Exploring the General Characteristics of Amino-Acid-Functionalized

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Explore the General Characteristic of Amino Acid Functionalized Ionic Liquid through Experimental and Quantum Chemical Calculation Yuhao Qian, Guo-Hua Jing, Bihong Lv, and Zuoming Zhou Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b03268 • Publication Date (Web): 06 Mar 2017 Downloaded from http://pubs.acs.org on March 14, 2017

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Title of the manuscript:

Explore the General Characteristic of Amino Acid Functionalized Ionic Liquid through Experimental and Quantum Chemical Calculation

Order of Authors 1. Yuhao Qian;

Huaqiao University,

2. Guohua Jing;

Huaqiao University

3. Bihong Lv;

Huaqiao University,

4. Zuoming Zhou;

Huaqiao University,

1

ACS Paragon Plus Environment

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Highlights 1. The CO2 absorption capacity of AAILs had positive correlations with their interaction energy. 2. The viscosity of AAILs was negatively correlated to their interaction energy due to the steric hindrance. 3. Activation barrier and chain length of AAILs cation influenced the AAILs regeneration efficiency. 4. CO2 capture into AAILs was more likely to occur neutralizing rather than the zwitterions mechanism.

2


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Explore the General Characteristic of Amino Acid Functionalized Ionic Liquid through Experimental and Quantum Chemical Calculation

Yuhao Qian, Guohua Jing*, Bihong Lv, Zuoming Zhou (College of Chemical Engineering, Huaqiao University, Xiamen 361021, China)

ABSTRACT Amino acid functionalized ionic liquids (AAILs) show significant potential for energy-efficient post-combustion CO2 capture. In this work, the interaction energy calculation was performed with Gaussian 09 package and the activation barriers and energy change calculation were performed with Material Studio 7.0 package. The experimental and quantum chemical calculation results showed that both the CO2 absorption capacity and the viscosity of AAILs were negatively correlated to their interaction energy. The results of 13C NMR analysis and activation barriers indicated that under the same conditions, the effect of AAILs cation on the regeneration ability was more significant than that of anion. In our previous work, CO2 absorption into AAILs solution was proved to be divided into two periods. In the first period, carbamate was produced after CO2 absorption reaction; in the second period, the production was carbonate. Research on thermodynamic properties in this work made the mechanism for CO2 capture into AAILs to be more clear. The activation barrier,





Corresponding author. Tel: +86-592-6166216; Fax: +86-592-6162300;

E-mail address: [email protected] (G.H. Jing) 3


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energy change and enthalpy change during the two periods revealed that the AAILs-CO2 absorption reaction should be a neutralizing and exothermic reaction in the first period, and a hydrolysis and endothermic reaction in the second period. Keyword Ionic liquids; CO2 absorption; Quantum chemistry; Activation barrier

1.Introduction Carbon dioxide (CO2 ) is one of the major greenhouse gases known to contribute to climate change and give rise to environmental problems. 1 It is urgent for us to control the emission of CO2. Organic amine had been widely used for CO2 capture, due to its relatively good results on CO2 absorption.2, 3 However, it still suffered some inherent drawbacks such as solvent loss and equipment corrosion. Ionic liquids (ILs) had drawn wide attentions since Blanchard et al.4 found that CO2 could be dissolved into this new solvent. The physical and chemical properties of ILs could be improved significantly by changing the structure of the cation and anion ion pair.5 Therefore, some functionalized ILs became a hot topic for scientists to study.6 Among them, amino or amino acids functionalized ionic liquid (AILs or AAILs) was the most promising one for CO2 capture, in which amino or amino acids was introduced as functional group to both the anions and cations of ILs. Bates et al.5 synthesized

an

AILs

1-aminopropyl-3-butylimidazolium

tetrafluoroborate

[APbim][BF4], and found that this new ILs was renewable. It reacted reversibly with CO2

to

form

carbamate

salt.

Zhang

et

al.7

synthesized

4


a

series

of

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double-amino-functionalized ILs with an absorption capacity of 1.0 mol CO 2/mol ILs, and they found that the CO2 capacity was related to the number of the functional groups. Subsequently, based on the designability of ILs, some researches were trying to increase the number of functional groups or adjust the ionic structure in order to enhance the absorption capacity of ILs,8,

