Design and Synthesis of Ultramicroporous Zinc-azolate-based MOFs for Selective CO2 Capture

Abstract

Global warming remains a significant challenge, primarily caused by greenhouse gases such as CO₂, CH₄, and N₂O, which trap heat in the atmosphere. Since the industrial revolution, CO₂ levels have risen from approximately 270 ppm to 424 ppm due to human activities, leading to rising temperatures, glacier melts, and extreme weather events. Carbon Capture and Storage (CCS) has emerged as a crucial strategy to mitigate these effects. While conventional CO₂ capture relies on energy intensive liquid amines, solid sorbents such as zeolites, porous carbons, silica gels and metal organic frameworks (MOFs) offer more efficient alternatives. MOFs gain a special interest owing to their easy structural and chemical designability. Many MOFs have been investigated for carbon capture; of these, the ultramicroporous (< 6 Å) ones are quite effective. CALF-20, an ultramicroporous Zn-triazolato-oxalate MOF, has been demonstrated at industrial scale to capture multi tons of CO₂ per day from flue gas. Its strong metal–ligand bonds, high selectivity and steam stability make it a promising candidate for humid CO₂ separation. However, CALF-20's pore space limits further enhancement of its intrinsic capacity and also its capture capacity at extremely low CO2 pressures is insufficient. In this thesis we focus on developing design principles for zinc-azolate MOFs to achieve superior CO2 capture characteristics. Also, adhering to simple gram-scale synthesizability as a key requirement. Thus the thesis contributes to the development of next-generation MOFs with enhanced low-pressure CO₂ capture is essential in supporting global decarbonization efforts.