On the hydration and hydrolysis of carbon dioxide

England, Alice H.; Duffin, Andrew M.; Schwartz, Craig P.; Uejio, Janel S.; Prendergast, David; Saykally, Richard J.

doi:10.1016/j.cplett.2011.08.063

Cited by 121 publications

(136 citation statements)

References 46 publications

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“…At low pH, the amount of H 2 CO 3 relative to CO 2 (aq) is extremely small, less than 0.2% (Falcke and Eberle, 1990;Tossell, 2006;Adamczyk et al, 2009;England et al, 2011;Soli and Byrne, 2002 In order to calculate a composite D 63 for the DIC pool at low pH, we make the following assumptions. Since the hydration of CO 2 (aq) occurs at a much slower rate than the deprotonization of H 2 CO 3 to HCO À 3 (i.e., stripping off a proton occurs much more rapidly than acquiring an extra O to form a carbonate ion) (Adamczyk et al, 2009), we assume that any carbonate mineral precipitating rapidly from a DIC pool at low pH will form from the instantaneous H 2 CO 3 and HCO À 3 components of the DIC pool and not directly from CO 2 (aq).…”

Section: Discussionmentioning

confidence: 99%

Theoretical constraints on the effects of pH, salinity, and temperature on clumped isotope signatures of dissolved inorganic carbon species and precipitating carbonate minerals

Hill

Tripati

Schauble

2014

Geochimica et Cosmochimica Acta

145

194

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The use of carbonate 'clumped isotope' thermometry as a geochemical technique to determine temperature of formation of a carbonate mineral is predicated on the assumption that the mineral has attained an internal thermodynamic equilibrium. If true, then the clumped isotope signature is dependent solely upon the temperature of formation of the mineral without the need to know the isotopic or elemental composition of coeval fluids. However, anomalous signatures can arise under disequilibrium conditions that can make the estimation of temperatures uncertain by several degrees Celsius. Here we use ab initio calculations to examine the potential disequilibrium mineral signatures that may arise from the incorporation of dissolved inorganic carbon (DIC) species (predominantly aqueous carbonate and bicarbonate ions) into growing crystals without full equilibration with the crystal lattice.We explore theoretically the nature of clumping in the individual DIC species and the composite DIC pool under varying pH, salinity, temperature, and isotopic composition, and speculate about their effects upon the resultant disequilibrium clumping of the precipitates. We also calculate equilibrium clumped signatures for the carbonate minerals calcite, aragonite, and witherite. Our models indicate that each DIC species has a distinct equilibrium clumped isotope signature such that, (witherite). We define the calcite clumped crossover pH as the pH at which the composite D 47 (DIC pool) = D 47 (equilibrium calcite). If disequilibrium D 47 (calcite) is misinterpreted as equilibrium D 47 (calcite), it is possible to overestimate or underestimate the growth temperature by small but significant amounts. Increases in salinity lower the clumped crossover pH and may cause larger effects. Extreme effects of pH, salinity, and temperature, such as between cold freshwater lakes at high latitudes to hot hypersaline environments, are predicted to have sizeable effects on the clumped isotope composition of aqueous DIC pools.In order to determine the most reliable and efficient modeling methods to represent aqueous dissolved inorganic carbon (DIC) species and carbonate minerals, we performed convergence and sensitivity testing on several different levels of theory. We used 4 different techniques for modeling the hydration of DIC: gas phase, implicit solvation (PCM and SMD), explicit solvation (ion with 3 water molecules) and supermolecular clusters (ion plus 21 to 32 water molecules with geometries generated by molecular dynamics). For each solvation technique, we performed sensitivity testing by combining different levels of theory (up to 8 ab initio/hybrid methods, each with up to 5 different sizes of basis sets) to understand the limits of each technique. We looked at the degree of convergence with the most complex (and accurate) models in order to select the most reliable and efficient modeling methods. The B3LYP method combined with the 6-311++G(2d,2p) basis set with supermolecular clusters worked well.

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Section: Discussionmentioning

confidence: 99%

Theoretical constraints on the effects of pH, salinity, and temperature on clumped isotope signatures of dissolved inorganic carbon species and precipitating carbonate minerals

Hill

Tripati

Schauble

2014

Geochimica et Cosmochimica Acta

145

194

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“…Instead, we make comparison to a theoretical standardthe isolated excited-and ground-state atom under the same periodic boundary conditions. 23 This is equivalent to computing a difference in formation energies between the excited and ground states, and formation energies are numerically well-defined within a pseudopotential framework. 22 In practice, we then align the computed spectrum of a well-defined system (MgO in this case) to experiment and use the same constant of alignment in all further calculations using the same excited-state pseudopotential for Mg.…”

