption-desorption performance The CO2 desorption and adsorption response of the QCS/PVA aerogels by humidity swing at room temperature (20°C) is shown in Figure 11. It can be observed that changes in relative humidity can rapidly induce CO2 desorption and adsorption. When the CO2 saturated QCS/PVA aerogel is put into the sample chamber and the relative humidity in the sample chamber is increased from 3% to 95%, CO2 desorbs from the aerogel and a desorption capacity of 0.181 mmol/g is obtained. When the relative humidity is decreased from 95% to 3%, the desorbed CO2


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is completely absorbed. In order to test the stability of the performance of the aerogel, the adsorption and desorption process was carried out 9 times by humidity swing. And performance degeneration is not observed, as shown in Figure 10. Increasing humidity, the bicarbonate ions in QCS/PVA convert into carbonate ions with the release of CO2. While decreasing humidity, the hydroxide ions produced by the hydrolysis of carbonate ions react with CO2 to generate hydrogen carbonate ions when CO2 is absorbed. The detailed mechanism of the transformation between the carbonate ion and bicarbonate ion controlled by moisture has been explored in our previous works.41,

42

And Considering hydration water, the overall reaction equation of the

transformation is41 CO( 2 ∙ %H( O ↔ HCO2 ∙ 6 H( O 7 OH ∙ 6( H( O 7 % 6 6( 1 H( O

(10)

Figure 11. CO2 desorption-adsorption of QCS/PVA aerogel at 20°C by humidity swing for 9 cycles.

Adsorption performance at 10°C and 30°C is also studied and the experimental results are shown in Figure 12. By fitting with the experimental results, the parameters of the MPFO model are obtained and given in Table 1. The regression coefficients R( are larger than 0.99 for the


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three temperature 10°C, 20°Cand 30°C, indicating the MPFO model can describe the experimental results well at different temperatures and the curves of experimental results and theoretical predictions are almost overlapped as shown in Figure 12. From Table 1, it is shown that when temperature increases from 10°C to 30°C, there is a slight increase in the equilibrium adsorption capacity. Besides, QCS/PVA aerogel has larger adsorption capacity compared with commercial Excellion membrane or modified carbon black (CB) material16. Compared with the Excellion membrane, CO2 adsorption capacity of QCS/PVA at 20°C increases about 38%. The absorption constant and ( (defined in Section 2.4), increase from 0.9×102s , 2.29×102 s to 4.46×102 s, 3.67×102 s, which means the adsorption rate is significantly increased with increasing temperature.

Figure 12. CO2 adsorption at 10°C, 20°C and 30°C. The solid lines are theoretical predictions of MPFO model and solid lines are experimental results.

Table 1. Parameters of MPFO model by fitting with the adsorption experimental results.


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:;

Temperature (°C)

(mmol g-1)

? @ =)

? @ =) (s)

10

0.179

0.90

2.29

0.9978

1244

20

0.181

2.60

2.62

0.9995

643

30

0.185

4.46

3.67

0.9983

416

Figure 13 shows the changes of CO2 adsorption rate with time at different temperatures. The MPFO model shows that the dryness of adsorbent is one of the dominant parameters to determine the absorption rate. Therefore, at the beginning of the adsorption, the adsorption rate isn’t the largest since the dryness of adsorbent is approximately zero. The peak value of the adsorption rate and the time to get the peak value are two characteristics, listed in Table 2. As the temperature is increased from 10°C to 30°C, the peak adsorption rate increases from 0.88×104

mmol g-1 s-1 to 2.75×10-4mmol g-1 s-1. Moreover, the time to get peak value is decreased from

670 s to 247s and the halftime of absorption is also decreased from 1244s to 416s. So, two effects of temperature on adsorption rate are concluded. First, it increases the peak adsorption rate and second it decreases the time to get peak value. There are two possible reasons for these phenomena. First, higher temperature corresponds to faster diffusion rate of H2O and CO2 and second the increasing of temperature accelerates the chemical reaction. From the view point of energy barrier, the kinetic energy of CO2 molecules increases as the temperature increases, which increases the proportion of activated CO2 molecules so as to increase the reaction rate. Therefore, the increasing of temperature may accelerate the adsorption reaction of CO2.


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Figure 13. Adsorption rate derived from MPFO model at 10°C, 20°C and 30°C.

Table 2. CO2 adsorption rate at 10°C, 20°C and 30°C.