9

and others were trying to investigate

functionalization of organic ions to adjust the physicochemical properties of the corresponding ILs.10-12 Recently, Li et al.13 mixed amino acid and an ionic liquid ([Bmim]BF4) together to reduce the energy penalty of CO2 capture and achieved a remarkable effect. However, most of the past works focused on the synthesis of new ILs and the investigation of their CO2 capture performance, which was inefficient. Recently, many researches gradually look on the theoretical simulation to improve the efficiency. Bowro et al.14 used molecular dynamics and neutron diffraction to study the structure of 1-ethyl-3-methylimidazolium acetate comprehensively, and they found that the spatial probability distributions revealed the main anion-to-cation features as in-plane interactions of anions with the three imidazolium ring hydrogens and cation-cation planar stacking above/below the imidazolium rings. Damas et al.15 used quantum chemistry to study the interaction between cation-anion and gas molecules for gas capture into ILs, and they found that the effect of anions was more significant than that of cation. Fernandes et al.16 used quantum chemistry to calculate the cation-anion interaction energy in ILs and found that chain length of cation had an impact on their CO2 absorption capacity. Gupta et al.17 combined the molecular simulation and ab 5


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initio calculation to study the nitrile based ILs, and they proved that CO2 solubility was governed by the binding energy of cation-anion, rather than the binding energy of CO2-anion. Furthermore, the quantum chemical calculation was combined with experiment method to explore the regularity of CO2 absorption into ILs. Arellano et al.18

used

quantum

chemistry

to

calculated

the

best

configuration

of

[Emim][Zn(TFSI)3] and found out its excellent model by combining the simulation and experimental results. Moreover, Chaban et al.19-21 used molecular dynamics simulations to develop some new force field for several selected AAILs, which could foster computational investigation of ILs. Therefore, the method combining the experiments and quantum chemical calculation was considered to be a high-efficiency method for ILs study. Our group has developed a wide variety of efficient AILs or AAILs. In order to find the relationship between the structure of AAILs and the CO2 absorption performance, the general characteristics of AAILs were investigated through experimental and quantum chemical calculation in the present work. Firstly, the structures, enthalpy and cation-anion interaction of different AAILs, e.g. 1-aminopropyl-3-methylimidazolium glycine ([APmim][Gly]), 1-aminoethyl-3-methylimidazolium lysine ([AEmim][Lys]), 1-aminopropyl-3-methylimidazolium tributylhexylphosphonium

lysine

lysine ([P6444][Lys]),

([APmim][Lys]) were

calculated

and at

the

B3LYP/6-311++G(d,p) level of theory under DFT method. Meanwhile, the activation barrier and reaction energy of cation-CO2 and anion-CO2 were also calculated by Materials Studio 7.0. Later, these four AAILs were synthesized, and their performance 6


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on CO2 capture such as absorption capacity, viscosity, regeneration ability and reaction mechanism were all carried out to find out the relationship between the quantum chemical calculation result and these experimental data, verify the theoretical results and to sum up the general law of AAILs, so as to provide some reliable basis for the systematic synthesis and study of ionic liquids in the future.

2. Materials and Methods 2.1 Materials 1-aminopropyl-3-methylimidazolium bromide ([APmim]Br), 1-aminoethyl-3methylimidazolium bromide ([AEmim]Br), tributylhexylphosphonium bromide ([P6444] Br) was obtained from Lanzhou Greenchem ILS, LICP, CAS, China. L-lysine, glycine, natrium hydroxydatum (NaOH) was obtain from Xiya reagent. D2O was provided by J&K Scientific Ltd. Mass purities of these chemicals were higher than 99.0%. The gas of CO2 (>99.999%) was supplied by Fujian Nanan Chenggong Gas Co., Ltd., China. 2.2 Synthesis The four AAILs [APmim][Lys], [AEmim][Lys], [P6444][Lys] and [APmim][Gly] used in this work were synthesized in laboratory in aqueous phase through two steps of the replacement and neutralization.22 Take [APmim][Lys] as an example, firstly, 0.5 mol of the pure [APmim][Br] was dissolved in water, it was turned into [APmim][OH] via the ion exchange. Secondly, [APmim][OH] and lysine (0.5 mol) were mixed together to form [APmim][Lys] by a neutralization reaction for 24 h at 25 oC under 7


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stirring.23 R1-OH + R2-COOH → R1-OOC-R2 + H2O

(1)

Then, the compound was concentrated under vacuum at 70 oC in rotary evaporators. After that, the product was diluted with water, and the concentration of the solvent was 0.5 mol/L. 2.3 Experimental Methods and Apparatus The schematic diagram of the absorption and desorption apparatus was presented in Figure 1. The concentrations of those four AAILs were 0.5 mol/L. During the absorption, the pure CO2 gas was bubbled into the solution, and the gas-flow rate was controlled at 30 ml/min by mass flow meter and continuously supplied to the bubble absorption bottle which was filled with ILs solution. Water bath temperature was controlled at 40 oC. The inlet and outlet gas flow rate of CO2 was measured by the soap film flow meter. After absorption, the CO2-saturated solutions were regenerated in a flask in oil bath for 1.5 h at 120 oC. Viscosity of the solvents was measured using ubbelohde viscometer(Capillary inner diameter: 0.5~ 0.6 mm), setting the temperature at 25 oC. The pH value was measured using pH meter(FE20) made by Mettler Toledo Co., Ltd., Shanghai, China. The general physical and chemical properties of AAILs were also need to be measured. To clarify the structure of the products during the absorption and regeneration, 0.5 mL of the samples were characterized by

13

C NMR (Bruker

AVIII500 MHz), using an internal standard of 0.1 mL D2O for the deuterium lock.

