Preferential Adsorption of CO₂ in an Ultramicroporous MOF with Cavities Lined by Basic Groups and Open-Metal Sites

Here, we present a new ultramicroporous Cu₂ paddlewheel based MOF. This ultramicroporous MOF has most of the features such as porosity (BET surface area = 945 m²/g), CO₂ capacity (3.5 mmol/g at ambient temperature and pressure), CO₂/N₂ selectivity (sCO₂/N₂ = 250), and fast CO₂ diffusion kinetics (<i>D</i>_c = 2.25 × 10^–9 m²/s), comparable to some of the other high-performing ultramicroporous MOFs, with strong binding sites. Typically, such MOFs exhibit strong CO₂–framework interactions (evidenced from a heat of adsorption ≥ 38 kJ/mol). However, the MOF explained here, despite having channels lined by the amine and the open-metal sites, possesses only a moderate CO₂–framework interaction (HOA = 26 kJ/mol). Using periodic DFT, we have probed this counterintuitive observation

Ultralow Parasitic Energy for Postcombustion CO₂ Capture Realized in a Nickel Isonicotinate Metal–Organic Framework with Excellent Moisture Stability

Metal–organic frameworks (MOFs) have attracted significant attention as solid sorbents in gas separation processes for low-energy postcombustion CO₂ capture. The parasitic energy (PE) has been put forward as a holistic parameter that measures how energy efficient (and therefore cost-effective) the CO₂ capture process will be using the material. In this work, we present a nickel isonicotinate based ultramicroporous MOF, <b>1</b> [Ni-(4PyC)₂·DMF], that has the lowest PE for postcombustion CO₂ capture reported to date. We calculate a PE of 655 kJ/kg CO₂, which is lower than that of the best performing material previously reported, Mg-MOF-74. Further, <b>1</b> exhibits exceptional hydrolytic stability with the CO₂ adsorption isotherm being unchanged following 7 days of steam-treatment (>85% RH) or 6 months of exposure to the atmosphere. The diffusion coefficient of CO₂ in <b>1</b> is also 2 orders of magnitude higher than in zeolites currently used in industrial scrubbers. Breakthrough experiments show that <b>1</b> only loses 7% of its maximum CO₂ capacity under humid conditions