Formation Of Bicarbonate Species Research Articles

Extended MOF-74-Type Variant with an Azine Linkage: Efficient Direct Air Capture and One-Pot Synthesis.

Direct air capture (DAC) shows considerable promise for the effective removal of CO2; however, materials applicable to DAC are lacking. Among metal-organic framework (MOF) adsorbents, diamine-Mg2(dobpdc) (dobpdc4- = 4,4-dioxidobiphenyl-3,3'-dicarboxylate) effectively removes low-pressure CO2, but the synthesis of the organic ligand requires high temperature, high pressure, and a toxic solvent. Besides, it is necessary to isolate the ligand for utilization in the synthesis of the framework. In this study, we synthesized a new variant of extended MOF-74-type frameworks, M2(hob) (M = Mg2+, Co2+, Ni2+, and Zn2+; hob4- = 5,5'-(hydrazine-1,2-diylidenebis(methanylylidene))bis(2-oxidobenzoate)), constructed from an azine-bonded organic ligand obtained through a facile condensation reaction at room temperature. Functionalization of Mg2(hob) with N-methylethylenediamine, N-ethylethylenediamine, and N,N'-dimethylethylenediamine (mmen) enables strong interactions with low-pressure CO2, resulting in top-tier adsorption capacities of 2.60, 2.49, and 2.91 mmol g-1 at 400 ppm of CO2, respectively. Under humid conditions, the CO2 capacity was higher than under dry conditions due to the presence of water molecules that aid in the formation of bicarbonate species. A composite material combining mmen-Mg2(hob) and polyvinylidene fluoride, a hydrophobic polymer, retained its excellent adsorption performance even after 7 days of exposure to 40% relative humidity. In addition, the one-pot synthesis of Mg2(hob) from a mixture of the corresponding monomers is achieved without separate ligand synthesis steps; thus, this framework is suitable for facile large-scale production. This work underscores that the newly synthesized Mg2(hob) and its composites demonstrate significant potential for DAC applications.

Water-Enhanced Direct Air Capture of Carbon Dioxide in Metal-Organic Frameworks.

We have developed two series of amine-functionalized zirconium (Zr) metal-organic framework-808 (MOF-808), which were produced by postsynthetic modifications to have either amino acids coordinated to Zr ions (MOF-808-AAs) or polyamines covalently bound to the chloro-functionalized structure (MOF-808-PAs). These MOF variants were comprehensively characterized by liquid-state 1H nuclear magnetic resonance (NMR) measurements and potentiometric acid-base titration to determine the amounts of amines, energy-dispersive X-ray spectroscopy to assess the extent of covalent substitution by polyamines, powder X-ray diffraction analysis to verify the maintenance of the MOF crystallinity and structure after postsynthetic modifications, nitrogen sorption isotherm measurements to confirm retention of the porosity, and water sorption isotherm measurements to find the water uptake in the pores of each member of the series. Evaluation and testing of these compounds in direct air capture (DAC) of CO2 showed improved CO2 capture performance for the functionalized forms, especially under humid conditions: In dry conditions, the l-lysine- and tris(3-aminopropyl)amine-functionalized variants, termed as MOF-808-Lys and MOF-808-TAPA, exhibited the highest CO2 uptakes at 400 ppm, measuring 0.612 and 0.498 mmol g-1, and further capacity enhancement was achieved by introducing 50% relative humidity, resulting in remarkable uptakes of 1.205 and 0.872 mmol g-1 corresponding to 97 and 75% increase compared to the dry uptakes, respectively. The mechanism underlying the enhanced uptake efficiency was revealed by 13C solid-state NMR and temperature-programmed desorption measurements, indicating the formation of bicarbonate species, and therefore a stoichiometry of 1:1 CO2 to each amine site.

CO2 Adsorption on Magnetite Fe3O4(111)

We monitored the adsorption of carbon dioxide (CO2) on well-ordered Fe3O4(111) films using infrared reflection-adsorption spectroscopy (IRAS) and temperature-programmed desorption (TPD). The result...

Effect of Amine Surface Coverage on the Co-Adsorption of CO2 and Water: Spectral Deconvolution of Adsorbed Species.

Three primary amine materials functionalized onto mesoporous silica with low, medium, and high surface amine coverages are prepared and evaluated for binary CO2/H2O adsorption under dilute conditions. Enhancement of amine efficiency due to humid adsorption is most pronounced for low surface amine coverage materials. In situ FT-IR spectra of adsorbed CO2 on these materials suggest this enhancement may be associated with the formation of bicarbonate species during adsorption on materials with low surface amine coverage, though such species are not observed on high surface coverage materials. On the materials with the lowest amine loading, bicarbonate is observed on longer time scales of adsorption, but only after spectral contributions from rapidly forming alkylammonium carbamate species are removed. This is the first time that direct evidence for bicarbonate formation, which is known to occur in liquid aqueous amine solutions, has been presented for CO2 adsorption on solid amine adsorbents.

