Solid-State Electrochemical Carbon Dioxide Capture by Conductive Metal-Organic Framework Incorporating Nickel Bis(diimine) Units

This paper presents the first implementation of electrically conductive metal-organic framework (MOF) Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2 (Ni3(HITP)2) integrated with nickel bis(diimine) (Ni-BDI) units for efficient solid-state electrochemical carbon dioxide (CO2) capture. The electrochemical cell assembled using Ni3(HITP)2 as working electrodes can reversibly capture and release CO2 through potential control. A high-capacity utilization of 96% and a Faraday efficiency of 98% have been achieved. The material also exhibits excellent electrochemical stability with its capacity maintained during 50 capture-release cycles and resistance to general interferences, including O2, H2O, NO2, and SO2. Capacity utilization of up to 35% is obtained at CO2 concentrations as low as 1%. The capture of CO2 at concentrations ranging from 1% to 100% requires exceptionally low energy consumption of only 30.5-72.4 kJ mol-1. Studies combining spectroscopic experiments and computational approaches reveal that the CO2 capture and release mechanism involves reversible carbamate formation on the N atom of the Ni-BDI unit in the MOF upon its one-electron redox reaction.

Recent Advances in the Chemistry of Metal Carbamates

Following a related review dating back to 2003, the present review discusses in detail the various synthetic, structural and reactivity aspects of metal species containing one or more carbamato ligands, representing a large family of compounds across all the periodic table. A preliminary overview is provided on the reactivity of carbon dioxide with amines, and emphasis is given to recent findings concerning applications in various fields.

(3-Ammonio-2,2-dimethyl-propyl)carbamate Dihydrate

(3-Ammonio-2,2-dimethylpropyl)carbamate dihydrate was synthesised. The title compound was characterised by single crystal X-ray diffraction and IR-/Raman-spectroscopy. It has been demonstrated that a mixture of dilute acetic acid and 2,2-dimethyl-1,3-diaminopropane is able to capture CO2 spontaneously from the atmosphere. An intramolecular hydrogen bond stabilises the conformation of the ylide-type title molecule. Intermolecular hydrogen bonds between all moieties connect them to a strand-type chain structure.

Bis-tris propane in DMSO as a wet scrubbing agent: carbamic acid as a sequestered CO2 species

We report the chemisorption of CO₂ by bis-tris propane dissolved in DMSO via carbamic acid formation.

Structurally simple complexes of CO2

A wide range of structurally characterized adducts of CO₂are discussed in this review, from the strongly bound, charge assisted carbamate complexes through the weaker halide and pseudo-halide complexes to the weakest possible inclusion complexes.

CO2 absorption and desorption in an aqueous solution of heavily hindered alkanolamine: structural elucidation of CO2-containing species

The pathways for the CO2 absorption and desorption in an aqueous solution of a heavily hindered alkanolamine, 2-(t-butylamino)ethanol (TBAE) were elucidated by X-ray crystallographic and (13)C NMR spectroscopic analysis. In the early stage of the CO2 absorption, the formation of carbonate species ([TBAEH]2CO3) was predominant, along with the generation of small amounts of zwitterionic species. With the progress of the absorption, the carbonate species was rapidly transformed into bicarbonate species ([TBAEH]HCO3), and the amounts of the zwitterionic species increased gradually. During desorption at elevated temperature in the absence of CO2, [TBAEH]HCO3 was found to transform into [TBAEH]2CO3, where CO3(2-) strongly interacts with two [TBAEH](+) via hydrogen bondings.

Reactivity of azole anions with CO₂ from the DFT perspective

Azole anions are key components in CO₂ capture materials that include ionic liquids and porous solids. Herein, we use density functional theory (DFT) and a Langmuir-type adsorption model to study azole anion-CO₂ interactions. Linear CO₂ has to be bent by approximately 45° to form an N-C bond within the azole ring. The energy cost of bending renders CO₂ absorption much more difficult compared to SO₂ absorption. For different azole anions, the number of nitrogen atoms in the ring and the natural bond orbital energy of the reacting nitrogen lone pair, both linearly correlate with the calculated reaction enthalpy and are useful handles for new sorbent designs. Unlike for SO₂, the azole parent architecture (unsubstituted) does not allow successive CO₂ absorption under mild conditions (<0.12 MPa and at room temperature). Experimental CO₂ and SO₂ absorption isotherms are reproduced by using the Langmuir model parameterized with the calibrated DFT reaction enthalpies. This study provides insight for designing azole-based CO₂-capture materials.

CO2 capture in alkanolamine-RTIL blends via carbamate crystallization: route to efficient regeneration

One of the major drawbacks of aqueous alkanolamine based CO(2) capture processes is the requirement of significantly higher energy of regeneration. This weakness can be overcome by separating the CO(2)-captured product to regenerate the corresponding amine, thus avoiding the consumption of redundant energy. Replacing aqueous phase with more stable and practically nonvolatile imidazolium based room-temperature ionic liquid (RTIL) provided a viable approach for carbamate to crystallize out as supernatant solid. In the present study, regeneration capabilities of solid carbamates have been investigated. Diethanolamine (DEA) carbamate as well as 2-amino-2-methyl-1-propanol (AMP) carbamate were obtained in crystalline form by bubbling CO(2) in alkanolamine-RTIL mixtures. Hydrophobic RTIL, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([hmim][Tf(2)N]), was used as aqueous phase substituent. Thermal behavior of the carbamates was observed by differential scanning calorimetry and thermogravimetric analysis, while the possible regeneration mechanism has been proposed through (13)C NMR and FTIR analyses. The results showed that decomposition of DEA-carbamate commenced at lower temperature (∼55 °C), compared to that of AMP-carbamate (∼75 °C); thus promising easy regeneration. The separation of carbamate as solid phase can offer two-way advantage by letting less volume to regenerate as well as by narrowing the gap between CO(2) capture and amine regeneration temperatures.

Improved solvent formulations for efficient CO₂ absorption and low-temperature desorption

This experimental study describes efficient CO₂ capture by 2-amino-2-methyl-1-propanol (AMP)/piperazine (PZ) in ethylene glycol monoethyl ether (EGMEE, 2-ethoxyethanol) containing approximately 15 wt % of water. In these experiments, the solvent is continuously circulated between the absorber (packed-bed reactor at 30, 40, or 45 °C) and the desorber (at 80, 85, or 90 °C). The CO₂ -solvent reaction equilibria have been investigated by using ¹³C NMR spectroscopy, which provides confirmatory evidence that the formation of mono- and biscarbamate derivatives of PZ accounts for most of the CO₂ absorbed by the AMP/PZ/EGMEE/H₂O blend. The solid-state structures of AMP carbamate and of the carbonate salt of protonated AMP have been determined by using XRD. Both AMPCO₂(-) and CO(3)(2-) species completely convert to the monoalkyl carbonates on dissolving the respective salts in methanol, ethanol, or ethylene glycol.