A series of closely related primary, secondary and tertiary alkanolamine model compounds were monitored in real time in aqueous solution via in-situ nuclear magnetic resonance (NMR) spectroscopy while purging CO2-rich gas through the solution over a range of temperatures. The real-time in-situ spectroscopic monitoring of this reaction chemistry provides new insight about reaction pathways through identification of primary products and their transformations into secondary products. New mechanistic pathways were observed and elucidated. The effects of CO2 loadings, relative absorption and desorption kinetics, pH, temperature, and other critical features of the amine/CO2 reaction system are discussed in detail. The effect of amine basicity and structure on these parameters was further elucidated by studying complementary electron-rich and -poor amines (pKa ~4.5-11) and guanidines (pKa ~ 14-15). While tertiary amines act only as simple proton acceptors, primary and secondary amines function as both bases and nucleophiles to form carbamates and (bi)carbonates whose product ratio is a function of both reaction conditions and amine steric and electronic properties. Water is also acting as a Lewis base by hydrolysis of carbamate species into bicarbonate which results in a more beneficial 1:1 CO2:amine ratio. Primary and secondary amines tend to react with CO2 similarly at different CO2 partial pressures, showing weak pressure dependence on CO2 loading; in contrast, reaction efficiencies of tertiary amines which generally form less stable carbonate and bicarbonate products are a strong function of CO2 pressure. Primary and secondary amines capture significantly less CO2 per mole of amine than tertiary amines (lower CO2 loading capacities) due to the formation of carbamate species. Their faster reaction rates with CO2 and high capture efficiencies at low CO2 partial pressures are advantageous. In contrast, tertiary amines more effectively react with CO2 at lower temperatures, capturing up to 1 CO2 per amine; initially, and unexpectedly, carbonate and bicarbonate species are initially formed simultaneously. Even at high pH carbonates evolve into a final bicarbonate product. The secondary benefit of forming bicarbonates are their lower thermal stability (greater ease of desorption). Unexpectedly guanidines do not form bicarbonates directly; reaction proceeds via exclusive initial formation of the guanidinium carbonate. In summary, varying amine basicity leads to significant changes in the carbamate/(bi)carbonate equilibrium and stability of reaction products.

Resolving single-crystal structures of two-dimensional covalent organic frameworks (2D COFs) is a great challenge, hindered in part by limited strategies for growing high-quality crystals. A better understanding of the growth mechanism facilitates development of methods to grow high-quality 2D COF single crystals. Here, we take a different perspective to explore the 2D COF growth process by tracing growth intermediates. We discover two different growth mechanisms, nucleation and self-healing, in which self-assembly and pre-arrangement of monomers and oligomers are important factors for obtaining highly crystalline 2D COFs. These findings enable us to grow micron-sized 2D single crystalline COF Py-1P. The crystal structure of Py-1P is successfully characterized by three-dimensional electron diffraction (3DED), which confirms that Py-1P does, in part, adopt the widely predicted AA stacking structure. In addition, we find the majority of Py-1P crystals (>90%) have a previously unknown structure, containing 6 stacking layers within one unit cell.

A new approach to non-aqueous CO 2 −amine carbon capture has been elucidated on the basis of the utilization of a combination of a nucleophilic amine CO 2 sorbent (Lewis base) with a second, non-nucleophilic Brønsted base, a "mixed base" system. The nucleophilic amines, typically alkanolamines, e.g., ethanolamine, react directly with CO 2 in the gas stream, while the typically stronger nitrogenous Brønsted non-nucleophilic proton-acceptor base, e.g., a guanidine, then forms a more stabilized mixed carbamate reaction product. The proper choice of these bases allows for tailoring absorbent structure and properties and reaction conditions (T and P) to specific applications. Significant increases in absorption capacity are achieved because CO 2 capture ratios greater than 1:1 on a molar basis (CO 2 per amine group) can be obtained, resulting also in enhanced cyclic regeneration efficiency. In non-aqueous solutions, primary amines are carboxylated by reaction with one or two CO 2 molecules, forming either mono-or di-N-carboxylated products. These carbamic acids, unstable in aqueous media, are then stabilized as guanidinium carboxylates. A total of 2 mol of CO 2 per mol of a primary alkanolamine is thereby captured. In addition, under non-aqueous conditions, the hydroxyl group of alkanolamine reacts with CO 2 (O-carbonation) to form an alkylcarbonic acid that is subsequently stabilized by forming the corresponding alkylbicarbonate salt on reaction with a guanidinine. Each hydroxyl group thereby also absorbs up to 1 mol of CO 2 . Thereby, enhanced capacity is achieved at both basic N and OH sites of monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), etc. These products may be decomposed by thermal treatment or CO 2 partial pressure decrease to liberate CO 2 and regenerate the liquid sorbent suitable for reuse in carbon capture operations.

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The first examples of core–shell porous molecular crystals are described. The physical properties of the core–shell crystals, such as surface hydrophobicity, CO2 /CH4 selectivity, are controlled by the chemical composition of the shell. This shows that porous core–shell molecular crystals can exhibit synergistic properties that out‐perform materials built from the individual, constituent molecules.