Designing Moisture-Swing CO2 Sorbents through Anion Screening of

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Designing moisture-swing CO2 sorbents through anion screening of polymeric ionic liquids Tao Wang, Kun Ge, Yusong Wu, Kexian Chen, Mengxiang Fang, and Zhongyang Luo Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.7b02200 • Publication Date (Web): 19 Sep 2017 Downloaded from http://pubs.acs.org on September 20, 2017

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Designing moisture-swing CO2 sorbents through anion screening of polymeric ionic liquids Tao Wang,*,† Kun Ge,† Yusong Wu,† Kexian Chen,*,‡ Mengxiang Fang,† Zhongyang Luo† †

State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou, Zhejiang Province 310018, P.R. China. ‡

School of Food Science and Biotechnology, Zhejiang Gongshang University, Hangzhou, Zhejiang Province 310018, P.R. China.

Abstract: Polymeric ionic liquids (PILs) are promising CO2 sorbents as their behaviors are tunable by assembling ion pairs. This work aims to design CO2 sorbents with unique moisture-swing adsorption performance by assembling different anions on quaternary-ammonium-based PILs. Two aspects of the sorbent design were studied: the suitability of the CO2 affinity for different applications (e.g., direct air capture or flue gas capture) and capability for moisture-swing adsorption. Carbonate, fluoride and acetate were chosen as counter anions as they are representative anions with different basicity, valence and water affinity. CO2 affinity was found to positively correlate with the pKa value of the counter anion, except for fluoride, which has an intrinsic character of attracting protons. The moisture swing capacity is determined by the difference between the hydration energies of the reactant and product after CO2 adsorption and followed the order carbonate > fluoride > acetate. Further investigations revealed that the repulsion between the two quaternary ammonium cations could promote the dissociation of hydrated water, which results in the lowest activation energy for CO2 adsorption for the PIL with carbonate. Therefore, the PIL with carbonate is potentially a desirable candidate for air capture and moisture-swing regeneration, while the PIL with acetate is suitable for CO2 capture under high partial ACS Paragon Plus Environment

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pressure and regeneration through conventional approaches. This study provides a quantitative microscopic insight into the role of the anion in CO2 adsorption and paves the way toward the optimal PIL structure for CO2 capture under specific circumstances.

Among PILs, the quaternary-ammonium-

1. INTRODUCTION Carbon dioxide capture and storage (CCS) is regarded

as

one

of

the

most

effective

approaches to alleviating global warming.1 Among

the

developed

CO2

capture

technologies, adsorption based on a solid material is advantageous since sorbents have unique interfacial properties, such as porous

based PILs have been highlighted in the literature due to their higher stability and CO2 sorption capacity than those of imidazoliumbased

PILs.10

More

interestingly,

when

coordinated with relatively basic anions such as OH- and CO32-, these PILs show the unique property of moisture-swing adsorption (MSA).11

structures, modifiable functional groups2,3, and

During the moisture-swing cycle, the sorbents

low emissions to the environment4. Recently,

adsorb CO2 in a dry atmosphere and release

polymeric ionic liquids (PILs) have been developed as a family of promising CO2 sorbents,

as

they

possess

the

unique

characteristics of ionic liquids (ILs) and the feasibility of a macromolecular framework.5-7 Both the CO2 adsorption capacity and rate of PILs can be substantially higher than those of

CO2 in a humid atmosphere. For poly[4vinylbenzyltrimethylammonium

carbonate]

(P[VBTEA][CO32-]), the equilibrium partial pressure of CO2 under wet conditions is two orders of magnitude higher than that under dry conditions.11

This

moisture-induced

cycle

utilizes the free energy released by water

their corresponding ionic liquid monomers.8

evaporation, and thus, it can avoid the use of

Similar to the fine tunability of ILs9, these

high-grade heat for sorbent regeneration and is

properties of PILs can further be tuned by the choice of cations and anions.

also environmentally benign. Of particular interest in this work is the screening of anions for PIL materials with MSA

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ability for CO2. Previous studies have shown

confined space, Shi et al.19 found that the free

that the type of anion plays a key role in

energy of CO32- hydrolysis in nanopores

defining the PIL features.12 After introducing

decreases

CO32- or OH- anions into P[VBTEA], the

availability.