Section: ■ Introductionmentioning

confidence: 99%

Probing Adsorption Interactions in Metal–Organic Frameworks using X-ray Spectroscopy

et al. 2013

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ABSTRACT:We explore the local electronic signatures of molecular adsorption at coordinatively unsaturated binding sites in the metal−organic framework Mg-MOF-74 using X-ray spectroscopy and first-principles calculations. In situ measurements at the Mg K-edge reveal distinct pre-edge absorption features associated with the unique, open coordination of the Mg sites which are suppressed upon adsorption of CO 2 and N,N′-dimethylformamide. Density functional theory shows that these spectral changes arise from modifications of local symmetry around the Mg sites upon gas uptake and are strongly dependent on the metal−adsorbate binding strength. The expanded MOF Mg 2 (dobpdc) displays the same behavior upon adsorption of CO 2 and N,N′-dimethylethylenediamine. Similar sensitivity to local symmetry is expected for any open metal site, making X-ray spectroscopy an ideal tool for examining adsorption in such MOFs. Qualitative agreement between ambient-temperature experimental and 0 K theoretical spectra is good, with minor discrepancies thought to result from framework vibrational motion. ■ INTRODUCTIONMetal−organic frameworks (MOFs) that feature internal pore surfaces replete with open metal sitesfive-coordinate metal cations known to behave as Lewis acidsare presently among the most promising solid adsorbents for selectively removing CO 2 from dry gas mixtures. Open metal sites preferentially adsorb CO 2 over N 2 or CH 4 due to its larger quadrupole moment and greater polarizability. The moderate heat of adsorption of CO 2 onto such sites produces selective, highcapacity adsorbents that can be easily regenerated via temperature or vacuum swing methods. The MOF-74 series of MOFs have been widely studied for their high performance in both gas separation and hydrogen storage applications.1−5 In particular, Mg-MOF-74 (CPO-27-Mg, Mg 2 (dobdc) (dobdc 4− = 2,5-dioxido-1,4-benzenedicarboxylate)) is a promising adsorbent for selective CO 2 adsorption due to its large CO 2 capacity and high selectivity for CO 2 over other gases.6−9 This MOF features a unique five-coordinate square-pyramidal geometry around the Mg sites; unlike other square-pyramidal Mg complexes, 10,11 the organic framework in Mg-MOF-74 constrains the bond angles at the Mg sites and ensures that a significant portion of the Mg coordination sphere is available for adsorbing other species. The Mg sites can therefore be considered quasi-octahedral, with the apical site vacant. To date, characterization efforts aimed at a microscopic understanding of interactions between gases and the adsorbent have consisted primarily of low-temperature X-ray and neutron diffraction experiments, 12−14 NMR spectroscopy, 15 infrared spectroscopy, 7 inelastic neutron scattering, 16 and theoretical studies. 7,17,18 These studies have determined a tilted, end-on binding configuration for CO 2 , but insight into any changes to the electronic structure of the MOF upon CO 2 adsorption have so far come solely from theoretical calculations. Experimental examination of these changes would vali...

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“…Within the XCH approach, the relative energy alignment of XAS corresponding to core-excitations on atoms in different chemical environments is carried out through total energy differences. 95 However, since the method is based on core-hole pseudopotentials and does not explicitly include the energy of core electrons, calibration of the absolute energy position of the calculated spectra with respect to experiment involves a rigid energy shift Δ, which was determined to be 1560.65…”

Section: Methodsmentioning

confidence: 99%

“…94 The XCH approach has been described previously in detail. [94][95][96] In this method, the lowest energy X-ray excited state of the system is modeled within an occupation-constrained DFT framework employing a periodic supercell formalism wherein the core-excited atom is described through a core-hole pseudopotential and the screening due to the excited electron is taken into account self-consistently. Higher-lying X-ray excited state energies are approximated through eigenvalue differences obtained from the Kohn-Sham (KS) spectrum of the lowest energy core-excited state.…”

Section: Methodsmentioning

confidence: 99%

Chemical and Morphological Inhomogeneity of Aluminum Metal and Oxides from Soft X-ray Spectromicroscopy

Altman

Pemmaraju²,

Alayoǧlu³

et al. 2017

Inorg. Chem.

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ABSTRACT. Oxygen and aluminum K-edge X-ray absorption spectroscopy (XAS), imaging from a scanning transmission X-ray microscope (STXM), and first principles calculations were used to probe the composition and morphology of bulk aluminum metal, α-and γ-Al2O3, and several types of aluminum nanoparticles. The imaging results agreed with earlier transmission electron microscopy studies that showed a 2 to 5 nm thick layer of Al2O3 on all the Al surfaces. Spectral interpretations were guided by examination of the calculated transition energies, which agreed well with the spectroscopic measurements. Features observed in the experimental O and Al K-edge XAS were used to determine the chemical structure and phase of the Al2O3 on the aluminum surfaces. For unprotected 18 and 100 nm Al nanoparticles, this analysis revealed an oxide layer that was similar to γ-Al2O3 and comprised of both tetrahedral and octahedral Al coordination sites. For oleic-acid protected Al nanoparticles, only tetrahedral Al oxide coordination sites were observed.The results were correlated to trends in the reactivity of the different materials, which suggests that the structures of different Al2O3 layers have an important role in the accessibility of the underlying Al metal towards further oxidation.Combined, the Al K-edge XAS and STXM results provided detailed chemical information that was not obtained from powder X-ray diffraction or imaging from a transmission electron microscope.

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On the hydration and hydrolysis of carbon dioxide

Cited by 121 publications

References 46 publications

Theoretical constraints on the effects of pH, salinity, and temperature on clumped isotope signatures of dissolved inorganic carbon species and precipitating carbonate minerals

Theoretical constraints on the effects of pH, salinity, and temperature on clumped isotope signatures of dissolved inorganic carbon species and precipitating carbonate minerals

Probing Adsorption Interactions in Metal–Organic Frameworks using X-ray Spectroscopy

Chemical and Morphological Inhomogeneity of Aluminum Metal and Oxides from Soft X-ray Spectromicroscopy

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