Inference of principal species in caustic aluminate solutions through solid-state spectroscopic characterization

Dembowski, Mateusz; Prange, Micah P.; Pouvreau, Maxime; Graham, Trent R.; Bowden, Mark E.; N’Diaye, Alpha T.; Schenter, Gregory K.; Clark, Sue; Clark, Aurora E.; Rosso, Kevin M.; Pearce, Carolyn I.

doi:10.1039/d0dt00229a

Cited by 10 publications

(14 citation statements)

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“…In addition to 1b), together comprising a series that was recently investigated using vibrational (Raman and infrared), X-ray absorption, and nuclear magnetic resonance spectroscopy. 26 However, INS is much more sensitive to the locations and dynamics of the protons in the structure, so the present study strongly complements this prior work. INS furthermore uniquely accesses vibrational modes forbidden by the selection rules 3.…”

Section: Introductionsupporting

confidence: 69%

“…Structure of the K-, Rb-, and Cs-Aluminate Salts. The structures of the dimeric 27 and monomeric 26 salt crystals, as determined by single-crystal diffraction, have been reported before and can be obtained from the Crystallography Open Database. 42 The Cs-aluminate hydrate structure, 26 however, is incomplete due to the lack of hydrogen positions.…”

Section: Resultsmentioning

confidence: 99%

“…The structures of the dimeric 27 and monomeric 26 salt crystals, as determined by single-crystal diffraction, have been reported before and can be obtained from the Crystallography Open Database. 42 The Cs-aluminate hydrate structure, 26 however, is incomplete due to the lack of hydrogen positions. Here, the Cs-aluminate salt has been re-examined with single-crystal Xray diffraction, and a revised experimental structure is being published separately.…”

Section: Resultsmentioning

confidence: 99%

“…Previous Raman studies have shown that the Al−O bond stretching of aluminate tetrahedra is well resolved for the dimeric (K-and Rbaluminate salts) versus monomeric (Cs-aluminate salt) structural motifs. 26 There are two strongly Raman-active bands for the symmetric Al−O stretching vibrations at ∼548 and ∼726 cm −1 in the dimeric salts (Figure 4; see also Table S1 for detailed peak assignments). The monomeric salt has only one main peak centered at ∼621 cm −1 for the symmetric Al−O stretching vibrations (Figure 4 and Table S1).…”

Section: Resultsmentioning

confidence: 99%

“…We focus on prediction of measured inelastic neutron scattering (INS) spectra for various compounds, which is sensitive to their structural OH- and H-bonding interactions, complemented by Raman spectroscopy. In addition to K 2 [Al 2 O(OH) 6 ] and Rb 2 [Al 2 O(OH) 6 ], we also examine the monomeric aluminate salt Cs[Al(OH) 4 ]·2H 2 O (Figure b), together comprising a series that was recently investigated using vibrational (Raman and infrared), X-ray absorption, and nuclear magnetic resonance spectroscopy . However, INS is much more sensitive to the locations and dynamics of the protons in the structure, so the present study strongly complements this prior work.…”

Section: Introductionmentioning

confidence: 82%

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Theory-Guided Inelastic Neutron Scattering of Crystalline Alkaline Aluminate Salts Bearing Principal Motifs of Solution-State Species

et al. 2021

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Aluminate salts precipitated from caustic alkaline solutions exhibit a correlation between the anionic speciation and the identity of the alkali cation in the precipitate, with the aluminate ions occurring either in monomeric (Al(OH) 4 − ) or dimeric (Al 2 O(OH) 6 2− ) forms. The origin of this correlation is poorly understood as are the roles that oligomeric aluminate species play in determining the solution structure, prenucleation clusters, and precipitation pathways. Characterization of aluminate solution speciation with vibrational spectroscopy results in spectra that are difficult to interpret because the ions access a diverse and dynamic configurational space. To investigate the Al(OH) 4 − and Al 2 O(OH) 6 2− anions within a well-defined crystal lattice, inelastic neutron scattering (INS) and Raman spectroscopic data were collected and simulated by density functional theory for K 2 [Al 2 O(OH) 6 ], Rb 2 [Al 2 O(OH) 6 ], and Cs[Al(OH) 4 ]•2H 2 O. These structures capture archetypal solution aluminate species: the first two salts contain dimeric Al 2 O(OH) 62− anions, while the third contains the monomeric Al(OH) 4 − anion. Comparisons were made to the INS and Raman spectra of sodium aluminate solutions frozen in a glassy state. In contrast to solution systems, the crystal lattice of the salts results in well-defined vibrations and associated resolved bands in the INS spectra. The use of a theory-guided analysis of the INS of this solid alkaline aluminate series revealed that differences were related to the nature of the hydrogen-bonding network and showed that INS is a sensitive probe of the degree of completeness and strength of the bond network in hydrogen-bonded materials. Results suggest that the ionic size may explain cation-specific differences in crystallization pathways in alkaline aluminate salts.

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Section: Introductionsupporting

confidence: 69%