The Structure of Silicate Anions in Aqueous Alkaline Solutions

Knight, Christopher T. G.; Balec, Raymond J.; Kinrade, Stephen D.

doi:10.1002/ange.200702986

Cited by 25 publications

(35 citation statements)

References 38 publications

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“…7b). We do not necessarily conclude that these solutions are comprised entirely of monomers and dimers -it seems likely that there will be additional oligomers present, given the range of oligomers seen in relatively dilute alkaline silica solutions at ambient conditions (Knight et al, 2007) -but they could be energetically modeled as if they were comprised entirely of monomers and dimers.…”

Section: Hydration State Of Silicamentioning

confidence: 98%

A thermodynamic model for the systemSiO2–H2Onear the upper critical end point based on quartz solubility experiments at 500–1100 °C and 5–20

Hunt

Manning

2012

Geochimica et Cosmochimica Acta

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Section: Hydration State Of Silicamentioning

confidence: 98%

A thermodynamic model for the systemSiO2–H2Onear the upper critical end point based on quartz solubility experiments at 500–1100 °C and 5–20

Hunt

Manning

2012

Geochimica et Cosmochimica Acta

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“…[19][20][21][22][23][24] To date, the structures of 48 different silicate anions have been determined in this manner. [25] They are all compact, containing no more than nine Si sites, and are largely based on three-, four-and fivemembered silicate rings. [26] They exist in dynamic equilibrium with one another [27,28] and their relative abundances are highly dependent on solution pH, concentration and temperature.…”

mentioning

confidence: 99%

“…[27,28] 29 Si NMR spectroscopy is uniquely suited to determining the structures of aqueous silicate anions since, being non-invasive, the equilibrium anion distribution remains undisturbed and structural information can be obtained directly from the spectrum. Using the experimental protocol described previously, [25] we undertook NMR analysis of potassium silicate solutions under conditions which favor a high degree of condensation (high Si concentration, [KOH]:[SiO 2 ] % 1:1). The silicate anion distribution in sodium and potassium silicate solutions is virtually the same, [31] but potassium silicates tend to yield slightly sharper resonances.…”

mentioning

confidence: 99%

“…The silicate anion distribution in sodium and potassium silicate solutions is virtually the same, [31] but potassium silicates tend to yield slightly sharper resonances. [25,32] We show in Figure 1 the 29 Si NMR spectrum of a solution containing 2.000 mol kg À1 29 SiO 2 and 2.001 mol kg À1 KOH. Together with the well attested 29 Si NMR resonances from the Q 0 , Q 1 , Q 2 and Q 3 sites of silicate anions, it exhibits a large number of weak overlapping signals between À28.8 and À36.1 ppm.…”

mentioning

confidence: 99%

“…The chemical environment corresponding to each signal was then inferred by comparing its chemical shift to known peak assignments. [25] Taking the relative signal areas into account, a list of plausible structures was created and then, where possible, 2 J( 29 Si-O- 29 Si) coupling constants were measured directly from the spectrum and used to generate a simulated spectrum. Finally, rudimentary molecular modelling was carried out for each proposed structure to ensure that it was physically viable.…”

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confidence: 99%

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Aqueous Alkali‐Metal Silicate Anions Containing Fully Condensed Four‐Coordinate Sites

