Amine-Functionalized Defective MOFs for Direct Air Capture by Postsynthetic Modification.

Area of Science:

• Materials Science
• Chemical Engineering
• Environmental Science

Background:

• Defective metal-organic frameworks (DM) offer potential for direct air capture (DAC) of carbon dioxide (CO2).
• Amine functionalization is a key strategy to enhance CO2 adsorption properties of sorbent materials.

Purpose of the Study:

• To investigate the efficacy of amine-functionalized chromium-based DM for DAC.
• To compare the performance of different amine functionalization strategies, including ethylenediamine (EDA), tris(2-aminoethyl)amine (TAEA), and polyethylene-polyamines (PEPA).

Main Methods:

• Post-synthetic modification of chromium-based DM with EDA, TAEA, and PEPA.
• Characterization using FTIR, XPS, PXRD, and SEM to confirm synthesis and structural integrity.
• Evaluation of CO2 adsorption capacity, regeneration energy, and cyclic stability under ambient conditions.

Main Results:

• 1:1-PEPA-DM demonstrated the highest CO2 adsorption capacity (1.26 mmol/g) and lowest regeneration energy (75.1 kJ/mol).
• The PEPA-grafted DM exhibited excellent durability, with only 26.62% capacity loss after 12 cycles.
• Physically impregnated PEPA showed lower capacity and significantly reduced cyclic stability compared to covalently grafted PEPA.

Conclusions:

• Covalent grafting of PEPA onto chromium-based DM is a highly effective strategy for developing durable and efficient DAC sorbents.
• The choice of amine and functionalization method significantly impacts DAC performance and material stability.