Supported by increasingly available reserves, natural gas is achieving greater adoption as a cleaner-burning alternative to coal in the power sector. As a result, carbon capture and sequestration from natural gas-fired power plants is an attractive strategy to mitigate global anthropogenic CO 2 emissions. However, the separation of CO 2 from other components in the flue streams of gas-fired power plants is particularly challenging due to the low CO 2 partial pressure (∼40 mbar), which necessitates that candidate separation materials bind CO 2 strongly at low partial pressures (≤4 mbar) to capture ≥90% of the emitted CO 2. High partial pressures of O 2 (120 mbar) and water (80 mbar) in these flue streams have also presented significant barriers to the deployment of new technologies for CO 2 capture from gas-fired power plants. Here, we demonstrate that functionalization of the metal−organic framework Mg 2 (dobpdc) (dobpdc 4− = 4,4′-dioxidobiphenyl-3,3′dicarboxylate) with the cyclic diamine 2-(aminomethyl)piperidine (2-ampd) produces an adsorbent that is capable of ≥90% CO 2 capture from a humid natural gas flue emission stream, as confirmed by breakthrough measurements. This material captures CO 2 by a cooperative mechanism that enables access to a large CO 2 cycling capacity with a small temperature swing (2.4 mmol CO 2 /g with ΔT ≥ 100°C). Significantly, multicomponent adsorption experiments, infrared spectroscopy, magic angle spinning solid-state NMR spectroscopy, and van der Waals-corrected density functional theory studies suggest that water enhances CO 2 capture in 2-ampd−Mg 2 (dobpdc) through hydrogen-bonding interactions with the carbamate groups of the ammonium carbamate chains formed upon CO 2 adsorption, thereby increasing the thermodynamic driving force for CO 2 binding. In light of the exceptional thermal and oxidative stability of 2-ampd−Mg 2 (dobpdc), its high CO 2 adsorption capacity, and its high CO 2 capture rate from a simulated natural gas flue emission stream, this material is one of the most promising adsorbents to date for this important separation. ■ INTRODUCTION 40 The combustion of fossil fuels in the energy sector is currently 41 responsible for the release of 32 Gt/year of CO 2 into the 42 atmosphere, or approximately 65% of annual anthropogenic 43 greenhouse gas emissions. 1,2 To limit the contribution of these 44 emissions to global climate change, mitigation strategies are 45 needed during the transition to cleaner fuel sources. 2 One of 46 the most widely studied emission mitigation strategies is 47 postcombustion carbon capture and sequestration (CCS), in 48 which CO 2 is selectively removed from the flue gas streams of 49 fossil fuel-or biomass-fired power plants and sequestered 50 underground. 1−4 To date, the large majority of efforts toward 51 implementing CCS have focused on coal-fired power plants, 52 which are currently responsible for approximately 45% of 53 energy-related CO 2 emissions. 4,5 However, global consump-54 tion of natural gas has been increasing steadily, and i...

Chiral metal-organic frameworks have attracted interest for enantioselective separations and catalysis because of their high crystallinity and pores with tunable shapes, sizes, and chemical environments. Chiral frameworks of the type M(dobpdc) (M = Mg, Mn, Fe, Co, Ni, Zn; dobpdc = 4,4'-dioxidobiphenyl-3,3'-dicarboxylate) seem particularly promising for potential applications because of their excellent stability, high internal surface areas, and strongly polarizing open metal coordination sites within the channels, but to date these materials have been isolated only in racemic form. Here, we demonstrate that when appended with the chiral diamine trans-1,2-diaminocyclohexane (dach), Mg(dobpdc) adsorbs carbon dioxide cooperatively to form ammonium carbamate chains, and the thermodynamics of CO capture are strongly influenced by enantioselective interactions within the chiral pores of the framework. We further show that it is possible to access both enantiomers of Mg(dobpdc) with high enantiopurity (≥90%) via framework synthesis in the presence of varying quantities of d-panthenol, an inexpensive chiral induction agent. Investigation of dach-M(dobpdc) samples following CO adsorption-using single-crystal and powder X-ray diffraction, solid-state nuclear magnetic resonance spectroscopy, and density functional theory calculations-revealed that the ammonium carbamate chains interact extensively with each other and with the chiral M(dobpdc) pore walls. Subtle differences in the non-covalent interactions accessible in each diastereomeric phase dramatically impact the thermodynamics of CO adsorption.

The drug olsalazine (H4olz) was employed as a ligand to synthesize a new series of mesoporous metal–organic frameworks that are expanded analogues of the well-known M2(dobdc) materials (dobdc4– = 2,5-dioxido-1,4-benzene­dicarboxylate; M-MOF-74). The M2(olz) frameworks (M = Mg, Fe, Co, Ni, and Zn) exhibit high surface areas with large hexagonal pore apertures that are approximately 27 Å in diameter. Variable temperature H2 adsorption isotherms revealed strong adsorption at the open metal sites, and in situ infrared spectroscopy experiments on Mg2(olz) and Ni2(olz) were used to determine site-specific H2 binding enthalpies. In addition to its capabilities for gas sorption, the highly biocompatible Mg2(olz) framework was also evaluated as a platform for the delivery of olsalazine and other encapsulated therapeutics. The Mg2(olz) material (86 wt % olsalazine) was shown to release the therapeutic linker through dissolution of the framework under simulated physiological conditions. Furthermore, Mg2(olz) was used to encapsulate phenethylamine (PEA), a model drug for a broad class of bioactive compounds. Under simulated physiological conditions, Mg2(olz)­(PEA)2 disassembled to release PEA from the pores and olsalazine from the framework itself, demonstrating that multiple therapeutic components can be delivered together at different rates. The low toxicity, high surface areas, and coordinatively unsaturated metal sites make these M2(olz) materials promising for a range of potential applications, including drug delivery in the treatment of gastrointestinal diseases.

Efficient removal of ammonia from air is demonstrated in a series of Brønsted acidic porous polymers under dry and humid conditions. The impact of acidic group strength and their spatial distribution on the ammonia uptake is investigated systematically.