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Felmy, Andrew R.; Cho, Herman M.; Rustad, James R.; Mason, Marvin J.

doi:10.1023/a:1010382701742

Cited by 97 publications

(82 citation statements)

References 22 publications

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“…At nearneutral pH and near the solubility limit of SiO 2 (am), the dimer Si 2 O 2 (OH) −1 5 was the only poly-Si species detected, and its concentration was at most 6% of the total Si in solution [22]. Felmy et al [24] recently developed a comprehensive model of Si solution speciation applicable for a wide range of conditions. Below the solubility limit of SiO 2 (am) and pH <11 (the conditions of these experiments), oligomeric species were indeed less than 5% of total aqueous Si.…”

Section: Solution and Surface Speciationmentioning

confidence: 99%

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Interaction of silicic acid with goethite

Hiemstra

Barnett

Riemsdijk

2007

Journal of Colloid and Interface Science

180

163

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Section: Solution and Surface Speciationmentioning

confidence: 99%

“…In the experiments, we will use a wide range of Si concentrations. At a high Si concentration and pH, aqueous Si-polymerization may be important [22][23][24]. It has been suggested that the oligomers may also be formed at the surface at a high Siloading [8].…”

Section: Introductionmentioning

confidence: 99%

Interaction of silicic acid with goethite

Hiemstra

Barnett

Riemsdijk

2007

Journal of Colloid and Interface Science

180

163

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“…To obtain the distribution of silicate species with pH and concentration, a silicate speciation model was set up using WinSGW program [33]. Formation constants are given by Sjöberg et al [34] for dilute solution ([Si]< 48 × 10 −3 mol L −1 ) and also by Felmy et al [35]. Constants given by Sjöberg et al are valid at 25 • C and 0.6 M NaCl medium but since the silicate speciation is influenced by ionic strength, the thermodynamic constants given by Felmy et al were preferred.…”

Section: Spectra Of Aqueous Sodium Silicatementioning

confidence: 99%

A study of sodium silicate in aqueous solution and sorbed by synthetic magnetite using in situ ATR-FTIR spectroscopy

Yang

Roonasi

Holmgren

2008

Journal of Colloid and Interface Science

167

105

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The sorption of sodium silicate by synthetic magnetite (Fe 3 O 4 ) at different pH conditions (pH 7-11) and initial silicate concentrations (1 × 10 −3 and 10 × 10 −3 mol L −1 ) was studied using in situ attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy. The analysis of infrared spectra of sodium silicate in solution as well as adsorbed on magnetite nano-particles clearly showed the evolution of different silicate species depending on pH and silica concentration. The silicate concentration studied (10 × 10 −3 mol L −1 ) contained polymeric or condensed silicate species at lower pH as well as monomers at high pH, as evident from infrared spectra. Condensation of monomers resulted in an increased intensity of absorptions in the high frequency part (>1050 cm −1 ) of the spectral region, which contains information about both silicate in solution and sorbed silicate viz. 1300 cm −1 -850 cm −1 . In the pH range studied, infrared spectra of sorbed silicate and sorbed silicate during desorption both indicated the presence of different types of surface complexes at the magnetite surface. The sorption mechanism proposed is in accordance with a ligand exchange reaction where both monodentate and bidentate complexes could exist at low surface loading level, the relative proportion of the complexes being due to both pH and concentration in solution. Oligomerization occurred on the magnetite surface at higher surface loading.

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“…Thus, whilst the species initially present in silicate gels can be characterized by NMR spectroscopy with some certainty, [3,4] their charge state is more difficult to probe. [5] Similarly, although scattering methods can be used to tentatively identify larger (possibly nucleation) species, [6,7] the relative stability and lifetime of the smallest clusters, significant in zeolitic structures, such as four-membered rings, remain unclear. Furthermore, in the postnucleation regime, there is much debate as to which species are responsible for crystal growth: small oligomers or larger subunits.…”

mentioning

confidence: 99%

“…[16] Experimentally, high pH is required for condensation reactions to occur: under such conditions the dominant silicate species will be anionic. [5] The basic reaction is given in Equation (1); further deprotonation gives H 2 SiO 4 2À and so…”

mentioning

confidence: 99%

Oligomerization and Cyclization Processes in the Nucleation of Microporous Silicas

2005

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The nucleation and growth of zeolites and other microporous solids continues to pose many questions. [1,2] Whilst the general features of self-assembly through condensation polymerization are understood for siliceous systems, the conditions under which both natural and synthetic zeolites form render such a complex process extremely difficult to characterize experimentally. Thus, whilst the species initially present in silicate gels can be characterized by NMR spectroscopy with some certainty, [3,4] their charge state is more difficult to probe.[5] Similarly, although scattering methods can be used to tentatively identify larger (possibly nucleation) species, [6,7] the relative stability and lifetime of the smallest clusters, significant in zeolitic structures, such as four-membered rings, remain unclear. Furthermore, in the postnucleation regime, there is much debate as to which species are responsible for crystal growth: small oligomers or larger subunits. Indeed, it has been suggested that the growth of silicalite-1 (MFI zeolite) is controlled by a unique nanocluster, [8] although there is some debate about this proposal.[9] Moreover, characterization of zeolite surfaces suggests that much smaller units are responsible for surface growth.[10]Here, we describe quantum chemical calculations that model some of the species present prior to nucleation and attempt to examine the pathways by which such key species may form and hence rationalize the assembly of zeolitic structures. In particular, we discuss the factors that drive the condensation polymerization of silicate oligomers and that favor the cyclization of such species: pH and solvent.In the past decade there have been a number of computational studies of model structures involved in the nucleation process of silicates. Structures and energies for small clusters containing up to five silicon atoms were obtained by Pereira et al. [11,12] One conclusion that can be drawn from these results is that linear silicate species are favored over cyclic structures-a situation not conducive to the formation of zeolitic structures but instead one that favors the formation of amorphous silicates.[11] These early calculations were performed using a local DFT method and considered only neutral species, although solvation effects were included using the COSMO method.[13] The roles of water and organic templates in prenucleation gels were studied by Lewis et al. [14] and Catlow et al. [15] by more approximate molecular mechan-

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Cited by 97 publications

References 22 publications

Interaction of silicic acid with goethite

Interaction of silicic acid with goethite

A study of sodium silicate in aqueous solution and sorbed by synthetic magnetite using in situ ATR-FTIR spectroscopy

Oligomerization and Cyclization Processes in the Nucleation of Microporous Silicas

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