sorbents exhibited such strong CO2 affinity that

structures, especially the types of anion, of

they were proposed for directly capturing CO2

quaternary-ammonium-based PILs would affect

from the ambient air (400 ppm).11,13-16 For

the

quaternary-ammonium-based salt hydrates with

capture remains unknown. Therefore, extensive

F- or acetate (Ac-), the CO2 absorption capacity

work is required to reveal the relationship

was observed to be affected by the hydration

between the structural and physicochemical

state17, which is similar to the MSA. The CO2

properties

adsorption isotherms indicate that they are

theoretical approaches.

with

the

decrease

However,

moisture-swing

of

the

chemical

performance

PILs,

for

especially

microscopic

MSA, several theoretical studies have been

physicochemical

conducted

on

reaction

ammonium-based PILs during CO2 adsorption.

pathways

and

Density

Quaternary-ammonium-based

energy.

insights

aim

through

sources (15-100 kPa).17 To gain insight into the

hydration

we

CO2

In

interactions,

work,

water

suitable for gas separation from concentrated

ionic

this

how

in

into

properties

to

the of

provide structure-

quaternary-

PILs

with

functional theory (DFT) calculations by Wang

different counter anions for CO2 capture are

et al.18 demonstrated the reaction pathways of

systematically

proton transfer for the PIL with the anion CO32-.

calculations. The counter anion should come

The results showed that the hydrated water acts

from weak acid, which have the ability of

as both a reactant and a catalyst during CO2

bonding hydrogen in water to show some

adsorption. By building a molecular dynamic

basicity

model for ion pairs of the quaternary-

Carbonate, fluoride and acetate are chosen as

ammonium cation (N(CH3)4+) and CO32- in a

counter anions because they are representative

to


investigated

react

with

through

CO2

DFT

chemically.

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anions with different basicity, valence and water

layered

affinity. The free energy of CO2 adsorption,

molecular mechanics) method22 was employed,

hydration energy and reaction pathways are

wherein the model compounds were separated

highlighted to evaluate the effect of the anions

into three layers with different calculation

on the CO2 adsorption performance of PILs.

methodologies (Figure 1). The high layer

These findings could pave the way toward

included anions, CO2 and hydrated water, which

determining

a

are the most active sites for CO2 adsorption18.

moisture-swing sorbent with specific adsorption

The medium layer included the quaternary

thermodynamics and kinetics.

ammonium cation, which directly interacts with

the

optimal

structure

of

integrated

molecular

orbital

and

the components of the high layer. The low layer

2. METHODS refers to the backbone of the PILs, which is The finite oligomer method20,21 was employed to calculate the electronic structure of the PILs. The sorbent material studied in this work is a polymer whose repeating unit is shown in Figure 1. The backbone of the PILs is polystyrene, and the quaternary ammonium cation is connected to it by a covalent bond. The counter anions interact with the cation through ionic bonds. Carbonate, fluoride and acetate were chosen as counter anions. Bicarbonate, bifluoride and hydroxide were also studied as

common polystyrene. The DFT-D3 method23 was employed for the high-layer calculations, which could take the long-range dispersion energy into account. The MP2 method was employed

CO2

adsorption.

To

reduce

the

single-point

energy

calculation of the high layer, because it was considered to be similarly accurate to the CCSD method.24,25 All the calculations in this work were carried out using the Gaussian09 software package.26 All calculation details can be found in the Supporting Information.

counter anions, as they are possible products after

for

the

computational cost, the ONIOM (our own n-


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can be disturbed by hydrated water, which is bonded to anions through hydrogen bonding (Figure 2). And parts of negative charges of the anions (qH2O) are transferred to the hydrated water. On the other hand, the hydrated water has a high dissociation potential owing to its strong Figure 1. Chemical structures of the model

hydrogen bond29,30, which would change the

compound

quaternary-ammonium-based

chemical properties of the ion pairs. Fluoride

PILs along with the definitions of the different

has the strongest hydrogen bond with hydrated

layers used in the ONIOM method.

water among the three anions, as it has

of

relatively large negative charges and three lone electron

3. RESULTS AND DISCUSSION

pairs.

