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Bogdanova, N. F.; Klebanov, A. V.; Ермакова, Л. Э.; Sidorova, M. P.

doi:10.1023/a:1016865916073

Cited by 5 publications

(6 citation statements)

References 3 publications

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“…126 -127 Moreover, to our knowledge, the only experimental data available in the case of boehmite is a pK measurement of 6.7 for the reaction (Al) n −OH + H + → (Al) n − OH 2 + (the coordination number n of the OH groups is unknown). 128 That the MUSIC model and the DFT-MD result provide quantitative different views is not surprising, as on the one hand the MUSIC model does not take into account the detailed local environment of the μ 1 -OH and μ 2 -OH sites at the surface and in particular does not take into account the nature of the hydrogen bonding with water (donor/acceptor characters of different strengths) nor the presence of the step at the surface, and on the other hand our estimate from DFT-MD is lacking statistics. Differences in pK of two sites of a surface have already been emphasized on the quartz/water interface, both theoretically 58 and experimentally.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Ab Initio Molecular Dynamics Study of the AlOOH Boehmite/Water Interface: Role of Steps in Interfacial Grotthus Proton Transfers

Motta

Costa

2012

J. Phys. Chem. C

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The investigation of metal oxide/water interfaces at the molecular level represents a fundamental issue for the understanding of chemical, physical, and biological processes involved in several fields such as erosion, heterogeneous catalysis, prebiotic chemistry, corrosion, hygiene, or biocompatibility. In this context we have studied the mineral (101) γ-AlOOH (boehmite) surface/water interface by means of density functional theory based molecular dynamics (DFT-MD). Boehmite ( 101) is a stepped surface, covered with monocoordinated (μ 1 ) OH groups placed at the step edge and dicoordinated (μ 2 ) OH groups placed along the terraces. At the surface, the respective concentrations of different OH species are found as 0.48 μ 2 -OH + 0.26 μ 1 -OH 2 + 0.24 μ 1 -OH + 0.02 μ 2 -OH 2 . We show that the interfacial water molecules are somehow frozen in specific orientations, with 60% having one proton pointing to the surface (water is a H-bond donor to the surface) and 40% with one proton directed away from the surface (water is a H-bond acceptor with the surface). The effect of the surface on the water organization is lost at 6 Å from the surface, where liquid bulk is fully recovered. Proton transfers are observed at the interface between μ 1 and μ 2 species involving a Grotthus mechanism between distant μ 1 /μ 2 groups. A bridge of interfacial water molecules has been found to assist this proton transfer. A pK value of 1.4 is calculated for this acid−base reaction, where μ 2 -HOH is found to be a stronger acid than μ 1 -HOH. These results represent a first step toward the understanding of the increased reactivity of defective surfaces in the presence of explicit solvent, using a first-principle representation of the full interface.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Ab Initio Molecular Dynamics Study of the AlOOH Boehmite/Water Interface: Role of Steps in Interfacial Grotthus Proton Transfers

Motta

Costa

2012

J. Phys. Chem. C

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“…High values of C Stern (greater than 1.7 F/m 2 ) for a nonporous surface can be attributed to complexation of ions in solution with silanol groups . This is because ionic complexation has been reported to shift the point of zero charge from its value as the mean of the p K a ’s, when only protons are the potential determining ions, to another value. According to our empirical relation, a slight difference in pH pzc results in a significant change in C Stern , e.g., compared to pH pzc = 2.44 with C Stern = 2.3 F/m 2 , pH pzc = 2.36 yields C Stern = 1.7 F/m 2 .…”