Temperature

Absorption-rate peak

(°C)

(10-4mmol g-1 s-1)

Absorption-rate peak time

Adsorption half-time (s)

(s)

10

0.88

670

1244

20

1.74

381

643

30

2.75

247

416

Figure 14 presents the comparison of CO2 adsorption halftime for different CO2 adsorbents from ambient air, including the QCS/PVA aerogels at 10°C, 20°C and 30°C in this work and


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other adsorbents in the literature3, 15, 37, 43. Among these adsorbents, QCS/PVA aerogel has the shortest halftime, i.e. 7min.

Figure 14. Comparison of CO2 adsorption half-time for different adsorbents. HAS: Hyperbranched aminosilica with different amine loading. I-200-90C: Ion exchange resin treated by 90°C water. P-100: PVC/IER membrane treated by different temperatures of water.

4. CONCLUSIONS In this work, the natural polymer chitosan, enriched with amine groups, is chosen as the lowcost raw material for the preparation of moisture swing CO2 adsorbent. The quaternary ammonium groups are grafted on the chitosan to provide the load sites for carbonate ions or bicarbonate ions. Through crosslinking between QCS and PVA, and freeze-drying, QCS/PVA aerogels with hierarchical porous structures are synthesized. SEM observation, FT-IR spectra analysis and TGA are carried out to confirm the structural and chemical characteristics of the QCS/PVA aerogels. CO2 capture capacity of QCS/PVA aerogels is about 0.18mmol/g at room temperature, 38% improvement compared with the commercial Excellion membrane. Besides,


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the adsorption halftime is much shorter than that of other air capture adsorbents and it is significantly improved by increasing temperature. And the results of the MPFO model proposed in this work agree with the experimental results fairly well. As one of the widely used biomass in nature, our results show that chitosan could be prepared into the QCS/PVA aerogel for moisture swing CO2 adsorbent with high absorption rate, opening up new possibilities for large-scale and low cost direct CO2 capture from ambient air. AUTHOR INFORMATION Corresponding Author *

E-mail: (Y.L.) [email protected]; (X.C.) [email protected]

ACKNOWLEDGMENTS Y.L. acknowledges the support from the National Natural Science Foundation of China (No. 11572239). X.C. acknowledges the support from the National Natural Science Foundation of China (Nos. 11372241 and 11572238), ARPA-E (DE-AR0000396) and AFOSR (FA9550-121-0159).

REFERENCES (1) Pearson, P. N.; Palmer, M. R. Pearson, P. N. & Palmer, M. R. Atmospheric carbon dioxide over the past 60 million years. Nature. 2000, 406, 695-699. (2) He, H. K.; Li, W. W.; Zhong, M. J.; Konkolewicz, D.; Wu, D. C.; Yaccato, K.; Rappold, T.; Sugar, G.; David, N. E.; Matyjaszewski, K. Reversible CO2 capture with porous polymers using the humidity swing. Energ Environ Sci. 2013, 6, 488-493. (3) Shi, X.; Li, Q.; Wang, T.; Lackner, K. S. Kinetic analysis of an anion exchange absorbent for CO2 capture from ambient air. Plos One. 2017, 12, e0179828. (4) Keith, D. W. Why capture CO2 from the atmosphere? Science. 2009, 325, 1654.