Acetate

has

the

weakest

hydrogen bond because of the small negative 3.1. Optimized structures of hydrated PILs charges remaining for its oxygen atom. The optimized structures of PILs with different anions and hydrated water are shown in Figure 2. The consistency between the characteristic peaks of the functional groups in the calculated values of the model compounds and the experimental values of the corresponding PILs verifies the reliability of the model compounds and our computational methods (see Figure S1). Strong interactions are found between anions and the cation, which are mainly attributed to the

electrostatic

interaction

of

the

ionic

Figure 2. The optimized structures of the model compounds of PILs with hydrated water. The dashed line represents the hydrogen bond between the anions and hydrated water. The red arrow shows the direction of the movement of the proton in hydrated water due to the

bond27,28. The symmetric structures of ion pairs ACS Paragon Plus Environment

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hydrogen bond. qH2O represents the negative

mechanism of a Brønsted base can be expressed

charges transferred to the hydrated water from

as Reaction (1-3)17,18,34,35: N+CO32-N+·H2O + CO2 = 2N+HCO3-

the anion.

N+F-·H2O + CO2 + N+F- = N+HCO3- + N+F2H3.2. Hydrated PILs break the relationship

N+CH3COO-·H2O + CO2 = N+HCO3- + CH3COOH The

between pKa and CO2 affinity.

thermodynamic

properties

of

CO2

Anions should be the most chemically active

adsorption under the two different mechanisms

sites for CO2 adsorption by quaternary-

are shown in Table 1. The calculated results

ammonium-based PILs, as indicated by the

show that the Brønsted base mechanism is

frontier molecular orbitals of the optimized

qualitatively

structures (Figure S3). The anion could react

experimental values. Under the Brønsted base

with CO2 due to its properties as a Lewis base31

mechanism, water would have a distinct effect

or a Brønsted base32. In the case of a Lewis

on CO2 adsorption, as can be seen from the

base, the anion has lone pairs of electrons and

relationship between the standard Gibbs free

can react directly with CO2, as shown in Figure

energy change (∆G0) and pKa. Generally, the

S4, which is the reaction mechanism of CO2

values of ∆G0 and pKa are positively related.36

adsorption by monoamines33. In the case of a

However, fluoride has the smallest pKa value,

Brønsted base, the anion could accept a proton

but its CO2 affinity is moderately strong as a

from hydrated water through a hydrogen bond.

counter anion for PIL. The pKa value is an index

This could transform PILs into an intermediate

to express the basicity of an anion in aqueous

state with a hydroxide anion, which has strong

solution. For PILs with a low hydration state,

basicity and would easily react with CO2 to

this ion could demonstrate unique hydration

produce a bicarbonate anion. The overall

properties37, e.g., sharply decreased permittivity

reactions between PILs and CO2 under the

and increased hydration energy with decreased

consistent

with

the

reported

hydration number38. Compared with acetate, the


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three lone pairs of electrons of fluoride could

which indicates a potential application for CO2

strongly attract the proton of hydrated water,

capture from a dilute source, e.g., air. The PILs

which could lead to a stronger Brønsted base

with fluoride and acetate as the counter anions

effect and stronger CO2 affinity. Based on the

adsorb CO2 with a relatively weak affinity,

value of ∆G0 under the Brønsted base

which consequently could be applied to an

mechanism, the CO2 partial pressures at

environment with a relatively higher CO2

equilibrium (PCO2) were calculated. For the PIL

concentration, e.g., flue gas.

with carbonate, the PCO2 is tens of pascals,

Table 1. Thermodynamic properties of CO2 adsorption by PILs Counter Anion

∆G10 a (kJ/mol)

∆G20 b (kJ/mol)

∆Gexp (kJ/mol)

pKa c

PCO2 d

CO32-

0.51

-23.92

-17.05 e

10.33

24 Pa

F-

-1.22

-12.37

-10.31 f

3.18

3.88 kPa

Ac-

2.37

1.53

2.12 f

4.76

1.77 MPa

a

∆G0 via Lewis base mechanism obtained from theoretical calculations. b ∆G0 via Brønsted base mechanism obtained from theoretical calculations. c The pKa values of the anions in aqueous solution are taken from ref. 39. d Partial pressure of CO2 when 90% of available adsorption sites are covered under standard reference conditions. Langmuir adsorption is assumed; see the Supporting Information for details. e Experimental value taken from ref. 40. f The values are calculated using experimental results of the CO2 adsorption capacity and equilibrium partial pressure taken from ref. 17.

