Ammoniated Covalent Organic Frameworks for Water-Lean Carbon Capture

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Traditional amine-based CO2 capture is limited by 2:1 amine-to-CO2 stoichiometry, increasing costs and energy demand.
• Water promotes 1:1 stoichiometry but causes amine degradation and higher regeneration energy needs.
• A need exists for efficient, stable, and low-energy CO2 sorbents, especially for dilute streams.

Purpose of the Study:

• To develop a water-lean carbon capture (WLCC) strategy using novel porous materials.
• To overcome the conventional 2:1 amine-to-CO2 stoichiometry limitation in CO2 capture.
• To investigate the potential of functionalized covalent organic frameworks (COFs) as efficient and low-energy CO2 sorbents.

Main Methods:

• Postsynthetic Mannich grafting of primary amines onto microporous covalent organic frameworks (COFs), NUS-44 and NUS-45.
• Characterization of CO2 chemisorption using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and isotopic labeling (13C/15N) solid-state nuclear magnetic resonance (ssNMR).
• Evaluation of CO2 uptake capacity at ultralow pressures, performance in varying humidity, regeneration temperature, and energy analysis of regeneration heat.

Main Results:

• NUS-44 demonstrated CO2 chemisorption via carbamic acid formation in the absence of water, stabilized by intrapore hydrogen bonding.
• Achieved a 1:1 amine-to-CO2 stoichiometry, overcoming the conventional 2:1 limitation, with high CO2 uptake at low pressures.
• Maintained performance in dry and humid conditions, regenerated at 80 °C, showing a 20.6-27.8% reduction in regeneration heat compared to water-containing systems.

Conclusions:

• Established hydrogen-bond-stabilized carbamic acid as a novel chemisorption motif in porous frameworks for CO2 capture.
• NUS-44 and NUS-45 represent promising low-energy, moisture-independent sorbents for next-generation carbon capture from dilute CO2 streams.
• The WLCC strategy offers significant energy savings and improved stability for CO2 capture applications.