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Unusual Moisture-enhanced CO₂ Capture within Microporous PCN-250 Frameworks
Summary:
The authors from School of Chemistry and Chemical Engineering, South China University of Technology, Key Laboratory for Advanced Materials, School of Chemistry and Molecular Engineering, East China University of Science and Technology, and School of Chemistry and Chemical Engineering, Guangzhou University developed PCN-250(Fe₃) and PCN-250(Fe₂Co), which have excellent moisture stability, good recyclability, and an unusual moisture-enhanced CO₂ adsorption feature, achieving efficient CO₂ capture from flue gas in the application of post-combustion CO₂ capture.
Background:
1. To address the problem of inefficient CO₂ capture under humid conditions, previous researchers explored various MOFs. While some had high adsorption capacities, most were moisture-sensitive or had reduced performance due to H₂O competitive adsorption, and few showed enhanced CO₂ uptake under high humidity.
2. The authors in this study proposed using iron-based MOFs PCN-250(Fe₃) and bimetallic PCN-250(Fe₂Co), which exhibit moisture-enhanced CO₂ adsorption, overcoming the negative impact of moisture.
Research Content:
1. Synthesis:
The authors synthesized Fe₃(μ₃-O)(CH₃COO)₆ and Fe₂Co(μ₃-O)(CH₃COO)₆ clusters by mixing metal nitrates with sodium acetate. PCN-250(Fe₃) and PCN-250(Fe₂Co) were then synthesized via solvothermal method using these clusters with H₄ABTC ligand and acetic acid in DMF, followed by activation through solvent exchange and drying.
2. Characterizations:
1) BET results showed PCN-250(Fe₃) has a surface area of 1470 m²/g and micropore volume of 0.506 cm³/g; PCN-250(Fe₂Co) has a surface area of 1653 m²/g and micropore volume of 0.573 cm³/g. Pore size distribution: PCN-250(Fe₃) has pores centered at 5.9 Å and 6.8-9.3 Å; PCN-250(Fe₂Co) mainly in 6.8-9.3 Å.
2) SEM tests show the particle size of the material: both have an average particle size of around 50 µm; PCN-250(Fe₃) is dodecahedral with small rhombic surfaces, PCN-250(Fe₂Co) is cubo-octahedral.
3) Other tests: PXRD confirmed high purity and structural integrity; TGA showed thermal stability up to 400 °C; moisture stability tests (30 days at 90% RH) confirmed unchanged structure and porosity; isosteric heat of adsorption indicated stronger CO₂ affinity in PCN-250(Fe₂Co).
3. Application:
The materials were tested in CO₂ capture from simulated flue gas (CO₂/N₂ = 15:85). Under dry conditions, CO₂ uptakes were 1.18 mmol/g (PCN-250(Fe₃)) and 1.32 mmol/g (PCN-250(Fe₂Co)). At 50% RH, uptakes increased by 54.2% and 68.9% to 1.82 and 2.23 mmol/g, respectively; at 90% RH, increases were 43.7% and 70.2%. Both showed excellent recyclability over 10 cycles.
4. Mechanism:
Molecular simulations revealed hydroxo functional groups (μ₃-O) in the framework interact with H₂O, forming a "plier-effect" that clamps CO₂ near metal sites, enhancing adsorption. Partial substitution of Fe³⁺ with Co²⁺ strengthens CO₂ affinity, increasing uptake and selectivity. H₂O promotes CO₂ adsorption by utilizing unsaturated sites without competitive adsorption.
Outlook:
This research reports moisture-enhanced CO₂ capture in PCN-250 frameworks, providing a new design paradigm for MOFs in practical humid flue gas CO₂ capture, with significant industrial application value.
Unusual Moisture-enhanced CO₂ Capture within Microporous PCN-250 Frameworks
Authors: Yongwei Chen, Zhiwei Qiao, Jiali Huang, Houxiao Wu, Jing Xiao, Qibin Xia, Hongxia Xi, Jun Hu, Jian Zhou, Zhong Li
DOI: 10.1021/acsami.8b14400
Link: http://pubs.acs.org/doi/10.1021/acsami.8b14400
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