8


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3 Calculation Methods The structures and atom-type notations of the [APmim] cation, [AEmim] cation, [P6444] cation, [Lys] anion and [Gly] anion were shown in Figure 2. The ion energy, optimal structure, vibrational frequency and enthalpy calculation were performed with Gaussian 09 package using the DFT method with the Becke’s three-parameter functional and the nonlocal correlation of Lee, Yang, and Parr (B3LYP) together with the 6-311++G(d,p) basis set.24, 25 The transition state and molecular energy calculation were performed with Material Studio 7.0 package using method B3LYP under DMol3 module. The total reaction energy(△E), activation barrier(△Eact), enthalpy change(△H) and reaction energy(△Q) were given by equation 2 and equation 3. △E (kJ/mol) = 2625.5[Eion

pair

- (Ecation + Eanion)]

△Eact /△H /△Q (kJ/mol) = 2625.5(Eproduct – Ereatant)

(2) (3)

where Eionpair is the energy of the ion pair and Ecation and Eanion are the energies of its cation and anion, respectively; Eproduct and Ereatant are the energies of product and reactant, respectively. All these data were calculated after basis set superposition error (BSSE) and zero point energy correction(ZPE), and all of them were expressed in units of au.

4.Results and Discussion 4.1 Quantum Chemistry Calculations. ILs would ionize in the solvent, so ion pairs were the basic structure units in the 9


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system. Though there were several conformations when the anion located around the cation at different positions, the lowest-energy conformers would be the most likely configuration formed in AAILs solution, which was analyzed by quantum chemistry calculations. The theoretical calculation of four types of AAILs, e.g. [APmim][Lys], [AEmim][Lys],

[APmim][Gly]

and

[P6444][Lys]

were

performed

by using

B3LYP/6-311++G(d,p) level under DFT method. The optimized geometries are shown in Figure 3, in which the hydrogen bond was expressed the dotted line. The hydrogen bond lengths, bond angles and other data could also be obtained in quantum chemistry calculation and the results are shown in Table 1. Generally speaking, a hydrogen bond can be identified if the distance between the donor group proton and the acceptor atom is shorter than the van der Waals distance, as well as the angle is greater than 90°. The van der Waals distances for H···O and H···N are 2.72, 2.75 Å, respectively.26 Based on the results of Figure 3 and Table 1, take [APmim][Gly] as an example, there were four H···O hydrogen bonds existing between the [APmim] cation and the [Gly] anion. Two hydrogen bonds were between the two O atoms of the anion and the 6H atom of the cation with distances of 1.712 and 2.432 Å, respectively. The distances between the O atoms of the anion and the 10H atom of the CH3 group, and the distances between the O atoms of the anion and the 9H atom of the C3H8N group was 2.071 and 2.698 Å, respectively. Similarly, four hydrogen bonds were also formed in [APmim][Lys] and [AEmim][Lys], but there were only three hydrogen bonds formed in [P6444][Lys]. In the present work, the interaction energies of the [APmim][Lys], 10


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[AEmim][Lys], [APmim][Gly] and [P6444][Lys] ion pairs were also calculated. The △E of each ion pair is also shown in Table 1. There were three amino functional groups in [APmim][Lys] and [AEmim][Lys] and two in [P6444][Lys] and [APmim][Gly]. It seemed that the hydrogen bond had a significant impact on the interaction energy: the increase of hydrogen bond, the more stable of the AAILs molecules, which could be seen from the interaction energy. The different conformation also impacted the interaction energy. Take [APmim][Lys] and [AEmim][Lys] for example, although they had a similar structure, their best conformation and hydrogen bond position were different with each other, which resulted in the different interaction energy of these two AAILs. 4.2 CO2 Absorption Capacity and Viscosity Measurements Herein, these four AAILs were synthesized and their CO2 absorption capacity and viscosity were related with their interaction energy. The results are shown in Table 2. From Table 2, it can be seen that the absorption capacity of [APmim][Lys], [AEmim][Lys], [P6444][Lys], [APmim][Gly] were 1.812, 1.543, 1.279 and 1.266 mol CO2/mol ILs, and the interaction energies were -361.7939, -398.8134, -340.5274, and -444.4972 kJ/mol, respectively. The CO2 absorption capacity of these four AAILs followed the order [APmim][Lys] > [AEmim][Lys] > [P6444][Lys] > [APmim][Gly]. The results indicated that the CO2 absorption capacity of AAILs was related to the interaction energy. As mentioned in the introduction, the CO2 absorption capacity of AAILs was depended on the number of the amine functional groups. The higher 11