3.3. Hydration energy of PILs determines the

the PIL is considered to react with CO2 as a

capacity of moisture-swing adsorption.

hydrate18, as shown in Reaction (4):

To evaluate PILs as a MSA sorbent, an important indicator is the capacity of moisture

N+R-·aH2O + CO2 = N+P-·bH2O + (a-b-1)H2O where

N+

represents

the

quaternary

swing, which can be measured by the variation

ammonium cation and the backbone covalently

in the equilibrium partial pressure of CO2 when

linked to it; R- denotes the anion before

the humidity changes. Under a certain humidity,

adsorption; P- represents the anion after the


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reaction; and a and b are the hydration numbers.

illustrated in Figure 3. According to Hess’s

The reactant anion and product anion usually

Law, the CO2 adsorption under a given

have different water affinities, which result in

humidity could be divided into three elementary

releasing or adsorbing gaseous water during

reactions, i.e., the dehydration of the reactant

CO2 adsorption. By assuming a Langmuir-type

(Reaction A in Figure 3(a)), CO2 adsorption

adsorption, the equilibrium partial pressure of

under a base hydration state (Reaction B) and

CO2 can be derived from ∆G0.

hydration

of

the

product

(Reaction

C).

The calculated energies and capabilities for

Therefore, the difference in ∆G0, i.e., (∆Gw0-

moisture swing of the PILs in this work are

∆Gd0), is equivalent to the sum of the free

shown in Table 2, which demonstrates the

energy changes of the reactant dehydration (-

significant difference between the swing size of

∆Gr-h) and that of the product hydration (∆Gp-h)

the PILs. Under the same coverage fraction, the

between the dry and wet states. As listed in

CO2 partial pressure over the PIL with carbonate

Table 2, the difference in ∆G0 for the PIL with

increases from 0.15 kPa to 15 kPa when the

carbonate anions is dominated by the free

humidity

evident

energy change of the reactant dehydration (-

moisture swing is observed in the case of

∆Gr-h). In the case of fluoride, both ∆Gr-h and

acetate. Intuitively, the capability for moisture

are ∆Gp-h are relatively large, which results in a

swing arises from the difference between ∆G0

moderate moisture swing size. In the case of

for the dry (∆Gd0) and wet states (∆Gw0). The

acetate, ∆Gr-h and ∆Gp-h are similar, and thus,

hydration process of PILs suggests several

no evident moisture swing would be observed.

changes.

However,

no

thermodynamic pathways for reaction (4), as

Table 2. Properties of the moisture swing of PILs with different counter anions

Counter Anions

∆G0 (kJ/mol)

a

PCO2 (kPa)

b

∆Gr-h c ∆Gp-h d Swing Size e (kJ/mol) (kJ/mol)


Page 9 of 20

CO3

-

F

-

Ac

2-

Dry f

-21.64

0.15

Wet g

-10.21

15.01

Dry f

-11.27

9.82

Wet g

-9.02

24.19

Dry f

1.536

1667

Wet g

1.543

1672

-19.17

-7.74

100.01

-21.60

-19.35

2.46

-7.75

-7.74

1.003

a

∆G0 obtained from theoretical calculations; see the Supporting Information for details. b Partial pressure of CO2 when 90% of available adsorption sites are covered under standard reference conditions. c Free energy change of reactant hydration from dry to wet. d Free energy change of product hydration from dry to wet. e The swing size is defined as the ratio between the equilibrium CO2 partial pressures under the wet and dry conditions. f The dry condition refers to a relative humidity (RH) of 1% at a temperature of 25 °C. g The wet condition denotes a RH of 100% at a temperature of 25 °C. moisture swing. The difference in ∆G0, i.e., (∆Gw0-∆Gd0), is equivalent to the sum of the free energy changes of the reactant dehydration (-∆Gr-h) and that of the product hydration (∆Gph)

between the dry and wet states. (b) Calculated

standard Gibbs free energy change of hydration reactions for PILs with different anions as a (a)

function of the number of hydrated water

0

molecules. ∆ G (kJ/mol)

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-10

The

hydration

properties

are

completely different for PILs with different counter anions.

PIL-Carbonate PIL-Fluoride PIL-Acetate PIL-Bicarbonate PIL-Bifluoride

-20

In screening CO2 sorbents with large

-30 0

1

2 3 4 5 Number of hydrated water (b)

6

7

Figure 3. (a) Thermodynamic cycles to show that the difference of the hydration properties between reactant and product is the origin of

moisture swing capability, the potential PIL candidate should possess a high absolute value of ∆Gr-h and a low absolute value of ∆Gp-h. As shown in Figure 3(b), for PILs with carbonate


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and fluoride, the water affinity of these reactants

In the Type I distribution, each hydrated

is strong and decreases sharply as the number of

water molecule directly interacts with a counter

hydrated water molecules increases, which

anion, which results in a high hydration energy.

