A thiophene-containing covalent triazine-based framework with ultramicropore for CO2 capture

doi:10.1016/j.jechem.2017.07.007

Journal of Energy Chemistry

Volume 26, Issue 5, September 2017, Pages 902-908

https://doi.org/10.1016/j.jechem.2017.07.007 Get rights and content

Abstract

In this work, a 2D covalent triazine-based framework was prepared by using 1,3-dicyanobenzo[c]thiophene (DCBT) as monomer to effectively capture CO₂. The resulting CTF-DCBT was characterized by FT-IR, XPS, PXRD, elemental analysis, SEM, TEM, and N₂ adsorption-desorption. The results indicate that CTF-DCBT is partially crystalline and has ultramicropore (6.5 Å) as well as high heteroatom contents (11.24 wt% and 12.61 wt% for N and S, respectively). In addition, the BET surface area and total pore volume of CTF-DCBT are 500 m²/g and 0.26 cm³/g, respectively. CTF-DCBT possesses excellent thermal stability (450 °C) and chemical stability towards boiling water, 4 M HCl, and 1 M NaOH. The CO₂ adsorption capacity of CTF-DCBT is 37.8 cm³/g at 1 bar and 25 °C. After six adsorption–desorption cycles, there is no obvious loss of CO₂ uptake observed. Due to the ultramicropore and high heteroatom contents, CTF-DCBT has high isosteric heats of adsorption for CO₂ and high selectivities of CO₂ over N₂ and CH₄. At 25 °C, the CO₂/N₂ and CO₂/CH₄ selectivities are 112.5 and 10.3, respectively, which are higher than those of most POFs. Breakthrough curves indicate that CTF-DCBT could effectively separate CO₂/N₂ and CO₂/CH₄ mixtures.

Graphical abstract

A covalent triazine-based framework with both ultramicropore and high heteroatom contents is obtained to selectively capture CO₂.

Introduction

Carbon dioxide (CO₂), as a major greenhouse gas, is excessively discharged into the atmosphere, which may cause global warming [1]. Therefore, the concentration of atmospheric CO₂ is attracting intense public attention in recent decades. The anthropogenic emission of CO₂ mainly is contributed to the continuous combustion of fossil fuels such as coal and petroleum [2]. Flue gas from coal-fired power plants contributes 30%–40% of the total anthropogenic CO₂ emissions [3]. The flue gas mainly consists of CO₂ (low concentration) and N₂ (high concentration). In addition, natural gas and landfill gas are mainly contaminated with CO₂, which could decrease the heating capacity and cause corrosion of equipment [4]. Therefore, the highly selective CO₂ capture from CO₂/N₂ and CO₂/CH₄ mixtures is crucial from the perspective of energy and the environment.

There are various approaches developed for CO₂ capture such as membrane separation [5], adsorption [6], absorption [7]. Among these approaches, selective adsorption using solid sorbents is deemed to be a promising approach due to its low energy penalty, fast regeneration, and easy operation. To effectively capture CO₂, the adsorbents should have high CO₂ adsorption capacity, high CO₂ selectivity over other gases, good thermal and chemical stability, and easy regeneration [8]. To that end, various kinds of adsorbents have been designed and synthesized so far, including metal-organic frameworks (MOFs) [9], porous organic frameworks (POFs) [10], porous carbons [11], zeolites [12], and so on [13]. MOFs and POFs are currently being intensively investigated attributed to their designable structure and various functional groups for wide applications [14], [15]. Compared with MOFs comprised of metal ions (or clusters) and organic ligands through coordination bonds, POFs are composed of organic building blocks linked by covalent bonds, thus generally having high chemical stability [10]. Therefore, POFs have great promise for application in industry. The POFs mainly include crystalline covalent-organic frameworks (COFs) [16], polymers intrinsic microporosity (PIMs) [17], porous aromatic frameworks (PAFs) [18], conjugated microporous polymers (CMPs) [19], hyper-crosslinked polymers (HCPs) [20], benzimidazole-linked polymers (BILPs) [21], porous imine-linked networks (PINs) [22], covalent triazine-based frameworks (CTFs) [23], and so on. In contrast to other POFs, the synthesis of CTFs in the presence of molten ZnCl₂ avoids the use of organic solvents and expensive catalysts such as Pd. In addition, the synthesis can be adapted on a large scale [24]. Therefore, CTFs have attracted intense interest over the past decade.

In general, under ambient conditions, the CO₂ adsorption capacity and selectivity of adsorbents are related to the affinity of adsorbents towards CO₂. Several strategies have been proposed to enhance the affinity. On the one hand, from the view of pore structure, small pore size could result in deep overlap of potential and thus strong interaction between adsorbent and gas molecules, such as CO₂, N₂, and CH₄ [25], [26], [27]. In addition, since quadrupole moment of CO₂ is larger than that of N₂ and CH₄, small pore size could increase the difference of isosteric adsorption heats between CO₂ and N₂ (CH₄), thereby increasing the CO₂/N₂ and CO₂/CH₄ selectivities [28]. Therefore, ultramicropore (<7 Å) is generally favorable to uptake CO₂ at low pressure. On the other hand, from the view of chemical composition, the heteroatoms including nitrogen, sulfur, and oxygen within the frameworks favor the adsorption and separation of CO₂. Basic nitrogen atoms in the frameworks could increase CO₂ uptake capacity due to the Lewis acid-Lewis base electrostatic interactions between the carbon atoms of the CO₂ molecules and the nitrogen atoms [29], [30]. In addition, other heteroatoms, such as sulfur and oxygen, also could strengthen interaction with CO₂ attributed to the heteroatoms increase polarity and basicity of frameworks [31]. Therefore, design and synthesis of porous materials with both ultramicropore and heteroatoms are reasonable for CO₂ capture.