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number of the amine functional groups, the higher absorption capacity of AAILs. From Figure 3 it can be seen that there was three amine functional groups in [APmim][Lys] and [AEmim][Lys], while two amine functional groups in [P6444][Lys] and [APmim][Gly]. Thus, their absorption capacities would be comparable. However, as shown in Table 2, even at the same number of amine functional group and the same absorption and calculation condition, their absorption capacity and the interaction energy were different with each other. That’s because there are still many factors influence the CO2 absorption capacity of AAILs, such as the activation barrier and the interaction energy of AAILs. It seemed that, with the same number of amine functional group, the stronger the interaction energy of AAILs, the lower the CO2 absorption capacity. These results were consistent with that reported by Gupta et al, and they also found that the solubility and diffusivity of CO2 increased as the interaction energy decreased,17 which would mainly influence the capacity of the physical absorption. But the physical absorption was slight in the absorption between AAIL and CO2. Thus, it can be seem that the interaction energy between [P6444][Lys] and [APmin][Gly] was significant but their absorption capacities were comparable. On the other hand, the result also showed that the viscosity of the AAILs followed the order [P6444][Lys] > [APmim][Lys] > [AEmim][Lys] > [APmim][Gly], which was adverse to the trend of the interaction energy. The results indicated that the viscosity of the AAILs decreased as the interaction energy increased, which was contrary to the results reported by Zhang et al.26. They calculated the interaction energy of [Emim][PO2F2], [Emim][SCN] and [Emim][N(CN)2] under the basis set 12


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6-31++G(d,p) and found that the stronger the interaction between the cation and anion, the higher the viscosity. Combined with the results of the experiments and the quantum chemistry calculation, the viscosity of the AAILs and the volume of anion increased as the alkyl chain length of anion increased, which was similar with the reported work.33 Thus, the geometric volume of anion in AAILs in the present work was much larger than that of the reported ILs such as [Emim][PO2F2], [Emim][SCN] and [Emim][N(CN)2]. Meanwhile, the steric hindrance of the AAILs would increase as the anion or cation volume increased, which was not conducive to the freedom movement of ILs in the solvent. Thus, different from the other ILs, the geometric volume was the main factor influencing the viscosity of the AAILs. That means the viscosity of AAILs was mainly influenced by the steric hindrance which was increased as the alkyl chain length of the anion or cation increased, but not the interaction energy between cation-anion pairs as the other ILs. 4.3 Regeneration Characteristic Measurements Besides the high absorption capacity and fast absorption rate, long-term stability is also important for any CO2 sequestration system.34 So the regeneration characteristic was also investigated in this work. The regeneration temperature was set to 120 oC.23, 35 Each AAIL was regenerated at least 5 times. Figure 4 presents the absorption capacities of these four AAILs after cyclic regeneration. As shown in Figure 4, all of these four AAILs had good regeneration stability, and the minimum absorption capacity after the 5th regeneration still kept 89.2 % of their original capacity. Among them, the regeneration stability of [APmim][Lys] and 13


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[APmim][Gly] was higher than that of the other two AAILs Meanwhile, pH value of these four AAILs before CO2 absorption and after the regeneration was measured to illustrate the regeneration efficiency and stability of these four AAILs. As shown in Table 3, it can be seen that the pH value of [APmim][Lys] and [APmim][Gly] changed slightly after the regeneration, while that of [AEmim][Lys] and [P6444][Lys] changed significantly. The results indicated that the effect of the cation of AAILs on the regeneration ability was probably larger than that of the anion. To further clarify the influence of the structure on regeneration ability, the activation barriers and reaction energy were calculated by Materials Studio 7.0. The data shown in Table 4 could explain why the regeneration efficiency of cation [APmim] was higher than that of cation [AEmim]. It was found that the chain length of [APmim] was longer than [AEmim] and the activation barriers of [APmim]-CO2 and [AEmim]-CO2 was 27.5126 KJ/mol and 578.0957 KJ/mol, respectively. The latter was nearly 20 times higher than the former. It meant that when cation [AEmim] absorbed CO2, the -NH2 on [AEmim] was hard to react with CO2 to form carbamate, and once the carbamate was formed, it would also hard to be decomposed. That's the reason why they owned the same animo functional group with the different absorption capacity and regeneration efficiency. The results of

13

C NMR

shown in Figure 5 also verified this conclusion. In the saturated solvent, the CO2 existence form in [AEmim][Lys] solution was carbonate due to its low activation barriers (35.1344 KJ/mol), and all the carbamate could be easily changed into carbonate. After regeneration, the carbamate still existed in the solution, which 14