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(5) He, H. K.; Zhong, M. J.; Konkolewicz, D.; Yacatto, K.; Rappold, T.; Sugar, G.; David, N. E.; Gelb, J.; Kotwal, N.; Merkle, A.; Matyjaszewski, K. Three-Dimensionally Ordered Macroporous Polymeric Materials by Colloidal Crystal Templating for Reversible CO2 Capture. Adv Funct Mater. 2013, 23, 4720-4728. (6) Solomon, S. IPCC (2007): Climate Change The Physical Science Basis. American Geophysical Union. 2007, 9, 123-124. (7) Cui, S.; Cheng, W.; Shen, X.; Fan, M.; Russell, A.; Wu, Z.; Yi, X. Mesoporous amine-modified SiO2 aerogel: a potential CO2 sorbent. Energ Environ Sci. 2011, 4, 2070-2074. (8) Valverde, J. M.; Duran, F. J.; Pontiga, F.; Moreno, H. CO2 capture enhancement in a fluidized bed of a modified Geldart C powder. Powder Technol. 2012, 224, 247-252. (9) Dai, W. L.; Luo, S. L.; Yin, S. F.; Au, C. T. The direct transformation of carbon dioxide to organic carbonates over heterogeneous catalysts. Applied Catalysis A General. 2009, 366, 212. (10) Smit, B.; Reimer, J. A.; Oldenburg, C. M.; Bourg, I. C. Introduction to Carbon Capture and Sequestration. Chaos. 2014, 24, 5880-5885. (11) Hasan, M. M. F.; Boukouvala, F.; First, E. L.; Floudas, C. A. Nationwide, Regional, and Statewide CO2 Capture, Utilization, and Sequestration Supply Chain Network Optimization. Ind Eng Chem Res. 2014, 53, 7489-7506. (12) Lackner, K. S.; Brennan, S.; Matter, J. M.; Park, A. H.; Wright, A.; Van, d. Z. B. The urgency of the development of CO2 capture from ambient air. P Natl Acad Sci Usa. 2012, 109, 13156. (13) Lackner, K. S.; Brennan, S., China 2049: Energy Security and Climate Change. 2015, p 213-238. (14) Lackner, K. S. Capture of carbon dioxide from ambient air. European Physical Journal Special Topics. 2009, 176, 93-106. (15) Wang, T.; Lackner, K. S.; Wright, A. Moisture swing sorbent for carbon dioxide capture from ambient air. Environ Sci Technol. 2011, 45, 6670-5. (16) He, H. K.; Zhong, M. J.; Konkolewicz, D.; Yacatto, K.; Rappold, T.; Sugar, G.; David, N. E.; Matyjaszewski, K. Carbon black functionalized with hyperbranched polymers: synthesis, characterization, and application in reversible CO2 capture. J Mater Chem A. 2013, 1, 68106821. (17) Yu, B.; Xu, J.; Liu, J. H.; Yang, S. T.; Luo, J.; Zhou, Q.; Wan, J.; Liao, R.; Wang, H.; Liu, Y. Adsorption behavior of copper ions on graphene oxide–chitosan aerogel. Journal of Environmental Chemical Engineering. 2013, 1, 1044-1050. (18) Merrifield, J. D.; Davids, W. G.; Macrae, J. D.; Amirbahman, A. Uptake of mercury by


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Page 24 of 27

thiol-grafted chitosan gel beads. Water Res. 2004, 38, 3132-8. (19) Ngah, W. S. W.; Liang, K. H. Adsorption of gold(III) ions onto chitosan and Ncarboxymethyl chitosan: Equilibrium studies. Ind Eng Chem Res. 1999, 38, 1411-1414. (20) Alhwaige, A. A.; Agag, T.; Ishida, H.; Qutubuddin, S. Biobased chitosan hybrid aerogels with superior adsorption: Role of graphene oxide in CO2 capture. Rsc Adv. 2013, 3, 1601116020. (21) Chang, X.; Chen, D.; Jiao, X. Chitosan-based aerogels with high adsorption performance. J Phys Chem B. 2008, 112, 7721-5. (22) Alhwaige, A. A.; Ishida, H.; Qutubuddin, S. Carbon Aerogels with Excellent CO2 Adsorption Capacity Synthesized from Clay-Reinforced Biobased Chitosan-Polybenzoxazine Nanocomposites. Acs Sustain Chem Eng. 2016, 4. (23) Zhao, X.; Wu, H.; Guo, B.; Dong, R.; Qiu, Y.; Ma, P. X. Antibacterial anti-oxidant electroactive injectable hydrogel as self-healing wound dressing with hemostasis and adhesiveness for cutaneous wound healing. Biomaterials. 2017, 122, 34. (24) Zhao, X.; Li, P.; Guo, B.; Ma, P. X. Antibacterial and conductive injectable hydrogels based on quaternized chitosan-graft-polyaniline/oxidized dextran for tissue engineering. Acta Biomater. 2015, 26, 236. (25) Ricci, A.; Bernardi, L.; Gioia, C.; Vierucci, S.; Robitzer, M.; Quignard, F. ChemInform Abstract: Chitosan Aerogel: A Recyclable, Heterogeneous Organocatalyst for the Asymmetric Direct Aldol Reaction in Water. Chem Commun. 2010, 46, 6288-90. (26) Thanou, M.; Florea, B. I.; Geldof, M.; Junginger, H. E.; Borchard, G. Quaternized chitosan oligomers as novel gene delivery vectors in epithelial cell lines. Biomaterials. 2002, 23, 153. (27) Takeshita, S.; Yoda, S. Chitosan Aerogels: Transparent, Flexible Thermal Insulators. Chem Mater. 2015, 27. (28) Sowmya, A.; Meenakshi, S. An efficient and regenerable quaternary amine modified chitosan beads for the removal of nitrate and phosphate anions. Journal of Environmental Chemical Engineering. 2013, 1, 906-915. (29) Fernandes, S. C. M.; Freire, C. S. R.; Silvestre, A. J. D.; Desbrieres, J.; Gandini, A.; Neto, C. P. Production of Coated Papers with Improved Properties by Using a Water-Soluble Chitosan Derivative. Ind Eng Chem Res. 2010, 49, 6432-6438. (30) Li, W. L.; Lu, K.; Walz, J. Y. Freeze casting of porous materials: review of critical factors in microstructure evolution. Int Mater Rev. 2012, 57, 37-60. (31) Cho, J.; Grant, J.; Piquette-Miller, M.; Allen, C. Synthesis and physicochemical and dynamic mechanical properties of a water-soluble chitosan derivative as a biomaterial.