Section: Resultsmentioning

confidence: 99%

Solution Titration by Wall Deprotonation during Capillary Filling of Silicon Oxide Nanochannels

et al. 2008

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This paper describes a fundamental challenge when using silicon oxide nanochannels for analytical systems, namely the occurrence of a strong proton release or proton uptake from the walls in any transient situation such as channel filling. Experimentally, when fluorescein solutions were introduced into silicon oxide nanochannels through capillary pressure, a distinct bisection of the fluorescence was observed, the zone of the fluid near the entrance fluoresced, while the zone near the meniscus, was dark. The ratio between the zones was found to be constant in time and to depend on ionic strength, pH, and the presence of a buffer and its characteristics. Theoretically, using the Gouy-Chapman-Stern model of the electrochemical double layer, we demonstrate that this phenomenon can be effectively modeled as a titration of the solution by protons released from silanol groups on the walls, as a function of the pH and ionic strength of the introduced solution. The results demonstrate the dominant influence of the surface on the fluid composition in nanofluidic experiments, in transient situations such as filling, and changes in solvent properties such as the pH or ionic strength. The implications of these fundamental properties of silicon oxide nanochannels are important for analytical strategies and in particular the analysis of complex biological samples.

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“…Changes in pH upon the introduction of salts can be understood by analyzing site-binding models for the boehmite–water interface. − Most are 2-p K a triple-layer models, although Hiemstra developed a simplified 1-p K a model. These place the pristine point of zero charge between 8.5 and 9.1.…”

Section: Discussionmentioning

confidence: 99%

“…These place the pristine point of zero charge between 8.5 and 9.1. Data on ionic adsorption are limited, but Bogdanova et al 87 and Klebanov et al 89 compared NaCl and KCl salts and Wood et al 91 considered KNO 3 salts. While Bogdanova et al 87 found that Na + , K + , and Cl − have roughly equivalent binding strengths, Wood et al 91 determined that K + binds more strongly than NO 3 − , driving pH shifts at high ionic strength.…”

Section: Discussionmentioning

confidence: 99%

Frustrated Coulombic and Cation Size Effects on Nanoscale Boehmite Aggregation: A Tumbler Small- and Ultra-Small-Angle Neutron Scattering Study

et al. 2022

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To better understand the effects of solution chemistry on particle aggregation in the complex legacy tank wastes at the Hanford (WA) and Savannah River (SC) sites, we have performed a series of tumbler small- and ultra-small-angle neutron scattering experiments on 20 wt % solid slurries of nanoparticulate aluminum oxyhydroxide (boehmite) with M1+ nitrates of various concentrations and radii. The solutes consisted of H, Li, Na, K, and Rb nitrates at 10–5, 10–3, 10–1, 2, and 4 molal (m) concentrations, as well as in pure H2O. Synthetic boehmite nanoparticles were used with a size range from ∼20 to 30 nm. Tumbler cells were used to keep the solids from settling. Although particles initially form individual rhombohedral platelets, once placed in solution, they quickly form well-bonded stacks, primary aggregates, up to ∼1500 Å long, and a second level of aggregates whose concentration and structure vary as a function of cation type and concentration. Aggregation generally increases with increased solute concentration and with cation radius up to a concentration somewhat above 10–1 m, at which point the trend reverses. Primary aggregates become more rodlike and larger. The Kirkwood-like reversal probably reflects a change from Derjaguin–Landau–Verwey–Overbeek (DLVO)/Debye behavior controlled by surface chemistry to a frustrated Coulombic system controlled by the solution structure. These data suggest that an understanding of the effects of salt concentration and chemistry on nanoparticle aggregate structures provides useful physical insights into the microscopic origin of slurry rheology in the Hanford and Savannah River legacy wastes.

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Cited by 5 publications

References 3 publications

Ab Initio Molecular Dynamics Study of the AlOOH Boehmite/Water Interface: Role of Steps in Interfacial Grotthus Proton Transfers

Ab Initio Molecular Dynamics Study of the AlOOH Boehmite/Water Interface: Role of Steps in Interfacial Grotthus Proton Transfers

Solution Titration by Wall Deprotonation during Capillary Filling of Silicon Oxide Nanochannels

Frustrated Coulombic and Cation Size Effects on Nanoscale Boehmite Aggregation: A Tumbler Small- and Ultra-Small-Angle Neutron Scattering Study

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