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reduced the regeneration efficiency. 4.4 Reaction Mechanism of AAILs In most reported works, the zwitterions mechanism proposed by Michael Caplow36 and supplemented by Danckwerts37 was used to explain the reaction mechanism between primary amines, secondary amines and CO2. However, the AAILs solvents were much more complex than amine solution, and it was needed to further clarify the reaction mechanism. In our previous work, it had proved that CO2 absorption into AAILs divided into two periods: in the first period, it produced carbamate according zwitterionic mechanism, and in the second period, it produced carbonate.23 The reaction mechanism changed as the CO2 loading of the solvent increased. In the fresh solution, the concentration of AAIL was high, and the chemical reaction between CO2 and AAIL was the main reaction. Take the reaction between CO2 and the amine functional group of anion (Lys-NH2) for example. Theoretically, CO2 would react with Lys-NH2 based on the zwitterionic mechanism s-

-

s-

s-

(4)

Nevertheless, since the AAIL solution was alkalinity, the solvent also would be hydrolyzed firstly, and then CO2 was reacted with AAILs by neutralizing reaction. This reaction was called as ‘h drol sis and neutralization’ mechanism, and was presented as follows ss-

-

s-

s-

-

15


(5) (6)

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Both of these two reaction mechanisms of CO2 capture into Lys-NH2 would also occur in the solvent. The activation energy and reaction energy of anion pairs by these two mechanisms were calculated by materials studio. The results are compared in Table 5. As shown in Table 5, the activation energy of the reaction according to the zwitterionic mechanism was 519. 898 KJ/mol, while that of ‘h drol sis and neutralization’ mechanism was 75.65 8 KJ/mol, which meant that the former reaction mechanism needed much more energy than the latter reaction mechanism. As the reaction carried on, the concentration of AAIL in the solvent was decreased. The chemical reaction between CO2 and AAIL was weakened, and the CO2 hydrolysis in water was enhanced. Herein, take [APmim][Lys] for example, the change of temperature and pH during the CO2 absorption into different solvents are compared in Figure 6. The temperature of these two solvents both increased firstly and then decreased, while pH was gradually decreased as the reaction time increased. It seemed that the change of temperature and pH of CO2 absorption into [APmim][Lys] was similar with that of lysine, while the maximum temperature and pH of CO2 absorption into [APmim][Br] was much lower. Since temperature indirectly reflected the reaction capacity, the results indicated that the contribution of lysine on CO2 absorption was higher than that of [APmim][Br]. Moreover, the thermodynamics data of all reaction substances of [APmim][Gly] and [APmim][Lys] was calculated by Gaussian 09 package. The results are shown in Table 6, which was the basic data used for calculation in Table 7. Table 7 clearly showed the △H of all reaction periods of the AAILs-CO2 16


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reaction. The first period of CO2 absorption into these two AAILs to form carbamate was both an exothermic reaction, and the hydrolysis of CO2 in this period could be ignored. The second period was the relatively complex process, there were several reactions carried out at the same time. On one hand, the carboxyl in carbamate showed buffer solution property, thus AAILs-NHCOO- and AAILs-NHCOOH both existed in the solution. On the other hand, CO2 would also hydrolyze in the solution. As shown in Table 7, the second period(hydrolysis reaction) had both exothermic reaction and endothermic reaction, it was hard to affirm the ratio of each reaction. But as we know, once the first period finished, the hydrolysis of CO2 could no longer be ignored. The △H of CO2 + H2O reaction was 1423.2886 KJ/mol, much larger than other reactions. Therefore, on the whole, the second period was endothermic reaction.

4.Conclusions In this work, quantum chemistry calculation software Gaussian 09 package was used to calculate the interaction energy and enthalpy of the ionic liquids [P6444][Lys], [APmim][Lys], [AEmim][Lys] and [APmim][Gly]. Materials Studio was used to calculate the activation barriers and reaction energy of them. Combined quantum chemistry simulation and experimental results, it was found that the CO2 absorption capacity of AAILs was related to the interaction energy, the stronger the interaction energy, the lower the CO2 absorption capacity. And due to the steric hindrance of the AAILs cation and anion, the viscosity of the AAILs was also adverse to the trend of the interaction energy that it was decreased as the interaction energy increased. 17


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Besides, the regeneration characteristic was investigated in this work. The result showed that the cation of AAILs had a significant effect on the regeneration ability of AAILs. Through the quantum chemistry calculation and the experimental results, the reaction mechanism and the thermodynamic properties of AAILs were also clarified. The result showed that the mechanism of CO2 capture into AAILs was divided into two periods, in which CO2 was firstly reacted with AAILs to form carbamate and then hydrolyzed to form carbonate. The results proved that a neutralizing reaction mechanism was more likely to occur in the first period of AAILs-CO2 reaction than that of the zwitterionic mechanism, and the second period of the reaction was proved to be an endothermic process.