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Page 25 of 27 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


Biomacromolecules. 2006, 7, 2845-55. (32) Yu, Q.; Song, Y.; Shi, X.; Xu, C.; Bin, Y. Preparation and properties of chitosan derivative/poly(vinyl alcohol) blend film crosslinked with glutaraldehyde. Carbohyd Polym. 2011, 84, 465-470. (33) Yang, X.; Alduri, B. Kinetic modeling of liquid-phase adsorption of reactive dyes on activated carbon. Journal of Colloid & Interface Science. 2005, 287, 25-34. (34) Li, J.; Amr Henni, A.; Tontiwachwuthikul, P. Reaction Kinetics of CO2 in Aqueous Ethylenediamine, Ethyl Ethanolamine, and Diethyl Monoethanolamine Solutions in the Temperature Range of 298−313 K, Using the Stopped-Flow Technique. Ind Eng Chem Res. 2007, 47, 4426-4434. (35) Sarı, A.; Şahinoğlu, G.; Tüzen, M. Antimony(III) Adsorption from Aqueous Solution Using Raw Perlite and Mn-Modified Perlite: Equilibrium, Thermodynamic, and Kinetic Studies. Ind Eng Chem Res. 2012, 51, 6877–6886. (36) Zhang, S.; Zhou, Y.; Nie, W.; Song, L.; Zhang, T. Preparation of Uniform Magnetic Chitosan Microcapsules and Their Application in Adsorbing Copper Ion(II) and Chromium Ion(III). Ind Eng Chem Res. 2012, 51, 14099-14106. (37) Choi, S.; Drese, J. H.; Eisenberger, P. M.; Jones, C. W. Application of Amine-Tethered Solid Sorbents for Direct CO2 Capture from the Ambient Air. Environ Sci Technol. 2011, 45, 2420. (38) Xu, X.; Zhang, Q.; Yu, Y.; Chen, W.; Hu, H.; Li, H. Naturally Dried Graphene Aerogels with Superelasticity and Tunable Poisson's Ratio. Adv Mater. 2016, 28, 9223-9230. (39) Feketefoldi, B.; Cermenek, B.; Spirk, C.; Schenk, A.; Grimmer, C.; Bodner, M.; Koller, M.; Ribitsch, V.; Hacker, V. Chitosan-Based Anion Exchange Membranes for Direct Ethanol Fuel Cells. 2016. (40) Tripathi, S.; Mehrotra, G. K.; Dutta, P. K. Physicochemical and bioactivity of cross-linked chitosan–PVA film for food packaging applications. Int J Biol Macromol. 2009, 45, 372. (41) Shi, X.; Xiao, H.; Lackner, K. S.; Chen, X. Capture CO2 from Ambient Air Using Nanoconfined Ion Hydration. Angew Chem Int Ed Engl. 2016, 55, 4026-9. (42) Shi, X.; Xiao, H.; Chen, X.; Lackner, K. S. The Effect of Moisture on the Hydrolysis of Basic Salts. Chemistry. 2016, 22, 18326-18330. (43) Choi, S.; Gray, M. L.; Jones, C. W. Amine-tethered solid adsorbents coupling high adsorption capacity and regenerability for CO2 capture from ambient air. Chemsuschem. 2011, 4, 628-35.


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