CO₂ Capture on Amine-Modified Mesostructured Silicas: A Comparative Study with Metal–Organic Frameworks

Within the Carbon Capture and Utilization technologies framework, porous materials—such as Ordered Mesostructured Silicas (OMSs) and Metal–Organic Frameworks (MOFs)—are promising sorbents for CO₂ capture due to their high adsorption capacities, ease of regeneration, and stability. This work focuses on a comparison between two classes of hybrid organic–inorganic adsorbents for CO₂ capture: amino-modified OMSs and MOFs. Among the OMSs, two MCM-41 samples composed of 100–500nm particles with 3 nm mesopores were synthesized using different silicon sources: TEOS (tetraethyl orthosilicate) and FSA (fluorosilicic acid) derived from industrial waste. Owing to their high surface area resulting from their mesostructure, these materials are well-suited for surface functionalization to improve CO₂ adsorption. In this study, both samples were functionalized with (3-aminopropyl)triethoxysilane, yielding NH₂@TEOS-MCM-41 and NH₂@FSA-MCM-41. For comparison a 3D ultramicroporous MOF based on a benzoquinone derivative—3,6-N-ditriazolyl-2,5-dihydroxy-1,4-benzoquinone (trz₂An)—coordinated with cobalt(II) (CoMOF) was proposed. Its pore size (3.4 Å) enables selective CO₂ separation via size-dependent adsorption (molecular sieving), as this dimension closely match the kinetic diameter of CO₂. CO₂ capture performance was assessed through dynamic adsorption tests using 5–10% CO₂ in N₂. At 10% CO₂ and 30 °C, NH₂@TEOS-MCM-41 showed a higher uptake (~1000 μmol/g) than CoMOF (~700 μmol/g), with the difference becoming more pronounced at 5% CO₂: ~829 μmol/g and ~317 μmol/g respectively. Conversely, CoMOF offered easier regeneration at room temperature under N₂, whereas NH₂@TEOS-MCM-41 required also heating at 120 °C. The different performances arise mainly from their distinct CO₂ adsorption mechanisms: chemisorption for NH₂@TEOS-MCM-41, forming ammonium carbamates through interactions between amino groups and CO₂ and physisorption for CoMOF, governed by weak intermolecular forces with MOF’s porous surface. The adsorption heats derived from microcalorimetry and the FTIR confirm the mentioned mechanisms. Additionally, NH₂@FSA-MCM-41, synthesized from FSA with similar amine loading, showed even better performance: ~1000 μmol/g (5% CO₂) and ~1200 μmol/g (10% CO₂).