Acknowledgments This work was sponsored by the National Natural Science Foundation of China (21576109 and 21676110), and the Natural Science Foundation of Fujian Province (2016J05038). We also thank the Instrumental Analysis Center of Huaqiao University for analysis support and the ‘subsidized project for cultivating postgraduates’ innovative ability in scientific research of Huaqiao University’.

Reference [1]Kerr, R. A.; Sci. 2007, 316, 188-190. [2]Gao, H. X.; Xu, B.; Liu, H. L.; Liang, Z. W.; Energy Fuels. 2016, 30, 7481-7488.

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[3]Zhang, S. H.; Lu, H.; Lu, Y. Q.; Environ. Sci. Technol. 2013, 47, 1 88 −1 888. [4]Blanchard, L. A.; Brennecke, J. F.; Ind. Eng. Chem. Res. 2001, 30, 287-437. [5]Bates, E.D.; Mayton, R. D.; Ntai, A. I.; Davis, J. H.; J. Am. Chem. Soc. 2002, 124, 926-927. [6]Li, S. J.; Zhao, C. J.; Sun, C.; Shi, Y.; Li, W.; Energy Fuels. 2016, 30, 8535-8544. [7]Zhang, Y. Q.; Zhang, S. J.; Lu, X. M.; Zhou, Q.; Fan, W.; Zhang, X. P.; J. Chem. Eur. 2009, 15, 3003-3011. [8]Zhang, J. Z.; Jia, C.; Dong, H. F.; Wang, J. Q.; Zhang, X. P.; Zhang, S. J.; Ind. Eng. Chem. Res. 2013, 52, 5835-5841. [9]Xue, Z. M.; Zhang, Z. F.; Han, J.; Chen, Y.; Mu, T. C.; Int. J. Greenh. Gas. Con. 2011, 5, 628-633. [10]Chaban, V. V.; Prezhdo, O. V.; J. Phys. Chem. B. 2015, 119, 9920-9924. [11]Chaban, V.; J. Chem. Thermodyn. 2016, 98, 81-85. [12]Anouti, M.; Caillon-Caravanier, M.; Dridi, Y.; Galiano, H.; Lemordant, D.; J. Phys. Chem. B. 2008, 112, 13335-13343. [13]Li, W.; Zhang, X. L.; Lu, B. H.; Sun, C.; Li, S. J.; Zhang, S. H.; Int. J. Greenh. Gas. Con. 2015, 42, 400-404. [14]Bowron, D. T.; Agostino, C. D.; Gladden, L. F.; Hardacre, C.; Holbrey, J. D.; Lagunas, M. C.; McGregor, J.; Mantle, M. D.; Mullan, C. L.; Youngs, T. G. A.; J. Phys. Chem. B. 2010, 114, 7760-7768. [15]Damas, G. B.; Dias, A. B. A.; Costa, L. T.; J. Phys. Chem. B. 2014, 118, 9046-9064. 19


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[16]Fernandes, A. M.; Rocha, M. A. A.; Freire, M. G.; Marrucho, I. M.; Coutinho, J. A. P.; Santos, L. M. N. B. F.; J. Phys. Chem. B. 2011, 115, 4033-4041. [17]Gupta, K. M.; Jiang, J. W.; J. Phys. Chem. C. 2014, 118, 3110-3118. [18]Arellano, I. H.; Huang, J. H.; Pendleton, P.; Spectrochim. Acta. A. 2016, 153, 6-15. [19]Fileti, E. E.; Chaban, V. V.; Chem. Phys. Lett. 2014, 616-617, 205-211. [20]Fileti, E. E.; Chaban, V. V.; Chem. Phys. Lett. 2015, 633, 132-138. [21]Chaban, V. V.; Fileti, E. E.; J. Mol. Model. 2015, 21, 236. [22]Clare, B.; Sirwardana, A.; Macfarlane, D. R.; Top. Curr. Chem. 2009, 290, 1-40. [23]Lv, B. H.; Jing, G. H.; Qian, Y. H.; Zhou, Z. M.; Chem. Eng. J. 2016, 289, 212-218. [24]Becke, A. D.; J. Chem. Phys. 1993, 98, 5648-5653. [25]Bene, J. E. D.; Ditchfield, R.; Pople, J. A.; J. Chem. Phys. 1971, 54, 724-728. [26]Zhang, X. C.; Huo, F.; Liu, X. M.; Dong, K.; He, H. Y.; Yao, X. Q.; Jiang, S. J.; Ind. Eng. Chem. Res. 2015, 54, 3505-3514. [27]Guo, B. S.; Jing, G. H.; Zhou, Z. M.; Int. J. Greenh. Gas. Con. 2015, 34, 31-38. [28]Mohajeri, A.; Ashrafi, A.; J. Phys. Chem. A. 2011, 115, 6589-6593. [29]Muhammad, N.; Man, Z. B.; Bustam, M. A.; Mutalib, M. I. A.; Wilfred, C. D.; Rafiq, S.; J. Chem. Eng. Data. 2011, 56, 3157-3162. [30]Matsumoto, K.; Hagiwara, R.; Inorg. Chem. 2009, 48, 7350-7358. [31]Larriba, M.; Navarro, P.; García, J.; Rodrí guez, F.; J. Chem. Thermodyn. 2014, 79, 266-271. 20


