Title : Halogen-enhanced metal-organic frameworks: Selective CO2 capture and sustainable chemical fixation
Abstract:
Three novel halogen-appended cadmium(II) metal-organic frameworks (MOFs) denoted as [Cd2(L1)2(4,4’-Bipy)2]n.4n(DMF) (1), [Cd2(L2)2(4,4’-Bipy)2]n.3n(DMF) (2), and [Cd(L3)(4,4’-Bipy)]n.2n(DMF) (3), were synthesized through solvothermal reactions The new MOFs are constructed using new multifunctional halogen-based dicarboxylic acid pro-ligands, namely 5-{(4-bromobenzyl)amino}isophthalic acid (H2L1), 5-{(4-chlorobenzyl)amino}isophthalic acid (H2L2), and 5-{(4-fluorobenzyl)amino}isophthalic acid (H2L3), alongside Cd(NO3)2•4H2O. Crystal structure analyses reveal that these MOFs share a similar three-dimensional architecture, with 1 and 2 exhibiting enhanced thermal and chemical stability compared to 3. The MOFs, featuring diverse functional groups such as halogen, carboxylate, and amine, present themselves as promising candidates for applications in gas storage and separation. Gas adsorption analyses highlight their remarkable capability to selectively adsorb CO2 over N2 and CH4 at different temperatures (273 and 298 K) and pressures (120-275 kPa). Specifically, MOF 2 displays the highest CO2 adsorption capacity of approximately 2.58 mmol/g at 273K, accompanied by a BET surface area of 281 m2/g. Computational studies using configurational bias Monte Carlo simulations corroborate these findings, emphasizing the stronger interaction between our MOFs and CO2 compared to N2 and CH4. Beyond gas adsorption, these MOFs exhibit another facet of their versatility by serving as efficient Lewis acid-based heterogeneous catalysts for solvent-free CO2 fixation reactions with epoxides. In the presence of tetrabutyl ammonium bromide (TBAB), the MOFs facilitate the conversion of CO2 into industrially valuable cyclic carbonates. Notably, the MOFs exhibit high conversion rates (96-99%) of epichlorohydrin to the corresponding cyclic carbonate after 12 hours of reaction time at 65 °C under 1 bar of CO2 pressure. Size-selectivity of the MOFs towards smaller and larger substrates is demonstrated, and catalytic recycling experiments reveal that these MOFs can be reused for at least three cycles without a considerable loss of activity. This work unveils halogen-enhanced Cd(II)-MOFs as multifaceted materials, showcasing exceptional selectivity in CO2 capture and sustainable catalytic performance in chemical fixation reactions. The findings hold significant promise for addressing environmental challenges by offering efficient and reusable materials for selective carbon dioxide capture and conversion into industrially relevant cyclic carbonates.
Audience Takeaway Notes:
- Global Climate Change and Greenhouse Gas Emissions: Understand the current environmental challenges posed by global climate change, emphasizing the role of greenhouse gases, particularly carbon dioxide (CO2), and the need for effective mitigation strategies.
- Significance of CO2 Capture Technologies: Explore the importance of developing advanced CO2 capture technologies in the context of rising atmospheric CO2 concentrations, driven by industrial activities and fossil fuel combustion, and the limitations of existing methods. synthesized MOFs
- Versatility of Metal-Organic Frameworks (MOFs): Gain insights into the diverse applications of MOFs, including their large surface area, permanent porosity, high thermal and chemical stability, and tunable functionality, positioning them as promising materials in various scientific and industrial fields.
- Challenges in Catalyzing CO2 Fixation: Recognize the challenges associated with catalyzing the chemical fixation of CO2, especially in the context of developing suitable catalysts that exhibit high efficiency under mild conditions, addressing issues related to energy consumption and reaction pressure.