2012

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The chemistry of aqueous silicates has long been investigated owing to its geochemical significance [1,2] and its numerous industrial applications in fields as diverse as cements and geopolymers, [3,4] pulp/textile bleaching, [5] sol-gel derived ceramics, [6] and waste/water treatment. [7] Many studies have been carried out recently to identify silicate molecules which participate directly in the pre-nucleation, nucleation and crystal growth of zeolites (microporous solids used for heterogeneous catalysis, separations and ion-exchange processes), based on the premise that a zeolites unique properties are encoded at its earliest stages of formation in hydrothermal solution. [8][9][10][11] Additionally, research has been conducted to determine the mechanistic pathways employed by organisms such as diatoms, grasses and sponges to produce hierarchically ordered biosilica, with the goal of developing novel biomimetic ceramics. [6,[12][13][14][15] The first 29 Si NMR spectrum of a concentrated alkalimetal silicate solution (commercial "waterglass") was reported in 1973, [16,17] and revealed broad resonance bands which were assigned to end (Q 1 ), middle (Q 2 ) and branching (Q 3 ) silicate centers by analogy to the 29 Si NMR spectra of polyalkylsiloxanes. [18] A broad peak at the low-frequency end of the spectrum, centered at À35 ppm with respect to the orthosilicate (Q 0 ) signal, was assigned to tetrafunctional (Q 4 ) units in colloidal silica. Improvements in spectrometer technology, combined with attention to factors such as solution composition and 29 Si NMR relaxation phenomena, have resulted in the ability to resolve signals from the individual spin sites of silicate anions. By employing materials that are highly 29 Si enriched together with structure elucidation techniques such as COSY, it thus becomes possible to characterize the parent anions. [19][20][21][22][23][24] To date, the structures of 48 different silicate anions have been determined in this manner. [25] They are all compact, containing no more than nine Si sites, and are largely based on three-, four-and fivemembered silicate rings. [26] They exist in dynamic equilibrium with one another [27,28] and their relative abundances are highly dependent on solution pH, concentration and temperature. [24] Conspicuous by their absence, however, are 1) specialized building units that appear in zeolite frameworks ("secondary building units") [8,11,29] and 2) pre-nucleation or protomineral species which contain fully condensed Q 4 sites. Indeed, only two Q 4 -containing structures have ever been found in solution and then only in the presence of tetraalkylammonium (TAA) cations, both being derivatives of the TAA-stabilized cubic octamer species. [30] We report herein the existence of aqueous silicate ions containing fully condensed Q 4 sites in alkali-metal hydroxide solution, thereby providing the first definitive evidence of the chemical nature of protomineral species in such systems.Surprisingly, little direct mechanistic information has so far been obtained...

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Multi‐Step Nucleation of a Crystalline Silicate Framework via a Structurally Precise Prenucleation Cluster

et al. 2023

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Hierarchical nucleation pathways are ubiquitous in the synthesis of minerals and materials. In the case of zeolites and metal–organic frameworks, pre‐organized multi‐ion “secondary building units” (SBUs) have been proposed as fundamental building blocks. However, detailing the progress of multi‐step reaction mechanisms from monomeric species to stable crystals and defining the structures of the SBUs remains an unmet challenge. Combining in situ nuclear magnetic resonance, small‐angle X‐ray scattering, and atomic force microscopy, we show that crystallization of the framework silicate, cyclosilicate hydrate, occurs through an assembly of cubic octameric Q38 polyanions formed through cross‐linking and polymerization of smaller silicate monomers and other oligomers. These Q38 are stabilized by hydrogen bonds with surrounding H2O and tetramethylammonium ions (TMA+). When Q38 levels reach a threshold of ≈32 % of the total silicate species, nucleation occurs. Further growth proceeds through the incorporation of [(TMA)x(Q38)⋅n H2O](x−8) clathrate complexes into step edges on the crystals.

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The Structure of Silicate Anions in Aqueous Alkaline Solutions

Cited by 25 publications

References 38 publications

A thermodynamic model for the systemSiO2–H2Onear the upper critical end point based on quartz solubility experiments at 500–1100 °C and 5–20

A thermodynamic model for the systemSiO2–H2Onear the upper critical end point based on quartz solubility experiments at 500–1100 °C and 5–20

Aqueous Alkali‐Metal Silicate Anions Containing Fully Condensed Four‐Coordinate Sites

Multi‐Step Nucleation of a Crystalline Silicate Framework via a Structurally Precise Prenucleation Cluster

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