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[32]Macfarlane, D. R.; Golding, J.; Forsyth, S.; Forsyth, M.; Deacon, G. B.; Chem Commun, 2001, 16, 1430-1431. [33]Chaban, V. V.; Fileti, E. E.; J. Phys. Chem. B. 2014, 119, 3824-3828. [34]Hwang, C. C.; Jin, Z.; Lu, W.; Sun, Z. Z.; Alemany, L. B.; Lomeda, J. R.; Tour, J. M.; Acs. Appl. Mater. Interfaces. 2011, 3, 4782-4786. [35]Zhou, Z. M.; Zhou, X. B.; Jing, G. H.; Lv, B. H.; Energy Fuels. 2016, 30, 7489-7495. [36]Caplow, M.; J. Am. Chem. Soc. 2002, 90, 6795-6803. [37]Danckwerts, P. V.; Chem. Eng. Sci. 1979, 34, 443-446.

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Figure captions Figure 1. Schematic diagram of the (a)absorption and (b)desorption experimental apparatus: 1) CO2 cylinder; 2) mass flow meter; 3) bubble absorption bottle; 4) temperature controller; 5) soap film flow meter. 6) condenser pipe; 7) three-necked flask; 8) oil bath.

Figure 2. Structures and atom-type notations of (a) [APmim] cation, (b) [AEmim] cation, (c) [P6444] cation (d) [Gly] anion and (e) [Lys] anion.

Figure 3. The optimized geometries and atom-type notations of different AAILs.

Figure 4. The absorption capacity of these four AAILs after cyclic regeneration.

Figure 5. The 13C NMR of [AEmim][Lys] and [APmim][Lys] (1)before and (2)after regeneration.

Figure 6. The change of temperature and pH into different solvents during the CO2 absorption.

22


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Energy & Fuels

Table 1. Hydrogen bond lengths, bond angles and interaction energy. Bonds and angles

[APmim][Gly]

[AEmim][Lys]

9H…11O ∠14C-9H…11O 6H…11O ∠1C-6H…11O 6H…12O ∠1C-6H…12O 10H…12O ∠25C-10H…12O 21H…34O ∠19C-21H…34O 4H…34O ∠3C-4H…34O 4H…47O ∠3C-4H…47O 17H…43N ∠15N-17H…43N 3H…81O ∠2C-3H…81O 17H…69O ∠15C-17H…69O 33H…69O ∠31C-33H…69O

2.698 139.98 1.712 166.64 2.432 130.01 2.071 163.31

2.663 133.54 1.756 164.02 2.393 130.14 2.068 161.59

△E kJ/mol

-444.4972

[APmim][Lys]

[P6444][Lys]

1.970 155.94 2.647 112.25 1.803 152.86 2.297 177.23 1.960 174.84 1.963 175.41 2.293 157.75 -398.8134

-361.7939

23


-340.5274

Energy & Fuels

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Page 24 of 35

Table 2. The absorption capacity, viscosity and interaction energy of AAILs. ILs

Concentration

Interaction energy △E kJ/mol

Viscosity(298.15K) μ / mPa·s

Absorption capacity （323K）mol /mol

[P6444][Lys]

0.5 mol/L

-340.5274

2.0285

1.279

[APmim][Gly]

0.5 mol/L

-444.4972

1.0319

1.266

[APmim][Lys]

0.5 mol/L

-361.7939

1.2894

1.812

[AEmim][Lys]

0.5 mol/L

-398.8134

1.2294

1.543

[N1111][Gly]

0.5 mol/L

-355.4958

1.727

0.627

[Emim][Gly]

Pure

-94.8628

61.5129

--

[Emim][Ala]

Pure

-94.3728

171.1929

--

[Emim][Ser]

Pure

-92.2528

410.8629

--

[Emim][PO2F2]

Pure

−519.2826

3530

--

[Emim][SCN]

Pure

−508.2526

23.7931

--

[Emim][N(CN)2]

Pure

−499.2526

2132

--

24


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Energy & Fuels

Table 3. The pH of four AAILs before absorption and after regeneration. Before CO2 absorption

After regeneration

[P6444][Lys]

10.65

9.73

[APmim][Gly]

9.79

9.70

[APmim][Lys]

