Neutron diffraction study of hydrogen in birnessite structures

Post, Jeffrey E.; Heaney, Peter J.; Cho, Yunchul

doi:10.2138/am.2011.3629

Cited by 12 publications

(17 citation statements)

References 21 publications

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“…4) that represent bending and stretching of H 2 O and OH bonds, although it is important to note that absorbed water also 297 contributes to these regions (Potter & Rossman 1979). Interestingly, in the region from ~2950 to 298 ~3670 cm -1 , the peaks in the FTIR spectrum for triclinic Na-birnessite are sharper than for hexagonal H-birnessite, suggesting that water is relatively well-ordered in Na-birnessite, as is consistent with the neutron and modeling studies of Post et al (2011) and Cygan et al (2012).…”

Section: Distinguishing Triclinic and Hexagonal Birnessite With Xrsupporting

confidence: 76%

Fourier-transform infrared spectroscopy (FTIR) analysis of triclinic and hexagonal birnessites

Ling

Post

Heaney

et al. 2017

Spectrochimica Acta Part A: Molecular and Biomolecular Spectros

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The characterization of birnessite structures is particularly challenging for poorly crystalline materials of biogenic origin, and a determination of the relative concentrations of triclinic and hexagonal birnessite in a mixed assemblage has typically required synchrotron-based spectroscopy and diffraction approaches. In this study, Fourier-transform infrared spectroscopy (FTIR) is demonstrated to be capable of differentiating synthetic triclinic Na-birnessite and synthetic hexagonal H-birnessite. Furthermore, IR spectral deconvolution of peaks resulting from MnO lattice vibrations between 400 and 750cm yield results comparable to those obtained by linear combination fitting of synchrotron X-ray absorption fine structure (EXAFS) data when applied to known mixtures of triclinic and hexagonal birnessites. Density functional theory (DFT) calculations suggest that an infrared absorbance peak at ~1628cm may be related to OH vibrations near vacancy sites. The integrated intensity of this peak may show sensitivity to vacancy concentrations in the Mn octahedral sheet for different birnessites.

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Section: Distinguishing Triclinic and Hexagonal Birnessite With Xrsupporting

confidence: 76%

Fourier-transform infrared spectroscopy (FTIR) analysis of triclinic and hexagonal birnessites

Ling

Post

Heaney

et al. 2017

Spectrochimica Acta Part A: Molecular and Biomolecular Spectros

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“…Because the shoulder peak contribution was greater in Cs-birnessite than K-birnessite, Cs-birnessite would have more extensive intermolecular H-bonds than K-birnessite. A neutron diffraction study proposed a type-I water structure in Na-birnessite, but a type-III water structure in K-birnessite . However, in our simulations, type-I was the dominant water structure both in Na-birnessite and K-birnessite, perhaps due to the strong interaction of the negatively charged sheets with water molecules, although type-III was additionally present only in K-birnessite (Figure b).…”

Section: Resultscontrasting

confidence: 54%

“…In Na-birnessite, the distances between Na + and the second-nearest shell O s were greater than 3.6 Å due to the Na + positions near the O bbd (Figure S3a). A neutron diffraction study also reported that the distance from the cation to the second-nearest O s in K-birnessite was shorter than that in Na-birnessite (3.0–3.3 vs 3.4–3.6 Å) …”

Section: Resultsmentioning

confidence: 96%

Atomistic Insights into the Interlayer Cation and Water Structures of Na-, K-, and Cs-Birnessite

Park

2021

ACS Earth Space Chem.

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Birnessite is a key mineral involved in the geochemical cycles of trace metals through its high cation sorption capacity. Information about cation and water structures in the interlayer regions, as well as about the layer spacing and associated changes, is essential to understanding the cation exchange mechanism. However, this fundamental knowledge is lacking for birnessite due to the complexity of its structure and the insufficient ability to probe the interlayer species, water molecules in particular. In this study, we performed molecular dynamics (MD) computer simulations of Na-, K-, and Cs-birnessite as a function of the interlayer hydration state and cation exchange ratio. As the monolayer hydrate state transitioned to a bilayer hydrate state, the d-spacing of Na-birnessite increased from ∼7 to ∼10 Å, Na + cations maintained a position at the midplane of the interlayer, and water molecules were reoriented to form intermolecular H-bonds rather than Hbonds with birnessite surfaces. In the bilayer hydrate states of K-and Cs-birnessite, the interlayer cations were positioned near the birnessite surface rather than the midplane of the interlayer. As the K + ratio increased in Na 0.29−x K x MnO 2 •0.75H 2 O, the d-spacing contracted in the initial stage of cation exchange but increased in the subsequent stage. In Na 0.29−x Cs x MnO 2 •0.75H 2 O, the d-spacing expanded continuously with an increasing Cs + -to-Na + ratio. In our MD simulations, interlayer water molecules needed to be deintercalated during cation exchange to reproduce the experimentally observed trends in d-spacing changes of Na-birnessite during cation exchange. These results suggest the important role of interlayer water in the cation sorption of birnessite that is often neglected in understanding the birnessite reactivity.

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“…The 2 W state of birnessite, known as buserite, is therefore not achieved by exposure of water vapor under ambient pressure and temperature. 14 , 62 , 63 …”

Section: Discussionmentioning

confidence: 99%

“…To gain direct molecular-scale insight into the hydration of birnessite, molecular dynamics (MD) simulations of K + -saturated birnessite at different water loadings were also undertaken. The lattice of one UC 14 was expanded into a system containing 6 × 12 × 4 UCs, with a composition of K 144 [Mn 576 O 1152 ] × (H 2 O) 3840 . This initial composition corresponded to an average of 0.25 K + ions and 13.333 water molecules per UC.…”

Section: Methodsmentioning

confidence: 99%

Nanoscale Hydration in Layered Manganese Oxides

et al. 2021

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Birnessite is a layered MnO 2 mineral capable of intercalating nanometric water films in its bulk. With its variable distributions of Mn oxidation states (Mn IV , Mn III , and Mn II ), cationic vacancies, and interlayer cationic populations, birnessite plays key roles in catalysis, energy storage solutions, and environmental (geo)chemistry. We here report the molecular controls driving the nanoscale intercalation of water in potassium-exchanged birnessite nanoparticles. From microgravimetry, vibrational spectroscopy, and X-ray diffraction, we find that birnessite intercalates no more than one monolayer of water per interlayer when exposed to water vapor at 25 °C, even near the dew point. Molecular dynamics showed that a single monolayer is an energetically favorable hydration state that consists of 1.33 water molecules per unit cell. This monolayer is stabilized by concerted potassium–water and direct water–birnessite interactions, and involves negligible water–water interactions. Using our composite adsorption–condensation–intercalation model, we predicted humidity-dependent water loadings in terms of water intercalated in the internal and adsorbed at external basal faces, the proportions of which vary with particle size. The model also accounts for additional populations condensed on and between particles. By describing the nanoscale hydration of birnessite, our work secures a path for understanding the water-driven catalytic chemistry that this important layered manganese oxide mineral can host in natural and technological settings.

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Neutron diffraction study of hydrogen in birnessite structures

Cited by 12 publications

References 21 publications

Fourier-transform infrared spectroscopy (FTIR) analysis of triclinic and hexagonal birnessites

Fourier-transform infrared spectroscopy (FTIR) analysis of triclinic and hexagonal birnessites

Atomistic Insights into the Interlayer Cation and Water Structures of Na-, K-, and Cs-Birnessite

Nanoscale Hydration in Layered Manganese Oxides

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