Coadsorption properties of CO2 and H2O on TiO2 rutile (110): A dispersion-corrected DFT study

Adsorption and reactions of CO(2) in the presence of H(2)O and OH species on the TiO(2) rutile (110)-(1×1) surface were investigated using dispersion-corrected density functional theory and scanning tunneling microscopy. The coadsorbed H(2)O (OH) species slightly increase the CO(2) adsorption energies, primarily through formation of hydrogen bonds, and create new binding configurations that are not present on the anhydrous surface. Proton transfer reactions to CO(2) with formation of bicarbonate and carbonic acid species were investigated and found to have barriers in the range 6.1-12.8 kcal/mol, with reactions involving participation of two or more water molecules or OH groups having lower barriers than reactions involving a single adsorbed water molecule or OH group. The reactions to form the most stable adsorbed formate and bicarbonate species are exothermic relative to the unreacted adsorbed CO(2) and H(2)O (OH) species, with formation of the bicarbonate species being favored. These results are consistent with single crystal measurements which have identified formation of bicarbonate-type species following coadsorption of CO(2) and water on rutile (110).

Mechanism of the interaction of CO2 and humidity with primary amino group systems for room temperature CO2 sensors

The use of primary amino groups as receptors to detect CO2 is promising because of their ability to perform reversible acid-base-reactions. In contrast to other sensitive materials using this effect, evaluable signals can be obtained even at ambient temperature. The effect discussed for most of the previously used sensing layers is the formation of bicarbonate species, which needs H2O as well as an increased temperature. The use of primary amino groups and work function readout appears to be dominated by another reaction, the reversible formation of carbamate, which does not require any water presence and, in addition to that, is more efficient at lower temperatures. To confirm this hypothesis, IR-, Raman-, XPS- and NMR-spectroscopy were used.

The effect of iron on the adsorption properties of CuMnZrO2 catalysts studied by temperature-programmed desorption and FTIR spectroscopy

Abstract The adsorption of CO on the precipitated Fe-CuMnZrO 2 catalysts for mixture alcohols synthesis were investigated using temperature-programmed desorption and FTIR spectra recorded at adsorption temperature in the range 298–673 K, in order to detect any synergy in the adsorption of CO on CuMnZrO 2 as a result of iron addition. In the case of CuMnZrO 2 catalyst, only one kind of CO adsorbed or desorbed, which was ascribed to weakly adsorbed CO species on copper sites, was detected in FTIR and TPD study. Moreover, for CuMnZrO 2 catalyst the formation of bidentate carbonate species was favored at 298 K, and bicarbonate species formed at higher temperature. When iron was introduced in CuMnZrO 2 catalyst, it was found that the adsorption features of catalysts changed significantly. The presence of iron improved the copper dispersion, which resulted in increasing of the total adsorption of CO, and intensified the reaction between CO and catalyst surface. Several kinds of CO adsorbed or desorbed were detected on Fe-CuMnZrO 2 . The formation of bicarbonate species took place at 298 K, and formate species was detected at higher temperature, suggesting that the presence of iron greatly influenced the process of methanol synthesis.

Reduction of chromia/alumina catalyst monitored by DRIFTS-mass spectrometry and TPR-Raman spectroscopy

The reduction of alumina-supported chromia with 13 wt.% chromium was investigated by X-ray photoelectron and X-ray absorption spectroscopies, in situ temperature-programmed Raman spectroscopy and in situ temperature-programmed diffuse reflectance infrared Fourier transform spectroscopy combined with mass spectrometry. For comparison, unsupported chromia was also studied. The oxidised chromia/alumina contained Cr3+ and Cr6+, whereas after reduction by carbon monoxide or hydrogen mainly Cr3+ was detected, although the formation of Cr2+ in carbon monoxide reduction was not ruled out. The polymeric chromates on chromia/alumina were more reducible than the monomeric ones due to the weaker interaction of the polychromates with the support. During reduction with hydrogen at high temperatures, hydroxyl species formed on chromia and chromia/alumina. In addition, surface restructuring to more crystalline chromia species took place on chromia/alumina. Measurements on the reduction by carbon monoxide suggested that the reduction could occur through formation of bicarbonate species. With increasing temperature, formate species—probably formed by reaction of Cr3+–CO species with surface hydroxyls—were observed, which reacted further to carbonates on chromia, and inorganic carboxylates and other carbonaceous species on chromia/alumina.