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Acid-base dissociation mechanisms and energetics at the silica–water interface: an activationless process

Acid-base dissociation mechanisms and energetics at the silica–water interface: an activationless process
Acid-base dissociation mechanisms and energetics at the silica–water interface: an activationless process
Hypothesis: Silanol groups at the silica–water interface determine not only the surface charge, but also have an important role in the binding of ions and biomolecules. As the pH is increased above pH 2, the silica surface develops a net negative charge primarily due to deprotonation of the silanol group. An improved understanding of the energetics and mechanisms of this fundamentally important process would further understanding of the relevant dynamics.

Simulations: Density Functional Theory ab initio molecular dynamics and geometry optimisations were used to investigate the mechanisms of surface neutralisation and charging in the presence of OH- and H3O+ respectively. This charging mechanism has received little attention in the literature.

Findings: The protonation or deprotonation of isolated silanols in the presence of H3O+ or OH-, respectively, was shown to be a highly rapid, exothermic reaction with no significant activation energy. This process occurred via a concerted motion of the protons through ‘water wires’. Geometry optimisations of large water clusters at the silica surface demonstrated proton transfer to the surface occurring via the rarely discussed ‘proton holes’ mechanism. This indicates that surface protonation is possible even when the hydronium ion is distant (at least 4 water molecules separation) from the surface.
Surface charging, deprotonation, proton transfer, proton binding, proton holes, grotthuss, DFT AIMD, ONETEP, surface acidity
0021-9797
231-244
Lowe, Benjamin
69b560bf-d230-4b2a-b103-8e2b485c58a7
Skylaris, Chris-Kriton
8f593d13-3ace-4558-ba08-04e48211af61
Green, Nicolas G
d9b47269-c426-41fd-a41d-5f4579faa581
Lowe, Benjamin
69b560bf-d230-4b2a-b103-8e2b485c58a7
Skylaris, Chris-Kriton
8f593d13-3ace-4558-ba08-04e48211af61
Green, Nicolas G
d9b47269-c426-41fd-a41d-5f4579faa581

Lowe, Benjamin, Skylaris, Chris-Kriton and Green, Nicolas G (2015) Acid-base dissociation mechanisms and energetics at the silica–water interface: an activationless process. Journal of Colloid and Interface Science, 451, 231-244. (doi:10.1016/j.jcis.2015.01.094). (PMID:25898118)

Record type: Article

Abstract

Hypothesis: Silanol groups at the silica–water interface determine not only the surface charge, but also have an important role in the binding of ions and biomolecules. As the pH is increased above pH 2, the silica surface develops a net negative charge primarily due to deprotonation of the silanol group. An improved understanding of the energetics and mechanisms of this fundamentally important process would further understanding of the relevant dynamics.

Simulations: Density Functional Theory ab initio molecular dynamics and geometry optimisations were used to investigate the mechanisms of surface neutralisation and charging in the presence of OH- and H3O+ respectively. This charging mechanism has received little attention in the literature.

Findings: The protonation or deprotonation of isolated silanols in the presence of H3O+ or OH-, respectively, was shown to be a highly rapid, exothermic reaction with no significant activation energy. This process occurred via a concerted motion of the protons through ‘water wires’. Geometry optimisations of large water clusters at the silica surface demonstrated proton transfer to the surface occurring via the rarely discussed ‘proton holes’ mechanism. This indicates that surface protonation is possible even when the hydronium ion is distant (at least 4 water molecules separation) from the surface.

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More information

Accepted/In Press date: 25 January 2015
Published date: 1 August 2015
Keywords: Surface charging, deprotonation, proton transfer, proton binding, proton holes, grotthuss, DFT AIMD, ONETEP, surface acidity
Organisations: Chemistry, Nanoelectronics and Nanotechnology

Identifiers

Local EPrints ID: 376852
URI: http://eprints.soton.ac.uk/id/eprint/376852
ISSN: 0021-9797
PURE UUID: a855b272-9ec9-4a58-9224-a6ea5029846f
ORCID for Chris-Kriton Skylaris: ORCID iD orcid.org/0000-0003-0258-3433
ORCID for Nicolas G Green: ORCID iD orcid.org/0000-0001-9230-4455

Catalogue record

Date deposited: 12 May 2015 11:50
Last modified: 17 Mar 2021 02:40

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