Bearing these in our mind, here we prepare an ultramicroporous CTF with both S and N atoms for CO₂ capture by using monomer containing benzo[c]thiophene. In contrast to other monomers for preparing CTFs, 1,3-dicyanobenzo[c]thiophene (DCBT) not only has wide structure but also has two angled linker sites. These two structure properties are envisaged to decrease porosity. In addition, the S and N atoms are retained in the framework after isothermal polymerization. As a result, the CTF possesses excellent performance for selective CO₂ capture.

Section snippets

Synthesis of DCBT

The DCBT was synthesized according to the literature procedure [32]. A solution of diisopropylamine (15.75 g, 157.5 mmol) in tetrahydrofuran (THF, 175 mL) was cooled to −78 °C (under N₂ atmosphere). Then n-butyllithium (61.25 mL, 157.5 mmol) was added to the above solution slowly under stirred condition. After stirring for 15 min, a solution of 1,2-benzenediacetonitrile (8.05 g, 52.5 mmol) in THF (175 mL) was added slowly. After stirring for another 15 min, a solution of thionyl chloride

Synthesis and characterization of CTF-DCBT

The synthesized DCBT was confirmed by ¹H NMR and ¹³C NMR characterization (see Figs. S2 and S3). As reported previously by other literatures [23], [33], most CTFs were synthesized by ionothermal polymerization using dicyano monomers and ZnCl₂. Under polymerization condition, the molten ZnCl₂ serves as Lewis acid catalyst, solvent, and porogen. Three nitrile groups could be cyclized to obtain a triazine group (C₃N₃). In contrast to polymerization catalyzed by strong Brønsted acid such as CF₃SO₃H

Conclusions

We synthesized an ultramicroporous CTF-DCBT with high nitrogen and sulfur contents (11.24 wt% and 12.61 wt% respectively) by using 1,3-dicyanobenzo[c]thiophene as a monomer. The resulting CTF-DCBT has excellent chemical and thermal stability. In addition, CTF-DCBT possesses high CO₂ capture capacity (37.8 cm³/g at 1 bar and 25 °C) and great recyclability. After six adsorption–desorption cycles, CO₂ uptake of CTF-DCBT do not decrease. In addition, the CO₂/N₂ and CO₂/CH₄ selectivities of CTF-DCBT

Acknowledgments

This work was supported by the National Key R&D Program of China (2016YFB0600901) and the Natural Science Foundation of China (grant nos. 21536001 and 21606007).

References (64)

Z. Liu et al.
J. Energy Chem.
(2015)
L. Wang et al.
J. Energy Chem.
(2014)
J. Yang et al.
Microporous Mesoporous Mater.
(2014)
C. Gu et al.
Polym. Chem.
(2015)
H. Huang et al.
Chem. Eng. J.
(2016)
Y. Xia et al.
Carbon
(2012)
P. Puthiaraj et al.
Chem. Eng. J.
(2016)
C. Han et al.
J. Power Sources
(2014)
S.K. Das et al.
Chem. Eng. Sci.
(2016)
K. Sumida et al.
Chem. Rev.
(2012)

Q. Yang et al.

J. Phys. Chem. C

(2008)

K. Adil et al.

Chem. Soc. Rev.

(2017)

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A thiophene-containing covalent triazine-based framework with ultramicropore for CO2 capture

Abstract

Graphical abstract

Introduction

Section snippets

Synthesis of DCBT

Synthesis and characterization of CTF-DCBT

Conclusions

Acknowledgments

J. Energy Chem.

J. Energy Chem.

Microporous Mesoporous Mater.

Polym. Chem.

Chem. Eng. J.

Carbon

Chem. Eng. J.

J. Power Sources

Chem. Eng. Sci.

Chem. Rev.

Energy Environ. Sci.

Environ. Sci. Technol.

Environ. Sci. Technol.

Ind. Eng. Chem. Res.

Chem. Soc. Rev.

Chem. Commun.

Ind. Eng. Chem. Res.

Energy Fuels

Environ. Sci. Technol.

Acc. Chem. Res.

Chem. Soc. Rev.

J. Am. Chem. Soc.

Ind. Eng. Chem. Res.

CrystEngComm

J. Am. Chem. Soc.

J. Mater. Chem.

Chem. Mater.

J. Mater. Chem. A

Acc. Chem. Res.

J. Mater. Chem. A

J. Phys. Chem. C

Chem. Soc. Rev.

A thiophene-containing covalent triazine-based framework with ultramicropore for CO₂ capture