10.22

10.20

[AEmim][Lys]

10.56

9.85

25


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Table 4. The activation barriers and reaction energy of cation pairs. 3D model

Activation barriers (△Eact)KJ/mol

Reaction energy (△Q)KJ/mol

27.5126

-32.3068

2AP-NH2+CO2→AP-NHCOO- + AP-NH3+

578.0957

-44.7436

2AE-NH2+CO2→AE-NHCOO- + AE-NH3+ 35.1344

-33.3806

AE-NHCOO- +H++H2O→HCO3- + AE-NH3+ 49.4241 AP-NHCOO- +H++H2O→HCO3- + AP-NH3+

26


-57.4862

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Energy & Fuels

Table 5. The activation energy and reaction energy of anion pairs. 3D model

activation barriers (△Eact)KJ/mol

Reaction energy (△Q)KJ/mol

519.2898

-28.2556

2Lys-NH2+CO2 → Lys-NHCOO- + Lys-NH3+

32.2306

-179.3216

H2O + Lys-NH2 → Lys-NH3+ + OH- (Partial protonated process) CO2 + Lys-NH2 + OH- → Lys-NHCOO- + H2O 502.5049

-28.5208

2Gly-NH2+CO2 → Gly-NHCOO- + Gly-NH3+ 86.7184

-164.8880

H2O + Gly-NH2 → Gly-NH3+ + OH- (Partial protonated process) CO2 +Gly-NH2 + OH- → Gly-NHCOO- + H2O

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Table 6. The thermodynamics data of all reaction substances.

ε0 (a.u.)

Hcorr (a.u.)

ZPE (a.u.)

ε0+ Hcorr

H+

0.0000

0.00236

0.0000

0.00236

H2O

-76.4585

0.02507

0.02129

-76.4334

OH-

-75.8274

0.01184

0.008535

-75.8156

CO2

-188.6469

0.01525

0.01169

-188.6316

HCO3-

-264.5510

0.03048

0.02598

-264.5205

[APmim][Gly]

-723.4538

0.3004

0.2813

-723.1534

[APmim][Gly-NH3+]

-723.8756

0.3139

0.2951

-723.5617

[APmim][Gly-NHCOO-]

-911.6467

0.3058

0.2852

-911.3410

[APmim][Gly-NHCOOH]

-912.2105

0.3182

0.2967

-911.8923

[APmim][Lys]

-936.0556

0.4385

0.4136

-935.6171

[APmim][Lys-NH3+]

-936.4895

0.4534

0.4275

-936.0361

[APmim][Lys-NHCOO-]

-1124.2371

0.4429

0.4162

-1123.7942

[APmim][Lys-NHCOOH]

-1124.8296

0.4566

0.4288

-1124.3730

ε0 Total electronic energy Hcorr Thermal correction to enthalpy

28


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Energy & Fuels

Table 7. The reaction equation and the △H. Chemical Reaction Equation

△H(KJ/mol)

First period (neutralizing reaction) CO2 + [APmim][Gly] + OH- → [APmim][Gly-NHCOO-] + H2O

-456.3119

CO2 + [APmim][Lys] + OH- → [APmim][Lys-NHCOO-] + H2O

-428.7442

Second period (hydrolysis reaction) [APmim][Gly-NHCOO-] + H2O + H+ → [APmim][Gly-NH3+] + HCO3-

-801.9327

[APmim][Gly-NHCOOH] + H2O → [APmim][Gly-NH3+] + HCO3-

639.3092

[APmim][Lys-NHCOO-] + H2O + H+ → [APmim][Lys-NH3+] + HCO3-

-857.5933

[APmim][Lys-NHCOOH] + H2O → [APmim][Lys-NH3+] + HCO3-

655.8499

CO2 + H2O →H+ + HCO3-

29


1423.2886

Energy & Fuels

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(a)

Page 30 of 35

(b) Fig 1.

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Energy & Fuels

Fig 2.

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[APmim][Gly]

Page 32 of 35

[AEmim][Lys]

[APmim][Lys]

[P6444][Lys] Fig 3.

32


Page 33 of 35

2.0

original

1st

2nd

3rd

4th

5th

1.8

Absorption capacity mol/mol

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

Energy & Fuels

1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0

[APmim][Lys]

[AEmim][Lys]

[P6444][Lys]

Fig 4.

33


[APmim][Gly]

Energy & Fuels

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AEmimLys

Page 34 of 35

APmimLys Fig 5.

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Page 35 of 35

34

13

33

12

Lysine [APmim]Br

32

11

31

10

30

9

29

8

28

7

27 -10

pH

o

T/ C

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

Energy & Fuels

0

10

20

30

40

50

60

70

80

time/min

Fig 6.

35


90

100

6 110

Exploring the General Characteristics of Amino-Acid-Functionalized

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