generates a high value of ∆Gr-h. In addition, the

The PIL with carbonate as the counter anion has

hydration energy of their product is relatively

the strongest affinity to water because of the

small and decreases slightly as the number of

large negative charges on the anion. The

hydrated water molecules increases, which

hydration energy of the PIL with carbonate

generates a low value of ∆Gp-h. The above

decreases sharply as the number of hydrated

phenomenon indicates that the hydrophilic

water molecules increases, since the carbonate

property of PILs changes significantly during

anion interacts with two quaternary ammonium

CO2 adsorption.

cations, and remaining free sites that can

To further elucidate the mechanism of this

interact with hydrated water are limited. The

hydrophilic property change, the optimized

PIL with fluoride as the counter anion has the

structures of PILs with three hydrated water

second strongest water affinity because of the

molecules are shown in Figure 4. According to

intrinsic strong potential of fluoride to attract

the relative positions between the hydrated

protons44. The hydration energy of the PIL with

water and counter anions, two types of hydrated

fluoride decreases moderately owing to the

water distribution are highlighted. For PILs with

three lone pairs of electrons on fluoride and

carbonate, fluoride and bifluoride as counter

sufficient free space around the fluoride ion.

anions, the hydrated water is uniformly located

The PIL with bifluoride has a moderately strong

around the anion (Type I). In contrast, in the

water affinity due to the strong intramolecular

cases of acetate and bicarbonate, the hydrated

hydrogen bond formed between the two fluoride

water forms hydrogen bonds between other

ions. The hydration energy of the PIL with

water

bifluoride decreases slowest with the increase in

molecules,

which

association41-43 (Type II).

is

called

self-

the number of hydrated water molecules


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because the two fluorine atoms in the anion could serve as active sites to interact with the hydrated water. The hydrated water tends to form a Type II distribution because the negative charges on the anions are small, and the affinity of the anions to hydrated water is weak. The intermolecular hydrogen bonds formed during self-association could partly offset the decrease in the hydration energy when the number of hydrated water molecules increases. Therefore, the hydration energy of the PILs with bicarbonate and acetate decreases gently. An ideal MSA sorbent should possess a Type I distribution for the reactant and a Type II distribution for the product. Note that the hydrophilic property of PILs can be tuned by

Figure 4. Optimized structures of PILs with three hydrated water molecules. The hydrated water molecules self-associate or form clusters in PILs with acetate or bicarbonate, while the hydrated water molecules locate around the anion uniformly in the cases of carbonate, fluoride and bifluoride.

screening not only anions but also other factors,

3.4. Two-step reaction pathways of the

e.g., cations and the polymer backbone45.

Brønsted base mechanism. As discussed in Section 3.2, PILs with basic counter anions adsorb CO2 through the Brønsted base mechanism, wherein one proton of the hydrated water is transferred to the anion, and a strongly basic hydroxide anion is produced.18 However, the hydration properties and reaction pathways


of

CO2

adsorption

can

differ

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dramatically for PILs with different anions46,

instead of one step (Figure 6; detailed

which

information on the structural parameters is listed

could

result

in

different

kinetic

performance.

in Table S3), which would significantly lower

Figure 5 shows the reaction pathways and

the activation energy47. On the other hand, a

the corresponding potential energy profiles for

two-step

CO2 adsorption by PILs with different anions.

quaternary ammonium cations are involved in

For the PILs with fluoride and carbonate, CO2 is

the reaction pathways. The repulsion between

adsorbed through a two-step mechanism. In this

these two cations could promote the dissociation

mechanism, a steady intermediate (IM) with a

of hydrated water.48,49

mechanism

implies

that

two

high energy is produced before adsorbing CO2,

As shown in Figure 6, the PIL with fluoride

and two quaternary ammonium cations are

also has the potential to adsorb CO2 through a

required

one-step mechanism, similarly to acetate (see

to

adsorb

one

CO2

molecule.

Meanwhile, in the case of acetate, CO2 is

Figure

absorbed in one step, wherein the dissociation

geometries), since both fluoride and acetate

of hydrated water coincides with the production

anions have a maximum of one negative charge.

of bicarbonate, and no IM is found in this

However, the activation energy of the one-step

mechanism.

is

reaction pathway for the PIL with fluoride is

advantageous for CO2 adsorption, because only

14.61 kJ/mol higher than that of the two-step

one acetate anion is required to adsorb one CO2

reaction pathway, which indicates that the two-

molecule. However, the activation energy of

step

this mechanism is higher than that of the two-

feasibility of the two-step mechanism could be

step mechanism, which is a disadvantage.

attributed to the intrinsic proton-attraction

Through the two-step mechanism, the huge

property of fluoride44, which will result in a

structural variations due to CO2 adsorption are

reaction between the hydrofluoric acid molecule

accomplished with two small successive steps

thus formed and fluoride to generate a

This

one-step

mechanism

S6

for

mechanism


its

optimized

reaction

is more favorable.

The

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Reaction

pathways

and

the

bifluoride anion. The PIL with acetate would

Figure

not easily adsorb CO2 through the two-step

corresponding potential energy profiles for CO2

mechanism, because the steric hindrance of

adsorption by PILs with different anions. RC,

acetate anion50,51 would prevent the formed

TS, IM and PC are abbreviations for reactant

acetic acid molecule from bonding with another

complex, transition state, intermediate state and

acetate anion.

product complex, respectively. The PILs with

5.

carbonate or fluoride adsorb CO2 via two steps with an intermediate state, while the PIL with acetate adsorbs CO2 via one step with a high activation energy. Energy values were corrected by ZPVE.

Figure 6. Optimized reaction geometries of two different reaction pathways for CO2 adsorption by the PILs with fluoride. The arrows and values under the panels show the variations in the key structural


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Page 14 of 20

parameters during CO2 adsorption. The structural variation of the one-step mechanism is larger than that of the two-step mechanism, which results in the higher activation energy. suitable for capturing CO2 at a high partial pressure because of its large capacity and its

4. CONCLUSIONS Quaternary-ammonium-based

PILs

are

promising sorbents for CO2 capture. In this work, theoretical studies were performed to systematically investigate the effect of varying the counter anion on CO2 adsorption. Our results showed that the PIL with carbonate as the counter anion has the lowest activation energy, strongest CO2 affinity and largest swing size, and it functions through a two-step mechanism, which indicates that it is a better candidate as a sorbent to capture CO2 from ultra-low concentration mixtures, such as that of air. The PIL with fluoride as the counter anion has a low activation energy, strong CO2 affinity, medium-to-large swing size, and it adsorbs CO2 through a two-step mechanism, owing to the

feasibility

to

be

regenerated

through

conventional approaches. Further investigations revealed that the repulsion between the two quaternary ammonium cations, which interact with the carbonate anion or two fluoride anions, could promote the dissociation of hydrated water and lower the activation energy of the CO2 adsorption. The two-step reaction pathways also exhibit low activation energy owing to the relatively small structural changes of each step. Our findings could provide a fundamental understanding of CO2 capture by quaternaryammonium-based PILs and pave the way toward determining the optimal structure of a PIL to be used for CO2 capture in specific circumstances.

unique ability of fluoride to strongly attract

ASSOCIATED CONTENT

protons. The PIL with acetate as the counter

SUPPORTING INFORMATION.

This material is available free of charge via the anion has a high activation energy, weak CO2 Internet at http://pubs.acs.org. affinity and small swing size, and functions with a one-step mechanism, which indicates that it is ACS Paragon Plus Environment

Page 15 of 20

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

Computational

Energy & Fuels

details,

calculation

of

equilibrium parameters and number of hydrated water molecules, Figure S1-S7, Table S1-S3.

Report of the Intergovernmental Panel on Climate Change, 2014. (2) Wang, J.; Huang, L.; Yang, R.; Zhang, Z.;

AUTHOR INFORMATION

Wu, J.; Gao, Y.; Wang, Q.; O'Hare, D.; Zhong,

Corresponding Author

Z., Recent advances in solid sorbents for CO2

*[email protected]

capture and new development trends. Energy Environ. Sci. 2014, 7, 3478-3518.

*[email protected]

(3) Cogswell, C. F.; Jiang, H.; Ramberger, J.;

Notes The authors declare no competing financial

Accetta, D.; Willey, R. J.; Choi, S., Effect of Pore

interest.

Structure

on

CO2

Adsorption

Characteristics of Aminopolymer Impregnated ACKNOWLEDGMENT

MCM-36. Langmuir 2015, 15, 4534-4541.

This study is supported by the National Natural Science Foundation of China (No.

(4) Wang, Q.; Luo, J.; Zhong, Z.; Borgna, A.,

51676169) and the Fundamental Research

CO2 capture by solid adsorbents and their

Funds for the Central Universities.

applications: current status and new trends. Energy Environ. Sci. 2011, 4, 42-55.

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